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Sample records for beam epitaxy grown

  1. Photoluminescence of ingaas/inp grown by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Harmand Jean Christophe

    2004-01-01

    Full Text Available Photoluminescence (PL measurements due to temperature and excitation power were carried out in as function of sample containing a In0,53Ga0,47. As layer, grown by Molecular Beam Epitaxy on an InP substrate. The origins of the several luminescence processes observed at low temperature were determined by studying their different behaviors with increasing temperature and excitation power and by comparing the results with the data found in the literature. The following transitions have been identified: one transition involving localized excitons and two transitions involving acceptor impurities. A review of the main works published in the literature related to the optical transitions observed at low temperature in InGaAs/InP is also presented.

  2. Nitrides optoelectronic devices grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kauer, M.; Bousquet, V.; Hooper, S.E.; Barnes, J.M.; Windle, J.; Tan, W.S.; Heffernan, J. [Sharp Laboratories of Europe, Edmund Halley Road, Oxford Science Park, Oxford OX4 4GB (United Kingdom)

    2007-01-15

    We report on the characteristics of our recent room temperature continuous-wave InGaN quantum well laser diodes grown by by molecular beam epitaxy (MBE). Uncoated ridge waveguide lasers fabricated on freestanding GaN substrates have a continuous-wave (cw) threshold current of 110 mA, corresponding to a threshold current density of 5.5 kA cm{sup -2}. We report on our steps taken to reduce threshold voltage to 7 V. Lasers with uncoated facets have a maximum cw output power of 14 mW and a cw characteristic temperature T{sub 0} of 123 K. Cw laser lifetime vs. power dissipation data is presented, with a maximum lifetime of 2.6 hours for the best laser. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Metallic impurities in gallium nitride grown by molecular beam epitaxy

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    McHugo, S.A.; Krueger, J.; Kisielowski, C. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    Transition metals are often encountered in trace amounts in semiconductors. They have been extensively studied in most elemental and compound systems, since they form deep donor and/or acceptor levels which usually degrade the electronic and optical material properties. Only very little is known about transition metals in recent III-V semiconducting materials, such as GaN, AlN and InN. These few studies have been done exclusively on Metal-Organic Chemical Vapor Deposition (MOCVD) or Hybrid Vapor Phase Epitaxy HVPE-grown GaN. Preliminary x-ray fluorescence studies at the Advanced Light Source, beamline 10.3.1, Lawrence Berkeley National Laboratory have revealed that GaN materials grown by Molecular Beam Epitaxy (MBE) have Fe, Ni and Cr as the dominant transition metal contaminants. This finding is commensurate with the extremely high concentrations of hydrogen, carbon and oxygen (up to 10{sup 20} cm{sup {minus}3}) measured by Secondary Ion Mass Spectroscopy (SIMS). Preliminary work using the mapping capabilities of the x-ray fluorescence microprobe revealed the metal impurities were inhomogeneously distributed over the film. Future work of this collaboration will be to find a correlation between the existence of transition metals in MBE films, as revealed by x-ray fluorescence, and Photoluminescence (PL) spectra taken in the infrared region. Also, the authors will make use of the 1 {mu}m spatial resolution of x-ray microprobe to locate the contaminants in relation to structural defects in the GaN films. Because of the large strain caused by the lattice mismatch between the GaN films and the substrates, the films grow in a columnar order with high densities of grain boundaries and dislocations. These structural defects offer preferential sites for metal precipitation or agglomeration which could degrade the optical properties of this material more so than if the impurities were left dissolved in the GaN.

  4. Deep ultraviolet emission in hexagonal boron nitride grown by high-temperature molecular beam epitaxy

    Science.gov (United States)

    Vuong, T. Q. P.; Cassabois, G.; Valvin, P.; Rousseau, E.; Summerfield, A.; Mellor, C. J.; Cho, Y.; Cheng, T. S.; Albar, J. D.; Eaves, L.; Foxon, C. T.; Beton, P. H.; Novikov, S. V.; Gil, B.

    2017-06-01

    We investigate the opto-electronic properties of hexagonal boron nitride grown by high temperature plasma-assisted molecular beam epitaxy. We combine atomic force microscopy, spectroscopic ellipsometry, and photoluminescence spectroscopy in the deep ultraviolet to compare the quality of hexagonal boron nitride grown either on sapphire or highly oriented pyrolytic graphite. For both substrates, the emission spectra peak at 235 nm, indicating the high optical quality of hexagonal boron nitride grown by molecular beam epitaxy. The epilayers on highly oriented pyrolytic graphite demonstrate superior performance in the deep ultraviolet (down to 210 nm) compared to those on sapphire. These results reveal the potential of molecular beam epitaxy for the growth of hexagonal boron nitride on graphene, and more generally, for fabricating van der Waals heterostructures and devices by means of a scalable technology.

  5. Graphitic carbon grown on fluorides by molecular beam epitaxy.

    Science.gov (United States)

    Jerng, Sahng-Kyoon; Lee, Jae Hong; Kim, Yong Seung; Chun, Seung-Hyun

    2013-01-03

    We study the growth mechanism of carbon molecules supplied by molecular beam epitaxy on fluoride substrates (MgF2, CaF2, and BaF2). All the carbon layers form graphitic carbon with different crystallinities depending on the cation. Especially, the growth on MgF2 results in the formation of nanocrystalline graphite (NCG). Such dependence on the cation is a new observation and calls for further systematic studies with other series of substrates. At the same growth temperature, the NCG on MgF2 has larger clusters than those on oxides. This is contrary to the general expectation because the bond strength of the carbon-fluorine bond is larger than that of the carbon-oxygen bond. Our results show that the growth of graphitic carbon does not simply depend on the chemical bonding between the carbon and the anion in the substrate.

  6. InPBi single crystals grown by molecular beam epitaxy.

    Science.gov (United States)

    Wang, K; Gu, Y; Zhou, H F; Zhang, L Y; Kang, C Z; Wu, M J; Pan, W W; Lu, P F; Gong, Q; Wang, S M

    2014-06-26

    InPBi was predicted to be the most robust infrared optoelectronic material but also the most difficult to synthesize within In-VBi (V = P, As and Sb) 25 years ago. We report the first successful growth of InPBi single crystals with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InPBi thin films reveal excellent surface, structural and optical qualities making it a promising new III-V compound family member for heterostructures. The Bi concentration is found to be 2.4 ± 0.4% with 94 ± 5% Bi atoms at substitutional sites. Optical absorption indicates a band gap of 1.23 eV at room temperature while photoluminescence shows unexpectedly strong and broad light emission at 1.4-2.7 μm which can't be explained by the existing theory.

  7. Origin of Spontaneous Core-Shell AIGaAs Nanowires Grown by Molecular Beam Epitaxy

    DEFF Research Database (Denmark)

    Dubrovskii, V. G.; Shtrom, I. V.; Reznik, R. R.;

    2016-01-01

    Based on the high-angle annular dark-field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy studies, we unravel the origin of spontaneous core shell AlGaAs nanowires grown by gold-assisted molecular beam epitaxy. Our AlGaAs nanowires have a cylindrical core...

  8. Scanning Tunneling Microscopy Studies of Topological Insulators Grown by Molecular Beam Epitaxy

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    Xue Qikun

    2012-03-01

    Full Text Available We summarize our recent scanning tunneling microscopy (STM study of topological insulator thin films grown by molecular beam epitaxy (MBE, which includes the observation of electron standing waves on topological insulator surface and the Landau quantization of topological surface states. The work has provided valuable information to the understanding of intriguing properties of topological insulators, as predicted by theory.

  9. Photoluminescence Characterization of Boron-doped Si Layers Grown by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    LI Cheng; LAI Hong-kai; CHEN Song-yan

    2005-01-01

    Photoluminescence spectra were used to characterize the boron-doped Si layers grown by molecular beam epitaxy using HBO2 as the doping source. The influence of boron doping concentration on the dislocation-related photoluminescence spectra of molecular beam epitaxy Si layers annealed at 900 ℃ was studied with different doping concentrations and growth temperature. The broad photoluminescence band(from 0.75 eV to 0.90 eV) including D1 and D2 bands was associated with high boron doping concentration in the samples, while D3 and D4 bands might be related to oxygen precipitates.

  10. Effect of growth temperature on defects in epitaxial GaN film grown by plasma assisted molecular beam epitaxy

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    S. S. Kushvaha

    2014-02-01

    Full Text Available We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001 substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 108 cm−2 at 750 °C than that of the low temperature grown sample (1.1 × 109 cm−2 at 730 °C. A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

  11. Effect of growth temperature on defects in epitaxial GaN film grown by plasma assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kushvaha, S. S., E-mail: kushvahas@nplindia.org; Pal, P.; Shukla, A. K.; Joshi, Amish G.; Gupta, Govind; Kumar, M.; Singh, S.; Gupta, Bipin K.; Haranath, D. [CSIR- National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi, India 110012 (India)

    2014-02-15

    We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 10{sup 8} cm{sup −2} at 750 °C) than that of the low temperature grown sample (1.1 × 10{sup 9} cm{sup −2} at 730 °C). A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

  12. Epitaxial Properties of Co-Doped ZnO Thin Films Grown by Plasma Assisted Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    CAO Qiang; DENG Jiang-Xia; LIU Guo-Lei; CHEN Yan-Xue; YAN Shi-Shen

    2007-01-01

    High quality Co-doped ZnO thin films are grown on single crystalline Al2O3(0001) and ZnO(0001) substrates by oxygen plasma assisted molecular beam epitaxy at a relatively lower substrate temperature of 450 ℃. The epitaxial conditions are examined with in-situ reflection high energy electron diffraction (RHEED) and ex-situ high resolution x-ray diffraction (HRXRD). The epitaxial thin films are single crystal at film thickness smaller than 500nm and nominal concentration of Co dopant up to 20%. It is indicated that the Co cation is incorporated into the ZnO matrix as Co2+ substituting Zn2+ ions. Atomic force microscopy shows smooth surfaces with rms roughness of 1.9nm. Room-temperature magnetization measurements reveal that the Co-doped ZnO thin films are ferromagnetic with Curie temperatures TC above room temperature.

  13. Diffusion of Pt in molecular beam epitaxy grown ZnSe

    Science.gov (United States)

    Slotte, J.; Salonen, R.; Ahlgren, T.; Räisänen, J.; Rauhala, E.; Uusimaa, P.

    1998-05-01

    Diffusion of platinum in zinc selenide has been studied by the use of the 4He and 12C ion backscattering techniques. The samples were thin films grown by molecular beam epitaxy on GaAs (100) epitaxial layers followed by evaporation of platinum and annealing in the temperature range 500-800 °C. The diffusion coefficients were determined by the fitting of a concentration independent solution of the diffusion equation to the experimental depth profiles. The activation energy and the pre-exponential factor of the diffusion process were found to be 1.7 eV and 6.4×10-6 cm2/s, respectively.

  14. Site-controlled Ag nanocrystals grown by molecular beam epitaxy-Towards plasmonic integration technology

    OpenAIRE

    Urbańczyk, Adam; NöTZEL, R

    2012-01-01

    We demonstrate site-controlled growth of epitaxial Ag nanocrystals on patterned GaAs substrates by molecular beam epitaxy with high degree of long-range uniformity. The alignment is based on lithographically defined holes in which position controlled InAs quantum dots are grown. The Ag nanocrystals self-align preferentially on top of the InAs quantum dots. No such ordering is observed in the absence of InAs quantum dots, proving that the ordering is strain-driven. The presented technique faci...

  15. Pure electron-electron dephasing in percolative aluminum ultrathin film grown by molecular beam epitaxy.

    Science.gov (United States)

    Lin, Shih-Wei; Wu, Yue-Han; Chang, Li; Liang, Chi-Te; Lin, Sheng-Di

    2015-01-01

    We have successfully grown ultrathin continuous aluminum film by molecular beam epitaxy. This percolative aluminum film is single crystalline and strain free as characterized by transmission electron microscopy and atomic force microscopy. The weak anti-localization effect is observed in the temperature range of 1.4 to 10 K with this sample, and it reveals that, for the first time, the dephasing is purely caused by electron-electron inelastic scattering in aluminum.

  16. Mn2Au: body-centered-tetragonal bimetallic antiferromagnets grown by molecular beam epitaxy.

    Science.gov (United States)

    Wu, Han-Chun; Liao, Zhi-Min; Sofin, R G Sumesh; Feng, Gen; Ma, Xiu-Mei; Shick, Alexander B; Mryasov, Oleg N; Shvets, Igor V

    2012-12-11

    Mn(2)Au, a layered bimetal, is successfully grown using molecular beam epitaxy (MBE). The experiments and theoretical calculations presented suggest that Mn(2)Au film is antiferromagnetic with a very low critical temperature. The antiferromagnetic nature is demonstrated by measuring the exchange-bias effect of Mn(2)Au/Fe bilayers. This study establishes a primary basis for further research of this new antiferromagnet in spin-electronic device applications.

  17. Properties of Ga1-xMnxN Epilayers Grown by Molecular Beam Epitaxy

    Science.gov (United States)

    Marcet, S.; Bellet, E.; Biquard, X.; Bougerol, C.; Cibert, J.; Ferrand, D.; Giraud, R.; Halley, D.; Kulatov, E.; Kuroda, S.; Mariette, H.; Titov, A.

    2005-06-01

    Wurtzite (Ga,Mn)N epilayers were grown by plasma-assisted molecular beam epitaxy. Mn incorporation strongly depends on growth conditions. Infrared optical absorption shows absorption bands related to neutral Mn acceptor A0 at 1.412 eV and 1.43 eV. Magnetic circular dichroism spectroscopyat the band gap edge, in agreement with magnetization data, exhibits temperature and magnetic field dependence revealing paramagnetic properties of Mn-doped GaN.

  18. High-mobility BaSnO3 grown by oxide molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Santosh Raghavan

    2016-01-01

    Full Text Available High-mobility perovskite BaSnO3 films are of significant interest as new wide bandgap semiconductors for power electronics, transparent conductors, and as high mobility channels for epitaxial integration with functional perovskites. Despite promising results for single crystals, high-mobility BaSnO3 films have been challenging to grow. Here, we demonstrate a modified oxide molecular beam epitaxy (MBE approach, which supplies pre-oxidized SnOx. This technique addresses issues in the MBE of ternary stannates related to volatile SnO formation and enables growth of epitaxial, stoichiometric BaSnO3. We demonstrate room temperature electron mobilities of 150 cm2 V−1 s−1 in films grown on PrScO3. The results open up a wide range of opportunities for future electronic devices.

  19. High-mobility BaSnO{sub 3} grown by oxide molecular beam epitaxy

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    Raghavan, Santosh; Schumann, Timo; Kim, Honggyu; Zhang, Jack Y.; Cain, Tyler A.; Stemmer, Susanne, E-mail: stemmer@mrl.ucsb.edu [Materials Department, University of California, Santa Barbara, California 93106-5050 (United States)

    2016-01-01

    High-mobility perovskite BaSnO{sub 3} films are of significant interest as new wide bandgap semiconductors for power electronics, transparent conductors, and as high mobility channels for epitaxial integration with functional perovskites. Despite promising results for single crystals, high-mobility BaSnO{sub 3} films have been challenging to grow. Here, we demonstrate a modified oxide molecular beam epitaxy (MBE) approach, which supplies pre-oxidized SnO{sub x}. This technique addresses issues in the MBE of ternary stannates related to volatile SnO formation and enables growth of epitaxial, stoichiometric BaSnO{sub 3}. We demonstrate room temperature electron mobilities of 150 cm{sup 2} V{sup −1} s{sup −1} in films grown on PrScO{sub 3}. The results open up a wide range of opportunities for future electronic devices.

  20. ZnS:N and ZnS:N,Ag grown by molecular beam epitaxy

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    Ichino, K.; Kotani, A.; Tanaka, H.; Kawai, T. [Department of Information and Electronics, Tottori University, 4-101 Koyama-minami, Tottori 680-8552 (Japan)

    2010-06-15

    The N-doping conditions have been investigated in the growth of ZnS:N by molecular beam epitaxy using RF plasma of N{sub 2} gas. As a result, high growth temperatures are found to be suitable for the effective incorporation and the activation of N acceptors. The capacitance versus voltage data of the ZnS:N layers grown at around 350 C exhibit p-type behavior, while the undoped layers show an n-type characteristic due to residual donors. ZnS:N,Ag epitaxial layers were also grown to investigate the effect of Ag-co-doping. It is shown that the p-type behavior of the N-doped layers is enhanced by the Ag-co-doping. This suggests the formation of Ag-related complex centers compensating residual donors (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. High-efficiency AlGaInP solar cells grown by molecular beam epitaxy

    Science.gov (United States)

    Faucher, J.; Sun, Y.; Jung, D.; Martin, D.; Masuda, T.; Lee, M. L.

    2016-10-01

    AlGaInP is an ideal material for ultra-high efficiency, lattice-matched multi-junction solar cells grown by molecular beam epitaxy (MBE) because it can be grown lattice-matched to GaAs with a wide 1.9-2.2 eV bandgap. Despite this potential, AlGaInP grown by molecular beam epitaxy (MBE) has yet to be fully explored, with the initial 2.0 eV devices suffering from poor performance due to low minority carrier diffusion lengths in both the emitter and base regions of the solar cell. In this work, we show that implementing an AlGaInP graded layer to introduce a drift field near the front surface of the device enabled greatly improved internal quantum efficiency (IQE) across all wavelengths. In addition, optimizing growth conditions and post-growth annealing improved the long-wavelength IQE and the open-circuit voltage of the cells, corresponding to a 3× increase in diffusion length in the base. Taken together, this work demonstrates greatly improved IQE, attaining peak values of 95%, combined with an uncoated AM1.5G efficiency of 10.9%, double that of previously reported MBE-grown devices.

  2. AlN Nanowall Structures Grown on Si (111) Substrate by Molecular Beam Epitaxy.

    Science.gov (United States)

    Tamura, Yosuke; Hane, Kazuhiro

    2015-12-01

    AlN nanowall structures were grown on Si (111) substrate using molecular beam epitaxy at substrate temperature of 700 °C with N/Al flux ratios ranging from 50 to 660. A few types of other AlN nanostructures were also grown under the nitrogen-rich conditions. The AlN nanowalls were ranged typically 60-120 nm in width and from 190 to 470 nm in length by changing N/Al flux ratio. The AlN nanowall structures grown along the c-plane consisted of AlN (0002) crystal with full-width at half maximum of the rocking curve about 5000 arcsec.

  3. Investigation of InN layers grown by molecular beam epitaxy on GaN templates

    Energy Technology Data Exchange (ETDEWEB)

    Vilalta-Clemente, A.; Mutta, G.R.; Chauvat, M.P.; Morales, M.; Doualan, J.L.; Ruterana, P. [CIMAP UMR 6252 CNRS-ENSICAEN-CEA-UCBN, Caen (France); Grandal, J.; Sanchez-Garcia, M.A.; Calle, F. [ISOM y Department de Ingenieria Electronica, E.T.S.I. Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria (Spain); Valcheva, E.; Kirilov, K. [Faculty of Physics, Sofia University (Bulgaria)

    2010-05-15

    An investigation of InN layers grown on GaN templates by molecular beam epitaxy (MBE) has been carried out by X-ray diffraction (XRD), Raman spectroscopy (RS) and photoluminescence (PL). A good correlation is noticed between their crystalline quality and optical properties. The best samples exhibit a PL emission between 0.6 and 0.7 eV. The surface structure was quite different from one sample to the other, pointing out to a critical role of the growth conditions, which probably need to be tightly optimized for a good reproducibility. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  4. Near-bandgap optical properties of pseudomorphic GeSn alloys grown by molecular beam epitaxy

    Science.gov (United States)

    D'Costa, Vijay Richard; Wang, Wei; Yeo, Yee-Chia

    2016-08-01

    We investigated the compositional dependence of the near-bandgap dielectric function and the E0 critical point in pseudomorphic Ge1-xSnx alloys grown on Ge (100) substrate by molecular beam epitaxy. The complex dielectric functions were obtained using spectroscopic ellipsometry from 0.5 to 4.5 eV at room temperature. Analogous to the E1 and E1+Δ1 transitions, a model consisting of the compositional dependence of relaxed alloys along with the strain contribution predicted by the deformation potential theory fully accounts for the observed compositional dependence in pseudomorphic alloys.

  5. GaAs Core/SrTiO3 Shell Nanowires Grown by Molecular Beam Epitaxy.

    Science.gov (United States)

    Guan, X; Becdelievre, J; Meunier, B; Benali, A; Saint-Girons, G; Bachelet, R; Regreny, P; Botella, C; Grenet, G; Blanchard, N P; Jaurand, X; Silly, M G; Sirotti, F; Chauvin, N; Gendry, M; Penuelas, J

    2016-04-13

    We have studied the growth of a SrTiO3 shell on self-catalyzed GaAs nanowires grown by vapor-liquid-solid assisted molecular beam epitaxy on Si(111) substrates. To control the growth of the SrTiO3 shell, the GaAs nanowires were protected using an arsenic capping/decapping procedure in order to prevent uncontrolled oxidation and/or contamination of the nanowire facets. Reflection high energy electron diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were performed to determine the structural, chemical, and morphological properties of the heterostructured nanowires. Using adapted oxide growth conditions, it is shown that most of the perovskite structure SrTiO3 shell appears to be oriented with respect to the GaAs lattice. These results are promising for achieving one-dimensional epitaxial semiconductor core/functional oxide shell nanostructures.

  6. Lattice constant and substitutional composition of GeSn alloys grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Bhargava, Nupur; Coppinger, Matthew; Prakash Gupta, Jay; Kolodzey, James [Department of Electrical and Computer Engineering, University of Delaware, Newark, Delaware 19716 (United States); Wielunski, Leszek [Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854 (United States)

    2013-07-22

    Single crystal epitaxial Ge{sub 1−x}Sn{sub x} alloys with atomic fractions of tin up to x = 0.145 were grown by solid source molecular beam epitaxy on Ge (001) substrates. The Ge{sub 1−x}Sn{sub x} alloys formed high quality, coherent, strained layers at growth temperatures below 250 °C, as shown by high resolution X-ray diffraction. The amount of Sn that was on lattice sites, as determined by Rutherford backscattering spectrometry channeling, was found to be above 90% substitutional in all alloys. The degree of strain and the dependence of the effective unstrained bulk lattice constant of Ge{sub 1−x}Sn{sub x} alloys versus the composition of Sn have been determined.

  7. Raman investigation of GaP–Si interfaces grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Bondi, A.; Cornet, C.; Boyer, S.; Nguyen Thanh, T.; Létoublon, A.; Pedesseau, L.; Durand, O. [Université Européenne de Bretagne, INSA, FOTON, UMR CNRS 6082, 20 Avenue des Buttes de Coësmes, F-35708 Rennes (France); Moreac, A. [Institut de Physique de Rennes, UMR-CNRS n°6251, Université Rennes1, Campus de Beaulieu — 35042 Rennes cedex (France); Ponchet, A. [CEMES, UPR CNRS 8011, F-31055 Toulouse (France); Le Corre, A. [Université Européenne de Bretagne, INSA, FOTON, UMR CNRS 6082, 20 Avenue des Buttes de Coësmes, F-35708 Rennes (France); Even, J., E-mail: jacky.even@insa.rennes.fr [Université Européenne de Bretagne, INSA, FOTON, UMR CNRS 6082, 20 Avenue des Buttes de Coësmes, F-35708 Rennes (France)

    2013-08-31

    Raman spectroscopy was used to investigate the residual strain in thin GaP layers deposited on Si substrates by molecular beam epitaxy. Different growth conditions were used to obtain a clean GaP–Si interface, including migration enhanced epitaxy. The strain induced Raman shifts of the longitudinal and the transverse optical GaP lattice modes were analyzed. The effects of crystalline defects are discussed, supported by high resolution transmission electron microscopy and X-ray scattering studies. Finally, Raman Spectroscopy reveals the presence of disorder (or surface)-activated optical phonons. This result is discussed in the light of surface morphology analyses. - Highlights: ► GaP thin layers grown by molecular beam epitaxy on Si substrates. ► Strain-induced Raman shifts of the optical GaP modes are analyzed. ► Simulation of optical GaP modes by density functional perturbation theory. ► Comparison with X-ray diffraction and electron and scanning probe microscopy data.

  8. N-H related defects in GaAsN grown through chemical beam epitaxy

    Science.gov (United States)

    Ohshita, Yoshio; Ikeda, Kazuma; Suzuki, Hidetoshi; Machida, Hideaki; Sudoh, Hiroshi; Tanaka, Tomohiro; Honda, Takahiko; Inagaki, Makoto; Yamaguchi, Masafumi

    2014-03-01

    The local vibration modes of N-H related defects in GaAsN are studied using isotopes. When GaAsN is grown through chemical beam epitaxy (CBE) using triethylgallium/tris(dimethylamino)arsenic/monomethylhydrazine gas, there are several local vibration modes (LVMs) in Fourier transform infrared (FTIR) spectra. Signals with stretching mode peaks at 2952, 3098, and 3125 cm-1 are reported, along with new wagging and stretching mode peaks at 960 and 3011 cm-1, which exist only in crystals grown through CBE. When the film is grown using deuterated MMHy as a nitrogen source, new peaks at 2206, 2302, 2318, 2245, and 714 cm-1 appear. This suggests that D related defects are created because of the deuterated MMHy. The ratios of frequencies of these new peaks to those obtained from crystals grown using MMHy are nearly 1.34. This suggests that all defects in GaAsN grown through CBE, which appear as LVMs, are N-H related defects. Especially, those with LVMs at 960 and 3011 cm-1 are new N-H defects only found in GaAsN grown through CBE.

  9. Photoluminescence studies of ZnO nanorods grown by plasma-assisted molecular beam epitaxy.

    Science.gov (United States)

    Kim, Min Su; Nam, Giwoong; Leem, Jae-Young

    2013-05-01

    Metal catalyst-free ZnO nanorods were grown on PS with buffer layers grown at 450 degrees C by plasma-assisted molecular beam epitaxy. Room temperature and temperature-dependent photoluminescence were carried out to investigate the optical properties of the ZnO nanorods with the average diameter of 120 nm and length of 300 nm. Three emission peaks, free excition, neutral-donor exciton, and free electron-to-neutral acceptor, were observed at 10 K. Huang-Rhys factor S of the ZnO nanorods was 0.978, which is much higher than that of ZnO thin films. The values of Varshni's empirical equation fitting parameters were alpha = 4 x 10(-3) eV/K, beta = 4.1 x 10(4) K, and E9(0) = 3.388 eV and the activation energy was about 96 meV.

  10. Controlling crystal phases in GaAs nanowires grown by Au-assisted molecular beam epitaxy.

    Science.gov (United States)

    Dheeraj, D L; Munshi, A M; Scheffler, M; van Helvoort, A T J; Weman, H; Fimland, B O

    2013-01-11

    Control of the crystal phases of GaAs nanowires (NWs) is essential to eliminate the formation of stacking faults which deteriorate the optical and electronic properties of the NWs. In addition, the ability to control the crystal phase of NWs provides an opportunity to engineer the band gap without changing the crystal material. We show that the crystal phase of GaAs NWs grown on GaAs(111)B substrates by molecular beam epitaxy using the Au-assisted vapor-liquid-solid growth mechanism can be tuned between wurtzite (WZ) and zinc blende (ZB) by changing the V/III flux ratio. As an example we demonstrate the realization of WZ GaAs NWs with a ZB GaAs insert that has been grown without changing the substrate temperature.

  11. Self-organized dots of GaN:Mn grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kuroda, S.; Marcet, S. [CEA-CNRS Group ' ' Nanophysique et Semiconducteurs' ' , Laboratoire de Spectrometrie Physique, Universite Joseph Fourier, Grenoble I and CEA/DRFMC/SP2M, 17 avenue des Martyrs, 38054 Grenoble, Cedex 9 (France); Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Halley, D.; Ferrand, D.; Mariette, H. [CEA-CNRS Group ' ' Nanophysique et Semiconducteurs' ' , Laboratoire de Spectrometrie Physique, Universite Joseph Fourier, Grenoble I and CEA/DRFMC/SP2M, 17 avenue des Martyrs, 38054 Grenoble, Cedex 9 (France); Cibert, J. [Laboratoire Louis Neel, CNRS, BP 166, 38042 Grenoble (France); Yamamoto, S.; Sakai, T.; Ohshima, T.; Itoh, H. [Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gumma 370-1292 (Japan)

    2006-07-01

    Self-organized dots of Mn-doped GaN were grown on AlN by plasma-assisted molecular beam epitaxy. The growth was performed in the nitrogen-rich growth regime with the addition of small amount of Mn flux. The in-situ surface observation using reflection high energy electron diffraction (RHEED) and the ex-situ examination using atomic force microscope (AFM) revealed that the dot formation was observed only in the case where the amount of Mn flux was small. The estimate of Mn composition using particle induced X-ray emission (PIXE) experiment showed that the Mn composition in the dots layer was much higher than in thick (Ga,Mn)N layers grown with the same amount of Mn flux. The maximum Mn composition for the high-density dot formation was about x=0.01. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Double acceptor in p-type GaAsN grown by chemical beam epitaxy

    Science.gov (United States)

    Elleuch, Omar; Wang, Li; Lee, Kan-Hua; Ikeda, Kazuma; Kojima, Nobuaki; Ohshita, Yoshio; Yamaguchi, Masafumi

    2015-12-01

    The properties of the acceptor states in GaAsN grown by chemical beam epitaxy (CBE) are studied by analyzing their charges based on the Poole-Frenkel model. Deep level transient spectroscopy (DLTS) shows two acceptor levels at 0.11 and 0.19 eV above the valence band maximum. The emission rates of carriers from these states are enhanced with increasing the electric field during the DLTS measurement, which indicates that the energies required for the emission are decreased. By analyzing this field-enhanced emission process, the polarizabilities of the levels at 0.11 and 0.19 eV are found to be -1 (±0.1) and -2 (±0.1), respectively. In addition, these states have almost the same concentration. Therefore, we conclude that they originate from the same defect, acting as a double acceptor in GaAsN film grown by CBE.

  13. Study of electrical properties of single GaN nanowires grown by molecular beam epitaxy

    Science.gov (United States)

    Mozharov, A. M.; Komissarenko, F. E.; Vasiliev, A. A.; Bolshakov, A. D.; Moiseev, E. I.; Mukhin, M. S.; Cirlin, G. E.; Mukhin, I. S.

    2016-08-01

    Electrical properties of single GaN nanowires grown by means of molecular beam epitaxy with N-plasma source were studied. Ohmic contacts connected to single n-type GaN wires were produced by the combination of electron beam lithography, metal vacuum evaporation and rapid thermal annealing technique. The optimal annealing temperature to produce ohmic contacts implemented in the form of Ti/Al/Ti/Au stack has been determined. By means of 2-terminal measurement wiring diagram the conductivity of single NW has been obtained for NWs with different growth parameters. The method of MESFET measurement circuit layout of single GaN nanowires (NWs) has been developed. In accordance with performed numerical calculation, free carriers' concentration and mobility of single NWs could be independently estimated using MESFET structure.

  14. Nitride-based laser diodes grown by plasma-assisted molecular beam epitaxy

    Science.gov (United States)

    Skierbiszewski, C.; Turski, H.; Muziol, G.; Siekacz, M.; Sawicka, M.; Cywiński, G.; Wasilewski, Z. R.; Porowski, S.

    2014-02-01

    The progress in the growth of nitride-based laser diodes (LDs) made by plasma-assisted molecular beam epitaxy (PAMBE) is reviewed. In this work we describe the GaN and InGaN growth peculiarities, p-type doping efficiency, and the properties of InGaN quantum wells (QWs) grown by PAMBE. We demonstrate continuous wave (cw) LDs operating in the range from 410 to 482 nm. These LDs were grown on low dislocation (0 0 0 1) c-plane bulk GaN substrate, which allow one to fabricate cw LDs with a lifetime exceeding 2000 h. Also, the ultraviolet LDs at 388 nm grown on (2 0 -2 1) semipolar substrates are discussed. The use of high active nitrogen fluxes up to 2 µm/h during the InGaN growth was essential for pushing the lasing wavelengths of PAMBE LDs above 460 nm. Recent advancement of InGaN growth by PAMBE allows one to demonstrate high-quality quantum QWs and excellent morphology for thick layers. We discuss the influence of LDs design on their parameters such as lasing threshold current and laser beam quality.

  15. InGaAsP-based uni-travelling carrier photodiode structure grown by solid source molecular beam epitaxy.

    Science.gov (United States)

    Natrella, Michele; Rouvalis, Efthymios; Liu, Chin-Pang; Liu, Huiyun; Renaud, Cyril C; Seeds, Alwyn J

    2012-08-13

    We report the first InGaAsP-based uni-travelling carrier photodiode structure grown by Solid Source Molecular Beam Epitaxy; the material contains layers of InGaAsP as thick as 300 nm and a 120 nm thick InGaAs absorber. Large area vertically illuminated test devices have been fabricated and characterised; the devices exhibited 0.1 A/W responsivity at 1550 nm, 12.5 GHz -3 dB bandwidth and -5.8 dBm output power at 10 GHz for a photocurrent of 4.8 mA. The use of Solid Source Molecular Beam Epitaxy enables the major issue associated with the unintentional diffusion of zinc in Metal Organic Vapour Phase Epitaxy to be overcome and gives the benefit of the superior control provided by MBE growth techniques without the costs and the risks of handling toxic gases of Gas Source Molecular Beam Epitaxy.

  16. Impact of growth parameters on the morphology and microstructure of epitaxial GaAs nanowires grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Z.Y. [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083 (China); Chen, P.P., E-mail: ppchen@mail.sitp.ac.cn [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083 (China); Liao, Z.M. [Materials Engineering, University of Queensland, St. Lucia, QLD 4072 (Australia); Shi, S.X.; Sun, Y.; Li, T.X.; Zhang, Y.H. [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083 (China); Zou, J. [Materials Engineering, University of Queensland, St. Lucia, QLD 4072 (Australia); Center for Microscopy and Microanalysis, University of Queensland, St. Lucia, QLD 4072 (Australia); Lu, W. [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083 (China)

    2013-12-15

    Highlights: •Defect-free wurtzite GaAs nanowires were obtained by MBE at low growth temperature. •Some GaAs nanowires grown at low temperature show the morphology of two shoulders. •High growth temperature favors the formation of nanowires with uniform diameter. •Low V/III flux ratio causes many kinked GaAs nanowires. •A phase separation of the catalyst is observed under very Ga-rich condition. -- Abstract: The effect of the growth temperature and V/III flux ratio on the morphology and microstructure of GaAs nanowires grown on GaAs (1 1 1){sub B} substrates by Au-assisted molecular beam epitaxy with solid As{sub 4} source was investigated. It has been found that a low growth temperature of 400 °C can result in defect-free wurtzite structured nanowire with syringe-like morphology, while nanowires with more homogeneous diameter can be obtained at high temperatures (500 °C and 550 °C) with many stacking faults. It was also found that, at a low V/III flux ratio, GaAs nanowires had a shrinking neck section, while a high V/III flux ratio may result in disappearance of the shrinking necking section. For the Ga very rich condition, a phase separation of the catalysts can be observed, leaving a small Au–Ga droplet covered by the outer pure Ga droplet.

  17. Intense terahertz emission from molecular beam epitaxy-grown GaAs/GaSb(001)

    Energy Technology Data Exchange (ETDEWEB)

    Sadia, Cyril P.; Laganapan, Aleena Maria; Agatha Tumanguil, Mae; Estacio, Elmer; Somintac, Armando; Salvador, Arnel [National Institute of Physics, University of the Philippines Diliman, Quezon City 1101 (Philippines); Que, Christopher T. [Physics Department, De La Salle University, 2401 Taft Avenue, Manila 1004 (Philippines); Yamamoto, Kohji; Tani, Masahiko [Research Center for Development of Far-Infrared Region, University of Fukui, Fukui 910-8507 (Japan)

    2012-12-15

    Intense terahertz (THz) electromagnetic wave emission was observed in undoped GaAs thin films deposited on (100) n-GaSb substrates via molecular beam epitaxy. GaAs/n-GaSb heterostructures were found to be viable THz sources having signal amplitude 75% that of bulk p-InAs. The GaAs films were grown by interruption method during the growth initiation and using various metamorphic buffer layers. Reciprocal space maps revealed that the GaAs epilayers are tensile relaxed. Defects at the i-GaAs/n-GaSb interface were confirmed by scanning electron microscope images. Band calculations were performed to infer the depletion region and electric field at the i-GaAs/n-GaSb and the air-GaAs interfaces. However, the resulting band calculations were found to be insufficient to explain the THz emission. The enhanced THz emission is currently attributed to a piezoelectric field induced by incoherent strain and defects.

  18. Deep levels in Ga-doped ZnSe grown by molecular-beam epitaxy

    Science.gov (United States)

    Venkatesan, S.; Pierret, R. F.; Qiu, J.; Kobayashi, M.; Gunshor, R. L.; Kolodziejski, L. A.

    1989-10-01

    Results of a deep-level transient spectroscopy study of Ga-doped ZnSe thin films grown by molecular-beam epitaxy are presented. Two prominent deep levels were observed in all the samples investigated. The concentration of the trap detected at 0.34 eV below the conduction-band edge was essentially independent of the doping concentration and is attributed to native defects arising from Se vacancies in the ZnSe films. The second level with an activation energy of 0.26 eV shows a very strong doping dependence and is tentatively identified as arising from dopant-site (gallium-on-zinc-site) defects complexed with selenium vacancies. Preliminary results also indicate that planar doping of ZnSe significantly reduces the concentration of the Ga-vacancy complex.

  19. Investigation of Localized States in GaAsSb Epilayers Grown by Molecular Beam Epitaxy.

    Science.gov (United States)

    Gao, Xian; Wei, Zhipeng; Zhao, Fenghuan; Yang, Yahui; Chen, Rui; Fang, Xuan; Tang, Jilong; Fang, Dan; Wang, Dengkui; Li, Ruixue; Ge, Xiaotian; Ma, Xiaohui; Wang, Xiaohua

    2016-07-06

    We report the carrier dynamics in GaAsSb ternary alloy grown by molecular beam epitaxy through comprehensive spectroscopic characterization over a wide temperature range. A detailed analysis of the experimental data reveals a complex carrier relaxation process involving both localized and delocalized states. At low temperature, the localized degree shows linear relationship with the increase of Sb component. The existence of localized states is also confirmed by the temperature dependence of peak position and band width of the emission. At temperature higher than 60 K, emissions related to localized states are quenched while the band to band transition dominates the whole spectrum. This study indicates that the localized states are related to the Sb component in the GaAsSb alloy, while it leads to the poor crystal quality of the material, and the application of GaAsSb alloy would be limited by this deterioration.

  20. Thin film phase diagram of iron nitrides grown by molecular beam epitaxy

    Science.gov (United States)

    Gölden, D.; Hildebrandt, E.; Alff, L.

    2017-01-01

    A low-temperature thin film phase diagram of the iron nitride system is established for the case of thin films grown by molecular beam epitaxy and nitrided by a nitrogen radical source. A fine-tuning of the nitridation conditions allows for growth of α ‧ -Fe8Nx with increasing c / a -ratio and magnetic anisotropy with increasing x until almost phase pure α ‧ -Fe8N1 thin films are obtained. A further increase of nitrogen content below the phase decomposition temperature of α ‧ -Fe8N (180 °C) leads to a mixture of several phases that is also affected by the choice of substrate material and symmetry. At higher temperatures (350 °C), phase pure γ ‧ -Fe4N is the most stable phase.

  1. Molecular-Beam Epitaxially Grown MgB2 Thin Films and Superconducting Tunnel Junctions

    Directory of Open Access Journals (Sweden)

    Jean-Baptiste Laloë

    2011-01-01

    Full Text Available Since the discovery of its superconducting properties in 2001, magnesium diboride has generated terrific scientific and engineering research interest around the world. With a of 39 K and two superconducting gaps, MgB2 has great promise from the fundamental point of view, as well as immediate applications. Several techniques for thin film deposition and heterojunction formation have been established, each with its own advantages and drawbacks. Here, we will present a brief overview of research based on MgB2 thin films grown by molecular beam epitaxy coevaporation of Mg and B. The films are smooth and highly crystalline, and the technique allows for virtually any heterostructure to be formed, including all-MgB2 tunnel junctions. Such devices have been characterized, with both quasiparticle and Josephson tunneling reported. MgB2 remains a material of great potential for a multitude of further characterization and exploration research projects and applications.

  2. Structural and optical characterizations of InPBi thin films grown by molecular beam epitaxy.

    Science.gov (United States)

    Gu, Yi; Wang, Kai; Zhou, Haifei; Li, Yaoyao; Cao, Chunfang; Zhang, Liyao; Zhang, Yonggang; Gong, Qian; Wang, Shumin

    2014-01-13

    InPBi thin films have been grown on InP by gas source molecular beam epitaxy. A maximum Bi composition of 2.4% is determined by Rutherford backscattering spectrometry. X-ray diffraction measurements show good structural quality for Bi composition up to 1.4% and a partially relaxed structure for higher Bi contents. The bandgap was measured by optical absorption, and the bandgap reduction caused by the Bi incorporation was estimated to be about 56 meV/Bi%. Strong and broad photoluminescence signals were observed at room temperature for samples with xBi < 2.4%. The PL peak position varies from 1.4 to 1.9 μm, far below the measured InPBi bandgap.

  3. Infrared electroluminescence from GeSn heterojunction diodes grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, Jay Prakash; Bhargava, Nupur; Kim, Sangcheol; Kolodzey, James [Department of Electrical and Computer Engineering, University of Delaware, Newark, Delaware 19716 (United States); Adam, Thomas [Nanofab, University of Albany, SUNY, Albany, New York 12203 (United States)

    2013-06-24

    Infrared electroluminescence was observed from GeSn/Ge p-n heterojunction diodes with 8% Sn, grown by molecular beam epitaxy. The GeSn layers were boron doped, compressively strained, and pseudomorphic on Ge substrates. Spectral measurements indicated an emission peak at 0.57 eV, about 50 meV wide, increasing in intensity with applied pulsed current, and with reducing device temperatures. The total integrated emitted power from a single edge facet was 54 {mu}W at an applied peak current of 100 mA at 100 K. These results suggest that GeSn-based materials maybe useful for practical light emitting diodes operating in the infrared wavelength range near 2 {mu}m.

  4. Infrared photoresponse of GeSn/n-Ge heterojunctions grown by molecular beam epitaxy.

    Science.gov (United States)

    Kim, Sangcheol; Bhargava, Nupur; Gupta, Jay; Coppinger, Matthew; Kolodzey, James

    2014-05-05

    Heterojunction devices of Ge(1-x)Sn(x) / n-Ge were grown by solid source molecular beam epitaxy (MBE), and the mid-infrared (IR) photocurrent response was measured. With increasing Sn composition from 4% to 12%, the photocurrent spectra became red-shifted, suggesting that the bandgap of Ge(1-x)Sn(x) alloys was lowered compared to pure Ge. At a temperature of 100 K, the wavelengths of peak photocurrent were shifted from 1.42 µm for pure Ge (0% Sn) to 2.0 µm for 12% Sn. The bias dependence of the device response showed that the optimum reverse bias was > 0.5 volts for saturated photocurrent. The responsivity of the Ge(1-x)Sn(x) devices was estimated to be 0.17 A/W for 4% Sn. These results suggest that Ge(1-x)Sn(x) photodetectors may have practical applications in the near/mid IR wavelength regime.

  5. Reduction in the crystal defect density of Zn Se layers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lopez L, M.; Perez C, A.; Luyo A, J.; Melendez L, M.; Tamura, M. [Departamento de Fisica, Centro de Investigacion y de Estudios Avanzados del instituto politecnico Nacional, A.P. 14-740, 07000 Mexico D.F. (Mexico); Mendez G, V.H.; Vidal, M.A. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, 78000 San Luis Potosi (Mexico)

    2000-07-01

    We present a study of the molecular beam epitaxial (MBE) grown of Zn Se layers on Ga-As and Si substrates. For the growth on GaAs substrates we investigated the effects of introducing buffer layers of Al{sub x}Ga{sub 1-x} As and In{sub x}Ga{sub 1-x} As with x = 0.01. Moreover, an analysis by secondary ion mass spectroscopy revealed that the use of AlGaAs buffer layers effectively suppress the Ga segregation onto the Zn Se layers surface. On the other hand, for the growth of Zn Se on Si substrates, we achieved a significant improvement in the crystal quality of Zn Se by irradiating the Si substrates with plasma of nitrogen prior to the growth. (Author)

  6. Performance and degradation characteristics of blue-violet laser diodes grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Tan, W.S.; Kauer, M.; Hooper, S.E.; Smeeton, T.M.; Bousquet, V.; Rossetti, M.; Heffernan, J. [Sharp Laboratories of Europe Ltd., Edmund Halley Road, Oxford Science Park, Oxford, OX4 4GB (United Kingdom); Xiu, H.; Humphreys, C.J. [Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ (United Kingdom)

    2009-06-15

    This paper reports the state of the art performance for blue-violet laser diodes (LD) grown by molecular beam epitaxy. Improvements in device design and growth have resulted in a threshold current density of 3.6 kA/cm{sup 2}, which translates into improved cw lifetime of up to 42 hours. Reducing the internal loss resulted in a high cw slope efficiency of 1.08 W/A and a maximum cw output power of 145 mW. To obtain a better understanding of the LD failure mechanism, degraded LDs were analysed using surface mapping techniques such as photoluminescence and electroluminescence on a micrometric scale, which allows the identification of failure regions. These measurements revealed increased nonradiative recombination in localized regions and increased current injection non-uniformities as possible mechanisms for LD performance degradation after aging. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. InAs/InP nanowires grown by catalyst assisted molecular beam epitaxy on silicon substrates

    Science.gov (United States)

    Khmissi, H.; Naji, K.; Hadj Alouane, M. H.; Chauvin, N.; Bru-Chevallier, C.; Ilahi, B.; Patriarche, G.; Gendry, M.

    2012-04-01

    InP nanowires (NWs) with an InAs insertion were grown on (001)- and (111)-oriented silicon substrates by catalyst assisted molecular beam epitaxy. To prevent the crystallization of the catalyst droplet we propose a procedure based on the realization of the switching of the elements V flux during a growth interruption. With this procedure and with the growth conditions we have used, the crystal structure of the NWs is purely wurtzite without any stacking faults. With these growth conditions, both radial and axial growths occur simultaneously and we show that the growth time of the InAs insertion could be adjusted to obtain radial quantum well emitting in the 1.3-1.6 μm telecom band at room temperature.

  8. Si Incorporation in InP Nanowires Grown by Au-Assisted Molecular Beam Epitaxy

    Directory of Open Access Journals (Sweden)

    Lorenzo Rigutti

    2009-01-01

    Full Text Available We report on the growth, structural characterization, and conductivity studies of Si-doped InP nanowires grown by Au-assisted molecular beam epitaxy. It is shown that Si doping reduces the mean diffusion length of adatoms on the lateral nanowire surface and consequently reduces the nanowire growth rate and promotes lateral growth. A resistivity as low as 5.1±0.3×10−5 Ω⋅cm is measured for highly doped nanowires. Two dopant incorporation mechanisms are discussed: incorporation via catalyst particle and direct incorporation on the nanowire sidewalls. The first mechanism is shown to be less efficient than the second one, resulting in inhomogeneous radial dopant distribution.

  9. Photoluminescence properties of MgxZn1-xO films grown by molecular beam epitaxy

    Science.gov (United States)

    Wu, T. Y.; Huang, Y. S.; Hu, S. Y.; Lee, Y. C.; Tiong, K. K.; Chang, C. C.; Chou, W. C.; Shen, J. L.

    2017-02-01

    The optical properties of MgxZn1-xO films with x=0.03, 0.06, 0.08, and 0.11 grown by molecular beam epitaxy (MBE) have been studied by temperature-dependent photoluminescence (PL) measurement. It is presented that the full-width at half-maximum (FWHM) of the 12 K PL spectrum of MgZnO films increases with increasing Mg concentration and would deviate significantly from the simulation curve of Schubert model with higher Mg contents. The abnormal broader PL FWHM is inferred from larger compositional fluctuation by incorporating higher Mg contents, which results in larger effect of excitonic localization to induce more significant S-shaped behavior of the PL peak energy with temperature dependence. Additionally, the degree of localization increases as the linear proportion of the PL FWHM, indicating that the excitonic behavior in MgZnO films belong to the strong localization effect.

  10. InGaN violet laser diodes grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Heffernan, J.; Kauer, M.; Hooper, S.E.; Bousquet, V.; Johnson, K. [Sharp Laboratories of Europe Ltd, Edmund Halley Road, Oxford Science Park, Oxford, OX4 4GB (United Kingdom)

    2004-09-01

    We report on the first InGaN quantum well laser diodes grown by molecular beam epitaxy (MBE). Devices were grown by gas-source MBE using ammonia as a source of nitrogen and elemental group III sources. The devices were grown on commercially available GaN template substrates. The lasers consist of a separate confinement heterostructure including an active region consisting of three In{sub 0.1}Ga{sub 0.9}N quantum wells with a nominal thickness of 2 nm. P-type doping of GaN and AlGaN cladding regions was obtained without the use of post-growth thermal annealing. The lasers were fabricated into a ridge-stripe geometry with ridge width of 5 {mu}m and length of 500-1500 {mu}m. Electron cyclotron resonance (ECR) dry-etching was used to fabricate the laser facets. Under pulsed current injection conditions, the lasers exhibit a room temperature threshold current density of 22 kA cm{sup -2} emitting at 400 nm. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Strain-Engineered Graphene Grown on Hexagonal Boron Nitride by Molecular Beam Epitaxy.

    Science.gov (United States)

    Summerfield, Alex; Davies, Andrew; Cheng, Tin S; Korolkov, Vladimir V; Cho, YongJin; Mellor, Christopher J; Foxon, C Thomas; Khlobystov, Andrei N; Watanabe, Kenji; Taniguchi, Takashi; Eaves, Laurence; Novikov, Sergei V; Beton, Peter H

    2016-03-01

    Graphene grown by high temperature molecular beam epitaxy on hexagonal boron nitride (hBN) forms continuous domains with dimensions of order 20 μm, and exhibits moiré patterns with large periodicities, up to ~30 nm, indicating that the layers are highly strained. Topological defects in the moiré patterns are observed and attributed to the relaxation of graphene islands which nucleate at different sites and subsequently coalesce. In addition, cracks are formed leading to strain relaxation, highly anisotropic strain fields, and abrupt boundaries between regions with different moiré periods. These cracks can also be formed by modification of the layers with a local probe resulting in the contraction and physical displacement of graphene layers. The Raman spectra of regions with a large moiré period reveal split and shifted G and 2D peaks confirming the presence of strain. Our work demonstrates a new approach to the growth of epitaxial graphene and a means of generating and modifying strain in graphene.

  12. Magnetic, transport and structural properties of Co/Ir multilayers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Colis, S.; Dinia, A.; Ulhaq-Bouillet, C.; Panissod, P.; Meny, C.; Schmerber, G.; Arabski, J. [IPCMS-GEMME (UMR 7504 du CNRS), 23 rue du Loess, BP 34, F-67034 Strasbourg Cedex 2 (France)

    2003-09-01

    We report on the structural properties of a [Co{sub 30}/Ir{sub 10}]{sub 10} {sub x} (A) superlattice, as well as on the magnetic and transport properties of a Co{sub 15}/Ir{sub 5}/Co{sub 30} (A) artificial ferrimagnetic system. The samples were grown by molecular beam epitaxy (MBE) on MgO(001) substrates covered with a Ir{sub 130} (A) buffer layer. High resolution cross section and plan view transmission electron microscopy (TEM) images present a high quality epitaxial stack [100]MgO(001) parallel [100]Ir(001) parallel [100]Co(001), with a tetragonalization of the Co fcc structure, due to strains induced by the Ir buffer. TEM images also show that the Co/Ir interfaces are flat, while the layers are continuous and free of bridges. These observations are consistent with zero field nuclear magnetic resonance measurements which indicate an fcc structure of the Co layers, and an interface mixing between Co and Ir limited to one atomic layer. As a consequence the antiferromagnetically coupled Co/Ir/Co sandwich presents large saturation and coercive fields which exceed 20 kOe and 220 Oe, respectively. Annealing made on the same sandwich indicate that the magnetic and transport properties are stable up to 300 C. (copyright 2003 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Graphene films grown on sapphire substrates via solid source molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Tang Jun; Kang Chao-Yang; Li Li-Min; Liu Zhong-Liang; Yan Wen-Sheng; Wei Shi-Qiang; Xu Peng-Shou

    2012-01-01

    A method for growing graphene on a sapphire substrate by depositing an SiC buffer layer and then annealing at high temperature in solid source molecular beam epitaxy(SSMBE)equipment was presented.The structural and electronic properties of the samples were characterized by reflection high energy diffraction(RHEED),X-ray diffractionφ scans,Raman spectroscopy,and near edge X-ray absorption fine structure(NEXAFS)spectroscopy.The results of the RHEED and φ scan,as well as the Raman spectra,showed that an epitaxial hexagonal α-SiC layer was grown on the sapphire substrate.The results of the Raman and NEXAFS spectra revealed that the graphene films with the AB Bernal stacking structure were formed on the sapphire substrate after annealing.The layer number of the graphene was between four and five,and the thickness of the unreacted SiC layer was about 1-1.5 mm.

  14. Surface optical phonons in GaAs nanowires grown by Ga-assisted chemical beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    García Núñez, C., E-mail: carlos.garcia@uam.es; Braña, A. F.; Pau, J. L.; Ghita, D.; García, B. J. [Grupo de Electrónica y Semiconductores, Departamento de Física Aplicada, Universidad Autónoma de Madrid, 28049 Madrid (Spain); Shen, G.; Wilbert, D. S.; Kim, S. M.; Kung, P. [Department of Electrical and Computer Engineering, The University of Alabama, Tuscaloosa, Alabama 35487 (United States)

    2014-01-21

    Surface optical (SO) phonons were studied by Raman spectroscopy in GaAs nanowires (NWs) grown by Ga-assisted chemical beam epitaxy on oxidized Si(111) substrates. NW diameters and lengths ranging between 40 and 65 nm and between 0.3 and 1.3 μm, respectively, were observed under different growth conditions. The analysis of the Raman peak shape associated to either longitudinal or surface optical modes gave important information about the crystal quality of grown NWs. Phonon confinement model was used to calculate the density of defects as a function of the NW diameter resulting in values between 0.02 and 0.03 defects/nm, indicating the high uniformity obtained on NWs cross section size during growth. SO mode shows frequency downshifting as NW diameter decreases, this shift being sensitive to NW sidewall oxidation. The wavevector necessary to activate SO phonon was used to estimate the NW facet roughness responsible for SO shift.

  15. Impact of extended defects on recombination in CdTe heterostructures grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Zaunbrecher, Katherine N. [Department of Physics, Colorado State University, Fort Collins, Colorado 80523, USA; National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Kuciauskas, Darius [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Swartz, Craig H. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; Dippo, Pat [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Edirisooriya, Madhavie [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; Ogedengbe, Olanrewaju S. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; Sohal, Sandeep [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; Hancock, Bobby L. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; LeBlanc, Elizabeth G. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; Jayathilaka, Pathiraja A. R. D. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; Barnes, Teresa M. [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Myers, Thomas H. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA

    2016-08-29

    Heterostructures with CdTe and CdTe 1-xSex (x ~ 0.01) absorbers between two wider-band-gap Cd1-xMgxTe barriers (x ~ 0.25-0.3) were grown by molecular beam epitaxy to study carrier generation and recombination in bulk materials with passivated interfaces. Using a combination of confocal photoluminescence (PL), time-resolved PL, and low-temperature PL emission spectroscopy, two extended defect types were identified and the impact of these defects on charge-carrier recombination was analyzed. The dominant defects identified by confocal PL were dislocations in samples grown on (211)B CdTe substrates and crystallographic twinning-related defects in samples on (100)-oriented InSb substrates. Low-temperature PL shows that twin-related defects have a zero-phonon energy of 1.460 eV and a Huang-Rhys factor of 1.50, while dislocation-dominated samples have a 1.473-eV zero-phonon energy and a Huang-Rhys factor of 1.22. The charge carrier diffusion length near both types of defects is ~6 um, suggesting that recombination is limited by diffusion dynamics. For heterostructures with a low concentration of extended defects, the bulk lifetime was determined to be 2.2 us with an interface recombination velocity of 160 cm/s and an estimated radiative lifetime of 91 us.

  16. Impact of extended defects on recombination in CdTe heterostructures grown by molecular beam epitaxy

    Science.gov (United States)

    Zaunbrecher, Katherine N.; Kuciauskas, Darius; Swartz, Craig H.; Dippo, Pat; Edirisooriya, Madhavie; Ogedengbe, Olanrewaju S.; Sohal, Sandeep; Hancock, Bobby L.; LeBlanc, Elizabeth G.; Jayathilaka, Pathiraja A. R. D.; Barnes, Teresa M.; Myers, Thomas H.

    2016-08-01

    Heterostructures with CdTe and CdTe1-xSex (x ˜ 0.01) absorbers between two wider-band-gap Cd1-xMgxTe barriers (x ˜ 0.25-0.3) were grown by molecular beam epitaxy to study carrier generation and recombination in bulk materials with passivated interfaces. Using a combination of confocal photoluminescence (PL), time-resolved PL, and low-temperature PL emission spectroscopy, two extended defect types were identified and the impact of these defects on charge-carrier recombination was analyzed. The dominant defects identified by confocal PL were dislocations in samples grown on (211)B CdTe substrates and crystallographic twinning-related defects in samples on (100)-oriented InSb substrates. Low-temperature PL shows that twin-related defects have a zero-phonon energy of 1.460 eV and a Huang-Rhys factor of 1.50, while dislocation-dominated samples have a 1.473-eV zero-phonon energy and a Huang-Rhys factor of 1.22. The charge carrier diffusion length near both types of defects is ˜6 μm, suggesting that recombination is limited by diffusion dynamics. For heterostructures with a low concentration of extended defects, the bulk lifetime was determined to be 2.2 μs with an interface recombination velocity of 160 cm/s and an estimated radiative lifetime of 91 μs.

  17. Atom probe tomography characterisation of a laser diode structure grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Bennett, Samantha E.; Humphreys, Colin J.; Oliver, Rachel A. [Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ (United Kingdom); Smeeton, Tim M.; Hooper, Stewart E.; Heffernan, Jonathan [Sharp Laboratories of Europe Limited, Edmund Halley Road, Oxford Science Park, Oxford, OX4 4GB (United Kingdom); Saxey, David W.; Smith, George D. W. [Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH (United Kingdom)

    2012-03-01

    Atom probe tomography (APT) has been used to achieve three-dimensional characterization of a III-nitride laser diode (LD) structure grown by molecular beam epitaxy (MBE). Four APT data sets have been obtained, with fields of view up to 400 nm in depth and 120 nm in diameter. These data sets contain material from the InGaN quantum well (QW) active region, as well as the surrounding p- and n-doped waveguide and cladding layers, enabling comprehensive study of the structure and composition of the LD structure. Two regions of the same sample, with different average indium contents (18% and 16%) in the QW region, were studied. The APT data are shown to provide easy access to the p-type dopant levels, and the composition of a thin AlGaN barrier layer. Next, the distribution of indium within the InGaN QW was analyzed, to assess any possible inhomogeneity of the distribution of indium (''indium clustering''). No evidence for a statistically significant deviation from a random distribution was found, indicating that these MBE-grown InGaN QWs do not require indium clusters for carrier localization. However, the APT data show steps in the QW interfaces, leading to well-width fluctuations, which may act to localize carriers. Additionally, the unexpected presence of a small amount (x = 0.005) of indium in a layer grown intentionally as GaN was revealed. Finally, the same statistical method applied to the QW was used to show that the indium distribution within a thick InGaN waveguide layer in the n-doped region did not show any deviation from randomness.

  18. Dielectric and Structural Properties of SrTiO_3 Thin Films Grown by Laser Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Dielectric and Structural Properties of SrTiO_3 Thin Films Grown by Laser Molecular Beam Epitaxy[1]Hao J H,Gao J,Wang Z,et al.Interface structure and phase of epitaxial SrTi O3(110)thin fil ms grown directly on silicon[J].Appl Phys Lett,2005,87:131908. [2]Hao J H,Gao J,Wang HK.SrTi O3(110)thin fil ms grown directly on different oriented silicon substrates[J].Appl Phys A,2005,81:1233. [3]Aki mov I A,Sirenko A A,Clark A M,et al.Electric-field-induced soft-mode hardening in SrTi O3fil ms[J].Phys Rev Lett...

  19. Effects of magnesium contents in ZnMgO ternary alloys grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Sheng-Yao, E-mail: shenghu2729@yahoo.com [Department of Digital Technology Design, Tungfang Design Institute, Hunei, Kaohsiung 82941, Taiwan (China); Chou, Wu-Ching [Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan (China); Weng, Yu-Hsiang [Department of Electrical Engineering, National Taiwan Ocean University, Keelung 20224, Taiwan (China)

    2015-07-05

    Highlights: • ZnMgO alloys with different Mg contents have been produced by MBE. • Optical and structural properties have been measured and investigated. • Stress is tensile and is increased as the increasing of Mg contents. • The asymmetric behavior of the Raman mode was influenced due to the Mg contents. - Abstract: Ternary alloys of ZnMgO samples with different magnesium contents have been grown by molecular beam epitaxy on the sapphire substrates. Room temperature photoluminescence energy of ZnMgO shifted as high as 3.677 eV by increasing Mg contents corresponding to the higher Urbach average localization energy which indicates more randomness in the alloys with higher Mg contents. XRD results are also verified that the c-axis length decreases as the increasing Mg contents linking to the increased tensile stress produced by the Mg atoms. Raman spectra analyzed by the spatial correlation model to describe that the linewidth Γ is decreased but the correlation length L is increased as the increasing of Mg contents.

  20. Polarized infrared reflectance study of free standing cubic GaN grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lee, S.C., E-mail: saicheonglee86@yahoo.com [Nano-Optoelectronics Research Laboratory, School of Physics, Universiti Sains Malaysia, 11800 Penang (Malaysia); Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ng, S.S.; Hassan, H. Abu; Hassan, Z.; Zainal, N. [Nano-Optoelectronics Research Laboratory, School of Physics, Universiti Sains Malaysia, 11800 Penang (Malaysia); Novikov, S.V.; Foxon, C.T.; Kent, A.J. [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

    2014-07-01

    Optical properties of free standing cubic gallium nitride grown by molecular beam epitaxy system are investigated by a polarized infrared (IR) reflectance technique. A strong reststrahlen band, which reveals the bulk-like optical phonon frequencies, is observed. Meanwhile, continuous oscillation fringes, which indicate the sample consists of two homogeneous layers with different dielectric constants, are observed in the non-reststrahlen region. By obtaining the first derivative of polarized IR reflectance spectra measured at higher angles of incidence, extra phonon resonances are identified at the edges of the reststrahlen band. The observations are verified with the theoretical results simulated based on a multi-oscillator model. - Highlights: • First time experimental studies of IR optical phonons in bulk like, cubic GaN layer. • Detection of extra phonon modes of cubic GaN by polarized IR reflectance technique. • Revelation of IR multiphonon modes of cubic GaN by first derivative numerical method. • Observation of multiphonon modes requires very high angle of incidence. • Resonance splitting effect induced by third phonon mode is a qualitative indicator.

  1. Thermal Stability of Annealed Germanium-Tin Alloys Grown by Molecular Beam Epitaxy

    Science.gov (United States)

    Bhargava, Nupur; Gupta, Jay Prakash; Faleev, Nikolai; Wielunski, Leszek; Kolodzey, James

    2017-01-01

    The thermal stability of undoped and boron-doped germanium tin (Ge1-x Sn x ) alloys grown by molecular beam epitaxy with varying composition and layer thickness was investigated. The alloys were annealed in forming gas at various temperatures up to 800°C for 1 min using rapid thermal processing, and were characterized using high-resolution x-ray diffraction and Rutherford backscattering spectrometry. It was found that the Ge1-x Sn x alloys were stable to well above the growth temperature, but the stability decreased with increasing thickness, Sn content, and doping. Ge1-x Sn x alloys with low Sn composition (x ˜ 0.025) were stable up to 700°C, and for a given Sn composition, the undoped alloys were more thermally stable than the doped alloys. As the thickness of the Ge0.975Sn0.025 alloys increased to about 950 nm, the temperature of thermal stability dropped to 500°C. As the Sn composition of the 90 nm-Ge1-x Sn x alloys increased up to x = 0.08, the temperature of thermal stability dropped to 300°C. At higher annealing temperatures, the Ge1-x Sn x alloy degraded with lower crystal quality, and a gradient in the Sn composition appeared, which may be due to Sn diffusion or segregation.

  2. Structural and electrical properties of large area epitaxial VO2 films grown by electron beam evaporation

    Science.gov (United States)

    Théry, V.; Boulle, A.; Crunteanu, A.; Orlianges, J. C.; Beaumont, A.; Mayet, R.; Mennai, A.; Cosset, F.; Bessaudou, A.; Fabert, M.

    2017-02-01

    Large area (up to 4 squared inches) epitaxial VO2 films, with a uniform thickness and exhibiting an abrupt metal-insulator transition with a resistivity ratio as high as 2.85 × 10 4 , have been grown on (001)-oriented sapphire substrates by electron beam evaporation. The lattice distortions (mosaicity) and the level of strain in the films have been assessed by X-ray diffraction. It is demonstrated that the films grow in a domain-matching mode where the distortions are confined close to the interface which allows growth of high-quality materials despite the high film-substrate lattice mismatch. It is further shown that a post-deposition high-temperature oxygen annealing step is crucial to ensure the correct film stoichiometry and provide the best structural and electrical properties. Alternatively, it is possible to obtain high quality films with a RF discharge during deposition, which hence do not require the additional annealing step. Such films exhibit similar electrical properties and only slightly degraded structural properties.

  3. Electrical properties of GaAsN film grown by chemical beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Nishimura, K. [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan)], E-mail: sd05501@toyota-ti.ac.jp; Suzuki, H.; Saito, K.; Ohshita, Y.; Kojima, N.; Yamaguchi, M. [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan)

    2007-12-15

    The local vibrational modes (LVMs) observed by Fourier transform infrared (FTIR) spectroscopy in GaAsN films grown by chemical beam epitaxy (CBE) was studied, and the influence of the nitrogen-hydrogen bond (N-H) concentration on the hole concentration was investigated. The absorption peak around 936 cm{sup -1} is suggested to be the second harmonic mode of the substitutional N, N{sub As}, LVM around 469 cm{sup -1}. The absorption peak around 960 cm{sup -1} is suggested to be the wagging mode of the N-H, where the stretch mode is observed around 3098 cm{sup -1}. The hole concentration linearly increases with increasing N-H concentration, and the slope increases with increasing growth temperature. It indicates that the hole concentration in GaAsN film is determined by both the number of the N-H and unknown defect, such as impurities, vacancies, and interstitials. This defect concentration increases with increasing growth temperature, suggesting that it is determined by Arrhenius type reaction.

  4. Growth and structural characterization of III-V nanowires grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Dheeraj, D.L.

    2010-10-15

    Heterostructured semiconductor nanowires (NWs) have attracted considerable attention in recent years because of their potential in future nano-electronic and nano-photonic device applications. NWs are usually grown by vapor-liquid-solid (VLS) growth mechanism using techniques such as metal-organic vapor phase epitaxy, chemical beam epitaxy and molecular beam epitaxy (MBE). Of all the available techniques, MBE is known to be the technique which yields highest purity materials. In this study, the growth of GaAs NWs, GaAsSb NWs, as well as GaAs/GaAsSb axial and GaAs/AlGaAs radial heterostructured NWs on GaAs(111)B substrates by MBE is demonstrated. The structural and optical properties of the NWs grown are characterized by electron microscopy techniques such as scanning and transmission electron microscopy, and micro-photoluminescence, respectively. Firstly, the optimum growth conditions to obtain rod shaped GaAs NWs on GaAs(111)B substrates by MBE is determined. It has been found that in-addition to the V/III ratio and substrate temperature, buffer growth conditions also play an important role on the orientation of the NWs. The effect of V/III ratio, substrate temperature, and the arsenic species (As{sub 2}/As{sub 4}) on the morphology of GaAs NWs has been determined. Transmission electron microscopy (TEM) characterization of NWs revealed that GaAs in NW form exhibit wurtzite (WZ) crystal phase in contrast to zinc blende (ZB) phase adapted in its bulk form. Since WZ crystal phase is a metastable phase of GaAs, the WZ GaAs NWs often exhibit stacking faults. The stacking faults are known to be a detrimental problem, if not properly controlled. To gain more insight on the growth kinetics of GaAs NWs grown by MBE, several samples such as GaAs NWs grown for different time durations, and GaAs NWs with three GaAsSb inserts, where GaAsSb inserts acts as markers, have been grown. Interestingly, the growth rates of the GaAs segments and GaAsSb inserts were observed to vary

  5. Emission control of InGaN nanocolumns grown by molecular-beam epitaxy on Si(111) substrates

    OpenAIRE

    Albert, S; Bengoechea-Encabo, A.; Lefebvre, P.; Sanchez-Garcia, M. A.; Calleja, E.; Jahn, U.; Trampert, A

    2011-01-01

    International audience; This work studies the effect of the growth temperature on the morphology and emission characteristics of self-assembled InGaN nanocolumns grown by plasma assisted molecular beam epitaxy. Morphology changes are assessed by scanning electron microscopy, while emission is measured by photoluminescence. Within the growth temperature range of 750 to 650°C, an increase in In incorporation for decreasing temperature is observed. This effect allows tailoring the InGaN nanocolu...

  6. Impact of extended defects on recombination in CdTe heterostructures grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Zaunbrecher, Katherine N. [Department of Physics, Colorado State University, Fort Collins, Colorado 80523 (United States); National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Kuciauskas, Darius; Dippo, Pat; Barnes, Teresa M. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Swartz, Craig H.; Edirisooriya, Madhavie; Ogedengbe, Olanrewaju S.; Sohal, Sandeep; Hancock, Bobby L.; LeBlanc, Elizabeth G.; Jayathilaka, Pathiraja A. R. D.; Myers, Thomas H. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666 (United States)

    2016-08-29

    Heterostructures with CdTe and CdTe{sub 1-x}Se{sub x} (x ∼ 0.01) absorbers between two wider-band-gap Cd{sub 1-x}Mg{sub x}Te barriers (x ∼ 0.25–0.3) were grown by molecular beam epitaxy to study carrier generation and recombination in bulk materials with passivated interfaces. Using a combination of confocal photoluminescence (PL), time-resolved PL, and low-temperature PL emission spectroscopy, two extended defect types were identified and the impact of these defects on charge-carrier recombination was analyzed. The dominant defects identified by confocal PL were dislocations in samples grown on (211)B CdTe substrates and crystallographic twinning-related defects in samples on (100)-oriented InSb substrates. Low-temperature PL shows that twin-related defects have a zero-phonon energy of 1.460 eV and a Huang-Rhys factor of 1.50, while dislocation-dominated samples have a 1.473-eV zero-phonon energy and a Huang-Rhys factor of 1.22. The charge carrier diffusion length near both types of defects is ∼6 μm, suggesting that recombination is limited by diffusion dynamics. For heterostructures with a low concentration of extended defects, the bulk lifetime was determined to be 2.2 μs with an interface recombination velocity of 160 cm/s and an estimated radiative lifetime of 91 μs.

  7. Molecular beam epitaxy and properties of GaAsBi/GaAs quantum wells grown by molecular beam epitaxy: effect of thermal annealing.

    Science.gov (United States)

    Makhloufi, Hajer; Boonpeng, Poonyasiri; Mazzucato, Simone; Nicolai, Julien; Arnoult, Alexandre; Hungria, Teresa; Lacoste, Guy; Gatel, Christophe; Ponchet, Anne; Carrère, Hélène; Marie, Xavier; Fontaine, Chantal

    2014-03-17

    We have grown GaAsBi quantum wells by molecular beam epitaxy. We have studied the properties of a 7% Bi GaAsBi quantum well and their variation with thermal annealing. High-resolution X-ray diffraction, secondary ion mass spectrometry, and transmission electron microscopy have been employed to get some insight into its structural properties. Stationary and time-resolved photoluminescence shows that the quantum well emission, peaking at 1.23 μm at room temperature, can be improved by a rapid annealing at 650°C, while the use of a higher annealing temperature leads to emission degradation and blue-shifting due to the activation of non-radiative centers and bismuth diffusion from the quantum well.

  8. Synthesis of as-grown superconducting MgB_2 thin films by molecular beam epitaxy in UHV conditions

    OpenAIRE

    Harada, Y.; Udsuka, M.; Nakanishi, Y.; Yoshizawa, M.

    2004-01-01

    As-grown superconducting MgB_2 thin films have been grown on SrTiO_3(001), MgO(001), and Al_2O_3(0001) substrates by a molecular beam epitaxy (MBE) method with novel co-evaporation conditions of low deposition rate in ultra-high vacuum. The structural and physical properties of the films were studied by RHEED, XRD, electrical resistivity measurements, and SQUID magnetometer. The RHEED patterns indicate three-dimensional growth for MgB_2. The highest T_c determined by resistivity measurement w...

  9. Molecular Beam Epitaxy-Grown InGaN Nanowires and Nanomushrooms for Solid State Lighting

    KAUST Repository

    Gasim, Anwar A.

    2012-05-01

    InGaN is a promising semiconductor for solid state lighting thanks to its bandgap which spans the entire visible regime of the electromagnetic spectrum. InGaN is grown heteroepitaxially due to the absence of a native substrate; however, this results in a strained film and a high dislocation density—two effects that have been associated with efficiency droop, which is the disastrous drop in efficiency of a light-emitting diode (LED) as the input current increases. Heteroepitaxially grown nanowires have recently attracted great interest due to their property of eliminating the detrimental effects of the lattice mismatch and the corollary efficiency droop. In this study, InGaN nanowires were grown on a low-cost Si (111) substrate via molecular beam epitaxy. Unique nanostructures, taking the form of mushrooms, have been observed in localized regions on the samples. These nanomushrooms consist of a nanowire body with a wide cap on top. Photoluminescence characterization revealed that the nanowires emit violet-blue, whilst the nanomushrooms emit a broad yellow-orange-red luminescence. The simultaneous emission from the nanowires and nanomushrooms forms white light. Structural characterization of a single nanomushroom via transmission electron microscopy revealed a simultaneous increase in indium and decrease in gallium at the interface between the body and the cap. Furthermore, the cap itself was found to be indium-rich, confirming it as the source of the longer wavelength yellow-orange-red luminescence. It is believed that the nanomushroom cap formed as a consequence of the saturation of growth on the c-plane of the nanowire. It is proposed that the formation of an indium droplet on the tip of the nanowire saturated growth on the c-plane, forcing the indium and gallium adatoms to incorporate on the sidewall m-planes instead, but only at the nanowire tip. This resulted in the formation of a mushroom-like cap on the tip. How and why the indium droplets formed is not

  10. Improvement of the crystallinity of CdTe epitaxial film grown on Si substrates by molecular beam epitaxy using the two-step growth method

    Energy Technology Data Exchange (ETDEWEB)

    Han, M.S.; Ryu, Y.S.; Song, B.K.; Kang, T.W. [Dongguk Univ., Seoul (Korea, Republic of). Dept. of Phys.; Kim, T.W. [Department of Physics, Kwangwoon University, Seoul 139-701 (Korea, Republic of)

    1997-01-05

    Molecular beam epitaxy growth of CdTe epitaxial layers on Si (100) substrates using the two-step growth method was performed to produce high-quality CdTe thin layers. The reflection high-energy electron diffraction patterns were streaky with clear Kikuchi lines, which is direct evidence for layer-by-layer two-dimensional growth of CdTe on Si. From the X-ray diffraction analysis, the grown layer was found to be a CdTe (111) epitaxial film, regardless of the film thickness. Photoluminescence (PL) measurements at 12 K showed that the defect density of the CdTe film grown on Si using two-step growth decreased in comparison with that grown using direct growth. The bound exciton appearing in the PL measurements shifted to the low energy side as the thickness of the CdTe increased. When the CdTe thickness increased from 1 to 1.8 {mu}m, the peak position of the bound exciton shifted by 7.2 meV, and the stress obtained from the exciton peak shift was -12.405 kbar. These results indicate that high quality CdTe films grown by two-step growth hold promise for applications as buffer layers for the subsequent growth of Hg{sub x}Cd{sub 1-x}Te. (orig.) 16 refs.

  11. Minority carrier lifetime in iodine-doped molecular beam epitaxy-grown HgCdTe

    Energy Technology Data Exchange (ETDEWEB)

    Madni, I.; Umana-Membreno, G. A.; Lei, W.; Gu, R.; Antoszewski, J.; Faraone, L. [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, Crawley, Western Australia 6009 (Australia)

    2015-11-02

    The minority carrier lifetime in molecular beam epitaxy grown layers of iodine-doped Hg{sub 1−x}Cd{sub x}Te (x ∼ 0.3) on CdZnTe substrates has been studied. The samples demonstrated extrinsic donor behavior for carrier concentrations in the range from 2 × 10{sup 16} cm{sup −3} to 6 × 10{sup 17} cm{sup −3} without any post-growth annealing. At a temperature of 77 K, the electron mobility was found to vary from 10{sup 4} cm{sup 2}/V s to 7 × 10{sup 3} cm{sup 2}/V s and minority carrier lifetime from 1.6 μs to 790 ns, respectively, as the carrier concentration was increased from 2 × 10{sup 16} cm{sup −3} to 6 × 10{sup 17} cm{sup −3}. The diffusion of iodine is much lower than that of indium and hence a better alternative in heterostructures such as nBn devices. The influence of carrier concentration and temperature on the minority carrier lifetime was studied in order to characterize the carrier recombination mechanisms. Measured lifetimes were also analyzed and compared with the theoretical models of the various recombination processes occurring in these materials, indicating that Auger-1 recombination was predominant at higher doping levels. An increase in deep-level generation-recombination centers was observed with increasing doping level, which suggests that the increase in deep-level trap density is associated with the incorporation of higher concentrations of iodine into the HgCdTe.

  12. Ge/GeSn heterostructures grown on Si (100) by molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Sadofyev, Yu. G., E-mail: sadofyev@hotmail.com; Martovitsky, V. P.; Bazalevsky, M. A.; Klekovkin, A. V. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Averyanov, D. V.; Vasil’evskii, I. S. [National Research Nuclear University MEPhI (Russian Federation)

    2015-01-15

    The growth of GeSn layers by molecular-beam epitaxy on Si (100) wafers coated with a germanium buffer layer is investigated. The properties of the fabricated structures are controlled by reflection high-energy electron diffraction, atomic-force microscopy, X-ray diffractometry, Rutherford backscattering, and Raman scattering. It is shown that GeSn layers with thicknesses up to 0.5 μm and Sn molar fractions up to 0.073 manifest no sign of plastic relaxation upon epitaxy. The lattice constant of the GeSn layers within the growth plane is precisely the same as that of Ge. The effect of rapid thermal annealing on the conversion of metastable elastically strained GeSn layers into a plastically relaxed state is examined. Ge/GeSn quantum wells with Sn molar fraction up to 0.11 are obtained.

  13. Correlation between Defect Concentration and Carrier Lifetime of GaAs Grown by Molecular Beam Epitaxy at Different Temperatures

    Science.gov (United States)

    Lin, Gong-Ru; Liu, Tze-An; Pan, Ci-Ling

    2001-11-01

    A pump-probe study of GaAs grown by molecular beam epitaxy at low temperatures (LT-GaAs) is performed. Ultrashort carrier lifetimes of the as-grown LT-GaAs increase from Schokley-Read-Hall model. The decreasing trend in the amplitudes of continuous-wave and transient reflectivities (Δ R/R) as a function of the growth temperature for the LT-GaAs is explained as an induced absorption caused by dense arsenic antisite defects. The sign of the transient Δ R/R reversed for LT-GaAs grown at 200°C. This is tentatively attributed to the band gap renormalization effect.

  14. Magnetic and transport properties of epitaxial thin film MgFe2O4 grown on MgO (100) by molecular beam epitaxy.

    Science.gov (United States)

    Wu, Han-Chun; Mauit, Ozhet; Coileáin, Cormac Ó; Syrlybekov, Askar; Khalid, Abbas; Mouti, Anas; Abid, Mourad; Zhang, Hong-Zhou; Abid, Mohamed; Shvets, Igor V

    2014-11-12

    Magnesium ferrite is a very important magnetic material due to its interesting magnetic and electrical properties and its chemical and thermal stability. Here we report on the magnetic and transport properties of epitaxial MgFe2O4 thin films grown on MgO (001) by molecular beam epitaxy. The structural properties and chemical composition of the MgFe2O4 films were characterized by X-Ray diffraction and X-Ray photoelectron spectroscopy, respectively. The nonsaturation of the magnetization in high magnetic fields observed for M (H) measurements and the linear negative magnetoresistance (MR) curves indicate the presence of anti-phase boundaries (APBs) in MgFe2O4. The presence of APBs was confirmed by transmission electron microscopy. Moreover, post annealing decreases the resistance and enhances the MR of the film, suggesting migration of the APBs. Our results may be valuable for the application of MgFe2O4 in spintronics.

  15. Peculiarly strong room-temperature ferromagnetism from low Mn-doping in ZnO grown by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Zheng Zuo

    2013-03-01

    Full Text Available Strong room-temperature ferromagnetism is demonstrated in single crystalline Mn-doped ZnO thin films grown by molecular beam epitaxy. Very low Mn doping concentration is investigated, and the measured magnetic moment is much larger than what is expected for an isolated ion based on Hund's rules. The ferromagnetic behavior evolves with Mn concentration. Both magnetic anisotropy and anomalous Hall effect confirm the intrinsic nature of ferromagnetism. While the Mn dopant plays a crucial role, another entity in the system is needed to explain the observed large magnetic moments.

  16. Ultraviolet light-emitting diodes grown by plasma-assisted molecular beam epitaxy on semipolar GaN (2021) substrates

    Energy Technology Data Exchange (ETDEWEB)

    Sawicka, M.; Grzanka, S.; Skierbiszewski, C. [Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw (Poland); TopGaN Sp. z o.o., Sokolowska 29/37, 01-142 Warsaw (Poland); Cheze, C. [TopGaN Sp. z o.o., Sokolowska 29/37, 01-142 Warsaw (Poland); Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Turski, H.; Muziol, G.; Krysko, M.; Grzanka, E.; Sochacki, T. [Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw (Poland); Hauswald, C.; Brandt, O. [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Siekacz, M. [Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw (Poland); Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Kucharski, R. [Ammono S.A., Czerwonego Krzyza 2/31, 00-377 Warsaw (Poland); Remmele, T.; Albrecht, M. [Leibniz Institute for Crystal Growth, Max-Born Strasse 2, Berlin 12489 (Germany)

    2013-03-18

    Multi-quantum well (MQW) structures and light emitting diodes (LEDs) were grown on semipolar (2021) and polar (0001) GaN substrates by plasma-assisted molecular beam epitaxy. The In incorporation efficiency was found to be significantly lower for the semipolar plane as compared to the polar one. The semipolar MQWs exhibit a smooth surface morphology, abrupt interfaces, and a high photoluminescence intensity. The electroluminescence of semipolar (2021) and polar (0001) LEDs fabricated in the same growth run peaks at 387 and 462 nm, respectively. Semipolar LEDs with additional (Al,Ga)N cladding layers exhibit a higher optical output power but simultaneously a higher turn-on voltage.

  17. Emission control of InGaN nanocolumns grown by molecular-beam epitaxy on Si(111) substrates

    Energy Technology Data Exchange (ETDEWEB)

    Albert, S.; Bengoechea-Encabo, A.; Sanchez-Garcia, M. A.; Calleja, E. [ISOM and Departamento de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Lefebvre, P. [ISOM and Departamento de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Universite Montpellier 2, F-34095 Montpellier, Cedex 5 (France); Jahn, U.; Trampert, A. [Paul-Drude-Institut fuer Festkoeperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2011-09-26

    This work studies the effect of the growth temperature on the morphology and emission characteristics of self-assembled InGaN nanocolumns grown by plasma assisted molecular beam epitaxy. Morphology changes are assessed by scanning electron microscopy, while emission is measured by photoluminescence. Within the growth temperature range of 750 to 650 deg. C, an increase in In incorporation for decreasing temperature is observed. This effect allows tailoring the InGaN nanocolumns emission line shape by using temperature gradients during growth. Depending on the gradient rate, span, and sign, broad emission line shapes are obtained, covering the yellow to green range, even yielding white emission.

  18. GaN Schottky diodes with single-crystal aluminum barriers grown by plasma-assisted molecular beam epitaxy

    Science.gov (United States)

    Tseng, H. Y.; Yang, W. C.; Lee, P. Y.; Lin, C. W.; Cheng, Kai-Yuan; Hsieh, K. C.; Cheng, K. Y.; Hsu, C.-H.

    2016-08-01

    GaN-based Schottky barrier diodes (SBDs) with single-crystal Al barriers grown by plasma-assisted molecular beam epitaxy are fabricated. Examined using in-situ reflection high-energy electron diffractions, ex-situ high-resolution x-ray diffractions, and high-resolution transmission electron microscopy, it is determined that epitaxial Al grows with its [111] axis coincident with the [0001] axis of the GaN substrate without rotation. In fabricated SBDs, a 0.2 V barrier height enhancement and 2 orders of magnitude reduction in leakage current are observed in single crystal Al/GaN SBDs compared to conventional thermal deposited Al/GaN SBDs. The strain induced piezoelectric field is determined to be the major source of the observed device performance enhancements.

  19. In situ photoelectron spectroscopy of molecular-beam-epitaxy grown surfaces

    CERN Document Server

    Oshima, M; Okabayashi, J; Ono, K

    2003-01-01

    Two in situ high-resolution synchrotron radiation photoelectron spectroscopy (SRPES) systems combined with a molecular beam epitaxy (MBE) chamber for III-V compound semiconductors and a laser MBE chamber for strongly correlated oxide films, respectively, have been designed and fabricated to analyze intrinsic and surface/interface electronic structures of these unique materials. The importance of the in situ SRPES has been demonstrated by the results of 1) Si surface nanostructures, 2) GaAs surfaces/interfaces and nanostructures, 3) MnAs magnetic nanostructures, and 4) strongly-correlated La sub 1 sub - sub x Sr sub x MnO sub 3 surfaces/interfaces and superstructures.

  20. Photoconducting ultraviolet detectors based on GaN films grown by electron cyclotron resonance molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Misra, M.; Shah, K.S. [Radiation Monitoring Devices, Inc., Watertown, MA (United States); Moustakas, T.D.; Vaudo, R.P.; Singh, R. [Boston Univ., MA (United States). Molecular Beam Epitaxy Lab.

    1995-08-01

    We report for the first time, fabrication of photoconducting UV detectors made from GaN films grown by molecular beam epitaxy. Semi-instilating GaN films were grown by the method of electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy (ECR-MBE). Photoconductive devices with interdigitated electrodes were fabricated and their photoconducting properties were investigated. In this paper we report on the performance of the detectors in terms of UV responsivity, gain-quantum efficiency product, spectral response and response time. We have measured responsivity of 125A/W and gain-quantum efficiency product of 600 at 254nm and 25V. The response time was measured to be on the order of 20ns for our detectors, corresponding to a bandwidth of 25Mhz. The spectral response showed a sharp long-wavelength cutoff at 365nm, and remained constant in the 200nm to 365nm range. The response of the detectors to low-energy x-rays was measured and found to be linear for x-rays with energies ranging from 60kVp to 90kVp.

  1. Optical sites in Eu- and Mg-codoped GaN grown by NH3-source molecular beam epitaxy

    Science.gov (United States)

    Sekiguchi, Hiroto; Sakai, Masaru; Kamada, Takuho; Tateishi, Hiroki; Syouji, Atsushi; Wakahara, Akihiro

    2016-10-01

    Mg codoping can improve the luminescence properties of Eu-doped GaN. However, the enhanced optical sites differ depending on the fabrication method. In this study, the optical sites in Eu- and Mg-codoped GaN [GaN:(Eu, Mg)] grown by NH3-source molecular beam epitaxy (MBE) were evaluated. The optical properties of an Eu-Mg-related site grown by NH3-MBE were highly stable against thermal annealing. Although the luminescence at sites A (622.3 and 633.8 nm) and B (621.9 and 622.8 nm) was dominant under indirect excitation of Eu ions through GaN, four different optical site groups in addition to sites A and B were observed under resonant excitation. These optical sites are inconsistent with the Eu-Mg-related sites reportedly observed in GaN:(Eu, Mg) fabricated by organometallic vapor phase epitaxy, indicating that the optical site constitution strongly depends on the growth method. Furthermore, site A, with a high cross section, contributed to as much as 22% of the total photoluminescence (PL) integrated intensity for GaN:(Eu, Mg) grown by NH3-MBE, which resulted in a high PL intensity.

  2. Electrical and Optical Studies of Defect Structure of HgCdTe Films Grown by Molecular Beam Epitaxy

    Science.gov (United States)

    Świątek, Z.; Ozga, P.; Izhnin, I. I.; Fitsych, E. I.; Voitsekhovskii, A. V.; Korotaev, A. G.; Mynbaev, K. D.; Varavin, V. S.; Dvoretsky, S. A.; Mikhailov, N. N.; Yakushev, M. V.; Bonchyk, A. Yu.; Savytsky, H. V.

    2016-07-01

    Electrical and optical studies of defect structure of HgCdTe films grown by molecular beam epitaxy (MBE) are performed. It is shown that the peculiarity of these films is the presence of neutral defects formed at the growth stage and inherent to the material grown by MBE. It is assumed that these neutral defects are the Te nanocomplexes. Under ion milling, they are activated by mercury interstitials and form the donor centers with the concentration of 1017 cm-3, which makes it possible to detect such defects by measurements of electrical parameters of the material. Under doping of HgCdTe with arsenic using high temperature cracking, the As2 dimers are present in the arsenic flow and block the neutral Te nanocomplexes to form donor As2Te3 complexes. The results of electrical studies are compared with the results of studies carried out by micro-Raman spectroscopy.

  3. Synthesis of as-grown superconducting MgB{sub 2} thin films by molecular beam epitaxy in UHV conditions

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Y.; Uduka, M.; Nakanishi, Y.; Yoshimoto, N.; Yoshizawa, M

    2004-10-01

    As-grown superconducting MgB{sub 2} thin films have been grown on SrTiO{sub 3}(0 0 1), MgO(0 0 1), and Al{sub 2}O{sub 3}(0 0 0 1) substrates by a molecular beam epitaxy (MBE) method with novel co-evaporation conditions of low deposition rate in ultra-high vacuum. The structural and physical properties of the films were studied by RHEED, XRD, electrical resistivity measurements, and SQUID magnetometer. The RHEED patterns indicate three-dimensional growth for MgB{sub 2}. The highest T{sub c} determined by resistivity measurement was about 36 K in these samples. And a clear Meissner effect below T{sub c} was observed using magnetic susceptibility measurement. We will discuss the influence of B buffer layer on the structural and physical properties.

  4. Low Microwave Surface Resistance in NdBa2Cu3O7-d Films Grown by Molecular Beam Epitaxy

    OpenAIRE

    2004-01-01

    We report the growth of NdBa2Cu3O7-d films on (100) MgO substrate by Molecular Beam Epitaxy (MBE). Large area NdBa2Cu3O7-d films with homogeneous superconducting properties were grown by precise control of stoichiometry and the optimisation of growth parameters. The stoichiometric ratio of Nd:Ba:Cu close to 1:2:3 yields films with TC of 94 K and JC values above 3.5 MA/cm2 at 77 K on bare MgO substrate. The NdBa2Cu3O7-d films grown under optimised conditions had excellent in-plane texture and ...

  5. Characteristics of AlN/GaN nanowire Bragg mirror grown on (001) silicon by molecular beam epitaxy

    KAUST Repository

    Heo, Junseok

    2013-10-01

    GaN nanowires containing AlN/GaN distributed Bragg reflector (DBR) heterostructures have been grown on (001) silicon substrate by molecular beam epitaxy. A peak reflectance of 70% with normal incidence at 560 nm is derived from angle resolved reflectance measurements on the as-grown nanowire DBR array. The measured peak reflectance wavelength is significantly blue-shifted from the ideal calculated value. The discrepancy is explained by investigating the reflectance of the nanoscale DBRs with a finite difference time domain technique. Ensemble nanowire microcavities with In0.3Ga 0.7N nanowires clad by AlN/GaN DBRs have also been characterized. Room temperature emission from the microcavity exhibits considerable linewidth narrowing compared to that measured for unclad In0.3Ga0.7N nanowires. The resonant emission is characterized by a peak wavelength and linewidth of 575 nm and 39 nm, respectively. © 2013 AIP Publishing LLC.

  6. GaAs Based InAs/GaSb Superlattice Short Wavelength Infrared Detectors Grown by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    TANG Bao; XU Ying-Qiang; ZHOU Zhi-Qiang; HAO Rui-Ting; WANG Guo-Wei; REN Zheng-Wei; NIU Zhi-Chuan

    2009-01-01

    InAs/GaSb superlattice (SL) short wavelength infrared photoconduction detectors are grown by molecular beam epitaxy on GaAs(O01) semi-insulating substrates. An interracial misfit mode A1Sb quantum dot layer and a thick GaSb layer are grown as buffer layers. The detectors containing a 200-period 2 ML/8 ML InAs/GaSb SL active layer are fabricated with a pixel area of 800×800 μm2 without using passivation or antireflection coatings. Corresponding to the 50% cutoff wavelengths of 2.05 μm at 77K and 2.25 μ m at 300 K, the peak detectivities of the detectors are 4 × 109 cm·Hz1/2/W at 77K and 2 × 108 cm.Hz1/2/W at 30OK, respectively.

  7. Magnetotransport in MgO-based magnetic tunnel junctions grown by molecular beam epitaxy (invited)

    Energy Technology Data Exchange (ETDEWEB)

    Andrieu, S., E-mail: stephane.andrieu@univ-lorraine.fr; Bonell, F.; Hauet, T.; Montaigne, F. [Institut Jean Lamour, Nancy University/CNRS, Bd des Aiguillettes, BP239, 54506 Vandoeuvre-lès-Nancy (France); Calmels, L.; Snoeck, E. [CEMES, CNRS and Toulouse University, 29 rue Jeanne Marvig, 31055 Toulouse (France); Lefevre, P.; Bertran, F. [Synchrotron SOLEIL-CNRS, L' Orme des Merisiers, Saint-Aubin, BP48, 91192 Gif-sur-Yvette cedex (France)

    2014-05-07

    The strong impact of molecular beam epitaxy growth and Synchrotron Radiation characterization tools in the understanding of fundamental issues in nanomagnetism and spintronics is illustrated through the example of fully epitaxial MgO-based Magnetic Tunnel Junctions (MTJs). If ab initio calculations predict very high tunnel magnetoresistance (TMR) in such devices, some discrepancy between theory and experiments still exists. The influence of imperfections in real systems has thus to be considered like surface contaminations, structural defects, unexpected electronic states, etc. The influence of possible oxygen contamination at the Fe/MgO(001) interface is thus studied, and is shown to be not so detrimental to TMR as predicted by ab initio calculations. On the contrary, the decrease of dislocations density in the MgO barrier of MTJs using Fe{sub 1−x}V{sub x} electrodes is shown to significantly increase TMR. Finally, unexpected transport properties in Fe{sub 1−X}Co{sub x}/MgO/Fe{sub 1−X}Co{sub x} (001) are presented. With the help of spin and symmetry resolved photoemission and ab initio calculation, the TMR decrease for Co content higher than 25% is shown to come from the existence of an interface state and the shift of the empty Δ1 minority spin state towards the Fermi level.

  8. Composition control of quinary GaInNAsSb alloy grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Miyashita, Naoya; Ahsan, Nazmul; Okada, Yoshitaka [Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904 (Japan); Islam, Muhammad Monirul [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan)

    2013-11-15

    In order to precisely control the composition of quinary GaInNAsSb alloy, we investigated the incorporation behavior of constituent atoms during atomic hydrogen-assisted molecular beam epitaxial growth. The nitrogen (N) composition, in comparison of GaNAs and GaNAsSb, increased by the supply of antimony (Sb). However, addition of indium (In) decreases the N composition during Sb mediated growth of GaInNAsSb, which enables obtaining the same N composition when an adequate In composition is chosen. It was revealed that Sb incorporation was increased when (i) In composition decreased, (ii) Sb flux increased, (iii) growth temperature decreased, and (iv) growth rate increased. These results are thought to be related to the effect of competitive role among strain, coverage, desorption, and segregation. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. HfSe2 thin films: 2D transition metal dichalcogenides grown by molecular beam epitaxy.

    Science.gov (United States)

    Yue, Ruoyu; Barton, Adam T; Zhu, Hui; Azcatl, Angelica; Pena, Luis F; Wang, Jian; Peng, Xin; Lu, Ning; Cheng, Lanxia; Addou, Rafik; McDonnell, Stephen; Colombo, Luigi; Hsu, Julia W P; Kim, Jiyoung; Kim, Moon J; Wallace, Robert M; Hinkle, Christopher L

    2015-01-27

    In this work, we demonstrate the growth of HfSe2 thin films using molecular beam epitaxy. The relaxed growth criteria have allowed us to demonstrate layered, crystalline growth without misfit dislocations on other 2D substrates such as highly ordered pyrolytic graphite and MoS2. The HfSe2 thin films exhibit an atomically sharp interface with the substrates used, followed by flat, 2D layers with octahedral (1T) coordination. The resulting HfSe2 is slightly n-type with an indirect band gap of ∼ 1.1 eV and a measured energy band alignment significantly different from recent DFT calculations. These results demonstrate the feasibility and significant potential of fabricating 2D material based heterostructures with tunable band alignments for a variety of nanoelectronic and optoelectronic applications.

  10. All-wurtzite (In,Ga)As-(Ga,Mn)As core-shell nanowires grown by molecular beam epitaxy.

    Science.gov (United States)

    Siušys, Aloyzas; Sadowski, Janusz; Sawicki, Maciej; Kret, Sławomir; Wojciechowski, Tomasz; Gas, Katarzyna; Szuszkiewicz, Wojciech; Kaminska, Agnieszka; Story, Tomasz

    2014-08-13

    Structural and magnetic properties of (In,Ga)As-(Ga,Mn)As core-shell nanowires grown by molecular beam epitaxy on GaAs(111)B substrate with gold catalyst have been investigated. (In,Ga)As core nanowires were grown at high temperature (500 °C) whereas (Ga,Mn)As shells were deposited on the {11̅00} side facets of the cores at much lower temperature (220 °C). High-resolution transmission electron microscopy images and high spectral resolution Raman scattering data show that both the cores and the shells of the nanowires have wurtzite crystalline structure. Scanning and transmission electron microscopy observations show smooth (Ga,Mn)As shells containing 5% of Mn epitaxially deposited on (In,Ga)As cores containing about 10% of In without any misfit dislocations at the core-shell interface. With the In content in the (In,Ga)As cores larger than 5% the (In,Ga)As lattice parameter is higher than that of (Ga,Mn)As and the shell is in the tensile strain state. Elaborated magnetic studies indicate the presence of ferromagnetic coupling in (Ga,Mn)As shells at the temperatures in excess of 33 K. This coupling is maintained only in separated mesoscopic volumes resulting in an overall superparamagnetic behavior which gets blocked below ∼ 17 K.

  11. Interfacial stability of CoSi2/Si structures grown by molecular beam epitaxy

    Science.gov (United States)

    George, T.; Fathauer, R. W.

    1992-01-01

    The stability of CoSi2/Si interfaces was examined in this study using columnar silicide structures grown on (111) Si substrates. In the first set of experiments, Co and Si were codeposited using MBE at 800 C and the resulting columnar silicide layer was capped by epitaxial Si. Deposition of Co on the surface of the Si capping layer at 800 C results in the growth of the buried silicide columns. The buried columns grow by subsurface diffusion of the deposited Co, suppressing the formation of surface islands of CoSi2. The column sidewalls appear to be less stable than the top and bottom interfaces, resulting in preferential lateral growth and ultimately in the coalescence of the columns to form a continuous buried CoSi2 layer. In the second set of experiments, annealing of a 250 nm-thick buried columnar layer at 1000 C under a 100 nm-thick Si capping layer results in the formation of a surface layer of CoSi2 with a reduction in the sizes of the CoSi2 columns. For a sample having a thicker Si capping layer the annealing leads to Ostwald ripening producing buried equiaxed columns. The high CoSi2/Si interfacial strain could provide the driving force for the observed behavior of the buried columns under high-temperature annealing.

  12. Effects of growth temperature and device structure on GaP solar cells grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Vaisman, M.; Tomasulo, S.; Masuda, T.; Lang, J. R.; Faucher, J.; Lee, M. L. [Department of Electrical Engineering, Yale University, New Haven, Connecticut 06511 (United States)

    2015-02-09

    Gallium phosphide (GaP) is an attractive candidate for wide-bandgap solar cell applications, possessing the largest bandgap of the III-arsenide/phosphides without aluminum. However, GaP cells to date have exhibited poor internal quantum efficiency (IQE), even for photons absorbed by direct transitions, motivating improvements in material quality and device structure. In this work, we investigated GaP solar cells grown by molecular beam epitaxy over a range of substrate temperatures, employing a much thinner emitter than in prior work. Higher growth temperatures yielded the best solar cell characteristics, indicative of increased diffusion lengths. Furthermore, the inclusion of an AlGaP window layer improved both open-circuit voltage and short wavelength IQE.

  13. Upper critical field of as-grown MgB{sub 2} thin films by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Y. [Department of Material Science and Engineering, Iwate University, Iwate Industrial Promotion Center, Iioka shinden 3-35-2, Morioka 020-0852 (Japan)]. E-mail: yharada@luck.ocn.ne.jp; Udsuka, M. [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka 020-8551 (Japan); Takahashi, T. [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka 020-8551 (Japan); Nakanishi, Y. [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka 020-8551 (Japan); Yoshizawa, M. [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka 020-8551 (Japan)

    2005-04-30

    Superconducting thin films of magnesium diboride (MgB{sub 2}) were prepared on MgO(001) substrate by molecular beam epitaxy in the co-evaporation conditions of low deposition rate and ultra-high vacuum. A superconducting transition with the onset temperature of 31.2K was confirmed by both transport and magnetization measurements. The upper critical fields are obtained from measurement of the field dependence of the resistivity. It was estimated that the upper critical field at 0K was more than 15T. The upper critical field anisotropy ratio, H{sub C2,ab}(0)/H{sub C2,c}(0), was estimated to be 1.78 from the magnetic field-temperature phase diagram for as-grown MgB{sub 2} thin films.

  14. Formation of strained interfaces in AlSb/InAs multilayers grown by molecular beam epitaxy for quantum cascade lasers

    Energy Technology Data Exchange (ETDEWEB)

    Nicolaï, J.; Warot-Fonrose, B.; Gatel, C., E-mail: christophe.gatel@cemes.fr; Ponchet, A. [CEMES CNRS-UPR 8011, Université de Toulouse, 29 rue Jeanne Marvig, 31055 Toulouse (France); Transpyrenean Associated Laboratory for Electron Microscopy (TALEM), CEMES-INA, CNRS-Universidad de Zaragoza, Toulouse (France); Teissier, R.; Baranov, A. N. [IES CNRS-UMR 5214, 34095 Montpellier (France); Magen, C. [Transpyrenean Associated Laboratory for Electron Microscopy (TALEM), CEMES-INA, CNRS-Universidad de Zaragoza, Toulouse (France); Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA)—ARAID and Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50018 Zaragoza (Spain)

    2015-07-21

    Structural and chemical properties of InAs/AlSb interfaces have been studied by transmission electron microscopy. InAs/AlSb multilayers were grown by molecular beam epitaxy with different growth sequences at interfaces. The out-of-plane strain, determined using high resolution microscopy and geometrical phase analysis, has been related to the chemical composition of the interfaces analyzed by high angle annular dark field imaging. Considering the local strain and chemistry, we estimated the interface composition and discussed the mechanisms of interface formation for the different growth sequences. In particular, we found that the formation of the tensile AlAs-type interface is spontaneously favored due to its high thermal stability compared to the InSb-type interface. We also showed that the interface composition could be tuned using an appropriate growth sequence.

  15. Molecular beam epitaxy-grown wurtzite MgS thin films for solar-blind ultra-violet detection

    Energy Technology Data Exchange (ETDEWEB)

    Lai, Y. H.; He, Q. L. [Nano Science and Nano Technology Program, The Hong Kong University of Science and Technology, HKSAR, People' s Republic of China (China); Department of Physics and William Mong Institute of Nano Science and Technology, The Hong Kong University of Science and Technology, HKSAR, People' s Republic of China (China); Cheung, W. Y.; Lok, S. K.; Wong, K. S.; Sou, I. K. [Department of Physics and William Mong Institute of Nano Science and Technology, The Hong Kong University of Science and Technology, HKSAR, People' s Republic of China (China); Ho, S. K. [Faculty of Science and Technology, University of Macau, Macau, People' s Republic of China (China); Tam, K. W. [Department of Electrical and Electronics Engineering, University of Macau, Macau, People' s Republic of China (China)

    2013-04-29

    Molecular beam epitaxy grown MgS on GaAs(111)B substrate was resulted in wurtzite phase, as demonstrated by detailed structural characterizations. Phenomenological arguments were used to account for why wurtzite phase is preferred over zincblende phase or its most stable rocksalt phase. Results of photoresponse and reflectance measurements performed on wurtzite MgS photodiodes suggest a direct bandgap at around 5.1 eV. Their response peaks at 245 nm with quantum efficiency of 9.9% and enjoys rejection of more than three orders at 320 nm and close to five orders at longer wavelengths, proving the photodiodes highly competitive in solar-blind ultraviolet detection.

  16. Compositional variations in In(0.5)Ga(0.5)N nanorods grown by molecular beam epitaxy.

    Science.gov (United States)

    Cherns, D; Webster, R F; Novikov, S V; Foxon, C T; Fischer, A M; Ponce, F A; Haigh, S J

    2014-05-30

    The composition of InxGa1 - xN nanorods grown by molecular beam epitaxy with nominal x = 0.5 has been mapped by electron microscopy using Z-contrast imaging and x-ray microanalysis. This shows a coherent and highly strained core-shell structure with a near-atomically sharp boundary between a Ga-rich shell (x ∼ 0.3) and an In-rich core (x ∼ 0.7), which itself has In- and Ga-rich platelets alternating along the growth axis. It is proposed that the shell and core regions are lateral and vertical growth sectors, with the core structure determined by spinodal decomposition.

  17. Long-wavelength PtSi infrared detectors fabricated by incorporating a p(+) doping spike grown by molecular beam epitaxy

    Science.gov (United States)

    Lin, T. L.; Park, J. S.; George, T.; Jones, E. W.; Fathauer, R. W.; Maserjian, J.

    1993-01-01

    By incorporating a 1-nm-thick p(+) doping spike at the PtSi/Si interface, we have successfully demonstrated extended cutoff wavelengths of PtSi Schottky infrared detectors in the long wavelength infrared (LWIR) regime for the first time. The extended cutoff wavelengths resulted from the combined effects of an increased electric field near the silicide/Si interface due to the p(+) doping spike and the Schottky image force. The p(+) doping spikes were grown by molecular beam epitaxy at 450 C, using elemental boron as the dopant source, with doping concentrations ranging from 5 x 10 exp 19 to 2 x 10 exp 20/cu cm. Transmission electron microscopy indicated good crystalline quality of the doping spikes. The cutoff wavelengths were shown to increase with increasing doping concentrations of the p(+) spikes. Thermionic emission dark current characteristics were observed and photoresponses in the LWIR regime were demonstrated.

  18. Bending stability of GaN grown on a metallic flexible substrate by plasma-assisted molecular beam epitaxy

    Science.gov (United States)

    Rodríguez, A. G.; Chávez-Veloz, S. G.; Compeán-García, V. D.; López-Luna, E.; Vidal, M. A.

    2017-08-01

    GaN thin films were grown on flexible metallic substrates by molecular beam epitaxy. MgO buffer layers were deposited by spin coating on Ni-Mo-Cr (Hastelloy C-276) alloy tapes that were used as substrates. The structural characterization of the GaN/MgO/hastelloy samples was performed by x-ray diffraction and Raman spectroscopy. The obtained nanometric films have the stable hexagonal phase (α-GaN) with an average crystallite size of 18 nm. The long and short range order of GaN decrease when the structure is bent. The most significant variations in the structural properties occur between 100 and 250 bending cycles.

  19. Low-damping sub-10-nm thin films of lutetium iron garnet grown by molecular-beam epitaxy

    Science.gov (United States)

    Jermain, C. L.; Paik, H.; Aradhya, S. V.; Buhrman, R. A.; Schlom, D. G.; Ralph, D. C.

    2016-11-01

    We analyze the structural and magnetic characteristics of (111)-oriented lutetium iron garnet (Lu3Fe5O12) films grown by molecular-beam epitaxy, for films as thin as 2.8 nm. Thickness-dependent measurements of the in- and out-of-plane ferromagnetic resonance allow us to quantify the effects of two-magnon scattering, along with the surface anisotropy and the saturation magnetization. We achieve effective damping coefficients of 11.1 (9 )×10-4 for 5.3 nm films and 32 (3 )×10-4 for 2.8 nm films, among the lowest values reported to date for any insulating ferrimagnetic sample of comparable thickness.

  20. Correlation of nanochemistry and electrical properties in HfO2 films grown by metalorganic molecular-beam epitaxy

    Science.gov (United States)

    Moon, Tae-Hyoung; Ham, Moon-Ho; Myoung, Jae-Min

    2005-03-01

    We present the annealing effects on nanochemistry and electrical properties in HfO2 dielectrics grown by metalorganic molecular-beam epitaxy. After the postannealing treatment of HfO2 films in the temperature range of 600-800°C, the thicknesses and chemical states of the films were examined by high-resolution transmission electron microscopy and angle-resolved x-ray photoelectron spectroscopy. By comparing the line shapes of core-level spectra for the samples with different annealing temperatures, the concentrations of SiO and Hf-silicate with high dielectric constant are found to be highest for HfO2 film annealed at 700°C. This result supports that the accumulation capacitance of the sample annealed at 700°C is not deteriorated in spite of a steep increase in interfacial layer thickness compared with that of the sample annealed at 600°C.

  1. Perpendicular Magnetic Anisotropy and Spin Glass-like Behavior in Molecular Beam Epitaxy Grown Chromium Telluride Thin Films.

    Science.gov (United States)

    Roy, Anupam; Guchhait, Samaresh; Dey, Rik; Pramanik, Tanmoy; Hsieh, Cheng-Chih; Rai, Amritesh; Banerjee, Sanjay K

    2015-04-28

    Reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), vibrating sample magnetometry, and other physical property measurements are used to investigate the structure, morphology, magnetic, and magnetotransport properties of (001)-oriented Cr2Te3 thin films grown on Al2O3(0001) and Si(111)-(7×7) surfaces by molecular beam epitaxy. Streaky RHEED patterns indicate flat smooth film growth on both substrates. STM studies show the hexagonal arrangements of surface atoms. Determination of the lattice parameter from the atomically resolved STM image is consistent with the bulk crystal structures. Magnetic measurements show the film is ferromagnetic, having a Curie temperature of about 180 K, and a spin glass-like behavior was observed below 35 K. Magnetotransport measurements show the metallic nature of the film with a perpendicular magnetic anisotropy along the c-axis.

  2. Optical DLTS for the study of recombination centers in GaAsN grown by chemical beam epitaxy

    Science.gov (United States)

    Kowaki, Hiroyuki; Lee, Kan-Hua; Kojima, Takuto; Inagaki, Makoto; Ikeda, Kazuma; Bouzazi, Boussairi; Kojima, Nobuaki; Ohshita, Yoshio; Yamaguchi, Masafumi; Ekins-Daukes, N. J.

    2013-09-01

    New broad DLTS peak signals in GaAsN solar cell, grown by chemical beam epitaxy, were obtained using the combination of optical-irradiation and conventional Deep Level Transient Spectroscopy (DLTS). Those broad peak signals cannot be detected by conventional DLTS method in the dark. The broad peak signals were overlapped with three deep level states at least and showed the increase of DLTS peak intensity. However, the other deep level state (EV+0.60eV) showed no significant change of DLTS peak signals in the dark and optical excitation. The condition of minority carrier injection by optical irradiation indicated that the mechanism of carrier capture and emission at some deep centers had been changed.

  3. High quality InAlN single layers lattice-matched to GaN grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Gacevic, Z.; Fernandez-Garrido, S.; Calleja, E. [ISOM, Universidad Politecnica de Madrid, Avda. Complutense s/n, 28040 Madrid (Spain); Rebled, J. M.; Peiro, F. [LENS-MIND-IN2UB, Departament d' Electronica, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona (Spain); Estrade, S. [LENS-MIND-IN2UB, Departament d' Electronica, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona (Spain); TEM-MAT, CCiT-UB, Sole i Sabaris 1, 08028 Barcelona (Spain)

    2011-07-18

    We report on properties of high quality {approx}60 nm thick InAlN layers nearly in-plane lattice-matched to GaN, grown on c-plane GaN-on-sapphire templates by plasma-assisted molecular beam epitaxy. Excellent crystalline quality and low surface roughness are confirmed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. High annular dark field observations reveal a periodic in-plane indium content variation (8 nm period), whereas optical measurements evidence certain residual absorption below the band-gap. The indium fluctuation is estimated to be {+-} 1.2% around the nominal 17% indium content via plasmon energy oscillations assessed by electron energy loss spectroscopy with sub-nanometric spatial resolution.

  4. Cw and time-resolved spectroscopy in homoepitaxial GaN films and GaN-GaAlN quantum wells grown by molecular beam epitaxy.

    OpenAIRE

    Taliercio, Thierry; Gallart, Mathieu; Lefebvre, Pierre; Morel, Aurélien; Gil, Bernard; Allègre, Jacques; Grandjean, Nicolas; Massies, Jean; Grzegory, Izabella; Porowsky, Sylvester

    2001-01-01

    International audience; We have grown GaN films and GaN–AlGaN quantum wells (QWs) on homoepitaxial substrates, by molecular beam epitaxy using ammonia. Both the GaN film and the QW are found to have superior excitonic recombination properties which are extremely promising for the development of indium free ultra-violet lasers based on nitrides.

  5. Molecular beam epitaxy grown GeSn p-i-n photodetectors integrated on Si

    Energy Technology Data Exchange (ETDEWEB)

    Werner, J., E-mail: werner@iht.uni-stuttgart.de; Oehme, M.; Schirmer, A.; Kasper, E.; Schulze, J.

    2012-02-01

    GeSn p-i-n photodetectors with a low Sn mole fraction made by molecular beam epitaxy on Si substrates show higher optical responsivities for wavelength {lambda} > 1400 nm compared with p-i-n photodetectors made from pure Ge. The Sn incorporation in Ge is done by a low temperature growth step in order to minimize Sn segregation. The Sn incorporation and the alloy content are investigated by {mu}-Raman spectroscopy and calibrated Secondary Ion Mass Spectrometry. The photodetectors are manufactured with sharp doping transitions and are realized as double mesa structures with diameters from 1.5 {mu}m up to 80 {mu}m. The optical measurements are carried out with a broadband super continuum laser from {lambda} = 1200 nm up to {lambda} = 1700 nm. At a wavelength of {lambda} = 1550 nm the optical responsivity of these vertical GeSn diodes is 0.1 A/W. In comparison with a pure Ge detector of the same geometrical dimensions the optical responsivity is increased by factor of three as a result of Sn caused band gap reduction.

  6. Multiferroic fluoride BaCoF4 Thin Films Grown Via Molecular Beam Epitaxy

    Science.gov (United States)

    Borisov, Pavel; Johnson, Trent; García-Castro, Camilo; Kc, Amit; Schrecongost, Dustin; Cen, Cheng; Romero, Aldo; Lederman, David

    Multiferroic materials exhibit exciting physics related to the simultaneous presence of multiple long-range orders, in many cases consisting of antiferromagnetic (AF) and ferroelectric (FE) orderings. In order to provide a new, promising route for fluoride-based multiferroic material engineering, we grew multiferroic fluoride BaCoF4 in thin film form on Al2O3 (0001) substrates by molecular beam epitaxy. The films grow with the orthorhombic b-axis out-of-plane and with three in-plane structural twin domains along the polar c-axis directions. The FE ordering in thin films was verified by FE remanent hysteresis loops measurements at T = 14 K and by room temperature piezoresponse force microscopy (PFM). An AF behavior was found below Neel temperature TN ~ 80 K, which is in agreement with the bulk properties. At lower temperatures two additional magnetic phase transitions at 19 K and 41 K were found. First-principles calculations demonstrated that the growth strain applied to the bulk BaCoF4 indeed favors two canted spin orders, along the b- and a-axes, respectively, in addition to the main AF spin order along the c-axis. Supported by FAME (Contract 2013-MA-2382), WV Research Challenge Grant (HEPC.dsr.12.29), and DMREF-NSF 1434897.

  7. Ultrafast carrier dynamics and the role of grain boundaries in polycrystalline silicon thin films grown by molecular beam epitaxy

    Science.gov (United States)

    Titova, Lyubov V.; Cocker, Tyler L.; Xu, Sijia; Baribeau, Jean-Marc; Wu, Xiaohua; Lockwood, David J.; Hegmann, Frank A.

    2016-10-01

    We have used time-resolved terahertz spectroscopy to study microscopic photoconductivity and ultrafast photoexcited carrier dynamics in thin, pure, non-hydrogenated silicon films grown by molecular beam epitaxy on quartz substrates at temperatures ranging from 335 °C to 572 °C. By controlling the growth temperature, thin silicon films ranging from completely amorphous to polycrystalline with minimal amorphous phase can be achieved. Film morphology, in turn, determines its photoconductive properties: in the amorphous phase, carriers are trapped in bandtail states on sub-picosecond time scales, while the carriers excited in crystalline grains remain free for tens of picoseconds. We also find that in polycrystalline silicon the photoexcited carrier mobility is carrier-density-dependent, with higher carrier densities mitigating the effects of grain boundaries on inter-grain transport. In a film grown at the highest temperature of 572 °C, the morphology changes along the growth direction from polycrystalline with needles of single crystals in the bulk of the film to small crystallites interspersed with amorphous silicon at the top of the film. Depth profiling using different excitation wavelengths shows corresponding differences in the photoconductivity: the photoexcited carrier lifetime and mobility are higher in the first 100-150 nm from the substrate, suggesting that thinner, low-temperature grown polycrystalline silicon films are preferable for photovoltaic applications.

  8. Formation of long single quantum dots in high quality InSb nanowires grown by molecular beam epitaxy.

    Science.gov (United States)

    Fan, Dingxun; Li, Sen; Kang, N; Caroff, Philippe; Wang, L B; Huang, Y Q; Deng, M T; Yu, C L; Xu, H Q

    2015-09-28

    We report on realization and transport spectroscopy study of single quantum dots (QDs) made from InSb nanowires grown by molecular beam epitaxy (MBE). The nanowires employed are 50-80 nm in diameter and the QDs are defined in the nanowires between the source and drain contacts on a Si/SiO2 substrate. We show that highly tunable QD devices can be realized with the MBE-grown InSb nanowires and the gate-to-dot capacitance extracted in the many-electron regimes is scaled linearly with the longitudinal dot size, demonstrating that the devices are of single InSb nanowire QDs even with a longitudinal size of ∼700 nm. In the few-electron regime, the quantum levels in the QDs are resolved and the Landég-factors extracted for the quantum levels from the magnetotransport measurements are found to be strongly level-dependent and fluctuated in a range of 18-48. A spin-orbit coupling strength is extracted from the magnetic field evolutions of a ground state and its neighboring excited state in an InSb nanowire QD and is on the order of ∼300 μeV. Our results establish that the MBE-grown InSb nanowires are of high crystal quality and are promising for the use in constructing novel quantum devices, such as entangled spin qubits, one-dimensional Wigner crystals and topological quantum computing devices.

  9. Improvement of GaAsSb alloys on InP grown by molecular beam epitaxy with substrate tilting

    Science.gov (United States)

    Chou, C. Y.; Torfi, A.; Wang, W. I.

    2013-10-01

    GaAsSb alloys lattice-matched to InP substrate have been used in various electronic and optoelectronic applications due to their highly desirable band alignment for high-speed double heterojunction bipolar transistors. There is however an issue with GaAsSb alloys, composed approximately of 50% As and 50% Sb, lattice-matched to an InP substrate; it exhibits a miscibility gap, which is a significant problem for crystal growth. This paper addresses the effect of substrate tilting on the material properties of GaAsSb alloys closely lattice-matched to InP substrates by molecular beam epitaxy (MBE). InP(100) substrates tilted 0°off-(on-axis), 2°off-, 3°off-, and 4°off-axis were used for MBE growth, then the material qualities of GaAsSb epitaxial layers were compared using various techniques, including high resolution X-ray diffraction, photoluminescence (PL), Raman scattering, and transmission-line measurements (TLM). Substrate tilting improved the GaAsSb alloys with crystalline quality, shown by a narrower x-ray linewidth and enhanced optical quality as evidenced by a strong PL peak. The results of TLM show that the lowest sheet resistance was achieved at a 2° off-axis tilt. The results are expected to be applicable in devices that incorporate GaAsSb in the active layer grown by MBE.

  10. Growth and characterization of InP ringlike quantum-dot molecules grown by solid-source molecular beam epitaxy.

    Science.gov (United States)

    Jevasuwan, Wipakorn; Boonpeng, Poonyasiri; Panyakeow, Somsak; Ratanathammaphan, Somchai

    2010-11-01

    In this paper, we have studied the fabrication of InP ringlike quantum-dot molecules on GaAs(001) substrate grown by solid-source molecular beam epitaxy using droplet epitaxy technique and the effect of In deposition rate on the physical and optical properties of InP ringlike quantum-dot molecules. The In deposition rate is varied from 0.2 ML/s to 0.4, 0.8 and 1.6 ML/s. The surface morphology and cross-section were examined by ex-situ atomic force microscope and transmission electron microscope, respectively. The increasing of In deposition rate results in the decreasing of outer and inner diameters of InP ringlike quantum-dot molecules and height of InP quantum dots but increases the InP quantum dot and ringlike quantum-dot molecule densities. The photoluminescence peaks of InP ringlike quantum-dot molecules are blue-shifted and FWHM is narrower when In deposition rate is bigger.

  11. Critical issues for homoepitaxial GaN growth by molecular beam epitaxy on hydride vapor-phase epitaxy-grown GaN substrates

    Science.gov (United States)

    Storm, D. F.; Hardy, M. T.; Katzer, D. S.; Nepal, N.; Downey, B. P.; Meyer, D. J.; McConkie, Thomas O.; Zhou, Lin; Smith, David J.

    2016-12-01

    While the heteroepitaxial growth of gallium nitride-based materials and devices on substrates such as SiC, sapphire, and Si has been well-documented, the lack of a cost-effective source of bulk GaN crystals has hindered similar progress on homoepitaxy. Nevertheless, freestanding GaN wafers are becoming more widely available, and there is great interest in growing GaN films and devices on bulk GaN substrates, in order to take advantage of the greatly reduced density of threading dislocations, particularly for vertical devices. However, homoepitaxial GaN growth is far from a trivial task due to the reactivity and different chemical sensitivities of N-polar (000_1) and Ga-polar (0001) GaN surfaces, which can affect the microstructure and concentrations of impurities in homoepitaxial GaN layers. In order to achieve high quality, high purity homoepitaxial GaN, it is necessary to investigate the effect of the ex situ wet chemical clean, the use of in situ cleaning procedures, the sensitivity of the GaN surface to thermal decomposition, and the effect of growth temperature. We review the current understanding of these issues with a focus on homoepitaxial growth of GaN by molecular beam epitaxy (MBE) on c-plane surfaces of freestanding GaN substrates grown by hydride vapor phase epitaxy (HVPE), as HVPE-grown substrates are most widely available. We demonstrate methods for obtaining homoepitaxial GaN layers by plasma-assisted MBE in which no additional threading dislocations are generated from the regrowth interface and impurity concentrations are greatly reduced.

  12. Diffraction studies for stoichiometry effects in BaTiO3 grown by molecular beam epitaxy on Ge(001)

    Science.gov (United States)

    Hsu, Min-Hsiang Mark; Merckling, Clement; El Kazzi, Salim; Pantouvaki, Marianna; Richard, Oliver; Bender, Hugo; Meersschaut, Johan; Van Campenhout, Joris; Absil, Philippe; Van Thourhout, Dries

    2016-12-01

    In this work, we present a systematic study of the effect of the stoichiometry of BaTiO3 (BTO) films grown on the Ge(001) substrate by molecular-beam-epitaxy using different characterization methods relying on beam diffraction, including reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and selected-area electron diffraction in transmission electron microscopy. Surprisingly, over a wide range of [Ba]/[Ti] ratios, as measured by the Rutherford backscattering spectrometry, all the BTO layers exhibit the same epitaxial relationship BTO(001)//Ge(001) with the substrate, describing a 45° lattice rotation of the BTO lattice with respect to the Ge lattice. However, varying the [Ba]/[Ti] ratio does change the diffraction behavior. From RHEED patterns, we can derive that excessive [Ba] and [Ti] generate twinning planes and a rougher surface in the non-stoichiometric BTO layers. XRD allows us to follow the evolution of the lattice constants as a function of the [Ba]/[Ti] ratio, providing an option for tuning the tetragonality of the BTO layer. In addition, we found that the intensity ratio of the 3 lowest-order Bragg peaks I(001)/I(002), I(101)/I(002), and I(111)/I(002) derived from ω - 2θ scans characteristically depend on the BTO stoichiometry. To explain the relation between observed diffraction patterns and the stoichiometry of the BTO films, we propose a model based on diffraction theory explaining how excess [Ba] or [Ti] in the layer influences the diffraction response.

  13. Growth and characterization of molecular beam epitaxy-grown Bi2Te3-xSex topological insulator alloys

    Science.gov (United States)

    Tung, Y.; Chiang, Y. F.; Chong, C. W.; Deng, Z. X.; Chen, Y. C.; Huang, J. C. A.; Cheng, C.-M.; Pi, T.-W.; Tsuei, K.-D.; Li, Z.; Qiu, H.

    2016-02-01

    We report a systematic study on the structural and electronic properties of Bi2Te3-xSex topological insulator alloy grown by molecular beam epitaxy (MBE). A mixing ratio of Bi2Se3 to Bi2Te3 was controlled by varying the Bi:Te:Se flux ratio. X-ray diffraction and Raman spectroscopy measurements indicate the high crystalline quality for the as-grown Bi2Te3-xSex films. Substitution of Te by Se is also revealed from both analyses. The surfaces of the films exhibit terrace-like quintuple layers and their size of the characteristic triangular terraces decreases monotonically with increasing Se content. However, the triangular terrace structure gradually recovers as the Se content further increases. Most importantly, the angle-resolved photoemission spectroscopy results provide evidence of single-Dirac-cone like surface states in which Bi2Te3-xSex with Se/Te-substitution leads to tunable surface states. Our results demonstrate that by fine-tuned MBE growth conditions, Bi2Te3-xSex thin film alloys with tunable topological surface states can be obtained, providing an excellent platform for exploring the novel device applications based on this compound.

  14. Hybrid ZnO/GaN distributed Bragg reflectors grown by plasma-assisted molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    David Adolph

    2016-08-01

    Full Text Available We demonstrate crack-free ZnO/GaN distributed Bragg reflectors (DBRs grown by hybrid plasma-assisted molecular beam epitaxy using the same growth chamber for continuous growth of both ZnO and GaN without exposure to air. This is the first time these ZnO/GaN DBRs have been demonstrated. The Bragg reflectors consisted up to 20 periods as shown with cross-sectional transmission electron microscopy. The maximum achieved reflectance was 77% with a 32 nm wide stopband centered at 500 nm. Growth along both (0001 and (000 1 ̄ directions was investigated. Low-temperature growth as well as two-step low/high-temperature deposition was carried out where the latter method improved the DBR reflectance. Samples grown along the (0001 direction yielded a better surface morphology as revealed by scanning electron microscopy and atomic force microscopy. Reciprocal space maps showed that ZnO(000 1 ̄ /GaN reflectors are relaxed whereas the ZnO(0001/GaN DBRs are strained. The ability to n-type dope ZnO and GaN makes the ZnO(0001/GaN DBRs interesting for various optoelectronic cavity structures.

  15. Effects of growth temperature on nonpolar a-plane InN grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Rajpalke, Mohana K.; Bhat, Thirumaleshwara N.; Krupanidhi, S.B. [Materials Research Centre, Indian Institute of Science, Bangalore-560012 (India); Roul, Basanta [Materials Research Centre, Indian Institute of Science, Bangalore-560012 (India); Central Research Laboratory, Bharat Electronics, Bangalore-560013 (India); Kumar, Mahesh [Materials Research Centre, Indian Institute of Science, Bangalore-560012 (India); Centre of Excellence in Information and Communication Technology, Indian Institute of Technology, Jodhpur-342011 (India); Sinha, Neeraj [Office of Principal Scientific Advisor, Government of India, New Delhi 110011 (India); Department of Materials Science, Gulbarga University, Gulbarga 585 106 (India); Jali, V.M. [Department of Physics, Gulbarga University, Gulbarga 585 106 (India)

    2014-04-15

    Nonpolar a-plane InN films were grown on r-plane sapphire substrate by plasma assisted molecular beam epitaxy with GaN underlayer. Effect of growth temperature on structural, morphological, and optical properties has been studied. The growth of nonpolar a-plane (1 1 -2 0) orientation was confirmed by high resolution X-ray diffraction study. The film grown at 500 C shows better crystallinity with the rocking curve FWHM 0.67 and 0.85 along [0 0 0 1] and [1 -1 0 0] directions, respectively. Scanning electron micrograph shows formation of Indium droplets at higher growth temperature. Room tem-perature absorption spectra show growth temperature dependent band gap variation from 0.74-0.81 eV, consistent with the expected Burstein-Moss effect. The rectifying behaviour of the I-V curve indicates the existence of Schottky barrier at the InN and GaN interface. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Effects of AIN nucleation layer thickness on crystal quality of AIN grown by plasma-assisted molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Ren Fan; Hao Zhi-Biao; Hu Jian-Nan; Zhang Chen; Luo Yi

    2010-01-01

    In this paper,the effects of thickness of AIN nucleation layer grown at high temperature on AIN epi-layer crystalline quality are investigated.Crack-free AIN samples with various nucleation thicknesses are grown on sapphire substrates by plasma-assisted molecular beam epitaxy.The AIN crystalline quality is analysed by transmission electron microscope and x-ray diffraction(XRD)rocking curves in both(002)and(102)planes.The surface profiles of nucleation layer with different thicknesses after in-situ annealing are also analysed by atomic force microscope.A critical nucleation thickness for realising high quality AIN films is found.When the nucleation thickness is above a certain value,the(102)XRD full width at half maximum(FWHM)of AIN bulk increases with nucleation thickness increasing,whereas the(002)XRD FWHM shows an opposite trend.These phenomena can be attributed to the characteristics of nucleation islands and the evolution of crystal grains during AIN main layer growth.

  17. Submicron FETs Using Molecular Beam Epitaxy.

    Science.gov (United States)

    1979-08-01

    C NISMIMOTO N0001-77-C-0655 UNCLASSIFIED NLIiiII/mlum.. varian SUBMICRON FETs USING MOLECULAR BEAM EPITAXY 00 ANNUAL REPORT NO. 2 (August 1978...Ohmic Contacts to Highly Doped n-type GaAs Layers Grown by Molecular Beam Epitaxy (MBE) for Field-Effect Trans- istors," J. Appl. Phys. 50, 951 (1979...36 ’A, References (Cont.) 8. D. M. Collins, "The Use of SnTe as the Source of Donor Impurities in GaAs Grown by Molecular Beam Epitaxy ," Appl. Phys

  18. Enhancement of minority carrier lifetime of GaInP with lateral composition modulation structure grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Park, K. W.; Ravindran, Sooraj; Kang, S. J.; Hwang, H. Y.; Jho, Y. D. [School of Information and Communications, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of); Park, C. Y. [School of Information and Communications, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of); Jo, Y. R.; Kim, B. J. [School of Material Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of); Lee, Y. T., E-mail: ytlee@gist.ac.kr [School of Information and Communications, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of); Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of)

    2014-07-28

    We report the enhancement of the minority carrier lifetime of GaInP with a lateral composition modulated (LCM) structure grown using molecular beam epitaxy (MBE). The structural and optical properties of the grown samples are studied by transmission electron microscopy and photoluminescence, which reveal the formation of vertically aligned bright and dark slabs corresponding to Ga-rich and In-rich GaInP regions, respectively, with good crystal quality. With the decrease of V/III ratio during LCM GaInP growth, it is seen that the band gap of LCM GaInP is reduced, while the PL intensity remains high and is comparable to that of bulk GaInP. We also investigate the minority carrier lifetime of LCM structures made with different flux ratios. It is found that the minority carrier lifetime of LCM GaInP is ∼37 times larger than that of bulk GaInP material, due to the spatial separation of electrons and holes by In-rich and Ga-rich regions of the LCM GaInP, respectively. We further demonstrate that the minority carrier lifetime of the grown LCM GaInP structures can easily be tuned by simply adjusting the V/III flux ratio during MBE growth, providing a simple yet powerful technique to tailor the electrical and optical properties at will. The exceptionally high carrier lifetime and the reduced band gap of LCM GaInP make them a highly attractive candidate for forming the top cell of multi-junction solar cells and can enhance their efficiency, and also make them suitable for other optoelectronics devices, such as photodetectors, where longer carrier lifetime is beneficial.

  19. Electron beam pumped III-V nitride vertical cavity surface emitting lasers grown by molecular beam epitaxy

    Science.gov (United States)

    Ng, Hock Min

    The design and fabrication by molecular beam epitaxy of a prototype vertical cavity laser based on the III-V nitrides were investigated in this work. The bottom mirror of the laser consists of distributed Bragg reflectors (DBRs) based on quarterwave AlN (or AlxGa1-xN) and GaN layers. Such DBRs were designed for maximum reflectivity in the spectral region from 390--600 nm. The epitaxial growth of these two binaries on each other revealed that while AlN grows on GaN in a two-dimensional mode (Frank-van der Merwe mode), GaN grows on AlN in a three-dimensional mode (Stranski-Krastanov mode). In spite of that, DBRs with peak reflectance up to 99% and bandwidths of 45nm were fabricated. The measured reflectance spectra were compared with simulations using the transmission matrix method. The mechanical stability of these DBR structures due to non-uniform distribution of strain arising from lattice or thermal mismatch of the various components were also addressed. The active region of the laser consists of InGaN/GaN multiple quantum wells (MQWs). The existence of up to the third order diffraction peaks in the x-ray diffraction spectra suggests that the interfaces between InGaN and GaN are sharp with little interdiffusion at the growth temperature. The photoluminescence and cathodoluminescence spectra were analyzed to determine the optical quality of the MQWs. The best MQWs were shown to have a single emission peak at 397nm with full width half maximum (FWHM) of 11nm. Cathodoluminescence studies showed that there are spatially localized areas of intense light emission. The complete device was formed on (0001) sapphire substrates using the previously described DBRs as bottom mirrors and the MQWs as the active region. The top mirror of the device consists of metallic silver. The device was pumped by an electron beam from the top mirror side and the light output was collected from the sapphire side. Measurements at 100K showed narrowing of the linewidth with increasing pump

  20. Electric field-tunable BaxSr1-xTiO3 films with high figures of merit grown by molecular beam epitaxy

    Science.gov (United States)

    Mikheev, Evgeny; Kajdos, Adam P.; Hauser, Adam J.; Stemmer, Susanne

    2012-12-01

    We report on the dielectric properties of BaxSr1-xTiO3 (BST) films grown by molecular beam epitaxy on epitaxial Pt bottom electrodes. Paraelectric films (x ≲ 0.5) exhibit dielectric losses that are similar to those of BST single crystals and ceramics. Films with device quality factors greater than 1000 and electric field tunabilities exceeding 1:5 are demonstrated. The results provide evidence for the importance of stoichiometry control and the use of a non-energetic deposition technique for achieving high figures of merit of tunable devices with BST thin films.

  1. Structural, electrical, and optical characterization of coalescent p-n GaN nanowires grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kolkovsky, Vl. [Technische Universität Dresden, 01062 Dresden (Germany); Zytkiewicz, Z. R.; Sobanska, M.; Klosek, K. [Institute of Physics Polish Academy of Sciences, al. Lotnikow 32-46, 02-668 Warsaw (Poland); Korona, K. P. [Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw (Poland)

    2015-12-14

    The electrical, structural, and optical properties of coalescent p-n GaN nanowires (NWs) grown by molecular beam epitaxy on Si (111) substrate are investigated. From photoluminescence measurements the full width at half maximum of bound exciton peaks AX and DA is found as 1.3 and 1.2 meV, respectively. These values are lower than those reported previously in the literature. The current-voltage characteristics show the rectification ratio of about 10{sup 2} and the leakage current of about 10{sup −4} A/cm{sup 2} at room temperature. We demonstrate that the thermionic mechanism is not dominant in these samples and spatial inhomogeneties and tunneling processes through a ∼2 nm thick SiN{sub x} layer between GaN and Si could be responsible for deviation from the ideal diode behavior. The free carrier concentration in GaN NWs determined by capacitance-voltage measurements is about 4 × 10{sup 15 }cm{sup −3}. Two deep levels (H190 and E250) are found in the structures. We attribute H190 to an extended defect located at the interface between the substrate and the SiN{sub x} interlayer or near the sidewalls at the bottom of the NWs, whereas E250 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect.

  2. Kinetic limitation of chemical ordering in Bi2Te3-x Se x layers grown by molecular beam epitaxy.

    Science.gov (United States)

    Schreyeck, S; Brunner, K; Kirchner, A; Bass, U; Grauer, S; Schumacher, C; Gould, C; Karczewski, G; Geurts, J; Molenkamp, L W

    2016-04-13

    We study the chemical ordering in Bi2Te3-x Se x grown by molecular beam epitaxy on Si substrates. We produce films in the full composition range from x = 0 to 3, and determine their material properties using energy dispersive x-ray spectroscopy, x-ray diffraction and Raman spectroscopy. By fitting the parameters of a kinetic growth model to these results, we obtain a consistent description of growth at a microscopic level. Our main finding is that despite the incorporation of Se in the central layer being much more probable than that of Te, the formation of a fully ordered Te-Bi-Se-Bi-Te layer is prevented by kinetic of the growth process. Indeed, the Se concentration in the central layer of Bi2Te2Se1 reaches a maximum of only ≈ 75% even under ideal growth conditions. A second finding of our work is that the intensity ratio of the 0 0 12 and 0 0 6 x-ray reflections serves as an experimentally accessible quantitative measure of the degree of ordering in these films.

  3. Photoconductivity of ultra-thin Ge(GeSn) layers grown in Si by low-temperature molecular beam epitaxy

    Science.gov (United States)

    Talochkin, A. B.; Chistokhin, I. B.; Mashanov, V. I.

    2016-04-01

    Photoconductivity (PC) spectra of Si/Ge(GeSn)/Si structures with the ultra-thin (1.0-2.3 nm) Ge and GeSn alloy layers grown by the low-temperature (T = 100 °C) molecular beam epitaxy are studied. Photoresponse in the range of 1.2-0.4 eV related to light absorption in the buried Ge(GeSn) layer is observed. It is shown that in case of lateral PC, a simple diffusion model can be used to determine the absorption coefficient of this layer α ˜ 105 cm-1. This value is 100 times larger than that of a single Ge quantum dot layer and is reached significantly above the band gap of most bulk semiconductors. The observed absorption is caused by optical transitions between electron and hole states localized at the interfaces. The anomalous high value of α can be explained by the unusual state of Ge(GeSn) layer with high concentration of dangling bonds, the optical properties of which have been predicted theoretically by Knief and von Niessen (Phys. Rev. B 59, 12940 (1999)).

  4. Impedance spectroscopy characterization of GaAs nanowire bundles grown by metal-catalyzed molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Tirado, M., E-mail: mtirado@herrera.unt.edu.a [Laboratorio de Propiedades Dielectricas de la Materia, Dep. Fisica, FACET, Universidad Nacional de Tucuman, Avda. Independencia 1800, 4000 Tucuman (Argentina); Comedi, D. [Laboratorio de Fisica del Solido, Dep. Fisica, FACET, Universidad Nacional de Tucuman, Avda. Independencia 1800, 4000 Tucuman (Argentina); Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) (Argentina); LaPierre, R.R. [Dep. Eng. Physics, McMaster University, 1280 Main W, Hamilton L8S 4L7, ON (Canada)

    2010-04-16

    Vertically aligned GaAs nanowire (NW) bundles grown by gas-source molecular beam epitaxy on an n-doped GaAs substrate by a metal catalysis method and embedded in an insulating matrix (SU8-2) were studied by impedance spectroscopy. The DC current-voltage characteristics measured between Au dot contacts to the NW tips and the substrate exhibited Schottky behavior. A detailed analysis of the impedance data measured in reverse bias conditions is presented, which enables the elimination of the stray capacitance due to the insulating matrix, and the separation of the different contributions to the total admittance from the metal/NW Schottky interface and from the NW region beyond the barrier region. The observed NW conductances and capacitances are shown to be consistent with rough estimates based on the GaAs conductivity and permittivity data and the NW dimensions, and the NW conductance increases as a power law of the frequency. Possible charge transport mechanisms to explain this result are discussed.

  5. Behaviors of beryllium compensation doping in InGaAsP grown by gas source molecular beam epitaxy

    Science.gov (United States)

    Ma, Y. J.; Zhang, Y. G.; Gu, Y.; Xi, S. P.; Chen, X. Y.; Liang, Baolai; Juang, Bor-Chau; Huffaker, Diana L.; Du, B.; Shao, X. M.; Fang, J. X.

    2017-07-01

    We report structural properties as well as electrical and optical behaviors of beryllium (Be)-doped InGaAsP lattice-matched to InP grown by gas source molecular beam epitaxy. P type layers present a high degree of compensation on the order of 1018 cm-3, and for Be densities below 9.5×1017 cm-3, they are found to be n type. Enhanced incorporation of oxygen during Be doping is observed by secondary ion mass spectroscopy. Be in forms of interstitial donors or donor-like Be-O complexes for cell temperatures below 800°C is proposed to account for such anomalous compensation behaviors. A constant photoluminescence energy of 0.98 eV without any Moss-Burstein shift for Be doping levels up to 1018 cm-3 along with increased emission intensity due to passivation effect of Be is also observed. An increasing number of minority carriers tend to relax via Be defect state-related Shockley-Read-Hall recombination with the increase of Be doping density.

  6. Behaviors of beryllium compensation doping in InGaAsP grown by gas source molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Y. J. Ma

    2017-07-01

    Full Text Available We report structural properties as well as electrical and optical behaviors of beryllium (Be-doped InGaAsP lattice-matched to InP grown by gas source molecular beam epitaxy. P type layers present a high degree of compensation on the order of 1018 cm−3, and for Be densities below 9.5×1017 cm−3, they are found to be n type. Enhanced incorporation of oxygen during Be doping is observed by secondary ion mass spectroscopy. Be in forms of interstitial donors or donor-like Be-O complexes for cell temperatures below 800°C is proposed to account for such anomalous compensation behaviors. A constant photoluminescence energy of 0.98 eV without any Moss-Burstein shift for Be doping levels up to 1018 cm−3 along with increased emission intensity due to passivation effect of Be is also observed. An increasing number of minority carriers tend to relax via Be defect state-related Shockley-Read-Hall recombination with the increase of Be doping density.

  7. Defects, strain relaxation, and compositional grading in high indium content InGaN epilayers grown by molecular beam epitaxy

    Science.gov (United States)

    Bazioti, C.; Papadomanolaki, E.; Kehagias, Th.; Walther, T.; Smalc-Koziorowska, J.; Pavlidou, E.; Komninou, Ph.; Karakostas, Th.; Iliopoulos, E.; Dimitrakopulos, G. P.

    2015-10-01

    We investigate the structural properties of a series of high alloy content InGaN epilayers grown by plasma-assisted molecular beam epitaxy, employing the deposition temperature as variable under invariant element fluxes. Using transmission electron microscopy methods, distinct strain relaxation modes were observed, depending on the indium content attained through temperature adjustment. At lower indium contents, strain relaxation by V-pit formation dominated, with concurrent formation of an indium-rich interfacial zone. With increasing indium content, this mechanism was gradually substituted by the introduction of a self-formed strained interfacial InGaN layer of lower indium content, as well as multiple intrinsic basal stacking faults and threading dislocations in the rest of the film. We show that this interfacial layer is not chemically abrupt and that major plastic strain relaxation through defect introduction commences upon reaching a critical indium concentration as a result of compositional pulling. Upon further increase of the indium content, this relaxation mode was again gradually succeeded by the increase in the density of misfit dislocations at the InGaN/GaN interface, leading eventually to the suppression of the strained InGaN layer and basal stacking faults.

  8. Morphology and optical properties of InN layers grown by molecular beam epitaxy on silicon substrates

    Energy Technology Data Exchange (ETDEWEB)

    Grandal, J.; Sanchez-Garcia, M.A.; Calle, F.; Calleja, E. [Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain)

    2005-05-01

    This work reports on the morphology and photoluminescence (PL) properties of wurtzite InN layers grown by plasma assisted molecular beam epitaxy (PA-MBE) on AlN-buffered Si(111) substrates. The layer morphology can be controlled by the effective indium to nitrogen molecular flux ratio, from N-rich conditions that lead to columnar InN layers, to stoichiometric conditions leading to coalesced InN layers. X-Ray Diffraction (XRD) rocking curves around the InN (002) reflection yield a minimum value of 682 arcsec full width at half maximum (FWHM) for a coalesced InN layer. PL intensity from columnar InN samples is two orders of magnitude stronger than that corresponding to coalesced material, pointing to a much higher crystalline quality of the former. PL spectra in columnar InN layers reveal an emission at 0.75 eV (16 K) that follows the typical band-gap temperature dependence and shows a linear trend with the excitation power, suggesting a band-edge recombination that yields an estimate of the energy gap for InN around 0.72 eV at room temperature. No other emissions are observed at higher energies. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Recombination-current suppression in GaAs p-n junctions grown on AlGaAs buffer layers by molecular-beam epitaxy

    Science.gov (United States)

    Rancour, D. P.; Melloch, M. R.; Pierret, R. F.; Lundstrom, M. S.; Klausmeier-Brown, M. E.; Kyono, C. S.

    1987-08-01

    n+pp+GaAs and n+pP+ GaAs/GaAs/Al0.3Ga0.7As mesa diodes have been fabricated from films grown by molecular-beam epitaxy. The diodes made from films employing an AlGaAs buffer layer show marked improvements (a factor of 5 reduction) in recombination current densities. Deep level transient spectroscopy measurements moreover indicate that deep level concentrations are reduced by the AlGaAs buffer.

  10. Metamorphic InGaAs Quantum Well Laser Diodes at 1.5 μm on GaAs Grown by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    WANG Hai-Li; I. Tang-ring; S. M. Wang; WU Dong-Hai; WU ning-peng; NI Hqiao-Qiao; HUANG She-Song; XIONG Yong-Hua; WANG Peng-Fei; HAN Qin; NIU Zhi-Chuan

    2009-01-01

    We report a 1.5-μm InGaAs/GaAs quantum well laser diode grown by molecular beam epitaxy on InGaAs metamorphic buffers. At 150K, for a 1500×10μm2 ridge waveguide laser, the lasing wavelength is centred at 1.508μm and the threshold current density is 667 A/cm2 under pulsed operation. The pulsed lasers can operate up to 286 K.

  11. Studies of arsenic incorporation and P-type doping in epitaxial mercury cadmium telluride thin films grown by molecular beam epitaxy

    Science.gov (United States)

    Zandian, Majid

    Doped layer semiconductor structures provide possibilities for novel electronic devices. Growth of Hg1-xCdxTe by molecular beam epitaxy (MBE) allows precise control over the doping profile and position of heterojunctions as well as structural properties of this ternary alloy. Even though n-type doping using indium is well established, little is known about p-type doping in this material system by MBE. Several elements such as Ag, Au, Sb, Bi and P have been previously used, however high diffusion coefficient and amphoteric behavior of these atoms in HgCdTe has restricted their use in heterojunction devices where control over doping profiles and concentrations is needed. We investigated arsenic incorporation efficiency as a function of As 4 flux and growth temperature. The sticking coefficient of As is substantially higher at lower growth temperature compared to growth at 190°C. For samples grown at 170°C, the etch pit density (EPD) is higher compared to p-type As doped samples grown at 190°C. Higher EPD is associated with columnar twin defects observed in transmission electron microscopy (TEM) studies of low growth temperature samples. Growth at low temperature of 170°C causes Hg rich condition promoting twin formation. Therefore, growth of p-type layers doped with As at low temperatures require optimization of II/VI flux ratio to eliminate columnar twin defects. It is possible to incorporate As at normal MBE growth temperature of 190°C but very high flux of As has to used to overcome low sticking coefficient of As at these temperatures. We proposed a mechanism for the activation of As involving Hg vacancies (VHg··) where Te is moved to a Hg vacancy, leaving behind a Te vacancy, which is then filled by an As atom. The Te that is now on a Hg site (i.e., Te antisite) migrates to the surface and leaves the crystal.

  12. Molecular beam epitaxy

    CERN Document Server

    Pamplin, Brian R

    1980-01-01

    Molecular Beam Epitaxy introduces the reader to the use of molecular beam epitaxy (MBE) in the generation of III-V and IV-VI compounds and alloys and describes the semiconductor and integrated optics reasons for using the technique. Topics covered include semiconductor superlattices by MBE; design considerations for MBE systems; periodic doping structure in gallium arsenide (GaAs); nonstoichiometry and carrier concentration control in MBE of compound semiconductors; and MBE techniques for IV-VI optoelectronic devices. The use of MBE to fabricate integrated optical devices and to study semicond

  13. Investigation of CuGaSe2/CuInSe2 double heterojunction interfaces grown by molecular beam epitaxy

    OpenAIRE

    Sathiabama Thiru; Masaki Asakawa; Kazuki Honda; Atsushi Kawaharazuka; Atsushi Tackeuchi; Toshiki Makimoto; Yoshiji Horikoshi

    2015-01-01

    In-situ reflection high-energy electron diffraction (RHEED) observation and X-ray diffraction measurements were performed on heterojunction interfaces of CuGaSe2/CnInSe2/CuGaSe2 grown on GaAs (001) using migration-enhanced epitaxy. The streaky RHEED pattern and persistent RHEED intensity oscillations caused by the alternate deposition of migration-enhanced epitaxy sequence are observed and the growths of smooth surfaces are confirmed. RHEED observation results also confirmed constituent mater...

  14. Inverted vertical algan deep ultraviolet leds grown on p-SiC substrates by molecular beam epitaxy

    Science.gov (United States)

    Nothern, Denis Maurice

    Deep ultraviolet light emitting diodes (UV LEDs) are an important emerging technology for a number of applications such as water/air/surface disinfection, communications, and epoxy curing. However, as of yet, deep UV LEDs grown on sapphire substrates are neither efficient enough nor powerful enough to fully serve these and other potential applications. The majority of UV LEDs reported so far in the literature are grown on sapphire substrates and their design consists of AlGaN quantum wells (QWs) embedded in an AlGaN p-i-n junction with the n-type layer on the sapphire. These devices suffer from a high concentration of threading defects originating from the large lattice mismatch between the sapphire substrate and AlGaN alloys. Other issues include the poor doping efficiency of the n- and particularly the p-AlGaN alloys, the extraction of light through the sapphire substrate, and the heat dissipation through the thermally insulating sapphire substrate. These problems have historically limited the internal quantum efficiency (IQE), injection efficiency (IE), and light extraction efficiency (EE) of devices. As a means of addressing these efficiency and power challenges, I have contributed to the development of a novel inverted vertical deep UV LED design based on AlGaN grown on p-SiC substrates. Starting with a p-SiC substrate that serves as the p-type side of the p-i-n junction largely eliminates the necessity for the notoriously difficult p-type doping of AlGaN alloys, and allows for efficient heat dissipation through the highly thermally conductive SiC substrate. UV light absorption in the SiC substrate can be addressed by first growing p-type doped distributed Bragg reflectors (DBRs) on top of the substrate prior to the deposition of the active region of the device. A number of n-AlGaN films, AlGaN/AlGaN multiple quantum wells, and p-type doped AlGaN DBRs were grown by molecular beam epitaxy (MBE). These were characterized in situ by reflected high energy electron

  15. Superconducting thin films of As-free pnictide LaPd{sub 1-x}Sb{sub 2} grown by reactive molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Retzlaff, Reiner; Buckow, Alexander; Kurian, Jose; Alff, Lambert [Institute of Materials Science, Technische Universitaet Darmstadt, Petersenstr. 23, 64287 Darmstadt (Germany)

    2013-07-01

    We use reactive molecular beam epitaxy as synthesis technique for the search of arsenic free pnictide superconductors. Epitaxial thin films of LaPd{sub 1-x}Sb{sub 2} were grown on (100) MgO substrates from elemental sources by simultaneous evaporation of high purity La, Pd and Sb metals by e-gun. LaPd{sub 1-x}Sb{sub 2} belongs to a novel class of pnictide superconductors with a peculiar pnictide square net layer. Previously, we have reported epitaxial growth of isostructural Bi based compounds. The substitution of Bi by Sb leads to thin films with metallic behavior and room temperature resistivity of about 85 μΩ cm. The highest observed transition temperature T{sub c} inLaPd{sub 1-x}Sb{sub 2} is 3.1 K and does not depend on x. We discuss strategies to increase T{sub c} in this pnictide subfamily.

  16. As-free pnictide LaNi{sub 1-x}Sb{sub 2} thin films grown by reactive molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Retzlaff, Reiner; Buckow, Alexander; Kurian, Jose; Alff, Lambert [Institute of Materials Science, Technische Universitaet Darmstadt, Petersenstr. 23, 64287 Darmstadt (Germany)

    2012-07-01

    We use reactive molecular beam epitaxy (RMBE) as synthesis technique for the search of arsenic free pnictide superconductors. Epitaxial thin films of LaNi{sub 1-x}Sb{sub 2} were grown on (100)MgO substrates from elemental sources by simultaneous evaporation of high purity La, Ni and Sb metals by e-gun. The LaNi{sub 1-x}Sb{sub 2} thin films grow epitaxially and are (00l) oriented with high crystalline quality, as evident from RHEED and X-Ray diffraction studies. The Ni deficient LaNi{sub 1-x}Sb{sub 2} thin films show metallic behavior with a room temperature resistivity of 110 {mu}{Omega} cm, while the stoichiometric compound is a semiconductor/insulator. The isostructural compound with Bi as pnictide shows a superconducting transition with a T{sub C}(0) of 3.1 K.

  17. Laplace DLTS of molecular beam epitaxy GaAs grown on (100) and (211)B substrates

    Energy Technology Data Exchange (ETDEWEB)

    Mari, R.H.; Shafi, M.; Henini, M. [School of Physics and Astronomy, Nottingham Nanotechnology and Nanoscience Centre University of Nottingham, Nottingham NG7 2RD (United Kingdom)

    2009-12-15

    Deep Level Transient Spectroscopy (DLTS) and Laplace DLTS (LDLTS) techniques have been employed to study defects in n-type GaAs grown by MBE on (100) and (211)B GaAs planes. The DLTS spectra were different for the two GaAs substrate orientations. Five and four defect states are found in samples grown on (100) and (211)B GaAs planes, respectively with activation energies ranging from 0.054 eV to 0.570 eV. For all of the traps observed in our samples we obtained small activation energies as compared to the previous data published in literature on n-GaAs samples grown by MBE. This can be explained by the fact that the emission of the carriers depends on the applied electric field and temperature dependence of the carrier concentration. These two phenomena seem to explain the small trap energies seen in our samples. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Vacancy-type defects in Mg-doped GaN grown by ammonia-based molecular beam epitaxy probed using a monoenergetic positron beam

    Science.gov (United States)

    Uedono, Akira; Malinverni, Marco; Martin, Denis; Okumura, Hironori; Ishibashi, Shoji; Grandjean, Nicolas

    2016-06-01

    Vacancy-type defects in Mg-doped GaN were probed using a monoenergetic positron beam. GaN films with a thickness of 0.5-0.7 μm were grown on GaN/sapphire templates using ammonia-based molecular beam epitaxy and characterized by measuring Doppler broadening spectra. Although no vacancies were detected in samples with a Mg concentration [Mg] below 7 × 1019 cm-3, vacancy-type defects were introduced starting at above [Mg] = 1 × 1020 cm-3. The major defect species was identified as a complex between Ga vacancy (VGa) and multiple nitrogen vacancies (VNs). The introduction of vacancy complexes was found to correlate with a decrease in the net acceptor concentration, suggesting that the defect introduction is closely related to the carrier compensation. We also investigated Mg-doped GaN layers grown using In as the surfactant. The formation of vacancy complexes was suppressed in the subsurface region (≤80 nm). The observed depth distribution of defects was attributed to the thermal instability of the defects, which resulted in the introduction of vacancy complexes during the deposition process.

  19. Spin dynamics of ZnSe-ZnTe nanostructures grown by migration enhanced molecular beam epitaxy

    Science.gov (United States)

    Deligiannakis, Vasilios; Dhomkar, Siddharth; Ji, Haojie; Pagliero, Daniela; Kuskovsky, Igor L.; Meriles, Carlos A.; Tamargo, Maria C.

    2017-03-01

    We study the spin dynamics of ZnSe layers with embedded type-II ZnTe quantum dots using time resolved Kerr rotation (TRKR). Three samples were grown with an increasing amount of Te, which correlates with increased quantum dot (QD) density. Samples with a higher quantum dot density exhibit longer electron spin lifetimes, up to ˜1 ns at low temperatures. Tellurium isoelectronic centers, which form in the ZnSe spacer regions as a result of the growth conditions, were probed via spectrally dependent TRKR. Temperature dependent TRKR results show that samples with high QD density are not affected by an electron-hole exchange dephasing mechanism.

  20. Characterization of GaAlAs optical waveguide heterostructures grown by molecular beam epitaxy

    Science.gov (United States)

    Radens, C. J.; Jackson, H. E.; Boyd, J. T.; Bhasin, K. B.; Pouch, J. J.

    1988-01-01

    Multiple-layer GaAlAs optical waveguide heterostructures have been grown by MBE. These samples were designed to operate at 840 nm with negligible coupling of guided light to the absorbing GaAs substrate. The Al concentration was 13 percent for the guiding layer and was 16 percent for the cladding layers. The process for growing waveguide layers was calibrated primarily by high-energy electron diffraction, with the optical quality confirmed by photoluminescence measurements. Channel waveguide structures having widths of 5 microns were etched in a low-pressure magnetically confined multipolar plasma reactor. The resulting waveguide structures were characterized by Raman spectroscopy, ellipsometry, AES, and optical-waveguide loss measurements.

  1. Scanning Tunneling Microscopy and Spectroscopy of Air Exposure Effects on Molecular Beam Epitaxy Grown WSe2 Monolayers and Bilayers.

    Science.gov (United States)

    Park, Jun Hong; Vishwanath, Suresh; Liu, Xinyu; Zhou, Huawei; Eichfeld, Sarah M; Fullerton-Shirey, Susan K; Robinson, Joshua A; Feenstra, Randall M; Furdyna, Jacek; Jena, Debdeep; Xing, Huili Grace; Kummel, Andrew C

    2016-04-26

    The effect of air exposure on 2H-WSe2/HOPG is determined via scanning tunneling microscopy (STM). WSe2 was grown by molecular beam epitaxy on highly oriented pyrolytic graphite (HOPG), and afterward, a Se adlayer was deposited in situ on WSe2/HOPG to prevent unintentional oxidation during transferring from the growth chamber to the STM chamber. After annealing at 773 K to remove the Se adlayer, STM images show that WSe2 layers nucleate at both step edges and terraces of the HOPG. Exposure to air for 1 week and 9 weeks caused air-induced adsorbates to be deposited on the WSe2 surface; however, the band gap of the terraces remained unaffected and nearly identical to those on decapped WSe2. The air-induced adsorbates can be removed by annealing at 523 K. In contrast to WSe2 terraces, air exposure caused the edges of the WSe2 to oxidize and form protrusions, resulting in a larger band gap in the scanning tunneling spectra compared to the terraces of air-exposed WSe2 monolayers. The preferential oxidation at the WSe2 edges compared to the terraces is likely the result of dangling edge bonds. In the absence of air exposure, the dangling edge bonds had a smaller band gap compared to the terraces and a shift of about 0.73 eV in the Fermi level toward the valence band. However, after air exposure, the band gap of the oxidized WSe2 edges became about 1.08 eV larger than that of the WSe2 terraces, resulting in the electronic passivation of the WSe2.

  2. Deep levels in a-plane, high Mg-content Mg{sub x}Zn{sub 1-x}O epitaxial layers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Guer, Emre [Department of Physics, Faculty of Science, Atatuerk University, Erzurum 25240 (Turkey); 205 Dreese Laboratory, Department of Electrical and Computer Engineering, The Ohio State University, 2015 Neil Avenue, Columbus, Ohio 43210-1272 (United States); Tabares, G.; Hierro, A. [Dpto. Ingenieria Electronica and ISOM, Universidad Politecnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Arehart, A.; Ringel, S. A. [205 Dreese Laboratory, Department of Electrical and Computer Engineering, Ohio State University, 2015 Neil Avenue, Columbus, Ohio 43210-1272 (United States); Chauveau, J. M. [CRHEA-CNRS, 06560 Valbonne (France); University of Nice Sophia Antipolis, ParcValrose, 06102 Nice Cedex 2 (France)

    2012-12-15

    Deep level defects in n-type unintentionally doped a-plane Mg{sub x}Zn{sub 1-x}O, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of Mg{sub x}Zn{sub 1-x}O were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of E{sub c} - 1.4 eV, 2.1 eV, 2.6 V, and E{sub v} + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at E{sub c} - 2.1 eV, E{sub v} + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at E{sub v} + 0.3 eV and E{sub c} - 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the E{sub v} + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the E{sub c} - 1.4 eV and E{sub c} - 2.6 eV levels in Mg alloyed samples.

  3. Anisotropy of superconductivity of as-grown MgB$_2$ thin films by molecular beam epitaxy

    OpenAIRE

    Harada, Y.; Udsuka, M.; Nakanishi, Y.; Yoshizawa, M.

    2004-01-01

    Superconducting thin films of magnesium diboride (MgB$_2$) were prepared on MgO (001) substrate by a molecular beam epitaxy (MBE) method with the co-evaporation conditions of low deposition rate in ultra-high vacuum. The structural and physical properties of the films were studied by RHEED, XRD, XPS, resistivity and magnetization measurements.All films demonstrated superconductivity without use of any post-annealing process.The highest {\\it T}$_{c,onset}$ determined by resistivity measurement...

  4. Materials fundamentals of molecular beam epitaxy

    CERN Document Server

    Tsao, Jeffrey Y

    1992-01-01

    The technology of crystal growth has advanced enormously during the past two decades. Among, these advances, the development and refinement of molecular beam epitaxy (MBE) has been among the msot important. Crystals grown by MBE are more precisely controlled than those grown by any other method, and today they form the basis for the most advanced device structures in solid-state physics, electronics, and optoelectronics. As an example, Figure 0.1 shows a vertical-cavity surface emitting laser structure grown by MBE. * Provides comprehensive treatment of the basic materials and surface science principles that apply to molecular beam epitaxy * Thorough enough to benefit molecular beam epitaxy researchers * Broad enough to benefit materials, surface, and device researchers * Referenes articles at the forefront of modern research as well as those of historical interest.

  5. Accurate determination of optical bandgap and lattice parameters of Zn{sub 1-x}Mg{sub x}O epitaxial films (0{<=}x{<=}0.3) grown by plasma-assisted molecular beam epitaxy on a-plane sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Laumer, Bernhard [Walter Schottky Institut and Physics Department, Technische Universitaet Muenchen, Am Coulombwall 4, 85748 Garching (Germany); I. Physikalisches Institut, Justus-Liebig-Universitaet Giessen, Heinrich-Buff-Ring 16, 35392 Giessen (Germany); Schuster, Fabian; Stutzmann, Martin [Walter Schottky Institut and Physics Department, Technische Universitaet Muenchen, Am Coulombwall 4, 85748 Garching (Germany); Bergmaier, Andreas; Dollinger, Guenther [Universitaet der Bundeswehr Muenchen, Fakultaet fuer Luft- und Raumfahrttechnik, Werner-Heisenberg-Weg 39, 85577 Neubiberg (Germany); Eickhoff, Martin [I. Physikalisches Institut, Justus-Liebig-Universitaet Giessen, Heinrich-Buff-Ring 16, 35392 Giessen (Germany)

    2013-06-21

    Zn{sub 1-x}Mg{sub x}O epitaxial films with Mg concentrations 0{<=}x{<=}0.3 were grown by plasma-assisted molecular beam epitaxy on a-plane sapphire substrates. Precise determination of the Mg concentration x was performed by elastic recoil detection analysis. The bandgap energy was extracted from absorption measurements with high accuracy taking electron-hole interaction and exciton-phonon complexes into account. From these results a linear relationship between bandgap energy and Mg concentration is established for x{<=}0.3. Due to alloy disorder, the increase of the photoluminescence emission energy with Mg concentration is less pronounced. An analysis of the lattice parameters reveals that the epitaxial films grow biaxially strained on a-plane sapphire.

  6. Investigation of CuGaSe2/CuInSe2 double heterojunction interfaces grown by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Sathiabama Thiru

    2015-02-01

    Full Text Available In-situ reflection high-energy electron diffraction (RHEED observation and X-ray diffraction measurements were performed on heterojunction interfaces of CuGaSe2/CnInSe2/CuGaSe2 grown on GaAs (001 using migration-enhanced epitaxy. The streaky RHEED pattern and persistent RHEED intensity oscillations caused by the alternate deposition of migration-enhanced epitaxy sequence are observed and the growths of smooth surfaces are confirmed. RHEED observation results also confirmed constituent material interdiffusion at the heterointerface. Cross-sectional transmission electron microscopy showed a flat and abrupt heterointerface when the substrate temperature is as low as 400 °C. These have been confirmed even by X-ray diffraction and photoluminescence measurements.

  7. Analysis of Mg content of Zn1-xMgxO film grown on sapphire substrates by plasma-assisted molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    YAN Fengping; JIAN Shuisheng; K. Ogata; K. Koike; S. Sasa; M. Inoue; M. Yano

    2004-01-01

    The Mg content of Zn1-xMgxO film grown on A-sapphire substrates by plasma-assisted molecular beam epitaxy is measured by inductively coupled plasma (ICP)and electronic probe microanalysis (EPMA). A theoretical model for analyzing the difference in the Mg content between Zn-rich and Zn-deficient conditions in the growth process is established, and the mathematical relation between Mg content and the temperature of the Mg cell is formulated under Zn-rich condition. The formula derived is proven to be correct by experiments.

  8. High efficiency green/yellow and red InGaN/AlGaN nanowire light-emitting diodes grown by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    M.R. Philip

    2017-06-01

    Full Text Available We report on the achievement of high efficiency green, yellow, and red InGaN/AlGaN dot-in-a-wire nanowire light-emitting diodes grown on Si(111 by molecular beam epitaxy. The peak emission wavelengths were altered by varying the growth conditions, including the substrate temperature, and In/Ga flux ratio. The devices demonstrate relatively high (>40% internal quantum efficiency at room temperature, relative to that measured at 5 K. Moreover, negligible blue-shift in peak emission spectrum associated with no efficiency droop was measured when injection current was driven up to 556 A/cm2.

  9. High-Tc and high-Jc SmFeAs(O,F) films on fluoride substrates grown by molecular beam epitaxy

    Science.gov (United States)

    Ueda, Shinya; Takeda, Soichiro; Takano, Shiro; Yamamoto, Akiyasu; Naito, Michio

    2011-12-01

    Superconducting thin films of SmFeAs(O,F) were prepared by molecular beam epitaxy on fluoride substrates. In our process, F-free SmFeAsO films were grown first, and F was subsequently introduced to the films by diffusion from an overlayer of SmF3. By this simple process, record high Tc, namely, Tcon (Tcend) = 57.8 K (56.4 K) was obtained in a film on CaF2. Furthermore, the films on CaF2 showed high critical current density over 1 MA/cm2 in the self-field at 5 K. The correlation between superconductivity and epitaxial strain in SmFeAs(O,F) films is discussed.

  10. High-T{sub c} and high-J{sub c} SmFeAs(O,F) films on fluoride substrates grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Ueda, Shinya; Takeda, Soichiro; Takano, Shiro; Naito, Michio [Department of Applied Physics, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan); TRIP, Japan Science and Technology Agency (JST), Chiyoda, Tokyo 102-0075 (Japan); Yamamoto, Akiyasu [Department of Applied Chemistry, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2011-12-05

    Superconducting thin films of SmFeAs(O,F) were prepared by molecular beam epitaxy on fluoride substrates. In our process, F-free SmFeAsO films were grown first, and F was subsequently introduced to the films by diffusion from an overlayer of SmF{sub 3}. By this simple process, record high T{sub c}, namely, T{sub c}{sup on} (T{sub c}{sup end}) = 57.8 K (56.4 K) was obtained in a film on CaF{sub 2}. Furthermore, the films on CaF{sub 2} showed high critical current density over 1 MA/cm{sup 2} in the self-field at 5 K. The correlation between superconductivity and epitaxial strain in SmFeAs(O,F) films is discussed.

  11. Phase transformation of molecular beam epitaxy-grown nanometer-thick Gd₂O₃ and Y₂O₃ on GaN.

    Science.gov (United States)

    Chang, Wen-Hsin; Wu, Shao-Yun; Lee, Chih-Hsun; Lai, Te-Yang; Lee, Yi-Jun; Chang, Pen; Hsu, Chia-Hung; Huang, Tsung-Shiew; Kwo, J Raynien; Hong, Minghwei

    2013-02-01

    High quality nanometer-thick Gd₂O₃ and Y₂O₃ (rare-earth oxide, R₂O₃) films have been epitaxially grown on GaN (0001) substrate by molecular beam epitaxy (MBE). The R₂O₃ epi-layers exhibit remarkable thermal stability at 1100 °C, uniformity, and highly structural perfection. Structural investigation was carried out by in situ reflection high energy electron diffraction (RHEED) and ex-situ X-ray diffraction (XRD) with synchrotron radiation. In the initial stage of epitaxial growth, the R₂O₃ layers have a hexagonal phase with the epitaxial relationship of R₂O₃ (0001)(H)(H)//GaN(0001)(H)(H). With the increase in R₂O₃ film thickness, the structure of the R₂O₃ films changes from single domain hexagonal phase to monoclinic phase with six different rotational domains, following the R₂O₃ (201)(M)[020](M)//GaN(0001)(H)(H) orientational relationship. The structural details and fingerprints of hexagonal and monoclinic phase Gd₂O₃ films have also been examined by using electron energy loss spectroscopy (EELS). Approximate 3-4 nm is the critical thickness for the structural phase transition depending on the composing rare earth element.

  12. Structural and optical properties of self-catalytic GaAs:Mn nanowires grown by molecular beam epitaxy on silicon substrates

    DEFF Research Database (Denmark)

    Gas, Katarzyna; Sadowski, Janusz; Kasama, Takeshi

    2013-01-01

    Mn-doped GaAs nanowires were grown in the self-catalytic growth mode on the oxidized Si(100) surface by molecular beam epitaxy and characterized by scanning and transmission electron microscopy, Raman scattering, photoluminescence, cathodoluminescence, and electron transport measurements. The tra......Mn-doped GaAs nanowires were grown in the self-catalytic growth mode on the oxidized Si(100) surface by molecular beam epitaxy and characterized by scanning and transmission electron microscopy, Raman scattering, photoluminescence, cathodoluminescence, and electron transport measurements.......e., it is much lower than the Mn/Ga flux ratio (about 3%) used during the MBE growth. The resistivity measurements of individual nanowires confirmed that they are conductive, in accordance with the photoluminescence measurements which showed the presence of Mn2+ acceptors located at Ga sites of the GaAs host...... lattice of the nanowires. An anomalous temperature dependence of the photoluminescence related to excitons was demonstrated for Mn-doped GaAs nanowires....

  13. Influence of growth temperature on laser molecular beam epitaxy and properties of GaN layers grown on c-plane sapphire

    Science.gov (United States)

    Dixit, Ripudaman; Tyagi, Prashant; Kushvaha, Sunil Singh; Chockalingam, Sreekumar; Yadav, Brajesh Singh; Sharma, Nita Dilawar; Kumar, M. Senthil

    2017-04-01

    We have investigated the influence of growth temperature on the in-plane strain, structural, optical and mechanical properties of heteroepitaxially grown GaN layers on sapphire (0001) substrate by laser molecular beam epitaxy (LMBE) technique in the temperature range 500-700 °C. The GaN epitaxial layers are found to have a large in-plane compressive stress of about 1 GPa for low growth temperatures but the strain drastically reduced in the layer grown at 700 °C. The nature of the in-plane strain has been analyzed using high resolution x-ray diffraction, atomic force microscopy (AFM), Raman spectroscopy and photoluminescence (PL) measurements. From AFM, a change in GaN growth mode from grain to island is observed at the high growth temperature above 600 °C. A blue shift of 20-30 meV in near band edge PL emission line has been noticed for the GaN layers containing the large in-plane strain. These observations indicate that the in-plane strain in the GaN layers is dominated by a biaxial strain. Using nanoindentation, it is found that the indentation hardness and Young's modulus of the GaN layers increases with increasing growth temperature. The results disclose the critical role of growth mode in determining the in-plane strain and mechanical properties of the GaN layers grown by LMBE technique.

  14. Influence of AlN Buffer Thickness on GaN Grown on Si(111) by Gas Source Molecular Beam Epitaxy with Ammonia

    Institute of Scientific and Technical Information of China (English)

    LIN Guo-Qiang; ZENG Yi-Ping; WANG Xiao-Liang; LIU Hong-Xin

    2008-01-01

    Hexagonal GaN is grown on a Si(111) substrate with AlN as a buffer layer by gas source molecular beam epitaxy(GSMBE) with ammonia. The thickness of AlN buffer is changed from 9 to 72nm. When the thickness of AlN buffer is 36nm, the surface morphology and crystal quality of GaN is optimal. The in-situ reflection high energy electron diffraction (RHEED) reveals that the transition to a two-dimensional growth mode of AlN is the key to the quality of GaN. However, the thickness of AlN buffer is not so critical to the residual in-plane tensile stress in GaN grown on Si(111) by GSMBE for AlN thickness between 9 to 72nm.

  15. Thermal stability and relaxation mechanisms in compressively strained Ge0.94Sn0.06 thin films grown by molecular beam epitaxy

    Science.gov (United States)

    Fleischmann, C.; Lieten, R. R.; Hermann, P.; Hönicke, P.; Beckhoff, B.; Seidel, F.; Richard, O.; Bender, H.; Shimura, Y.; Zaima, S.; Uchida, N.; Temst, K.; Vandervorst, W.; Vantomme, A.

    2016-08-01

    Strained Ge1-xSnx thin films have recently attracted a lot of attention as promising high mobility or light emitting materials for future micro- and optoelectronic devices. While they can be grown nowadays with high crystal quality, the mechanism by which strain energy is relieved upon thermal treatments remains speculative. To this end, we investigated the evolution (and the interplay) of composition, strain, and morphology of strained Ge0.94Sn0.06 films with temperature. We observed a diffusion-driven formation of Sn-enriched islands (and their self-organization) as well as surface depressions (pits), resulting in phase separation and (local) reduction in strain energy, respectively. Remarkably, these compositional and morphological instabilities were found to be the dominating mechanisms to relieve energy, implying that the relaxation via misfit generation and propagation is not intrinsic to compressively strained Ge0.94Sn0.06 films grown by molecular beam epitaxy.

  16. Self-catalyzed GaAsP nanowires grown on silicon substrates by solid-source molecular beam epitaxy.

    Science.gov (United States)

    Zhang, Yunyan; Aagesen, Martin; Holm, Jeppe V; Jørgensen, Henrik I; Wu, Jiang; Liu, Huiyun

    2013-08-14

    We realize the growth of self-catalyzed GaAsP nanowires (NWs) on silicon (111) substrates using solid-source molecular beam epitaxy. By optimizing the V/III and P/As flux ratios, as well as the Ga flux, high-crystal-quality GaAsP NWs have been demonstrated with almost pure zinc-blende phase. Comparing the growth of GaAsP NWs with that of the conventional GaAs NWs indicates that the incorporation of P has significant effects on catalyst nucleation energy, and hence the nanowire morphology and crystal quality. In addition, the incorporation ratio of P/As between vapor-liquid-solid NW growth and the vapor-solid thin film growth has been compared, and the difference between these two growth modes is explained through growth kinetics. The vapor-solid epitaxial growth of radial GaAsP shell on core GaAsP NWs is further demonstrated with room-temperature emission at ~710 nm. These results give valuable new information into the NW nucleation mechanisms and open up new perspectives for integrating III-V nanowire photovoltaics and visible light emitters on a silicon platform by using self-catalyzed GaAsP core-shell nanowires.

  17. Arrayed van der Waals Vertical Heterostructures Based on 2D GaSe Grown by Molecular Beam Epitaxy.

    Science.gov (United States)

    Yuan, Xiang; Tang, Lei; Liu, Shanshan; Wang, Peng; Chen, Zhigang; Zhang, Cheng; Liu, Yanwen; Wang, Weiyi; Zou, Yichao; Liu, Cong; Guo, Nan; Zou, Jin; Zhou, Peng; Hu, Weida; Xiu, Faxian

    2015-05-13

    Vertically stacking two-dimensional (2D) materials can enable the design of novel electronic and optoelectronic devices and realize complex functionality. However, the fabrication of such artificial heterostructures on a wafer scale with an atomically sharp interface poses an unprecedented challenge. Here, we demonstrate a convenient and controllable approach for the production of wafer-scale 2D GaSe thin films by molecular beam epitaxy. In situ reflection high-energy electron diffraction oscillations and Raman spectroscopy reveal a layer-by-layer van der Waals epitaxial growth mode. Highly efficient photodetector arrays were fabricated, based on few-layer GaSe on Si. These photodiodes show steady rectifying characteristics and a high external quantum efficiency of 23.6%. The resultant photoresponse is super-fast and robust, with a response time of 60 μs. Importantly, the device shows no sign of degradation after 1 million cycles of operation. We also carried out numerical simulations to understand the underlying device working principles. Our study establishes a new approach to produce controllable, robust, and large-area 2D heterostructures and presents a crucial step for further practical applications.

  18. Oxygen engineering of HfO{sub 2-x} thin films grown by reactive molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Hildebrandt, Erwin; Kurian, Jose; Alff, Lambert [Institut fuer Materialwissenschaft, TU-Darmstadt (Germany); Zaumseil, Peter; Schroeder, Thomas [IHP, Frankfurt, Oder (Germany)

    2010-07-01

    Reactive molecular beam epitaxy (R-MBE) is an ideal tool for tailoring physical properties of thin films to specific needs. For the development of cutting-edge oxides for thin film applications a precise control of oxygen defects is crucial. R-MBE in combination with rf-activated oxygen allows reproducibly growing oxide thin films with precise oxidation conditions enabling oxygen engineering. R-MBE was used to grow Hf and HfO{sub 2{+-}}{sub x} thin films with different oxidation conditions on sapphire single crystal substrates. Structural characterization was carried out using rotating anode x-ray diffraction revealing highly textured to epitaxial thin films on c-cut sapphire. Furthermore, switching of film orientation by varying the oxidation conditions was observed demonstrating the role of oxygen in the growth procedure. The investigation of electrical properties using a four probe measurement setup showed conductivities in the range of 1000 {mu}{omega}cm for oxygen deficient HfO{sub 2-x} thin films. Optical properties were investigated using a photospectrometer and additionally x-ray photoelectron spectroscopy was carried out to study the band gap and valence states. Both techniques were used to monitor the oxygen content in deficient HfO{sub 2-x} thin films. Our results demonstrate the importance of oxygen engineering even in the case of 'simple' oxides.

  19. Ge doping of β-Ga2O3 films grown by plasma-assisted molecular beam epitaxy

    Science.gov (United States)

    Ahmadi, Elaheh; Koksaldi, Onur S.; Kaun, Stephen W.; Oshima, Yuichi; Short, Dane B.; Mishra, Umesh K.; Speck, James S.

    2017-04-01

    The Ge doping of β-Ga2O3(010) films was investigated using plasma-assisted molecular beam epitaxy as the growth method. The dependences of the amount of Ge incorporated on the substrate temperature, Ge-cell temperature, and growth regime were studied by secondary ion mass spectrometry. The electron concentration and mobility were investigated using Van der Pauw Hall patterns. Hall measurement confirmed that Ge acts as an n-dopant in β-Ga2O3(010) films. These results were compared with similar films doped by Sn. The Hall data showed an improved electron mobility for the same electron concentration when Ge is used instead of Sn as the dopant.

  20. Elemental boron-doped p(+)-SiGe layers grown by molecular beam epitaxy for infrared detector applications

    Science.gov (United States)

    Lin, T. L.; George, T.; Jones, E. W.; Ksendzov, A.; Huberman, M. L.

    1992-01-01

    SiGe/Si heterojunction internal photoemission (HIP) detectors have been fabricated utilizing molecular beam epitaxy of p(+)-SiGe layers on p(-)-Si substrates. Elemental boron from a high-temperature effusion cell was used as the dopant source during MBE growth, and high doping concentrations have been achieved. Strong infrared absorption, mainly by free-carrier absorption, was observed for the degenerately doped SiGe layers. The use of elemental boron as the dopant source allows a low MBE growth temperature, resulting in improved crystalline quality and smooth surface morphology of the Si(0.7)Ge(0.3) layers. Nearly ideal thermionic emission dark current characteristics have been obtained. Photoresponse of the HIP detectors in the long-wavelength infrared regime has been demonstrated.

  1. Conductivity of Oriented Samaria-Doped Ceria Thin Films Grown by Oxygen-plasma-assisted Molecular Beam Epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Zhongqing; Kuchibhatla, Satyanarayana V N T; Saraf, Laxmikant V.; Marina, Olga A.; Wang, Chong M.; Engelhard, Mark H.; Shutthanandan, V.; Nachimuthu, Ponnusamy; Thevuthasan, Suntharampillai

    2008-03-11

    We have used oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE) to grow highly oriented Ce1-xSmxO2-δ films on single crystal c-Al2O3. The samarium concentration, x, was varied in the range 1-33 atom%. It was observed that dominant (111) orientation in Ce1-xSmxO2-δ films can be maintained up to about 10 samarium atom% concentration. Films higher than 10 atom% Sm concentration started to show polycrystalline features. The highest conductivity of 0.04 S.cm-1, at 600 0C, was observed for films with ~ 5 atom% Sm concentration. A loss of orientation, triggering an enhanced grain boundary scattering, appears to be responsible for the decrease in conductivity at higher dopant concentrations.

  2. Misfit dislocation free InAs/GaSb core-shell nanowires grown by molecular beam epitaxy.

    Science.gov (United States)

    Rieger, T; Grützmacher, D; Lepsa, M I

    2015-01-07

    In this report, we present the growth and structural analyses of broken gap InAs/GaSb core-shell nanowires by molecular beam epitaxy using an Au-free approach. Depending on the shell growth temperature, two distinct growth regimes for the GaSb shells are identified resulting in conformal or tapered shells. Morphological analyses reveal a dodecagonal nanowire cross-section after GaSb shell growth. Detailed transmission electron microscope investigations from different zone axes confirm that the small lattice mismatch of 0.6% allows the deposition of 40 nm thick GaSb shells free of misfit dislocations. Additionally, an abrupt interface from InAs to GaSb is found. These nanowires are suitable for future devices such as TFETs.

  3. Structural and Electrical Properties of MoTe2 and MoSe2 Grown by Molecular Beam Epitaxy.

    Science.gov (United States)

    Roy, Anupam; Movva, Hema C P; Satpati, Biswarup; Kim, Kyounghwan; Dey, Rik; Rai, Amritesh; Pramanik, Tanmoy; Guchhait, Samaresh; Tutuc, Emanuel; Banerjee, Sanjay K

    2016-03-23

    We demonstrate the growth of thin films of molybdenum ditelluride and molybdenum diselenide on sapphire substrates by molecular beam epitaxy. In situ structural and chemical analyses reveal stoichiometric layered film growth with atomically smooth surface morphologies. Film growth along the (001) direction is confirmed by X-ray diffraction, and the crystalline nature of growth in the 2H phase is evident from Raman spectroscopy. Transmission electron microscopy is used to confirm the layered film structure and hexagonal arrangement of surface atoms. Temperature-dependent electrical measurements show an insulating behavior that agrees well with a two-dimensional variable-range hopping model, suggesting that transport in these films is dominated by localized charge-carrier states.

  4. Heterostructures with CdTe/ZnTe quantum dots for single photon emitters grown by molecular beam epitaxy

    Science.gov (United States)

    Sorokin, S. V.; Sedova, I. V.; Gronin, S. V.; Belyaev, K. G.; Rakhlin, M. V.; Toropov, A. A.; Mukhin, I. S.; Ivanov, S. V.

    2016-12-01

    We report on the molecular beam epitaxy (MBE) of heterostructures with CdTe/ZnTe quantum dots (QDs) with relatively low surface density, which could be used as single-photon emitters. The QDs were formed on the surface of a 3.1- to 4.5-monolayer-thick two-dimensional strained CdTe layer by depositing amorphous Te layer and its fast thermal desorption. Subsequent thermal annealing of the surface with QDs in the absence of external Te flux led to strong broadening and short-wavelength shift of the QD photoluminescence (PL) peak. Measurement of the micro-PL spectra of individual CdTe/ZnTe quantum dots in fabricated mesastructures with a diameter of 200—1000 nm allowed estimation of the QD surface density as 1010 cm-2.

  5. Real time spectroscopic ellipsometry investigation of homoepitaxial GaN grown by plasma assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Tong-Ho; Choi, Soojeong; Wu, Pae; Brown, April [Department of Electrical and Computer Engineering, Duke University, 128 Hudson Hall, Durham, NC (United States); Losurdo, Maria; Giangregorio, Maria M.; Bruno, Giovanni [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona, 4, 70126 Bari (Italy); Moto, Akihiro [Innovation Core SEI, Inc., 3235 Kifer Road, Santa Clara, CA 95051 (United States)

    2006-06-15

    The growth of GaN by plasma assisted molecular beam epitaxy on GaN template substrates (GaN on sapphire) is investigated with in-situ multi-channel spectroscopic ellipsometry. Growth is performed under various Ga/N flux ratios at growth temperatures in the range 710-780 C. The thermal roughening of the GaN template caused by decomposition of the surface is investigated through the temporal variation of the GaN pseudodielectric function over the temperature range of 650 C to 850 C. The structural, morphological, and optical properties are also discussed. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. GaAs-based long-wavelength InAs bilayer quantum dots grown by molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Zhu Yan; Li Mifeng; He Jifang; Yu Ying; Ni Haiqiao; Xu Yingqiang; Wang Juan; He Zhenhong; Niu Zhichuan

    2011-01-01

    Molecular beam epitaxy growth ofa bilayer stacked InAs/GaAs quantum dot structure on a pure GaAs matrix has been systemically investigated.The influence of growth temperature and the InAs deposition of both layers on the optical properties and morphologies of the bilayer quantum dot (BQD) structures is discussed.By optimizing the growth parameters,InAs BQD emission at 1.436μm at room temperature with a narrower FWHM of 27 meV was demonstrated.The density of QDs in the second layer is around 9 × 109 to 1.4 × 1010 cm-2.The BQD structure provides a useful way to extend the emission wavelength of GaAs-based material for quantum functional devices.

  7. Structure,Electrical,and Optical Properties of Nb-doped BaTiO3 Thin Films Grown by Laser Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    GUO Hai-Zhong; LIU Li-Feng; LU Hui-Bin; FEI Yi-Yan; XIANG Wen-Feng; ZHOU Yue-Liang; CHEN Zheng-Hao

    2004-01-01

    @@ Structure, electrical, and optical properties of Nb-doped BaTiO3 (Nb:BTO) thin films on MgO substrates grown by laser molecular beam epitaxy with increasing Nb content were investigated. The Nb:BTO thin films with high crystallinity are epitaxially grown on MgO substrates. With more Nb-doped content, the impurity phases are found in Nb:BTO thin films. Hall measurement at room temperature confirms that the charge carriers of the Nb:BTO thin films are n-type. When the Nb-doped content increases, the carrier concentration and carrier mobility increase. Meanwhile the optical transmittance decreases with the increase of the Nb-doping, and the width of the forbidden band in each group is not affected by the presence of Nb in the samples. Raman spectra show that the structural phase transition may occur with the increase of the Nb-doping content, in the meantime more defects and impurities exist in the Nb:BTO thin films.

  8. Indium incorporation in semipolar (20 2 ̅ 1) and nonpolar (10 1 ̅ 0) InGaN grown by plasma assisted molecular beam epitaxy

    Science.gov (United States)

    Sawicka, M.; Feduniewicz-Żmuda, A.; Kryśko, M.; Turski, H.; Muziol, G.; Siekacz, M.; Wolny, P.; Skierbiszewski, C.

    2017-02-01

    Semipolar (20 2 ̅ 1) , nonpolar m-plane (10 1 ̅ 0) and polar c-plane (0001) GaN and InGaN layers were grown by plasma-assisted molecular beam epitaxy. The surface of semipolar and nonpolar GaN grown under Ga-rich conditions is very smooth. The indium incorporation efficiency in InGaN layers grown under In-rich growth conditions is studied on three surface orientations (i) as a function of temperature from 570 to 650 °C and (ii) for varied active nitrogen flux from 0.41 to 2.03 μm/h. The In content follows the relation (10 1 ̅ 0) experiments. Indium composition in InGaN layers can be increased (i) by the decrease of the growth temperature and (ii) increase of the applied nitrogen flux for all studied surface orientations. Additionally, surface morphology of semipolar, nonpolar and c-polar InGaN layers grown at 650, 640 and 620 °C is compared. No increase in surface roughness for semipolar and nonpolar InGaN was observed in contrast to c-plane counterparts.

  9. Anomalously low Ga incorporation in high Al-content AlGaN grown on (11 anti 20) non-polar plane by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Ueta, Shunsaku; Horita, Masahiro; Suda, Jun [Department of Electronic Science and Engineering, Kyoto University, Kyoto University Katsura Campus, Nishikyo-ku, Kyoto, 615-8510 (Japan); Kimoto, Tsunenobu [Department of Electronic Science and Engineering, Kyoto University, Kyoto University Katsura Campus, Nishikyo-ku, Kyoto, 615-8510 (Japan); Photonics and Electronics Science and Engineering Center (PESEC), Kyoto University Katsura Campus, Nishikyo-ku, Kyoto, 615-8510 (Japan)

    2011-07-15

    Crystalline orientation dependence of Ga incorporation in growth of high Al-content AlGaN was investigated. Growth was carried out by molecular-beam epitaxy (MBE) using elemental Al, Ga, and rf-plasma-excited nitrogen under various V/III ratios. 6H-SiC (0001), 4H-SiC and 4H-SiC were used as substrates. Ga incorporation increased with increase of V/III ratio in the layers grown on (0001) and planes. On the other hand, Ga was not incorporated in the layer grown on plane even when the layer was grown under a nitrogen rich condition, indicating much lower Ga incorporation on plane than those of other planes. AlGaN with good quality was successfully grown on plane. Utilization of plane is suitable in MBE growth of AlGaN-based deep-ultraviolet light emitting devices. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  10. Above-bandgap optical properties of biaxially strained GeSn alloys grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Richard D’Costa, Vijay, E-mail: elevrd@nus.edu.sg; Wang, Wei; Zhou, Qian; Yeo, Yee-Chia, E-mail: eleyeoyc@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583 (Singapore); Soon Tok, Eng [Department of Physics, National University of Singapore, Singapore 117551 (Singapore)

    2014-01-13

    The complex dielectric function of biaxially strained Ge{sub 1−x}Sn{sub x} (0 ≤ x ≤ 0.17) alloys grown on Ge (100) has been determined by spectroscopic ellipsometry from 1.2 to 4.7 eV. The effect of substitutional Sn incorporation and the epitaxial strain on the energy transitions E{sub 1}, E{sub 1} + Δ{sub 1}, E{sub 0}′, and E{sub 2} of GeSn alloys is investigated. Our results indicate that the strained GeSn alloys show Ge-like electronic bandstructure with all the transitions shifted downward due to the alloying of Sn. The strain dependence of E{sub 1} and E{sub 1} + Δ{sub 1} transitions is explained using the deformation potential theory, and values of −5.4 ± 0.4 eV and 3.8 ± 0.5 eV are obtained for the hydrostatic and shear deformation potentials, respectively.

  11. Compositionally graded InGaN layers grown on vicinal N-face GaN substrates by plasma-assisted molecular beam epitaxy

    Science.gov (United States)

    Hestroffer, Karine; Lund, Cory; Koksaldi, Onur; Li, Haoran; Schmidt, Gordon; Trippel, Max; Veit, Peter; Bertram, Frank; Lu, Ning; Wang, Qingxiao; Christen, Jürgen; Kim, Moon J.; Mishra, Umesh K.; Keller, Stacia

    2017-05-01

    This work reports on compositionally graded (0 0 0 1 bar) N-polar InxGa1-xN layers. The InGaN grades with different final In compositions xf up to 0.25 were grown by plasma-assisted molecular beam epitaxy on vicinal GaN base layers with a miscut angle of 4° towards the m-direction. When increasing xf the surface morphology evolved from an interlacing finger structure, attributed to the Ehrlich-Schwöbel effect, towards fully strain-relaxed columnar features. Regardless of the crystal morphology and the strain state each graded sample exhibited a bright photoluminescence signal at room temperature spanning the whole visible range. Cross-sectional nanoscale cathodoluminescence evidenced a red-shift of the luminesced signal from 420 to 580 nm along the grade and also showed strong lateral emission inhomogeneities.

  12. Study of the conduction-type conversion in Si-doped (631)A GaAs layers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Cruz-Hernandez, E.; Vazquez-Cortes, D.; Mendez-Garcia, V.H. [Coordinacion para la Innovacion y Aplicacion de la Ciencia y Tecnologia, Universidad Autonoma de San Luis Potosi, Av. Sierra Leona 550, Col. Lomas 2a. Seccion, San Luis Potosi, S.L.P. 78210 (Mexico); Shimomura, S. [Graduate School of Science and Engineering, Ehime University, 3 Bukyo-cho, Matsuyama, Ehime 790-8577 (Japan); Lopez-Lopez, M. [Physics Department, Centro de Investigacion y de Estudios Avanzados del IPN, Apartado Postal 14-740, Mexico DF 07000 (Mexico)

    2011-02-15

    We report the Si-doping of GaAs (631)A layers grown by molecular beam epitaxy under different As overpressure. From Hall effect measurements, we have found that the increase of the As pressure induces conduction conversion from p- to n-type, which is presumably related to lattice site switching of Si occupying an As site (where Si is acceptor) to a Ga site (where Si acts as a donor). This conversion is also studied by photoluminescence (PL) spectroscopy. The sharp conductivity conversion, at a critical As pressure value of 1.4-1.7 x 10{sup -5} mbar is reflected in the optical properties of the samples by a change of As vacancy defects into pairs of Ga vacancy and Ga antisite defects. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Evaluation of HgCdTe on GaAs Grown by Molecular Beam Epitaxy for High-Operating-Temperature Infrared Detector Applications

    Science.gov (United States)

    Wenisch, J.; Schirmacher, W.; Wollrab, R.; Eich, D.; Hanna, S.; Breiter, R.; Lutz, H.; Figgemeier, H.

    2015-09-01

    Molecular beam epitaxy (MBE) growth of HgCdTe (MCT) on alternative substrates enables production of both cheaper and more versatile (third-generation) infrared (IR) detectors. After rapid progress in the development of MBE-grown MCT on GaAs in recent years, the question of whether the considerable benefits of this material system are also applicable to high-operating-temperature (HOT) applications demands attention. In this paper, we present a mid-wavelength-IR 640 × 512 pixel, 15- μm-pitch focal-plane array with operability of 99.71% at operating temperature of 120 K and low dark current density. In the second part of the paper, MBE growth of short-wavelength IR material with Cd fraction of up to 0.8 is investigated as the basis for future evaluation of the material for low-light-level imaging HOT applications.

  14. Nanoelectronic devices--resonant tunnelling diodes grown on InP substrates by molecular beam epitaxy with peak to valley current ratio of 17 at room temperature

    Institute of Scientific and Technical Information of China (English)

    Zhang Yang; Zeng Yi-Ping; Ma Long; Wang Bao-Qiang; Zhu Zhan-Ping; Wang Liang-Chen; Yang Fu-Hua

    2006-01-01

    This paper reports that InAs/In0.53Ga0.47As/AlAs resonant tunnelling diodes have been grown on InP substrates by molecular beam epitaxy. Peak to valley current ratio of these devices is 17 at 300K. A peak current density of 3kA/cm2 has been obtained for diodes with AlAs barriers of ten monolayers, and an In0.53Ga0.47As well of eight monolayers with four monolayers of InAs insert layer. The effects of growth interruption for smoothing potential barrier interfaces have been investigated by high resolution transmission electron microscope.

  15. 1.1-μm InAs/GaAs quantum-dot light-emitting transistors grown by molecular beam epitaxy.

    Science.gov (United States)

    Wu, Cheng-Han; Chen, Hsuan-An; Lin, Shih-Yen; Wu, Chao-Hsin

    2015-08-15

    In this Letter, we report the enhanced radiative recombination output from an AlGaAs/GaAs heterojunction bipolar transistor with InAs quantum dots embedded in the base region to form a quantum-dot light-emitting transistor (QDLET) grown by molecular beam epitaxy systems. For the device with a 100  μm×100  μm emitter area, we demonstrate the dual output characteristics with an electrical output and an optical output when the device is operating in the common-emitter configuration. The quantum-dot light-emitting transistor exhibits a base recombination radiation in the near-infrared spectral range with a dominant peak at λ of 1100 nm.

  16. Magnetically Hard Fe3Se4 Embedded in Bi2Se3 Topological Insulator Thin Films Grown by Molecular Beam Epitaxy.

    Science.gov (United States)

    Vasconcelos, Hugo Menezes do Nascimento; Eddrief, Mahmoud; Zheng, Yunlin; Demaille, Dominique; Hidki, Sarah; Fonda, Emiliano; Novikova, Anastasiia; Fujii, Jun; Torelli, Piero; Salles, Benjamin Rache; Vobornik, Ivana; Panaccione, Giancarlo; de Oliveira, Adilson Jesus Aparecido; Marangolo, Massimiliano; Vidal, Franck

    2016-01-26

    We investigated the structural, magnetic, and electronic properties of Bi2Se3 epilayers containing Fe grown on GaAs(111) by molecular beam epitaxy. It is shown that, in the window of growth parameters leading to Bi2Se3 epilayers with optimized quality, Fe atom clustering leads to the formation of FexSey inclusions. These objects have platelet shape and are embedded within Bi2Se3. Monoclinic Fe3Se4 is identified as the main secondary phase through detailed structural measurements. Due to the presence of the hard ferrimagnetic Fe3Se4 inclusions, the system exhibits a very large coercive field at low temperature and room temperature magnetic ordering. Despite this composite structure and the proximity of a magnetic phase, the surface electronic structure of Bi2Se3 is preserved, as shown by the persistence of a gapless Dirac cone at Γ.

  17. Impact of growth and annealing conditions on the parameters of Ge/Si(001) relaxed layers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Yurasov, D. V., E-mail: Inquisitor@ipm.sci-nnov.ru [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Bobrov, A. I. [Lobachevsky State University of Nizhny Novgorod (Russian Federation); Daniltsev, V. M.; Novikov, A. V. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Pavlov, D. A. [Lobachevsky State University of Nizhny Novgorod (Russian Federation); Skorokhodov, E. V.; Shaleev, M. V.; Yunin, P. A. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2015-11-15

    Influence of the Ge layer thickness and annealing conditions on the parameters of relaxed Ge/Si(001) layers grown by molecular beam epitaxy via two-stage growth is investigated. The dependences of the threading dislocation density and surface roughness on the Ge layer thickness, annealing temperature and time, and the presence of a hydrogen atmosphere are obtained. As a result of optimization of the growth and annealing conditions, relaxed Ge/Si(001) layers which are thinner than 1 μm with a low threading dislocation density on the order of 10{sup 7} cm{sup –2} and a root mean square roughness of less than 1 nm are obtained.

  18. Photoluminescence and photocurrent from InP nanowires with InAsP quantum dots grown on Si by molecular beam epitaxy.

    Science.gov (United States)

    Kuyanov, P; LaPierre, R R

    2015-08-07

    InP nanowires with InAsP quantum dots (QDs) were grown by molecular beam epitaxy on a Si (111) substrates. The structure of the InAsP QDs were studied using transmission electron microscopy, allowing the development of a model where QD growth occurs by group V desorption from the surrounding substrate surface. Micro-photoluminescence was performed at 10 K showing emission at 1.47-1.49 eV from the InP wurtzite structure, and various emission peaks between 0.93 and 1.33 eV attributed to the QDs. The emission was tuned by the QD composition. The effectiveness of an AlInP passivation shell was demonstrated via an improvement in the photoluminescence intensity. Spectrally-resolved photocurrent measurements at room temperature demonstrated infrared response due to absorption within the QDs. The absorption red-shifted with increasing As composition of the QD.

  19. InGaAs Photodetectors Cut-off at 1.9μm Grown by Gas-Source Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yong-Gang; HAO Guo-Qiang; GU Yi; ZHU Cheng; LI Ai-Zhen; LIU Tian-Dong

    2005-01-01

    @@ Using a linear graded Inx Ga1- x As as the buffer layer, positive-intrinsic-negative wavelength-extended In0.6Ga0.4As photodetectors with 50% cut-off wavelength of 1.9μm at room temperature were grown by using gas-source molecular beam epitaxy, and their performance over a wide temperature range has been extensively investigated. The detectors show typical dark current at bias voltage 50mV and the resistance-area product RO A of 7nA/765Ωcm2 and 31pA/404kΩcm2 at 290K and 210K, respectively. The thermal activation energy of the dark current in the temperature range 250-350 K is 0.488 eV.

  20. Formation behavior of Be{sub x}Zn{sub 1-x}O alloys grown by plasma-assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Mingming; Zhu, Yuan; Su, Longxing; Zhang, Quanlin; Chen, Anqi; Ji, Xu; Xiang, Rong; Gui, Xuchun; Wu, Tianzhun [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Pan, Bicai [Department of Physics and Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Tang, Zikang [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong (China)

    2013-05-20

    We report the phase formation behavior of Be{sub x}Zn{sub 1-x}O alloys grown by plasma-assisted molecular beam epitaxy. We find the alloy with low- and high-Be contents could be obtained by alloying BeO into ZnO films. X-ray diffraction measurements shows the c lattice constant value shrinks, and room temperature absorption shows the energy band-gap widens after Be incorporated. However, the alloy with intermediate Be composition are unstable and segregated into low- and high-Be contents BeZnO alloys. We demonstrate the phase segregation of Be{sub x}Zn{sub 1-x}O alloys with intermediate Be composition resulted from large internal strain induced by large lattice mismatch between BeO and ZnO.

  1. Transport properties of the two-dimensional electron gas in GaN/AlGaN heterostructures grown by ammonia molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Pogosov, A.G.; Budantsev, M.V.; Lavrov, R.A.; Mansurov, V.G.; Nikitin, A.Yu.; Preobrazhenskii, V.V.; Zhuravlev, K.S. [Institute of Semiconductor Physics, 13 Lavrentiev Avenue, 630090 Novosibirsk (Russian Federation)

    2006-07-15

    Transport properties of the two-dimensional electron gas in AlGaN/GaN heterostructures grown by ammonia molecular-beam epitaxy are experimentally investigated. Conventional Hall and Shubnikov-de Haas measurements as well as investigations of quantum transport phenomena are reported. It is found that negative magnetoresistance (NMR) caused by weak localization demonstrates an unusual behavior at low temperature (1.8 K). The observed NMR cannot be described by the ordinary theory of quantum corrections to conductivity based on a single phase breaking time {tau}{sub {phi}}. The anomalous NMR behavior can be explained by the presence of two occupied quantum subbands, characterized by their own phase breaking times {tau} {sub {phi}} {sub 1} and {tau} {sub {phi}} {sub 2}. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Morphology and electronic properties of metal organic molecular beam epitaxy grown ZnO on hydrogen passivated 6H-SiC(0001)a)

    Science.gov (United States)

    Andres, Stefan; Pettenkofer, Christian; Speck, Florian; Seyller, Thomas

    2008-05-01

    Thin ZnO films were grown on hydrogen passivated 6H-SiC(0001) substrates by metal organic molecular beam epitaxy. The initial growth as well as the electronic properties of the growing interface were monitored by low electron diffraction and photoelectron spectroscopy (PES). From the PES intensities of the substrate and ZnO film a layered Frank-van-der-Merwe-like growth mode could be observed within the first 10nm. The ZnO films grow preferentially in (0001) direction and show a pronounced facetting in the {101¯2} direction. The experimentally determined band alignment reveals band offsets of ΔEVBM≈1.6eV and ΔECBM≈1.2eV between the valence and conduction bands, respectively. With growing ZnO thickness a band bending of about -0.51eV is observed in the SiC substrate.

  3. Optical and electrical studies of arsenic-implanted HgCdTe films grown with molecular beam epitaxy on GaAs and Si substrates

    Science.gov (United States)

    Izhnin, I. I.; Voitsekhovsky, A. V.; Korotaev, A. G.; Fitsych, O. I.; Bonchyk, A. Yu.; Savytskyy, H. V.; Mynbaev, K. D.; Varavin, V. S.; Dvoretsky, S. A.; Mikhailov, N. N.; Yakushev, M. V.; Jakiela, R.

    2017-03-01

    A defect study was performed on arsenic-implanted Hg1-xCdxTe (x = 0.23-0.30) films with graded-gap surface layers, grown with molecular-beam epitaxy on GaAs and Si substrates and designed for fabrication of 'p+-n'-type photodiodes. First, formation of n+-p structure was investigated in p-type material, in order to study radiation-induced donor defects. Next, formation of p+-n structure was investigated in the course of implantation in n-type material and arsenic activation annealing. Influence of the graded-gap surface layer was found to be expressed in the degree of saturation of the concentration of radiation-induced defects, with results obtained on arsenic- and boron-implanted material differing due to the difference in the ion masses.

  4. Optical Properties and Carrier Dynamics of GaAs/GaInAs Multiple-Quantum-Well Shell Grown on GaAs Nanowire by Molecular Beam Epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Park, Kwangwook; Ravindran, Sooraj; Ju, Gun Wu; Min, Jung-Wook; Kang, Seokjin; Myoung, NoSoung; Yim, Sang-Youp; Jo, Yong-Ryun; Kim, Bong-Joong; Lee, Yong Tak

    2016-12-01

    GaAs/GaInAs multiple-quantum-well (MQW) shells having different GaInAs shell width formed on the surface of self-catalyzed GaAs core nanowires (NWs) are grown on (100) Si substrate using molecular beam epitaxy. The photoluminescence emission from GaAs/GaInAs MQW shells and the carrier lifetime could be varied by changing the width of GaInAs shell. Time-resolved photoluminescence measurements showed that the carrier lifetime had a fast and slow decay owing to the mixing of wurtzite and zinc-blende structures of the NWs. Furthermore, strain relaxation caused the carrier lifetime to decrease beyond a certain thickness of GaInAs quantum well shells.

  5. From ultraviolet to green InGaN-based conventional and resonant-cavity light-emitting diodes grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Naranjo, F.B.; Fernandez, S.; Calle, F.; Sanchez-Garcia, M.A.; Calleja, E. [ISOM, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Dpto. Ingenieria Electronica, ETSI Telecomunicacion, Universidad Polittecnica de Madrid (Spain)

    2002-08-16

    InGaN/GaN multiple quantum wells grown by molecular beam epitaxy were used as the active layer of standard and resonant-cavity light emitting diodes. Varying the In content in the wells from 1% to 35% and the well thickness from 1 to 2.5 nm, the room temperature electroluminescence can be tuned from 370 nm (ultraviolet) to 510 nm (green). The main factor that determines the emission energy in the well is the exciton localization for narrow wells, whereas for well thicknesses larger than 3 nm the piezoelectric field is the key factor, even for high In contents. Green resonant-cavity light emitting diodes have been successfully fabricated with a semitransparent AlGaN/GaN-based distributed bragg reflector as bottom mirror and an Al coating as top mirror. The external efficiency of those devices is increased by a factor of 10 compared to standard light emitting diodes. (Abstract Copyright[2002], Wiley Periodicals, Inc.)

  6. AlGaN nanocolumns and AlGaN/GaN/AlGaN nanostructures grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Ristic, J.; Sanchez-Garcia, M.A.; Ulloa, J.M.; Calleja, E. [Departamento de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Sanchez-Paramo, J.; Calleja, J.M. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Jahn, U.; Trampert, A.; Ploog, K.H. [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2002-12-01

    This work reports on the characterization of hexagonal, single crystal AlGaN nanocolumns with diameters in the range of 30 to 100 nm grown by molecular beam epitaxy on Si(111) substrates. The change of the flux ratio between the Al and the total III-element controls the alloy composition. The Al composition trend versus the Al flux is consistent both with the E{sub 2} phonon energy values measured by inelastic light scattering and the luminescence emission peaks position. High quality low dimensional AlGaN/GaN/AlGaN heterostructures with five GaN quantum discs, 2 and 4 nm thick, embedded into the AlGaN columns, were designed in order to study the quantum confinement effects. (Abstract Copyright [2002], Wiley Periodicals, Inc.)

  7. Growth and characterization of lattice-matched InAlN/GaN Bragg reflectors grown by plasma-assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Gacevic, Z.; Fernandez-Garrido, S.; Calleja, E. [ISOM and Dpt. de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Avda. Complutense s/n, 28040 Madrid (Spain); Luna, E.; Trampert, A. [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2009-06-15

    We demonstrate six to ten period lattice-matched In{sub 0.18}Al{sub 0.82}N/GaN distributed Bragg reflectors with peak reflectivity centred around 400 nm, grown by molecular beam epitaxy. Thanks to the well-tuned ternary alloy composition crack-free layers have been obtained as confirmed by both optical and scanning electron microscopy. In addition, cross-sectional analysis by high resolution transmission electron microscopy reveals highly periodic structure with abrupt interfaces. When the number of DBRs periods increased from six to ten, peak reflectivity increased from 45% to 60%. This increase was found to be in reasonable agreement with theoretical simulations. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. High-peak-power low-threshold AlGaAs/GaAs stripe laser diodes on Si substrates grown by migration-enhanced molecular beam epitaxy

    Science.gov (United States)

    Kim, Jae-Hoon; Nouhi, Akbar; Radhakrishnan, Gouri; Liu, John K.; Lang, Robert J.

    1988-01-01

    A high-peak-power low-threshold AlGaAs/GaAs double-heterostructure stripe laser diode on Si substrats, grown by hybrid migration-enhanced molecular beam epitaxy (MEMBE) and metalorganic chemical vapor deposition (MOCVD) has been demonstrated for the first time. These devices showed the highest peak powers of up to 184 mW per facet reported so far for double-heterostructure stripe laser diodes on Si substrates, room-temperature pulsed threshold currents as low as 150 mA, and differential quantum efficiencies as high as 30 percent without mirror facet coating. An intrinsic threshold current density has been estimated to be about 2 kA/sq cm when taking current spreading and lateral diffusion effects into account. Low dislocation density shows that MEMBE can be a useful method to grow high-quality GaAs and AlGaAs/GaAs layers on Si substrates by combining with MOCVD.

  9. Distribution of carriers in gradient-doping transmission-mode GaAs photocathodes grown by molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Zhang Yi-Jun; Chang Ben-Kang; Yang Zhi; Niu Jun; Zou Ji-Jun

    2009-01-01

    The gradient-doping structure is first applied to prepare the transmission-mode OaAs photocathode and the integral sensitivity of the sealed image tube achieves 1420μA/lm. This paper studies the inner carrier concentration distribution of the gradient-doping transmission-mode GaAs photocathode after molecular beam epitaxy (MBE) growth using the electrochemical capacitance-voltage profiling. The results show that an ideal gradient-doping structure can be obtained by using MBE growth. The total band-bending energy in the gradient-doping GaAs active-layer with doping concentration ranging from 1×10~(19) cm~(-3) to 1×10~(18) cm~(-3) is calculated to be 46.3 meV, which helps to improve the photoexcited electrons movement toward surface for the thin epilayer. In addition, by analysis of the band offsets, it is found that the worse carrier concentration discrepancy between GaAs and GaAlAs causes a lower back interface electron potential barrier which decreases the amount of high-energy photoelectrons and affects the short-wave response.

  10. Threading and misfit-dislocation motion in molecular-beam epitaxy-grown HgCdTe epilayers

    Science.gov (United States)

    Carmody, M.; Lee, D.; Zandian, M.; Phillips, J.; Arias, J.

    2003-07-01

    Lattice mismatch between the substrate and the absorber layer in single-color HgCdTe infrared (IR) detectors and between band 1 and band 2 in two-color detectors results in the formation of crosshatch lines on the surface and an array of misfit dislocations at the epi-interfaces. Threading dislocations originating in the substrate can also bend into the interface plane and result in misfit dislocations because of the lattice mismatch. The existence of dislocations threading through the junction region of HgCdTe IR-photovoltaic detectors can greatly affect device performance. High-quality CdZnTe substrates and controlled molecular-beam epitaxy (MBE) growth of HgCdTe can result in very low threading-dislocation densities as measured by the etch-pit density (EPD ˜ 104cm-2). However, dislocation gettering to regions of high stress (such as etched holes, voids, and implanted-junction regions) at elevated-processing temperatures can result in a high density of dislocations in the junction region that can greatly reduce detector performance. We have performed experiments to determine if the dislocations that getter to these regions of high stress are misfit dislocations at the substrate/absorber interface that have a threading component extending to the upper surface of the epilayer, or if the dislocations originate at the cap/absorber interface as misfit dislocations. The preceding mechanisms for dislocation motion are discussed in detail, and the possible diode-performance consequences are explored.

  11. Investigation on the lattice site location of the excess arsenic atoms in GaAs layers grown by low temperature molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Kin Man; Liliental-Weber, Z.

    1991-11-01

    We have measured the excess As atoms present in gaze layers grown by molecular beam epitaxy at low substrate temperatures using particle induced x-ray emission technique. The amount of excess As atoms in layers grown by MBE at 200{degrees}C were found to be {approximately} 4 {times} 10{sup 20} cm{sup {minus}2}. Subsequent annealing of the layers under As overpressure at 600{degrees}C did not result in any substantial As loss. However, transmission electron microscopy revealed that As precipitates (2-5nm in diameter) were present in the annealed layers. The lattice location of the excess As atoms in the as grown layers was investigated by ion channeling methods. Angular scans were performed in the <110> axis of the crystal. Our results strongly suggest that a large fraction of these excess As atoms are located in an interstitial position close to an As row. These As intersitials'' are located at a site slightly displaced from the tetrahedral site in a diamond cubic lattice. No interstitial As signal is observed in the annealed layers.

  12. Investigation on the lattice site location of the excess arsenic atoms in GaAs layers grown by low temperature molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Kin Man; Liliental-Weber, Z.

    1991-11-01

    We have measured the excess As atoms present in gaze layers grown by molecular beam epitaxy at low substrate temperatures using particle induced x-ray emission technique. The amount of excess As atoms in layers grown by MBE at 200{degrees}C were found to be {approximately} 4 {times} 10{sup 20} cm{sup {minus}2}. Subsequent annealing of the layers under As overpressure at 600{degrees}C did not result in any substantial As loss. However, transmission electron microscopy revealed that As precipitates (2-5nm in diameter) were present in the annealed layers. The lattice location of the excess As atoms in the as grown layers was investigated by ion channeling methods. Angular scans were performed in the <110> axis of the crystal. Our results strongly suggest that a large fraction of these excess As atoms are located in an interstitial position close to an As row. These As ``intersitials`` are located at a site slightly displaced from the tetrahedral site in a diamond cubic lattice. No interstitial As signal is observed in the annealed layers.

  13. Morphological and microstructural stability of N-polar InAlN thin films grown on free-standing GaN substrates by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Hardy, Matthew T., E-mail: matthew.hardy.ctr@nrl.navy.mil; Storm, David F.; Downey, Brian P.; Katzer, D. Scott; Meyer, David J. [Electronics Science and Technology Division, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington DC 20375 (United States); McConkie, Thomas O.; Smith, David J. [Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States); Nepal, Neeraj [Sotera Defense Solutions, 2200 Defense Hwy Suite 405, Crofton, Maryland 21114 (United States)

    2016-03-15

    The sensitivity of the surface morphology and microstructure of N-polar-oriented InAlN to variations in composition, temperature, and layer thickness for thin films grown by plasma-assisted molecular beam epitaxy (PAMBE) has been investigated. Lateral compositional inhomogeneity is present in N-rich InAlN films grown at low temperature, and phase segregation is exacerbated with increasing InN fraction. A smooth, step-flow surface morphology and elimination of compositional inhomogeneity can be achieved at a growth temperature 50 °C above the onset of In evaporation (650 °C). A GaN/AlN/GaN/200-nm InAlN heterostructure had a sheet charge density of 1.7 × 10{sup 13 }cm{sup −2} and no degradation in mobility (1760 cm{sup 2}/V s) relative to 15-nm-thick InAlN layers. Demonstration of thick-barrier high-electron-mobility transistors with good direct-current characteristics shows that device quality, thick InAlN layers can be successfully grown by PAMBE.

  14. Electron Traps in GaAs Grown by Molecular Beam Epitaxy on On-axis (100 and Off-axis Substrates

    Directory of Open Access Journals (Sweden)

    R. Sarmiento

    2003-06-01

    Full Text Available Deep level transient spectroscopy (DLTS was used to characterize the electron traps present in the bulkGaAs grown by molecular beam epitaxy (MBE on on-axis (100 and off-axis (4° towards the (111 Adirection substrates. Two electron traps were obtained for each sample having identical correspondingpeak locations in the DLTS spectra. The layer grown on the on-axis substrate has electron traps withactivation energies of EC–0.454 eV and EC–0.643 eV and capture cross-sections of 1.205 x 10-14 cm2 and3.88 x 10-15 cm2, respectively. The layer grown on the off-axis substrate has traps with activation energiesof EC–0.454 eV and EC–0.723 eV and capture cross-sections of 2.060 x 10-14 cm2 and 4.40 x 10-14 cm2.The electron traps are possibly the M4 (or EL3 and EL2 (or EB4 traps commonly found in GaAs layers.Due to the high trap concentrations obtained and to the non-uniform trap concentration profile, Asdesorption may be considerable during growth.

  15. Effects of Rapid Thermal Annealing on Optical Properties of GaInNAs/GaAs Single Quantum Well Grown by Plasma-Assisted Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The effects of Rapid Thermal Annealing (RTA) on the optical properties of GaInNAs/GaAs Single Quantum Well (SQW) grown by plasma-assisted molecular beam epitaxy are investigated. Ion removal magnets were applied to reduce the ion damage during the growth process and the optical properties of GaInNAs/GaAs SQW are remarkably improved.RTA was carried out at 650℃ and its effect was studied by the comparising the roomtemperature PhotoLuminescence (PL) spectra for the non ion-removed (grown without magnets) sample with for the ion-removed (grown with magnets) one. The more significant improvement of PL characteristics for non ion-removed GaInNAs/GaAs SQW after annealing (compared with those for ion-removed) indicates that the nonradiative centers removed by RTA at 650℃ are mainly originated from ion damage. After annealing the PL blue shift for non ionremoved GaInNAs/GaAs SQW is much larger than those for InGaAs/GaAs and ion-removed GaInNAs/GaAs SQW. It is found that the larger PL blue shift of GaInNAs/GaAs SQW is due to the defect-assisted In-Ga interdiffusion rather than defect-assisted N-As interdiffusion.

  16. Stress evolution of GaN/AlN heterostructure grown on 6H-SiC substrate by plasma assisted molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    M. Agrawal

    2017-01-01

    Full Text Available The stress evolution of GaN/AlN heterostructure grown on 6H-SiC substrate by plasma assisted molecular beam epitaxy (PA-MBE has been studied. AlN nucleation layer and GaN layer were grown as a function of III/V ratio. GaN/AlN structure is found to form buried cracks when AlN is grown in the intermediate growth regime(III/V∼1and GaN is grown under N-rich growth regime (III/V<1. The III/V ratio determines the growth mode of the layers that influences the lattice mismatch at the GaN/AlN interface. The lattice mismatch induced interfacial stress at the GaN/AlN interface relaxes by the formation of buried cracks in the structure. Additionally, the stress also relaxes by misorienting the AlN resulting in two misorientations with different tilts. Crack-free layers were obtained when AlN and GaN were grown in the N-rich growth regime (III/V<1 and metal rich growth regime (III/V≥1, respectively. AlGaN/GaN high electron mobility transistor (HEMT heterostructure was demonstrated on 2-inch SiC that showed good two dimensional electron gas (2DEG properties with a sheet resistance of 480 Ω/sq, mobility of 1280 cm2/V.s and sheet carrier density of 1×1013 cm−2.

  17. In Situ Oxidation of GaN Layer and Its Effect on Structural Properties of Ga2O3 Films Grown by Plasma-Assisted Molecular Beam Epitaxy

    Science.gov (United States)

    Ngo, Trong Si; Le, Duc Duy; Tran, Duy Khanh; Song, Jung-Hoon; Hong, Soon-Ku

    2017-06-01

    Plasma-assisted molecular beam epitaxy (PAMBE) was used to grow Ga2O3 films on oxidized GaN layers on nitrided sapphire substrates. The GaN layer was grown by PAMBE, and the in situ oxidation of the GaN layer was achieved through exposure to oxygen plasma, which resulted in the formation of monoclinic β-Ga2O3. Crystalline monoclinic β-Ga2O3 films were grown on the GaN layers, with and without oxidation. The orientation relationships were [11\\overline{2} 0] Al2O3//[1\\overline{1} 00] AlN//[1\\overline{1} 00] GaN//[102] β-Ga2O3 and [1\\overline{1} 00] Al2O3//[11\\overline{2} 0] AlN//[11\\overline{2} 0] GaN//[010] β-Ga2O3. The grown β-Ga2O3 films were not single-crystalline but showed rotational domains along the growth direction with three variations, which resulted in six-fold rotational symmetry instead of two-fold rotational symmetry. The surface roughness of the grown β-Ga2O3 film was closely reflected to that of as-grown GaN and oxidized GaN. By analyzing the x-ray omega rocking curves for the on-axis (\\overline{2} 01) and off-axis (002) reflections, it was concluded that rotational domains dominantly affected the crystal quality of the β-Ga2O3 films.

  18. Characterization of HgCdTe Films Grown on Large-Area CdZnTe Substrates by Molecular Beam Epitaxy

    Science.gov (United States)

    Arkun, F. Erdem; Edwall, Dennis D.; Ellsworth, Jon; Douglas, Sheri; Zandian, Majid; Carmody, Michael

    2017-09-01

    Recent advances in growth of Hg1- x Cd x Te films on large-area (7 cm × 7.5 cm) CdZnTe (CZT) substrates is presented. Growth of Hg1- x Cd x Te with good uniformity on large-area wafers is achieved using a Riber 412 molecular beam epitaxy (MBE) tool designed for growth of Hg1- x Cd x Te compounds. The reactor is equipped with conventional CdTe, Te, and Hg sources for achieving uniform exposure of the wafer during growth. The composition of the Hg1- x Cd x Te compound is controlled in situ by employing a closed-loop spectral ellipsometry technique to achieve a cutoff wavelength ( λ co) of 14 μm at 78 K. We present data on the thickness and composition uniformity of films grown for large-format focal-plane array applications. The composition and thickness nonuniformity are determined to be maps show the spatial distribution of defects generated during the epitaxial growth of the Hg1- x Cd x Te films. Microdefect densities are in the low 103 cm-2 range, and void defects are below 500 cm-2. Dislocation densities less than 5 × 105 cm-2 are routinely achieved for Hg1- x Cd x Te films grown on CZT substrates. HgCdTe 4k × 4k focal-plane arrays with 15 μm pitch for astronomical wide-area infrared imagers have been produced using the recently developed MBE growth process at Teledyne Imaging Sensors.

  19. Summary of Schottky barrier height data on epitaxially grown n-and p-GaAs

    CSIR Research Space (South Africa)

    Myburg, G

    1998-07-18

    Full Text Available epitaxially (OMVPE) grown (100) n-type GaAs material and 13 metals on molecular beam epitaxially grown (MBE) p-GaAs, are presented. Of all the metals involved in this study, Ga had the lowest mean Schottky barrier height of about 0.60 eV on n-GaAs...

  20. Structural, morphological, and magnetic characterization of In{sub 1-x}Mn{sub x}As quantum dots grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Ferri, F. A.; Marega, E. Jr. [Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Sao Carlos 13560-970, SP (Brazil); Coelho, L. N. [Instituto de Fisica, Universidade de Brasilia, Brasilia 70919-970, DF (Brazil); Kunets, V. P.; Salamo, G. J. [Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701 (United States)

    2012-08-01

    In this paper, we present a method to order low temperature (LT) self-assembled ferromagnetic In{sub 1-x}Mn{sub x}As quantum dots (QDs) grown by molecular beam epitaxy (MBE). The ordered In{sub 1-x}Mn{sub x}As QDs were grown on top of a non-magnetic In{sub 0.4}Ga{sub 0.6}As/GaAs(100) QDs multi-layered structure. The modulation of the chemical potential, due to the stacking, provides a nucleation center for the LT In{sub 1-x}Mn{sub x}As QDs. For particular conditions, such as surface morphology and growth conditions, the In{sub 1-x}Mn{sub x}As QDs align along lines like chains. This work also reports the characterization of QDs grown on plain GaAs(100) substrates, as well as of the ordered structures, as function of Mn content and growth temperature. The substitutional Mn incorporation in the InAs lattice and the conditions for obtaining coherent and incoherent structures are discussed from comparison between Raman spectroscopy and x-ray analysis. Ferromagnetic behavior was observed for all structures at 2 K. We found that the magnetic moment axis changes from [110] in In{sub 1-x}Mn{sub x}As over GaAs to [1-10] for the ordered In{sub 1-x}Mn{sub x}As grown over GaAs template.

  1. Optimization of co-evaporation conditions of as-grown MgB{sub 2} thin films by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Y. [Iwate Industry Promotion Center, Iioka-shinden 3-35-2, Morioka, Iwate 020-0852 (Japan)]. E-mail: yharada@luck.ocn.ne.jp; Takahashi, T. [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551 (Japan); Iriuda, H. [Department of Materials Science and Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Kuroha, M. [Department of Materials Science and Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Nakanishi, Y. [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551 (Japan); Yoshizawa, M. [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551 (Japan)

    2005-10-01

    We have made as-grown MgB{sub 2} film deposited by molecular beam epitaxy (MBE) under co-evaporation conditions of low temperature, low growth rate, and ultra high vacuum on three types of substrates, MgO(1 0 0), Al{sub 2}O{sub 3}(0 0 0 1), and SrTiO{sub 3}(1 0 0). The optimization of these conditions was investigated with respect to (1) growth temperature (T {sub s} < 250 deg. C) (2) B deposition rate, and (3) Mg/B deposition ratio. The film properties were investigated by RHEED, XRD, AFM, electrical resistivity, and SQUID magnetometer. The film grown at 200 deg. C, B deposition rate of 0.3 A/s and Mg/B ratio of 8 showed the highest T {sub c,onset} of 35 K and had a sharp transition ({delta}T {sub c} = 0.5 K). We report the upper critical field and anisotropy ratio of these films.

  2. Effects of Sb incorporation in GaAsSb-capping layer on the optical properties of InAs/GaAs QDs grown by Molecular Beam Epitaxy

    Science.gov (United States)

    Salhi, A.; Alshaibani, S.; Alhamdan, M.; Albrithen, H.; Alyamani, A.; El-Desouki, M.

    2017-01-01

    We have investigated the effect of antimony incorporation in GaAsSb as a capping layer on the optical properties of InAs quantum dots grown by Molecular Beam Epitaxy. Atomic Force Microscopy (AFM), High Resolution X-Ray Diffraction (HRXRD), photoluminescence (PL) and power dependent PL at 77 K and 300 K have been used for the characterization of the grown samples. Our analysis showed that the emission wavelength increases with Sb content and reaches ∼1.5 μm for Sb concentration of 22%. To achieve this wavelength, a reduction of the growth temperature of the GaAsSb layer from 500 °C to 440 °C was necessary. The wavelength increase is accompanied by a transition from a type I to type II band alignment and a broadening of the PL spectrum to a value of ∼237 nm for an excitation power of 100 mW. This broadening is attributed to the QD size inhomogeneity increase and Sb atoms redistribution during the in-situ annealing during the growth of the barriers at elevated temperature. Our results show the potential of the InAs/GaAsSb system in the development of broadband light sources and super-luminescent light emitting diodes in 1.2-1.5 μm wavelength range.

  3. Peculiarities of strain relaxation in linearly graded InxGa1-xAs/GaAs(001) metamorphic buffer layers grown by molecular beam epitaxy

    Science.gov (United States)

    Sorokin, S. V.; Klimko, G. V.; Sedova, I. V.; Sitnikova, A. A.; Kirilenko, D. A.; Baidakova, M. V.; Yagovkina, M. A.; Komissarova, T. A.; Belyaev, K. G.; Ivanov, S. V.

    2016-12-01

    This paper presents a comprehensive study of structural, optical and electrical properties of heterostructures with linearly graded InxGa1-xAs metamorphic buffer layers (MBLs) grown by molecular beam epitaxy on GaAs (001) substrates. The low density of threading dislocations (well below 106 cm-2) in 1-μm-thick In0.3Ga0.7As layers grown atop of the linearly graded InxGa1-xAs/GaAs MBLs has been confirmed by using transmission electron microscopy (TEM). X-ray diffraction (XRD) data demonstrate good agreement between the experimentally measured In step-back and its calculations in the frames of existing models. Combining the XRD reciprocal space maps (RSM) of the structures and the spatially-resolved selective area electron diffraction measurements by cross-sectional TEM in depth-profiled RSM diagrams allowed direct visualization of the strain relaxation dynamics during the MBL growth. Strong effect of the azimuth angle and the value of an unintentional initial miscut of nominally (001) oriented GaAs substrate on the strain relaxation dynamics was observed.

  4. Effect of double AlN buffer layer on the qualities of GaN films grown by radio-frequency molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Li Xin-Hua; Zhong Fei; Qiu Kai; Yin Zhi-Jun; Ji Chang-Jian

    2008-01-01

    This paper reports that the GaN thin films with Ga-polarity and high quality were grown by radio-frequency molecular beam epitaxy on sapphire (0001) substrate with a double A1N buffer layer. The buffer layer consists of a high-temperature (HT) AlN layer and a low-temperature (LT) AlN layer grown at 800℃ and 600℃, respectively. It is demonstrated that the HT-AlN layer can result in the growth of GaN epilayer in Ga-polarity and the LT-AlN layer is helpful for the improvement of the epilayer quality. It is observed that the carrier mobility of the GaN epilayer increases from 458 to 858cm2/V.s at room temperature when the thickness of LT-AlN layer varies from 0 to 20nm. The full width at half maximum of x-ray rocking curves also demonstrates a substantial improvement in the quality of GaN epilayers by the utilization of LT-AlN layer.

  5. Fe-doped semi-insulating GaN with solid Fe source grown on (110) Si substrates by NH3 molecular beam epitaxy

    Science.gov (United States)

    Noh, Young Kyun; Lee, Sang Tae; Kim, Moon Deock; Oh, Jae Eung

    2017-02-01

    Iron doped GaN layers were grown on (110) Si substrates by ammonia molecular beam epitaxy (MBE) using solid elemental iron as a source. Specular films with concentrations up to 1×1020 cm-3, as determined by secondary ion mass spectroscopy, were grown, unlike a limited incorporation of Fe into GaN by metal-rich rf plasma MBE. The Fe concentration in the film showed an exponential dependence on the inverse of source temperature with an activation energy of 3.4 eV, which agrees well to the reported value for the sublimation of Fe. A 1.5 μm thick GaN film with a sheet resistance of 1 GΩ/sq. was obtained by compensating unintentional residual donors with a small Fe concentration of 1×1017 cm-3. X-ray diffraction rocking curves indicated high crystalline quality, very similar to an undoped film, showing that the Fe incorporation required to obtain the semi-insulating film properties did not affect the structural properties of the film. The low-temperature PL spectra of highly resistive and semi-insulating Fe:GaN in the range of 1017 1018 cm-3 show dominant exciton emissions and enhanced donor-acceptor-pair (DAP) emissions, implying that Fe ions contribute to the DAP transition between donor levels and Fe-related acceptor levels, possibly compensating the residual donors to achieve the semi-insulating electrical properties.

  6. Thermal stability and relaxation mechanisms in compressively strained Ge{sub 0.94}Sn{sub 0.06} thin films grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Fleischmann, C.; Lieten, R. R.; Shimura, Y.; Vandervorst, W. [Instituut voor Kern-en Stralingsfysica, KU Leuven, Celestijnenlaan 200D, 3001 Leuven (Belgium); imec, Kapeldreef 75, 3001 Leuven (Belgium); Hermann, P.; Hönicke, P.; Beckhoff, B. [Physikalisch-Technische Bundesanstalt (PTB), Abbestraße 2-12, 10587 Berlin (Germany); Seidel, F. [Instituut voor Kern-en Stralingsfysica, KU Leuven, Celestijnenlaan 200D, 3001 Leuven (Belgium); imec, Kapeldreef 75, 3001 Leuven (Belgium); Institut für Elektronik-und Sensormaterialien, TU Bergakademie Freiberg, Gustav-Zeuner-Str. 3, 09599 Freiberg (Germany); Richard, O.; Bender, H. [imec, Kapeldreef 75, 3001 Leuven (Belgium); Zaima, S. [Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Uchida, N. [Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba West SCR, 16-1 Onogawa, Tsukuba, Ibaraki 305-8569 (Japan); Temst, K.; Vantomme, A. [Instituut voor Kern-en Stralingsfysica, KU Leuven, Celestijnenlaan 200D, 3001 Leuven (Belgium)

    2016-08-28

    Strained Ge{sub 1-x}Sn{sub x} thin films have recently attracted a lot of attention as promising high mobility or light emitting materials for future micro- and optoelectronic devices. While they can be grown nowadays with high crystal quality, the mechanism by which strain energy is relieved upon thermal treatments remains speculative. To this end, we investigated the evolution (and the interplay) of composition, strain, and morphology of strained Ge{sub 0.94}Sn{sub 0.06} films with temperature. We observed a diffusion-driven formation of Sn-enriched islands (and their self-organization) as well as surface depressions (pits), resulting in phase separation and (local) reduction in strain energy, respectively. Remarkably, these compositional and morphological instabilities were found to be the dominating mechanisms to relieve energy, implying that the relaxation via misfit generation and propagation is not intrinsic to compressively strained Ge{sub 0.94}Sn{sub 0.06} films grown by molecular beam epitaxy.

  7. Growth and characterization of molecular beam epitaxy-grown Bi{sub 2}Te{sub 3−x}Se{sub x} topological insulator alloys

    Energy Technology Data Exchange (ETDEWEB)

    Tung, Y.; Chiang, Y. F.; Chong, C. W., E-mail: cheongwei2000@yahoo.com, E-mail: jcahuang@mail.ncku.edu.tw, E-mail: makalu@nsrrc.org.tw; Deng, Z. X.; Chen, Y. C. [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China); Huang, J. C. A., E-mail: cheongwei2000@yahoo.com, E-mail: jcahuang@mail.ncku.edu.tw, E-mail: makalu@nsrrc.org.tw [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China); Advanced Optoelectronic Technology Center (AOTC), National Cheng Kung University, Tainan 70101, Taiwan (China); Taiwan Consortium of Emergent Crystalline Materials (TCECM), Ministry of Science and Technology, Taipei 10622, Taiwan (China); Cheng, C.-M., E-mail: cheongwei2000@yahoo.com, E-mail: jcahuang@mail.ncku.edu.tw, E-mail: makalu@nsrrc.org.tw; Pi, T.-W.; Tsuei, K.-D. [National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan (China); Li, Z.; Qiu, H. [School of Electronic Science and Applied Physics, HeFei University of Technology, Anhui (China)

    2016-02-07

    We report a systematic study on the structural and electronic properties of Bi{sub 2}Te{sub 3−x}Se{sub x} topological insulator alloy grown by molecular beam epitaxy (MBE). A mixing ratio of Bi{sub 2}Se{sub 3} to Bi{sub 2}Te{sub 3} was controlled by varying the Bi:Te:Se flux ratio. X-ray diffraction and Raman spectroscopy measurements indicate the high crystalline quality for the as-grown Bi{sub 2}Te{sub 3−x}Se{sub x} films. Substitution of Te by Se is also revealed from both analyses. The surfaces of the films exhibit terrace-like quintuple layers and their size of the characteristic triangular terraces decreases monotonically with increasing Se content. However, the triangular terrace structure gradually recovers as the Se content further increases. Most importantly, the angle-resolved photoemission spectroscopy results provide evidence of single-Dirac-cone like surface states in which Bi{sub 2}Te{sub 3−x}Se{sub x} with Se/Te-substitution leads to tunable surface states. Our results demonstrate that by fine-tuned MBE growth conditions, Bi{sub 2}Te{sub 3−x}Se{sub x} thin film alloys with tunable topological surface states can be obtained, providing an excellent platform for exploring the novel device applications based on this compound.

  8. Optical properties and structural investigations of (11-22)-oriented GaN/Al{sub 0.5}Ga{sub 0.5}N quantum wells grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Rosales, Daniel; Gil, Bernard; Bretagnon, Thierry [CNRS, Laboratoire Charles Coulomb, UMR 5221, F-34095 Montpellier (France); Université de Montpellier, Laboratoire Charles Coulomb, UMR 5221, F-34095 Montpellier (France); Brault, Julien; Vennéguès, Philippe; Nemoz, Maud; Mierry, Philippe de; Damilano, Benjamin; Massies, Jean [CNRS Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications, 06560 Valbonne (France); Bigenwald, Pierre [Institut Pascal, Campus des Cézeaux, 24 avenue des Landais, 63171 Aubière Cedex (France)

    2015-07-14

    We have grown (11-22)-oriented GaN/Al{sub 0.5}Ga{sub 0.5}N quantum wells (QWs) using molecular beam epitaxy on GaN (11-22)-oriented templates grown by metal-organic vapor phase epitaxy on m-plane oriented sapphire substrates. The performance of epitaxial growth of GaN/Al{sub 0.5}Ga{sub 0.5}N heterostructures on the semi-polar orientation (11-22) in terms of surface roughness and structural properties, i.e., strain relaxation mechanisms is discussed. In addition, high resolution transmission electron microscopy reveals very smooth QW interfaces. The photoluminescence of such samples are strictly originating from radiative recombination of free excitons for temperatures above 100 K. At high temperature, the population of localized excitons, moderately trapped (5 meV) at low temperature, is negligible.

  9. Schottky barrier height of Ni to β-(AlxGa1‑x)2O3 with different compositions grown by plasma-assisted molecular beam epitaxy

    Science.gov (United States)

    Ahmadi, Elaheh; Oshima, Yuichi; Wu, Feng; Speck, James S.

    2017-03-01

    Coherent β-(AlxGa1‑x)2O3 films (x = 0, 0.038, 0.084, 0.164) were grown successfully on a Sn-doped β-Ga2O3 (010) substrate using plasma-assisted molecular beam epitaxy. Atom probe tomography, transmission electron microscopy, and high resolution x-ray diffraction were used to verify the alloy composition and high quality of the films. Schottky diodes were then fabricated using Ni as the Schottky metal. Capacitance–voltage measurements revealed a very low (current–voltage (I–V) measurements performed at temperatures varying from 300 K to 500 K on the Schottky diodes. These measurements revealed that the apparent Schottky barrier height could have similar values for different compositions of β-(AlxGa1‑x)2O3. We believe this is attributed to the lateral fluctuation in the alloy’s composition. This results in a lateral variation in the barrier height. Therefore, the average Schottky barrier height extracted from I–V measurements could be similar for β-(AlxGa1‑x)2O3 films with different compositions.

  10. Structural and optical properties of self-catalytic GaAs:Mn nanowires grown by molecular beam epitaxy on silicon substrates.

    Science.gov (United States)

    Gas, Katarzyna; Sadowski, Janusz; Kasama, Takeshi; Siusys, Aloyzas; Zaleszczyk, Wojciech; Wojciechowski, Tomasz; Morhange, Jean-François; Altintaş, Abdulmenaf; Xu, H Q; Szuszkiewicz, Wojciech

    2013-08-21

    Mn-doped GaAs nanowires were grown in the self-catalytic growth mode on the oxidized Si(100) surface by molecular beam epitaxy and characterized by scanning and transmission electron microscopy, Raman scattering, photoluminescence, cathodoluminescence, and electron transport measurements. The transmission electron microscopy studies evidenced the substantial accumulation of Mn inside the catalyzing Ga droplets on the top of the nanowires. Optical and transport measurements revealed that the limit of the Mn content for self-catalysed growth of GaAs nanowires corresponds to the doping level, i.e., it is much lower than the Mn/Ga flux ratio (about 3%) used during the MBE growth. The resistivity measurements of individual nanowires confirmed that they are conductive, in accordance with the photoluminescence measurements which showed the presence of Mn(2+) acceptors located at Ga sites of the GaAs host lattice of the nanowires. An anomalous temperature dependence of the photoluminescence related to excitons was demonstrated for Mn-doped GaAs nanowires.

  11. Photoluminescence of InGaAs/GaAsBi/InGaAs type-II quantum wells grown by gas source molecular beam epitaxy

    Science.gov (United States)

    Pan, Wenwu; Zhang, Liyao; Zhu, Liang; Song, Yuxin; Li, Yaoyao; Wang, Chang; Wang, Peng; Wu, Xiaoyan; Zhang, Fan; Shao, Jun; Wang, Shumin

    2017-01-01

    In x Ga1-x As/GaAs1-y Bi y /In x Ga1-x As (0.20 ≤ x ≤ 0.22, 0.035 ≤ y ≤ 0.045) quantum wells (QWs) were grown on GaAs substrates by gas source molecular beam epitaxy for realizing the type-II band edge line-up. Both type-I and type-II transitions were observed in the Bi containing W QWs and the photoluminescence intensity was enhanced in the sample with a high Bi content, which is mainly due to the improvement of carrier confinement. The 8 band k · p model was used to analyze the electronic properties in the QWs and the calculated transition energies fit well with the experiment results. Our study shows that the proposed type-II QW is a promising candidate for realizing GaAs-based near infrared light emitting devices near 1.3 μm.

  12. Spontaneous core–shell elemental distribution in In-rich In(x)Ga1-xN nanowires grown by molecular beam epitaxy.

    Science.gov (United States)

    Gómez-Gómez, M; Garro, N; Segura-Ruiz, J; Martinez-Criado, G; Cantarero, A; Mengistu, H T; García-Cristóbal, A; Murcia-Mascarós, S; Denker, C; Malindretos, J; Rizzi, A

    2014-02-21

    The elemental distribution of self-organized In-rich In(x)Ga1-xN nanowires grown by plasma-assisted molecular beam epitaxy has been investigated using three different techniques with spatial resolution on the nanoscale. Two-dimensional images and elemental profiles of single nanowires obtained by x-ray fluorescence and energy-dispersive x-ray spectroscopy, respectively, have revealed a radial gradient in the alloy composition of each individual nanowire. The spectral selectivity of resonant Raman scattering has been used to enhance the signal from very small volumes with different elemental composition within single nanowires. The combination of the three techniques has provided sufficient sensitivity and spatial resolution to prove the spontaneous formation of a core–shell nanowire and to quantify the thicknesses and alloy compositions of the core and shell regions. A theoretical model based on continuum elastic theory has been used to estimate the strain fields present in such inhomogeneous nanowires. These results suggest new strategies for achieving high quality nonpolar heterostructures.

  13. Optical properties and band bending of InGaAs/GaAsBi/InGaAs type-II quantum well grown by gas source molecular beam epitaxy

    Science.gov (United States)

    Pan, Wenwu; Zhang, Liyao; Zhu, Liang; Li, Yaoyao; Chen, Xiren; Wu, Xiaoyan; Zhang, Fan; Shao, Jun; Wang, Shumin

    2016-09-01

    Photoluminescence (PL) properties of In0.2Ga0.8As/GaAs0.96Bi0.04/In0.2Ga0.8As quantum well (QW) grown on GaAs substrates by gas source molecular beam epitaxy were studied by varying excitation power and temperature, respectively. The type-II transition energy shifts from 1.149 eV to 1.192 eV when increasing the excitation power from 10 mW to 150 mW at 4.5 K, which was ascribed to the band-bending effect. On the other hand, the type-II PL quenches quickly along with fast redshift with the increasing temperature due to the relaxation of the band bending caused by the thermal excitation process. An 8 band k.p model was used to analyze the electronic properties and the band-bending effect in the type-II QW. The calculated subband levels and transition energy fit well with the experiment results, and two thermal activation energies of 8.7 meV and 50 meV, respectively, are deduced.

  14. Visible photoluminescence and room temperature ferromagnetism in high In-content InGaN:Yb nanorods grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Dasari, K.; Palai, R., E-mail: r.palai@upr.edu [Department of Physics, University of Puerto Rico, San Juan, Puerto Rico 00936 (United States); Wang, J.; Jadwisienczak, W. M. [School of Electrical Engineering and Computer Science, Ohio University, Athens, Ohio 45701-2979 (United States); Guinel, M. J.-F. [Department of Physics, University of Puerto Rico, San Juan, Puerto Rico 00936 (United States); Department of Chemistry, University of Puerto Rico, San Juan, Puerto Rico 00936 (United States); Huhtinen, H. [Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, Turku FI-20014 (Finland); Mundle, R.; Pradhan, A. K. [Department of Engineering, Norfolk State University, 700 Park Avenue, Norfolk, Virginia 23504 (United States)

    2015-09-28

    We report the growth of high indium content InGaN:Yb nanorods grown on c-plane sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The in situ reflection high energy electron diffraction patterns recorded during and after the growth revealed crystalline nature of the nanorods. The nanorods were examined using electron microscopy and atomic force microscopy. The photoluminescence studies of the nanorods showed the visible emissions. The In composition was calculated from x-ray diffraction, x-ray photoelectron spectroscopy, and the photoluminescence spectroscopy. The In-concentration was obtained from photoluminescence using modified Vegard's law and found to be around 37% for InGaN and 38% for Yb (5 ± 1%)-doped InGaN with a bowing parameter b = 1.01 eV. The Yb-doped InGaN showed significant enhancement in photoluminescence properties compared to the undoped InGaN. The Yb-doped InGaN nanorods demonstrated the shifting of the photoluminescence band at room temperature, reducing luminescence amplitude temperature dependent fluctuation, and significant narrowing of excitonic emission band as compared to the undoped InGaN. The magnetic properties measured by superconducting quantum interference devices reveals room temperature ferromagnetism, which can be explained by the double exchange mechanism and magnetostriction.

  15. Hole traps associated with high-concentration residual carriers in p-type GaAsN grown by chemical beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Elleuch, Omar, E-mail: mr.omar.elleuch@gmail.com; Wang, Li; Lee, Kan-Hua; Demizu, Koshiro; Ikeda, Kazuma; Kojima, Nobuaki; Ohshita, Yoshio; Yamaguchi, Masafumi [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan)

    2015-01-28

    The hole traps associated with high background doping in p-type GaAsN grown by chemical beam epitaxy are studied based on the changes of carrier concentration, junction capacitance, and hole traps properties due to the annealing. The carrier concentration was increased dramatically with annealing time, based on capacitance–voltage (C–V) measurement. In addition, the temperature dependence of the junction capacitance (C–T) was increased rapidly two times. Such behavior is explained by the thermal ionization of two acceptor states. These acceptors are the main cause of high background doping in the film, since the estimated carrier concentration from C–T results explains the measured carrier concentration at room temperature using C–V method. The acceptor states became shallower after annealing, and hence their structures are thermally unstable. Deep level transient spectroscopy (DLTS) showed that the HC2 hole trap was composed of two signals, labeled HC21 and HC22. These defects correspond to the acceptor levels, as their energy levels obtained from DLTS are similar to those deduced from C–T. The capture cross sections of HC21 and HC22 are larger than those of single acceptors. In addition, their energy levels and capture cross sections change in the same way due to the annealing. This tendency suggests that HC21 and HC22 signals originate from the same defect which acts as a double acceptor.

  16. Initial growth stages of Si–Ge–Sn ternary alloys grown on Si (100) by low-temperature molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Tuktamyshev, A. R., E-mail: tuktamyshev@isp.nsc.ru; Mashanov, V. I.; Timofeev, V. A.; Nikiforov, A. I.; Teys, S. A. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation)

    2015-12-15

    Temperature dependence of the critical thickness of the transition from two-dimensional to threedimensional growth of the Ge{sub 1–5x}Si{sub 4x}Sn{sub x} films grown on Si (100) by molecular-beam epitaxy in the temperature range 150–450°C has been experimentally determined. This dependence is nonmonotonic and is similar to that of the critical thickness for the transition from two-dimensional to three-dimensional growth in the case of the deposition of pure Ge on Si (100) and is caused by a change in the mechanism of two-dimensional growth. Data on the average size and the density of islands, and the ratio between the height of the islands and their lateral size are obtained by the methods of atomic force microscopy and scanning tunneling microscopy. As the growth temperature is increased from 200 to 400°C, the average size of the nanoislands increases from 4.7 to 23.6 nm.

  17. Double carriers pulse DLTS for the characterization of electron-hole recombination process in GaAsN grown by chemical beam epitaxy

    Science.gov (United States)

    Bouzazi, Boussairi; Suzuki, Hidetoshi; Kojima, Nobuaki; Ohshita, Yoshio; Yamaguchi, Masafumi

    2011-03-01

    A nitrogen-related electron trap (E1), located approximately 0.33 eV from the conduction band minimum of GaAsN grown by chemical beam epitaxy, was confirmed by investigating the dependence of its density with N concentration. This level exhibits a high capture cross section compared with that of native defects in GaAs. Its density increases significantly with N concentration, persists following post-thermal annealing, and was found to be quasi-uniformly distributed. These results indicate that E1 is a stable defect that is formed during growth to compensate for the tensile strain caused by N. Furthermore, E1 was confirmed to act as a recombination center by comparing its activation energy with that of the recombination current in the depletion region of the alloy. However, this technique cannot characterize the electron-hole (e-h) recombination process. For that, double carrier pulse deep level transient spectroscopy is used to confirm the non-radiative e -h recombination process through E1, to estimate the capture cross section of holes, and to evaluate the energy of multi-phonon emission. Furthermore, a configuration coordinate diagram is modeled based on the physical parameters of E1.

  18. Molecular Beam Epitaxy-Grown InGaN Nanomushrooms and Nanowires for White Light Source Applications

    KAUST Repository

    Gasim, Anwar A.

    2012-01-01

    We report the observation of coexisting InGaN nanomushrooms and nanowires grown via MBE. Photoluminescence characterization shows that the nanostructures emit yellow and blue light, respectively. The combined emission is promising for white-LEDs.

  19. Calcium impurity as a source of non-radiative recombination in (In,Ga)N layers grown by molecular beam epitaxy

    Science.gov (United States)

    Young, E. C.; Grandjean, N.; Mates, T. E.; Speck, J. S.

    2016-11-01

    Ca as an unintentional impurity has been investigated in III-nitride layers grown by molecular beam epitaxy (MBE). It is found that Ca originates from the substrate surface, even if careful cleaning and rinsing procedures are applied. The initial Ca surface coverage is ˜1012 cm-2, which is consistent with previous reports on GaAs and silicon wafers. At the onset of growth, the Ca species segregates at the growth front while incorporating at low levels. The incorporation rate is strongly temperature dependent. It is about 0.03% at 820 °C and increases by two orders of magnitude when the temperature is reduced to 600 °C, which is the typical growth temperature for InGaN alloy. Consequently, [Ca] is as high as 1018 cm-3 in InGaN/GaN quantum well structures. Such a huge concentration might be detrimental for the efficiency of light emitting diodes (LEDs) if one considers that Ca is potentially a source of Shockley-Read-Hall (SRH) defects. We thus developed a specific growth strategy to reduce [Ca] in the MBE grown LEDs, which consisted of burying Ca in a low temperature InGaN/GaN superlattice (SL) before the growth of the active region. Finally, two LED samples with and without an SL were fabricated. An increase in the output power by one order of magnitude was achieved when Ca was reduced in the LED active region, providing evidence for the role of Ca in the SRH recombination.

  20. Calcium impurity as a source of non-radiative recombination in (In,Ga)N layers grown by molecular beam epitaxy

    KAUST Repository

    Young, E. C.

    2016-11-23

    Ca as an unintentional impurity has been investigated in III-nitride layers grown by molecular beam epitaxy (MBE). It is found that Ca originates from the substrate surface, even if careful cleaning and rinsing procedures are applied. The initial Ca surface coverage is ∼1012 cm−2, which is consistent with previous reports on GaAs and silicon wafers. At the onset of growth, the Ca species segregates at the growth front while incorporating at low levels. The incorporation rate is strongly temperature dependent. It is about 0.03% at 820 °C and increases by two orders of magnitude when the temperature is reduced to 600 °C, which is the typical growth temperature for InGaN alloy. Consequently, [Ca] is as high as 1018 cm−3 in InGaN/GaN quantum well structures. Such a huge concentration might be detrimental for the efficiency of light emitting diodes (LEDs) if one considers that Ca is potentially a source of Shockley-Read-Hall (SRH) defects. We thus developed a specific growth strategy to reduce [Ca] in the MBE grown LEDs, which consisted of burying Ca in a low temperature InGaN/GaN superlattice (SL) before the growth of the active region. Finally, two LED samples with and without an SL were fabricated. An increase in the output power by one order of magnitude was achieved when Ca was reduced in the LED active region, providing evidence for the role of Ca in the SRH recombination.

  1. Nitridation effects of Si(1 1 1) substrate surface on InN nanorods grown by plasma-assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Shan [Faculty of Materials Science and Chemistry, China University of Geosciences, Wuhan 430074 (China); Tan, Jin, E-mail: jintan_cug@163.com [Faculty of Materials Science and Chemistry, China University of Geosciences, Wuhan 430074 (China); Engineering Research Center of Nano-Geomaterials of Ministry of Education, China University of Geosciences, Wuhan 430074 (China); Li, Bin; Song, Hao; Wu, Zhengbo; Chen, Xin [Faculty of Materials Science and Chemistry, China University of Geosciences, Wuhan 430074 (China)

    2015-02-05

    Graphical abstract: The morphology evolution of InN nanorods in samples (g)–(i). The alignment of InN nanorods is improved and the deviation angle distribution narrows down with increase in nitriding time. It suggests that extending the nitriding time can enhance the vertical orientation of InN nanorods. - Highlights: • InN nanorods were grown on surface nitrided Si(1 1 1) substrate using PAMBE system. • Nitridation of substrate surface has a strong effect on morphology of InN nanorods. • InN nanorods cannot be formed with 1 min nitridation of Si(1 1 1) substrate. • Increasing nitriding time will increase optimum growth temperature of InN nanorods. • Increasing nitriding time can enhance vertical orientation of InN nanorods. - Abstract: The InN nanorods were grown on Si(1 1 1) substrate by plasma-assisted molecular beam epitaxy (PAMBE) system, with a substrate nitridation process. The effect of nitriding time of Si(1 1 1) substrate on morphology, orientation and growth temperature of InN nanorods was characterized via scanning electron microscopy (SEM) and X-ray diffraction (XRD). The deviation angle of InN nanorods was measured to evaluate the alignment of arrays. The results showed that InN nanorods could not be formed with 1 min nitridation of Si(1 1 1) substrate, but they could be obtained again when the nitriding time was increased to more than 10 min. In order to get aligned InN nanorods, the growth temperature needed to increase with longer nitriding time. The vertical orientation of InN nanorods could be enhanced with increase in nitriding time. The influence of the substrate nitridation on the photoluminescence (PL) spectra of InN nanorods has been investigated.

  2. GaAsBi/GaAs multi-quantum well LED grown by molecular beam epitaxy using a two-substrate-temperature technique

    Science.gov (United States)

    Kisan Patil, Pallavi; Luna, Esperanza; Matsuda, Teruyoshi; Yamada, Kohki; Kamiya, Keisuke; Ishikawa, Fumitaro; Shimomura, Satoshi

    2017-03-01

    We report a GaAs0.96Bi0.04/GaAs multiple quantum well (MQW) light emitting diode (LED) grown by molecular beam epitaxy using a two-substrate-temperature (TST) technique. In particular, the QWs and the barriers in the intrinsic region were grown at the different temperatures of {T}{{GaAsBi}} = 350 °C and {T}{{GaAs}} = 550 ^\\circ {{C}}, respectively. Investigations of the microstructure using transmission electron microscopy (TEM) reveal homogeneous MQWs free of extended defects. Furthermore, the local determination of the Bi distribution profile across the MQWs region using TEM techniques confirm the uniform Bi distribution, while revealing a slightly chemically graded GaAs-on-GaAsBi interface due to Bi surface segregation. Despite this small broadening, we found that Bi segregation is significantly reduced (up to 18% reduction) compared to previous reports on Bi segregation in GaAsBi/GaAs MQWs. Hence, the TST procedure proves as a very efficient method to reduce Bi segregation and thus increase the quality of the layers and interfaces. These improvements positively reflect in the optical properties. Room temperature photoluminescence and electroluminescence (EL) at 1.23 μm emission wavelength are successfully demonstrated using TST MQWs containing less Bi content than in previous reports. Finally, LED fabricated using the present TST technique show current–voltage (I–V) curves with a forward voltage of 3.3 V at an injection current of 130 mA under 1.0 kA cm‑2 current excitation. These results not only demonstrate that TST technique provides optical device quality GaAsBi/GaAs MQWs but highlight the relevance of TST-based growth techniques on the fabrication of future heterostructure devices based on dilute bismides.

  3. InAsSb-based XB nn bariodes grown by molecular beam epitaxy on GaAs

    Science.gov (United States)

    Weiss, Eliezer; Klin, Olga; Grossmann, Steve; Snapi, Noam; Lukomsky, Inna; Aronov, Daniel; Yassen, Michael; Berkowicz, Eyal; Glozman, Alex; Klipstein, Philip; Fraenkel, Avraham; Shtrichman, Itay

    2012-01-01

    XB nn mid-wave infrared (MWIR) detector arrays aimed at high operating temperature (HOT) applications, also known as barrier detectors or " bariodes", are based on device elements with an InAsSb/AlSbAs heterostructure. There is no depletion layer in the narrow bandgap active layer of such devices, suppressing the usual Generation-Recombination (G-R) and Trap Assisted Tunneling (TAT) mechanisms for dark current that exist in standard narrow bandgap diodes. This yields lower dark currents in bariodes than in diodes with the same bandgap wavelength. InAsSb- bariode detectors, grown on lattice matched GaSb substrates have been shown previously to exhibit low dark current densities of ˜10 -7 A/cm 2 at 150 K. In this communication we show crystallographic and electro-optical characteristics of bariode structures grown on GaAs. Although the 7.8% mismatch causes a high density of dislocations, the devices still demonstrate electr-optical performance comparable with equivalent structures grown on GaSb, both for test devices and for focal plane array detectors (FPAs) with a 640×512 pixel format and a 15 μm pitch. This is in contrast to the behavior reported for InAsSb pin photodiodes grown on lattice mismatched substrates. The large leakage currents seen in the latter and attributed to a TAT mechanism, do not occur in the InAsSb-based bariodes grown on GaAs.

  4. Identification of N–H related acceptor defects in GaAsN grown by chemical beam epitaxy using hydrogen isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Elleuch, Omar, E-mail: mr.omar.elleuch@gmail.com; Wang, Li; Lee, Kan-Hua; Ikeda, Kazuma; Kojima, Nobuaki; Ohshita, Yoshio; Yamaguchi, Masafumi

    2015-11-15

    The N–H related acceptor defects in GaAsN grown by chemical beam epitaxy (CBE) are studied by hydrogen isotopes, H and D. When the films are grown by a conventional arsenic source, deep level transient spectroscopy (DLTS) reveals two energy levels at 0.11 and 0.19 eV above the valence band. These levels were considered to act as a double acceptor in the literature. When the films are grown by a deuterated arsenic source, new signals appear in DLTS spectra at 0.15 and 0.23 eV. This indicates that the new signals are originated from D-related defects. The energy differences between 0.15 and 0.11 eV, and that between 0.23 and 0.19 eV are same (0.04 eV). Although these energy levels become deeper with increasing the growth temperature, the energy differences are almost constant independent of the growth condition. In addition, the intensity ratios of the peaks at 0.15 (0.23) eV to that at 0.11 (0.19) eV have a good correlation with the isotopic concentration ratio of D to H in the grown films. Therefore, we conclude that the energy differences and intensity ratios of the DLTS peaks occur due to the structural change from N–H to N−D in the same type of defect, and that this acceptor is an N–H related defect. - Highlights: • The DLTS signals at 0.11 and 0.19 eV originate from a double acceptor. • Growth by D-TDMAAs: new defects that contain D are generated at 0.15 and 0.23 eV. • Energy differences between 0.15 (0.23) eV and 0.11 (0.19) eV: same, independent of T{sub G}. • Intensity ratios of peaks at 0.15 (0.23) eV to that at 0.11 (0.19) eV ≈ [D]/{[H]+[D]}. • Therefore, this acceptor is related to H.

  5. In situ transmission electron microscopy analyses of thermally annealed self catalyzed GaAs nanowires grown by molecular beam epitaxy

    DEFF Research Database (Denmark)

    Ambrosini, S.; Wagner, Jakob Birkedal; Booth, Tim;

    2011-01-01

    Self catalyzed GaAs nanowires grown on Si-treated GaAs substrates were studied with a transmission electron microscope before and after annealing at 600◦C. At room temperature the nanowires have a zincblende structure and are locally characterized by a high density of rotational twins and stackin...

  6. Magnetotransport in an aluminum thin film on a GaAs substrate grown by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Lin Sheng-Di

    2011-01-01

    Full Text Available Abstract Magnetotransport measurements are performed on an aluminum thin film grown on a GaAs substrate. A crossover from electron- to hole-dominant transport can be inferred from both longitudinal resistivity and Hall resistivity with increasing the perpendicular magnetic field B. Also, phenomena of localization effects can be seen at low B. By analyzing the zero-field resistivity as a function of temperature T, we show the importance of surface scattering in such a nanoscale film.

  7. Admittance spectroscopy of Mg-doped GaN grown by molecular beam epitaxy using RF nitrogen sources

    CERN Document Server

    Kim, D J; Kim, K H; Bojarczuk, N A; Karasinski, J; Guha, S; Lee, H G

    1999-01-01

    Thermal activation energies of Mg in GaN grown using RF nitrogen source with varying Mg flux were examined using an admittance spectroscopy technique. There was no noticeable difference or trend in the activation energy with varying Mg flux. The thermal activation energy for GaN:Mg was approx 115 meV under the investigated Mg flux range. Negligible persistent photo-conductivity and yellow luminescence peak in PL observed in the samples suggest possible reduction of the thermal activation energies compared to the values in the literature.

  8. Defect-related luminescence in InAlAs on InP grown by molecular beam epitaxy

    Science.gov (United States)

    Gilinsky, A. M.; Dmitriev, D. V.; Toropov, A. I.; Zhuravlev, K. S.

    2017-09-01

    The photoluminescence (PL) of InAlAs grown on InP has been studied in a wide range of temperatures and excitation intensities. A novel emission ascribed to the presence of defects has been found by about 120-180 meV below the near band edge (NBE) line. The novel wide PL band is observed in the spectra only in a limited range of temperatures of 50-160 K, and is seen neither at liquid helium nor at room temperatures. The analysis of the PL behaviour with sample temperature and excitation power together with non-stationary PL kinetics allows us to conclude that both the NBE PL and the novel PL band are controlled by transitions via states of band tails formed due to alloy disorder in these films. The NBE PL is caused by recombination of carriers in the band tails, while deep levels related to defects and located in the same regions as the deepest band tail states are supposedly involved in the defect-related PL transitions. We demonstrate that no defect-related PL is found in the spectra if quasi-stoichiometric growth conditions were used during film growth, which resulted in a PL efficiency by about 1-2 orders of magnitude greater than that of samples grown under more common As-rich conditions.

  9. Robust optical properties of sandwiched lateral composition modulation GaInP structure grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Park, Kwangwook; Kang, Seokjin; Ravindran, Sooraj; Min, Jung-Wook; Hwang, Hyeong-Yong; Jho, Young-Dahl; Lee, Yong Tak

    2016-12-26

    Double-hetero structure lateral composition modulated (LCM) GaInP and sandwiched LCM GaInP having the same active layer thickness were grown and their optical properties were compared. Sandwiched LCM GaInP showed robust optical properties due to periodic potential nature of the LCM structure, and the periodicity was undistorted even for thickness far beyond the critical layer thickness. A thick LCM GaInP structure with undistorted potential that could preserve the properties of native LCM structure was possible by stacking thin LCM GaInP structures interspaced with strain compensating GaInP layers. The sandwiched structure could be beneficial in realizing the LCM structure embedded high efficiency solar cells.

  10. Cross-sectional scanning thermal microscopy of ErAs/GaAs superlattices grown by molecular beam epitaxy.

    Science.gov (United States)

    Park, K W; Krivoy, E M; Nair, H P; Bank, S R; Yu, E T

    2015-07-03

    Scanning thermal microscopy has been implemented in a cross-sectional geometry, and its application for quantitative, nanoscale analysis of thermal conductivity is demonstrated in studies of an ErAs/GaAs nanocomposite superlattice. Spurious measurement effects, attributable to local thermal transport through air, were observed near large step edges, but could be eliminated by thermocompression bonding to an additional structure. Using this approach, bonding of an ErAs/GaAs superlattice grown on GaAs to a silicon-on-insulator wafer enabled thermal signals to be obtained simultaneously from Si, SiO2, GaAs, and ErAs/GaAs superlattice. When combined with numerical modeling, the thermal conductivity of the ErAs/GaAs superlattice measured using this approach was 11 ± 4 W m(-1) K(-1).

  11. Bandgap measurements and the peculiar splitting of E2H phonon modes of InxAl1-xN nanowires grown by plasma assisted molecular beam epitaxy

    KAUST Repository

    Tangi, Malleswararao

    2016-07-26

    The dislocation free Inx Al 1-xN nanowires (NWs) are grown on Si(111) by nitrogen plasma assisted molecular beam epitaxy in the temperature regime of 490 °C–610 °C yielding In composition ranges over 0.50 ≤ x ≤ 0.17. We study the optical properties of these NWs by spectroscopic ellipsometry (SE), photoluminescence, and Raman spectroscopies since they possesses minimal strain with reduced defects comparative to the planar films. The optical bandgap measurements of Inx Al 1-xN NWs are demonstrated by SE where the absorption edges of the NW samples are evaluated irrespective of substrate transparency. A systematic Stoke shift of 0.04–0.27 eV with increasing x was observed when comparing the micro-photoluminescence spectra with the Tauc plot derived from SE. The micro-Raman spectra in the NWs with x = 0.5 showed two-mode behavior for A1(LO) phonons and single mode behavior for E2 H phonons. As for x = 0.17, i.e., high Al content, we observed a peculiar E2 H phonon mode splitting. Further, we observe composition dependent frequency shifts. The 77 to 600 K micro-Raman spectroscopy measurements show that both AlN- and InN-like modes of A1(LO) and E2 H phonons in Inx Al 1-xN NWs are redshifted with increasing temperature, similar to that of the binary III group nitride semiconductors. These studies of the optical properties of the technologically important Inx Al 1-xN nanowires will path the way towards lasers and light-emitting diodes in the wavelength of the ultra-violet and visible range.

  12. Bandgap tuning in GaAs1‑xSbx axial nanowires grown by Ga-assisted molecular beam epitaxy

    Science.gov (United States)

    Ahmad, Estiak; Ojha, S. K.; Kasanaboina, P. K.; Reynolds, C. L., Jr.; Liu, Y.; Iyer, S.

    2017-03-01

    In this work we present a comprehensive study on the effects of Sb incorporation on the composition modulation, structural and optical properties of self-assisted axial GaAs1‑xSbx nanowires of 2–6 μm in length grown on (111) Si substrate by molecular beam epitaxy. The Sb composition in the GaAs1‑xSbx axial nanowire (NW) was varied from 2.8–16 at.%, as determined from energy dispersive x-ray spectroscopy. Lower Sb composition leads to thinner nanowires and inhomogeneous Sb composition distribution radially with a depleted Sb surface region inducing weak type-II optical emission, the presence of an additional peak at higher Bragg angle in the x-ray diffraction spectra and an electric-field-induced strong Raman LO mode. Higher Sb composition of 16 at.% leads to a more uniform Sb compositional distribution radially leading to type-I optical transitions exhibiting the lowest PL peak energy occurring at 1.13 eV. In addition, the high quality of these nanowires exhibiting pure zinc blende crystal structure, largely free of any planar defects, is borne out by high resolution transmission electron microscopy and selected area diffraction patterns. The shift and broadening of the Raman LO and TO modes reveal evidence of increased Sb incorporation in the nanowires. Significant improvement in optical characteristics was achieved by the incorporation of a Al0.2Ga0.8As passivating shell. The results are very promising and reveal the potential to further red shift the optical emission wavelength by fine tuning of the fluxes during growth.

  13. Electron transport in unipolar InGaN/GaN multiple quantum well structures grown by NH3 molecular beam epitaxy

    KAUST Repository

    Browne, David A.

    2015-05-14

    © 2015 AIP Publishing LLC. Unipolar-light emitting diode like structures were grown by NH3 molecular beam epitaxy on c plane (0001) GaN on sapphire templates. Studies were performed to experimentally examine the effect of random alloy fluctuations on electron transport through quantum well active regions. These unipolar structures served as a test vehicle to test our 2D model of the effect of compositional fluctuations on polarization-induced barriers. Variables that were systematically studied included varying quantum well number from 0 to 5, well thickness of 1.5 nm, 3 nm, and 4.5 nm, and well compositions of In0.14Ga0.86N and In0.19Ga0.81N. Diode-like current voltage behavior was clearly observed due to the polarization-induced conduction band barrier in the quantum well region. Increasing quantum well width and number were shown to have a significant impact on increasing the turn-on voltage of each device. Temperature dependent IV measurements clearly revealed the dominant effect of thermionic behavior for temperatures from room temperature and above. Atom probe tomography was used to directly analyze parameters of the alloy fluctuations in the quantum wells including amplitude and length scale of compositional variation. A drift diffusion Schrödinger Poisson method accounting for two dimensional indium fluctuations (both in the growth direction and within the wells) was used to correctly model the turn-on voltages of the devices as compared to traditional 1D simulation models.

  14. The effects of annealing on the structural, optical, and vibrational properties of lattice-matched GaAsSbN/GaAs grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Bharatan, S. [North Carolina A& T State University; Iyer, Prof Shanthi [North Carolina A& T State University; Nunna, K. [North Carolina A& T State University; Collis, W J [North Carolina A& T State University; Matney, K. [Bede Scientific Inc, Englewood, Colorado; Reppert, J. [Clemson University; Rao, A. M. [Clemson University; Kent, Paul R [ORNL

    2007-01-01

    The structural, optical, and vibrational properties of a GaAsSbN epilayer lattice matched to GaAs with a band gap of 1 eV have been investigated using a variety of characterization techniques. These layers have potential applications in GaAs based tandem solar cells that utilize the near infrared region of the solar spectrum. The epilayers were grown in an elemental solid source molecular beam epitaxy system with a rf plasma nitrogen source. The Sb and N compositions of the nearly lattice-matched layers are 6.8% and 2.6%, respectively, as determined by high resolution x-ray diffraction and secondary ion mass spectroscopy (SIMS) analysis. The high crystalline quality of the layers is attested by the presence of well resolved Pendellosung fringes on a triple axis (004) x-ray scan and dynamical truncation rods observed on the corresponding (004) reciprocal space map. The effects of in situ annealing in As ambient and ex situ annealing in N ambient on the low temperature photoluminescence (PL) characteristics are discussed. Ex situ (in situ) annealed samples display an 8 K PL peak energy of 1 eV with a full width at half maximum of 18 meV (26 meV). Raman spectral analysis, the temperature dependence of the PL peak energy, and SIMS profiles indicate that outdiffusions of N and As are suppressed in the in situ annealed samples and improvement in Ga-N bonding is observed, leading to higher PL intensities in these samples. In addition, indirect evidence of atomic scale ordering has been observed. The stability of these structures appears to be dependent on the annealing conditions.

  15. Double carriers pulse DLTS for the characterization of electron-hole recombination process in GaAsN grown by chemical beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Bouzazi, Boussairi, E-mail: sd08503@toyota-ti.ac.j [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan); Suzuki, Hidetoshi; Kojima, Nobuaki; Ohshita, Yoshio; Yamaguchi, Masafumi [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan)

    2011-03-01

    A nitrogen-related electron trap (E1), located approximately 0.33 eV from the conduction band minimum of GaAsN grown by chemical beam epitaxy, was confirmed by investigating the dependence of its density with N concentration. This level exhibits a high capture cross section compared with that of native defects in GaAs. Its density increases significantly with N concentration, persists following post-thermal annealing, and was found to be quasi-uniformly distributed. These results indicate that E1 is a stable defect that is formed during growth to compensate for the tensile strain caused by N. Furthermore, E1 was confirmed to act as a recombination center by comparing its activation energy with that of the recombination current in the depletion region of the alloy. However, this technique cannot characterize the electron-hole (e-h) recombination process. For that, double carrier pulse deep level transient spectroscopy is used to confirm the non-radiative e-h recombination process through E1, to estimate the capture cross section of holes, and to evaluate the energy of multi-phonon emission. Furthermore, a configuration coordinate diagram is modeled based on the physical parameters of E1. -- Research Highlights: {yields} Double carrier pulse DLTS method confirms the existence of SRH center. {yields} The recombination center in GaAsN depends on nitrogen concentration. {yields} Minority carrier lifetime in GaAsN is less than 1 ns. {yields} A non-radiative recombination center exits in GaAsN.

  16. An aberration-corrected STEM study of structural defects in epitaxial GaN thin films grown by ion beam assisted MBE.

    Science.gov (United States)

    Poppitz, David; Lotnyk, Andriy; Gerlach, Jürgen W; Lenzner, Jörg; Grundmann, Marius; Rauschenbach, Bernd

    2015-06-01

    Ion-beam assisted molecular-beam epitaxy was used for direct growth of epitaxial GaN thin films on super-polished 6H-SiC(0001) substrates. The GaN films with different film thicknesses were studied using reflection high energy electron diffraction, X-ray diffraction, cathodoluminescence and primarily aberration-corrected scanning transmission electron microscopy techniques. Special attention was devoted to the microstructural characterization of GaN thin films and the GaN-SiC interface on the atomic scale. The results show a variety of defect types in the GaN thin films and at the GaN-SiC interface. A high crystalline quality of the produced hexagonal GaN thin films was demonstrated. The gained results are discussed.

  17. Comparison of single junction AlGaInP and GaInP solar cells grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Masuda, T; Tomasulo, S; Lang, JR; Lee, ML

    2015-03-07

    We have investigated similar to 2.0 eV (AlxGa1-x)(0.51)In0.49P and similar to 1.9 eV Ga0.51In0.49P single junction solar cells grown on both on-axis and misoriented GaAs substrates by molecular beam epitaxy (MBE). Although lattice-matched (AlxGa1-x)(0.51)In0.49P solar cells are highly attractive for space and concentrator photovoltaics, there have been few reports on the MBE growth of such cells. In this work, we demonstrate open circuit voltages (V-oc) ranging from 1.29 to 1.30 V for Ga0.51In0.49P cells, and 1.35-1.37 V for (AlxGa1-x)(0.51)In0.49P cells. Growth on misoriented substrates enabled the bandgap-voltage offset (W-oc = E-g/q - V-oc) of Ga0.51In0.49P cells to decrease from similar to 575 mV to similar to 565 mV, while that of (AlxGa1-x)(0.51)In0.49P cells remained nearly constant at 620 mV. The constant Woc as a function of substrate offcut for (AlxGa1-x)(0.51)In0.49P implies greater losses from non-radiative recombination compared with the Ga0.51In0.49P devices. In addition to larger Woc values, the (AlxGa1-x)(0.51)In0.49P cells exhibited significantly lower internal quantum efficiency (IQE) values than Ga0.51In0.49P cells due to recombination at the emitter/window layer interface. A thin emitter design is experimentally shown to be highly effective in improving IQE, particularly at short wavelengths. Our work shows that with further optimization of both cell structure and growth conditions, MBE-grown (AlxGa1-x)(0.51)In0.49P will be a promising wide-bandgap candidate material for high-efficiency, lattice-matched multi-junction solar cells. (C) 2015 AIP Publishing LLC.

  18. Effect of the annealing temperature on the low-temperature photoluminescence in Si:Er light-emitting structures grown by molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Andreev, B. A. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Sobolev, N. A., E-mail: nick@sobolev.ioffe.ru; Denisov, D. V.; Shek, E. I. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)

    2013-10-15

    The photoluminescence spectra of light-emitting structures based on silicon doped with erbium during the course of molecular-beam epitaxy at a temperature of 500 Degree-Sign C are studied at 4.2 K on being annealed at 800-900 Degree-Sign C. Three sets of lines belonging to the emitting centers of erbium in silicon with a low oxygen-impurity concentration are revealed.

  19. Self-assembled flower-like nanostructures of InN and GaN grown by plasma-assisted molecular beam epitaxy

    Indian Academy of Sciences (India)

    Mahesh Kumar; T N Bhat; M K Rajpalke; B Roul; P Misra; L M Kukreja; Neeraj Sinha; A T Kalghatgi; S B Krupanidhi

    2010-06-01

    Nanosized hexagonal InN flower-like structures were fabricated by droplet epitaxy on GaN/Si(111) and GaN flower-like nanostructure fabricated directly on Si(111) substrate using radio frequency plasma-assisted molecular beam epitaxy. Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the crystallinity and morphology of the nanostructures. Moreover, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to investigate the chemical compositions and optical properties of nano-flowers, respectively. Activation energy of free exciton transitions in GaN nano-flowers was derived to be ∼ 28.5 meV from the temperature dependent PL studies. The formation process of nanoflowers is investigated and a qualitative mechanism is proposed.

  20. The effect of metal-rich growth conditions on the microstructure of Sc{sub x}Ga{sub 1-x}N films grown using molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Tsui, H.C.L.; Moram, M.A. [Department of Materials, Imperial College London (United Kingdom); Goff, L.E. [Department of Materials, Imperial College London (United Kingdom); Department of Physics, University of Cambridge (United Kingdom); Barradas, N.P. [CTN - Centro de Ciencias e Tecnologias Nucleares, Instituto Superior Tecnico, Universidade de Lisboa, Bobadela LRS (Portugal); Alves, E. [IPFN - Instituto de Plasmas e Fusao Nuclear, Lisboa (Portugal); Laboratorio de Aceleradores e Tecnologias de Radiacao, Instituto Superior Tecnico, Universidade de Lisboa, Bobadela LRS (Portugal); Pereira, S. [CICECO and Department of Physics, Universidade de Aveiro (Portugal); Beere, H.E.; Farrer, I.; Nicoll, C.A.; Ritchie, D.A. [Department of Physics, University of Cambridge (United Kingdom)

    2015-12-15

    Epitaxial Sc{sub x}Ga{sub 1-x}N films with 0 ≤ x ≤ 0.50 were grown using molecular beam epitaxy under metal-rich conditions. The Sc{sub x}Ga{sub 1-x}N growth rate increased with increasing Sc flux despite the use of metal-rich growth conditions, which is attributed to the catalytic decomposition of N{sub 2} induced by the presence of Sc. Microstructural analysis showed that phase-pure wurtzite Sc{sub x}Ga{sub 1-x}N was achieved up to x = 0.26, which is significantly higher than that previously reported for nitrogen-rich conditions, indicating that the use of metal-rich conditions can help to stabilise wurtzite phase Sc{sub x}Ga{sub 1-x}N. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Comparison of single junction AlGaInP and GaInP solar cells grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Masuda, Taizo, E-mail: taizo.masuda@yale.edu; Tomasulo, Stephanie; Lang, Jordan R.; Lee, Minjoo Larry [Department of Electrical Engineering, Yale University, New Haven, Connecticut 06511 (United States)

    2015-03-07

    We have investigated ∼2.0 eV (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P and ∼1.9 eV Ga{sub 0.51}In{sub 0.49}P single junction solar cells grown on both on-axis and misoriented GaAs substrates by molecular beam epitaxy (MBE). Although lattice-matched (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P solar cells are highly attractive for space and concentrator photovoltaics, there have been few reports on the MBE growth of such cells. In this work, we demonstrate open circuit voltages (V{sub oc}) ranging from 1.29 to 1.30 V for Ga{sub 0.51}In{sub 0.49}P cells, and 1.35–1.37 V for (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P cells. Growth on misoriented substrates enabled the bandgap-voltage offset (W{sub oc} = E{sub g}/q − V{sub oc}) of Ga{sub 0.51}In{sub 0.49}P cells to decrease from ∼575 mV to ∼565 mV, while that of (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P cells remained nearly constant at 620 mV. The constant W{sub oc} as a function of substrate offcut for (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P implies greater losses from non-radiative recombination compared with the Ga{sub 0.51}In{sub 0.49}P devices. In addition to larger W{sub oc} values, the (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P cells exhibited significantly lower internal quantum efficiency (IQE) values than Ga{sub 0.51}In{sub 0.49}P cells due to recombination at the emitter/window layer interface. A thin emitter design is experimentally shown to be highly effective in improving IQE, particularly at short wavelengths. Our work shows that with further optimization of both cell structure and growth conditions, MBE-grown (Al{sub x}Ga{sub 1−x}){sub 0.51}In{sub 0.49}P will be a promising wide-bandgap candidate material for high-efficiency, lattice-matched multi-junction solar cells.

  2. Elimination of columnar microstructure in N-face InAlN, lattice-matched to GaN, grown by plasma-assisted molecular beam epitaxy in the N-rich regime

    Energy Technology Data Exchange (ETDEWEB)

    Ahmadi, Elaheh; Wienecke, Steven; Keller, Stacia; Mishra, Umesh K. [Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106 (United States); Shivaraman, Ravi; Wu, Feng; Kaun, Stephen W.; Speck, James S. [Materials Department, University of California, Santa Barbara, California 93106 (United States)

    2014-02-17

    The microstructure of N-face InAlN layers, lattice-matched to GaN, was investigated by scanning transmission electron microscopy and atom probe tomography. These layers were grown by plasma-assisted molecular beam epitaxy (PAMBE) in the N-rich regime. Microstructural analysis shows an absence of the lateral composition modulation that was previously observed in InAlN films grown by PAMBE. A room temperature two-dimensional electron gas (2DEG) mobility of 1100 cm{sup 2}/V s and 2DEG sheet charge density of 1.9 × 10{sup 13} cm{sup −2} was measured for N-face GaN/AlN/GaN/InAlN high-electron-mobility transistors with lattice-matched InAlN back barriers.

  3. On the evolution of InAs thin films grown by molecular beam epitaxy on the GaAs(001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Grabowski, Jan

    2010-12-14

    Semiconductor nanostructures are currently of high interest for a wide variety of electronic and optoelectronic applications. A large number of devices, in particular for the optical data transmission in the long-wavelength range, essential in modern communication, are based on InAs/GaAs quantum dot (QD) structures. Though the properties of the InAs/GaAs QDs have been extensively studied, only little is known about the formation and structure of the wetting layer (WL) yet. In the present work, the pathway of the InAs WL evolution is studied in detail. For this purpose, InAs thin films in the range of one monolayer (ML) are deposited on the GaAs(001) surface by molecular beam epitaxy (MBE) and studied by reflection high energy electron diffraction (RHEED) and in particular by scanning tunneling microscopy (STM). The InAs thin films are grown in both typical growth regimes, on the GaAs-c(4 x 4) and the GaAs-{beta}2(2 x 4) reconstructed surface, in a variety of thicknesses starting from submonolayers with 0.09 ML of InAs up to 1.65 ML of InAs exceeding the critical thickness for QD growth. In principle, three growth stages are found. At low InAs coverages, the indium adsorbs in agglomerations of typically eight In atoms at energetically preferable surface sites. In the STM images, the signatures of these In agglomerations appear with a clear bright contrast. A structural model for the initial formation of these signatures is presented, and its electronic and strain related properties are discussed. At an InAs coverage of about 0.67ML the initial surface transforms into a (4 x 3) reconstructed In{sub 2/3}Ga{sub 1/3}As ML and the detailed structure and strain properties of this surface are unraveled. On top of the InGaAs ML further deposited InAs forms a second layer, characterized by a typical zig-zag alignment of (2 x 4) reconstructed unit cells, with an alternating {alpha}2/{alpha}2-m configuration. In contrast to the previous surface reconstructions, where

  4. Low temperature laser molecular beam epitaxy and characterization of AlGaN epitaxial layers

    Science.gov (United States)

    Tyagi, Prashant; Ch., Ramesh; Kushvaha, S. S.; Kumar, M. Senthil

    2017-05-01

    We have grown AlGaN (0001) epitaxial layers on sapphire (0001) by using laser molecular beam epitaxy (LMBE) technique. The growth was carried out using laser ablation of AlxGa1-x liquid metal alloy under r.f. nitrogen plasma ambient. Before epilayer growth, the sapphire nitradation was performed at 700 °C using r.f nitrogen plasma followed by AlGaN layer growth. The in-situ reflection high energy electron diffraction (RHEED) was employed to monitor the substrate nitridation and AlGaN epitaxial growth. High resolution x-ray diffraction showed wurtzite hexagonal growth of AlGaN layer along c-axis. An absorption bandgap of 3.97 eV is obtained for the grown AlGaN layer indicating an Al composition of more than 20 %. Using ellipsometry, a refractive index (n) value of about 2.19 is obtained in the visible region.

  5. Strain-Balanced InAs/InAs1-xSbx Type-II Superlattices Grown by Molecular Beam Epitaxy on GaSb Substrates

    Science.gov (United States)

    2011-12-21

    C. Four samples A, B, C, and D with 20 period SLs were grown under identical condi- tions with varying Sb/(Asþ Sb) beam equivalent pressure ( BEP ) flux...incorporation can be achieved. Thus, the InAs1xSbx layers in samples A, B, C, and D have Sb/(AsþSb) BEP ratios of 0.32, 0.347, 0.378, and 0.412

  6. Topography and structure of ultrathin topological insulator Sb2Te3 films on Si(111) grown by means of molecular beam epitaxy

    Science.gov (United States)

    Lanius, M.; Kampmeier, J.; Kölling, S.; Mussler, G.; Koenraad, P. M.; Grützmacher, D.

    2016-11-01

    We have studied the growth process of the topological insulator (TI) Sb2 Te3 on Si(111) by scanning tunneling microscopy. High quality thin films from more than 22 nm down to 1 nm in thickness have been deposited by molecular beam epitaxy. To determine the thickness and domain formation of the films, x-ray reflectivity and x-ray diffraction were utilized. In comparison to previous studies of the TI Bi2 Te3 , the growth mechanism of Sb2 Te3 shows a similar transition from nucleation and growth in Sb-Te and Te-Te bilayers, respectively, to mound formation for thicker films. Atom probe tomography measurements reveal a intermixed interface between Sb2 Te3 and Si(111) substrate. These findings can explain the high density of defects and domains.

  7. Vertical transport through AlGaN barriers in heterostructures grown by ammonia molecular beam epitaxy and metalorganic chemical vapor deposition

    Science.gov (United States)

    Browne, David A.; Fireman, Micha N.; Mazumder, Baishakhi; Kuritzky, Leah Y.; Wu, Yuh-Renn; Speck, James S.

    2017-02-01

    The results of vertical transport through AlGaN heterobarriers are presented for ammonia molecular beam epitaxy (NH3-MBE) on c-plane GaN on sapphire templates and on m-plane bulk GaN substrates, as well as by metalorganic chemical vapor deposition (MOCVD) on m-plane bulk GaN substrates. Experiments were performed to determine the role of the AlGaN alloy as an effective barrier to vertical transport, which is an essential component of both optoelectronic and power electronic devices. The alloy composition, thickness, and doping levels of the AlGaN layers, as well as substrate orientation, were systematically varied to examine their influence on electron transport. Atom probe tomography (APT) was used to directly determine the alloy composition at the atomic scale to reveal the presence of random alloy fluctuations which provides insight into the nature of the observed transport.

  8. Effect of Nitridation on the Regrowth Interface of AlGaN/GaN Structures Grown by Molecular Beam Epitaxy on GaN Templates

    Science.gov (United States)

    Wong, Yuen-Yee; Huang, Wei-Ching; Trinh, Hai-Dang; Yang, Tsung-Hsi; Chang, Jet-Rung; Chen, Micheal; Chang, Edward Yi

    2012-08-01

    AlGaN/GaN structures were regrown on GaN templates using plasma- assisted molecular beam epitaxy (PA-MBE). Prior to the regrowth, nitridation was performed using nitrogen plasma in the MBE chamber for different durations (0 min to 30 min). Direct-current measurements on high-electron-mobility transistor devices showed that good pinch-off characteristics and good interdevice isolation were achieved for samples prepared with a 30-min nitridation process. Current-voltage measurements on Schottky barrier diodes also revealed that, for samples prepared without nitridation, the reverse-bias gate leakage current was approximately two orders of magnitudes larger than that of samples prepared with a 30-min nitridation process. The improvement in the electrical properties is a result of contaminant removal at the regrowth interface which may be induced by the etching effect of nitridation.

  9. Low threshold 1.55 {mu}m wavelength InAsP/InGaAsP strained multiquantum well laser diode grown by chemical beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Carlin, J.F.; Syrbu, A.V.; Berseth, C.A.; Behrend, J.; Rudra, A.; Kapon, E. [Institut de Micro- et Optoelectronique, Departement de Physique, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne (Switzerland)

    1997-07-01

    By using chemical beam epitaxy at growth temperatures as low as 460{endash}480{degree}C, we have overcome strain relaxation problems that prevented so far the successful use of InAsP quantum wells in 1.55 {mu}m lasers. Five quantum well InAsP/InGaAsP horizontal cavity lasers showed 88{percent} internal efficiency, 1.6cm{sup {minus}1} losses per well, and 33A/cm{sup 2} transparency current density per well, which equal or even surpass the best published characteristics for 1.55 {mu}m wavelength lasers based on any material system. Moreover, up to 17 quantum wells were integrated in a strain-balanced laser, which showed equally good characteristics. {copyright} {ital 1997 American Institute of Physics.}

  10. Molecular beam epitaxy a short history

    CERN Document Server

    Orton, J W

    2015-01-01

    This volume describes the development of molecular beam epitaxy from its origins in the 1960s through to the present day. It begins with a short historical account of other methods of crystal growth, both bulk and epitaxial, to set the subject in context, emphasising the wide range of semiconductor materials employed. This is followed by an introduction to molecular beams and their use in the Stern-Gerlach experiment and the development of the microwave MASER.

  11. Silicon Holder For Molecular-Beam Epitaxy

    Science.gov (United States)

    Hoenk, Michael E.; Grunthaner, Paula J.; Grunthaner, Frank J.

    1993-01-01

    Simple assembly of silicon wafers holds silicon-based charge-coupled device (CCD) during postprocessing in which silicon deposited by molecular-beam epitaxy. Attains temperatures similar to CCD, so hotspots suppressed. Coefficients of thermal expansion of holder and CCD equal, so thermal stresses caused by differential thermal expansion and contraction do not develop. Holder readily fabricated, by standard silicon processing techniques, to accommodate various CCD geometries. Silicon does not contaminate CCD or molecular-beam-epitaxy vacuum chamber.

  12. Textured Sb2Te3 films and GeTe/Sb2Te3 superlattices grown on amorphous substrates by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Jos E. Boschker

    2017-01-01

    Full Text Available The realization of textured films of 2-dimensionally (2D bonded materials on amorphous substrates is important for the integration of this material class with silicon based technology. Here, we demonstrate the successful growth by molecular beam epitaxy of textured Sb2Te3 films and GeTe/Sb2Te3 superlattices on two types of amorphous substrates: carbon and SiO2. X-ray diffraction measurements reveal that the out-of-plane alignment of grains in the layers has a mosaic spread with a full width half maximum of 2.8°. We show that a good texture on SiO2 is only obtained for an appropriate surface preparation, which can be performed by ex situ exposure to Ar+ ions or by in situ exposure to an electron beam. X-ray photoelectron spectroscopy reveals that this surface preparation procedure results in reduced oxygen content. Finally, it is observed that film delamination can occur when a capping layer is deposited on top of a superlattice with a good texture. This is attributed to the stress in the capping layer and can be prevented by using optimized deposition conditions of the capping layer. The obtained results are also relevant to the growth of other 2D materials on amorphous substrates.

  13. Textured Sb2Te3 films and GeTe/Sb2Te3 superlattices grown on amorphous substrates by molecular beam epitaxy

    Science.gov (United States)

    Boschker, Jos E.; Tisbi, E.; Placidi, E.; Momand, Jamo; Redaelli, Andrea; Kooi, Bart J.; Arciprete, Fabrizio; Calarco, Raffaella

    2017-01-01

    The realization of textured films of 2-dimensionally (2D) bonded materials on amorphous substrates is important for the integration of this material class with silicon based technology. Here, we demonstrate the successful growth by molecular beam epitaxy of textured Sb2Te3 films and GeTe/Sb2Te3 superlattices on two types of amorphous substrates: carbon and SiO2. X-ray diffraction measurements reveal that the out-of-plane alignment of grains in the layers has a mosaic spread with a full width half maximum of 2.8°. We show that a good texture on SiO2 is only obtained for an appropriate surface preparation, which can be performed by ex situ exposure to Ar+ ions or by in situ exposure to an electron beam. X-ray photoelectron spectroscopy reveals that this surface preparation procedure results in reduced oxygen content. Finally, it is observed that film delamination can occur when a capping layer is deposited on top of a superlattice with a good texture. This is attributed to the stress in the capping layer and can be prevented by using optimized deposition conditions of the capping layer. The obtained results are also relevant to the growth of other 2D materials on amorphous substrates.

  14. Dopant incorporation in Al0.9Ga0.1As0.06Sb0.94 grown by molecular beam epitaxy

    Science.gov (United States)

    Patra, Saroj Kumar; Tran, Thanh-Nam; Vines, Lasse; Kolevatov, Ilia; Monakhov, Edouard; Fimland, Bjørn-Ove

    2017-04-01

    Incorporation of beryllium (Be) and tellurium (Te) dopants in epitaxially grown Al0.9Ga0.1As0.06Sb0.94 layers was investigated. Carrier concentrations and mobilities of the doped layers were obtained from room temperature Hall effect measurements, and dopant densities from secondary ion mass spectrometry depth profiling. An undoped Al0.3Ga0.7As cap layer and side wall passivation were used to reduce oxidation and improve accuracy in Hall effect measurements. The measurements on Be-doped samples revealed high doping efficiency and the carrier concentration varied linearly with dopant density up to the highest Be dopant density of 2.9 × 1019 cm-3, whereas for Te doped samples the doping efficiency was in general low and the carrier concentration saturated for Te-dopant densities above 8.0 × 1018 cm-3. The low doping efficiency in Te-doped Al0.9Ga0.1As0.06Sb0.94 layer was studied by deep-level transient spectroscopy, revealing existence of deep trap levels and related DX-centers which explains the low doping efficiency.

  15. X-ray study of chromium oxide films epitaxially grown on MgO

    NARCIS (Netherlands)

    Du, XS; Hak, S; Rogojami, OC; Hibma, T

    2004-01-01

    Chromium oxide films grown by molecular beam epitaxy on MgO (001) substrates were characterized by x-ray diffraction (XRD) and x-ray reflectivity (XRR) measurements. The absence of random oriented peaks in the theta-2theta spectra indicated that the thin films were a single phase. Reciprocal space

  16. Widely tunable alloy composition and crystal structure in catalyst-free InGaAs nanowire arrays grown by selective area molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Treu, J., E-mail: Julian.Treu@wsi.tum.de, E-mail: Gregor.Koblmueller@wsi.tum.de; Speckbacher, M.; Saller, K.; Morkötter, S.; Xu, X.; Riedl, H.; Abstreiter, G.; Finley, J. J.; Koblmüller, G., E-mail: Julian.Treu@wsi.tum.de, E-mail: Gregor.Koblmueller@wsi.tum.de [Walter Schottky Institut, Physik Department, Center of Nanotechnology and Nanomaterials, Technische Universität München, Am Coulombwall 4, Garching 85748 (Germany); Döblinger, M. [Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, Munich 81377 (Germany)

    2016-02-01

    We delineate the optimized growth parameter space for high-uniformity catalyst-free InGaAs nanowire (NW) arrays on Si over nearly the entire alloy compositional range using selective area molecular beam epitaxy. Under the required high group-V fluxes and V/III ratios, the respective growth windows shift to higher growth temperatures as the Ga-content x(Ga) is tuned from In-rich to Ga-rich InGaAs NWs. Using correlated x-ray diffraction, transmission electron microscopy, and micro-photoluminescence spectroscopy, we identify structural defects to govern luminescence linewidths in In-rich (x(Ga) < 0.4) and Ga-rich (x(Ga) > 0.6) NWs, whereas limitations at intermediate Ga-content (0.4 < x(Ga) < 0.6) are mainly due to compositional inhomogeneities. Most remarkably, the catalyst-free InGaAs NWs exhibit a characteristic transition in crystal structure from wurtzite to zincblende (ZB) dominated phase near x(Ga) ∼ 0.4 that is further reflected in a cross-over from blue-shifted to red-shifted photoluminescence emission relative to the band edge emission of the bulk ZB InGaAs phase.

  17. Catalyst-free InGaN/GaN nanowire light emitting diodes grown on (001) silicon by molecular beam epitaxy.

    Science.gov (United States)

    Guo, Wei; Zhang, Meng; Banerjee, Animesh; Bhattacharya, Pallab

    2010-09-08

    Catalyst-free growth of (In)GaN nanowires on (001) silicon substrate by plasma-assisted molecular beam epitaxy is demonstrated. The nanowires with diameter ranging from 10 to 50 nm have a density of 1-2 x 10(11) cm(-2). P- and n-type doping of the nanowires is achieved with Mg and Si dopant species, respectively. Structural characterization by high-resolution transmission electron microscopy (HRTEM) indicates that the nanowires are relatively defect-free. The peak emission wavelength of InGaN nanowires can be tuned from ultraviolet to red by varying the In composition in the alloy and "white" emission is obtained in nanowires where the In composition is varied continuously during growth. The internal quantum efficiency varies from 20-35%. Radiative and nonradiative lifetimes of 5.4 and 1.4 ns, respectively, are obtained from time-resolved photoluminescence measurements at room temperature for InGaN nanowires emitting at lambda = 490 nm. Green- and white-emitting planar LEDs have been fabricated and characterized. The electroluminescence from these devices exhibits negligible quantum confined Stark effect or band-tail filling effect.

  18. Ge quantum dot arrays grown by ultrahigh vacuum molecular-beam epitaxy on the Si(001 surface: nucleation, morphology, and CMOS compatibility

    Directory of Open Access Journals (Sweden)

    Yuryev Vladimir

    2011-01-01

    Full Text Available Abstract Issues of morphology, nucleation, and growth of Ge cluster arrays deposited by ultrahigh vacuum molecular beam epitaxy on the Si(001 surface are considered. Difference in nucleation of quantum dots during Ge deposition at low (≲600°C and high (≳600°C temperatures is studied by high resolution scanning tunneling microscopy. The atomic models of growth of both species of Ge huts--pyramids and wedges-- are proposed. The growth cycle of Ge QD arrays at low temperatures is explored. A problem of lowering of the array formation temperature is discussed with the focus on CMOS compatibility of the entire process; a special attention is paid upon approaches to reduction of treatment temperature during the Si(001 surface pre-growth cleaning, which is at once a key and the highest-temperature phase of the Ge/Si(001 quantum dot dense array formation process. The temperature of the Si clean surface preparation, the final high-temperature step of which is, as a rule, carried out directly in the MBE chamber just before the structure deposition, determines the compatibility of formation process of Ge-QD-array based devices with the CMOS manufacturing cycle. Silicon surface hydrogenation at the final stage of its wet chemical etching during the preliminary cleaning is proposed as a possible way of efficient reduction of the Si wafer pre-growth annealing temperature.

  19. GaAs:Mn nanowires grown by molecular beam epitaxy of (Ga,Mn)as at MnAs segregation conditions.

    Science.gov (United States)

    Sadowski, Janusz; Dłuzewski, Piotr; Kret, Sławomir; Janik, Elzbieta; Lusakowska, Elzbieta; Kanski, Janusz; Presz, Adam; Terki, Ferial; Charar, Salam; Tang, Dong

    2007-09-01

    GaAs:Mn nanowires were obtained on GaAs(001) and GaAs(111)B substrates by molecular beam epitaxial growth of (Ga,Mn)As at conditions leading to MnAs phase separation. Their density is proportional to the density of catalyzing MnAs nanoislands, which can be controlled by the Mn flux and/or the substrate temperature. After deposition corresponding to a 200 nm thick (Ga,Mn)As layer the nanowires are around 700 nm long. Their shapes are tapered, with typical diameters around 30 nm at the base and 7 nm at the tip. The wires grow along the 111 direction, i.e., along the surface normal on GaAs(111)B and inclined on GaAs(001). In the latter case they tend to form branches. Being rooted in the ferromagnetic semiconductor (Ga,Mn)As, the nanowires combine one-dimensional properties with the magnetic properties of (Ga,Mn)As and provide natural, self-assembled structures for nanospintronics.

  20. Self-catalyzed ternary core-shell GaAsP nanowire arrays grown on patterned Si substrates by molecular beam epitaxy.

    Science.gov (United States)

    Zhang, Yunyan; Wu, Jiang; Aagesen, Martin; Holm, Jeppe; Hatch, Sabina; Tang, Mingchu; Huo, Suguo; Liu, Huiyun

    2014-08-13

    The growth of self-catalyzed ternary core-shell GaAsP nanowire (NW) arrays on SiO2 patterned Si(111) substrates has been demonstrated by using solid-source molecular beam epitaxy. A high-temperature deoxidization step up to ∼ 900 °C prior to NW growth was used to remove the native oxide and/or SiO2 residue from the patterned holes. To initiate the growth of GaAsP NW arrays, the Ga predeposition used for assisting the formation of Ga droplets in the patterned holes, was shown to be another essential step. The effects of the patterned-hole size on the NW morphology were also studied and explained using a simple growth model. A lattice-matched radial GaAsP core-shell NW structure has subsequently been developed with room-temperature photoluminescence emission around 740 nm. These results open up new perspectives for integrating position-controlled III-V NW photonic and electronic structures on a Si platform.

  1. Ge quantum dot arrays grown by ultrahigh vacuum molecular-beam epitaxy on the Si(001) surface: nucleation, morphology, and CMOS compatibility.

    Science.gov (United States)

    Yuryev, Vladimir A; Arapkina, Larisa V

    2011-09-05

    Issues of morphology, nucleation, and growth of Ge cluster arrays deposited by ultrahigh vacuum molecular beam epitaxy on the Si(001) surface are considered. Difference in nucleation of quantum dots during Ge deposition at low (≲600°C) and high (≳600°C) temperatures is studied by high resolution scanning tunneling microscopy. The atomic models of growth of both species of Ge huts--pyramids and wedges-- are proposed. The growth cycle of Ge QD arrays at low temperatures is explored. A problem of lowering of the array formation temperature is discussed with the focus on CMOS compatibility of the entire process; a special attention is paid upon approaches to reduction of treatment temperature during the Si(001) surface pre-growth cleaning, which is at once a key and the highest-temperature phase of the Ge/Si(001) quantum dot dense array formation process. The temperature of the Si clean surface preparation, the final high-temperature step of which is, as a rule, carried out directly in the MBE chamber just before the structure deposition, determines the compatibility of formation process of Ge-QD-array based devices with the CMOS manufacturing cycle. Silicon surface hydrogenation at the final stage of its wet chemical etching during the preliminary cleaning is proposed as a possible way of efficient reduction of the Si wafer pre-growth annealing temperature.

  2. Effects of AlN buffer layers on the structural and the optical properties of GaN epilayers grown on Al{sub 2}O{sub 3} substrates by using plasma-assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Jeon, Heechang; Lee, Seungjoo; Kumar, Sunil; Kang, Taewon [Dongguk University, Seoul (Korea, Republic of); Lee, Namhyun; Kim, Taewhan [Hanyang University, Seoul (Korea, Republic of)

    2014-04-15

    GaN epilayers on AlN buffer layers with various thicknesses were grown on sapphire substrates by using plasma-assisted molecular-beam epitaxy. The GaN epilayer with an AlN buffer layer was much smaller than the GaN epilayer without an AlN buffer layer. The crystal quality of the GaN active layer was improved by utilizing an AlN layer, which acted as a nucleation layer. The reduced defect density promoted GaN coalition. The double-crystal rocking curves and the photoluminescence spectra showed that the GaN epilayer grown on a 4-nm AlN buffer layer had the best quality among the several kinds of samples. The photoluminescence intensity of the GaN epilayer which is related to the density of the crystal defects was lower when an AlN buffer layer was used the thin AlN nucleation layer protected against stain propagation. These results indicate that GaN epilayers grown on AIN buffer layers hold promise for applications in short-wavelength optoelectronic devices.

  3. Effect of oxygen-to-metal flux ratio on incorporation of metal species into quaternary BeMgZnO grown by plasma-assisted molecular beam epitaxy

    Science.gov (United States)

    Toporkov, M.; Ullah, M. B.; Demchenko, D. O.; Avrutin, V.; Morkoç, H.; Özgür, Ü.

    2017-06-01

    Owing to its large bandgap covering the UV region of the optical spectrum, the quaternary BeMgZnO is of interest, particularly the collective effect Be and Mg fluxes on the solid composition. Incorporation of Be, Mg, and Zn in the wurtzite BeMgZnO quaternary alloy was found to depend strongly on the reactive-oxygen to metal flux ratio during growth by plasma-assisted molecular beam epitaxy under metal-rich conditions. For a given set of metal fluxes, reducing the VI/II (oxygen to metal flux) ratio from 1.0 to 0.6 increased the bandgap from 4.0 eV to 4.5 eV and decreased the c lattice parameter from 5.08 Å to 5.02 Å. The corresponding change in composition from Be0.07Mg0.21Zn0.72O to Be0.10Mg0.34Zn0.56O was consistent with a systematic reduction in the Zn incorporation coefficient from 0.23 to 0.12, while those of Be and Mg remained at ∼1. This behavior was explained by the substantially lower formation enthalpies of wurtzite BeO and MgO, -5.98 eV and -5.64 eV, respectively, compared to that of ZnO, -3.26 eV, determined using first principles calculations, as well as the high equilibrium vapor pressure of Zn, which results in re-evaporation of excessive Zn from the growing surface, details of which are the topic of this manuscript.

  4. The temperature dependent variation of bulk and surface composition of In(x)Ga(1-x)As on GaAs grown by chemical beam epitaxy studied by RHEED, X-ray diffraction and XPS

    Science.gov (United States)

    Hansen, H. S.; Bensaoula, A.; Tougaard, S.; Zborowski, J.; Ignatiev, A.

    1992-01-01

    The paper investigates the bulk as well as near-surface composition of In(x)Ga(1-x)As epilayers on GaAs grown by chemical beam epitaxy (CBE) as a function of triethylindium flow rate and substrate temperature by reflection high energy electron diffraction (RHEED), X-ray diffraction, and XPS. To clarify whether the bulk stoichiometry of CBE-grown ternaries can be extracted from the growth rate change as determined by the change in the period of RHEED oscillations from binary to ternary compound growth, a systematic study of growth rate change as a function of ternary bulk composition determined by X-ray diffraction was performed at various temperatures. It is shown that for low growth temperatures there is a linear relationship between the two methods of determination, whereas no correlation is found for higher growth temperatures, in contrast to the MBE case where the two methods of determination yield identical results. In the near surface region the epilayer composition is determined in situ by XPS.

  5. Modelling, Design, Growth and Characterization of Strain Balanced Quantum Cascade Lasers (3-11mum), grown by Gas Source Molecular Beam Epitaxy

    Science.gov (United States)

    Bandyopadhyay, Neelanjan

    Quantum Cascade Laser (QCL) is a compact room temperature (RT) source of mid-infrared radiation, which can be used for spectroscopic detection of trace amount of chemicals. The mid-infrared spectral range between (3-11 microm), has a dense array of absorption lines of numerous molecules, due to the presence of fundamental vibrational modes. The goal of this thesis can be subdivided into two parts. Firstly, short wavelength QCLs, emitting below 4microm, perform poorly at RT, due to inter-valley Gamma --- L carrier scattering, carrier escape to the continuum, heat removal from the core region at high power density corresponding to short wavelength operation, and large interface scattering due to highly strained materials. Secondly, it is desirable to have a single QCL based source emitting between 6-10microm, which be used to detect multiple molecules having their peak absorptions far apart, inside this spectral range. However, gain bandwidth of a single core QCL is relatively small, so laser emission cannot be tuned over a wide spectral range. This thesis describes the working principle of a QCL based on superlattice transport, rate equations, scattering mechanism, and waveguide design. The choice of the material system for this work and the fundamentals of band structure engineering has been derived. Gas source molecular beam epitaxy - growth optimization and characterization is one of the most important features of this work, especially for short wavelength QCLs, and has been explained in depth. Different strategies for design of active region design of short wavelength QCL and heterogeneous broadband QCL has been explored. The major milestones, of this research was the world's first watt level continuous wave (CW), RT demonstration at 3.76 microm, which was followed by another milestone of the first CW, RT demonstration at 3.39microm and 3.55microm, and finally the elusive result of QCL emitting at CW, RT at a wavelength as short as lambda ~3microm, a record. In

  6. Deposition of hetero-epitaxial In{sub 2}O{sub 3} thin films by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Taga, N.; Maekawa, M. [Asahi Glass Co., Ltd., Yokohama (Japan). Research Center; Shigesato, Y.; Yasui, I. [Univ. of Tokyo (Japan). Inst. of Industrial Science; Haynes, T.E. [Oak Ridge National Lab., TN (United States). Solid State Div.

    1996-05-01

    Highly oriented thin film In{sub 2}O{sub 3} was heteroepitaxially grown on optically polished (100) plane of single crystalline yttria stabilized zirconia (YSZ) substrate using Molecular Beam Epitaxy (MBE). Full-width at half-maximum (FWHM) of X-ray rocking-curve showed 0.08{degree} for In{sub 2}O{sub 3} 200 nm thick layers indicating that excellent uniformity orientation compared with the heteroepitaxially-grown In{sub 2}O{sub 3} epitaxially deposited by the conventional methods such as electron-beam (e-beam) evaporation or sputtering method. The minimum yield ({chi}{sub min}) of the MBE grown in In{sub 2}O{sub 3} film of Rutherford Backscattering Spectrometry (RBS) was also extremely small value 3.1%, implying the very high crystallinity.

  7. Kinetics of self-induced nucleation and optical properties of GaN nanowires grown by plasma-assisted molecular beam epitaxy on amorphous Al{sub x}O{sub y}

    Energy Technology Data Exchange (ETDEWEB)

    Sobanska, M., E-mail: sobanska@ifpan.edu.pl; Zytkiewicz, Z. R.; Klosek, K.; Tchutchulashvili, G. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Korona, K. P. [Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw (Poland)

    2015-11-14

    Nucleation kinetics of GaN nanowires (NWs) by molecular beam epitaxy on amorphous Al{sub x}O{sub y} buffers deposited at low temperature by atomic layer deposition is analyzed. We found that the growth processes on a-Al{sub x}O{sub y} are very similar to those observed on standard Si(111) substrates, although the presence of the buffer significantly enhances nucleation rate of GaN NWs, which we attribute to a microstructure of the buffer. The nucleation rate was studied vs. the growth temperature in the range of 720–790 °C, which allowed determination of nucleation energy of the NWs on a-Al{sub x}O{sub y} equal to 6 eV. This value is smaller than 10.2 eV we found under the same conditions on nitridized Si(111) substrates. Optical properties of GaN NWs on a-Al{sub x}O{sub y} are analyzed as a function of the growth temperature and compared with those on Si(111) substrates. A significant increase of photoluminescence intensity and much longer PL decay times, close to those on silicon substrates, are found for NWs grown at the highest temperature proving their high quality. The samples grown at high temperature have very narrow PL lines. This allowed observation that positions of donor-bound exciton PL line in the NWs grown on a-Al{sub x}O{sub y} are regularly lower than in samples grown directly on silicon suggesting that oxygen, instead of silicon, is the dominant donor. Moreover, PL spectra suggest that total concentration of donors in GaN NWs grown on a-Al{sub x}O{sub y} is lower than in those grown under similar conditions on bare Si. This shows that the a-Al{sub x}O{sub y} buffer efficiently acts as a barrier preventing uptake of silicon from the substrate to GaN.

  8. Transmission electron microscopy study of vertical quantum dots molecules grown by droplet epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez-Maldonado, D., E-mail: david.hernandez@uca.es [Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Cadiz (Spain); Herrera, M.; Sales, D.L. [Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Cadiz (Spain); Alonso-Gonzalez, P.; Gonzalez, Y.; Gonzalez, L. [Instituto de Microelectronica de Madrid (CNM-CSIC), Isaac Newton 8 (PTM), 28760 Tres Cantos, Madrid (Spain); Pizarro, J.; Galindo, P.L. [Departamento de Lenguajes y Sistemas Informaticos, CASEM, Universidad de Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Cadiz (Spain); Molina, S.I. [Departamento de Ciencia de los Materiales e I.M. y Q.I., Facultad de Ciencias, Universidad de Cadiz, Campus Rio San Pedro, s/n, 11510 Puerto Real, Cadiz (Spain)

    2010-07-01

    The compositional distribution of InAs quantum dots grown by molecular beam epitaxy on GaAs capped InAs quantum dots has been studied in this work. Upper quantum dots are nucleated preferentially on top of the quantum dots underneath, which have been nucleated by droplet epitaxy. The growth process of these nanostructures, which are usually called as quantum dots molecules, has been explained. In order to understand this growth process, the analysis of the strain has been carried out from a 3D model of the nanostructure built from transmission electron microscopy images sensitive to the composition.

  9. Observation of the Intrinsic Bandgap Behavior in As-Grown Epitaxial Twisted Graphene (Postprint)

    Science.gov (United States)

    2015-01-06

    technology . Here, we present evidence that direct growth by carbon source molecular beam epitaxy (CMBE) with C60 molecular on pre grown template graphene...sp3 C C bonding carbon . Discussion The sp3 C C interlayer bonding has been experimentally observed in graphite and carbon nanotubes modified by... carbon nanotube fibers. ACS Nano 5, 1921 1927 (2011). 19. Hass, J. et al. Structural properties of the multilayer graphene/4H-SiC ð0001Þ system as

  10. Enhancement of Two-Dimensional Electron-Gas Properties by Zn Polar ZnMgO/MgO/ZnO Structure Grown by Radical-Source Laser Molecular Beam Epitaxy

    Directory of Open Access Journals (Sweden)

    Li Meng

    2015-01-01

    Full Text Available A Zn polar ZnMgO/MgO/ZnO structure with low Mg composition Zn1-xMgxO layer (x = 0.05 grown on a-plane (11–20 sapphire by radical-source laser molecular beam epitaxy was reported. The insertion of a thin (1 nm MgO layer between ZnMgO and ZnO layers in the ZnMgO/ZnO 2DEG structures results in an increase of 2DEG sheet density and affects electron mobility slightly. The carrier concentration reached a value as high as 1.1 × 1013 cm−2, which was confirmed by C-V measurements. A high Hall mobility of 3090 cm2/Vs at 10 K and 332 cm2/Vs at RT was observed from Zn0.95Mg0.05O/MgO/ZnO heterostructure. The choice of the thickness of MgO was discussed. The dependence of carrier sheet density of 2DEG on ZnMgO layer thickness was calculated in theory and the theoretical prediction and experimental results agreed well.

  11. Structure and magnetism in strained Ge{sub 1-x-y}Sn{sub x}Mn{sub y} films grown on Ge(001) by low temperature molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Prestat, E. [INAC, SP2M, CEA and Universite Joseph Fourier, 17 rue des Martyrs, 38054 Grenoble (France); Karlsruher Institut fuer Technologie (KIT), Laboratorium fuer Elektronenmikroskopie, D-76128 Karlsruhe (Germany); Barski, A.; Bellet-Amalric, E.; Morel, R.; Tainoff, D.; Jain, A.; Porret, C.; Bayle-Guillemaud, P.; Jamet, M. [INAC, SP2M, CEA and Universite Joseph Fourier, 17 rue des Martyrs, 38054 Grenoble (France); Jacquot, J.-F. [INAC, SCIB, CEA and Universite Joseph Fourier, 17 rue des Martyrs, 38054 Grenoble (France)

    2013-07-01

    In this letter, we study the structural and magnetic properties of Ge{sub 1-x-y}Sn{sub x}Mn{sub y} films grown on Ge(001) by low temperature molecular beam epitaxy using X-ray diffraction, high resolution transmission electron microscopy, and superconducting quantum interference device. Like in Mn doped Ge films, Mn atoms diffuse during the growth and aggregate into vertically aligned Mn-rich nanocolumns of a few nanometers in diameter. Transmission electron microscopy observations in plane view clearly indicate that the Sn incorporation is not uniform with concentration in Mn rich vertical nanocolumns lower than the detection limit of electron energy loss spectroscopy. The matrix exhibits a GeSn solid solution while there is a Sn-rich GeSn shell around GeMn nanocolumns. The magnetization in Ge{sub 1-x-y}Sn{sub x}Mn{sub y} layers is higher than in Ge{sub 1-x}Mn{sub x} films. This magnetic moment enhancement in Ge{sub 1-x-y}Sn{sub x}Mn{sub y} is probably related to the modification of the electronic structure of Mn atoms in the nanocolumns by the Sn-rich shell, which is formed around the nanocolumns.

  12. Effect of Ⅲ/Ⅴ Ratio of HT-AlN Buffer Layer on Polarity Selection and Electrical Quality of GaN Films Grown by Radio Frequency Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    ZHONG Fei; CHEN Jia-Rong; WANG Yu-Qi; QIU Kai; LI Xin-Hua; YIN Zhi-Jun; XIE Xin-Jian; WANG Yang; JI Chang-Jian; CAO Xian-Cun; HAN Qi-Feng

    2007-01-01

    @@ We investigate the effect of Al/N ratio of the high temperature (HT) AlN buffer layer on polarity selection and electrical quality of GaN films grown by radio frequency molecular beam epitaxy. The results show that low Al/N ratio results in N-polarity GaN films and intermediate Al/N ratio leads to mixed-polarity GaN films with poor electrical quality. GaN films tend to grow with Ga polarity on Al-rich AlN buffer layers. GaN films with different polarities are confirmed by in-situ reflection high-energy electron diffraction during the growth process.Wet chemical etching, together with atomic force microscopy, also proves the polarity assignments. The optimum value for room-temperature Hall mobility of the Ga-polarity GaN film is 703cm2/V.s, which is superior to the N-polarity and mixed-polarity GaN films.

  13. Depletion-mode In 0.2Ga 0.8As/GaAs MOSFET with molecular beam epitaxy grown Al 2O 3/Ga 2O 3(Gd 2O 3) as gate dielectrics

    Science.gov (United States)

    Lin, C. A.; Lin, T. D.; Chiang, T. H.; Chiu, H. C.; Chang, P.; Hong, M.; Kwo, J.

    2009-03-01

    Depletion-mode In 0.2Ga 0.8As/GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated with molecular beam epitaxy (MBE) grown Al 2O 3/Ga 2O 3(Gd 2O 3) as the gate dielectric in two comparable processes. In the "metal-gate-last" process, a 12 μm gate-length depletion-mode n-channel InGaAs/GaAs MOSFET with a Ga 2O 3(Gd 2O 3) gate oxide 6 nm thick shows an accumulated drain current density of 135 mA/mm at Vg=2 V. In the other process of "metal-gate-first" process, the device with same gate dielectric, channel, and gate length exhibits a larger drain current density of 175 mA/mm at the same gate bias. In addition, there is a broader transfer characteristics and higher extrinsic peak transconductance of 48 mS/mm in the metal-gate-first process. MOS capacitors from both processes have exhibited excellent capacitance-voltage ( C- V) characteristics with minor dispersion, negligible hysteresis, and κ values of 13.7-13.9 in Ga 2O 3(Gd 2O 3).

  14. Electron molecular beam epitaxy: Layer-by-layer growth of complex oxides via pulsed electron-beam deposition

    Energy Technology Data Exchange (ETDEWEB)

    Comes, Ryan; Liu Hongxue; Lu Jiwei [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Gu, Man [Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States); Khokhlov, Mikhail; Wolf, Stuart A. [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Guilford College, Greensboro, North Carolina 27410 (United States)

    2013-01-14

    Complex oxide epitaxial film growth is a rich and exciting field, owing to the wide variety of physical properties present in oxides. These properties include ferroelectricity, ferromagnetism, spin-polarization, and a variety of other correlated phenomena. Traditionally, high quality epitaxial oxide films have been grown via oxide molecular beam epitaxy or pulsed laser deposition. Here, we present the growth of high quality epitaxial films using an alternative approach, the pulsed electron-beam deposition technique. We demonstrate all three epitaxial growth modes in different oxide systems: Frank-van der Merwe (layer-by-layer); Stranski-Krastanov (layer-then-island); and Volmer-Weber (island). Analysis of film quality and morphology is presented and techniques to optimize the morphology of films are discussed.

  15. Electron molecular beam epitaxy: Layer-by-layer growth of complex oxides via pulsed electron-beam deposition

    Science.gov (United States)

    Comes, Ryan; Gu, Man; Khokhlov, Mikhail; Liu, Hongxue; Lu, Jiwei; Wolf, Stuart A.

    2013-01-01

    Complex oxide epitaxial film growth is a rich and exciting field, owing to the wide variety of physical properties present in oxides. These properties include ferroelectricity, ferromagnetism, spin-polarization, and a variety of other correlated phenomena. Traditionally, high quality epitaxial oxide films have been grown via oxide molecular beam epitaxy or pulsed laser deposition. Here, we present the growth of high quality epitaxial films using an alternative approach, the pulsed electron-beam deposition technique. We demonstrate all three epitaxial growth modes in different oxide systems: Frank-van der Merwe (layer-by-layer); Stranski-Krastanov (layer-then-island); and Volmer-Weber (island). Analysis of film quality and morphology is presented and techniques to optimize the morphology of films are discussed.

  16. Epitaxy of an Al-Droplet-Free AlN Layer with Step-Flow Features by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    PAN Jian-Hai; WANG Xin-Qiang; CHEN Guang; LIU Shi-Tao; FENG Li; XU Fu-Jun; TANG Ning; SHEN Bo

    2011-01-01

    We investigate epitaxy of A1N layers on sapphire substrates by molecular beam epitaxy. It is found that an atomically Bat surface can be obtained under Al-rich conditions at growth temperature of 780°C. However, the growth window to obtain an Al-droplet-free surface is too narrow to be well-controlled. However, the growth window can be greatly broadened by increasing the growth temperature up to 950 "C, where an Al-droplet-free surface with a step-How feature is obtained due to the enhanced re-evaporization rate and migration ability of Al adatoms. The samples grown at the higher temperature also show a higher crystalline quality than those grown at lower temperatures.%@@ We investigate epitaxy of AlN layers on sapphire substrates by molecular beam epitaxy.It is found that an atomically fiat surface can be obtained under Al-rich conditions at growth temperature of 780℃.However, the growth window to obtain an Al-droplet-free surface is too narrow to be well-controlled.However, the growth window can be greatly broadened by increasing the growth temperature up to 950℃, where an Al-droplet-free surface with a step-flow feature is obtained due to the enhanced re-evaporization rate and migration ability of Al adatoms.The samples grown at the higher temperature also show a higher crystalline quality than those grown at lower temperatures.

  17. Selective area growth of heterostructure bipolar transistors by metalorganic molecular beam epitaxy

    Science.gov (United States)

    Hamm, R. A.; Feygenson, A.; Ritter, D.; Wang, Y. L.; Temkin, H.; Yadvish, R. D.; Panish, M. B.

    1992-08-01

    Heterostructure bipolar transistors (HBT) have been grown by selective area epitaxy (SAE) using metalorganic molecular beam epitaxy (MOMBE). dc characteristics, comparable to those for devices grown on unprocessed substrates, were obtained after removal of the edge growth. Data is also presented for devices in which the emitter mesas were regrown by SAE into openings which had been previously defined by photolithography on a structure containing only the collector and base layers. In both cases we use an in situ cleaning process consisting of an Ar ion beam sputtering and Cl2 etching. This step results in significantly improved junction quality.

  18. Oxygen incorporation in homoepitaxial N-polar GaN grown by radio frequency-plasma assisted molecular beam epitaxy: Mitigation and modeling

    Energy Technology Data Exchange (ETDEWEB)

    Storm, D. F.; Katzer, D. S.; Meyer, D. J.; Binari, S. C. [Electronics Science and Technology Division, Naval Research Laboratory, Code 6852, 4555 Overlook Avenue SW, Washington DC 20375 (United States)

    2012-07-01

    We have investigated the effect of gallium deposition and desorption cycles and ultrathin (15 A) AlN layers on the oxygen impurity concentrations in homoepitaxial N-polar GaN layers. Secondary ion mass spectroscopy (SIMS) indicates that three Ga deposition and desorption cycles reduce the total oxygen by 70%-80%, while ten cycles reduces the total oxygen by more than 90%. We present a model of surface segregation and incorporation which accurately captures the distribution of oxygen in these layers. By fitting the model to the SIMS data, we are able to determine the fraction of an oxygen layer adsorbed on a GaN surface which segregates upon initiation of epitaxial GaN growth. Under the conditions investigated, we find this fraction to be 80%.

  19. Micro-Photoluminescence (micro-PL) Study of Core Shell GaAs/GaAsSb Nanowires Grown by Self-Assisted Molecular Beam Epitaxy

    Science.gov (United States)

    2015-06-18

    transistor (FET) and light emitting diode (LED) applications. In this thesis, room temperature and low temperature (4K) micro- photoluminescence (micro...public release; distribution is unlimited. Micro- Photoluminescence (micro-PL) Study of Core-Shell GaAs/GaAsSb Nanowires grown by Self-Assisted Molecular...U.S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 GaAsSb, Core Shell Nanowires, Micro Photoluminescence

  20. Large-area, laterally-grown epitaxial semiconductor layers

    Energy Technology Data Exchange (ETDEWEB)

    Han, Jung; Song, Jie; Chen, Danti

    2017-07-18

    Structures and methods for confined lateral-guided growth of a large-area semiconductor layer on an insulating layer are described. The semiconductor layer may be formed by heteroepitaxial growth from a selective growth area in a vertically-confined, lateral-growth guiding structure. Lateral-growth guiding structures may be formed in arrays over a region of a substrate, so as to cover a majority of the substrate region with laterally-grown epitaxial semiconductor tiles. Quality regions of low-defect, stress-free GaN may be grown on silicon.

  1. Fabrication of as-grown MgB{sub 2} films on ZnO (0 0 0 1) substrates by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Y. [Iwate Industry Promotion Center, 3-35-2 Iiokashinden, Morioka, Iwate 020-0852 (Japan)]. E-mail: yharada@luck.ocn.ne.jp; Takahashi, T. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Kuroha, M. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Iriuda, H. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Nakanishi, Y. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Izumida, F. [Iwate Industrial Research Institute, 3-35-2 Iiokashinden, Morioka, Iwate 020-0852 (Japan); Endo, H. [Iwate Industrial Research Institute, 3-35-2 Iiokashinden, Morioka, Iwate 020-0852 (Japan); Yoshizawa, M. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan)

    2006-10-01

    The intermetallic superconductor magnesium diboride (MgB{sub 2}) is a promising candidate for use in superconducting electronic devices because its high transition temperature (T{sub c}). These applications require the development of a high-quality film fabrication process. We report the first ever attempt to use ZnO (0 0 0 1) substrate to fabricate as-grown MgB{sub 2} films. The lattice mismatch between ZnO and MgB{sub 2} is smaller than for previous reported substrates. The structural and physical properties of the films were investigated by RHEED, XRD, XPS, and resistivity measurements. The resistivity measurements suggest the maximum transition temperature of these films to be 35 K; their resistivity at 300 K is 8.9 {mu}{omega} cm. Our results indicate that these films, when deposited on ZnO substrates, have potential for the fabrication of higher quality MgB{sub 2} films. We also investigate the growth temperature dependence and substrate dependence for superconductivity of MgB{sub 2} films. We discuss the most important conditions and the effectiveness of ZnO substrate for fabricating as-grown MgB{sub 2} films.

  2. Perspective: Oxide molecular-beam epitaxy rocks!

    Energy Technology Data Exchange (ETDEWEB)

    Schlom, Darrell G., E-mail: schlom@cornell.edu [Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA and Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853 (United States)

    2015-06-01

    Molecular-beam epitaxy (MBE) is the “gold standard” synthesis technique for preparing semiconductor heterostructures with high purity, high mobility, and exquisite control of layer thickness at the atomic-layer level. Its use for the growth of multicomponent oxides got off to a rocky start 30 yr ago, but in the ensuing decades, it has become the definitive method for the preparation of oxide heterostructures too, particularly when it is desired to explore their intrinsic properties. Examples illustrating the unparalleled achievements of oxide MBE are given; these motivate its expanding use for exploring the potentially revolutionary states of matter possessed by oxide systems.

  3. Silicon/Germanium Molecular Beam Epitaxy

    OpenAIRE

    2006-01-01

    Molecular Beam Epitaxy (MBE) is a well-established method to grow low-dimensional structures for research applications. MBE has given many contributions to the rapid expanding research-area of nano-technology and will probably continuing doing so. The MBE equipment, dedicated for Silicon/Germanium (Si/Ge) systems, at Karlstads University (Kau) has been studied and started for the first time. In the work of starting the system, all the built in interlocks has been surveyed and connected, and t...

  4. Perspective: Oxide molecular-beam epitaxy rocks!

    Directory of Open Access Journals (Sweden)

    Darrell G. Schlom

    2015-06-01

    Full Text Available Molecular-beam epitaxy (MBE is the “gold standard” synthesis technique for preparing semiconductor heterostructures with high purity, high mobility, and exquisite control of layer thickness at the atomic-layer level. Its use for the growth of multicomponent oxides got off to a rocky start 30 yr ago, but in the ensuing decades, it has become the definitive method for the preparation of oxide heterostructures too, particularly when it is desired to explore their intrinsic properties. Examples illustrating the unparalleled achievements of oxide MBE are given; these motivate its expanding use for exploring the potentially revolutionary states of matter possessed by oxide systems.

  5. Barrier height enhancement of InP-based n-Ga(0.47)In(0.53)As Schottky-barrier diodes grown by molecular beam epitaxy

    Science.gov (United States)

    Kim, J. H.; Li, S. S.; Figueroa, L.

    1988-01-01

    Barrier height enhancement of an InP-based p(+)n-Ga(0.47)In(0.53)As Schottky diode grown by MBE has been demonstrated for infra-red photodetector applications. A barrier height of 0.35 eV for n-Ga(0.47)In(0.53)As Schottky barrier diodes, was increased to the effective barrier height of 0.55 eV, with a p(+)-Ga(0.47)In(0.53)As surface layer of 30 nm thick. The results show a reverse leakage current density of 0.0015 A/sq cm and a junction capacitance of 0.3 pF, which are comparable to those of p-Ga(0.47)In(0.53)As Schottky-barrier diodes at a reverse bias voltage of 5 V.

  6. Growth, Antimony Incorporation Behaviour and Beryllium Doping of GaAs1-ySby Grown on GaAs by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    GAO Han-Chao; WANG Wen-Xin; JIANG Zhong-Wei; LIU Jian; YANG Cheng-Liang; WU Dian-Zhong; ZHOU Jun-Ming; CHEN Hong

    2008-01-01

    @@ A series of GaAs1-ySby epilayers are grown on GaAs substrates under different growth conditions, Different antimony compositions of samples with beryllium doping are obtained.A non-equilibrium thermodynamics model is used to calibrate and fit the Sb composition.Activation energy of 0.37eV for the dissociation process of Sb4 molecules is obtained.Carrier mobility and concentration of samples are influenced by the Sb composition.Quasi-qualitative analysis of mobility is used to explain the relations among Sb composition, carrier mobility and concentration.High resolution x-ray diffraction (HRXRD) rocking curves and Hall effects measurements are used to determine the crystal quality, carrier mobility and concentration.

  7. In-situ NC-AFM measurements of high quality AlN(0001 layers grown at low growth rate on 4H-SiC(0001 and Si(111 substrates using ammonia molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Florian Chaumeton

    2015-06-01

    Full Text Available Nitride wide-band-gap semiconductors are used to make high power electronic devices or efficient light sources. The performance of GaN-based devices is directly linked to the initial AlN buffer layer. During the last twenty years of research on nitride growth, only few information on the AlN surface quality have been obtained, mainly by ex-situ characterization techniques. Thanks to a Non Contact Atomic Force Microscope (NC-AFM connected under ultra high vacuum (UHV to a dedicated molecular beam epitaxy (MBE chamber, the surface of AlN(0001 thin films grown on Si(111 and 4H-SiC(0001 substrates has been characterized. These experiments give access to a quantitative determination of the density of screw and edge dislocations at the surface. The layers were also characterized by ex-situ SEM to observe the largest defects such as relaxation dislocations and hillocks. The influence of the growth parameters (substrate temperature, growth speed, III/V ratio and of the initial substrate preparation on the dislocation density was also investigated. On Si(111, the large in-plane lattice mismatch with AlN(0001 (19% induces a high dislocation density ranging from 6 to 12×1010/cm2 depending on the growth conditions. On 4H-SiC(0001 (1% mismatch with AlN(0001, the dislocation density decreases to less than 1010/cm2, but hillocks appear, depending on the initial SiC(0001 reconstruction. The use of a very low growth rate of 10 nm/h at the beginning of the growth process allows to decrease the dislocation density below 2 × 109/cm2.

  8. High critical current density under magnetic fields in as-grown MgB{sub 2} thin films deposited by molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Haruta, M [Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Fujiyoshi, T [Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Kihara, S [Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Sueyoshi, T [Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Miyahara, K [Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Harada, Y [Iwate Industry Promotion Centre, Iioka-shinden 3-35-2, Morioka, Iwate 020-0852 (Japan); Yoshizawa, M [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551 (Japan); Takahashi, T [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551 (Japan); Iriuda, H [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551 (Japan); Oba, T [Graduate School of Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551 (Japan); Awaji, S [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Watanabe, K [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Miyagawa, R [Kumamoto Industrial Research Institute, 3-11-38 Higashi-machi, Kumamoto 862-0901 (Japan)

    2007-01-15

    As-grown MgB{sub 2} thin films were prepared by a MBE method under the conditions of low temperature, low deposition rate and high vacuum for applications in electric devices. The MgB{sub 2} thin films deposited on MgO and Ti buffered ZnO substrates have considerably higher J{sub c} under magnetic fields among MgB{sub 2} thin films reported before. The value of J{sub c} for the MgB{sub 2} thin film deposited on Ti buffered ZnO has been 5.8 x 10{sup 5} A cm{sup -2} at 10 K, 5 T in the magnetic field applied parallel to the c axis. In the angular dependence of J{sub c}, the peak of J{sub c} attributable to c-axis-correlated pinning centres has been observed when the magnetic field was applied parallel to the c axis. (rapid communication)

  9. Polarization-resolved electroluminescence study of InGaN/GaN dot-in-a-wire light-emitting diodes grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Li, K.H.; Wang, Q.; Nguyen, H.P.T.; Zhao, S.; Mi, Z. [Department of Electrical and Computer Engineering, McGill University, Montreal, Quebec (Canada)

    2015-05-15

    The polarization properties of light emission from InGaN nanowire (NW) light-emitting diodes (LEDs) have been studied with the use of goniometric setup. A maximum polarization ratio of ∝0.7 has been obtained from the edge emission of NW array-based LEDs and the light is mainly polarized parallel to the c-axis of NWs. The nearly isotropic polarization response from a core-shell NW LED structure is also observed, and it is found that the degree of polarization is strongly depended on the NW diameter. With the growth of the AlGaN shell, the resulting diameter of core-shell NWs becomes larger and is comparable to the emission wavelength, thus weakening the optical confinement effect and the polarization behavior. The size-dependent polarization properties of NW structures are further verified by the finite-difference time-domain simulation. NWs with diameters much less than the emission wavelength render a strong contrast between the p- and s-polarized light emissions. (Left) FE-SEM image of MBE-grown NWs covered with polyimide. (Right) Plot of integrated electroluminescence intensity as a function of polarizer angle for a NW LED. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  10. Ferromagnetism at room temperature of c- and m-plane GaN : Gd films grown on different substrates by reactive molecular beam epitaxy

    Science.gov (United States)

    Ranchal, R.; Yadav, B. S.; Trampert, A.

    2013-02-01

    We report the magnetic properties of c- and m-plane GaN : Gd films grown on different substrate materials. Additionally, we have investigated the magnetic behaviour of the bare substrates in order to analyse their possible contribution on the properties of this material system. For the growth of c-phase GaN : Gd we have used 6H-SiC(0 0 0 1) and GaN/Al2O3 templates. Whereas templates only exhibit a diamagnetic behaviour, the SiC substrates show clear signatures of ferromagnetism at room temperature. Rutherford backscattering spectroscopy and secondary ions mass spectrometry have revealed traces of Fe in the SiC substrates. This Fe contamination seems to be related to the ferromagnetic ordering observed in these substrates. LiAlO2(0 0 1) is a good choice for growth of m-plane diluted nitrides due to its diamagnetic behaviour. The hysteresis loops of c- and m-phase GaN : Gd deposited on template and LiAlO2, respectively, show coercivity and magnetic saturation. These characteristics together with the magnetization curves are indications of an intrinsic ferromagnetic behaviour in the GaN : Gd.

  11. Photocurrent and Photoluminescence Investigations of GaInNAs and GaInNAs(Sb Quantum Wells Grown by Molecular Beam Epitaxy

    Directory of Open Access Journals (Sweden)

    S. B. Bouzid

    2005-01-01

    Full Text Available We have investigated photocurrent (PC and photoluminescence (PL in sequentially grown GaInNAs/GaAs and GaInNAs(Sb/GaAsSbN quantum wells. Photocurrent transitions are analyzed by theoretical calculations using envelope function formalism taking into account the strain effect and the strong coupling between nitrogen localized state and the GaInAs band gap. The results are consistent with a type I band alignment and a conduction band offset ratio of about 80 %. Additionally, our results suggest an increase of the electron effective mass by as much as 0.035 m0 resulting from the flattening of the conduction band under nitrogen effect. The temperature evolution of the PL peak energy and the integrated PL intensity of GaInNAsSb QW show evidence of strong localization of carriers. Both, the high delocalization temperature, in the 230 K range and the strong shift between the PC and PL spectra of GaInNAsSb QW, indicate the presence of deeper localized states as compared to that in the GaInNAs QW.

  12. Epitaxial Cu(001) films grown on a Cr/Ag/Fe/GaAs(001) buffer system

    Energy Technology Data Exchange (ETDEWEB)

    Gottlob, Daniel M., E-mail: d.gottlob@fz-juelich.de [Peter Grünberg Institut, Electronic Properties (PGI-6), Forschungszentrum Jülich, 52425 Jülich (Germany); Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universität Duisburg-Essen, 47048 Duisburg (Germany); Jansen, Thomas [Peter Grünberg Institut, Electronic Properties (PGI-6), Forschungszentrum Jülich, 52425 Jülich (Germany); Jülich-Aachen Research Alliance, Fundamentals for Future Information Technology (JARA-FIT), Forschungszentrum Jülich, 52425 Jülich (Germany); Hoppe, Michael [Peter Grünberg Institut, Electronic Properties (PGI-6), Forschungszentrum Jülich, 52425 Jülich (Germany); Bürgler, Daniel E. [Peter Grünberg Institut, Electronic Properties (PGI-6), Forschungszentrum Jülich, 52425 Jülich (Germany); Jülich-Aachen Research Alliance, Fundamentals for Future Information Technology (JARA-FIT), Forschungszentrum Jülich, 52425 Jülich (Germany); and others

    2014-07-01

    We present a procedure to prepare single-crystalline, high-purity Cu(001) films (templates) suitable as substrates for subsequent epitaxial thin-film growth. The template films were grown in a dedicated molecular-beam epitaxy system on a Cr/Ag/Fe/GaAs(001) buffer layer system. Low-energy electron diffraction and X-ray diffraction were applied to determine the surface orientation and the epitaxial relationship between all layers of the stack. Post-annealing at moderate temperatures enhances the quality of the film as shown by low-energy electron diffraction and atomic force microscopy. X-ray photoemission and Auger electron spectroscopy confirm that no atoms of the buffer layers diffuse into the Cu film during the initial preparation and the post-annealing treatment. The completed Cu(001) template system can be exposed to air and afterwards refurbished by Ar{sup +}-ion bombardment and annealing, enabling the transfer between vacuum systems. The procedure provides suitable conductive thin film templates for studies of epitaxial thin films, e.g. on the magnetic and magnetotransport properties of Co and Ni based films and multilayers. - Highlights: • Preparation of epitaxial Cu(001) template films on an insulating substrate • Characterization of template structure, orientation, cleanness, and roughness • Template films can be exposed to air and refurbished in different vacuum system. • Template films are suitable for further thin film growth at up to 570 K.

  13. Determination of Kinetic Parameters of Molecular Beam Epitaxy,

    Science.gov (United States)

    1985-04-17

    A kinetic growth model for molecular beam epitaxy (MBE) was discussed. Furthermore, high energy electron diffraction (HEED) was used as a surface...characterization method to provide evidence for this model. GaAs was used as an example to study the growth rate of molecular beam epitaxy . The relation

  14. Control of ion content and nitrogen species using a mixed chemistry plasma for GaN grown at extremely high growth rates >9 μm/h by plasma-assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Gunning, Brendan P.; Clinton, Evan A.; Merola, Joseph J.; Doolittle, W. Alan, E-mail: alan.doolittle@ece.gatech.edu [Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); Bresnahan, Rich C. [Veeco Instruments, St. Paul, Minnesota 55127 (United States)

    2015-10-21

    Utilizing a modified nitrogen plasma source, plasma assisted molecular beam epitaxy (PAMBE) has been used to achieve higher growth rates in GaN. A higher conductance aperture plate, combined with higher nitrogen flow and added pumping capacity, resulted in dramatically increased growth rates up to 8.4 μm/h using 34 sccm of N{sub 2} while still maintaining acceptably low operating pressure. It was further discovered that argon could be added to the plasma gas to enhance growth rates up to 9.8 μm/h, which was achieved using 20 sccm of N{sub 2} and 7.7 sccm Ar flows at 600 W radio frequency power, for which the standard deviation of thickness was just 2% over a full 2 in. diameter wafer. A remote Langmuir style probe employing the flux gauge was used to indirectly measure the relative ion content in the plasma. The use of argon dilution at low plasma pressures resulted in a dramatic reduction of the plasma ion current by more than half, while high plasma pressures suppressed ion content regardless of plasma gas chemistry. Moreover, different trends are apparent for the molecular and atomic nitrogen species generated by varying pressure and nitrogen composition in the plasma. Argon dilution resulted in nearly an order of magnitude achievable growth rate range from 1 μm/h to nearly 10 μm/h. Even for films grown at more than 6 μm/h, the surface morphology remained smooth showing clear atomic steps with root mean square roughness less than 1 nm. Due to the low vapor pressure of Si, Ge was explored as an alternative n-type dopant for high growth rate applications. Electron concentrations from 2.2 × 10{sup 16} to 3.8 × 10{sup 19} cm{sup −3} were achieved in GaN using Ge doping, and unintentionally doped GaN films exhibited low background electron concentrations of just 1–2 × 10{sup 15} cm{sup −3}. The highest growth rates resulted in macroscopic surface features due to Ga cell spitting, which is an engineering challenge still to be

  15. Growth of Gold-assisted Gallium Arsenide Nanowires on Silicon Substrates via Molecular Beam Epitaxy

    Directory of Open Access Journals (Sweden)

    Ramon M. delos Santos

    2008-06-01

    Full Text Available Gallium arsenide nanowires were grown on silicon (100 substrates by what is called the vapor-liquid-solid (VLS growth mechanism using a molecular beam epitaxy (MBE system. Good quality nanowires with surface density of approximately 108 nanowires per square centimeter were produced by utilizing gold nanoparticles, with density of 1011 nanoparticles per square centimeter, as catalysts for nanowire growth. X-ray diffraction measurements, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy revealed that the nanowires are epitaxially grown on the silicon substrates, are oriented along the [111] direction and have cubic zincblende structure.

  16. Molecular beam epitaxy and metalorganic chemical vapor deposition growth of epitaxial CdTe on (100) GaAs/Si and (111) GaAs/Si substrates

    Science.gov (United States)

    Nouhi, A.; Radhakrishnan, G.; Katz, J.; Koliwad, K.

    1988-01-01

    Epitaxial CdTe has been grown on both (100)GaAs/Si and (111)GaAs/Si substrates. A combination of molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) has been employed for the first time to achieve this growth: the GaAs layers are grown on Si substrates by MBE and the CdTe film is subsequently deposited on GaAs/Si by MOCVD. The grown layers have been characterized by X-ray diffraction, scanning electron microscopy, and photoluminescence.

  17. Gas source molecular beam epitaxial growth of GaN

    Science.gov (United States)

    Brown, Duncan W.

    1992-11-01

    Aluminum gallium nitride (AlGaN) has long been recognized as a promising radiation hard optoelectronic material. AlGaN has a wide direct band gap and therefore has potential applications in the fabrication of short wave-length devices, e.g., detectors and light-emitting diodes in the visible to ultraviolet region. Additionally, its piezoelectric properties and high acoustic velocities make it attractive for acoustic devices. The technical objective in Phase 1 was to determine if low temperature sources based on covalently bonded Group 3-nitrogen compounds could be used to prepare AlGaN films by gas source molecular beam epitaxy. The program required to investigate low temperature AlGaN source materials was separated into two parts: (1) the synthesis, purification, and pyrolysis of gallium-nitrogen adducts and aluminum-nitrogen adducts; and (2) the growth of GaN by chemical beam epitaxy. We clearly demonstrated under CBE conditions GaN(x)C(y) films could be grown using compounds with pre-existing Ga-N bonds whereas no films were formed using trimethylgallium. Dimethylgallium amide was shown to produce dramatically lower carbon content films in the presence of ammonia than did trimethylgallium in the presence of ammonia.

  18. Epitaxial yttrium iron garnet films grown by pulsed laser deposition

    Science.gov (United States)

    Dorsey, P. C.; Bushnell, S. E.; Seed, R. G.; Vittoria, C.

    1993-07-01

    Epitaxial Y3Fe5O12 (YIG) films have been grown by the pulsed laser deposition (PLD) technique on (111) gadolinium gallium garnet substrates. The effect of substrate temperature and oxygen partial pressure on the structure, composition, and magnetic properties of the films was investigated and compared to liquid phase epitaxy YIG films. The results demonstrated that epitaxial YIG films could be prepared under a wide range of deposition conditions, but narrow linewidth (ΔH≂1 Oe) films were producible only at low oxygen partial pressures (O2temperatures (Ts≳800 °C). Since the linewidth of single-crystal YIG is dominated by surface and volume defects and/or impurities, the narrow linewidth indicated that PLD is a viable technique for producing high-quality ferrite films for microwave device applications. In addition, under all deposition conditions (50-1000 mTorr and 700-850 °C) there is a uniaxial axis perpendicular to the film plane. However, at low oxygen pressure the uniaxial anisotropy energy constant Ku is negative while at high oxygen pressure Ku is positive.

  19. Infrared Rugates by Molecular Beam Epitaxy

    Science.gov (United States)

    Rona, M.

    1993-01-01

    Rugates are optical structures that have a sinusoidal index of refraction (harmonic gradient-index field). As their discrete high/ low index filter counterparts, they can be used as narrow rejection band filters. However, since rugates do not have abrupt interfaces, they tend to have a smaller absorption, hence deliver a higher in band reflectivity. The absence of sharp interfaces makes rugates even more desirable for high-energy narrow band reflectors. In this application, the lack of a sharp interface at the maximum internal standing wave electric field results in higher breakdown strengths. Our method involves fabricating rugates, with molecular beam epitaxy, on GaAs wafers as an Al(x)Ga(1-x)As single-crystal film.

  20. Effects of shutter transients in molecular beam epitaxy.

    Science.gov (United States)

    Gozu, Shin-Ichiro; Mozume, Teruo; Kuwatsuka, Haruhiko; Ishikawa, Hiroshi

    2012-11-12

    : We have studied the effects of shutter transients (STs) in molecular beam epitaxy (MBE). Two series of samples were grown by MBE and evaluated by X-ray diffraction (XRD) and X-ray reflectivity (XRR) measurements. The effects of STs were evaluated by growth rate (GR) analysis using a combination of growth time (GT) and thickness evaluated by XRD and XRR measurements. We revealed two opposite effects of STs: (1) overshoot of GR and (2) increase in GR with GT and subsequent saturation. Each effect was consistent with the previous studies; however, the previous studies showed no relationships between these two effects. By considering closing time of the shutter, the two opposite effects were well understood.

  1. Molecular beam epitaxy for high-efficiency nitride optoelectronics

    Energy Technology Data Exchange (ETDEWEB)

    Heffernan, J.; Kauer, M.; Windle, J.; Hooper, S.E.; Bousquet, V.; Zellweger, C.; Barnes, J.M. [Sharp Laboratories of Europe, Edmund Halley Road, Oxford Science Park, Oxford OX4 4GB (United Kingdom)

    2006-06-15

    We review the significant progress made in the development of nitride laser diodes by molecular beam epitaxy (MBE). We report on our recent result of room temperature continuous-wave operation of InGaN quantum well laser diodes grown by MBE. Ridge waveguide lasers fabricated on freestanding GaN substrates have a continuous-wave threshold current of 125 mA, corresponding to a threshold current density of 5.7 kA cm{sup -2}. The lasers have a threshold voltage of 8.6 V and a lifetime of several minutes. We outline the further technical challenges associated with demonstrating lifetimes of several thousand hours and present an assessment of the potential of MBE as a growth method for commercial quality nitride optoelectronic devices. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Effect of free-carrier concentration and optical injection on carrier lifetimes in undoped and iodine doped CdMgTe/CdSeTe double heterostructures grown by molecular beam epitaxy

    Science.gov (United States)

    Sohal, S.; Edirisooriya, M.; Ogedengbe, O. S.; Petersen, J. E.; Swartz, C. H.; LeBlanc, E. G.; Myers, T. H.; Li, J. V.; Holtz, M.

    2016-12-01

    Time-resolved and time integrated photoluminescence (PL) studies are reported for undoped and doped CdMgTe/CdSeTe double heterostructures (DHs) grown by molecular beam epitaxy. Undoped DHs are studied with absorber layer thickness varying from 0.5 to 2.5 µm. The n-type free-carrier concentration is varied ~7  ×  1015, 8.4  ×  1016, and 8.4  ×  1017 cm-3 using iodine as a dopant in different absorber layer thicknesses (0.25-2.0 µm). Optical injection is varied from 1  ×  1010 to 3  ×  1011 photons/pulse/cm2, corresponding to the initial injection of photo-carriers up to ~8  ×  1015 cm-3, to examine the effects of excess carrier concentration on the PL lifetimes. Undoped DHs exhibit an initial rapid decay followed by a slower dependence with carrier lifetimes up to ~485 ns. The dependence of carrier lifetimes on the thickness of the absorber layers (0.5-2.5 µm) suggests interface recombination velocities ({{v}\\operatorname{int}}~ ) ~ 1288 and 238 cm s-1 in the initial and later decay times, respectively, corresponding to high and low photo-carrier concentrations. The Shockley-Read-Hall model is used to describe the results in which variations are observed in {{v}\\operatorname{int}}~ for undoped DHs. The lifetimes of doped DHs show a consistent trend with thickness. The {{v}\\operatorname{int}}~ ~ 80-200 cm s-1 is estimated for doping n ~ 7  ×  1015 cm-3 and 240-410 cm s-1 for n ~ 8.4  ×  1016 cm-3. The observed decrease in carrier lifetimes with increasing n is consistent with growing importance of the radiative recombination rate due to the excess carrier concentration. The effect of carrier concentration on the PL spectrum is also discussed.

  3. Gallium Nitride Nanowires Grown by Hydride Vapor Phase Epitaxy

    Institute of Scientific and Technical Information of China (English)

    LIU Zhan-Hui; XIU Xiang-Qan; YAN Huai-Yue; ZHANG Rong; XIE Zi-Li; HAN Ping; SHI Yi; ZHENG You-Dou

    2011-01-01

    @@ GaN nanowires are grown by hydride vapor phase epitaxy using nickel as a catalyst.The properties of the obtained GaN nanowires are characterized by scanning and transmission electron microscopy,electron diffraction,roomtemperature photoluminescence and energy dispersive spectroscopy.The results show that the nanowires are wurtzite single crystals growing along the[0001]direction and a redshift in the photoluminescence is observed due to a superposition of several effects.The Raman spectra are close to those of the bulk GaN and the significantly broadening of those modes indicates the phonon confinement effects associated with the nanoscale dimensions of the system.%GaN nanowires are grown by hydride vapor phase epitaxy using nickel as a catalyst. The properties of the obtained GaN nanowires are characterized by scanning and transmission electron microscopy, electron diffraction, room-temperature photoluminescence and energy dispersive spectroscopy. The results show that the nanowires are wurtzite single crystals growing along the [0001] direction and a redshift in the photoluminescence is observed due to a superposition of several effects. The Raman spectra are close to those of the bulk GaN and the significantly broadening of those modes indicates the phonon confinement effects associated with the nanoscale dimensions of the system.

  4. Influence of Illumination on the Electrical Properties of p-(ZnMgTe/ZnTe:N)/CdTe/n-(CdTe:I)/GaAs Heterojunction Grown by Molecular Beam Epitaxy (MBE)

    Science.gov (United States)

    Jum'h, I.; Abd El-Sadek, M. S.; Al-Taani, H.; Yahia, I. S.; Karczewski, G.

    2016-11-01

    Heterostructure p-(ZnMgTe/ZnTe:N)/CdTe/n-(CdTe:I)/GaAs was evaporated using molecular beam epitaxy and investigated for photovoltaic energy conversion application. The electrical properties of the studied heterostructure were measured and characterized in order to understand the relevant electrical transport mechanisms. Electrical properties derived from the current-voltage (I-V) characteristics of solar cells provide essential information necessary for the analysis of performance losses and device efficiency. I-V characteristics are investigated in dark conditions and under different light intensities. All the electrical and power parameters of the heterostructure were measured, calculated and explained.

  5. Influence of Illumination on the Electrical Properties of p-(ZnMgTe/ZnTe:N)/CdTe/n-(CdTe:I)/GaAs Heterojunction Grown by Molecular Beam Epitaxy (MBE)

    Science.gov (United States)

    Jum'h, I.; Abd El-Sadek, M. S.; Al-Taani, H.; Yahia, I. S.; Karczewski, G.

    2017-02-01

    Heterostructure p-(ZnMgTe/ZnTe:N)/CdTe/n-(CdTe:I)/GaAs was evaporated using molecular beam epitaxy and investigated for photovoltaic energy conversion application. The electrical properties of the studied heterostructure were measured and characterized in order to understand the relevant electrical transport mechanisms. Electrical properties derived from the current-voltage ( I- V) characteristics of solar cells provide essential information necessary for the analysis of performance losses and device efficiency. I- V characteristics are investigated in dark conditions and under different light intensities. All the electrical and power parameters of the heterostructure were measured, calculated and explained.

  6. Pyroelectric and piezoelectric responses of thin AlN films epitaxy-grown on a SiC/Si substrate

    Science.gov (United States)

    Kukushkin, S. A.; Osipov, A. V.; Sergeeva, O. N.; Kiselev, D. A.; Bogomolov, A. A.; Solnyshkin, A. V.; Kaptelov, E. Yu.; Senkevich, S. V.; Pronin, I. P.

    2016-05-01

    This paper presents the results of pyroelectric and piezoelectric studies of AlN films formed by chloride-hydride epitaxy (CHE) and molecular beam epitaxy (MBE) on epitaxial SiC nanolayers grown on Si by the atom substitution method. The surface topography and piezoelectric and pyroelecrtric responses of AlN films have been analyzed. The results of the study have shown that the vertical component of the piezoresponse in CHE-grown AlN films is more homogeneous over the film area than that in MBE-grown AlN films. However, the signal from the MBE-synthesized AlN films proved to be stronger. The inversion of the polar axis (polarization vector) on passage from MBE-grown AlN films to CHE-grown AlN films has been found experimentally. It has been shown that the polar axis in MBE-grown films is directed from the free surface of the film toward the Si substrate while, in CHE-grown films, the polarization vector is directed toward the free surface.

  7. Interfacial, electrical, and spin-injection properties of epitaxial Co2MnGa grown on GaAs(100)

    DEFF Research Database (Denmark)

    Damsgaard, Christian Danvad; Hickey, M. C.; Holmes, S. N.

    2009-01-01

    The interfacial, electrical, and magnetic properties of the Heusler alloy Co2MnGa grown epitaxially on GaAs(100) are presented with an emphasis on the use of this metal-semiconductor combination for a device that operates on the principles of spin-injection between the two materials. Through...... systematic growth optimization the stoichiometry in the bulk Co2MnGa can be controlled to better than ±2%, although the interface is disordered and limits the spin-injection efficiency in a practical spintronic device irrespective of the half-metallic nature of the bulk metal. Molecular beam epitaxial growth...

  8. Epitaxially Grown Layered MFI–Bulk MFI Hybrid Zeolitic Materials

    KAUST Repository

    Kim, Wun-gwi

    2012-11-27

    The synthesis of hybrid zeolitic materials with complex micropore-mesopore structures and morphologies is an expanding area of recent interest for a number of applications. Here we report a new type of hybrid zeolite material, composed of a layered zeolite material grown epitaxially on the surface of a bulk zeolite material. Specifically, layered (2-D) MFI sheets were grown on the surface of bulk MFI crystals of different sizes (300 nm and 10 μm), thereby resulting in a hybrid material containing a unique morphology of interconnected micropores (∼0.55 nm) and mesopores (∼3 nm). The structure and morphology of this material, referred to as a "bulk MFI-layered MFI" (BMLM) material, was elucidated by a combination of XRD, TEM, HRTEM, SEM, TGA, and N2 physisorption techniques. It is conclusively shown that epitaxial growth of the 2-D layered MFI sheets occurs in at least two principal crystallographic directions of the bulk MFI crystal and possibly in the third direction as well. The BMLM material combines the properties of bulk MFI (micropore network and mechanical support) and 2-D layered MFI (large surface roughness, external surface area, and mesoporosity). As an example of the uses of the BMLM material, it was incorporated into a polyimide and fabricated into a composite membrane with enhanced permeability for CO2 and good CO2/CH4 selectivity for gas separations. SEM-EDX imaging and composition analysis showed that the polyimide and the BMLM interpenetrate into each other, thereby forming a well-adhered polymer/particle microstructure, in contrast with the defective interfacial microstructure obtained using bare MFI particles. Analysis of the gas permeation data with the modified Maxwell model also allows the estimation of the effective volume of the BMLM particles, as well as the CO2 and CH4 gas permeabilities of the interpenetrated layer at the BMLM/polyimide interface. © 2012 American Chemical Society.

  9. Growth and characterization of GaAs layers on Si substrates by migration-enhanced molecular beam epitaxy

    Science.gov (United States)

    Kim, Jae-Hoon; Liu, John K.; Radhakrishnan, Gouri; Katz, Joseph; Sakai, Shiro

    1988-01-01

    Migration-enhanced molecular beam epitaxial (MEMBE) growth and characterization of the GaAs layer on Si substrates (GaAs/Si) are reported. The MEMBE growth method is described, and material properties are compared with those of normal two-step MBE-grown or in situ annealed layers. Micrographs of cross-section view transmission electron microscopy and scanning surface electron microscopy of MEMBE-grown GaAs/Si showed dislocation densities of 10 to the 7th/sq cm. AlGaAs/GaAs double heterostructures have been successfully grown on MEMBE GaAs/Si by both metalorganic chemical vapor deposition and liquid phase epitaxy.

  10. Influence of substrate orientation on the structural quality of GaAs nanowires in molecular beam epitaxy.

    Science.gov (United States)

    Zhang, Zhi; Shi, Sui-Xing; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2015-01-26

    In this study, the effect of substrate orientation on the structural quality of Au-catalyzed epitaxial GaAs nanowires grown by a molecular beam epitaxy reactor has been investigated. It was found that the substrate orientations can be used to manipulate the nanowire catalyst composition and the catalyst surface energy and, therefore, to alter the structural quality of GaAs nanowires grown on different substrates. Defect-free wurtzite-structured GaAs nanowires grown on the GaAs (110) substrate have been achieved under our growth conditions.

  11. Epitaxial Growth of Si(111)/Er2O3(111) Structure on Si(111) by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    XU Run; TANG Min-Yan; ZHU Yan-Yan; WANG Lin-Jun

    2011-01-01

    The Si overlayers are grown by molecular beam epitaxy on atomically smllth Er2O3(111) films prepared on Si(111) substrates. Single crystalline Si overlayers are achieved and are evident due to the spot-like reflective high energy electron diffraction(RHEED) patterns and x-ray diffraction patterns. The epitaxial relationship of the Si overlayer along the surface with respect to the orientation of EreO3 and the Si substrate is as follows:overgrown Si(111)//Er2O3(111)//Si(111).The rough surface of Si overlayers, as identified by both RHEED patterns and atomic force microscopy images, indicates a three-dimensional growth mode. The reason for this is based on the interfacial energy argument. Further growth of Er2O3 films on this rough Si overlayer leads to the polycrystalline nature of the topmost Er2O3 layer.

  12. Thermal stability of MBE-grown epitaxial MoSe2 and WSe2 thin films

    Science.gov (United States)

    Chang, Young Jun; Choy, Byoung Ki; Phark, Soo-Hyon; Kim, Minu

    Layered transition metal dichalcogenides (TMDs) draw much attention, because of its unique optical properties and band structures depending on the layer thicknesses. However, MBE growth of epitaxial films demands information about thermal stability of stoichiometry and related electronic structure for high temperature range. We grow epitaxial MoSe2 and WSe2 ultrathin films by using molecular beam epitaxy (MBE). We characterize stoichiometry of films grown at various growth temperature by using various methods, XPS, EDX, and TOF-MEIS. We further test high temperature stability of electronic structure for those films by utilizing in-situ ellipsometry attached to UHV chamber. We discuss threshold temperatures up to 700~1000oC, at which electronic phases changes from semiconductor to metal due to selenium deficiency. This information can be useful for potential application of TMDs for fabrication of Van der Waals multilayers and related devices. This research was supported by Nano.Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning. (2009-0082580), NRF-2014R1A1A1002868.

  13. Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

    Science.gov (United States)

    Lin, T. L.; Liu, J. K.; Sadwick, L.; Wang, K. L.; Kao, Y. C.

    1987-01-01

    GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

  14. Molecular beam epitaxial growth and structural characterization of ZnS on (001) GaAs

    Science.gov (United States)

    Benz, R. G., II; Huang, P. C.; Stock, S. R.; Summers, C. J.

    1988-01-01

    The effect of surface nucleation processes on the quality of ZnS layers grown on (001) GaAs substrates by molecular beam epitaxy is reported. Reflection high energy electron diffraction indicated that nucleation at high temperatures produced more planar surfaces than nucleation at low temperatures, but the crystalline quality as assessed by X-ray double crystal diffractometry is relatively independent of nucleation temperature. A critical factor in layer quality was the initial roughness of the GaAs surfaces.

  15. Preparation of Porous GaN Buffer and Its Influence on the Residual Stress of GaN Epilayers Grown by Hydride Vapor Phase Epitaxy

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The preparation of porous structure on the molecular beam epitaxy (MBE)-grown mixed-polarity GaN epilayers was reported by using the wet chemical etching method. The effect of this porous structure on the residual stress of subsequent-growth GaN epilayers was studied by Raman and photoluminescence (PL) spectrum.Substantial decrease in the biaxial stresse can be achieved by employing the porous buffers in the hydride vapour phase epitaxy (HVPE) epilayer growth.

  16. Size-dependent shape and tilt transitions in In2O3 nanoislands grown on cubic Y-stabilized ZrO2(001) by molecular beam epitaxy.

    Science.gov (United States)

    Zhang, Kelvin H L; Bourlange, Anne; Egdell, Russell G; Collins, Stephen P; Bean, Richard J; Robinson, Ian K; Cowley, Roger A

    2012-08-28

    The growth of In(2)O(3) on cubic Y-stabilized ZrO(2)(001) by molecular beam epitaxy leads to formation of nanoscale islands which may tilt relative to the substrate in order to help accommodate the 1.7% tensile mismatch between the epilayer and the substrate. High-resolution synchrotron-based X-ray diffraction has been used in combination with atomic force microscopy to probe the evolution in island morphology, orientation, and tilt with island size. Very small islands formed at low substrate coverage are highly strained but exhibit no tilt, while intermediate islands are tilted randomly in all directions, giving rise to distinctive doughnut-shaped structure in three-dimensional reciprocal space isosurfaces. The largest islands with lateral sizes on the order of 1 μm tilt away from the four equivalent in-plane directions, giving three-dimensional scattering isosurfaces dominated by structure at the four corners of a square. Spatially resolved reciprocal space mapping using an X-ray beam with dimensions on the order of 1 μm suggests that the four-fold symmetry observed using a larger beam arises from averaging over an ensemble of islands, each with an individual tilt down one direction, rather than from the coexistence of differently tilted domains within a given island.

  17. Thermoelectric properties of epitaxial β-FeSi2 thin films grown on Si(111) substrates with various film qualities

    Science.gov (United States)

    Watanabe, Kentaro; Taniguchi, Tatsuhiko; Sakane, Shunya; Aoki, Shunsuke; Suzuki, Takeyuki; Fujita, Takeshi; Nakamura, Yoshiaki

    2017-05-01

    Si-based epitaxial β-FeSi2 thin films are attractive as materials for on-chip thermoelectric power generators. We investigated the structure, crystallinity, and thermoelectric properties of β-FeSi2 thin films epitaxially grown on Si(111) substrates by using three different techniques: conventional reactive deposition epitaxy followed by molecular beam epitaxy (RDE+MBE), solid phase epitaxy (SPE) based on codeposition of Fe and Si presented previously, and SPE followed by MBE (SPE+MBE) presented newly by this work. Their epitaxial growth temperatures were fixed at 530 °C for comparison. RDE+MBE thin films exhibited high crystalline quality, but rough surfaces and rugged β-FeSi2/Si(111) interfaces. On the other hand, SPE thin films showed flat surfaces and abrupt β-FeSi2/Si(111) interfaces but low crystallinity. We found that SPE+MBE thin films realized crystallinity higher than SPE thin films, and also had flatter surfaces and sharper interfaces than RDE+MBE thin films. In SPE+MBE thin film growth, due to the initial SPE process with low temperature codeposition, thermal interdiffusion of Fe and Si was suppressed, resulting in the surface flatness and abrupt interface. Second high temperature MBE process improved the crystallinity. We also investigated thermoelectric properties of these β-FeSi2 thin films. Structural factors affecting the thermoelectric properties of RDE+MBE, SPE, and SPE+MBE thin films were investigated.

  18. Adsorption-controlled growth of BiVO4 by molecular-beam epitaxy

    Directory of Open Access Journals (Sweden)

    S. Stoughton

    2013-10-01

    Full Text Available Single-phase epitaxial films of the monoclinic polymorph of BiVO4 were synthesized by reactive molecular-beam epitaxy under adsorption-controlled conditions. The BiVO4 films were grown on (001 yttria-stabilized cubic zirconia (YSZ substrates. Four-circle x-ray diffraction, scanning transmission electron microscopy (STEM, and Raman spectroscopy confirm the epitaxial growth of monoclinic BiVO4 with an atomically abrupt interface and orientation relationship (001BiVO4 ∥ (001YSZ with [100]BiVO4 ∥ [100]YSZ. Spectroscopic ellipsometry, STEM electron energy loss spectroscopy (STEM-EELS, and x-ray absorption spectroscopy indicate that the films have a direct band gap of 2.5 ± 0.1 eV.

  19. The influence of epitaxial Ti buffer layers for fabricating as-grown MgB{sub 2} films

    Energy Technology Data Exchange (ETDEWEB)

    Oba, T. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan)]. E-mail: t3806005@iwate-u.ac.jp; Sun, P. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Harada, Y. [JST Satellite Iwate, 3-35-2 Iioka-shinden, Morioka, Iwate 020-0852 (Japan); Takahashi, T. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Iriuda, H. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Seki, M. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Nakanishi, Y. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); Noguchi, S. [Department of Physics and Electronics, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan); JST-CREST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Ishida, T. [Department of Physics and Electronics, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan); JST-CREST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Yoshizawa, M. [Graduate School of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551 (Japan); JST Satellite Iwate, 3-35-2 Iioka-shinden, Morioka, Iwate 020-0852 (Japan)

    2007-03-15

    We have measured the magnetic field dependence of the resistivity using a 35T pulsed magnet for the as-grown MgB{sub 2} films fabricated on the epitaxial Ti buffer layer grown on c-plane ZnO and Al{sub 2}O{sub 3} substrates by molecular beam epitaxy (MBE). We will report the upper critical fields (H{sub c2}) along H||c-axis and H||ab-plane. The anisotropy ratio were obtained from these H{sub c2} values. The effects of Ti buffer layer on the H{sub c2} and the anisotropy of MgB{sub 2} film were discussed.

  20. High quality GaN-based LED epitaxial layers grown in a homemade MOCVD system

    Institute of Scientific and Technical Information of China (English)

    Yin Haibo; Wang Xiaoliang; Ran Junxue; Hu Guoxin; Zhang Lu; Xiao Hongling; Li Jing; Li Jinmin

    2011-01-01

    A homemade 7 × 2 inch MOCVD system is presented.With this system,high quality GaN epitaxial layers,InGaN/GaN multi-quantum wells and blue LED structural epitaxial layers have been successfully grown.The non-uniformity of undoped GaN epitaxial layers is as low as 2.86%.Using the LED structural epitaxial layers,blue LED chips with area of 350 × 350μm2 were fabricated.Under 20 mA injection current,the optical output power of the blue LED is 8.62 mW.

  1. Oxygen Ion Conductance in Epitaxially Grown Thin Film Electrolytes

    Energy Technology Data Exchange (ETDEWEB)

    Thevuthasan, Suntharampillai; Yu, Zhongqing; Kuchibhatla, Satyanarayana V N T; Saraf, Laxmikant V.; Marina, Olga A.; Shutthanandan, V.; Nachimuthu, Ponnusamy; Wang, Chong M.

    2009-04-01

    This paper briefly summarizes the results from a project aimed to develop an understanding of oxygen ionic transport processes in highly oriented thin film oxide materials to enable the design of new types of electrolyte materials for solid state electrochemical devices. We have used oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE) to grow highly oriented doped ceria, zriconia thin films on single crystal c-Al2O3 along with multilayered hetero-structures. The influence of dopant concentration, interfaces, defects and crystalline quality on oxygen ionic conductivity has been critically analyzed using various surface and bulk sensitive capabilities. Although, preferred (111) orientation was preserved in high quality samaria doped ceria films up to a 10 atom% Sm doping, the films started to show polycrystalline features for higher Sm doping. Maximum conductivity was obtained for 5 atom% Sm doping in ceria. In the case of gadolinia doped ceria/zirconia multi-layer films, total conductivity was found to increase with the increasing number of layers.

  2. Growth of MoO3 films by oxygen plasma assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Altman, Eric I.; Droubay, Timothy C.; Chambers, Scott A.

    2002-07-22

    The growth of MoO₃ films on SrLaAlO₄(0 0 1), a substrate lattice-matched to b-MoO , by oxygen plasma assisted molecular beam epitaxy was characterized using reflection high-energy electron diffraction (RHEED), X-ray photoelectron spectroscopy, Xray diffraction (XRD), and atomic force and scanning tunneling microscopies (AFM and STM).It was found that the flux of reactive oxygen species to the surface was not high enough to maintain the proper stoichiometry, even at the lowest measurable deposition rates. Therefore, the films were grown by depositing Mo in small increments and then allowing the Mo to oxidize. At 675 K, the films grew epitaxially but in a three-dimensional manner. XRD of films grown under these conditions revealed atetragonal structure that has not been previously observed in bulk MoO₃ samples.

  3. Applying CLIPS to control of molecular beam epitaxy processing

    Science.gov (United States)

    Rabeau, Arthur A.; Bensaoula, Abdelhak; Jamison, Keith D.; Horton, Charles; Ignatiev, Alex; Glover, John R.

    1990-01-01

    A key element of U.S. industrial competitiveness in the 1990's will be the exploitation of advanced technologies which involve low-volume, high-profit manufacturing. The demands of such manufacture limit participation to a few major entities in the U.S. and elsewhere, and offset the lower manufacturing costs of other countries which have, for example, captured much of the consumer electronics market. One such technology is thin-film epitaxy, a technology which encompasses several techniques such as Molecular Beam Epitaxy (MBE), Chemical Beam Epitaxy (CBE), and Vapor-Phase Epitaxy (VPE). Molecular Beam Epitaxy (MBE) is a technology for creating a variety of electronic and electro-optical materials. Compared to standard microelectronic production techniques (including gaseous diffusion, ion implantation, and chemical vapor deposition), MBE is much more exact, though much slower. Although newer than the standard technologies, MBE is the technology of choice for fabrication of ultraprecise materials for cutting-edge microelectronic devices and for research into the properties of new materials.

  4. ’Molecular Beam Epitaxial Growth, Characterization, and Devices of Modulated Semiconductor Structures’

    Science.gov (United States)

    1990-02-28

    on reverse if necessary and identify by block number) Key Words: Molecular Beam Epitaxv, X-ray diffraction, RHEED, GeSn , AlGaSb, Surface Structure iLb...equipment so far has been used in the study of metastable GeSn alloys grown on InP and GaSb substrates, and in analysis of the (Al, Ga)Sb material system...Homma, "Molecular beam epitaxial 6 growth of metastable GeSn alloys", Sept. 13-15, 1989, North Carolina State University, Raleigh, N.C. Also to be

  5. Structural and morphological properties of GaN buffer layers grown by ammonia molecular beam epitaxy on SiC substrates for AlGaN/GaN high electron mobility transistors

    Science.gov (United States)

    Corrion, A. L.; Poblenz, C.; Wu, F.; Speck, J. S.

    2008-05-01

    The impact of growth conditions on the surface morphology and structural properties of ammonia molecular beam epitaxy GaN buffers layers on SiC substrates was investigated. The threading dislocation (TD) density was found to decrease with decreasing NH3:Ga flux ratio, which corresponded to an increase in surface roughness and reduction in residual compressive lattice mismatch stress. Furthermore, the dislocation density and compressive stress decreased for increasing buffer thickness. TD inclination was proposed to account for these observations. Optimized surface morphologies were realized at high NH3:Ga flux ratios and were characterized by monolayer-high steps, spiral hillocks, and pyramidal mounds, with rms roughness of ˜1.0 nm over 2×2 μm2 atomic force microscopy images. Smooth surface morphologies were realized over a large range of growth temperatures and fluxes, and growth rates of up to 1 μm/h were achieved. TD densities in the buffers as low as 3×109 cm-2 were demonstrated. These buffers were highly insulating and were used in recently reported AlGaN/GaN HEMTs with power densities of >11 W/mm at 4 and 10 GHz.

  6. Growth and Characterization of N-Polar GaN Films on Si(111) by Plasma Assisted Molecular Beam Epitaxy

    Science.gov (United States)

    Dasgupta, Sansaptak; Nidhi; Wu, Feng; Speck, James S.; Mishra, Umesh K.

    2012-11-01

    Smooth N-polar GaN films were epitaxially grown by plasma assisted molecular beam epitaxy (PAMBE) on on-axis p-Si(111). The structural quality of the as-grown GaN films was further improved by insertion of AlGaN/GaN superlattice structures, resulting in reduced threading dislocation density and also efficient stress management in the GaN film to mitigate crack formation. The structural quality of these films was comparable to N-polar GaN grown on C-SiC by MBE. Convergent beam electron diffraction (CBED) imaging and KOH etch studies were performed to confirm the N-polarity of the sample. Room temperature photoluminescence measurements revealed strong GaN band-edge emission.

  7. Mobility enhanced photoactivity in sol-gel grown epitaxial anatase TiO2 films.

    Science.gov (United States)

    Jung, Hyun Suk; Lee, Jung-Kun; Lee, Jaegab; Kang, Bo Soo; Jia, Quanxi; Nastasi, Michael; Noh, Jun Hong; Cho, Chin-Moo; Yoon, Sung Hoon

    2008-03-18

    Epitaxial anatase thin films were grown on single-crystal LaAlO3 substrates by a sol-gel process. The epitaxial relationship between TiO2 and LaAlO3 was found to be [100]TiO2||[100]LaAlO3 and (001)TiO2||(001)LaAlO3 based on X-ray diffraction and a high-resolution transmission electron microscopy. The epitaxial anatase films show significantly improved photocatalytic properties, compared with polycrystalline anatase film on fused silica substrate. The increase in the photocatalytic activity of epitaxial anatase films is explained by enhanced charge carrier mobility, which is traced to the decreased grain boundary density in the epitaxial anatase film.

  8. Reduced free carrier absorption loss in midinfrared double heterostructure diode lasers grown by liquid phase epitaxy. .

    OpenAIRE

    Yin, M; Krier, A.; Jones, Robert; Carrington, Peter

    2007-01-01

    An improved InAsSb/InAsSbP double heterojunction ridge laser was designed and grown by liquid phase epitaxy. The cladding layer absorption loss was minimized by the introduction of two undoped quaternary layers on either side of the active region to form a five layer epitaxial structure. The inserted layers also helped alleviate interdiffusion of unwanted dopants into the active region and reduced current leakage in the device. The resulting diode lasers operate readily in pulsed mode near 3....

  9. The structural state of epitaxial GaP films of different polarities grown on misoriented Si(001) substrates

    Science.gov (United States)

    Loshkarev, I. D.; Vasilenko, A. P.; Trukhanov, E. M.; Kolesnikov, A. V.; Putyato, M. A.; Esin, M. Yu.; Petrushkov, M. O.

    2017-02-01

    The structure of GaP films grown by molecular-beam epitaxy on vicinal Si(1113) substrates has been studied by X-ray diffraction. It is established that the crystalline lattice of a pseudomorphic film rotates about the axis toward increasing deviation from the singular orientation, while the subsequent relaxation leads to rotation in the opposite direction. This is valid for the films of both (001) and (001¯) polarities. Differences between the surface morphologies of relaxed and pseudomorphic GaP films are revealed.

  10. Epitaxial relationship of semipolar s-plane (1101) InN grown on r-plane sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Dimitrakopulos, G. P. [Department of Physics, Aristotle University of Thessaloniki, GR 541 26 Thessaloniki (Greece)

    2012-07-02

    The heteroepitaxy of semipolar s-plane (1101) InN grown directly on r-plane sapphire by plasma-assisted molecular beam epitaxy is studied using transmission electron microscopy techniques. The epitaxial relationship is determined to be (1101){sub InN} Parallel-To (1102){sub Al{sub 2O{sub 3}}}, [1120]{sub InN} Parallel-To [2021]{sub Al{sub 2O{sub 3}}}, [1102]{sub InN}{approx} Parallel-To [0221]{sub Al{sub 2O{sub 3}}}, which ensures a 0.7% misfit along [1120]{sub InN}. Two orientation variants are identified. Proposed geometrical factors contributing to the high density of basal stacking faults, partial dislocations, and sphalerite cubic pockets include the misfit accommodation and reduction, as well as the accommodation of lattice twist.

  11. Direct growth of graphene on in situ epitaxial hexagonal boron nitride flakes by plasma-assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Zhongguang; Zheng, Renjing; Khanaki, Alireza; Zuo, Zheng; Liu, Jianlin, E-mail: jianlin@ece.ucr.edu [Quantum Structures Laboratory, Department of Electrical and Computer Engineering, University of California, Riverside, California 92521 (United States)

    2015-11-23

    Hexagonal boron nitride (h-BN) single-crystal domains were grown on cobalt (Co) substrates at a substrate temperature of 850–900 °C using plasma-assisted molecular beam epitaxy. Three-point star shape h-BN domains were observed by scanning electron microscopy, and confirmed by Raman and X-ray photoelectron spectroscopy. The h-BN on Co template was used for in situ growth of multilayer graphene, leading to an h-BN/graphene heterostructure. Carbon atoms preferentially nucleate on Co substrate and edges of h-BN and then grow laterally to form continuous graphene. Further introduction of carbon atoms results in layer-by-layer growth of graphene on graphene and lateral growth of graphene on h-BN until it may cover entire h-BN flakes.

  12. Influence of GaAs substrate on the transmission performance of epitaxially grown Fabry-Pérot filter

    Institute of Scientific and Technical Information of China (English)

    Wei Wang; Yongqing Huang; Xiaofeng Duan; Qiang Yan; Xiaomin Ren; Shiwei Cai; Jingwei Guo; Hui Huang

    2011-01-01

    The influence of GaAs substrate on the transmission performance of a multi-film Fabry-Perot filter (FPF), fabricated by metalorganic chemical vapor deposition epitaxial growth on GaAs substrate, is investigated using the transfer matrix method. On the basis of the theoretical simulation, we determine that the quality of the resonant transmission peak of this epitaxially grown FPP (BG-FPF) deteriorates through splitting when the substrate is taken into account. Rapid periodic oscillation of peak-transmittivity along with the alteration of substrate thickness is also observed in the simulation results. Finally, a remarkably improved transmission performance of the EG-FPF is obtained by thinning the substrate down to a suitable thickness range through well-controlled grinding and polishing.%Fabry-Pérot filters (FPFs) have been investigated in various microstructural systems for the past few decades[1-4].Along with the development of technologies and techniques such as metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy,depositing highquality epitaxial thin films onto different kinds of substrates using various materials has become possible[5-7].

  13. Growth of layered superconductor β-PdBi2 films using molecular beam epitaxy

    Science.gov (United States)

    Denisov, N. V.; Matetskiy, A. V.; Tupkalo, A. V.; Zotov, A. V.; Saranin, A. A.

    2017-04-01

    Bulk β-PdBi2 layered material exhibits advanced properties and is supposed to be probable topological superconductor. We present a method based on molecular beam epitaxy that allows us to grow β-PdBi2 films from a single β-PdBi2 triple layer up to the dozens of triple layers, using Bi(111) film on Si(111) as a template. The grown films demonstrate structural, electronic and superconducting properties similar to those of bulk β-PdBi2 crystals. Ability to grow the β-PdBi2 films of desired thickness opens the promising possibilities to explore fascinating properties of this advanced material.

  14. Growth of GaSb1-xBix by molecular beam epitaxy

    DEFF Research Database (Denmark)

    Song, Yuxin; Wang, Shumin; Roy, Ivy Saha

    2012-01-01

    Molecular beam epitaxy for GaSb1-xBix is investigated in this article. The growth window for incorporation of Bi in GaSb was found. Strategies of avoiding formation of Bi droplets and enhancing Bi incorporation were studied. The Bi incorporation was confirmed by SIMS and RBS measurements. The Bi...... concentration in the samples was found to increase with increasing growth temperature and Bi flux. The position of GaSb1-xBix layer peak in XRD rocking curves is found to be correlated to Bi composition. Surface and structural properties of the samples were also investigated. Samples grown on GaSb and Ga...

  15. Molecular beam epitaxy growth and optical properties of single crystal Zn3N2 films

    Science.gov (United States)

    Wu, Peng; Tiedje, T.; Alimohammadi, H.; Bahrami-Yekta, V.; Masnadi-Shirazi, M.; Wang, Cong

    2016-10-01

    Single crystal Zn3N2 films with (100) orientation have been grown by plasma-assisted molecular beam epitaxy on MgO and A-plane sapphire substrates with in situ optical reflectance monitoring of the growth. The optical bandgap was found to be 1.25-1.28 eV and an electron Hall mobility as high as 395 cm2 V-1 s-1 was measured. The films were n-type with carrier concentrations in the 1018-1019 cm-3 range.

  16. Cleaning chemistry of InSb(100) molecular beam epitaxy substrates

    Science.gov (United States)

    Vasquez, R. P.; Lewis, B. F.; Grunthaner, F. J.

    1983-01-01

    InSb has been used as a substrate for molecular beam epitaxy. For good epitaxial growth, a substrate surface which is smooth and clean on an atomic scale is required. Chemical cleaning procedures provide an oxide film to passivate the surface. This film is then desorbed by in situ heating. The material forming the film should, therefore, have a high vapor pressure at some temperature less than the substrate melting temperature. A chloride film appears to satisfy the latter requirement. The present investigation is, therefore, concerned with the formation of a chloride film rather than an oxide film. Carbon contamination has been found to cause problems in chemical cleaning procedures. The level of carbon contamination found in the case of chloride film formation, is therefore compared with the corresponding level observed in procedures using oxide films. It appears that a chloride film grown in connection with a short exposure time to a Cl2 plasma is preferable to other passivation films studied.

  17. Real-time reflectance-difference spectroscopy of GaAs molecular beam epitaxy homoepitaxial growth

    Directory of Open Access Journals (Sweden)

    A. Lastras-Martínez

    2014-03-01

    Full Text Available We report on real time-resolved Reflectance-difference (RD spectroscopy of GaAs(001 grown by molecular beam epitaxy, with a time-resolution of 500 ms per spectrum within the 2.3–4.0 eV photon energy range. Through the analysis of transient RD spectra we demonstrated that RD line shapes are comprised of two components with different physical origins and determined their evolution during growth. Such components were ascribed to the subsurface strain induced by surface reconstruction and to surface stoichiometry. Results reported in this paper render RD spectroscopy as a powerful tool for the study of fundamental processes during the epitaxial growth of zincblende semiconductors.

  18. InAs nanowire growth modes on Si (111) by gas source molecular beam epitaxy

    Science.gov (United States)

    Robson, M. T.; LaPierre, R. R.

    2016-02-01

    InAs nanowires (NWs) were grown on silicon substrates by gas source molecular beam epitaxy using five different growth modes: (1) Au-assisted growth, (2) positioned (patterned) Au-assisted growth, (3) Au-free growth, (4) positioned Au-assisted growth using a patterned oxide mask, and (5) Au-free selective-area epitaxy (SAE) using a patterned oxide mask. Optimal growth conditions (temperature, V/III flux ratio) were identified for each growth mode for control of NW morphology and vertical NW yield. The highest yield (72%) was achieved with the SAE method at a growth temperature of 440 °C and a V/III flux ratio of 4. Growth mechanisms are discussed for each of the growth modes.

  19. Fabrication of atomically smooth SrRuO3 thin films by laser molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    High-quality SrRuO3 (SRO) thin films and SrTiO3/SRO bilayer were grown epitaxially on SrTiO3 (STO)(001) substrates by laser molecular beam epitaxy. The results of in situ observation of reflection high-energy electron diffraction and ex situ X-ray diffraction θ -2θ scan indicate that the SRO thin films have good crystallinity. The measurements of atomic force microscopy and scan tunneling microscopy reveal that the surface of the SRO thin film is atomically smooth. The resistivity of the SRO thin film is 300 μΩ·cm at room temperature. Furthermore, the transmission electron microscopy study shows that the interfaces of STO/SRO and SRO/STO are very clear and no interfacial reaction layer was observed. The experimental results show that the SRO thin film is an excellent electrode material for devices based on perovskite oxide materials.

  20. Topological Insulator Film Growth by Molecular Beam Epitaxy: A Review

    OpenAIRE

    2016-01-01

    In this article, we will review recent progress in the growth of topological insulator (TI) thin films by molecular beam epitaxy (MBE). The materials we focus on are the V2-VI3 family of TIs. These materials are ideally bulk insulating with surface states housing Dirac excitations which are spin-momentum locked. These surface states are interesting for fundamental physics studies (such as the search for Majorana fermions) as well as applications in spintronics and other fields. However, the m...

  1. Molecular beam epitaxy and characterization of thin Bi2Se3 films on Al2O3 (110)

    Science.gov (United States)

    Tabor, Phillip; Keenan, Cameron; Urazhdin, Sergei; Lederman, David

    2011-07-01

    The structural and electronic properties of thin Bi2Se3 films grown on Al2O3 (110) by molecular beam epitaxy are investigated. The epitaxial films grow in the Frank-van der Merwe mode and are c-axis oriented. They exhibit the highest crystallinity, the lowest carrier concentration, and optimal stoichiometry at a substrate temperature of 200 °C determined by the balance between surface kinetics and desorption of Se. The crystallinity of the films improves with increasing Se/Bi flux ratio. Our results enable studies of thin topological insulator films on inert, non-conducting substrates that allow optical access to both film surfaces.

  2. Epitaxial Al/GaN and Au/GaN junctions on as-grown GaN(0001) 1 x 1 surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Orani, D.; Rubini, S.; Pelucchi, E.; Bonanni, B. [Laboratorio Nazionale TASC-INFM, Area di Ricerca, S.S. 14, Km. 163.5, 34012 Trieste (Italy); Piccin, M. [Laboratorio Nazionale TASC-INFM, Area di Ricerca, S.S. 14, Km. 163.5, 34012 Trieste (Italy); Also with Dipartimento di Fisica, Universita' di Trieste, 34127 Trieste (Italy); Franciosi, A. [Laboratorio Nazionale TASC-INFM, Area di Ricerca, S.S. 14, Km. 163.5, 34012 Trieste (Italy); Passaseo, A.; Cingolani, R. [INFM e Dipartimento di Scienza dei Materiali, Universita' di Lecce, Via per Arnesano, 73100 Lecce (Italy); Khan, A. [Department of Electrical and Computer Engineering, University of South Carolina, Columbia, SC 29208 (United States)

    2005-04-01

    GaN(0001) epilayers were fabricated by rf-plasma enhanced molecular beam epitaxy on GaN templates. The templates were grown by metalorganic chemical vapor deposition on sapphire. The layers exhibited the 2 x 2 reconstruction of the Ga-face during growth and the 1 x 1 reconstruction upon cooling. On such surfaces, Al/n-GaN and Au/n-GaN junctions were fabricated in-situ by molecular beam epitaxy. X-ray photoemission spectroscopy studies allowed us to determine n-type Schottky barrier heights of 0.61{+-}0.06 and 0.98{+-}0.06 eV, respectively, for the two types of epitaxial junctions. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. A Review of Liquid Phase Epitaxial Grown Gallium Arsenide

    OpenAIRE

    Alexiev, D.; Prokopovich, D. A.; Thomson, S.; Mo, L.; Rosenfeld, A B; Reinhard, M

    2004-01-01

    Liquid phase epitaxy of gallium arsenide (LPE GaAs) has been investigated intensively from the late 1960's to the present and has now a special place in the manufacture of wide band, compound semiconductor radiation detectors. Although this particular process appears to have gained prominence in the last three decades, it is interesting to note that its origins reach back to 1836 when Frankenheim made his first observations. A brief review is presented from a semiconductor applications point ...

  4. Molecular alignments in sexiphenyl thin films epitaxially grown on muscovite

    Energy Technology Data Exchange (ETDEWEB)

    Plank, H.; Resel, R.; Sitter, H.; Andreev, A.; Sariciftci, N.S.; Hlawacek, G.; Teichert, C.; Thierry, A.; Lotz, B

    2003-10-22

    The epitaxial orientations of highly crystalline para-sexiphenyl (C{sub 36}H{sub 26}) films on mica (001) surfaces are investigated by selected area electron diffraction (SAED) and transmission electron microscopy (TEM). Films at the early growth stage (growth time 26 s) and at an advanced growth stage (growth time 10 min) are studied. Films at the early growth stage exhibit only three-dimensional islands with an average size of 60x30x10 nm{sup 3}, whereas films at an advanced growth stage consist of long oriented nano-fibres with a needle-like morphology. We identified three different types of epitaxial relations between the mica (001) substrate and the sexiphenyl crystallites, which are the same in both growth stages. Moreover, within a single island as well as within a single fibre crystalline domains with these three epitaxial orientations are observed. At the advanced growth stage, these domains are aligned antiparallel or perpendicular to the fibre axes; the typical size of the domains is 20 nm.

  5. TEM EDS analysis of epitaxially-grown self-assembled indium islands

    Directory of Open Access Journals (Sweden)

    Jasmine Sears

    2017-05-01

    Full Text Available Epitaxially-grown self-assembled indium nanostructures, or islands, show promise as nanoantennas. The elemental composition and internal structure of indium islands grown on gallium arsenide are explored using Transmission Electron Microscopy (TEM Energy Dispersive Spectroscopy (EDS. Several sizes of islands are examined, with larger islands exhibiting high (>94% average indium purity and smaller islands containing inhomogeneous gallium and arsenic contamination. These results enable more accurate predictions of indium nanoantenna behavior as a function of growth parameters.

  6. TEM EDS analysis of epitaxially-grown self-assembled indium islands

    Science.gov (United States)

    Sears, Jasmine; Gibson, Ricky; Gehl, Michael; Zandbergen, Sander; Keiffer, Patrick; Nader, Nima; Hendrickson, Joshua; Arnoult, Alexandre; Khitrova, Galina

    2017-05-01

    Epitaxially-grown self-assembled indium nanostructures, or islands, show promise as nanoantennas. The elemental composition and internal structure of indium islands grown on gallium arsenide are explored using Transmission Electron Microscopy (TEM) Energy Dispersive Spectroscopy (EDS). Several sizes of islands are examined, with larger islands exhibiting high (>94%) average indium purity and smaller islands containing inhomogeneous gallium and arsenic contamination. These results enable more accurate predictions of indium nanoantenna behavior as a function of growth parameters.

  7. Epitaxial growth of dilute nitride-arsenide compound semiconductors by molecular beam epitaxy

    Science.gov (United States)

    Adamcyk, Martin

    InyGa1-yAs 1-xNx containing a small amount of nitrogen (x narrow bandgap semiconductor alloy that has advantageous properties for the fabrication of optoelectronic devices. In this thesis, we seek to improve the material quality of InGaAsN and GaAsN by studying how the epitaxial growth conditions affect both the structural and electronic properties of the alloy. We describe a novel RF plasma source based on a helical resonator design that was developed for the incorporation of nitrogen into GaAsN and InGaAsN thin films grown by molecular beam epitaxy. The plasma source is equipped with a baffle apparatus that decreases the ion content of the flux. We show how the structural and electronic properties of InGaAsN epilayers depend on the growth conditions. In situ light scattering measurements and atomic force microscopy show that a faceted surface morphology occurs when growth conditions increase adatom surface diffusion: slow growth rate, high substrate temperature and high V/III ratio. Large nitrogen concentrations also favour the faceted growth mode. The residual strain in relaxed InGaAsN films is found to be higher than in InGaAs epilayers having the same lattice mismatch. In situ substrate curvature measurements were used to monitor the strain state of the sample in real time during the growth. Ex situ transmission electron microscopy and x-ray diffraction measurements agree with the residual strain determined with the in situ monitor. These characterization results also indicate that threading dislocation glide is slower in InGaAsN than in InGaAs. Finally, we find that the electronic properties of InGaAsN are generally degraded with increasing nitrogen content. However, by choosing appropriate growth conditions, we demonstrate InGaAsN quantum wells with room temperature photoluminescence efficiencies that are comparable to InGaAs structures. These photoluminescence results may be related to the faceting transition that was observed during GaAsN growth. In

  8. High electron mobility of modulation doped GaAs after growing InP by solid source molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    SHU Yong-chun; PI Biao; LIN Yao-wang; XING Xiao-dong; YAO Jiang-hong; WANG Zhan-guo; XU Jing-jun

    2005-01-01

    Modulation-doped AlGaAs/GaAs structures were grown on GaAs(100) substrate by solid source molecular beam epitaxy (SSMBE) system. The factors which influence the electron mobility were investigated. After growing InP based materials, growth conditions were deteriorated, but by an appropriate method and using reasonaand growth conditions have been studied and optimized via Hall measurements. For a typical sample, 2.0 K electron served.

  9. Molecular Beam Epitaxy Growth of High Crystalline Quality LiNbO3

    Science.gov (United States)

    Tellekamp, M. Brooks; Shank, Joshua C.; Goorsky, Mark S.; Doolittle, W. Alan

    2016-12-01

    Lithium niobate is a multi-functional material with wide reaching applications in acoustics, optics, and electronics. Commercial applications for lithium niobate require high crystalline quality currently limited to bulk and ion sliced material. Thin film lithium niobate is an attractive option for a variety of integrated devices, but the research effort has been stagnant due to poor material quality. Both lattice matched and mismatched lithium niobate are grown by molecular beam epitaxy and studied to understand the role of substrate and temperature on nucleation conditions and material quality. Growth on sapphire produces partially coalesced columnar grains with atomically flat plateaus and no twin planes. A symmetric rocking curve shows a narrow linewidth with a full width at half-maximum (FWHM) of 8.6 arcsec (0.0024°), which is comparable to the 5.8 arcsec rocking curve FWHM of the substrate, while the film asymmetric rocking curve is 510 arcsec FWHM. These values indicate that the individual grains are relatively free of long-range disorder detectable by x-ray diffraction with minimal measurable tilt and twist and represents the highest structural quality epitaxial material grown on lattice mismatched sapphire without twin planes. Lithium niobate is also grown on lithium tantalate producing high quality coalesced material without twin planes and with a symmetric rocking curve of 193 arcsec, which is nearly equal to the substrate rocking curve of 194 arcsec. The surface morphology of lithium niobate on lithium tantalate is shown to be atomically flat by atomic force microscopy.

  10. Structure analysis of Ni thin films epitaxially grown on bcc metal underlayers formed on MgO(100 substrates

    Directory of Open Access Journals (Sweden)

    Futamoto Masaaki

    2013-01-01

    Full Text Available Ni thin films are prepared on Cr, V, and Nb underlayers with bcc structure formed on MgO(100 single-crystal substrates by molecular beam epitaxy. The growth behavior and the crystallographic properties are investigated by in-situ reflection high-energy electron diffraction and pole-figure X-ray diffraction. Cr(100 and V(100 single-crystal underlayers grow epitaxially on the substrates, whereas an Nb epitaxial_underlayer consisting of two bcc(110 variants is formed on the MgO(100 substrate. Metastable crystals nucleate on the Cr and the V underlayers, where the metastable hcp structure is stabilized through heteroepitaxial growth. With increasing the film thickness, the hcp structure starts to transform into more stable fcc structure by atomic displacement parallel to the hcp(0001 close-packed plane. The resulting films are consisting of mixtures of hcp and fcc crystals. On the other hand, only the formation of fcc crystal is recognized for the Ni film grown on Nb(110 underlayer.

  11. Epitaxial thin films grown by pulsed laser deposition

    NARCIS (Netherlands)

    Blank, D.H.A.

    2005-01-01

    In this paper, we present the pulsed laser deposition (PLD) technique to control the growth of metal oxide materials at atomic level using high-pressure reflective high-energy electron diffraction and ellipsometry. These developments have helped to make PLD a grown-up technique to fabricate complex

  12. Molecular beam epitaxy growth of germanium junctions for multi-junction solar cell applications

    Science.gov (United States)

    Masuda, T.; Faucher, J.; Lee, M. L.

    2016-11-01

    We report on the molecular beam epitaxy (MBE) growth and device characteristics of Ge solar cells. Integrating a Ge bottom cell beneath a lattice-matched triple junction stack grown by MBE could enable ultra-high efficiencies without metamorphic growth or wafer bonding. However, a diffused junction cannot be readily formed in Ge by MBE due to the low sticking coefficient of group-V molecules on Ge surfaces. We therefore realized Ge junctions by growth of homo-epitaxial n-Ge on p-Ge wafers within a standard III-V MBE system. We then fabricated Ge solar cells, finding growth temperature and post-growth annealing to be key factors for achieving high efficiency. Open-circuit voltage and fill factor values of ~0.175 V and ~0.59 without a window layer were obtained, both of which are comparable to diffused Ge junctions formed by metal-organic vapor phase epitaxy. We also demonstrate growth of high-quality, single-domain GaAs on the Ge junction, as needed for subsequent growth of III-V subcells, and that the surface passivation afforded by the GaAs layer slightly improves the Ge cell performance.

  13. High-resolution hydrogen profiling in AlGaN/GaN heterostructures grown by different epitaxial methods

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez-Posada Flores, F; Redondo-Cubero, A; Bengoechea, A; Brana, A F; Munoz, E [Instituto de Sistemas Optoelectronicos y Microtecnologia (ISOM) and Dpto. IngenierIa Electronica (DIE), ETSI de Telecomunicacion, Universidad Politecnica de Madrid, E-28040 Madrid (Spain); Gago, R [Centro de Micro-Analisis de Materiales, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Jimenez, A [Dpto. Electronica, Escuela Politecnica Superior, Universidad de Alcala, E-28805 Alcala de Henares, Madrid (Spain); Grambole, D, E-mail: fposada@die.upm.e [Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, PF 51019, D-01314 Dresden (Germany)

    2009-03-07

    Hydrogen (H) incorporation into AlGaN/GaN heterostructures used in high electron mobility transistors, grown by different methods, is studied by high-resolution depth profiling. Samples grown on sapphire and Si(1 1 1) substrates by molecular-beam epitaxy and metal-organic vapour phase epitaxy; involving H-free and H-containing precursors, were analysed to evaluate the eventual incorporation of H into the wafer. The amount of H was measured by means of nuclear reaction analysis (NRA) using the {sup 1}H({sup 15}N,{alpha}{gamma}){sup 12}C reaction up to a depth of {approx}110 nm into the heterostructures. Interestingly, the H profiles are similar in all the samples analysed, with an increasing H content towards the surface and a negligible H incorporation into the GaN layer (0.24 {+-} 0.08 at%) or at the AlGaN/GaN interface. Therefore, NRA shows that H uptake is not related to the growth process or technique employed and that H contamination may be due to external sources after growth. The eventual correlation between topographical defects on the AlGaN surface and the H concentration are also discussed.

  14. Integration of carbon nanotubes with semiconductor technology: fabrication of hybrid devices by III–V molecular beam epitaxy

    DEFF Research Database (Denmark)

    Stobbe, Søren; Lindelof, P. E.; Nygård, J.

    2006-01-01

    on incorporation of singlewall nanotubes in III–V semiconductor heterostructures grown by molecular beam epitaxy (MBE). We demonstrate that singlewall carbon nanotubes can be overgrown using MBE; electrical contacts to the nanotubes are obtained by GaMnAs grown at 250 °C. The resulting devices can exhibit field......We review a number of essential issues regarding the integration of carbon nanotubes in semiconductor devices for electronics: material compatibility, electrical contacts, functionalities, circuit architectures and reliability. In the second part of the paper, we present our own recent results...

  15. Hybrid molecular beam epitaxy for the growth of stoichiometric BaSnO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Prakash, Abhinav, E-mail: praka019@umn.edu; Dewey, John; Yun, Hwanhui; Jeong, Jong Seok; Mkhoyan, K. Andre; Jalan, Bharat, E-mail: bjalan@umn.edu [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

    2015-11-15

    Owing to its high room-temperature electron mobility and wide bandgap, BaSnO{sub 3} has recently become of significant interest for potential room-temperature oxide electronics. A hybrid molecular beam epitaxy (MBE) approach for the growth of high-quality BaSnO{sub 3} films is developed in this work. This approach employs hexamethylditin as a chemical precursor for tin, an effusion cell for barium, and a radio frequency plasma source for oxygen. BaSnO{sub 3} films were thus grown on SrTiO{sub 3} (001) and LaAlO{sub 3} (001) substrates. Growth conditions for stoichiometric BaSnO{sub 3} were identified. Reflection high-energy electron diffraction (RHEED) intensity oscillations, characteristic of a layer-by-layer growth mode were observed. A critical thickness of ∼1 nm for strain relaxation was determined for films grown on SrTiO{sub 3} using in situ RHEED. Scanning transmission electron microscopy combined with electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy confirmed the cube-on-cube epitaxy and composition. The importance of precursor chemistry is discussed in the context of the MBE growth of BaSnO{sub 3}.

  16. Growth, structural, and electrical properties of germanium-on-silicon heterostructure by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Aheli Ghosh

    2017-09-01

    Full Text Available The growth, morphological, and electrical properties of thin-film Ge grown by molecular beam epitaxy on Si using a two-step growth process were investigated. High-resolution x-ray diffraction analysis demonstrated ∼0.10% tensile-strained Ge epilayer, owing to the thermal expansion coefficient mismatch between Ge and Si, and negligible epilayer lattice tilt. Micro-Raman spectroscopic analysis corroborated the strain-state of the Ge thin-film. Cross-sectional transmission electron microscopy revealed the formation of 90  ° Lomer dislocation network at Ge/Si heterointerface, suggesting the rapid and complete relaxation of Ge epilayer during growth. Atomic force micrographs exhibited smooth surface morphology with surface roughness < 2 nm. Temperature dependent Hall mobility measurements and the modelling thereof indicated that ionized impurity scattering limited carrier mobility in Ge layer. Capacitance- and conductance-voltage measurements were performed to determine the effect of epilayer dislocation density on interfacial defect states (Dit and their energy distribution. Finally, extracted Dit values were benchmarked against published Dit data for Ge MOS devices, as a function of threading dislocation density within the Ge layer. The results obtained were comparable with Ge MOS devices integrated on Si via alternative buffer schemes. This comprehensive study of directly-grown epitaxial Ge-on-Si provides a pathway for the development of Ge-based electronic devices on Si.

  17. Effects of pulsed laser radiation on epitaxial self-assembled Ge quantum dots grown on Si substrates

    Energy Technology Data Exchange (ETDEWEB)

    Perez del Pino, A; Marcus, I C; Alonso, M I [Instituto de Ciencia de Materiales de Barcelona, Consejo Superior de Investigaciones Cientificas (ICMAB-CSIC), Campus UAB, 08193 Bellaterra (Spain); Gyoergy, E; Roqueta, J, E-mail: aperez@icmab.es [Centro de Investigaciones en Nanociencia y Nanotecnologia, (CIN2-CSIC), Consejo Superior de Investigaciones Cientificas, Campus UAB, 08193 Bellaterra (Spain)

    2011-07-22

    Laser irradiation of Ge quantum dots (QDs) grown on Si(100) substrates by solid-source molecular beam epitaxy has been performed using a Nd:YAG laser (532 nm wavelength, 5 ns pulse duration) in a vacuum. The evolution of the Ge QD morphology, strain and composition with the number of laser pulses incident on the same part of the surface, have been studied using atomic force microscopy, scanning electron microscopy and Raman spectroscopy. The observed changes in the topographical and structural properties of the QDs are discussed in terms of Ge-Si diffusion processes. Numerical simulations have been developed for the investigation of the temperature evolution of the QDs during laser irradiation. The obtained results indicate that the thermal behaviour and structural variation of the nanostructures differ from conventional thermal annealing treatments and can be controlled by the laser parameters. Moreover, an unusual island motion has been observed under the action of subsequent laser pulses.

  18. Microstructural analysis of lead telluride obtained by epitaxial grown; Analise microestrutural de telureto de chumbo obtido por crescimento epitaxial

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, Miriam Kasumi

    2000-07-01

    Lead telluride (PbTe) films applied in devices to detect infrared radiation, were grown on silicon (100) and barium fluoride (111) substrates by Hot Wall Epitaxy (HWE). The films were investigated by X ray diffraction, to verify the crystallinity and the growth planes; scanning electron microscopy, to observe the topography; transmission electron microscopy, to study the films microstructure in the cross section and selected-area electron diffraction to analyse the growth directions. PbTe films grown on barium fluoride (BaF{sub 2}) show good crystallinity and homogeneity, their growth is according to Frank-van der Merwe's Model. On the other hand, PbTe films grown on silicon (Si) substrate were not so crystalline and homogeneous owing to the impurities presence, great difference in the substrate and film lattice parameters and the thermal expansion coefficient mismatch. On Si substrate the growth follows the Volmer-Weber Model (Island). X ray diffraction provided enough data for testing the crystallography quality and the scanning and transmission electron microscopy analyses completed the study. (author)

  19. Epitaxially grown polycrystalline silicon thin-film solar cells on solid-phase crystallised seed layers

    Energy Technology Data Exchange (ETDEWEB)

    Li, Wei, E-mail: weili.unsw@gmail.com; Varlamov, Sergey; Xue, Chaowei

    2014-09-30

    Highlights: • Crystallisation kinetic is used to analyse seed layer surface cleanliness. • Simplified RCA cleaning for the seed layer can shorten the epitaxy annealing duration. • RTA for the seed layer can improve the quality for both seed layer and epi-layer. • Epitaxial poly-Si solar cell performance is improved by RTA treated seed layer. - Abstract: This paper presents the fabrication of poly-Si thin film solar cells on glass substrates using seed layer approach. The solid-phase crystallised P-doped seed layer is not only used as the crystalline template for the epitaxial growth but also as the emitter for the solar cell structure. This paper investigates two important factors, surface cleaning and intragrain defects elimination for the seed layer, which can greatly influence the epitaxial grown solar cell performance. Shorter incubation and crystallisation time is observed using a simplified RCA cleaning than the other two wet chemical cleaning methods, indicating a cleaner seed layer surface is achieved. Cross sectional transmission microscope images confirm a crystallographic transferal of information from the simplified RCA cleaned seed layer into the epi-layer. RTA for the SPC seed layer can effectively eliminate the intragrain defects in the seed layer and improve structural quality of both of the seed layer and the epi-layer. Consequently, epitaxial grown poly-Si solar cell on the RTA treated seed layer shows better solar cell efficiency, V{sub oc} and J{sub sc} than the one on the seed layer without RTA treatment.

  20. Raman scattering by the E{sub 2h} and A{sub 1}(LO) phonons of In{sub x}Ga{sub 1-x}N epilayers (0.25 < x < 0.75) grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Oliva, R.; Ibanez, J.; Cusco, R.; Artus, L. [Institut Jaume Almera, Consell Superior d' Investigacions Cientifiques (CSIC), Lluis Sole i Sabaris s.n, 08028 Barcelona, Catalonia (Spain); Kudrawiec, R. [Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland); Serafinczuk, J. [Faculty of Microsystem Electronics and Photonics, Wroclaw University of Technology, Janiszewskiego 11/17, 50-372 Wroclaw (Poland); Martinez, O.; Jimenez, J. [Departamento de Fisica de la Materia Condensada, Cristalografia, y Mineralogia, Universidad de Valladolid, 47011 Valladolid (Spain); Henini, M. [Nottingham Nanotechnology and Nanoscience Centre, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Boney, C.; Bensaoula, A. [Department of Physics, University of Houston, 4800 Calhoun, Houston, Texas 77004 (United States)

    2012-03-15

    We use Raman scattering to investigate the composition behavior of the E{sub 2h} and A{sub 1}(LO) phonons of In{sub x}Ga{sub 1-x}N and to evaluate the role of lateral compositional fluctuations and in-depth strain/composition gradients on the frequency of the A{sub 1}(LO) bands. For this purpose, we have performed visible and ultraviolet Raman measurements on a set of high-quality epilayers grown by molecular beam epitaxy with In contents over a wide composition range (0.25 < x < 0.75). While the as-measured A{sub 1}(LO) frequency values strongly deviate from the linear dispersion predicted by the modified random-element isodisplacement (MREI) model, we show that the strain-corrected A{sub 1}(LO) frequencies are qualitatively in good agreement with the expected linear dependence. In contrast, we find that the strain-corrected E{sub 2h} frequencies exhibit a bowing in relation to the linear behavior predicted by the MREI model. Such bowing should be taken into account to evaluate the composition or the strain state of InGaN material from the E{sub 2h} peak frequencies. We show that in-depth strain/composition gradients and selective resonance excitation effects have a strong impact on the frequency of the A{sub 1}(LO) mode, making very difficult the use of this mode to evaluate the strain state or the composition of InGaN material.

  1. High breakdown single-crystal GaN p-n diodes by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Qi, Meng; Zhao, Yuning; Yan, Xiaodong; Li, Guowang; Verma, Jai; Fay, Patrick [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Nomoto, Kazuki; Zhu, Mingda; Hu, Zongyang; Protasenko, Vladimir; Song, Bo; Xing, Huili Grace; Jena, Debdeep, E-mail: djena@cornell.edu [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Departments of ECE and MSE, Cornell University, Ithaca, New York 14853 (United States); Bader, Samuel [Departments of ECE and MSE, Cornell University, Ithaca, New York 14853 (United States)

    2015-12-07

    Molecular beam epitaxy grown GaN p-n vertical diodes are demonstrated on single-crystal GaN substrates. A low leakage current <3 nA/cm{sup 2} is obtained with reverse bias voltage up to −20 V. With a 400 nm thick n-drift region, an on-resistance of 0.23 mΩ cm{sup 2} is achieved, with a breakdown voltage corresponding to a peak electric field of ∼3.1 MV/cm in GaN. Single-crystal GaN substrates with very low dislocation densities enable the low leakage current and the high breakdown field in the diodes, showing significant potential for MBE growth to attain near-intrinsic performance when the density of dislocations is low.

  2. Molecular beam epitaxy growth and magnetic properties of Cr-Co-Ga Heusler alloy films

    Directory of Open Access Journals (Sweden)

    Wuwei Feng

    2015-11-01

    Full Text Available We have re-investigated growth and magnetic properties of Cr2CoGa films using molecular beam epitaxy technique. Phase separation and precipitate formation were observed experimentally again in agreement with observation of multiple phases separation in sputtered Cr2CoGa films by M. Meinert et al. However, significant phase separation could be suppressed by proper control of growth conditions. We showed that Cr2CoGa Heusler phase, rather than Co2CrGa phase, constitutes the majority of the sample grown on GaAs(001 at 450 oC. The measured small spin moment of Cr2CoGa is in agreement with predicted HM-FCF nature; however, its Curie temperature is not as high as expected from the theoretical prediction probably due to the off-stoichiometry of Cr2CoGa and the existence of the disorders and phase separation.

  3. Formation of GeSn alloy on Si(100) by low-temperature molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Talochkin, A. B., E-mail: tal@isp.nsc.ru [A. V. Rzhanov Institute of Semiconductor Physics, Lavrentyev Avenue 13, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Mashanov, V. I. [A. V. Rzhanov Institute of Semiconductor Physics, Lavrentyev Avenue 13, Novosibirsk 630090 (Russian Federation)

    2014-12-29

    GeSn alloys grown on Si(100) by the low-temperature (100 °C) molecular beam epitaxy are studied using scanning tunneling microscopy and Raman spectroscopy. It is found that the effect of Sn as a surfactant modifies substantially the low-temperature growth mechanism of Ge on Si. Instead of the formation of small Ge islands surrounded by amorphous Ge, in the presence of Sn, the growth of pure Ge islands appears via the Stranski-Krastanov growth mode, and a partially relaxed Ge{sub 1−x}Sn{sub x} alloy layer with the high Sn-fraction up to 40 at. % is formed in the area between them. It is shown that the observed growth mode induced by high surface mobility of Sn and the large strain of the pseudomorphic state of Ge to Si ensures the minimum elastic-strain energy of the structure.

  4. Nickel enhanced graphene growth directly on dielectric substrates by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Wofford, Joseph M., E-mail: joewofford@gmail.com, E-mail: lopes@pdi-berlin.de; Lopes, Joao Marcelo J., E-mail: joewofford@gmail.com, E-mail: lopes@pdi-berlin.de; Riechert, Henning [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Speck, Florian; Seyller, Thomas [Technische Universität Chemnitz, Institut für Physik, Reichenhainer Str. 70, 09126 Chemnitz (Germany)

    2016-07-28

    The efficacy of Ni as a surfactant to improve the crystalline quality of graphene grown directly on dielectric Al{sub 2}O{sub 3}(0001) substrates by molecular beam epitaxy is examined. Simultaneously exposing the substrate to a Ni flux throughout C deposition at 950 °C led to improved charge carrier mobility and a Raman spectrum indicating less structural disorder in the resulting nanocrystalline graphene film. X-ray photoelectron spectroscopy confirmed that no residual Ni could be detected in the film and showed a decrease in the intensity of the defect-related component of the C1s level. Similar improvements were not observed when a lower substrate temperature (850 °C) was used. A close examination of the Raman spectra suggests that Ni reduces the concentration of lattice vacancies in the film, possibly by catalytically assisting adatom incorporation.

  5. Epitaxially grown polycrystalline silicon thin-film solar cells on solid-phase crystallised seed layers

    Science.gov (United States)

    Li, Wei; Varlamov, Sergey; Xue, Chaowei

    2014-09-01

    This paper presents the fabrication of poly-Si thin film solar cells on glass substrates using seed layer approach. The solid-phase crystallised P-doped seed layer is not only used as the crystalline template for the epitaxial growth but also as the emitter for the solar cell structure. This paper investigates two important factors, surface cleaning and intragrain defects elimination for the seed layer, which can greatly influence the epitaxial grown solar cell performance. Shorter incubation and crystallisation time is observed using a simplified RCA cleaning than the other two wet chemical cleaning methods, indicating a cleaner seed layer surface is achieved. Cross sectional transmission microscope images confirm a crystallographic transferal of information from the simplified RCA cleaned seed layer into the epi-layer. RTA for the SPC seed layer can effectively eliminate the intragrain defects in the seed layer and improve structural quality of both of the seed layer and the epi-layer. Consequently, epitaxial grown poly-Si solar cell on the RTA treated seed layer shows better solar cell efficiency, Voc and Jsc than the one on the seed layer without RTA treatment.

  6. Study on GaN buffer leakage current in AlGaN/GaN high electron mobility transistor structures grown by ammonia-molecular beam epitaxy on 100-mm Si(111)

    Energy Technology Data Exchange (ETDEWEB)

    Ravikiran, L.; Radhakrishnan, K., E-mail: ERADHA@e.ntu.edu.sg; Ng, G. I. [NOVITAS-Nanoelectronics, Centre of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Munawar Basha, S.; Dharmarasu, N.; Agrawal, M.; Manoj kumar, C. M.; Arulkumaran, S. [Temasek Laboratories@NTU, Nanyang Technological University, Singapore 637553 (Singapore)

    2015-06-28

    The effect of carbon doping on the structural and electrical properties of GaN buffer layer of AlGaN/GaN high electron mobility transistor (HEMT) structures has been studied. In the undoped HEMT structures, oxygen was identified as the dominant impurity using secondary ion mass spectroscopy and photoluminescence (PL) measurements. In addition, a notable parallel conduction channel was identified in the GaN buffer at the interface. The AlGaN/GaN HEMT structures with carbon doped GaN buffer using a CBr{sub 4} beam equivalent pressure of 1.86 × 10{sup −7} mTorr showed a reduction in the buffer leakage current by two orders of magnitude. Carbon doped GaN buffers also exhibited a slight increase in the crystalline tilt with some pits on the growth surface. PL and Raman measurements indicated only a partial compensation of donor states with carbon acceptors. However, AlGaN/GaN HEMT structures with carbon doped GaN buffer with 200 nm thick undoped GaN near the channel exhibited good 2DEG characteristics.

  7. Comparative study of single InGaN layers grown on Si(111) and GaN(0001) templates: The role of surface wetting and epitaxial constraint

    Science.gov (United States)

    Gómez, V. J.; Gačević, Ž.; Soto-Rodríguez, P. E. D.; Aseev, P.; Nötzel, R.; Calleja, E.; Sánchez-García, M. A.

    2016-08-01

    This work presents a comparative study, based mainly on X-ray diffraction analysis, of compact (~100 nm thick) and uniform single crystal InGaN layers (In content <35%) grown by plasma-assisted molecular beam epitaxy. InGaN layers have been grown directly on Si(111) substrates and on commercially available GaN(0001)-on-sapphire templates.. A high reactivity of atomic N with Si leads to a formation of amorphous SiN on Si substrate, i.e. an indirect crystal-to-crystal InGaN/SiN/Si contact; the weak InGaN interaction with the underlying substrate (weak epitaxial constraint) further leads to poor surface "wetting" and consequent 3D nucleation. The InGaN growth on GaN is, on the other hand, characterized by a direct crystal-to-crystal InGaN/GaN contact; the strong InGaN interaction with the underlying substrate (strong epitaxial constraint) leads to good surface "wetting" and consequent 2D nucleation. All studied InGaN layers show single epitaxial relationship to both Si(111) and GaN(0001)-on-sapphire substrates as well as a relatively good compositional uniformity (no trace of InGaN phase separation). However, layers grown on Si show significantly lower strain and inferior crystallographic uniformity i.e. higher disorder in crystallographic tilt and twist. The surface "wetting" (poor vs. good) and epitaxial constraint (weak vs. strong) are suggested as the main origins of these discrepancies.

  8. Ge nanopillar solar cells epitaxially grown by metalorganic chemical vapor deposition

    Science.gov (United States)

    Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Park, Won-Kyu; Lee, Jaejin

    2017-02-01

    Radial junction solar cells with vertically aligned wire arrays have been widely studied to improve the power conversion efficiency. In this work, we report the first Ge nanopillar solar cell. Nanopillar arrays are selectively patterned on p-type Ge (100) substrates using nanosphere lithography and deep reactive ion etching processes. Nanoscale radial and planar junctions are realized by an n-type Ge emitter layer which is epitaxially grown by MOCVD using isobutylgermane. In situ epitaxial surface passivation is employed using an InGaP layer to avoid high surface recombination rates and Fermi level pinning. High quality n-ohmic contact is realized by protecting the top contact area during the nanopillar patterning. The short circuit current density and the power conversion efficiency of the Ge nanopillar solar cell are demonstrated to be improved up to 18 and 30%, respectively, compared to those of the Ge solar cell with a planar surface.

  9. Ge nanopillar solar cells epitaxially grown by metalorganic chemical vapor deposition

    Science.gov (United States)

    Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Park, Won-Kyu; Lee, Jaejin

    2017-01-01

    Radial junction solar cells with vertically aligned wire arrays have been widely studied to improve the power conversion efficiency. In this work, we report the first Ge nanopillar solar cell. Nanopillar arrays are selectively patterned on p-type Ge (100) substrates using nanosphere lithography and deep reactive ion etching processes. Nanoscale radial and planar junctions are realized by an n-type Ge emitter layer which is epitaxially grown by MOCVD using isobutylgermane. In situ epitaxial surface passivation is employed using an InGaP layer to avoid high surface recombination rates and Fermi level pinning. High quality n-ohmic contact is realized by protecting the top contact area during the nanopillar patterning. The short circuit current density and the power conversion efficiency of the Ge nanopillar solar cell are demonstrated to be improved up to 18 and 30%, respectively, compared to those of the Ge solar cell with a planar surface. PMID:28209964

  10. Molecular beam epitaxy, MBE; Epitaxia por haces moleculares

    Energy Technology Data Exchange (ETDEWEB)

    Ruiz Ruiz de Gopegui, A.

    2010-07-01

    The molecular beam epitaxy, MBE, is a physical technique of synthesis in which a sheet of a solid increases, in a chamber of ultra-high vacuum, the reaction of atomic or molecular beams of its elementary components in the vapor phase, the impact these on a monocrystalline substrate which is kept at proper temperature. Using this technique, films are obtained high purity and excellent crystalline quality, in which the composition and can be alternating layers control up to a limit of one atomic layer. In the beginning was dedicated only to the manufacture of III-V semiconductor heterostructures, but quickly transcended other material systems. It is an ideal technique for heterostructures considered as model systems in solid state physics (quantum wells, superlattices, quantum wires and dots ...) and for manufacturing devices with advanced new design. In addition, the current convergence of disciplines to the ubiquitous nano technology, the deep knowledge gained on the fundamental phenomena involved in MBE growth of very different systems materials, allows use of the technique beyond its intrinsic ability to control the process in the direction of growth, and apply it to obtain ordered nano structures and networks grounds on the nano scale. (author) 12 refs.

  11. Growth of GaN nanowall network on Si (111) substrate by molecular beam epitaxy.

    Science.gov (United States)

    Zhong, Aihua; Hane, Kazuhiro

    2012-12-27

    GaN nanowall network was epitaxially grown on Si (111) substrate by molecular beam epitaxy. GaN nanowalls overlap and interlace with one another, together with large numbers of holes, forming a continuous porous GaN nanowall network. The width of the GaN nanowall can be controlled, ranging from 30 to 200 nm by adjusting the N/Ga ratio. Characterization results of a transmission electron microscope and X-ray diffraction show that the GaN nanowall is well oriented along the C axis. Strong band edge emission centered at 363 nm is observed in the spectrum of room temperature photoluminescence, indicating that the GaN nanowall network is of high quality. The sheet resistance of the Si-doped GaN nanowall network along the lateral direction was 58 Ω/. The conductive porous nanowall network can be useful for integrated gas sensors due to the large surface area-to-volume ratio and electrical conductivity along the lateral direction by combining with Si micromachining.

  12. Improved crystalline quality of N-polar GaN epitaxial layers grown with reformed flow-rate-modulation technology

    Science.gov (United States)

    Zhang, Heng; Zhang, Xiong; Wang, Shuchang; Wang, Xiaolei; Zhao, Jianguo; Wu, Zili; Dai, Qian; Yang, Hongquan; Cui, Yiping

    2017-01-01

    A reformed flow-rate-modulation technology was developed for the metalorganic vapor phase epitaxy (MOVPE) growth of the N-polar GaN epitaxial layers. To improve the crystalline quality of the N-polar GaN epitaxial layers, a GaN nucleation layer was grown at relatively low temperature with carefully-controlled pulsed supply of Ga source and showed diverse morphology with atomic force microscope (AFM). Furthermore, the electrical and optical properties of the grown N-polar GaN epitaxial layers were investigated extensively by means of Hall effect, photoluminescence (PL), and X-ray rocking curve (XRC) measurements. The characterization results revealed that as compared with the N-polar GaN epitaxial layer grown over the conventional GaN nucleation layer which was deposited with continuous supply of both N and Ga sources, the electrical and optical properties of the N-polar GaN epitaxial layer grown with optimized supply of Ga source for the GaN nucleation layer were significantly improved.

  13. High quality YBCO superconductive thin films fabricated by laser molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    CHEN; Fan

    2001-01-01

    [1]Hirata,K.,Yamamoto,K.,Iijinma,J.et al.,Tunneling measurements on superconductor/insulator/superconductor junctions using single-crystal YBa2Cu3O7-x thin films,Appl.Phys.Lett.,1990,56(7):683-685.[2]Kingston,J.J.,Wellstood,F.C.,Lerch,P.et al.,Multilayer YBa2Cu3Ox-SrTiO3-YBa2Cu3Ox films for insulating crossovers,Appl.Phys.Lett.,1990,56(2):189-191.[3]Grundler,D.,Krumme,J.P.,David,B.et al.,YBa2Cu3O7 ramp-type junctions and superconducting quantum interference devices with an ultra thin barrier of NdGaO3,Appl.Phys.Lett.,1994,65(14):1841-1843.[4]Yang Guozhen,Lu Huibin,Chen Zhenghao et al.,Laser molecular beam epitaxy system and its key technologies,Science in China (in Chinese),Ser.A,1998,28(3):260-265.[5]Wang Ning,Lu Huibin,Chen,W.Z.et al.,Morphology and microstructure of BaTiO3/SrTiO3 superlattices grown on SrTiO3 by laser molecular-beam epitaxy,Appl.Phys.Lett.,1999,75(22):3464-3466.[6]Chen Li-Chyng,Particulates generated by pulsed laser ablation,in Pulsed Laser Deposition of Thin Films (eds.Chrisey,D.B.,Hulber,G.K.),New York:John Wiley & Sons,Inc.,1994,167-198.[7]Wang,H.S.,Dietsche,W.,Eissler,D.et al.,Molecular beam epitaxial growth and structure properties of DyBa2Cu3O7-y,J.Crys.Growth,1993,126:565-577.[8]Kita,R.,Hase,T.,Itti,R.et al.,Synthesis of CuO films using mass-separated,low-energy O+ ion beams,Appl.Phys.Lett.,1992,60(21):2684-2685.[9]Lu Huibin,Zhou Yueliang,Yang Guozhen et al.,Active gas source for thin film preparation,Chinese Patent (in Chinese),1996,No.ZL 96219046.2.[10]Wang Jing,Chen Fan,Zhao Tong et al.,Fabrication of high stable DC-SQUIDS with L-MBE YBCO thin films,Chinese Journal of Low Temperature Physics (in Chinese),1999,21(1):13-16.

  14. In-situ epitaxial growth of graphene/h-BN van der Waals heterostructures by molecular beam epitaxy.

    Science.gov (United States)

    Zuo, Zheng; Xu, Zhongguang; Zheng, Renjing; Khanaki, Alireza; Zheng, Jian-Guo; Liu, Jianlin

    2015-10-07

    Van der Waals materials have received a great deal of attention for their exceptional layered structures and exotic properties, which can open up various device applications in nanoelectronics. However, in situ epitaxial growth of dissimilar van der Waals materials remains challenging. Here we demonstrate a solution for fabricating van der Waals heterostructures. Graphene/hexagonal boron nitride (h-BN) heterostructures were synthesized on cobalt substrates by using molecular beam epitaxy. Various characterizations were carried out to evaluate the heterostructures. Wafer-scale heterostructures consisting of single-layer/bilayer graphene and multilayer h-BN were achieved. The mismatch angle between graphene and h-BN is below 1°.

  15. Surface organization of homoepitaxial InP films grown by metalorganic vapor-phase epitaxy

    OpenAIRE

    Gocalinska, A.; Manganaro, M.; Vvedensky, D. D.; Pelucchi, E.

    2012-01-01

    We present a systematic study of the morphology of homoepitaxial InP films grown by metalorganic vapor-phase epitaxy which are imaged with ex situ atomic force microscopy. These films show a dramatic range of different surface morphologies as a function of the growth conditions and substrate (growth temperature, V/III ratio, and miscut angle < 0.6deg and orientation toward A or B sites), ranging from stable step flow to previously unreported strong step bunching, over 10 nm in height. These o...

  16. Structural, electrical and luminescent characteristics of ultraviolet light emitting structures grown by hydride vapor phase epitaxy

    Directory of Open Access Journals (Sweden)

    A.Y. Polyakov

    2017-03-01

    Full Text Available Electrical and luminescent properties of near-UV light emitting diode structures (LEDs prepared by hydride vapor phase epitaxy (HVPE were studied. Variations in photoluminescence and electroluminescence efficiency observed for LEDs grown under nominally similar conditions could be attributed to the difference in the structural quality (dislocation density, density of dislocations agglomerates of the GaN active layers, to the difference in strain relaxation achieved by growth of AlGaN/AlGaN superlattice and to the presence of current leakage channels in current confining AlGaN layers of the double heterostructure.

  17. Irradiation induced improvement in crystallinity of epitaxially grown Ag thin films on Si substrates

    Energy Technology Data Exchange (ETDEWEB)

    Takahiro, Katsumi; Nagata, Shinji; Yamaguchi, Sadae [Tohoku Univ., Sendai (Japan). Inst. for Materials Research

    1997-03-01

    We report the improvement in crystallinity of epitaxially grown Ag films on Si(100) substrates with ion irradiation. The irradiation of 0.5 MeV Si ions to 2x10{sup 16}/cm{sup 2} at 200degC, for example, reduces the channeling minimum yield from 60% to 6% at Ag surface. The improvement originates from the decrease of mosaic spread in the Ag thin film. In our experiments, ion energy, ion species and irradiation temperature have been varied. The better crystallinity is obtained as the higher concentration of defect is generated. The mechanism involved in the irradiation induced improvement is discussed. (author)

  18. Epitaxially Grown Indium Phosphide Quantum Dots on a Virtual Ge Substrate Realized on Si(001)

    Science.gov (United States)

    Wiesner, Michael; Bommer, Moritz; Schulz, Wolfgang-Michael; Etter, Martin; Werner, Jens; Oehme, Michael; Schulze, Jörg; Jetter, Michael; Michler, Peter

    2012-04-01

    An ultrathin virtual Ge substrate (GeVS) with low defect density was realized on CMOS-compatible Si(001) by molecular beam epitaxy. On top, III-V layers were deposited by metal-organic vapor-phase epitaxy, at which diffusion of Ge was successfully suppressed. Nonclassical light emitters, based on InP quantum dots (QDs), were realized on a thin GaAs buffer (thickness ≈ 1 µm). The quantum dots show emission in the red spectral region, meeting the range of the highest detection efficiency of silicon avalanche photodiodes. The decay dynamics and emission characteristics of single QDs were investigated. Autocorrelation measurements prove single-photon emission with a value of g(2)(0)=0.32.

  19. The structural transition from epitaxial Fe/Pt multilayers to an ordered FePt film using low energy ion beam sputtering deposition with no buffer layer

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Chih-Hao, E-mail: chlee@mx.nthu.edu.tw [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Chen, Yu-Sheng [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Electronics and Optoelectronics Research Laboratories, Industrial Technology Research Institute, Hsinchu 31040, Taiwan (China); Liu, Li-Jung [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Huang, J.C.A. [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China)

    2014-11-03

    An epitaxial L1{sub 0} FePt thin film grown from an [Fe(10 Å)/Pt(10 Å)]{sub 15} multilayer with the orientation of (001) was prepared by an ion beam sputtering deposition method without buffer layer. From the measurement data of X-ray diffraction and X-ray reflectivity, the multilayer structure was totally disappeared and a uniform FePt alloy thin film was formed at temperatures higher than 600 °C. For the as-deposited thin film grown at 100 °C, the multilayer already possesses an epitaxial structure. The epitaxial relation is FePt(001)[100]//MgO(001)[100] and this epitaxial relation persists after sequential high temperature annealing. An epitaxial L1{sub 0} ordered FePt(001) film with order parameter of 0.95 was obtained when the annealing temperature reached 650 °C. The ordered FePt(001) thin film has a perpendicular magnetic anisotropy with a squareness of 0.95 ± 0.03 on the magnetic hysteresis loop. This experiment demonstrates that the low energy ion beam sputtering deposition will preserve the epitaxial relation with no buffer layer between multilayer and substrate. - Highlights: • The Fe/Pt films using ion sputtering deposition with no buffer layer is epitaxial. • Multilayer structure was totally disappeared at temperatures higher than 600 °C. • Order parameter reach 0.95 after annealing at 650 °C. • Interfacial epitaxial FePt alloy already formed at 100 °C.

  20. Chemical beam epitaxy growth of AlGaAs/GaAs tunnel junctions using trimethyl aluminium for multijunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Paquette, B.; DeVita, M.; Turala, A.; Kolhatkar, G.; Boucherif, A.; Jaouad, A.; Aimez, V.; Arès, R. [Institut Interdisciplinaire d' Innovation Technologique (3IT), Université de Sherbrooke, Sherbrooke, Québec (Canada); Wilkins, M.; Wheeldon, J. F.; Walker, A. W.; Hinzer, K. [Centre for Research in Photonics, University of Ottawa, Ottawa, ON (Canada); Fafard, S. [Cyrium Technologies Inc., Ottawa, ON (Canada)

    2013-09-27

    AlGaAs/GaAs tunnel junctions for use in high concentration multijunction solar cells were designed and grown by chemical beam epitaxy (CBE) using trimethyl aluminium (TMA) as the p-dopant source for the AlGaAs active layer. Controlled hole concentration up to 4⋅10{sup 20} cm{sup −3} was achieved through variation in growth parameters. Fabricated tunnel junctions have a peak tunneling current up to 6140 A/cm{sup 2}. These are suitable for high concentration use and outperform GaAs/GaAs tunnel junctions.

  1. Molecular beam epitaxial growth of a three-dimensional topological Dirac semimetal Na{sub 3}Bi

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yi, E-mail: YiZhang@lbl.gov [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Stanford Institute of Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Liu, Zhongkai; Shen, Zhi-Xun [Stanford Institute of Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Geballe Laboratory for Advanced Materials, Departments of Physics and Applied Physics, Stanford University, Stanford, California 94305 (United States); Zhou, Bo [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Geballe Laboratory for Advanced Materials, Departments of Physics and Applied Physics, Stanford University, Stanford, California 94305 (United States); Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Kim, Yeongkwan; Hussain, Zahid; Mo, Sung-Kwan, E-mail: SKMo@lbl.gov [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Chen, Yulin [Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom)

    2014-07-21

    We report a molecular beam epitaxial growth of Na{sub 3}Bi single-crystal thin films on two different substrates—epitaxial bilayer graphene terminated 6H-SiC(0001) and Si(111). Using reflection high-energy electron diffraction, we found that the lattice orientation of the grown Na{sub 3}Bi thin film was rotated by 30° respect to the surface lattice orientations of these two substrates. An in-situ angle-resolved photoemission spectroscopy clearly revealed the 3-dimensional Dirac-cone band structure in such thin films. Our approach of growing Na{sub 3}Bi thin film provides a potential route for further studying its intriguing electronic properties and for fabricating it into practical devices in future.

  2. Strain relief and growth optimization of GaSb on GaP by molecular beam epitaxy.

    Science.gov (United States)

    Wang, Y; Ruterana, P; Chen, J; Desplanque, L; El Kazzi, S; Wallart, X

    2012-08-22

    In this paper, the impact of growth parameters on the strain relaxation of highly lattice mismatched (11.8%) GaSb grown on GaP substrate by molecular beam epitaxy has been investigated. The surface morphology, misfit dislocation and strain relaxation of the GaSb islands are shown to be highly related to the initial surface treatment, growth rate and temperature. More specifically, Sb-rich surface treatment is shown to promote the formation of Lomer misfit dislocations. Analysis of the misfit dislocation and strain relaxation as functions of the growth temperature and rate led to an optimal growth window for a high quality GaSb epitaxial layer on (001) GaP. With this demonstrated optimized growth, a high mobility (25,500 cm(2) V (-1) s(-1) at room temperature) AlSb/InAs heterostructure on a semi-insulating (001) GaP substrate has been achieved.

  3. Roughness of CdTe thin films grown on glass by hot wall epitaxy.

    Science.gov (United States)

    Leal, F F; Ferreira, S O; Menezes-Sobrinho, I L; Faria, T E

    2005-01-12

    Cadmium telluride films were grown on glass substrates using the hot wall epitaxy (HWE) technique. The samples were polycrystalline with a preferential (111) orientation. Scanning electron micrographs reveal a grain size between 0.1 and 0.5 µm. The surface morphology of the samples was studied by measuring the roughness profile using a stylus profiler. The roughness as a function of growth time and scale size were investigated to determine the growth and roughness exponents, β and α, respectively. From the results we can conclude that the growth surface has a self-affine character with a roughness exponent α equal to 0.69 ± 0.03 and almost independent of growth time. The growth exponent β was equal to 0.38 ± 0.06. These values agree with that determined previously for CdTe(111) films grown on GaAs(100).

  4. Element-specific study of epitaxial NiO/Ag/CoO/Fe films grown on vicinal Ag(001) using photoemission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Y.; Li, J.; Tan, A.; Jin, E.; Son, J.; Park, J. S.; Doran, A.; Young, A. T.; Scholl, A.; Arenholz, E.; Wu, J.; Hwang, C.; Zhao, H. W.; Qiu, Z. Q.

    2011-01-10

    NiO/Ag/CoO/Fe single crystalline films are grown epitaxially on a vicinal Ag(001) substrate using molecular beam epitaxy and investigated by photoemission electron microscopy. We find that after zero-field cooling, the in-plane Fe magnetization switches from parallel to perpendicular direction of the atomic steps of the vicinal surface at thinner CoO thickness but remains in its original direction parallel to the steps at thicker CoO thickness. CoO and NiO domain imaging result shows that both CoO/Fe and NiO/CoO spins are perpendicularly coupled, suggesting that the Fe magnetization switching may be associated with the rotatable-frozen spin transition of the CoO film.

  5. Shadowing and mask opening effects during selective-area vapor-liquid-solid growth of InP nanowires by metalorganic molecular beam epitaxy.

    Science.gov (United States)

    Kelrich, A; Calahorra, Y; Greenberg, Y; Gavrilov, A; Cohen, S; Ritter, D

    2013-11-29

    Indium phosphide nanowires were grown by metalorganic molecular beam epitaxy using the selective-area vapor-liquid-solid method. We show experimentally and theoretically that the size of the annular opening around the nanowire has a major impact on nanowire growth rate. In addition, we observed a considerable reduction of the growth rate in dense two-dimensional arrays, in agreement with a calculation of the shadowing of the scattered precursors. Due to the impact of these effects on growth, they should be considered during selective-area vapor-liquid-solid nanowire epitaxy.

  6. Creating Ruddlesden-Popper phases by hybrid molecular beam epitaxy

    Science.gov (United States)

    Haislmaier, Ryan C.; Stone, Greg; Alem, Nasim; Engel-Herbert, Roman

    2016-07-01

    The synthesis of a 50 unit cell thick n = 4 Srn+1TinO3n+1 (Sr5Ti4O13) Ruddlesden-Popper (RP) phase film is demonstrated by sequentially depositing SrO and TiO2 layers in an alternating fashion using hybrid molecular beam epitaxy (MBE), where Ti was supplied using titanium tetraisopropoxide (TTIP). A detailed calibration procedure is outlined for determining the shuttering times to deposit SrO and TiO2 layers with precise monolayer doses using in-situ reflection high energy electron diffraction (RHEED) as feedback. Using optimized Sr and TTIP shuttering times, a fully automated growth of the n = 4 RP phase was carried out over a period of >4.5 h. Very stable RHEED intensity oscillations were observed over the entire growth period. The structural characterization by X-ray diffraction and high resolution transmission electron microscopy revealed that a constant periodicity of four SrTiO3 perovskite unit cell blocks separating the double SrO rocksalt layer was maintained throughout the entire film thickness with a very little amount of planar faults oriented perpendicular to the growth front direction. These results illustrate that hybrid MBE is capable of layer-by-layer growth with atomic level precision and excellent flux stability.

  7. Creating Ruddlesden-Popper phases by hybrid molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Haislmaier, Ryan C.; Stone, Greg; Alem, Nasim; Engel-Herbert, Roman, E-mail: rue2@psu.edu [Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)

    2016-07-25

    The synthesis of a 50 unit cell thick n = 4 Sr{sub n+1}Ti{sub n}O{sub 3n+1} (Sr{sub 5}Ti{sub 4}O{sub 13}) Ruddlesden-Popper (RP) phase film is demonstrated by sequentially depositing SrO and TiO{sub 2} layers in an alternating fashion using hybrid molecular beam epitaxy (MBE), where Ti was supplied using titanium tetraisopropoxide (TTIP). A detailed calibration procedure is outlined for determining the shuttering times to deposit SrO and TiO{sub 2} layers with precise monolayer doses using in-situ reflection high energy electron diffraction (RHEED) as feedback. Using optimized Sr and TTIP shuttering times, a fully automated growth of the n = 4 RP phase was carried out over a period of >4.5 h. Very stable RHEED intensity oscillations were observed over the entire growth period. The structural characterization by X-ray diffraction and high resolution transmission electron microscopy revealed that a constant periodicity of four SrTiO{sub 3} perovskite unit cell blocks separating the double SrO rocksalt layer was maintained throughout the entire film thickness with a very little amount of planar faults oriented perpendicular to the growth front direction. These results illustrate that hybrid MBE is capable of layer-by-layer growth with atomic level precision and excellent flux stability.

  8. Topological Insulator Film Growth by Molecular Beam Epitaxy: A Review

    Directory of Open Access Journals (Sweden)

    Theresa P. Ginley

    2016-11-01

    Full Text Available In this article, we will review recent progress in the growth of topological insulator (TI thin films by molecular beam epitaxy (MBE. The materials we focus on are the V2-VI3 family of TIs. These materials are ideally bulk insulating with surface states housing Dirac excitations which are spin-momentum locked. These surface states are interesting for fundamental physics studies (such as the search for Majorana fermions as well as applications in spintronics and other fields. However, the majority of TI films and bulk crystals exhibit significant bulk conductivity, which obscures these states. In addition, many TI films have a high defect density. This review will discuss progress in reducing the bulk conductivity while increasing the crystal quality. We will describe in detail how growth parameters, substrate choice, and growth technique influence the resulting TI film properties for binary and ternary TIs. We then give an overview of progress in the growth of TI heterostructures. We close by discussing the bright future for TI film growth by MBE.

  9. Ferromagnetism in Mn-Implanted Epitaxially Grown Ge on Si(100)

    Energy Technology Data Exchange (ETDEWEB)

    Guchhait, S.; Jamil, M.; Ohldag, H.; Mehta, A.; Arenholz, E.; Lian, G.; Li Fatou, A.; Ferrer, D. A.; Markert, J. T.; Colombo, L.; Banerjee, S. K.

    2011-01-05

    We have studied ferromagnetism of Mn-implanted epitaxial Ge films on silicon. The Ge films were grown by ultrahigh vacuum chemical vapor deposition using a mixture of germane (GeH{sub 4}) and methylgermane (CH{sub 3}GeH{sub 3}) gases with a carbon concentration of less than 1 at. %, and observed surface rms roughness of 0.5 nm, as measured by atomic force microscopy. Manganese ions were implanted in epitaxial Ge films grown on Si (100) wafers to an effective concentration of 16, 12, 6, and 2 at. %. Superconducting quantum interference device measurements showed that only the three highest Mn concentration samples are ferromagnetic, while the fourth sample, with [Mn] = 2 at. %, is paramagnetic. X-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements indicate that localized Mn moments are ferromagnetically coupled below the Curie temperature. Isothermal annealing of Mn-implanted Ge films with [Mn] = 16 at. % at 300 C for up to 1200 s decreases the magnetization but does not change the Curie temperature, suggesting that the amount of the magnetic phase slowly decreases with time at this anneal temperature. Furthermore, transmission electron microscopy and synchrotron grazing incidence x-ray diffraction experiments show that the Mn-implanted region is amorphous, and we believe that it is this phase that is responsible for the ferromagnetism. This is supported by our observation that high-temperature annealing leads to recrystallization and transformation of the material into a paramagnetic phase.

  10. Dilute GaAsN and GaInAsN grown by liquid phase epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Milanova, M; Koleva, G; Kakanakov, R [Central Laboratory of Applied Physics, Bulgarian Academy of Sciences, 59 St. Petersburg Blvd, 4000 Plovdiv (Bulgaria); Vitanov, P K; Alexieva, Z; Goranova, E A [Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia (Bulgaria); Arnaudov, B; Evtimova, S [Faculty of Physics, St. Kl. Ohridski University of Sofia, 5 J. Bourchier Blvd, 1164 Sofia (Bulgaria); Barthou, C; Clerjaud, B, E-mail: vitanov@phys.bas.b [Universite Pierre et Marie Curie, Institut des NanoSciences de Paris, rue de Lourmel 140, 75015 Paris (France)

    2010-04-01

    Dilute III-nitrides, such as GaAsN and GaInAsN, are of considerable current interest both from a fundamental point of view and for applications in solar cells, GaAs-based long-wavelength photodetectors and diode lasers. The addition of nitrogen leads to material properties that deviate strongly from those expected for conventional III-V solid solutions. The possibility was investigated to use liquid phase epitaxy to incorporate nitrogen in epitaxial GaAsN/GaAs and GaInAsN/GaAs heterostructures. The structures were grown from Ga- and Ga-In- melts containing powder GaN as a nitrogen source. The initial growth temperature was varied in the range 560{sup 0}C - 660{sup 0}C. The low temperature growth favors nitrogen incorporation in the epilayers. The optical transmission and photoluminescence spectra of a set of structures grown at different temperatures were studied showing ternary and quaternary dilute nitride solid solutions with nitrogen content about 0.2 at.%. The photoluminescence spectra show emission from localized nitrogen states as well.

  11. Dilute GaAsN and GaInAsN grown by liquid phase epitaxy

    Science.gov (United States)

    Milanova, M.; Koleva, G.; Kakanakov, R.; Vitanov, P. K.; Alexieva, Z.; Goranova, E. A.; Arnaudov, B.; Evtimova, S.; Barthou, C.; Clerjaud, B.

    2010-04-01

    Dilute III-nitrides, such as GaAsN and GaInAsN, are of considerable current interest both from a fundamental point of view and for applications in solar cells, GaAs-based long-wavelength photodetectors and diode lasers. The addition of nitrogen leads to material properties that deviate strongly from those expected for conventional III-V solid solutions. The possibility was investigated to use liquid phase epitaxy to incorporate nitrogen in epitaxial GaAsN/GaAs and GaInAsN/GaAs heterostructures. The structures were grown from Ga- and Ga-In- melts containing powder GaN as a nitrogen source. The initial growth temperature was varied in the range 560°C - 660°C. The low temperature growth favors nitrogen incorporation in the epilayers. The optical transmission and photoluminescence spectra of a set of structures grown at different temperatures were studied showing ternary and quaternary dilute nitride solid solutions with nitrogen content about 0.2 at.%. The photoluminescence spectra show emission from localized nitrogen states as well.

  12. Ferromagnetism in Mn-Implanted Epitaxially Grown Ge on Si(100)

    Energy Technology Data Exchange (ETDEWEB)

    Guchhait, S.; Jamil, M.; Ohldag, H.; Mehta, A.; Arenholz, E.; Lian, G.; Li Fatou, A.; Ferrer, D. A.; Markert, J. T.; Colombo, L.; Banerjee, S. K.

    2011-01-05

    We have studied ferromagnetism of Mn-implanted epitaxial Ge films on silicon. The Ge films were grown by ultrahigh vacuum chemical vapor deposition using a mixture of germane (GeH{sub 4}) and methylgermane (CH{sub 3}GeH{sub 3}) gases with a carbon concentration of less than 1 at. %, and observed surface rms roughness of 0.5 nm, as measured by atomic force microscopy. Manganese ions were implanted in epitaxial Ge films grown on Si (100) wafers to an effective concentration of 16, 12, 6, and 2 at. %. Superconducting quantum interference device measurements showed that only the three highest Mn concentration samples are ferromagnetic, while the fourth sample, with [Mn] = 2 at. %, is paramagnetic. X-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements indicate that localized Mn moments are ferromagnetically coupled below the Curie temperature. Isothermal annealing of Mn-implanted Ge films with [Mn] = 16 at. % at 300 C for up to 1200 s decreases the magnetization but does not change the Curie temperature, suggesting that the amount of the magnetic phase slowly decreases with time at this anneal temperature. Furthermore, transmission electron microscopy and synchrotron grazing incidence x-ray diffraction experiments show that the Mn-implanted region is amorphous, and we believe that it is this phase that is responsible for the ferromagnetism. This is supported by our observation that high-temperature annealing leads to recrystallization and transformation of the material into a paramagnetic phase.

  13. Periodic Two-Dimensional GaAs and InGaAs Quantum Rings Grown on GaAs (001) by Droplet Epitaxy.

    Science.gov (United States)

    Tung, Kar Hoo Patrick; Huang, Jian; Danner, Aaron

    2016-06-01

    Growth of ordered GaAs and InGaAs quantum rings (QRs) in a patterned SiO2 nanohole template by molecular beam epitaxy (MBE) using droplet epitaxy (DE) process is demonstrated. DE is an MBE growth technique used to fabricate quantum nanostructures of high crystal quality by supplying group III and group V elements in separate phases. In this work, ordered QRs grown on an ordered nanohole template are compared to self-assembled QRs grown with the same DE technique without the nanohole template. This study allows us to understand and compare the surface kinetics of Ga and InGa droplets when a template is present. It is found that template-grown GaAs QRs form clustered rings which can be attributed to low mobility of Ga droplets resulting in multiple nucleation sites for QR formation when As is supplied. However, the case of template-grown InGaAs QRs only one ring is formed per nanohole; no clustering is observed. The outer QR diameter is a close match to the nanohole template diameter. This can be attributed to more mobile InGa droplets, which coalesce from an Ostwald ripening to form a single large droplet before As is supplied. Thus, well-patterned InGaAs QRs are demonstrated and the kinetics of their growth are better understood which could potentially lead to improvements in the future devices that require the unique properties of patterned QRs.

  14. Epitaxial Fe3Si films on GaAs(100) substrates by means of electron beam evaporation

    Science.gov (United States)

    Thomas, J.; Schumann, J.; Vinzelberg, H.; Arushanov, E.; Engelhard, R.; Schmidt, O. G.; Gemming, T.

    2009-06-01

    This paper presents results on the preparation, structural, electrical and magnetic properties of Fe3Si films as a representative for a Heusler alloy-like compound which are known as half-metallic materials with ferromagnetic behaviour. The films have been prepared by means of ultra-high vacuum (UHV) electron beam evaporation with the aim of achieving epitaxial growth on GaAs(100) substrates. The main focus of this work is the structural characterization of the Fe3Si films grown on GaAs by means of high resolution transmission electron microscopy (TEM) to confirm the epitaxial growth. For Fe3Si with a composition in the vicinity of stoichiometry an almost lattice-matched growth on GaAs(001) has been observed characterized by a high crystalline quality and a good interface perfection. Besides the studies on cross-sectional samples by TEM data from reflection high energy electron diffraction (RHEED) and x-ray diffraction (XRD) were also included into the discussion. The electrical and magnetic parameters of the films studied are found to be in good agreement with data reported for the best Fe3Si molecular beam epitaxy (MBE) layers. As evidenced by x-ray diffraction, transmission electron microscopy, resistivity and magnetic measurements, we find an optimum growth temperature of 280-350 °C to obtain ferromagnetic layers with high crystal and interface perfection as well as a high degree of atomic ordering.

  15. Molecular beam epitaxy of thin HfTe2 semimetal films

    Science.gov (United States)

    Aminalragia-Giamini, S.; Marquez-Velasco, J.; Tsipas, P.; Tsoutsou, D.; Renaud, G.; Dimoulas, A.

    2017-03-01

    Epitaxial thin films of 1T-HfTe2 semimetal are grown by MBE on AlN(0001) substrates. The measured in-plane lattice parameter indicates an unstrained film which is also azimuthally aligned with the AlN substrate, albeit with an in-plane mosaic spread, as it would be expected for van der Waals epitaxy. Angle resolved photoemission spectroscopy combined with first principles electronic band structure calculations show steep linearly dispersing conduction and valence bands which cross near the Brillouin zone center, providing evidence that HfTe2/AlN is an epitaxial topological Dirac semimetal.

  16. Molecular beam epitaxy of InN dots on nitrided sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Romanyuk, Yaroslav E.; Dengel, Radu-Gabriel; Stebounova, LarissaV.; Leone, Stephen R.

    2007-04-20

    A series of self-assembled InN dots are grown by radio frequency (RF) plasma-assisted molecular beam epitaxy (MBE) directly on nitrided sapphire. Initial nitridation of the sapphire substrates at 900 C results in the formation of a rough AlN surface layer, which acts as a very thin buffer layer and facilitates the nucleation of the InN dots according to the Stranski-Krastanow growth mode, with a wetting layer of {approx}0.9 nm. Atomic force microscopy (AFM) reveals that well-confined InN nanoislands with the greatest height/width at half-height ratio of 0.64 can be grown at 460 C. Lower substrate temperatures result in a reduced aspect ratio due to a lower diffusion rate of the In adatoms, whereas the thermal decomposition of InN truncates the growth at T>500 C. The densities of separated dots vary between 1.0 x 10{sup 10} cm{sup -2} and 2.5 x 10{sup 10} cm{sup -2} depending on the growth time. Optical response of the InN dots under laser excitation is studied with apertureless near-field scanning optical microscopy and photoluminescence spectroscopy, although no photoluminescence is observed from these samples. In view of the desirable implementation of InN nanostructures into photonic devices, the results indicate that nitrided sapphire is a suitable substrate for growing self-assembled InN nanodots.

  17. Molecular beam epitaxy of InN dots on nitrided sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Romanyuk, Yaroslav E.; Dengel, Radu-Gabriel; Stebounova, LarissaV.; Leone, Stephen R.

    2007-04-20

    A series of self-assembled InN dots are grown by radio frequency (RF) plasma-assisted molecular beam epitaxy (MBE) directly on nitrided sapphire. Initial nitridation of the sapphire substrates at 900 C results in the formation of a rough AlN surface layer, which acts as a very thin buffer layer and facilitates the nucleation of the InN dots according to the Stranski-Krastanow growth mode, with a wetting layer of {approx}0.9 nm. Atomic force microscopy (AFM) reveals that well-confined InN nanoislands with the greatest height/width at half-height ratio of 0.64 can be grown at 460 C. Lower substrate temperatures result in a reduced aspect ratio due to a lower diffusion rate of the In adatoms, whereas the thermal decomposition of InN truncates the growth at T>500 C. The densities of separated dots vary between 1.0 x 10{sup 10} cm{sup -2} and 2.5 x 10{sup 10} cm{sup -2} depending on the growth time. Optical response of the InN dots under laser excitation is studied with apertureless near-field scanning optical microscopy and photoluminescence spectroscopy, although no photoluminescence is observed from these samples. In view of the desirable implementation of InN nanostructures into photonic devices, the results indicate that nitrided sapphire is a suitable substrate for growing self-assembled InN nanodots.

  18. Graphitic platform for self-catalysed InAs nanowires growth by molecular beam epitaxy.

    Science.gov (United States)

    Zhuang, Qian D; Anyebe, Ezekiel A; Sanchez, Ana M; Rajpalke, Mohana K; Veal, Tim D; Zhukov, Alexander; Robinson, Benjamin J; Anderson, Frazer; Kolosov, Oleg; Fal'ko, Vladimir

    2014-01-01

    We report the self-catalysed growth of InAs nanowires (NWs) on graphite thin films using molecular beam epitaxy via a droplet-assisted technique. Through optimising metal droplets, we obtained vertically aligned InAs NWs with highly uniform diameter along their entire length. In comparison with conventional InAs NWs grown on Si (111), the graphite surface led to significant effects on the NWs geometry grown on it, i.e. larger diameter, shorter length with lower number density, which were ascribed to the absence of dangling bonds on the graphite surface. The axial growth rate of the NWs has a strong dependence on growth time, which increases quickly in the beginning then slows down after the NWs reach a length of approximately 0.8 μm. This is attributed to the combined axial growth contributions from the surface impingement and sidewall impingement together with the desorption of adatoms during the diffusion. The growth of InAs NWs on graphite was proposed following a vapour-solid mechanism. High-resolution transmission electron microscopy reveals that the NW has a mixture of pure zinc-blende and wurtzite insertions.

  19. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R., E-mail: smitha2@ohio.edu [Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701 (United States)

    2014-04-15

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  20. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy.

    Science.gov (United States)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R

    2014-04-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  1. GaIn As Quantum Dots (QD) grown by Liquid Phase Epitaxy (LPE)

    Energy Technology Data Exchange (ETDEWEB)

    Ortiz Vazquez, F E; Mishurnyi, V A; Gorbatchev, A Yu; De Anda, F [Universidad Autonoma de San Luis Potosi, Instituto de Investigation en Comunicacion Optica, Av. Karakorum 1470, Col. Lomas 4a Sec., San Luis Potosi, SLP, CP 78210 (Mexico); Elyukhin, V A, E-mail: fcoe_ov@prodigy.net.m, E-mail: andre@cactus.iico.uaslp.m [CINVESTAV-IPN, Av. IPN 2508, Col. San Pedro Zacatenco, Mexico D.F., CP 07360 (Mexico)

    2009-05-01

    The majority of the semiconductor structures with QD today are grown by MBE and MOCVD. It is known that the best material quality can be achieved by LPE because, in contrast to MBE and MOCVD, this method is realized at near-equilibrium conditions. To develop QD LPE technology first of all it is necessary to find out a growth technique allowing the crystallization of epitaxial materials with very small volume. This can be done by means of different techniques. In this work we apply a low temperature short-time growth method, which allows the production not only of single, but also of multilayer heterostructures. We have grown Ga{sub x}In{sub 1-z}As QD on GaAs (100) substrates at 450 C. The details of the QD formation, depending on composition of the Ga{sub x}In{sub -x} As solid solutions, have been studied by atom-force microscopy. The photoluminescence spectra of investigated samples show, in addition to a short-wave GaAs related peak, a longer wavelength line, which disappears after removal of the grown GaInAs material using an etching solution. This fact, together with atom-force microscopy results can be interpreted as a proof that QD heterostructures were grown successfully by LPE.

  2. 垂直磁各向异性L10-Mn1.67Ga超薄膜分子束外延生长与磁性研究∗%Perp endicular magnetic prop erties of ultrathin L10-Mn1.67Ga films grown by molecular-beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    肖嘉星; 鲁军; 朱礼军; 赵建华

    2016-01-01

    Materials with large perpendicular magnetic anisotropies (PMAs) have drawn great attention because of their potential applications in advanced spintronic devices such as spin-transfer-torque magnetic random access memory (STT-MRAM) and ultrahigh-density perpendicular magnetic recording. To date, a large variety of PMA materials have been investigated, such as L10-ordered FePt, CoPt granular films, Co/(Pt,Pd,Ni) multilayers, ultra-thin CoFeB alloys and perpendicularly magnetized Co2FeAl films. Among the various kinds of materials with PMA, MnGa film with L10-structure has received the most attention because it has large PMA (Ku ∼107 erg/cm3), ultralow Gilbert damping constant (0.008) and theoretically predicted high spin polarization (more than 70%). All these properties make L10-ordered MnGa a good candidate for spintronic devices such as STT-MRAM and spin-torque oscillators. Meanwhile, from the viewpoint of STT related spintronic device, it is necessary to fabricate ultrathin perpendicularly magnetized L10-MnxGa films to lower the critical current for magnetization reversal. However, up to now, in the main researches the ultrathin L10-MnxGa films have been grown on MgO substrates, which makes it difficult to integrate the MnGa-based magnetic tunnel junctions into the semiconductor manufacturing process. In this work, ultrathin L10-Mn1.67Ga films with different thickness values (1–5 nm) are grown on traditional GaAa (001) substrates by a molecule-beam epitaxy system. During the deposition, in situ streaky surface reconstruction patterns are observed from reflection high-energy electron diffraction, which implies high crystalline quality of the L10-Mn1.67Ga film. Only MnGa superlattice (001) and MnGa fundamental (002) peaks can be observed in the X-ray diffraction patterns in a range from 20◦ to 70◦, which means that the L10-Mn1.67Ga film is a good single-crystalline with c-axis along the normal direction. The magnetic properties of these films are measured

  3. Molecular beam epitaxy engineered III-V semiconductor structures for low-power optically addressed spatial light modulators

    Science.gov (United States)

    Larsson, Anders G.; Maserjian, Joseph

    1992-01-01

    Device approaches are investigated for optically addressed SLMs based on molecular-beam epitaxy (MBE) engineered III-V materials and structures. Strong photooptic effects can be achieved in periodically delta-doped multiple-quantum-well structures, but are still insufficient for high-contrast modulation with only single- or double-pass absorption through active layers of practical thickness. The asymmetric Fabry-Perot cavity approach is employed to permit extinction of light due to interference of light reflected from the front and back surfaces of the cavity. This approach is realized with an all-MBE-grown structure consisting of GaAs/AlAs quarter-wave stack reflector grown over the GaAs substrate as the high reflectance mirror and the GaAs surface as the low reflectance mirror. High-contrast modulation is achieved using a low-power InGaAs/GaAs quantum well laser for the control signal.

  4. Columnar structured FePt films epitaxially grown on large lattice mismatched intermediate layer

    Science.gov (United States)

    Dong, K. F.; Deng, J. Y.; Peng, Y. G.; Ju, G.; Chow, G. M.; Chen, J. S.

    2016-09-01

    The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) //ZrN (001) //TiN (001) among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained.

  5. Impact of LT-GaAs layers on crystalline properties of the epitaxial GaAs films grown by MBE on Si substrates

    Science.gov (United States)

    Petrushkov, M. O.; Putyato, M. A.; Gutakovsky, A. K.; Preobrazhenskii, V. V.; Loshkarev, I. D.; Emelyanov, E. A.; Semyagin, B. R.; Vasev, A. V.

    2016-08-01

    GaAs films with low-temperature GaAs (LT-GaAs) layers were grown by molecular beam epitaxy (MBE) method on vicinal (001) Si substrates oriented 6° off towards [110]. The grown structures were different with the thickness of LT-GaAs layers and its arrangement in the film. The processes of epitaxial layers nucleation and growth were controlled by reflection high energy electron diffraction (RHEED) method. Investigations of crystalline properties of the grown structures were carried out by the methods of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The crystalline perfection of the GaAs films with LT-GaAs layers and the GaAs films without ones was comparable. It was found that in the LT- GaAs/Si layers the arsenic clusters are formed, as it occurs in the LT-GaAs/GaAs system without dislocation. It is shown that large clusters are formed mainly on the dislocations. However, the clusters have practically no effect on the density and the propagation path of threading dislocations. With increasing thickness of LT-GaAs layer the dislocations are partly bent along the LT-GaAs/GaAs interface due to the presence of stresses.

  6. Study of the defects in GaN epitaxial films grown on sapphire by HVPE

    Science.gov (United States)

    Liu, Zhanhui; Xiu, Xiangqian; Chen, Lin; Zhang, Rong; Xie, Zili; Han, Ping; Shi, Yi; Gu, Shulin; Zheng, Youdou

    2008-02-01

    In this paper, the defects in hexagonal GaN epitaxial layers grown on (0001) sapphire (Al IIO 3) substrates by HVPE with a horizontal tube reactor had been studied. The GaN epitaxial layers were etched by means of defect-selective etching (Orthodox etching in molten KOH). The samples were characterized by Scanning Electron Microscopy (SEM) and Cathodoluminescence spectra (CL). From surface morphology and cross-sectional images, the defects could be divided into various types: cracks, low angle grain boundary (LAGB), nano-pipes and dislocations. These different defects were discussed. The cracks were proposed as related to the strain. And the strain could not only come from the lattice mismatch and thermal mismatch between sapphire and GaN layer in their interface, but also from the HVPE growth process. It was found that these screw, mixed and edge type dislocations formed small hexagonal pits after etching. Some pits would be observed in the area near LAGB. Additionally, by CL mapping technique, some non-radiative recombination centers without surface terminations could be probed optically.

  7. Rare-earth-ion doped KY(WO4)2 optical waveguides grown by liquid-phase epitaxy

    NARCIS (Netherlands)

    Romanyuk, Y.E.; Apostolopoulos, V.; Utke, U.; Pollnau, Markus

    2004-01-01

    High-quality KY(WO4)2 thin layers doped with rare-earth-ions were grown using liquid-phase epitaxy. A low-temperature mixture of chlorides was used as the flux and undoped KY(WO4)2 crystals as substrates. The crystalline layers possessed thicknesses up to 10 µm. Passive and active planar waveguiding

  8. Green semipolar III-nitride light-emitting diodes grown by limited area epitaxy

    Science.gov (United States)

    Pynn, C. D.; Kowsz, S. J.; Oh, S. H.; Gardner, H.; Farrell, R. M.; Nakamura, S.; Speck, J. S.; DenBaars, S. P.

    2016-07-01

    The performance of multiple quantum well green and yellow semipolar light-emitting diodes (LEDs) is limited by relaxation of highly strained InGaN-based active regions and the subsequent formation of nonradiative defects. Limited area epitaxy was used to block glide of substrate threading dislocations and to reduce the density of misfit dislocations (MDs) directly beneath the active region of (20 2 ¯ 1 ) LEDs. Devices were grown and fabricated on a 1D array of narrow substrate mesas to limit the MD run length. Reducing the mesa width from 20 μm to 5 μm lowered the density of basal plane and non-basal plane MDs on the mesas and limited the number of defect-generating dislocation intersections. This improvement in material quality yielded a 73% enhancement in peak external quantum efficiency for the devices with the narrowest mesas compared to the devices with the widest mesas.

  9. Electronic and geometric corrugation of periodically rippled, self-nanostructured graphene epitaxially grown on Ru(0001)

    Energy Technology Data Exchange (ETDEWEB)

    Borca, Bogdana; Barja, Sara; Garnica, Manuela; Rodriguez-GarcIa, Josefa M; Hinarejos, Juan Jose; FarIas, Daniel; Parga, Amadeo L Vazquez de; Miranda, Rodolfo [Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, Cantoblanco 28049, Madrid (Spain); Minniti, Marina; Politano, Antonio, E-mail: al.vazquezdeparga@uam.e [Instituto Madrileno de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco 28049, Madrid (Spain)

    2010-09-15

    Graphene epitaxially grown on Ru(0001) displays a remarkably ordered pattern of hills and valleys in scanning tunneling microscopy (STM) images. The extent to which the observed 'ripples' are structural or electronic in origin has been much disputed recently. A combination of ultrahigh-resolution STM images and helium atom diffraction data shows that (i) the graphene lattice is rotated with respect to the lattice of Ru and (ii) the structural corrugation as determined from He diffraction is substantially smaller (0.15 A) than predicted (1.5 A) or reported from x-ray diffraction or low-energy electron diffraction. The electronic corrugation, on the contrary, is strong enough to invert the contrast between hills and valleys above +2.6 V as new, spatially localized electronic states enter the energy window of the STM. The large electronic corrugation results in a nanostructured periodic landscape of electron and hole pockets.

  10. Energy Bandgap and Edge States in an Epitaxially Grown Graphene/h-BN Heterostructure.

    Science.gov (United States)

    Hwang, Beomyong; Hwang, Jeongwoon; Yoon, Jong Keon; Lim, Sungjun; Kim, Sungmin; Lee, Minjun; Kwon, Jeong Hoon; Baek, Hongwoo; Sung, Dongchul; Kim, Gunn; Hong, Suklyun; Ihm, Jisoon; Stroscio, Joseph A; Kuk, Young

    2016-08-09

    Securing a semiconducting bandgap is essential for applying graphene layers in switching devices. Theoretical studies have suggested a created bulk bandgap in a graphene layer by introducing an asymmetry between the A and B sub-lattice sites. A recent transport measurement demonstrated the presence of a bandgap in a graphene layer where the asymmetry was introduced by placing a graphene layer on a hexagonal boron nitride (h-BN) substrate. Similar bandgap has been observed in graphene layers on metal substrates by local probe measurements; however, this phenomenon has not been observed in graphene layers on a near-insulating substrate. Here, we present bulk bandgap-like features in a graphene layer epitaxially grown on an h-BN substrate using scanning tunneling spectroscopy. We observed edge states at zigzag edges, edge resonances at armchair edges, and bandgap-like features in the bulk.

  11. TEM investigation of beta-SiC grown epitaxially on Si substrate by CVD

    Science.gov (United States)

    Chorey, C. M.; Pirouz, P.; Mitchell, T. E.; Powell, J. A.

    1987-01-01

    A transmission electron microscopy study is being conducted on the microstructure of beta-SiC films grown epitaxially on 001-plane silicon by chemical vapor deposition. Observations have been made in plain view and in cross-section. A high density of stacking faults has been found in the bulk of the epilayer which are bounded by partials of the Shockley type with Burgers vectors 1/6 211-line. Cross-sectional high resolution electron microscopy of the interface has shown it to be semicoherent with misfit dislocations to accommodate the lattice parameter difference between the substrate and the epilayer. In addition to misfit dislocations, a high density of twins and some stacking faults are present in the SiC near the interface. Mechanisms for the nucleation and growth of these defects are discussed.

  12. Energy Bandgap and Edge States in an Epitaxially Grown Graphene/h-BN Heterostructure

    Science.gov (United States)

    Hwang, Beomyong; Hwang, Jeongwoon; Yoon, Jong Keon; Lim, Sungjun; Kim, Sungmin; Lee, Minjun; Kwon, Jeong Hoon; Baek, Hongwoo; Sung, Dongchul; Kim, Gunn; Hong, Suklyun; Ihm, Jisoon; Stroscio, Joseph A.; Kuk, Young

    2016-08-01

    Securing a semiconducting bandgap is essential for applying graphene layers in switching devices. Theoretical studies have suggested a created bulk bandgap in a graphene layer by introducing an asymmetry between the A and B sub-lattice sites. A recent transport measurement demonstrated the presence of a bandgap in a graphene layer where the asymmetry was introduced by placing a graphene layer on a hexagonal boron nitride (h-BN) substrate. Similar bandgap has been observed in graphene layers on metal substrates by local probe measurements; however, this phenomenon has not been observed in graphene layers on a near-insulating substrate. Here, we present bulk bandgap-like features in a graphene layer epitaxially grown on an h-BN substrate using scanning tunneling spectroscopy. We observed edge states at zigzag edges, edge resonances at armchair edges, and bandgap-like features in the bulk.

  13. Step-Free GaN Hexagons Grown by Selective-Area Metalorganic Vapor Phase Epitaxy

    Science.gov (United States)

    Akasaka, Tetsuya; Kobayashi, Yasuyuki; Kasu, Makoto

    2009-09-01

    Selective-area metalorganic vapor phase epitaxy of GaN has been investigated using the optimized growth conditions for the layer (Frank-van der Merwe) growth and GaN-template substrates with low dislocation density. The surface of a GaN hexagon with 16-µm diameter has a single wide terrace over almost the whole area (step-free surface), when there are no screw-type dislocations in the finite area. Step-free GaN hexagons grew in the two-dimensional nucleus growth mode and had approximately an eight times lower growth rate than that of a GaN film grown in the step-flow mode under the growth conditions used in this study.

  14. Photopeak detection by an InSb radiation detector made of liquid phase epitaxially grown crystals

    Energy Technology Data Exchange (ETDEWEB)

    Sato, Yuki, E-mail: Y.Sato@nucleng.kyoto-u.ac.j [Graduate School of Engineering, Kyoto University, Sakyo, Kyoto 606-8501 (Japan); Morita, Yasunari; Harai, Tomoyuki; Kanno, Ikuo [Graduate School of Engineering, Kyoto University, Sakyo, Kyoto 606-8501 (Japan)

    2010-09-21

    We have fabricated a radiation detector using a p-type InSb crystal grown by liquid phase epitaxy (LPE). At temperatures below 100 K, the resistivity of the LPE crystal was over an order of magnitude higher than that of the commercial InSb crystal substrate. The resistance of the InSb detector is 680 k{Omega} at 4.2 K, which is one order of magnitude higher than that of detectors fabricated from commercial InSb wafers and, in an improvement over previous results, the energy resolution of {sup 241}Am alpha particles reaches 3%. In addition, we also observe the photopeak of gamma-rays emitted by {sup 133}Ba.

  15. Electrical transport and magnetic properties of epitaxial LSMO films grown on STO substrates

    Science.gov (United States)

    Yuan, Wei; Zhao, Yuelei; Su, Tang; Song, Qi; Han, Wei; Shi, Jing

    2015-03-01

    La0.7Sr0.3MnO3 (LSMO) is a very attractive material for spintronics due to its half-metallic ferromagnetic properties. The LSMO films are epitaxially grown on STO (100) substrates using pulsed laser deposition. The effects of substrate temperature, laser power, oxygen pressure, and annealing on the LSMO growth are systematically investigated by the reflection high energy electron diffraction and atomic force microscopy. Under the optimized growth condition, we have achieved atomically flat LSMO thin films with a wide terrace width of more than 5 micro-meters. The electrical transport properties of LSMO thin films of various thicknesses ranging from 8 to 20 monolayers are studied by measuring the resistivity as a function of temperature. We find that the growth condition plays an important role in the critical film thickness for the metal-insulator transition and the Curie temperature. The Ministry of Science and Technology of China.

  16. Strain-relaxation in NH{sub 3}-source molecular beam epitaxy of AlN epilayers on GaN epitaxial templates

    Energy Technology Data Exchange (ETDEWEB)

    Koyama, T.; Onuma, T.; Chichibu, S.F. [Institute of Applied Physics and Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573 (Japan); NICP, ERATO, Japan Science and Technology Agency (JST), Kawaguchi 332-0012 (Japan); Sugawara, M.; Uchinuma, Y. [Institute of Applied Physics and Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573 (Japan); Kaeding, J.F.; Sharma, R. [Department of Materials Engineering, University of California, Santa Barbara, CA 93106 (United States); Nakamura, S. [NICP, ERATO, Japan Science and Technology Agency (JST), Kawaguchi 332-0012 (Japan); Department of Materials Engineering, University of California, Santa Barbara, CA 93106 (United States)

    2006-05-15

    Temporal evolution of surface morphology in AlN epilayers grown by NH{sub 3}-source molecular beam epitaxy on the GaN/(0001) Al{sub 2}O{sub 3} epitaxial templates was correlated with changes in the degree of the residual strain and the layer thickness. They began to crack for the thickness as thin as 10 nm. However, atomic-layer step-and-terrace surface structures were maintained for the thickness up to 32 nm. Tensile biaxial stress decreased with further increase in the thickness due to the lattice relaxation, which caused surface roughening. An 1580-nm-thick, nearly strain-compensated AlN epilayer, of which threading dislocation density was reduced down to 6 x 10{sup 9} cm{sup -2}, exhibited excitonic photoluminescence peaks at 6.002 and 6.023 eV at 9 K and a near-band-edge peak at 5.872 eV at 293 K. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Very low-temperature epitaxial growth of Mn{sub 5}Ge{sub 3} and Mn{sub 5}Ge{sub 3}C{sub 0.2} films on Ge(111) using molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Petit, Matthieu, E-mail: matthieu.petit@univ-amu.fr [Aix-Marseille Université, CNRS, CINaM UMR 7325, 13288 Marseille (France); Michez, Lisa [Aix-Marseille Université, CNRS, CINaM UMR 7325, 13288 Marseille (France); Dutoit, Charles-Emmanuel; Bertaina, Sylvain; Dolocan, Voicu O. [Aix-Marseille Université, CNRS, IM2NP UMR7334, 13397 Cedex 20 Marseille (France); Heresanu, Vasile [Aix-Marseille Université, CNRS, CINaM UMR 7325, 13288 Marseille (France); Stoffel, Mathieu [Université de Lorraine, UMR CNRS 7198, Institut Jean Lamour, BP 70239, 54506 Vandeuvre-lès-Nancy (France); Le Thanh, Vinh [Aix-Marseille Université, CNRS, CINaM UMR 7325, 13288 Marseille (France)

    2015-08-31

    C-doped Mn{sub 5}Ge{sub 3} compound is ferromagnetic at temperature up to 430 K. Hence it is a potential spin injector into group-IV semiconductors. Segregation and diffusion of Mn at the Mn{sub 5}Ge{sub 3}/Ge interface could severely hinder the efficiency of the spin injection. To avoid these two phenomena we investigate the growth of Mn{sub 5}Ge{sub 3} and C-doped Mn{sub 5}Ge{sub 3} films on Ge(111) substrates by molecular beam epitaxy at room-temperature. The reactive deposition epitaxy method is used to deposit these films. Reflection high energy electron diffraction, X-ray diffraction analysis, transmission electron microscopy and atomic force microscopy indicate that the crystalline quality is very high. Magnetic characterizations by superconducting quantum interference device and ferromagnetic resonance reinforce the structural analysis results on the thin film quality. - Highlights: • Epitaxial Mn{sub 5}Ge{sub 3} and C-doped Mn{sub 5}Ge{sub 3} films grown on Ge(111) at room temperature. • Mn{sub 5}Ge{sub 3} and C-doped Mn{sub 5}Ge{sub 3} films grown by reactive deposition epitaxy. • RHEED, XRD and TEM measurements show a very high crystallinity. • Magnetic measurements support the structural analysis in the crystalline quality. • Ferromagnetic resonance linewidth is very narrow (3.5 mT at RT)

  18. Structural and magnetic properties of epitaxial Fe/Cu multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Y. E-mail: t5101008@iwate-u.ac.jp; Nakanishi, Y.; Yoshimoto, N.; Yamaguchi, A.; Nakamura, M.; Yoshizawa, M

    2004-05-01

    We have grown FCC-Fe/Cu multilayers by molecular beam epitaxy method. The structural and magnetic properties were studied by RHEED, XRD and magnetoresistance measurement (MR). The RHEED images confirmed that Fe/Cu multilayers were epitaxially grown on Cu(1 0 0). Furthermore, a clear negative MR was observed. The buffer layer condition for MR effect will be discussed.

  19. Observation of field emission from GeSn nanoparticles epitaxially grown on silicon nanopillar arrays

    Science.gov (United States)

    Di Bartolomeo, Antonio; Passacantando, Maurizio; Niu, Gang; Schlykow, Viktoria; Lupina, Grzegorz; Giubileo, Filippo; Schroeder, Thomas

    2016-12-01

    We apply molecular beam epitaxy to grow GeSn-nanoparticles on top of Si-nanopillars patterned onto p-type Si wafers. We use x-ray photoelectron spectroscopy to confirm a metallic behavior of the nanoparticle surface due to partial Sn segregation as well as the presence of a superficial Ge oxide. We report the observation of stable field emission (FE) current from the GeSn-nanoparticles, with turn on field of 65 {{V}} μ {{{m}}}-{{1}} and field enhancement factor β ˜ 100 at anode-cathode distance of ˜0.6 μm. We prove that FE can be enhanced by preventing GeSn nanoparticles oxidation or by breaking the oxide layer through electrical stress. Finally, we show that GeSn/p-Si junctions have a rectifying behavior.

  20. Surface state conductivity in epitaxially grown Bi1-x Sb x (111) films

    Science.gov (United States)

    Koch, Julian; Kröger, Philipp; Pfnür, Herbert; Tegenkamp, Christoph

    2016-09-01

    Topologically non-trivial surface states were reported first on {{Bi}}1-xSb x bulk crystals. In this study we present transport measurements performed on thin {{Bi}}1-xSb x -films (up to 24 nm thickness) grown epitaxially on Si(111) with various Sb-concentrations (up to x = 0.22). The analysis of the temperature dependency allowed us to distinguish between different transport channels originating from surface and bulk bands as well as impurity states. At temperatures below 30 K the transport is mediated by surface states while at higher temperatures activated transport via bulk channels sets in. The surface state conductivity and bulk band gaps can be tuned by the Sb-concentration and film thickness, respectively. For films as thin as 4 nm the surface state transport is strongly suppressed in contrast to Bi(111) films grown under identical conditions. The impurity channel is of intrinsic origin due to the growth and alloy formation process and turns out to be located at the buried interface.

  1. Mapping growth windows in quaternary perovskite oxide systems by hybrid molecular beam epitaxy

    Science.gov (United States)

    Brahlek, Matthew; Zhang, Lei; Zhang, Hai-Tian; Lapano, Jason; Dedon, Liv R.; Martin, Lane W.; Engel-Herbert, Roman

    2016-09-01

    Requisite to growing stoichiometric perovskite thin films of the solid-solution A'1-xAxBO3 by hybrid molecular beam epitaxy is understanding how the growth conditions interpolate between the end members A'BO3 and ABO3, which can be grown in a self-regulated fashion, but under different conditions. Using the example of La1-xSrxVO3, the two-dimensional growth parameter space that is spanned by the flux of the metal-organic precursor vanadium oxytriisopropoxide and composition, x, was mapped out. The evolution of the adsorption-controlled growth window was obtained using a combination of X-ray diffraction, atomic force microscopy, reflection high-energy electron-diffraction (RHEED), and Rutherford backscattering spectroscopy. It is found that the stoichiometric growth conditions can be mapped out quickly with a single calibration sample using RHEED. Once stoichiometric conditions have been identified, the out-of-plane lattice parameter can be utilized to precisely determine the composition x. This strategy enables the identification of growth conditions that allow the deposition of stoichiometric perovskite oxide films with random A-site cation mixing, which is relevant to a large number of perovskite materials with interesting properties, e.g., high-temperature superconductivity and colossal magnetoresistance, that emerge in solid solution A'1-xAxBO3.

  2. Molecular beam epitaxy growth and magnetic properties of Cr-Co-Ga Heusler alloy films

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Wuwei, E-mail: wfeng@cugb.edu.cn; Wang, Weihua [School of Materials Science and Technology, China University of Geosciences, Beijing 100083 (China); Zhao, Chenglong [Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Van Quang, Nguyen; Cho, Sunglae, E-mail: slcho@ulsan.ac.kr [Department of Physics, University of Ulsan, Ulsan 680-749 (Korea, Republic of); Dung, Dang Duc [Department of General Physics, School of Engineering Physics, Ha Noi University of Science and Technology, 1 Dai Co Viet Road, Ha Noi (Viet Nam)

    2015-11-15

    We have re-investigated growth and magnetic properties of Cr{sub 2}CoGa films using molecular beam epitaxy technique. Phase separation and precipitate formation were observed experimentally again in agreement with observation of multiple phases separation in sputtered Cr{sub 2}CoGa films by M. Meinert et al. However, significant phase separation could be suppressed by proper control of growth conditions. We showed that Cr{sub 2}CoGa Heusler phase, rather than Co{sub 2}CrGa phase, constitutes the majority of the sample grown on GaAs(001) at 450 {sup o}C. The measured small spin moment of Cr{sub 2}CoGa is in agreement with predicted HM-FCF nature; however, its Curie temperature is not as high as expected from the theoretical prediction probably due to the off-stoichiometry of Cr{sub 2}CoGa and the existence of the disorders and phase separation.

  3. Formation of Ge-Sn nanodots on Si(100 surfaces by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Yu Ing-Song

    2011-01-01

    Full Text Available Abstract The surface morphology of Ge0.96Sn0.04/Si(100 heterostructures grown at temperatures from 250 to 450°C by atomic force microscopy (AFM and scanning tunnel microscopy (STM ex situ has been studied. The statistical data for the density of Ge0.96Sn0.04 nanodots (ND depending on their lateral size have been obtained. Maximum density of ND (6 × 1011 cm-2 with the average lateral size of 7 nm can be obtained at 250°C. Relying on the reflection of high energy electron diffraction, AFM, and STM, it is concluded that molecular beam growth of Ge1-xSnx heterostructures with the small concentrations of Sn in the range of substrate temperatures from 250 to 450°C follows the Stranski-Krastanow mechanism. Based on the technique of recording diffractometry of high energy electrons during the process of epitaxy, the wetting layer thickness of Ge0.96Sn0.04 films is found to depend on the temperature of the substrate.

  4. Plasma-assisted molecular beam epitaxy growth of ZnSnN2

    Science.gov (United States)

    Feldberg, Nathaniel; Aldous, James; Yao, Yuan; Tanveer, Imtiaz; Keen, Benjamin; Linhart, Wojciech; Veal, Tim; Song, Young-Wook; Reeves, Roger; Durbin, Steve

    2012-02-01

    The Zn-IV-nitrides are a promising series of ``earth abundant element'' semiconductors with a predicted band gap range of 0.6 eV to 5.4 eV, which, like the (Al,Ga,In)N family, spans the entire visible solar spectrum. Considering this alternative family has a number of advantages, including the avoidance of indium, the price of which has varied almost an order of magnitude over the past decade, and surface electron accumulation which is present in the In-rich alloys. Not all members of this family have yet been synthesized, in particular ZnSnN2, the most important member for PV with its predicted band gap of approximately 2 eV. We have successfully grown a series of these films using plasma-assisted molecular beam epitaxy using elemental Zn and Sn sources. In this report, we discuss the relationship between process parameters and microstructure, as well as stoichiometry as determined by Rutherford backscattering spectrometry. Additionally, we provide preliminary estimates for its bandgap energy based on photoluminescence and optical absorption.

  5. Thin film growth of CaFe2As2 by molecular beam epitaxy

    Science.gov (United States)

    Hatano, T.; Kawaguchi, T.; Fujimoto, R.; Nakamura, I.; Mori, Y.; Harada, S.; Ujihara, T.; Ikuta, H.

    2016-01-01

    Film growth of CaFe2As2 was realized by molecular beam epitaxy on six different substrates that have a wide variation in the lattice mismatch to the target compound. By carefully adjusting the Ca-to-Fe flux ratio, we obtained single-phase thin films for most of the substrates. Interestingly, an expansion of the CaFe2As2 lattice to the out-of-plane direction was observed for all films, even when an opposite strain was expected. A detailed microstructure observation of the thin film grown on MgO by transmission electron microscope revealed that it consists of cube-on-cube and 45°-rotated domains. The latter domains were compressively strained in plane, which caused a stretching along the c-axis direction. Because the domains were well connected across the boundary with no appreciable discontinuity, we think that the out-of-plane expansion in the 45°-rotated domains exerted a tensile stress on the other domains, resulting in the unexpectedly large c-axis lattice parameter, despite the apparently opposite lattice mismatch.

  6. Carbon doping in molecular beam epitaxy of GaAs from a heated graphite filament

    Science.gov (United States)

    Malik, R. J.; Nottenberg, R. N.; Schubert, E. F.; Walker, J. F.; Ryan, R. W.

    1988-01-01

    Carbon doping of GaAs grown by molecular beam epitaxy has been obtained for the first time by use of a heated graphite filament. Controlled carbon acceptor concentrations over the range of 10 to the 17th-10 to the 20th/cu cm were achieved by resistively heating a graphite filament with a direct current power supply. Capacitance-voltage, p/n junction and secondary-ion mass spectrometry measurements indicate that there is negligible diffusion of carbon during growth and with postgrowth rapid thermal annealing. Carbon was used for p-type doping in the base of Npn AlGaAs/GaAs heterojunction bipolar transistors. Current gains greater than 100 and near-ideal emitter heterojunctions were obtained in transistors with a carbon base doping of 1 x 10 to the 19th/cu cm. These preliminary results indicate that carbon doping from a solid graphite source may be an attractive substitute for beryllium, which is known to have a relatively high diffusion coefficient in GaAs.

  7. Single-photon emission from electrically driven InP quantum dots epitaxially grown on CMOS-compatible Si(001)

    Science.gov (United States)

    Wiesner, M.; Schulz, W.-M.; Kessler, C.; Reischle, M.; Metzner, S.; Bertram, F.; Christen, J.; Roßbach, R.; Jetter, M.; Michler, P.

    2012-08-01

    The heteroepitaxy of III-V semiconductors on silicon is a promising approach for making silicon a photonic platform. Mismatches in material properties, however, present a major challenge, leading to high defect densities in the epitaxial layers and adversely affecting radiative recombination processes. However, nanostructures, such as quantum dots, have been found to grow defect-free even in a suboptimal environment. Here we present the first realization of indium phosphide quantum dots on exactly oriented Si(001), grown by metal-organic vapour-phase epitaxy. We report electrically driven single-photon emission in the red spectral region, meeting the wavelength range of silicon avalanche photodiodes’ highest detection efficiency.

  8. Effect of residual stress on the microstructure of GaN epitaxial films grown by pulsed laser deposition

    Science.gov (United States)

    Wang, Haiyan; Wang, Wenliang; Yang, Weijia; Zhu, Yunnong; Lin, Zhiting; Li, Guoqiang

    2016-04-01

    The stress-free GaN epitaxial films have been directly grown by pulsed laser deposition (PLD) at 850 °C, and the effect of different stress on the microstructure of as-grown GaN epitaxial films has been explored in detail. The as-grown stress-free GaN epitaxial films exhibit very smooth surface without any particles and grains, which is confirmed by the smallest surface root-mean-square roughness of 2.3 nm measured by atomic force microscopy. In addition, they also have relatively high crystalline quality, which is proved by the small full-width at half maximum values of GaN(0002) and GaN (10 1 bar 2) X-ray rocking curves as 0.27° and 0.68°, respectively. However, when the growth temperature is lower or higher than 850 °C, internal or thermal stress would be increased in as-grown GaN epitaxial films. To release the larger stress, a great number of dislocations are generated. Many irregular particulates, hexagonal GaN gains and pits are therefore produced on the films surface, and the crystalline quality is greatly reduced consequently. This work has demonstrated the direct growth of stress-free GaN epitaxial films with excellent surface morphology and high crystalline quality by PLD, and presented a comprehensive study on the origins and the effect of stress in GaN layer. It is instructional to achieve high-quality nitride films by PLD, and shows great potential and broad prospect for the further development of high-performance GaN-based devices.

  9. Fabrication of GeSn-multiple quantum wells by overgrowth of Sn on Ge by using molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, F. [Institute for Semiconductor Engineering, University of Stuttgart, 70569 Stuttgart (Germany); Centre of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Fischer, I. A.; Schulze, J. [Institute for Semiconductor Engineering, University of Stuttgart, 70569 Stuttgart (Germany); Benedetti, A. [CACTI, Univ. de Vigo, Campus Universitario Lagoas Marcosende 15, Vigo (Spain); Zaumseil, P. [IHP GmbH, Innovations for High Performance Microelectronics, Leibniz-Institut für innovative Mikroelektronik, Im Technologiepark 25, 15236 Frankfurt (Oder) (Germany); Cerqueira, M. F.; Vasilevskiy, M. I. [Centre of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Stefanov, S.; Chiussi, S. [Dpto. Fisica Aplicada, Univ. de Vigo, Rua Maxwell s/n, Campus Universitario Lagoas Marcosende, Vigo (Spain)

    2015-12-28

    We report on the fabrication and structural characterization of epitaxially grown ultra-thin layers of Sn on Ge virtual substrates (Si buffer layer overgrown by a 50 nm thick Ge epilayer followed by an annealing step). Samples with 1 to 5 monolayers of Sn on Ge virtual substrates were grown using solid source molecular beam epitaxy and characterized by atomic force microscopy. We determined the critical thickness at which the transition from two-dimensional to three-dimensional growth occurs. This transition is due to the large lattice mismatch between Ge and Sn (≈14.7%). By depositing Ge on top of Sn layers, which have thicknesses at or just below the critical thickness, we were able to fabricate ultra-narrow GeSn multi-quantum-well structures that are fully embedded in Ge. We report results on samples with one and ten GeSn wells separated by 5 and 10 nm thick Ge spacer layers that were characterized by high resolution transmission electron microscopy and X-ray diffraction. We discuss the structure and material intermixing observed in the samples.

  10. Fabrication of GeSn-multiple quantum wells by overgrowth of Sn on Ge by using molecular beam epitaxy

    Science.gov (United States)

    Oliveira, F.; Fischer, I. A.; Benedetti, A.; Zaumseil, P.; Cerqueira, M. F.; Vasilevskiy, M. I.; Stefanov, S.; Chiussi, S.; Schulze, J.

    2015-12-01

    We report on the fabrication and structural characterization of epitaxially grown ultra-thin layers of Sn on Ge virtual substrates (Si buffer layer overgrown by a 50 nm thick Ge epilayer followed by an annealing step). Samples with 1 to 5 monolayers of Sn on Ge virtual substrates were grown using solid source molecular beam epitaxy and characterized by atomic force microscopy. We determined the critical thickness at which the transition from two-dimensional to three-dimensional growth occurs. This transition is due to the large lattice mismatch between Ge and Sn (≈14.7%). By depositing Ge on top of Sn layers, which have thicknesses at or just below the critical thickness, we were able to fabricate ultra-narrow GeSn multi-quantum-well structures that are fully embedded in Ge. We report results on samples with one and ten GeSn wells separated by 5 and 10 nm thick Ge spacer layers that were characterized by high resolution transmission electron microscopy and X-ray diffraction. We discuss the structure and material intermixing observed in the samples.

  11. Molecular Beam Epitaxial Growth of ZnO on Si Substrate Using Ozone as an Oxygen Source

    Science.gov (United States)

    Fujita, Miki; Kawamoto, Noriaki; Tatsumi, Tomohiko; Yamagishi, Katsumi; Horikoshi, Yoshiji

    2003-01-01

    Epitaxial ZnO films have been grown on Si (111) substrates by molecular beam epitaxy using ozone as an oxygen source. An initial deposition of a Zn layer followed by its oxidation produces a superior template for the subsequent ZnO growth. The reflection high-energy electron diffraction measurement suggests that the initial Zn layer and ZnO film are rotated by 30° with respect to the Si substrate orientation. The X-ray diffraction measurement reveals that the as-grown ZnO films are strongly c-oriented and include no rotational domains. Although there exists a small trace of ZnO (10\\bar{1}1) domains, it easily disappears upon annealing at 1100°C for 1 min after growth. Low-temperature photoluminescence measurements indicate that the emission property is improved significantly after annealing. The bound-exciton emission at 3.354 eV is dominant and its full-width at half maximum is as small as 11 meV.

  12. Preparation of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} epitaxial thin films by pulsed ion-beam evaporation

    Energy Technology Data Exchange (ETDEWEB)

    Sorasit, S.; Yoshida, G.; Suzuki, T.; Suematsu, H.; Jiang, W.; Yatsui, K. [Nagaoka University of Technology, Extreme Energy-Density Research Institute, Nagaoka, Niigata (Japan)

    2001-09-01

    Thin films of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (Y-123) grown epitaxially have been successfully deposited by ion-beam evaporation (IBE). The c-axis oriented YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films were successfully deposited on MgO and SrTiO{sub 3} substrates. The Y-123 thin films which were prepared on the SrTiO{sub 3} substrates were confirmed to be epitaxially grown, by X-ray diffraction analysis. The instantaneous deposition rate of the Y-123 thin films was estimated as high as 4 mm/s. (author)

  13. Isotype InGaN/GaN heterobarrier diodes by ammonia molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Fireman, Micha N.; Browne, David A.; Speck, James S. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Mishra, Umesh K. [Electrical and Computer Engineering Department, University of California, Santa Barbara, California 93106 (United States)

    2016-02-07

    The design of isotype InGaN/GaN heterobarrier diode structures grown by ammonia molecular beam epitaxy is presented. On the (0001) Ga-polar plane, a structure consisting of a surface n{sup +} GaN contact layer, followed by a thin InGaN layer, followed by a thick unintentionally doped (UID) GaN layer, and atop a buried n{sup +} GaN contact layer induces a large conduction band barrier via a depleted UID GaN layer. Suppression of reverse and subthreshold current in such isotype barrier devices under applied bias depends on the quality of this composite layer polarization. Sample series were grown under fixed InGaN growth conditions that varied either the UID GaN NH{sub 3} flow rate or the UID GaN thickness, and under fixed UID GaN growth conditions that varied InGaN growth conditions. Decreases in subthreshold current and reverse bias current were measured for thicker UID GaN layers and increasing InGaN growth rates. Temperature-dependent analysis indicated that although extracted barrier heights were lower than those predicted by 1D Schrödinger Poisson simulations (0.9 eV–1.4 eV for In compositions from 10% to 15%), optimized growth conditions increased the extracted barrier height from ∼11% to nearly 85% of the simulated values. Potential subthreshold mechanisms are discussed, along with those growth factors which might affect their prevalence.

  14. Planarization and Processing of Metamorphic Buffer Layers Grown by Hydride Vapor-Phase Epitaxy

    Science.gov (United States)

    Zutter, Brian T.; Schulte, Kevin L.; Kim, Tae Wan; Mawst, Luke J.; Kuech, T. F.; Foran, Brendan; Sin, Yongkun

    2014-04-01

    Hydride vapor-phase epitaxy (HVPE) is a high-growth-rate, cost-effective means to grow epitaxial semiconductor material. Thick HVPE-based metamorphic buffer layers (MBLs) can serve as "pseudosubstrates" with controllable lattice parameter. In our structures, the indium content in In x Ga1- x As is gradually increased from zero to the final composition corresponding to the desired lattice constant, and then a thick (˜10 μm) constant-composition capping layer is grown. This thick capping layer promotes maximum strain relaxation while permitting use of polishing procedures to achieve surface planarity. Lattice-mismatched growth of MBLs invariably results in rough, cross-hatched surface morphology exhibiting up to 200 nm peak-to-valley roughness. This roughness can be eliminated by chemical mechanical planarization, thus creating a suitable surface for subsequent regrowth. Polishing of In x Ga1- x As is complicated by the sensitivity of the surface layer to the polishing parameters, particularly the applied pressure. Polishing at high applied pressure (12 psi) results in the formation of circular asperities hundreds of nanometers high and tens of microns in diameter. When lower applied pressure (4 psi) was used, the cross-hatching height of MBLs was lowered from 200 nm to <10 nm over a 350 μm lateral scale. The successfully planarized In0.20Ga0.80As MBLs were used as a substrate for a superlattice (SL) structure such as that used in quantum cascade lasers. Use of planarization before regrowth of the SL resulted in a reduction of the high-resolution x-ray diffraction peak full-width at half-maximum from 389″ to 159″.

  15. Incorporation of La in epitaxial SrTiO3 thin films grown by atomic layer deposition on SrTiO3-buffered Si (001) substrates

    Science.gov (United States)

    McDaniel, Martin D.; Posadas, Agham; Ngo, Thong Q.; Karako, Christine M.; Bruley, John; Frank, Martin M.; Narayanan, Vijay; Demkov, Alexander A.; Ekerdt, John G.

    2014-06-01

    Strontium titanate, SrTiO3 (STO), thin films incorporated with lanthanum are grown on Si (001) substrates at a thickness range of 5-25 nm. Atomic layer deposition (ALD) is used to grow the LaxSr1-xTiO3 (La:STO) films after buffering the Si (001) substrate with four-unit-cells of STO deposited by molecular beam epitaxy. The crystalline structure and orientation of the La:STO films are confirmed via reflection high-energy electron diffraction, X-ray diffraction, and cross-sectional transmission electron microscopy. The low temperature ALD growth (˜225 °C) and post-deposition annealing at 550 °C for 5 min maintains an abrupt interface between Si (001) and the crystalline oxide. Higher annealing temperatures (650 °C) show more complete La activation with film resistivities of ˜2.0 × 10-2 Ω cm for 20-nm-thick La:STO (x ˜ 0.15); however, the STO-Si interface is slightly degraded due to the increased annealing temperature. To demonstrate the selective incorporation of lanthanum by ALD, a layered heterostructure is grown with an undoped STO layer sandwiched between two conductive La:STO layers. Based on this work, an epitaxial oxide stack centered on La:STO and BaTiO3 integrated with Si is envisioned as a material candidate for a ferroelectric field-effect transistor.

  16. Molecular beam epitaxy growth of InSb1−xBix thin films

    DEFF Research Database (Denmark)

    Song, Yuxin; Wang, Shumin; Saha Roy, Ivy;

    2013-01-01

    Molecular beam epitaxy growth for InSb1−xBix thin films on (100) GaAs substrates is reported. Successful Bi incorporation for 2% is achieved, and up to 70% of the incorporated Bi atoms are at substitutional sites. The effects of growth parameters on Bi incorporation and surface morphology...

  17. Molecular beam epitaxy growth of InSb1-xBix thin films

    DEFF Research Database (Denmark)

    Yuxin Song; Shumin Wang; Saha Roy, Ivy;

    2013-01-01

    Molecular beam epitaxy growth for InSb1-xBix thin films on (100) GaAs substrates is reported. Successful Bi incorporation for 2% is achieved, and up to 70% of the incorporated Bi atoms are at substitutional sites. The effects of growth parameters on Bi incorporation and surface morphology...

  18. Optical properties of aluminum nitride thin films grown by direct-current magnetron sputtering close to epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Stolz, A. [Institut d' Electronique de Microélectronique et de Nanotechnologie (IEMN), UMR CNRS 8520, PRES Lille, Université Nord de France, Avenue Poincaré, 59652 Villeneuve d' Ascq Cedex (France); Soltani, A., E-mail: ali.soltani@iemn.univ-lille1.fr [Institut d' Electronique de Microélectronique et de Nanotechnologie (IEMN), UMR CNRS 8520, PRES Lille, Université Nord de France, Avenue Poincaré, 59652 Villeneuve d' Ascq Cedex (France); Abdallah, B. [Department of Materials Physics, Atomic Energy Commission of Syria, Damascus, P.O. Box 6091 (Syrian Arab Republic); Charrier, J. [Fonctions Optiques pour les Technologies de l' informatiON (FOTON), UMR CNRS 6082, 6, rue de Kerampont CS 80518, 22305 Lannion Cedex (France); Deresmes, D. [Institut d' Electronique de Microélectronique et de Nanotechnologie (IEMN), UMR CNRS 8520, PRES Lille, Université Nord de France, Avenue Poincaré, 59652 Villeneuve d' Ascq Cedex (France); Jouan, P.-Y.; Djouadi, M.A. [Institut des Matériaux Jean Rouxel – IMN, UMR CNRS 6502, 2, rue de la Houssinère BP 32229, 44322 Nantes (France); Dogheche, E.; De Jaeger, J.-C. [Institut d' Electronique de Microélectronique et de Nanotechnologie (IEMN), UMR CNRS 8520, PRES Lille, Université Nord de France, Avenue Poincaré, 59652 Villeneuve d' Ascq Cedex (France)

    2013-05-01

    Low-temperature Aluminum Nitride (AlN) thin films with a thickness of 3 μm were deposited by Direct-Current magnetron sputtering on sapphire substrate. They present optical properties similar to those of epitaxially grown films. Different characterization methods such as X-Ray Diffraction, Transmission Electron Microscopy and Atomic Force Microscopy were used to determine the structural properties of the films such as its roughness and crystallinity. Newton interferometer was used for stress measurement of the films. Non-destructive prism-coupling technique was used to determine refractive index and thickness homogeneity by a mapping on the whole sample area. Results show that AlN films grown on AlGaN layer have a high crystallinity close to epitaxial films, associated to a low intrinsic stress for low thickness. These results highlight that it is possible to grow thick sample with microstructure and optical properties close to epitaxy, even on a large surface. - Highlights: ► Aluminum Nitride sputtering technique with a low temperature growth process ► Epitaxial quality of two microns sputtered Aluminum Nitride film ► Optics as a non-destructive accurate tool for acoustic wave investigation.

  19. Systematic process development towards high performance transferred thin silicon solar cells based on epitaxially grown absorbers

    Science.gov (United States)

    Murcia Salazar, Clara Paola

    ). First principles modeling, however, predicts that efficiencies of 20+% are achievable with less than 20 mum of c-Si. In addition to a high voltage design, this work reports state of the art epitaxial c-Si solar cell performance and a path towards 20+%-efficient transferred epitaxial solar cells. The design and fabrication approach is based on high open circuit voltage first, high short circuit current second. A first design is a thin solar cell grown on a conductive silicon wafer. This structure allows developing processes to increase bulk lifetime and reduce surface recombination. Important processes that can be used for a transferred solar cell such as increased fill factor (FF) are developed at this stage. A second design is based on the use of a separation layer prior to the solar cell growth. We achieve a comparable performance with the second design. A third design includes the transfer of the solar cell to a secondary substrate. Initial processing development is reported for the transferred solar cells. Improvements in solar cell critical parameters have been characterized with a combination of predictive modeling and solar cell diagnostic tools such as quantum efficiency and voltage measurements. Fabrication processes have been developed to improve solar cell performance. The combination of process development, test structures, systematic fabrication, testing and analysis concludes with a path to high voltage, transferred thin c-Si solar cells towards 20+% efficiencies.

  20. InGaAsP Solar Cells Grown by Hydride Vapor Phase Epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Jain, Nikhil; Simon, John; Schulte, Kevin L.; Dippo, Patricia; Young, Michelle; Young, David L.; Ptak, Aaron J.

    2016-11-21

    Hydride vapor phase epitaxy (HVPE) has recently reemerged as a low-cost, high-throughput alternative to metalorganic chemical vapor deposition (MOCVD) for the growth of high-efficiency III-V solar cells. Quaternary InGaAsP solar cells in the bandgap range of ~1.7-1.8 eV are promising top-cell candidates for integration in Ill-V/Si tandem cells with projected one-sun efficiencies exceeding 30%. In this work, we report on the development of lattice-matched InGaAsP solar cells grown on GaAs substrates via HVPE at very high growth rates of ~0.7 um/min. We demonstrate prototype 1.7 eV InGaAsP solar cells with an open-circuit voltage of 1.11 V. The short-circuit current is limited by the lack of a window layer in these early stage devices. The photo response of 1.7 InGaAsP solar cell with ~1.1 um thick base layer is found to be nearly insensitive to variation in p-type base doping concentration in the range from Na - 4x1016 to - 1x1017 cm-3, indicating an effective carrier collection length on the order of - 1.1 um or higher in our devices. These initial InGaAsP cell results are encouraging and highlight the viability of HVPE to produce mixed arsenide-phosphide solar cells grown lattice-matched on GaAs.

  1. Photoluminescence of ZnSe-ZnS Single Quantum Wells Grown by Vapour Phase Epitaxy

    Institute of Scientific and Technical Information of China (English)

    吕有明; 申德振; 刘益春; 李炳辉; 张吉英; 范希武; 饭田诚之; 加藤有行

    2002-01-01

    We study the photoluminescence (PL) of ultra thin layer ZnSe quantum wells in ZnS barriers. Samples with different well widths are grown by vapour phase epitaxy and the PL spectra of these samples are measured by the excitation of a 500 W Hg lamp. The peak positions of the bands coming from the excitonic luminescence show a larger blueshift with respect to the energy of free excitons in the ZnSe bulk material. The observed variation of the full width at half maximum and peak position of the bands in the spectra with the well width are interpreted to the formation of the ZnSxSe1-x alloy layer due to the interdiffusion in the interfaces between ZnSe and ZnS.According to the behaviour of the excitons in the smaller conduction band offset, the exciton binding energy is estimated from the dependence of the PL intensity on the temperature. From this result, excitons seem to show nearly three-dimensional characteristics.

  2. Optical waveguide loss minimized into gallium nitride based structures grown by metal organic vapor phase epitaxy

    Science.gov (United States)

    Stolz, A.; Cho, E.; Dogheche, E.; Androussi, Y.; Troadec, D.; Pavlidis, D.; Decoster, D.

    2011-04-01

    The waveguide properties are reported for wide bandgap gallium nitride (GaN) structures grown by metal organic vapor phase epitaxy on sapphire using a AlN/GaN short period-superlattice (SPS) buffer layer system. A detailed optical characterization of GaN structures has been performed using the prism coupling technique in order to evaluate its properties and, in particular, the refractive index dispersion and the propagation loss. In order to identify the structural defects in the samples, we performed transmission electron microscopy analysis. The results suggest that AlN/GaN SPS plays a role in acting as a barrier to the propagation of threading dislocations in the active GaN epilayer; above this defective region, the dislocations density is remarkably reduced. The waveguide losses were reduced to a value around 0.65dB/cm at 1.55 μm, corresponding to the best value reported so far for a GaN-based waveguide.

  3. Control of native acceptor density in epitaxial Cu2O thin films grown by electrochemical deposition

    Science.gov (United States)

    Ashida, Atsushi; Sato, Shunsuke; Yoshimura, Takeshi; Fujimura, Norifumi

    2017-06-01

    Controlling the native carrier is essential for using Cu2O in devices such as solar cells. The origin of the native p-type carrier in Cu2O is thought to be copper vacancies (VCu). In this work, epitaxially grown Cu2O thin films were prepared by electrochemical deposition at a low temperature of 45 °C on a Pt (111) cathodic electrode. The sources of Cu and O for Cu2O were Cu2+ and OH- in the electrolyte and the ion concentrations were changed to control the stoichiometry of deposition and the density of VCu. The density of ionized acceptors (NA+) in the Cu2O films was evaluated by the C-V properties measured with Schottky electrodes. NA+ did not depend on [Cu2+], whereas NA+ increased with increasing [OH-] when [OH-] was larger than 10-3 mol/L (electrolyte pH >11) with [Cu2+] fixed at 10-1 mol/L. The ion concentration dependence of NA+ and the dependence of the total cathodic current density revealed that the generation of VCu was affected by a complex combination of the ion concentrations and film growth rate.

  4. STM studies of GeSi thin layers epitaxially grown on Si(111)

    Science.gov (United States)

    Motta, N.; Sgarlata, A.; De Crescenzi, M.; Derrien, J.

    1996-08-01

    Ge/Si alloys were prepared in UHV by solid phase epitaxy on Si(111) substrates. The alloy formation, as a function of the evaporation rate and the Ge layer thickness has been followed in situ by RHEED and scanning tunneling microscopy. The 5 × 5 surface reconstruction appeared after annealing at 450°C Ge layers (up to 10 Å thick), obtained from a low rate Knudsen cell evaporator. In this case a nearly flat and uniform layer of reconstructed alloy was observed. When using an e-gun high rate evaporator we needed to anneal the Ge layer up to 780°C to obtain a 5 × 5 reconstruction. The grown layer was not flat, with many steps and Ge clusters; at high coverages (10 Å and more) large Ge islands appeared. Moreover, we then succeeded in visualizing at atomic resolution the top of some of these Ge islands which displayed a 2 × 1 reconstruction, probably induced from the high compressive strain due to the lattice mismatch with the substrate. We suggest that this unusual behavior could be connected to the high evaporation rate, which helped the direct formation of Ge microcrystals on the Si substrate during the deposition process.

  5. Precipitation growth of graphene under exfoliated hexagonal boron nitride to form heterostructures on cobalt substrate by molecular beam epitaxy

    Science.gov (United States)

    Zheng, Renjing; Khanaki, Alireza; Tian, Hao; He, Yanwei; Cui, Yongtao; Xu, Zhongguang; Liu, Jianlin

    2017-07-01

    Research on graphene/hexagonal boron nitride (h-BN) heterostructures has attracted much attention for band engineering and device performance optimization of graphene. However, the growth of graphene/h-BN heterostructure is still challenging, which usually requires high growth temperature and long growth duration. In this paper, we demonstrate graphene/h-BN heterostructures by growing graphene onto the substrates which consist of exfoliated h-BN flakes on Co thin films using molecular beam epitaxy. The heterostructure samples grown at different temperatures and growth times were characterized by Raman, optical microscopy, atomic force microscopy, microwave impedance microscopy, and scanning tunneling microscopy. It is found that the graphene/h-BN heterostructures were formed by the formation of graphene underneath rather than on top of the h-BN flakes. The growth mechanism is discussed.

  6. Large-format multi-wafer production of 5" GaSb-based photodetectors by molecular beam epitaxy

    Science.gov (United States)

    Loubychev, Dmitri; Fastenau, Joel M.; Kattner, Michael; Frey, Phillip; Liu, Amy W. K.; Furlong, Mark J.

    2017-02-01

    GaSb and its heterostructures grown by molecular beam epitaxy (MBE) have received much attention given their application in a wide range of mid-wave and long-wave IR photodetector applications. With the maturation of the MBE growth process, focus is now turned to improving manufacturing readiness and the transition to the production of large-format wafers. We will discuss the transition from the development of early detector layer structures on 2" diameter GaSb substrates, through today's 3"/4" production standard, and to the onset of 5" pilot production from the perspective of volume compound semiconductor manufacturing. We will report on the growth of 5" GaSb-based MWIR nBn detector structures using a large format 5×5" production MBE platform. Structural and optical properties, as well as electrical data from large-area mesa diodes will be presented and compared with results achieved with smaller batch size MBE reactor platform.

  7. Molecular beam epitaxy of three dimensional topological insulator Bi₂Se₃ thin films

    OpenAIRE

    Guo, Xin; 郭欣

    2013-01-01

    In this thesis, molecular-beam epitaxy (MBE) of three-dimensional (3D) topological insulator (TI) Bi_2 Se_3 thin films on different substrates is presented. The substrates experimented include InP(111)A, GaAs(111)A, InP(001) and GaAs(001). Multiple characterization techniques are employed to investigate the film’s structural, morphological and electrical properties. To facilitate growth of high quality epitaxial Bi_2 Se_3, thermal treatment of the substrate surfaceturnsout to be crucial for b...

  8. Structural origin of perpendicular magnetic anisotropy in epitaxial CoPt3 nanostructures grown on WSe2(0001)

    Science.gov (United States)

    Liscio, F.; Maret, M.; Meneghini, C.; Mobilio, S.; Proux, O.; Makarov, D.; Albrecht, M.

    2010-03-01

    We present a detailed analysis of the local ordering in CoPt3 nanostructures epitaxially grown on WSe2(0001) and NaCl(001) low-energy surfaces. Polarized extended x-ray absorption fine-structure measurements at the CoK -edge show a local structural anisotropy in fcc CoPt3 nanostructures grown at 300 K on WSe2 . It is characterized by preferential Co-Co bonding along the in-plane direction balanced with preferential heteroatomic bonding along the out-of-plane direction and explains the unexpected perpendicular magnetic anisotropy. Such anisotropy almost vanishes in partially L12 -ordered nanostructures grown at 700 K. In contrast, the short-range order is isotropic in CoPt3 nanostructures grown on NaCl(001) at 370 K. These different behaviors emphasize the favorable role of Se segregated atoms of WSe2 in the dynamic segregation of Pt atoms at the advancing surface during codeposition, which governs the local structural anisotropy. In the absence of Se, as previously observed in epitaxial CoPt3 films grown on Ru buffer layers, the development of similar structural anisotropy requires higher growth temperatures (550-720 K).

  9. Fast atom diffraction inside a molecular beam epitaxy chamber, a rich combination

    Science.gov (United States)

    Debiossac, M.; Atkinson, P.; Zugarramurdi, A.; Eddrief, M.; Finocchi, F.; Etgens, V. H.; Momeni, A.; Khemliche, H.; Borisov, A. G.; Roncin, P.

    2017-01-01

    Two aspects of the contribution of grazing incidence fast atom diffraction (GIFAD) to molecular beam epitaxy (MBE) are reviewed here: the ability of GIFAD to provide in-situ a precise description of the atomic-scale surface topology, and its ability to follow larger-scale changes in surface roughness during layer-by-layer growth. Recent experimental and theoretical results obtained for the He atom beam incident along the highly corrugated [ 1 1 bar 0 ] direction of the β2(2 × 4) reconstructed GaAs(001) surface are summarized. We also discuss the measurements and calculations for the beam incidence along the weakly corrugated [010] direction where a periodicity twice smaller than expected is observed. The combination of the experiment, quantum scattering matrix calculations, and semiclassical analysis allows structural characteristics of the surface to be revealed. For the in situ measurements of GIFAD during molecular beam epitaxy of GaAs on GaAs surface we analyze the change in elastic and inelastic contributions in the scattered beam, and the variation of the diffraction pattern in polar angle scattering. This analysis outlines the robustness, the simplicity and the richness of the GIFAD as a technique to monitor the layer-by-layer epitaxial growth.

  10. Optical and Structural Properties of Microcrystalline GaN on an Amorphous Substrate Prepared by a Combination of Molecular Beam Epitaxy and Metal-Organic Chemical Vapor Deposition

    Energy Technology Data Exchange (ETDEWEB)

    Min, Jung-Wook; Hwang, Hyeong-Yong; Kang, Eun-Kyu; Park, Kwangwook; Kim, Ci-Hyun; Lee, Dong-Seon; Jho, Young-Dahl; Bae, Si-Young; Lee, Yong-Tak

    2016-05-01

    Microscale platelet-shaped GaN grains were grown on amorphous substrates by a combined epitaxial growth method of molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). First, MBE GaN was grown on an amorphous substrate as a pre-orienting layer and its structural properties were investigated. Second, MOCVD grown GaN samples using the different growth techniques of planar and selective area growth (SAG) were comparatively investigated by transmission electron microscopy (TEM), cathodoluminescence (CL), and photoluminescence (PL). In MOCVD planar GaN, strong bound exciton peaks dominated despite the high density of the threading dislocations (TDs). In MOCVD SAG GaN, on the other hand, TDs were clearly reduced with bending, but basal stacking fault (BSF) PL peaks were observed at 3.42 eV. The combined epitaxial method not only provides a deep understanding of the growth behavior but also suggests an alternative approach for the growth of GaN on amorphous substances.

  11. Comparative optical study of epitaxial InGaAs quantum rods grown with As{sub 2} and As{sub 4} sources

    Energy Technology Data Exchange (ETDEWEB)

    Nedzinskas, Ramūnas; Čechavičius, Bronislovas; Kavaliauskas, Julius; Karpus, Vytautas; Valušis, Gintaras [Semiconductor Physics Institute, Center for Physical Sciences and Technology, A. Goštauto 11, LT-01108 Vilnius (Lithuania); Li, Lianhe; Khanna, Suraj P.; Linfield, Edmund H. [School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT (United Kingdom)

    2013-12-04

    Photoreflectance and photoluminescence (PL) spectroscopies are used to examine the optical properties and electronic structure of InGaAs quantum rods (QRs), embedded within InGaAs quantum well (QW). The nanostructures studied were grown by molecular beam epitaxy using As{sub 2} or As{sub 4} sources. The impact of As source on spectral features associated with interband optical transitions in the QRs and the surrounding QW are demonstrated. A red shift of the QR- and a blue shift of the QW-related optical transitions, along with a significant increase in PL intensity, have been observed if an As{sub 4} source is used. The changes in optical properties are attributed mainly to carrier confinement effects caused by variation of In content contrast between the QR material and the surrounding well.

  12. High resolution X-ray diffraction studies of epitaxial ZnO nanorods grown by reactive sputtering

    Science.gov (United States)

    Nandi, R.; Appani, Shravan K.; Major, S. S.

    2017-06-01

    Vertically aligned and highly c-axis oriented ZnO nanorods were epitaxially grown on c-sapphire by dc reactive sputtering of zinc target in argon-oxygen atmosphere. Scanning electron microscopy shows that substrate temperature critically controls the morphology of sputtered ZnO films, eventually causing the formation of laterally oriented ZnO nanorods at higher temperatures (700 °C-750 °C), as confirmed by ϕ-scan measurements. High resolution X-ray diffraction was used to obtain the micro-structural parameters of ZnO columnar films/nanorods from Williamson-Hall plots of ω and ω-2θ scans, and rocking curves of asymmetric reflections. These results show that epitaxially grown ZnO nanorods exhibit substantially superior micro-structural parameters, namely, tilt (0.4°), twist (0.5°), and micro-strain (4 × 10-4), compared to columnar ZnO films grown at 500 °C-600 °C. The reciprocal space maps of (0002), (0004), (" separators="| 10 1 ¯ 1 ), (" separators="| 10 1 ¯ 4 ) , and ( 11 2 ¯ 0 ) planes of ZnO nanorods were carried out to obtain the lattice parameters of epitaxial ZnO nanorods and calculate lattice strain (9 × 10-4, for both "a" and "c"), which indicates the absence of biaxial strain. Room temperature photoluminescence of epitaxial ZnO nanorods shows a strong near-band-edge emission along with negligible defect emission, owing to their high crystalline quality and micro-structural parameters.

  13. Molecular beam epitaxy of free-standing wurtzite AlxGa1-xN layers

    Science.gov (United States)

    Novikov, S. V.; Staddon, C. R.; Martin, R. W.; Kent, A. J.; Foxon, C. T.

    2015-09-01

    Recent developments with group III nitrides present AlxGa1-xN based LEDs as realistic devices for new alternative deep ultra-violet light sources. Because there is a significant difference in the lattice parameters of GaN and AlN, AlxGa1-xN substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free-standing wurtzite AlxGa1-xN bulk crystals by plasma-assisted molecular beam epitaxy (PA-MBE). Thick wurtzite AlxGa1-xN films were grown by PA-MBE on 2-in. GaAs (111)B substrates and were removed from the GaAs substrate after growth to provide free standing AlxGa1-xN samples. X-ray microanalysis measurements confirm that the AlN fraction is uniform across the wafer and mass spectroscopy measurements show that the composition is also uniform in depth. We have demonstrated that free-standing wurtzite AlxGa1-xN wafers can be achieved by PA-MBE for a wide range of AlN fractions. In order to develop a commercially viable process for the growth of wurtzite AlxGa1-xN substrates, we have used a novel Riber plasma source and have demonstrated growth rates of GaN up to 1.8 μm/h on 2-in. diameter GaAs and sapphire wafers.

  14. Influence of the interface layer on the strain relaxation of ZnSe epitaxial layers grown by MBE on (001)GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Giannini, C.; Carlino, E.; Sciacovelli, P.; Tapfer, L. [Centro Nazionale Ricerca e Sviluppo Materiali (PASTIS-CNRSM), Brindisi (Italy); Sauvage-Simkin, M.; Jedrecy, N. [Laboratoire pour l' Utilisation du Rayonnement Electromagnetique (LURE), Batiment 209D, Universite Paris-Sud, Orsay (France); Laboratoire de Mineralogie-Cristallographie, CNRS-Universites P et M Curie et D Diderot, Paris (France); Garreau, Y.; Veron, M.B. [Laboratoire pour l' Utilisation du Rayonnement Electromagnetique (LURE), Batiment 209D, Universite Paris-Sud, Orsay (France); Pinchaux, P. [Laboratoire pour l' Utilisation du Rayonnement Electromagnetique LURE, Batiment 209D, Universite Paris-Sud, Orsay (France); Universite P et M Curie, Paris (France)

    1999-05-21

    ZnSe epilayers grown by molecular beam epitaxy on GaAs(001) substrates are investigated by grazing incidence x-ray diffraction, reciprocal space mapping and transmission electron microscopy. Our data show that the Zn/Se beam pressure ratio employed during the early stages of the ZnSe growth (2 nm) strongly affects the structural properties of the overgrown stoichiometric epilayer. The different strain status of the interface (tensile and compressive for the Zn-rich and Se-rich interfaces, respectively) is directly involved in the defects evolution mechanism. While the same order of magnitude of 60 deg. dislocations was measured in all the specimens, three orders of magnitude more stacking-faults were measured in samples with a Zn-rich interface with respect to those with a Se-rich interface. In addition, a contraction of the lattice parameter towards the sample surface along the growth direction is observed only in the sample grown with an excess of Se at the interface. This lattice gradient can be explained by the presence of point defects within the II-VI epilayer thickness. The formation of point defects could be favoured by the presence of the Se-rich compressive strained interface. (author)

  15. Laser Molecular Beam Epitaxy of Multilayer Heterostructure SrNb0.05 Ti0.95O3/La0.9Sr0.1MnO3 in 10000 Unit-Cell Layers

    Institute of Scientific and Technical Information of China (English)

    HUANG Yan-Hong; HE Meng; TIAN Huan-Fang; ZHAO Kun; L(U) Hui-Bin; JIN Kui-Juan; LI Jian-Qi; YANG Guo-Zhen

    2008-01-01

    Ten thousands of unit-cell multilayer heterosturctures, [SrNb0.05 Ti0.95 O3/La0.9Sr0.1MnO3]3 (SNTO/LSMO),have been epitaxial grown on SrTiO3 (001) substrates by laser molecular beam epitaxy. The monitor of insitu reflection high-energy electron diffraction demonstrates that the heterosturctures are layer-by-layer epitaxial growth. Atomic force microscope observation indicates that the surface of the heterosturcture is atomically smooth. The measurements of cross-sectional low magnification and high-resolution transmission electron microscopy as well as the corresponding selected area electron diffraction reveal that the interfaces are of perfect orientation, and the epitaxial crystalline structure shows the orientation relation of SNTO(001)//LSMO(001),and SNTO[100]//LSMO[100].

  16. Aluminum Nitride Micro-Channels Grown via Metal Organic Vapor Phase Epitaxy for MEMs Applications

    Energy Technology Data Exchange (ETDEWEB)

    Rodak, L.E.; Kuchibhatla, S.; Famouri, P.; Ting, L.; Korakakis, D.

    2008-01-01

    Aluminum nitride (AlN) is a promising material for a number of applications due to its temperature and chemical stability. Furthermore, AlN maintains its piezoelectric properties at higher temperatures than more commonly used materials, such as Lead Zirconate Titanate (PZT) [1, 2], making AlN attractive for high temperature micro and nanoelectromechanical (MEMs and NEMs) applications including, but not limited to, high temperature sensors and actuators, micro-channels for fuel cell applications, and micromechanical resonators. This work presents a novel AlN micro-channel fabrication technique using Metal Organic Vapor Phase Epitaxy (MOVPE). AlN easily nucleates on dielectric surfaces due to the large sticking coefficient and short diffusion length of the aluminum species resulting in a high quality polycrystalline growth on typical mask materials, such as silicon dioxide and silicon nitride [3,4]. The fabrication process introduced involves partially masking a substrate with a silicon dioxide striped pattern and then growing AlN via MOVPE simultaneously on the dielectric mask and exposed substrate. A buffered oxide etch is then used to remove the underlying silicon dioxide and leave a free standing AlN micro-channel. The width of the channel has been varied from 5 ìm to 110 ìm and the height of the air gap from 130 nm to 800 nm indicating the stability of the structure. Furthermore, this versatile process has been performed on (111) silicon, c-plane sapphire, and gallium nitride epilayers on sapphire substrates. Reflection High Energy Electron Diffraction (RHEED), Atomic Force Microscopy (AFM), and Raman measurements have been taken on channels grown on each substrate and indicate that the substrate is influencing the growth of the AlN micro-channels on the SiO2 sacrificial layer.

  17. Growth of polar and non-polar nitride semiconductor quasi-substrates by hydride vapor phase epitaxy for the development of optoelectronic devices by molecular beam epitaxy

    Science.gov (United States)

    Moldawer, Adam Lyle

    The family of nitride semiconductors has had a profound influence on the development of optoelectronics for a large variety of applications. However, as of yet there are no native substrates commercially available that are grown by liquid phase methods as with Si and GaAs. As a result, the majority of electronic and optoelectronic devices are grown heteroepitaxially on sapphire and SiC. This PhD research addresses both the development of polar and non-polar GaN and AIN templates by Hydride Vapor Phase Epitaxy (HVPE) on sapphire and SiC substrates, as well as the growth and characterization of optoelectronic devices on these templates by molecular beam epitaxy (MBE). Polar and non-polar GaN templates have been grown in a vertical HVPE reactor on the C- and R-planes of sapphire respectively. The growth conditions have been optimized to allow the formation for thick (50um) GaN templates without cracks. These templates were characterized structurally by studying their surface morphologies by SEM and AFM, and their structure through XRD and TEM. The polar C-plane GaN templates were found to be atomically smooth. However, the surface morphology of the non-polar GaN films grown on the R-plane of sapphire were found to have a facetted surface morphology, with the facets intersecting at 120° angles. This surface morphology reflects an equilibrium growth, since the A-plane of GaN grows faster than the M-planes of GaN due to the lower atomic density of the plane. For the development of deep-UV optoelectronics, it is required to grow AIGaN quantum wells on AIN templates. However, since AIN is a high melting point material, such templates have to be grown at higher temperatures, close to half the melting point of the material (1500 °C). As these temperatures cannot be easily obtained by traditional furnace heating, an HVPE reactor has been designed to heat the substrate inductively to these temperatures. This apparatus has been used to grow high-quality, transparent AIN films

  18. Correlation of growth temperature with stress, defect states and electronic structure in an epitaxial GaN film grown on c-sapphire via plasma MBE.

    Science.gov (United States)

    Krishna, Shibin; Aggarwal, Neha; Mishra, Monu; Maurya, K K; Singh, Sandeep; Dilawar, Nita; Nagarajan, Subramaniyam; Gupta, Govind

    2016-03-21

    The relationship of the growth temperature with stress, defect states, and electronic structure of molecular beam epitaxy grown GaN films on c-plane (0001) sapphire substrates is demonstrated. A minimum compressively stressed GaN film is grown by tuning the growth temperature. The correlation of dislocations/defects with the stress relaxation is scrutinized by high-resolution X-ray diffraction and photoluminescence measurements which show a high crystalline quality with significant reduction in the threading dislocation density and defect related bands. A substantial reduction in yellow band related defect states is correlated with the stress relaxation in the grown film. Temperature dependent Raman analysis shows the thermal stability of the stress relaxed GaN film which further reveals a downshift in the E2 (high) phonon frequency owing to the thermal expansion of the lattice at elevated temperatures. Electronic structure analysis reveals that the Fermi level of the films is pinned at the respective defect states; however, for the stress relaxed film it is located at the charge neutrality level possessing the lowest electron affinity. The analysis demonstrates that the generated stress not only affects the defect states, but also the crystal quality, surface morphology and electronic structure/properties.

  19. Room temperature ferromagnetism in epitaxial Cr{sub 2}O{sub 3} thin films grown on r-sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Punugupati, Sandhyarani, E-mail: spunugu@ncsu.edu; Narayan, Jagdish; Hunte, Frank [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)

    2015-05-21

    We report on the epitaxial growth and magnetic properties of Cr{sub 2}O{sub 3} thin films grown on r-sapphire substrate using pulsed laser deposition. The X-ray diffraction (XRD) (2θ and Φ) and TEM characterization confirm that the films are grown epitaxially. The r-plane (011{sup ¯}2) of Cr{sub 2}O{sub 3} grows on r-plane of sapphire. The epitaxial relations can be written as [011{sup ¯}2] Cr{sub 2}O{sub 3} ‖ [011{sup ¯}2] Al{sub 2}O{sub 3} (out-of-plane) and [1{sup ¯}1{sup ¯}20] Cr{sub 2}O{sub 3} ‖ [1{sup ¯}1{sup ¯}20] Al{sub 2}O{sub 3} (in-plane). The as-deposited films showed ferromagnetic behavior up to 400 K but ferromagnetism almost vanishes with oxygen annealing. The Raman spectroscopy data together with strain measurements using high resolution XRD indicate that ferromagnetism in r-Cr{sub 2}O{sub 3} thin films is due to the strain caused by defects, such as oxygen vacancies.

  20. Electrical, luminescent, and deep trap properties of Si doped n-GaN grown by pendeo epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Polyakov, A. Y. [National University of Science and Technology MISiS, Leninskiy pr. 4, Moscow 119049 (Russian Federation); Smirnov, N. B. [National University of Science and Technology MISiS, Leninskiy pr. 4, Moscow 119049 (Russian Federation); Institute of Rare Metals, B. Tolmachevsky, 5, Moscow 119017 (Russian Federation); Yakimov, E. B. [National University of Science and Technology MISiS, Leninskiy pr. 4, Moscow 119049 (Russian Federation); Institute of Microelectronics Technology and High Purity Materials, Russian Academy of Science, 6, Academician Ossipyan str., Chernogolovka, Moscow Region 142432 (Russian Federation); Lee, In-Hwan, E-mail: ihlee@jbnu.ac.kr [School of Advanced Materials Engineering and Research Center of Advanced Materials Development, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Pearton, S. J. [University of Florida, Gainesville, Florida 32611 (United States)

    2016-01-07

    Electrical and luminescent properties and deep trap spectra of Si doped GaN films grown by maskless epitaxial lateral overgrowth (MELO) are reported. The dislocation density in the wing region of the structure was 10{sup 6 }cm{sup −2}, while in the seed region it was 10{sup 8 }cm{sup −2}. The major electron traps present had activation energy of 0.56 eV and concentrations in the high 10{sup 15 }cm{sup −3} range. A comparison of diffusion length values and 0.56 eV trap concentration in MELO GaN and epitaxial lateral overgrowth (ELOG) GaN showed a good correlation, suggesting these traps could be effective in carrier recombination. The doped MELO films were more uniform in their electrical properties than either ELOG films or undoped MELO films. We also discuss the differences in deep trap spectra and luminescence spectra of low-dislocation-density MELO, ELOG, and bulk n-GaN samples grown by hydride vapor phase epitaxy. It is suggested that the observed differences could be caused by the differences in oxygen and carbon contamination levels.

  1. Two-step growth of high quality Bi{sub 2}Te{sub 3} thin films on Al{sub 2}O{sub 3} (0001) by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Harrison, S. E.; Huo, Y.; Harris, J. S. [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Li, S. [Department of Physics, Stanford University, Stanford, California 94305 (United States); Zhou, B.; Chen, Y. L. [Department of Physics, Stanford University, Stanford, California 94305 (United States); Department of Physics, University of Oxford, Parks Road, OX1 3PU Oxford (United Kingdom); Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2013-04-29

    Large-area topological insulator Bi{sub 2}Te{sub 3} thin films were grown on Al{sub 2}O{sub 3} (0001) using a two-temperature step molecular beam epitaxy growth process. By depositing a low temperature nucleation layer to serve as a template for high temperature epitaxial film growth, a high quality terrace-step surface morphology with a significant reduction in three-dimensional defect structures was achieved. X-ray diffraction measurements indicate that high crystalline quality Bi{sub 2}Te{sub 3} layers were grown incoherently by van der Waals epitaxy using this technique. Angle resolved photoemission spectroscopy measurements verified the integrity of this growth method by confirming the presence of metallic surface states on cleaved two-step Bi{sub 2}Te{sub 3} samples.

  2. High-quality single crystalline NiO with twin phases grown on sapphire substrate by metalorganic vapor phase epitaxy

    Directory of Open Access Journals (Sweden)

    Kazuo Uchida

    2012-12-01

    Full Text Available High-quality single crystalline twin phase NiO grown on sapphire substrates by metalorganic vapor phase epitaxy is reported. X-ray rocking curve analysis of NiO films grown at different temperatures indicates a minimum full width at half maximum of the cubic (111 diffraction peak of 0.107° for NiO film grown at as low as 550 °C. Detailed microstructural analysis by Φ scan X-ray diffraction and transmission electron microscopy reveal that the NiO film consists of large single crystalline domains with two different crystallographic orientations which are rotated relative to each other along the [111] axis by 60°. These single crystal domains are divided by the twin phase boundaries.

  3. Crystalline inverted membranes grown on surfaces by electrospray ion beam deposition in vacuum.

    Science.gov (United States)

    Rauschenbach, Stephan; Rinke, Gordon; Malinowski, Nikola; Weitz, R Thomas; Dinnebier, Robert; Thontasen, Nicha; Deng, Zhitao; Lutz, Theresa; de Almeida Rollo, Pedro Martins; Costantini, Giovanni; Harnau, Ludger; Kern, Klaus

    2012-05-22

    Crystalline inverted membranes of the nonvolatile surfactant sodium dodecylsulfate are found on solid surfaces after electrospray ion beam deposition (ES-IBD) of large SDS clusters in vacuum. This demonstrates the equivalence of ES-IBD to conventional molecular beam epitaxy.

  4. Two-dimensional semiconductor HfSe{sub 2} and MoSe{sub 2}/HfSe{sub 2} van der Waals heterostructures by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Aretouli, K. E.; Tsipas, P.; Tsoutsou, D.; Marquez-Velasco, J.; Xenogiannopoulou, E.; Giamini, S. A.; Vassalou, E.; Kelaidis, N.; Dimoulas, A., E-mail: a.dimoulas@inn.demokritos.gr [Institute of Nanoscience and Nanotechnology, National Center for Scientific Research “Demokritos,” 15310, Aghia Paraskevi, Athens (Greece)

    2015-04-06

    Using molecular beam epitaxy, atomically thin 2D semiconductor HfSe{sub 2} and MoSe{sub 2}/HfSe{sub 2} van der Waals heterostructures are grown on AlN(0001)/Si(111) substrates. Details of the electronic band structure of HfSe{sub 2} are imaged by in-situ angle resolved photoelectron spectroscopy indicating a high quality epitaxial layer. High-resolution surface tunneling microscopy supported by first principles calculations provides evidence of an ordered Se adlayer, which may be responsible for a reduction of the measured workfunction of HfSe{sub 2} compared to theoretical predictions. The latter reduction minimizes the workfunction difference between the HfSe{sub 2} and MoSe{sub 2} layers resulting in a small valence band offset of only 0.13 eV at the MoSe{sub 2}/HfSe{sub 2} heterointerface and a weak type II band alignment.

  5. Molecular beam epitaxy and characterization of thin Bi{sub 2}Se{sub 3} films on Al{sub 2}O{sub 3} (110)

    Energy Technology Data Exchange (ETDEWEB)

    Tabor, Phillip; Keenan, Cameron; Urazdhin, Sergei; Lederman, David

    2011-07-04

    The structural and electronic properties of thin Bi{sub 2}Se{sub 3} films grown on Al{sub 2}O{sub 3} (110) by molecular beam epitaxy are investigated. The epitaxial films grow in the Frank-van der Merwe mode and are c-axis oriented. They exhibit the highest crystallinity, the lowest carrier concentration, and optimal stoichiometry at a substrate temperature of 200 deg. C determined by the balance between surface kinetics and desorption of Se. The crystallinity of the films improves with increasing Se/Bi flux ratio. Our results enable studies of thin topological insulator films on inert, non-conducting substrates that allow optical access to both film surfaces.

  6. High active nitrogen flux growth of GaN by plasma assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    McSkimming, Brian M., E-mail: mcskimming@engineering.ucsb.edu; Speck, James S. [Materials Department, University of California, Santa Barbara, California 93106-5050 (United States); Chaix, Catherine [RIBER S.A., 3a Rue Casimir Périer, BP 70083, 95873 Bezons Cedex (France)

    2015-09-15

    In the present study, the authors report on a modified Riber radio frequency (RF) nitrogen plasma source that provides active nitrogen fluxes more than 30 times higher than those commonly used for plasma assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N{sub 2} gas flow rates between 5 and 25 sccm while varying the plasma source's RF forward power from 200 to 600 W. The highest growth rate, and therefore the highest active nitrogen flux, achieved was ∼7.6 μm/h. For optimized growth conditions, the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 × 3 μm) on the order of 1 nm. Secondary ion mass spectroscopy impurity analysis demonstrates oxygen and hydrogen incorporation of 1 × 10{sup 16} and ∼5 × 10{sup 17}, respectively. In addition, the authors have achieved PAMBE growth of GaN at a substrate temperature more than 150 °C greater than our standard Ga rich GaN growth regime and ∼100 °C greater than any previously reported PAMBE growth of GaN. This growth temperature corresponds to GaN decomposition in vacuum of more than 20 nm/min; a regime previously unattainable with conventional nitrogen plasma sources. Arrhenius analysis of the decomposition rate shows that samples with a flux ratio below stoichiometry have an activation energy greater than decomposition of GaN in vacuum while samples grown at or above stoichiometry have decreased activation energy. The activation energy of decomposition for GaN in vacuum was previously determined to be ∼3.1 eV. For a Ga/N flux ratio of ∼1.5, this activation energy was found to be ∼2.8 eV, while for a Ga/N flux ratio of ∼0.5, it was found to be ∼7.9 eV.

  7. Development of HgCdSe for Third Generation Focal Plane Arrays using Molecular Beam Epitaxy

    Science.gov (United States)

    2013-08-01

    chemomechanical polishing, or CMP ), or submerging the material and applying a potential difference ( electrochemical polishing). In addition to reducing...as Nate England, Eric Schires, and Dr. Ravi Droopad their work setting up the molecular beam epitaxy growth and characterization systems for the...would like to thank Dr. Craig H. Swartz at Texas State University—San Marcos for his work on the electrical characterization of Hg1-xCdxSe, and Dr

  8. Strain in epitaxial Bi{sub 2}Se{sub 3} grown on GaN and graphene substrates: A reflection high-energy electron diffraction study

    Energy Technology Data Exchange (ETDEWEB)

    Li, Bin; Guo, Xin; Ho, Wingkin; Xie, Maohai, E-mail: mhxie@hku.hk [Department of Physics, The University of Hong Kong, Pokfulam Road (Hong Kong)

    2015-08-24

    Topological insulator (TI) has been one of the focus research themes in condensed matter physics in recent years. Due to the relatively large energy bandgap, Bi{sub 2}Se{sub 3} has been identified as one of the most promising three-dimensional TIs with application potentials. Epitaxial Bi{sub 2}Se{sub 3} by molecular-beam epitaxy has been reported by many groups using different substrates. A common feature is that Bi{sub 2}Se{sub 3} grows readily along the c-axis direction irrespective of the type and condition of the substrate. Because of the weak van der Waals interaction between Bi{sub 2}Se{sub 3} quintuple layers, the grown films are reported to be strain-free, taking the lattice constant of the bulk crystal. At the very initial stage of Bi{sub 2}Se{sub 3} deposition, however, strain may still exist depending on the substrate. Strain may bring some drastic effects to the properties of the TIs and so achieving strained TIs can be of great fundamental interests as well as practical relevance. In this work, we employ reflection high-energy electron diffraction to follow the lattice constant evolution of Bi{sub 2}Se{sub 3} during initial stage depositions on GaN and graphene, two very different substrates. We reveal that epitaxial Bi{sub 2}Se{sub 3} is tensile strained on GaN but strain-free on graphene. Strain relaxation on GaN is gradual.

  9. Selective-area growth of GaN nanowires on SiO{sub 2}-masked Si (111) substrates by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kruse, J. E.; Doundoulakis, G. [Department of Physics, University of Crete, P. O. Box 2208, 71003 Heraklion (Greece); Institute of Electronic Structure and Laser, Foundation for Research and Technology–Hellas, N. Plastira 100, 70013 Heraklion (Greece); Lymperakis, L. [Max-Planck-Institut für Eisenforschung, Max-Planck-Straße 1, 40237 Düsseldorf (Germany); Eftychis, S.; Georgakilas, A., E-mail: alexandr@physics.uoc.gr [Department of Physics, University of Crete, P. O. Box 2208, 71003 Heraklion (Greece); Adikimenakis, A.; Tsagaraki, K.; Androulidaki, M.; Konstantinidis, G. [Institute of Electronic Structure and Laser, Foundation for Research and Technology–Hellas, N. Plastira 100, 70013 Heraklion (Greece); Olziersky, A.; Dimitrakis, P.; Ioannou-Sougleridis, V.; Normand, P. [Institute of Nanoscience and Nanotechnology, NCSR Demokritos, Patriarchou Grigoriou and Neapoleos 27, 15310 Aghia Paraskevi, Athens (Greece); Koukoula, T.; Kehagias, Th.; Komninou, Ph. [Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki (Greece)

    2016-06-14

    We analyze a method to selectively grow straight, vertical gallium nitride nanowires by plasma-assisted molecular beam epitaxy (MBE) at sites specified by a silicon oxide mask, which is thermally grown on silicon (111) substrates and patterned by electron-beam lithography and reactive-ion etching. The investigated method requires only one single molecular beam epitaxy MBE growth process, i.e., the SiO{sub 2} mask is formed on silicon instead of on a previously grown GaN or AlN buffer layer. We present a systematic and analytical study involving various mask patterns, characterization by scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy, as well as numerical simulations, to evaluate how the dimensions (window diameter and spacing) of the mask affect the distribution of the nanowires, their morphology, and alignment, as well as their photonic properties. Capabilities and limitations for this method of selective-area growth of nanowires have been identified. A window diameter less than 50 nm and a window spacing larger than 500 nm can provide single nanowire nucleation in nearly all mask windows. The results are consistent with a Ga diffusion length on the silicon dioxide surface in the order of approximately 1 μm.

  10. Selective-area growth of GaN nanowires on SiO2-masked Si (111) substrates by molecular beam epitaxy

    Science.gov (United States)

    Kruse, J. E.; Lymperakis, L.; Eftychis, S.; Adikimenakis, A.; Doundoulakis, G.; Tsagaraki, K.; Androulidaki, M.; Olziersky, A.; Dimitrakis, P.; Ioannou-Sougleridis, V.; Normand, P.; Koukoula, T.; Kehagias, Th.; Komninou, Ph.; Konstantinidis, G.; Georgakilas, A.

    2016-06-01

    We analyze a method to selectively grow straight, vertical gallium nitride nanowires by plasma-assisted molecular beam epitaxy (MBE) at sites specified by a silicon oxide mask, which is thermally grown on silicon (111) substrates and patterned by electron-beam lithography and reactive-ion etching. The investigated method requires only one single molecular beam epitaxy MBE growth process, i.e., the SiO2 mask is formed on silicon instead of on a previously grown GaN or AlN buffer layer. We present a systematic and analytical study involving various mask patterns, characterization by scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy, as well as numerical simulations, to evaluate how the dimensions (window diameter and spacing) of the mask affect the distribution of the nanowires, their morphology, and alignment, as well as their photonic properties. Capabilities and limitations for this method of selective-area growth of nanowires have been identified. A window diameter less than 50 nm and a window spacing larger than 500 nm can provide single nanowire nucleation in nearly all mask windows. The results are consistent with a Ga diffusion length on the silicon dioxide surface in the order of approximately 1 μm.

  11. Foreign-catalyst-free growth of InAs/InSb axial heterostructure nanowires on Si (111) by molecular-beam epitaxy.

    Science.gov (United States)

    So, Hyok; Pan, Dong; Li, Lixia; Zhao, Jianhua

    2017-03-01

    Epitaxial high-quality InAs/InSb axial heterostructure nanowires are of great interest due to their distinct advantages in fundamental research as well as applications in semiconductor electronic and quantum devices. Currently, nearly all the growth of InAs/InSb axial heterostructure nanowires is assisted with foreign catalysts such as Au, and work on foreign-catalyst-free growth of InAs/InSb axial heterostructure nanowires is lacking. Here we report on the growth of InAs/InSb axial heterostructure nanowires on Si (111) substrates by molecular-beam epitaxy without using any foreign catalysts. The Sb/In beam equivalent pressure (BEP) ratio is found to have important influence on the heterostructure nanowire morphology, and InSb nanowires can be epitaxially grown on InAs nanowire stems with a hexagonal prism and nanosheet-like shapes when the Sb/In BEP ratio varies from 10 to 20. Transmission electron microscopy studies reveal that the InAs nanowire stems have a mixture of zincblende (ZB) and wurtzite (WZ) crystal structures, while InSb nanowire parts have a pure ZB crystal structure free of stacking faults. Composition analysis of axial heterostructure nanowires provides clear evidence that the InSb nanowires are epitaxially grown on InAs nanowires in an In self-assisted vapor-liquid-solid manner. This study paves a new route for growing narrow-gap semiconductor heterostructures with strong spin-orbit interaction for the study of topological states, and the growth manner presented here is expected to be used to grow other In-based axial heterostructure nanowires.

  12. 1.3μm InGaAs/InAs/GaAs Self-Assembled Quantum Dot Laser Diode Grown by Molecular Beam Epitaxy%1.3μm自组织InGaAs/InAs/GaAs量子点激光器分子束外延生长

    Institute of Scientific and Technical Information of China (English)

    牛智川; 倪海桥; 方志丹; 龚政; 张石勇; 吴东海; 孙征; 赵欢; 彭红玲; 韩勤; 吴荣汉

    2006-01-01

    The growth of multi-layer InGaAs/InAs/GaAs self-assembled quantum dots (QDs) by molecular beam epitaxy (MBE) is investigated,and a QD laser diode lasing at 1.33μm in continuous operation mode at room temperature is reported. The full width at half maximum of the band edge emitting peaks of the photoluminescence(PL) spectra at room temperature is less than 35meV for most of the multi-layer QD samples,revealing good,reproducible MBE growth conditions. Moreover, atomic force microscopy images show that the QD surface density can be controlled in the range from 1 × 1010 to 7 × 1010cm-2. The best PL properties are obtained at a QD surface density of about 4 × 1010cm-2. Edge emitting lasers containing 3 and 5 stacked QD layers as the active layer lasing at room temperature in continuous wave operation mode are reported.%报道了分子束外延生长的1.3μm多层InGaAs/InAs/GaAs自组织量子点及其室温连续激射激光器.室温带边发射峰的半高宽小于35meV,表明量子点大小比较均匀.原子力显微镜图像显示,量子点密度可以控制在(1~7)×1010cm-2范围之内,而面密度处于4×1010cm-2时有良好的光致发光谱性能.含有三到五层1. 3μm量子点的激光器成功实现了室温连续激射.

  13. Molecular beam epitaxy of GeTe-Sb{sub 2}Te{sub 3} phase change materials studied by X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Shayduk, Roman

    2010-05-20

    The integration of phase change materials into semiconductor heterostructures may lead to the development of a new generation of high density non-volatile phase change memories. Epitaxial phase change materials allow to study the detailed structural changes during the phase transition and to determine the scaling limits of the memory. This work is dedicated to the epitaxial growth of Ge-Sb-Te phase change alloys on GaSb(001). We deposit Ge-Sb-Te (GST) films on GaSb(001) substrates by means of molecular beam epitaxy (MBE). The film orientation and lattice constant evolution is determined in real time during growth using grazing incidence X-ray diffraction (GID). The nucleation stage of the growth is studied in situ using reflection high energy electron diffraction (RHEED). Four growth regimes of GST on GaSb(001) were observed: amorphous, polycrystalline, incubated epitaxial and direct epitaxial. Amorphous film grows for substrate temperatures below 100 C. For substrate temperatures in the range 100-160 C, the film grows in polycrystalline form. Incubated epitaxial growth is observed at temperatures from 180 to 210 C. This growth regime is characterized by an initial 0.6nm thick amorphous layer formation, which crystallizes epitaxially as the film thickness increases. The determined lattice constant of the films is 6.01 A, very close to that of the metastable GST phase. The films predominantly possess an epitaxial cube-on-cube relationship. At higher temperatures the films grow epitaxially, however the growth rate is rapidly decreasing with temperature. At temperatures above 270 C the growth rate is zero. The composition of the grown films is close to 2:2:5 for Ge, Sb and Te, respectively. The determined crystal structure of the films is face centered cubic (FCC) with a rhombohedral distortion. The analysis of X-ray peak widths gives a value for the rhombohedral angle of 89.56 . We observe two types of reflections in reciprocal space indicating two FCC sublattices in

  14. Integrated DFB-DBR laser modulator grown by selective area metalorganic vapor phase epitaxy growth technique

    Science.gov (United States)

    Tanbun-Ek, T.; Chen, Y. K.; Grenko, J. A.; Byrne, E. K.; Johnson, J. E.; Logan, R. A.; Tate, A.; Sergent, A. M.; Wecht, K. W.; Sciortine, P. F.; Chu, S. N. G.

    1994-12-01

    A device quality of selective epitaxy growth of InGaAsP/InP multiple quantum well (MQW) structure using low-pressure metalorganic vapor phase epitaxy (MOVPE) technique is described. The technique is applied to a monolithically integrated electroabsorption modulator with distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers. Superior device characteristics such as efficient modulation, low threshold current and high efficiency operation of the integrated devices are obtained.

  15. Observation of a Distributed Epitaxial Oxide in Thermally Grown SiO{sub 2} on Si(001)

    Energy Technology Data Exchange (ETDEWEB)

    Munkholm, A.; Brennan, S. [Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Stanford, California 94309 (United States); Comin, F.; Ortega, L. [European Synchrotron Radiation Facility, B.P. 220, F-38043, Grenoble (France)

    1995-12-04

    We present direct evidence of an ordered oxide which is epitaxially related to the underlying Si(001) substrate and is distributed throughout thermally grown oxide films with thicknesses between 80 and 1000 A. This evidence consists of diffraction peaks at the {l_angle}1,1,0.45{r_angle} positions. For films with thickness in the range 80--160 A the integrated intensity of these diffraction peaks increases roughly linearly and the ordered oxide grain size parallel to the surface is constant at 130 A. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.

  16. Interface morphology studies of liquid phase epitaxy grown HgCdTe films by atomic force microscopy

    Science.gov (United States)

    Azoulay, M.; George, M. A.; Burger, A.; Collins, W. E.; Silberman, E.

    1994-04-01

    In this paper we report an investigation of the morphology of the interfaces of liquid phase epitaxy (LPE) grown HgCdTe thin films on CdTe and CdZnTe substrates by atomic force microscopy (AFM) on freshly cleaved (110) crystallographic planes. An empirical observation which may be linked to lattice mismatch was indicated by an angle between the cleavage steps of the substrate to those of the film. The precipitates with size ranging from 5 nm to 20 nm were found to be most apparent near the interface.

  17. Demonstration of isotype GaN/AlN/GaN heterobarrier diodes by NH{sub 3}-molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Fireman, Micha N.; Browne, David A.; Mazumder, Baishakhi; Speck, James S. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Mishra, Umesh K. [Electrical and Computer Engineering Department, University of California, Santa Barbara, California 93106 (United States)

    2015-05-18

    The results of vertical transport through nitride heterobarrier structures grown by ammonia molecular beam epitaxy are presented. Structures are designed with binary layers to avoid the effects of random alloy fluctuations in ternary nitride barriers. The unintentional incorporation of Ga in the AlN growth is investigated by atom probe tomography and is shown to be strongly dependent on both the NH{sub 3} flowrate and substrate temperature growth parameters. Once nominally pure AlN layer growth conditions are achieved, structures consisting of unintentionally doped (UID) GaN spacer layers adjacent to a nominally pure AlN are grown between two layers of n+ GaN, from which isotype diodes are fabricated. Varying the design parameters of AlN layer thickness, UID spacer layer thickness, and threading dislocation density show marked effects on the vertical transport characteristics of these structures. The lack of significant temperature dependence, coupled with Fowler-Nordheim and/or Milliken-Lauritsen analysis, point to a prevalently tunneling field emission mechanism through the AlN barrier. Once flatband conditions in the UID layer are achieved, electrons leave the barrier with significant energy. This transport mechanism is of great interest for applications in hot electron structures.

  18. Automated angle-scanning photoemission end-station with molecular beam epitaxy at KEK-PF BL-1C

    CERN Document Server

    Ono, K; Horiba, K; Oh, J H; Nakazono, S; Kihara, T; Nakamura, K; Mano, T; Mizuguchi, M; Oshima, M; Aiura, Y; Kakizaki, A

    2001-01-01

    In order to satisfy demands to study the electronic structure of quantum nanostructures, a VUV beamline and a high-resolution and high-throughput photoemission end-station combined with a molecular beam epitaxy (MBE) system have been constructed at the BL-1C of the Photon Factory. An angle-resolved photoemission spectrometer, having high energy- and angular-resolutions; VG Microtech ARUPS10, was installed. The total energy resolution of 31 meV at the 60 eV of photon energy is achieved. For the automated angle-scanning photoemission, the electron spectrometer mounted on a two-axis goniometer can be rotated in vacuum by the computer-controlled stepping motors. Another distinctive feature of this end-station is a connection to a MBE chamber in ultahigh vacuum (UHV). In this system, MBE-grown samples can be transferred into the photoemission chamber without breaking UHV. Photoemission spectra of MBE-grown GaAs(0 0 1) surfaces were measured with high-resolution and bulk and surface components are clearly resolved.

  19. Advanced Si IR detectors using molecular beam epitaxy

    Science.gov (United States)

    Lin, T. L.; Jones, E. W.; George, T.; Ksendzov, A.; Huberman, M. L.

    1991-01-01

    SiGe/Si heterojunction internal photoemission (HIP) long wavelength infrared (LWIR) detectors have been fabricated by MBE. The SiGe/Si HIP detector offers a tailorable spectral response in the long wavelength infrared regime by varying the SiGe/Si heterojunction barrier. Degenerately doped p(+) SiGe layers were grown using elemental boron, as the dopant source allows a low growth temperature. Good crystalline quality was achieved for boron-doped SiGe due to the reduced growth temperature. The dark current density of the boron-doped HIP detectors was found to be thermionic emission limited. HIP detectors with a 0.066 eV were fabricated and characterized using activation energy analysis, corresponding to a 18 micron cutoff wavelength. Photoresponse of the detectors at wavelengths ranging from 2 to 12 microns has been characterized with corresponding quantum efficiencies of 5 - 0.1 percent.

  20. Investigation of cracks in GaN films grown by combined hydride and metal organic vapor-phase epitaxial method

    Directory of Open Access Journals (Sweden)

    Yang Tieying

    2011-01-01

    Full Text Available Abstract Cracks appeared in GaN epitaxial layers which were grown by a novel method combining metal organic vapor-phase epitaxy (MOCVD and hydride vapor-phase epitaxy (HVPE in one chamber. The origin of cracks in a 22-μm thick GaN film was fully investigated by high-resolution X-ray diffraction (XRD, micro-Raman spectra, and scanning electron microscopy (SEM. Many cracks under the surface were first observed by SEM after etching for 10 min. By investigating the cross section of the sample with high-resolution micro-Raman spectra, the distribution of the stress along the depth was determined. From the interface of the film/substrate to the top surface of the film, several turnings were found. A large compressive stress existed at the interface. The stress went down as the detecting area was moved up from the interface to the overlayer, and it was maintained at a large value for a long depth area. Then it went down again, and it finally increased near the top surface. The cross-section of the film was observed after cleaving and etching for 2 min. It was found that the crystal quality of the healed part was nearly the same as the uncracked region. This indicated that cracking occurred in the growth, when the tensile stress accumulated and reached the critical value. Moreover, the cracks would heal because of high lateral growth rate.

  1. Effect of Phase Purity on Dislocation Density of Pressurized-Reactor Metalorganic Vapor Phase Epitaxy Grown InN

    Science.gov (United States)

    Iwabuchi, Takuya; Liu, Yuhuai; Kimura, Takeshi; Zhang, Yuantao; Prasertsuk, Kiattiwut; Watanabe, Haruna; Usami, Noritaka; Katayama, Ryuji; Matsuoka, Takashi

    2012-04-01

    The effect of the metastable zincblende (ZB) InN inclusion in the stable wurtzite (WZ) InN on the threading dislocation densities (TDDs) of an InN film grown by pressurized-reactor metalorganic vapor phase epitaxy has been studied by X-ray diffraction measurements. InN films are directly grown on c-plane sapphire substrates with nitrided surfaces at 1600 Torr with the different growth temperature from 500 to 700 °C. Films including ZB-InN show the correlation between the ZB volume fraction and the edge component of TDDs, not the screw component of TDDs. This result can be crystallographically understood by a simple model explaining how the ZB structure is included, i.e., ZB domains existing side-by-side with WZ domains and twined ZB domains. This can be clearly observed by electron backscatter diffraction.

  2. Highly resistive C-doped hydride vapor phase epitaxy-GaN grown on ammonothermally crystallized GaN seeds

    Science.gov (United States)

    Iwinska, Malgorzata; Piotrzkowski, Ryszard; Litwin-Staszewska, Elzbieta; Sochacki, Tomasz; Amilusik, Mikolaj; Fijalkowski, Michal; Lucznik, Boleslaw; Bockowski, Michal

    2017-01-01

    GaN crystals were grown by hydride vapor phase epitaxy (HVPE) and doped with C. The seeds were high-structural-quality ammonothermally crystallized GaN. The grown crystals were highly resistive at 296 K and of high structural quality. High-temperature Hall effect measurements revealed p-type conductivity and a deep acceptor level in the material with an activation energy of 1 eV. This is in good agreement with density functional theory calculations based on hybrid functionals as presented by the Van de Walle group. They obtained an ionization energy of 0.9 eV when C was substituted for N in GaN and acted as a deep acceptor.

  3. Influence of growth parameters on the surface morphology and crystallinity of InSb epilayers grown by liquid phase epitaxy

    Indian Academy of Sciences (India)

    N K Udayashankar; H L Bhat

    2003-12-01

    Unintentionally doped homoepitaxial InSb films have been grown by liquid phase epitaxy employing ramp cooling and step cooling growth modes. The effect of growth temperature, degree of supercooling and growth duration on the surface morphology and crystallinity were investigated. The major surface features of the grown film like terracing, inclusions, meniscus lines, etc are presented step-by-step and a variety of methods devised to overcome such undesirable features are described in sufficient detail. The optimization of growth parameters have led to the growth of smooth and continuous films. From the detailed morphological, X-ray diffraction, scanning electron microscopic and Raman studies, a correlation between the surface morphology and crystallinity has been established.

  4. MBE-grown Si and Si(1-x)Ge(x) quantum dots embedded within epitaxial Gd2O3 on Si(111) substrate for floating gate memory device.

    Science.gov (United States)

    Manna, S; Aluguri, R; Katiyar, A; Das, S; Laha, A; Osten, H J; Ray, S K

    2013-12-20

    Si and Si(1-x)Ge(x) quantum dots embedded within epitaxial Gd2O3 grown by molecular beam epitaxy have been studied for application in floating gate memory devices. The effect of interface traps and the role of quantum dots on the memory properties have been studied using frequency-dependent capacitance-voltage and conductance-voltage measurements. Multilayer quantum dot memory comprising four and five layers of Si quantum dots exhibits a superior memory window to that of single-layer quantum dot memory devices. It has also been observed that single-layer Si(1-x)Ge(x) quantum dots show better memory characteristics than single-layer Si quantum dots.

  5. Growth of CuInSe2 by molecular beam epitaxy

    Science.gov (United States)

    Grindle, S. P.; Clark, A. H.; Rezaie-Serej, S.; Falconer, E.; McNeily, J.; Kazmerski, L. L.

    1980-10-01

    Molecular beam epitaxy was used to grow CuInSe2 layers on CdS (001B) and other substrates. Epitaxial growth is obtained at a substrate temperature of 300 C. The ratio of the arrival rates of copper to indium is the key parameter governing layer stoichiometry. To produce low-resistivity p-type layers, the Cu/In arrival rate ratio must be slightly higher than that used to grow nominally stoichiometric layers. This suggests that a different defect is controlling electrical properties, rather than the copper vacancy complex which dominates bulk material. CuInSe2/CdS heterojunctions were fabricated which show a maximum solar conversion efficiency of about 5%.

  6. Epitaxial niobium dioxide thin films by reactive-biased target ion beam deposition

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yuhan, E-mail: yw9ep@virginia.edu; Kittiwatanakul, Salinporn; Lu, Jiwei [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Comes, Ryan B. [Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Wolf, Stuart A. [Department of Materials Science and Engineering and Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States)

    2015-03-15

    Epitaxial NbO{sub 2} thin films were synthesized on Al{sub 2}O{sub 3} (0001) substrates via reactive bias target ion beam deposition. X-ray diffraction and Raman spectra were used to confirm the tetragonal phase of pure NbO{sub 2}. Through XPS, it was found that there was a ∼1.3 nm thick Nb{sub 2}O{sub 5} layer on the surface and the bulk of the thin film was NbO{sub 2}. The epitaxial relationship between the NbO{sub 2} film and the substrate was determined. Electrical transport measurement was measured up to 400 K, and the conduction mechanism was discussed.

  7. Molecular beam epitaxy of cubic III-nitrides on GaAs substrates

    Energy Technology Data Exchange (ETDEWEB)

    As, D.J.; Schikora, D.; Lischka, K. [Dept. of Physics, Univ. of Paderborn, Paderborn (Germany)

    2003-07-01

    Molecular beam epitaxy has successfully been used to grow crystalline layers of group III-nitrides (GaN, AlN and InN) with cubic (zinc-blende) structure on GaAs substrates. In this article, we discuss these efforts that, despite inherent difficulties due to the metastability of the c-III nitrides, led to substantial improvements of the structural, electrical and optical quality of these wide gap semiconductors. We review experimental work concerned with the epitaxy of c-GaN and the control of the growth process in-situ, the important issue of p- and n-type doping of c-GaN and investigations of the structural and optical properties of c-InGaN and c-AlGaN. (orig.)

  8. Upright and Inverted Single-Junction GaAs Solar Cells Grown by Hydride Vapor Phase Epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Simon, John; Schulte, Kevin L.; Jain, Nikhil; Johnston, Steve; Young, Michelle; Young, Matthew R.; Young, David L.; Ptak, Aaron J.

    2017-01-01

    Hydride vapor phase epitaxy (HVPE) is a low-cost alternative to conventional metal-organic vapor phase epitaxy (MOVPE) growth of III-V solar cells. In this work, we show continued improvement of the performance of HVPE-grown single-junction GaAs solar cells. We show over an order of magnitude improvement in the interface recombination velocity between GaAs and GaInP layers through the elimination of growth interrupts, leading to increased short-circuit current density and open-circuit voltage compared with cells with interrupts. One-sun conversion efficiencies as high as 20.6% were achieved with this improved growth process. Solar cells grown in an inverted configuration that were removed from the substrate showed nearly identical performance to on-wafer cells, demonstrating the viability of HVPE to be used together with conventional wafer reuse techniques for further cost reduction. These devices utilized multiple heterointerfaces, showing the potential of HVPE for the growth of complex and high-quality III-V devices.

  9. The role of defects in fluorescent silicon carbide layers grown by sublimation epitaxy

    DEFF Research Database (Denmark)

    Schimmel, Saskia; Kaiser, Michl; Jokubavicius, Valdas;

    lifetimes, high nonradiative lifetimes are crucial for efficient light conversion. Despite the excellent crystalline quality that can generally be obtained by sublimation epitaxy according to XRD measurements, the role of defects in f-SiC is not yet well understood. Recent results from room temperature...... photoluminescence, charge carrier lifetime measurements by microwave detected photoconductivity and internal quantum efficiency measurements suggest that the internal quantum efficiency of f-SiC layers is significantly affected by the incorporation of defects during epitaxy. Defect formation seems to be related...

  10. Development of gallium nitride-based ultraviolet and visible light-emitting diodes using hydride vapor-phase epitaxy and molecular beam epitaxy

    Science.gov (United States)

    Cabalu, Jasper Sicat

    Much of the work done on ultraviolet (UV) and visible III-Nitrides-based light emitting diodes (LEDs) involves growth by metal-organic chemical vapor deposition (MOCVD). In this dissertation, the growth, development, and fabrication of III-Nitrides-based UV and visible LEDs with very high photon conversion and extraction efficiencies using hydride vapor-phase epitaxy (HVPE) and radio frequency (rf) plasma-assisted molecular beam epitaxy (PAMBE) is presented. High-power electrically-pumped UV-LEDs based on GaN/AlGaN multiple quantum wells (MQWs) emitting at 340 nm and 350 nm have been fabricated in a flip-chip configuration and evaluated. Under pulsed operation, UV-LEDs emitting at 340 nm have output powers that saturate, due to device heating, at approximately 3 mW. Devices emitting at 350 nm show DC operation output powers as high as 4.5 mW under 200 mA drive current. These results were found to be equivalent with those of UV-LEDs produced by the MOCVD and HVPE methods. The concept of using textured MQWs on UV-LED structures was tested by optical pumping of GaN/AlGaN MQWs grown on textured GaN templates. Results show highly enhanced (>700 times) blue-shifted photoluminescence (PL) at 360 nm compared to similarly produced MQWs on smooth GaN templates whose PL emission is red-shifted. These results are attributed partly to enhancement in light extraction efficiency (LEE) and partly to enhancement in internal quantum efficiency (IQE). The origin of the increase in IQE is partly due to reduction of the quantum-confined Stark effect (QCSE) on QW-planes not perpendicular to the polarization direction and partly due to charge redistribution in the QWs caused by the polarization component parallel to the planes of the QWs. Similar studies have been done for visible LEDs using InGaN/GaN MQWs. Growth of LED structures on textured GaN templates employing textured MQW-active regions resulted in the production of dichromatic (430 nm and 530 nm) phosphorless white LEDs with

  11. Alloy formation during molecular beam epitaxy growth of Si-doped InAs nanowires on GaAs[111]B.

    Science.gov (United States)

    Davydok, Anton; Rieger, Torsten; Biermanns, Andreas; Saqib, Muhammad; Grap, Thomas; Lepsa, Mihail Ion; Pietsch, Ullrich

    2013-08-01

    Vertically aligned InAs nanowires (NWs) doped with Si were grown self-assisted by molecular beam epitaxy on GaAs[111]B substrates covered with a thin SiO x layer. Using out-of-plane X-ray diffraction, the influence of Si supply on the growth process and nanostructure formation was studied. It was found that the number of parasitic crystallites grown between the NWs increases with increasing Si flux. In addition, the formation of a Ga0.2In0.8As alloy was observed if the growth was performed on samples covered by a defective oxide layer. This alloy formation is observed within the crystallites and not within the nanowires. The Ga concentration is determined from the lattice mismatch of the crystallites relative to the InAs nanowires. No alloy formation is found for samples with faultless oxide layers.

  12. High Quality InAs/InSb nanowire heterostructrues grown by metalorganic vapour phase epitaxy

    DEFF Research Database (Denmark)

    Caroff, Philippe; Wagner, Jakob Birkedal; Dick, Kimberly A.

    2008-01-01

    Growth and structural analysis of epitaxial InAs/InSb nanowire heterostructures are demonstrated for the first time. InSb segments are found to be perfect crystals, free of stacking faults or other major defects, and have a sharp interface with InAs (see image). After growth the seed particle is ...

  13. An ultra-compact, high-throughput molecular beam epitaxy growth system.

    Science.gov (United States)

    Baker, A A; Braun, W; Gassler, G; Rembold, S; Fischer, A; Hesjedal, T

    2015-04-01

    We present a miniaturized molecular beam epitaxy (miniMBE) system with an outer diameter of 206 mm, optimized for flexible and high-throughput operation. The three-chamber system, used here for oxide growth, consists of a sample loading chamber, a storage chamber, and a growth chamber. The growth chamber is equipped with eight identical effusion cell ports with linear shutters, one larger port for either a multi-pocket electron beam evaporator or an oxygen plasma source, an integrated cryoshroud, retractable beam-flux monitor or quartz-crystal microbalance, reflection high energy electron diffraction, substrate manipulator, main shutter, and quadrupole mass spectrometer. The system can be combined with ultrahigh vacuum (UHV) end stations on synchrotron and neutron beamlines, or equivalently with other complex surface analysis systems, including low-temperature scanning probe microscopy systems. Substrate handling is compatible with most UHV surface characterization systems, as the miniMBE can accommodate standard surface science sample holders. We introduce the design of the system, and its specific capabilities and operational parameters, and we demonstrate the epitaxial thin film growth of magnetoelectric Cr2O3 on c-plane sapphire and ferrimagnetic Fe3O4 on MgO (001).

  14. An ultra-compact, high-throughput molecular beam epitaxy growth system

    Energy Technology Data Exchange (ETDEWEB)

    Baker, A. A.; Hesjedal, T. [Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU (United Kingdom); Diamond Light Source, Didcot OX11 0DE (United Kingdom); Braun, W., E-mail: w.braun@fkf.mpg.de, E-mail: fischer@createc.de; Rembold, S.; Fischer, A., E-mail: w.braun@fkf.mpg.de, E-mail: fischer@createc.de [CreaTec Fischer and Co. GmbH, Industriestr. 9, 74391 Erligheim (Germany); Gassler, G. [Dr. Gassler Electron Devices GmbH, List Str. 4, 89079 Ulm (Germany)

    2015-04-15

    We present a miniaturized molecular beam epitaxy (miniMBE) system with an outer diameter of 206 mm, optimized for flexible and high-throughput operation. The three-chamber system, used here for oxide growth, consists of a sample loading chamber, a storage chamber, and a growth chamber. The growth chamber is equipped with eight identical effusion cell ports with linear shutters, one larger port for either a multi-pocket electron beam evaporator or an oxygen plasma source, an integrated cryoshroud, retractable beam-flux monitor or quartz-crystal microbalance, reflection high energy electron diffraction, substrate manipulator, main shutter, and quadrupole mass spectrometer. The system can be combined with ultrahigh vacuum (UHV) end stations on synchrotron and neutron beamlines, or equivalently with other complex surface analysis systems, including low-temperature scanning probe microscopy systems. Substrate handling is compatible with most UHV surface characterization systems, as the miniMBE can accommodate standard surface science sample holders. We introduce the design of the system, and its specific capabilities and operational parameters, and we demonstrate the epitaxial thin film growth of magnetoelectric Cr{sub 2}O{sub 3} on c-plane sapphire and ferrimagnetic Fe{sub 3}O{sub 4} on MgO (001)

  15. Existence and regularity of weak solutions to a model for coarsening in molecular beam epitaxy

    CERN Document Server

    Zhang, Jun

    2011-01-01

    Taking into account the occurrence of a zero of the surface diffusion current and the requirement of the Ehrlich-Schwoebel effect, Siegert et al \\cite{Siegert94} formulate a model of Langevin type that describes the growth of pyramidlike structures on a surface under conditions of molecular beam epitaxy, and that the slope of these pyramids is selected by the crystalline symmetries of the growing film. In this article, the existence and uniqueness of weak solution to an initial boundary value problem for this model is proved, in the case that the noise is neglected. The regularity of the weak solution to models, with/without slope selection, is also investigated.

  16. Perspective: Extremely fine tuning of doping enabled by combinatorial molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Wu, J.; Božović, I. [Brookhaven National Laboratory, Upton, New York 11973-5000 (United States)

    2015-06-01

    Chemical doping provides an effective method to control the electric properties of complex oxides. However, the state-of-art accuracy in controlling doping is limited to about 1%. This hampers elucidation of the precise doping dependences of physical properties and phenomena of interest, such as quantum phase transitions. Using the combinatorial molecular beam epitaxy, we improve the accuracy in tuning the doping level by two orders of magnitude. We illustrate this novel method by two examples: a systematic investigation of the doping dependence of interface superconductivity, and a study of the competing ground states in the vicinity of the insulator-to-superconductor transition.

  17. A portable molecular beam epitaxy system for in situ x-ray investigations at synchrotron beamlines.

    Science.gov (United States)

    Slobodskyy, T; Schroth, P; Grigoriev, D; Minkevich, A A; Hu, D Z; Schaadt, D M; Baumbach, T

    2012-10-01

    A portable synchrotron molecular beam epitaxy (MBE) system is designed and applied for in situ investigations. The growth chamber is equipped with all the standard MBE components such as effusion cells with shutters, main shutter, cooling shroud, manipulator, reflection high energy electron diffraction setup, and pressure gauges. The characteristic feature of the system is the beryllium windows which are used for in situ x-ray measurements. An UHV sample transfer case allows in vacuo transfer of samples prepared elsewhere. We describe the system design and demonstrate its performance by investigating the annealing process of buried InGaAs self-organized quantum dots.

  18. Crystallographic dependence of photocatalytic activity of WO3 thin films prepared by molecular beam epitaxy.

    Science.gov (United States)

    Li, Guoqiang; Varga, Tamas; Yan, Pengfei; Wang, Zhiguo; Wang, Chongmin; Chambers, Scott A; Du, Yingge

    2015-06-21

    We investigated the impact of crystallographic orientation on the photocatalytic activity of single crystalline WO3 thin films prepared by molecular beam epitaxy on the photodegradation of rhodamine B (RhB). A clear effect is observed, with (111) being the most reactive surface, followed by (110) and (001). Photoreactivity is directly correlated with the surface free energy determined by density functional theory calculations. The RhB photodegradation mechanism is found to involve hydroxyl radicals in solution formed from photo-generated holes and differs from previous studies performed on nanoparticles and composites.

  19. Perspective: Extremely fine tuning of doping enabled by combinatorial molecular-beam epitaxy

    Directory of Open Access Journals (Sweden)

    J. Wu

    2015-06-01

    Full Text Available Chemical doping provides an effective method to control the electric properties of complex oxides. However, the state-of-art accuracy in controlling doping is limited to about 1%. This hampers elucidation of the precise doping dependences of physical properties and phenomena of interest, such as quantum phase transitions. Using the combinatorial molecular beam epitaxy, we improve the accuracy in tuning the doping level by two orders of magnitude. We illustrate this novel method by two examples: a systematic investigation of the doping dependence of interface superconductivity, and a study of the competing ground states in the vicinity of the insulator-to-superconductor transition.

  20. Growth of CrTe thin films by molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Sreenivasan, M.G. [Data Storage Institute, 5 Engineering Drive 1, Singapore 117608 (Singapore); Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Hou, X.J. [Data Storage Institute, 5 Engineering Drive 1, Singapore 117608 (Singapore); Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Teo, K.L. [Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore)]. E-mail: eleteokl@nus.edu.sg; Jalil, M.B.A. [Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Liew, T. [Data Storage Institute, 5 Engineering Drive 1, Singapore 117608 (Singapore); Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Chong, T.C. [Data Storage Institute, 5 Engineering Drive 1, Singapore 117608 (Singapore)

    2006-05-18

    We report the growth of Cr{sub 1-{delta}}Te films on (100) GaAs substrates using ZnTe buffer layers by solid-source molecular-beam epitaxial technique. RHEED patterns indicate a clear structural change during the initial stages of deposition. Temperature-dependent magnetization results reveal that different NiAs-related phases of Cr{sub 1-{delta}}Te can be obtained at different substrate temperatures. By varying the film thickness, a metastable zinc blende structure of CrTe could be obtained at lower substrate temperature.