WorldWideScience

Sample records for beam induced epitaxial

  1. Induced base transistor fabricated by molecular beam epitaxy

    Science.gov (United States)

    Chang, C.-Y.; Liu, W. C.; Jame, M. S.; Wang, Y. H.; Luryi, S.

    1986-09-01

    A novel three-terminal hot-electron device, the induced base transistor (IBT), has been fabricated by molecular beam epitaxy. Two-dimensional electron gas induced by the applied collector field in an undoped GaAs quantum well is used as the base of the IBT. The common-base current gain alpha has been achieved as high as 0.96 under a collector bias of 2.5 V and an emitter current of 3 mA.

  2. Ion beam induced epitaxy in Ge- and B- coimplanted silicon

    International Nuclear Information System (INIS)

    The epitaxial regrowth of amorphous surface layers in and Si substrate has been studied under irradiation with 400 keV Ar+ ions at the temperature range from 300 to 435degC. The amorphous layers were obtained by Ge+ implantation, followed by B+ implantation. The ion beam assisted epitaxy was found to be sensitive to both the substrate orientation and the implanted Ge concentration, and the layer-by-layer epitaxial regrowth seemed to be precluded in Si layers with high doses of Ge implants, e.g., 2.5 x 1015 ions/cm2. Electrical activation of implanted dopant B was also measured in the recrystallized Si layer. (author)

  3. Ion-beam-induced epitaxial crystallization of implanted and chemical vapor deposited amorphous silicon

    Science.gov (United States)

    La Ferla, A.; Priolo, F.; Spinella, C.; Rimini, E.; Baroetto, F.; Ferla, G.

    1989-03-01

    The dependence of ion-beam enhanced epitaxial growth of amorphous Si layers on impurities either dissolved in the film or present at the film-substrate interface is considered. In the case of ion implanted layers, electrically active dopants, like B, P, As at concentrations above 1 × 10 20/cm 3, enhance the rate by a factor of 2 with respect to the undoped layer. The enhancement shows also a weak dependence on the dopant concentration. Inert impurities, like Ar, which prevent pure thermal regrowth, do not show any appreciable influence on the ion-beam-induced growth rate. Chemical vapor deposited Si layers with a thin native interfacial oxide layer can also be epitaxially regrown under ion irradiation. A critical fluence is needed before the interfacial oxide breaks down and broadens, allowing the epitaxial crystallization to take place. This process is characterized by an activation energy of 0.44 eV. The complex phenomenon of ion-beam-induced crystallization involves a dynamical interaction between production and annealing of point defects. The presence of electrically active dopants probably influences the lifetime of point defects. Impurities which prevent thermal regrowth are instead dissolved by ballistic effects and/or radiation-enhanced mixing.

  4. 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

  5. Erbium doping of silicon and silicon carbide using ion beam induced epitaxial crystallization

    Energy Technology Data Exchange (ETDEWEB)

    Boucaud, P.; Julien, F.H.; Lourtioz, J.M.; Bernas, H.; Clerc, C.; Chaumont, J. [Univ. Paris XI, Orsay (France); Bodnar, S.; Regolini, J.L. [France Telecom CNET-CNS, Meylan (France); Lin, X.W. [Lawrence Berkeley Lab., CA (United States)

    1995-12-31

    Erbium doping of silicon and silicon carbide using implantation followed by ion beam induced epitaxial crystallization (IBIEC) is investigated. The implanted concentration of Er was 1.4 at.% in both cases. In Si(100), Rutherford backscattering/channeling revealed that about 40% of the Er atoms evolved upon rapid thermal annealing from an undetermined position (room temperature) to an interstitial tetrahedral position (650 C) and finally to a substitutional position (950 C). The remaining Er atoms were presumably trapped in the small precipitates visible in high resolution transmission electron microscopy. The photoluminescence at 1.54 {micro}m of Er{sup 3+} is enhanced with annealing and persists up to room temperature after a 950 C 1 min anneal. The high concentration of optically active Er atoms is illustrated by the lack of saturation of the photoluminescence at high pumping excitation intensity. Erbium was also implanted into cubic silicon carbide films prepared by chemical vapor deposition on Si at 900 C. Both solid phase epitaxy (SPE) and IBIEC were performed. After a 950 C anneal, the low temperature photoluminescence at 1.54 {micro}m after IBIEC was five times higher in SiC than in silicon. The difference in photoluminescence linewidth between IBIEC (broad lines) and SPE (sharp lines) is explained in terms of interactions between optically active erbium atoms.

  6. Megaelectron volt ion beam-induced epitaxy of deposited silicon and germanium-silicon alloys on (100) silicon substrates

    International Nuclear Information System (INIS)

    Solid phase heteroepitaxial crystallization of GexSi1-x/(100) Si was induced by MeV ion bombardment while heating the substrate at low temperatures. Rutherford Backscatter Spectrometry (RBS), Ion Channeling, Secondary Ion Mass Spectroscopy (SIMS) and transmission electron microscopy (TEM) techniques were used to investigate the kinetics of the reordering process as well as characterize the strain in the resultant epitaxial layer. The epitaxial recrystallization of amorphous silicon and silicon-germanium layers on (100)silicon, deposited under medium (10-7 torr) vacuum conditions, was induced by 2.5 MeV Ar beam irradiation in the low temperature range of 200-400C. The regrowth follows an Arrhenius dependence with temperature and activation energies of ∼0.3 eV were determined for the regrowth of deposited Si and a Ge38Si62 alloy. Ion beam induced heteroepitaxy was found to be sensitive to interfacial contaminants. In addition, the resultant crystalline quality for Ge-rich alloys was poor after irradiation. Ion beam induced heteroepitaxy of MBE-deposited GexSi1-x/(100) Si, deposited under high vacuum conditions after strict interfacial preparation, resulted in layer-by-layer reordering for alloys up to 65 at. % Ge. Coherently strained epilayers were reported for ion beam annealed GeSi alloys with germanium concentration less than 15 at. %. The pseudomorphic epilayers were characterized by planar and axial channeling to measure the tetragonal distortion in the strained overlayers. Strained films, produced by MeV Ar bombardment while heating the substrate at temperatures as low as 300C, were observed to relax following extended furnace anneals at temperatures of 800-900C. Such results offer the possibility of extending defect-free growth of metastable strained layers to other lattice mismatched systems

  7. Self-induced growth of vertical free-standing InAs nanowires on Si(111) by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Koblmueller, G; Hertenberger, S; Vizbaras, K; Bichler, M; Abstreiter, G [Walter Schottky Institut and Physik Department, Technische Universitaet Muenchen, 85748 Garching (Germany); Bao, F; Zhang, J-P, E-mail: Gregor.Koblmueller@wsi.tum.de [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, 215125 Suzhou (China)

    2010-09-10

    We report self-induced growth of vertically aligned (i.e. along the [111] direction), free-standing InAs nanowires on Si(111) substrates by solid-source molecular beam epitaxy. Implementation of an ultrathin amorphous SiO{sub x} mask on Si(111) facilitated epitaxial InAs nanowire growth, as confirmed by high-resolution x-ray diffraction 2{theta}-{omega} scans and transmission electron microscopy. Depending on growth temperature (in the range of 400-520 deg. C) substantial size variation of both nanowire length and diameter was found under preservation of uniform, non-tapered hexagon-shaped geometries. The majority of InAs nanowires exhibited phase-pure zinc blende crystal structure with few defective regions consisting of stacking faults. Photoluminescence spectroscopy at 20 K revealed peak emission of the InAs nanowires at 0.445 eV, which is {approx} 30 meV blueshifted with respect to the emission of the bulk InAs reference due to radial quantum confinement effects. These results show a promising route towards integration of well-aligned, high structural quality InAs-based nanowires with the desired aspect ratio and tailored emission wavelengths on an Si platform.

  8. 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.

  9. Short-pulse chemical beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Suian; Cui, Jie; Aoyagi, Yoshinobu (RIKEN, The Institute of Physical and Chemical Research, Saitama (Japan)); Tanaka, Akihiko (Bentec Co., Tokyo (Japan))

    1994-03-10

    Short-pulse chemical beam epitaxy has been proposed and studied. The short pulses with supersonic characteristics and a width of milliseconds were generated by high speed valves and the related pumping lines on a purpose-built CBE system. Using a time-of-fight technique, we verified the dependence of pulse properties on the source pressures and the valve on-time. The results indicate that modulation of molecular kinetic energy and accurate control of molecule supply were obtained. GaAs epitaxial growth with use of trimethylgallium pulses was carried out and investigated by means of RHEED (reflection high-energy electron diffraction) observation. It was demonstrated that the newly developed short-pulse chemical beam epitaxy has the advantage of high controllability

  10. Laser Induced Surface Chemical Epitaxy

    Science.gov (United States)

    Stinespring, Charter D.; Freedman, Andrew

    1990-02-01

    Studies of the thermal and photon-induced surface chemistry of dimethyl cadmium (DMCd) and dimethyl tellurium (DMTe) on GaAs(100) substrates under ultrahigh vacuum conditions have been performed for substrate temperatures in the range of 123 K to 473 K. Results indicate that extremely efficient conversion of admixtures of DMTe and DMCd to CdTe can be obtained using low power (5 - 10 mJ cm-2) 193 nm laser pulses at substrate temperatures of 123 K. Subsequent annealing at 473 K produces an epitaxial film.

  11. Silicon/Germanium Molecular Beam Epitaxy

    OpenAIRE

    Ericsson, Leif

    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...

  12. 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.

  13. 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.

  14. Twenty years of molecular beam epitaxy

    Science.gov (United States)

    Cho, A. Y.

    1995-05-01

    The term "molecular beam epitaxy" (MBE) was first used in one of our crystal growth papers in 1970, after having conducted extensive surface physics studies in the late 1960's of the interaction of atomic and molecular beams with solid surfaces. The unique feature of MBE is the ability to prepare single crystal layers with atomic dimensional precision. MBE sets the standard for epitaxial growth and has made possible semiconductor structures that could not be fabricated with either naturally existing materials or by other crystal growth techniques. MBE led the crystal growth technologies when it prepared the first semiconductor quantum well and superlattice structures that gave unexpected and exciting electrical and optical properties. For example, the discovery of the fractional quantized Hall effect. It brought experimental quantum physics to the classroom, and practically all major universities throughout the world are now equipped with MBE systems. The fundamental principles demonstrated by the MBE growth of III-V compound semiconductors have also been applied to the growth of group IV, II-VI, metal, and insulating materials. For manufacturing, the most important criteria are uniformity, precise control of the device structure, and reproducibility. MBE has produced more lasers (3 to 5 million per month for compact disc application) than any other crystal growth technique in the world. New directions for MBE are to incorporate in-situ, real-time monitoring capabilities so that complex structures can be precisely "engineered". In the future, as environmental concerns increase, the use of toxic arsine and phosphine may be limited. Successful use of valved cracker cells for solid arsenic and phosphorus has already produced InP based injection lasers.

  15. Molecular Beam Epitaxy of LiMnAs

    OpenAIRE

    Novak, V.; Cukr, M.; Soban, Z.; Jungwirth, T.; Marti, X.; Holy, V.; Horodyska, P.; Nemec, P.

    2010-01-01

    We report on the molecular beam epitaxy (MBE) growth of high crystalline quality LiMnAs. The introduction of a group-I alkali metal element Li with flux comparable to fluxes of Mn and As has not caused any apparent damage to the MBE system after as many as fifteen growth cycles performed on the system to date.

  16. Thermal stability of epitaxial Fe films grown on Si substrates by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Epitaxial Fe films are grown on Si(0 0 1) and Si(1 1 1) substrates by molecular beam epitaxy at room temperature. Several samples of one Fe/Si structure are subjected to rapid thermal annealing from 100 to 500 °C. The annealing impact on the morphological, magnetic properties and interfacial heterostructures of these samples is examined by atomic force microscopy, vibrating sample magnetometer and transmission electron microscopy, respectively. The results demonstrate that the material system Fe/Si grown at room temperature exhibits an abrupt interface and is thermally stable up to a temperature of 150 °C.

  17. Hard proximity induced superconducting gap in semiconductor - superconductor epitaxial hybrids

    Science.gov (United States)

    Jespersen, Thomas; Krogstrup, Peter; Ziino, Nino; Albrecht, Sven; Chang, Willy; Madsen, Morten; Johnson, Erik; Kuemmeth, Ferdinand; Nygård, Jesper; Marcus, Charles

    2015-03-01

    We present molecular beam epitaxy grown InAs semiconductor nanowires capped with a shell of aluminum (superconductor). The hybrid wires are grown without breaking vacuum, resulting in an epitaxial interface between the two materials as demonstrated by detailed transmission electron microscopy and simulations. The domain matching at the interface is discussed. Incorporating the epitaxial nanowire hybrids in electrical devices we performed detailed tunneling spectroscopy of the proximity induced superconducting gap in the InAs core at 20 mK. We find the sub-gap conductance being at least a factor 200 smaller than the normal state value (gap hardness). This is a significant improvement compared to devices fabricated by conventional lithographic methods and metal evaporation showing no more than a factor of ~ 5 . The epitaxial hybrids seem to solve the soft gap problem associated with the use of nanowire hybrids for future applications in topological quantum information based on Majorana zero modes. Research supported by Microsoft Station Q, Danish National Research Foundation, Villum Foundation, Lundbeck Foundation, and the European Commission.

  18. A molecular beam epitaxy facility for in situ neutron scattering

    International Nuclear Information System (INIS)

    A molecular beam epitaxy (MBE) facility has been built to enable in situ neutron scattering measurements during growth of epitaxial layers. While retaining the full capabilities of a research MBE chamber, this facility has been optimized for polarized neutron reflectometry measurements. Optimization includes a compact lightweight portable design, a neutron window, controllable magnetic field, deposition across a large 76 mm diameter sample with exceptional flux uniformity, and sample temperatures continuously controllable from 38 to 1375 K. A load lock chamber allows for sample insertion, storage of up to 4 samples, and docking with other facilities. The design and performance of this chamber are described here.

  19. Pre-nitridation induced In incorporation in InxGa1−xN nanorods on Si(111) grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    We address the issue of obtaining high quality green emitting InGaN nanorods without any phase separation. Role of pre-nitridation of the Si(111) substrate and growth, temperature on the morphology, structural and optical properties of InxGa1−xN films grown by plasma assisted molecular beam epitaxy, has been studied. The nitrogen rich growth environment and surface nitridation results in the formation of vertically well-aligned single crystalline nanorods that are coalesced and isolated at 400 °C and 500 °C, respectively. In incorporation is also seen to be enhanced to ≈28% at 400 °C to yield a stable green emission, while the nanorods grown at 500 °C show blue band-edge emission. The orientation, phase separations, and optical properties characterized by Reflection High Energy Electron Diffraction, Field Emission Scanning Electron Microscopy, high resolution x-ray diffraction, x-ray photoelectron spectroscopy, and photoluminescence are corroborated to understand the underlying mechanism. The study optimizes conditions to grow high quality catalyst-free well-aligned InGaN rods on nitrided Si surface, whose band-edge emission can be tuned from blue to green by sheer control of the substrate temperature

  20. Photo-metalorganic molecular-beam epitaxy: A new epitaxial growth technique

    Energy Technology Data Exchange (ETDEWEB)

    Tokumitsu, E.; Yamada, T.; Konagai, M.; Takahashi, K.

    1989-05-01

    Metalorganic molecular-beam epitaxy (MOMBE) combines many important advantages of molecular-beam epitaxy and metalorganic chemical vapor deposition. One of the most important features of MOMBE is that photochemical reaction can be used and we can call this new technique ''photo-MOMBE.'' Triisobutylaluminum (TIBA) has been used in photo-MOMBE instead of triethylaluminum (TEA) as a new aluminum source in order to enhance the photodecomposition. The optical absorption coefficient of TIBA for 193 nm was found to be three times greater than that of TEA. Selective deposition of Al, AlAs, and GaAlAs was carried out by using an ArF excimer laser. The Al mole fraction of GaAlAs ternary alloy grown with the excimer laser irradiation was greater than that of the film grown without the laser irradiation.

  1. Photo-metalorganic molecular-beam epitaxy: A new epitaxial growth technique

    International Nuclear Information System (INIS)

    Metalorganic molecular-beam epitaxy (MOMBE) combines many important advantages of molecular-beam epitaxy and metalorganic chemical vapor deposition. One of the most important features of MOMBE is that photochemical reaction can be used and we can call this new technique ''photo-MOMBE.'' Triisobutylaluminum (TIBA) has been used in photo-MOMBE instead of triethylaluminum (TEA) as a new aluminum source in order to enhance the photodecomposition. The optical absorption coefficient of TIBA for 193 nm was found to be three times greater than that of TEA. Selective deposition of Al, AlAs, and GaAlAs was carried out by using an ArF excimer laser. The Al mole fraction of GaAlAs ternary alloy grown with the excimer laser irradiation was greater than that of the film grown without the laser irradiation

  2. Effects of high source flow and high pumping speed on gas source molecular beam epitaxy / chemical beam epitaxy

    Science.gov (United States)

    McCollum, M. J.; Jackson, S. L.; Szafranek, I.; Stillman, G. E.

    1990-10-01

    We report the growth of GaAs by molecular beam epitaxy (MBE), gas source molecular beam epitaxy (GSMBE), and chemical beam epitaxy (CBE) in an epitaxial III-V reactor which features high pumping speed. The system is comprised of a modified Perkin-Elmer 430P molecular beam epitaxy system and a custom gas source panel from Emcore. The growth chamber is pumped with a 7000 1/s (He) diffusion pump (Varian VHS-10 with Monsanto Santovac 5 oil). The gas source panel includes pressure based flow controllers (MKS 1150) allowing triethylaluminum (TEA), triethylgallium (TEG), and trimethylindium (TMI) to be supplied without the use of hydrogen. All source lines, including arsine and phosphine, are maintained below atmospheric pressure. The high pumping speed allows total system flow rates as high as 100 SCCM and V/III ratios as high as 100. The purity of GaAs grown by MBE in this system increases with pumping speed. GaAs layers grown by GSMBE with arsine flows of 10 and 20 SCCM have electron concentrations of 1 × 10 15 cm -3 (μ 77=48,000 cm 2/V·) and 2 × 10 14 cm -3 (μ 77=78,000 cm 2/V·s) respectively. El ectron concentration varies with hydride injector temperature such that the minimum in electron concentration occurs for less than complete cracking. The effect of V/III ratio and the use of a metal eutectic bubbler on residual carrier concentration in GaAs grown by CBE is presented. Intentional Si and Be doping of CBE grown GaAs is demonstrated at a high growth rate of 5.4 μm/h.

  3. III-V semiconducting nanowires by molecular beam epitaxy

    OpenAIRE

    Jabeen, Fauzia

    2009-01-01

    This thesis is devoted to the study of the growth of III-V nanowires (NWs) by catalyst assisted and catalyst free molecular beam epitaxy (MBE). The nanostructures have been routinely characterized by scanning electron microscopy (SEM) and, to a minor extent by transmission electron microscopy (TEM). X-ray photoemission spectroscopy (XPS), scanning photoemission microscopy (SPEM), extended X-ray absrorption fi ne structure analysis (EXAFS), photoluminescence (PL) and trans- port me...

  4. Wafer curvature in molecular beam epitaxy grown heterostructures

    International Nuclear Information System (INIS)

    Wafer curvature in strained molecular beam epitaxy grown heterostructures has been studied. Theories on semiconductor wafer curvature have been re-examined and errors that have persisted in the literature have been corrected. This paper presents an approach to calculating the wafer curvature for an arbitrary multilayer system using basic physical equations. X-ray diffraction measurements have been performed to measure the radius of curvature of several samples and the results are in good agreement with the theory presented here

  5. Changes in the electro-physical properties of MCT epitaxial films affected by a plasma volume discharge induced by an avalanche beam in atmospheric-pressure air

    Science.gov (United States)

    Grigoryev, D. V.; Voitsekhovskii, A. V.; Lozovoy, K. A.; Tarasenko, V. F.; Shulepov, M. A.

    2015-11-01

    In this paper the influence of the plasma volume discharge of nanosecond duration formed in a non-uniform electric field at atmospheric pressure on samples of epitaxial films HgCdTe (MCT) films are discussed. The experimental data show that the action of pulses of nanosecond volume discharge in air at atmospheric pressure leads to changes in the electrophysical properties of MCT epitaxial films due to formation of a near-surface high- conductivity layer of the n-type conduction. The preliminary results show that it is possible to use such actions in the development of technologies for the controlled change of the properties of MCT.

  6. Kinetic roughening in models of molecular-beam epitaxy growth

    International Nuclear Information System (INIS)

    A brief survey of recent progress in understanding the kinetic roughening in growth models with surface diffusion, which are relevant for growth by molecular-beam epitaxy, in given. The main emphasis is on results of computer simulations. Properties of several different models are described and compared. In particular, results for two models, the Wolf-Villain model (and its modifications) and the full diffusion model, in 1+1, 2+1 and also in higher dimensions are presented. The asymptotic behaviour of the Wolf-Villain model is of an Edwards-Wilkinson type. Both models show an unusual scaling behaviour of the height-height correlation function

  7. All-epitaxial Co{sub 2}FeSi/Ge/Co{sub 2}FeSi trilayers fabricated by Sn-induced low-temperature epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kawano, M.; Ikawa, M.; Arima, K.; Yamada, S.; Kanashima, T.; Hamaya, K., E-mail: hamaya@ee.es.osaka-u.ac.jp [Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka 560-8531 (Japan)

    2016-01-28

    We demonstrate low-temperature growth of all-epitaxial Co{sub 2}FeSi/Ge/Co{sub 2}FeSi trilayer structures by developing Sn-induced surfactant-mediated molecular beam epitaxy (SMBE) of Ge on Co{sub 2}FeSi. Despite the growth of a semiconductor on a metal, we verify that the inserted Sn monolayers between Ge and Co{sub 2}FeSi enable to promote the 2D epitaxial growth of Ge up to 5 nm at a T{sub G} of 250 °C. An understanding of the mechanism of the Sn-induced SMBE leads to the achievement of all-epitaxial Co{sub 2}FeSi/Ge/Co{sub 2}FeSi trilayer structures with spin-valve-like magnetization reversals. This study will open a way for vertical-type and high-performance Ge-based spintronics devices.

  8. Real-time reflectance-difference spectroscopy of GaAs molecular beam epitaxy homoepitaxial growth

    International Nuclear Information System (INIS)

    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

  9. Real-time reflectance-difference spectroscopy of GaAs molecular beam epitaxy homoepitaxial growth

    Energy Technology Data Exchange (ETDEWEB)

    Lastras-Martínez, A., E-mail: alm@cactus.iico.uaslp.mx, E-mail: alastras@gmail.com; Ortega-Gallegos, J.; Guevara-Macías, L. E.; Nuñez-Olvera, O.; Balderas-Navarro, R. E.; Lastras-Martínez, L. F. [Instituto de Investigación en Comunicación Optica, Universidad Autónoma de San Luis Potosí, Alvaro Obregón 64, San Luis Potosí, SLP 78000 (Mexico); Lastras-Montaño, L. A. [IBM T. J. Watson Research Center, Yorktown Heights, New York 10598 (United States); Lastras-Montaño, M. A. [Department of Electrical and Computer Engineering, University of California, Santa Barbara, Santa Barbara, California 93106 (United States)

    2014-03-01

    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.

  10. 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.

  11. Growth of epitaxial ZnO films on sapphire substrates by plasma assisted molecular beam epitaxy

    Science.gov (United States)

    Hyndman, Adam R.; Allen, Martin W.; Reeves, Roger J.

    2014-03-01

    Epitaxial layers of ZnO have been grown on c-plane, (0001) sapphire substrates by plasma assisted molecular beam epitaxy. The oxygen:zinc flux ratio was found to be crucial in obtaining a film with a smooth surface and good crystallinity. When increasing film thickness from ~80 to 220 nm we observed an increase in the streakiness of RHEED images, and XRD revealed a reduction in crystal strain and increase in crystal alignment. A film with surface roughness of 0.5 nm and a XRD rocking curve FWHM of 0.1 for the main ZnO peak (0002) was achieved by depositing a low temperature ZnO buffer layer at 450 °C and then growing for 120 minutes at 700 °C with a Zn-cell temperature of 320 °C and an oxygen partial pressure of 7e-7 Torr. We found novel structures on two samples grown outside of our ideal oxygen:zinc flux ratio. SEM images of a sample believed to have been grown in a Zn-rich environment showed flower like structures up to 150 um in diameter which appear to have formed during growth. Another sample believed to have been deposited in a Zn-deficient environment had rings approximately 1.5 um in diameter scattered on its surface.

  12. Demonstration of molecular beam epitaxy and a semiconducting band structure for I-Mn-V compounds

    International Nuclear Information System (INIS)

    Our ab initio theory calculations predict a semiconducting band structure of I-Mn-V compounds. We demonstrate on LiMnAs that high-quality materials with group-I alkali metals in the crystal structure can be grown by molecular beam epitaxy. Optical measurements on the LiMnAs epilayers are consistent with the theoretical electronic structure. Our calculations also reproduce earlier reports of high antiferromagnetic ordering temperature and predict large, spin-orbit-coupling-induced magnetic anisotropy effects. We propose a strategy for employing antiferromagnetic semiconductors in high-temperature semiconductor spintronics.

  13. Chemical beam epitaxy growth of III–V semiconductor nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Mohummed Noori, Farah T. [University of Baghdad , College of science, Physics department , Jadiriya ,Baghdad (Iraq)

    2013-12-16

    Indium- Arsenide (InAs) nanowires were grown in a high vacuum chemical beam epitaxy (CBE) unit on InAs(111) wafers substrates at 425–454°C. Two types of nanogold were used as orientation catalyst, 40nm and 80nm. The measurements were performed using scanning electron microscopy showed that uniform nanowires. The nanowires orient vertically in the InAs nanowire scanning electron microscopy of an array 80nm diameter InAs nanowire with length is in the range 0.5–1 μm and of an array 40nm diameter with length is in the range 0.3–0.7μm. The nanowire length with growth time shows that the linear increase of nanowires start to grow as soon as TMIn is available. The growth rate with temperature was studied.

  14. Influence of a thin interfacial oxide layer on the ion beam assisted epitaxial crystallization of deposited Si

    Science.gov (United States)

    Priolo, F.; La Ferla, A.; Spinella, C.; Rimini, E.; Ferla, G.; Baroetto, F.; Licciardello, A.

    1988-12-01

    The epitaxial crystallization of chemical vapor deposited Si layers on Si substrates with a thin interfacial oxide layer was induced by a 600 keV Kr beam in the temperature range 350-500 °C. During irradiation the single crystal-amorphous interface velocity was measured in situ by monitoring the reflectivity of He-Ne laser light. We show that a critical irradiation dose is needed before the interfacial oxide breaks down and epitaxial regrowth can take place. This critical dose depends exponentially on the reciprocal temperature with an activation energy of 0.44 eV.

  15. Perspective: Rapid synthesis of complex oxides by combinatorial molecular beam epitaxy

    Science.gov (United States)

    Bollinger, A. T.; Wu, J.; Božović, I.

    2016-05-01

    The molecular beam epitaxy (MBE) technique is well known for producing atomically smooth thin films as well as impeccable interfaces in multilayers of many different materials. In particular, molecular beam epitaxy is well suited to the growth of complex oxides, materials that hold promise for many applications. Rapid synthesis and high throughput characterization techniques are needed to tap into that potential most efficiently. We discuss our approach to doing that, leaving behind the traditional one-growth-one-compound scheme and instead implementing combinatorial oxide molecular beam epitaxy in a custom built system.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  17. Energy band alignment of atomic layer deposited HfO2 on epitaxial (110)Ge grown by molecular beam epitaxy

    OpenAIRE

    Hudait, Mantu K.; Zhu, Y.; Maurya, Deepam; Priya, Shashank

    2013-01-01

    The band alignment properties of atomic layer HfO2 film deposited on epitaxial (110)Ge, grown by molecular beam epitaxy, was investigated using x-ray photoelectron spectroscopy. The cross-sectional transmission electron microscopy exhibited a sharp interface between the (110)Ge epilayer and the HfO2 film. The measured valence band offset value of HfO2 relative to (110)Ge was 2.28 +/- 0.05 eV. The extracted conduction band offset value was 2.66 +/- 0.1 eV using the bandgaps of HfO2 of 5.61 eV ...

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

    OpenAIRE

    S. S. Kushvaha; P.Pal; Shukla, A. K.; Joshi, Amish G; Govind Gupta; M. Kumar; Singh, S.; Bipin K. Gupta; Haranath, D.

    2014-01-01

    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 s...

  19. Chemical ordering in magnetic FePd/Pd(001) epitaxial thin films induced by annealing

    International Nuclear Information System (INIS)

    Chemically disordered FePd epitaxial layers are grown at room temperature by molecular beam epitaxy on a Pd(001) buffer layer and then annealed in order to induce the chemically ordered L10 (AuCu I) structure. Contrary to what is observed in the case of ordering during growth above room temperature, the ordered structure appears here with the three possible variants of the L10 phase. The ratio of the three different variant volumes is set by the residual epitaxial strain in the layer before annealing. It thus explains that for long annealing times, the long-range order parameter associated with the L10 variant with c along the (100) growth direction saturates at a value close to 0.65, and never reaches unity. Magnetic consequences of the ordering are studied

  20. 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.

  1. On the Growth of Complex Oxides by Molecular Beam Epitaxy

    Science.gov (United States)

    Fong, Dillon

    Functional materials based on complex oxides in thin film form offer new and exciting strategies for meeting many of our outstanding energy challenges through systematic control of layer sequencing, strain, etc. However, the synthesis of such oxide films can be a major challenge even when utilizing reactive molecular-beam epitaxy (MBE), a powerful deposition technique that allows the construction of materials atomic plane by atomic plane. To understand the fundamental physics of oxide growth by reactive MBE, we present in situ surface x-ray diffraction results on the growth of SrTiO3 and SrO-SrTiO3 thin films on (001)-oriented SrTiO3 substrates. For homoepitaxy, we compare sequential deposition (alternating Sr and Ti monolayer doses) with that of co-deposition of Sr and Ti, both in a background of oxygen pressure, and observe drastically different growth pathways due to the presence of a TiO2 double layer. For heteroepitaxial growth of Ruddlesden-Popper SrO-SrTiO3 films, we find that layers rearrange dynamically, resulting in layer sequences distinct from the shutter sequence. In general, the starting surface structure and composition, in combination with local thermodynamic considerations, strongly influence our ability to atomically construct new complex oxides.

  2. Structural and band alignment properties of Al2O3 on epitaxial Ge grown on (100), (110), and (111)A GaAs substrates by molecular beam epitaxy

    OpenAIRE

    Hudait, Mantu K.; Zhu, Yizheng; Maurya, Deepam; Priya, Shashank; Patra, Prabir K.; Ma, Anson W. K.; Aphale, Ashish; Macwan, Isaac

    2013-01-01

    Structural and band alignment properties of atomic layer Al2O3 oxide film deposited on crystallographically oriented epitaxial Ge grown in-situ on (100), (110), and (111)A GaAs substrates using two separate molecular beam epitaxy chambers were investigated using cross-sectional transmission microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). High-resolution triple axis x-ray measurement demonstrated pseudomorphic and high-quality Ge epitaxial layer on crystallographically oriented Ga...

  3. Redundant Sb condensation on GaSb epilayers grown by molecular beam epitaxy during cooling procedure

    International Nuclear Information System (INIS)

    The effect of four different cooling receipts on the surface morphologies of unintentionally-doped GaSb epilayers on GaSb (100) substrates grown by molecular beam epitaxy is reported. Those receipts include three different Sb beam equivalent pressure (BEP) levels and two different termination temperatures. Surface morphologies of epilayers were examined by wet etching, surface profiler, atomic force microscopy, scanning electron microscopy and Raman spectroscopy. The results demonstrate that during the cooling period, a Sb BEP of 4.00 × 10−4 Pa at a termination temperature of 400 °C induces a smooth surface without Sb condensation whereas same Sb BEP at a termination temperature of 350 °C forms a 300 nm thick Sb layer on the surface. In addition, it is revealed that by applying a wet etching procedure and using a surface profiler it is possible to identify this condensed layer from the two-sloped feature of mesa profile. - Highlights: • Sb beam flux termination temperature is crucial for redundant Sb condensation. • Sb beam flux level has a role on the thickness of redundant condensed Sb layer. • Redundant Sb layer thickness can be measured by two-sloped mesa structure

  4. Chemical beam epitaxy of CdTe, HgTe, and HgCdTe

    Energy Technology Data Exchange (ETDEWEB)

    Benz, R.G. II; Wagner, B.K.; Rajavel, D.; Summers, C.J. (Physical Sciences Lab., Georgia Tech Research Inst., Atlanta, GA (USA))

    1991-05-01

    A chemical beam epitaxy (CBE) system has been implemented for the growth of CdTe, HgTe, and their alloys. The system is briefly described. Results on the cracking of the organometallic source gases are presented. Epitaxial layers have been grown from gas sources of diethylcadmium, diisopropyltelluride and Hg vapor, as well as conventional solid sources. Optical and electrical properties are reported, demonstrating the potential of CBE for growing high quality solar cell and infrared detector material. (orig.).

  5. 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.

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

    International Nuclear Information System (INIS)

    We investigate epitaxy of AlN layers on sapphire substrates by molecular beam epitaxy. It is found that an atomically flat 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-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. (cross-disciplinary physics and related areas of science and technology)

  7. High growth rate metal-organic molecular beam epitaxy for the fabrication of GaAs space solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Freundlich, A.; Newman, F.; Monier, C.; Street, S. [University of Houston, TX (United States). Space Vacuum Epitaxy Center; Dargan, P.; Levy, M. [Riber Inc., Edison, NJ (United States)

    2000-06-01

    In this work, the epitaxial growth of GaAs photovoltaic devices using metalorganic molecular beam epitaxy (MOMBE) and chemical beam epitaxy (CBE) with growth rates in excess of 3 {mu}m/h is undertaken. The performance of these preliminary devices offer encouraging evidence for MOMBE and CBE as possible alternatives to the more common metalorganic chemical vapor deposition (MOCVD) for the production of III-V solar cells. (author)

  8. 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.

  9. Laser molecular beam epitaxy of ZnO thin films and heterostructures

    OpenAIRE

    Opel, Matthias; Geprägs, Stephan; Althammer, Matthias; Brenninger, Thomas; Gross, Rudolf

    2013-01-01

    We report on the growth of epitaxial ZnO thin films and ZnO based heterostructures on sapphire substrates by laser molecular beam epitaxy (MBE). We first discuss some recent developments in laser-MBE such as flexible ultra-violet laser beam optics, infrared laser heating systems or the use of atomic oxygen and nitrogen sources, and describe the technical realization of our advanced laser-MBE system. Then we describe the optimization of the deposition parameters for ZnO films such as laser flu...

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

    Directory of Open Access Journals (Sweden)

    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. Structural and electronic properties of epitaxial GaN layer grown on sapphire (0001) using laser molecular beam epitaxy

    International Nuclear Information System (INIS)

    Epitaxial GaN films were grown on sapphire (0001) substrates by an ultra-high vacuum laser assisted molecular beam epitaxy (MBE) system using GaN solid target with laser energy density of ∼3 J cm−2 at various growth conditions. The influence of growth temperature, layer thickness and growth rate on the structural properties of the GaN layers have been studied using high resolution x-ray diffraction, field emission scanning electron microscopy and scanning tunneling microscopy at room temperature. The epitaxial GaN layers grown at 700 °C exhibited good crystalline properties with a screw dislocation density of 3.1 × 108 cm−2 as calculated from the x-ray rocking curve measurements. The electronic properties such as core levels and valence band of GaN film were examined using x-ray photoelectron spectroscopy. Chemical composition of the GaN layer was determined using core level spectroscopy. (paper)

  12. Growth of CdTe films on GaAs by ionized cluster beam epitaxy

    Science.gov (United States)

    Tang, H. P.; Feng, J. Y.; Fan, Y. D.; Li, H. D.

    1991-06-01

    Stoichiometric epitaxial films of CdTe were grown on (100)GaAs substrates by ionized cluster beam (ICB) epitaxy. Streaky RHEED patterns indicated good crystallinity and surface flatness of the epitaxial CdTe films. CdTe(100) orientation was obtained when the substrate preheating temperature was 480°C, while CdTe growth inboth (100) and (111) orientations occured when the substrate preheating temperature was above 550°C. The characteristics of the ICB growth process were investigated and the cluster-involving growth behavior has been evidenced. When sufficient clusters were generated in the deposition beam under adequate source vapor pressures, the crystalline quality of the resulting CdTe epilayers improved significantly with the increase of kinetic energy of the CdTe clusters. The best CdTe epilayer obtained exhibited a CdTe(400) double crystal rocking curve (DCRC) having a FWHM of 630 arc sec.

  13. Growth of CdTe films on GaAs by ionized cluster beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Tang, H.P.; Feng, J.Y.; Fan, Y.D.; Li, H.D. (Dept. of Materials Science and Engineering, Tsinghua Univ., Beijing (China))

    1991-06-01

    Stoichiometric epitaxial films of CdTe were grown on (100)GaAs substrates by ionized cluster beam (ICB) epitaxy. Streaky RHEED patterns indicated good crystallinity and surface flatness of the epitaxial CdTe films. CdTe(100) orientation was obtained when the substrate preheating temperature was 480degC, while CdTe growth in both (100) and (111) orientations occurred when the substrate preheating temperature was above 550degC. The characteristics of the ICB growth process were investigated and the cluster-involving growth behavior has been evidenced. When sufficient clusters were generated in the deposition beam under adequate source vapor pressures, the crystalline quality of the resulting CdTe epilayers improved significantly with the increase of kinetic energy of the CdTe clusters. The best CdTe epilayer obtained exhibited a CdTe(400) double crystal rocking curve (DCRC) having a FWHM of 630 arc sec. (orig.).

  14. Superconductivity in oxygen doped iron telluride by molecular beam epitaxy

    Science.gov (United States)

    Zheng, Mao

    Iron base superconductor have gained much attention in the research community. They offer great potentials to improve our understanding of the subject of superconductivity by having another family of high temperature superconductors to compare and contrast to the cuprates. Practically, the iron based superconductors seems to be even better candidates for applications in power generation and power transmission. Iron telluride is regarded as the parent compound of the "11" family, the family of iron chalcogenide that has the simplest structure. Iron telluride itself is not a superconductor, by can become one when doped with oxygen. In this investigation, we developed the growth recipe of thin film iron telluride by Molecular Beam Epitaxy (MBE). We found the growth to be self-regulated, similar to that of GaAs. The initial layers of growth seem to experience a spontaneous crystallization, as the film quickly go from the initial polycrystalline phase to highly crystalline in just a few unit cells. We studied oxygen doping to the iron telluride thin films and the resultant superconductivity. We characterized the sample with AFM, XRD, transport, and STEM-EELS, and we found that interfacial strain is not an essential ingredient of superconductivity in this particular case. We investigated the doping conditions for two candidate oxygen doping modes: substitution and interstitial. We found that substitution occurs when the film grown in oxygen, while interstitial oxygen is primarily incorporated during annealing after growth. The substitutional oxygen are concentrated in small local regions where substitution is around 100%, but does not contribute to superconductivity. We estimated substitutional oxygen to be about 5%, and is the proximate cause of superconductivity. Hall experiment on our sample showed a shift of dominant carrier type from holes to electrons around 35 K, but the transition was set in motion as early as the structural phase transition around 70 K. We

  15. Molecular-beam epitaxy growth and characterization of 5-{mu}m quantum cascade laser

    Energy Technology Data Exchange (ETDEWEB)

    Mamutin, V V; Ustinov, V M; Ilyinskaya, N D; Baydakova, M V; Ber, B Ya; Kasantsev, D Yu, E-mail: boris.ber@mail.ioffe.ru [Ioffe Physical-Technical Institute of the Russian Academy of Sciences, St. Petersburg, 26 Polytechnicheskaya St, 194021 (Russian Federation)

    2011-04-01

    Molecular-beam epitaxy growth of 5 {mu}m emitting strain-compensated quantum semiconductor laser (QCL) is reported. The QCL structure is characterized by complementary techniques: high-resolution X-ray diffraction and dynamical secondary-ion mass-spectrometry, that reveal the high quality of QCL structure and in-depth distribution of chemical composition, respectively.

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

    Directory of Open Access Journals (Sweden)

    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.

  17. Molecular beam epitaxy growth of InSb1−xBix thin films

    DEFF Research Database (Denmark)

    Song, Yuxin; Wang, Shumin; Saha Roy, Ivy; Shi, Peixiong; Hallen, Anders; Lai, Zonghe

    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 are...

  18. Induced Superconductivity and Engineered Josephson Tunneling Devices in Epitaxial (111)-Oriented Gold/Vanadium Heterostructures.

    Science.gov (United States)

    Wei, Peng; Katmis, Ferhat; Chang, Cui-Zu; Moodera, Jagadeesh S

    2016-04-13

    We report a unique experimental approach to create topological superconductors by inducing superconductivity into epitaxial metallic thin film with strong spin-orbit coupling. Utilizing molecular beam epitaxy technique under ultrahigh vacuum conditions, we are able to achieve (111) oriented single phase of gold (Au) thin film grown on a well-oriented vanadium (V) s-wave superconductor film with clean interface. We obtained atomically smooth Au thin films with thicknesses even down to below a nanometer showing near-ideal surface quality. The as-grown V/Au bilayer heterostructure exhibits superconducting transition at around 3.9 K. Clear Josephson tunneling and Andreev reflection are observed in S-I-S tunnel junctions fabricated from the epitaxial bilayers. The barrier thickness dependent tunneling and the associated subharmonic gap structures (SGS) confirmed the induced superconductivity in Au (111), paving the way for engineering thin film heterostructures based on p-wave superconductivity and nano devices exploiting Majorana Fermions for quantum computing. PMID:26943807

  19. Palladium assisted hetroepitaxial growth of an InAs nanowire by molecular beam epitaxy

    International Nuclear Information System (INIS)

    The palladium (Pd) assisted epitaxial growth of technologically important InAs nanowires grown on GaAs{111}B substrates using molecular beam epitaxy is reported. The grown free-standing InAs nanowires adapted a vapor–liquid–solid growth mechanism. The impacts of the catalyst particle density, growth temperature and input V/III precursor ratio have been investigated to identify better growth conditions for getting high-density non-<111>-orientated InAs nanowires. We assert here that two kind of nanowires are observed, one having a pure zinc-blende crystalline structure free of stacking faults, and the other with a defect-free wurtzite crystalline structure. However, few of them have defect imperfections too. The L- and Y-shaped nanowires confirm similar surface free energies for possible <110> growth directions. These unusual growth directions are attributed to the effect of the catalyst material as well as the surface-induced strain at the interface between the grown nanowires with substrates. The structural features of the grown nanowires are studied by employing scanning and transmission electron microscopic techniques. The obtained TEM results confirm that the nanowire catalyst interface is not a straightforward zinc-blende structured nanowire. Energy dispersive x-ray (EDX) analysis reveals that the tip of the grown nanowires with the chemical composition of Pd and In have a nearly 50:50 ratio, while the nanowire body did not have any catalyst traces other than the composition of InAs for both type of nanowires. The obtained high angle annular dark field (HAADF) TEM image for both types of nanowires along with the intensity profile provided evidence for cubic as well as hexagonal facets. (paper)

  20. Structural evolution of Re (0001) thin films grown on Nb (110) surfaces by molecular beam epitaxy

    OpenAIRE

    Welander, Paul B.

    2010-01-01

    The heteroepitaxial growth of Re (0001) films on Nb (110) surfaces has been investigated. Nb/Re bilayers were grown on A-plane sapphire -- alpha-Al2O3 (11-20) -- by molecular beam epitaxy. While Re grew with a (0001) surface, the in-plane epitaxial relationship with the underlying Nb could be best described as a combination of Kurdjumov-Sachs and Nishiyama-Wassermann orientations. This relationship was true regardless of Re film thickness. However, an evolution of the surface morphology with ...

  1. Growth of GaN nanowall network on Si (111) substrate by molecular beam epitaxy

    OpenAIRE

    Zhong, Aihua; Hane, Kazuhiro

    2012-01-01

    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 ...

  2. 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.

  3. Growth of DyBa2Cu3Ox thin films by molecular beam epitaxy

    International Nuclear Information System (INIS)

    In-situ growth of superconducting DyBa2Cu3Ox thin films on single crystal SrTiO3 substrates has been investigated under molecular beam epitaxial conditions and using a dc glow discharge source to provide activated oxygen. The effect of the substrate temperature on phase formation and texture of the films has been investigated. Epitaxial films with c-axis orientation have been prepared at 700 degC. The films were found to undergo superconducting transition at ∼ 90K and exhibited a critical current density of ∼ 7x105 Amp/cm2 at 77K. (author)

  4. Lutetium-doped EuO films grown by molecular-beam epitaxy

    OpenAIRE

    Melville, A; Mairoser, T.; Mannhart, J.; Schlom, D. G.; Schmehl, A.; Shai, D. E.; Monkman, E. J.; Harter, J. W.; Heeg, T.; Holländer, B; Schubert, J; Shen, K. M.

    2012-01-01

    The effect of lutetium doping on the structural, electronic, and magnetic properties of epitaxial EuO thin films grown by reactive molecular-beam epitaxy is experimentally investigated. The behavior of Lu-doped EuO is contrasted with doping by lanthanum and gadolinium. All three dopants are found to behave similarly despite differences in electronic configuration and ionic size. Andreev reflection measurements on Lu-doped EuO reveal a spin-polarization of 96% in the conduction band, despite n...

  5. 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.

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

    International Nuclear Information System (INIS)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  8. 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.

  9. Direct growth of graphene on in situ epitaxial hexagonal boron nitride flakes by plasma-assisted molecular beam epitaxy

    International Nuclear Information System (INIS)

    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

  10. Laser molecular beam epitaxy of ZnO thin films and heterostructures

    International Nuclear Information System (INIS)

    We report on the growth of epitaxial ZnO thin films and ZnO-based heterostructures on sapphire substrates by laser molecular beam epitaxy (MBE). We first discuss some recent developments in laser-MBE such as flexible ultraviolet laser beam optics, infrared laser heating systems or the use of atomic oxygen and nitrogen sources, and describe the technical realization of our advanced laser-MBE system. Then we describe the optimization of the deposition parameters for ZnO films such as laser fluence and substrate temperature and the use of buffer layers. The detailed structural characterization by x-ray analysis and transmission electron microscopy shows that epitaxial ZnO thin films with high structural quality can be achieved, as demonstrated by a small out-of-plane and in-plane mosaic spread as well as the absence of rotational domains. We also demonstrate the heteroepitaxial growth of ZnO-based multilayers as a prerequisite for spin transport experiments and the realization of spintronic devices. As an example, we show that TiN/Co/ZnO/Ni/Au multilayer stacks can be grown on (0 0 0 1)-oriented sapphire with good structural quality of all layers and well defined in-plane epitaxial relations. (paper)

  11. Epitaxial growth of MgO and Fe/MgO/Fe magnetic tunnel junctions on (100)-Si by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Epitaxial growth of MgO barrier on Si is of technological importance due to the symmetry filtering effect of the MgO barrier in conjunction with bcc-ferromagnets. We study the epitaxial growth of MgO on (100)-Si by molecular beam epitaxy. MgO matches Si with 4:3 cell ratio, which renders Fe to be 45 deg. rotated relative to Si, in sharp contrast to the direct epitaxial growth of Fe on Si. The compressive strains from Si lead to the formation of small angle grain boundaries in MgO below 5 nm, and also affect the transport characteristics of Fe/MgO/Fe magnetic tunnel junctions formed on top

  12. Hollow-anode plasma source for molecular beam epitaxy of gallium nitride

    International Nuclear Information System (INIS)

    GaN films have been grown by molecular beam epitaxy (MBE) using a hollow-anode nitrogen plasma source. The source was developed to minimize defect formation as a result of contamination and ion damage. The hollow-anode discharge is a special form of glow discharge with very small anode area. A positive anode voltage drop of 30 endash 40 V and an increased anode sheath thickness leads to ignition of a relatively dense plasma in front of the anode hole. Driven by the pressure gradient, the open-quote open-quote anode close-quote close-quote plasma forms a bright plasma jet streaming with supersonic velocity towards the substrate. Films of GaN have been grown on (0001) SiC and (0001) Al2O3 at 600 endash 800 degree C. The films were investigated by photoluminescence, cathodoluminescence, x-ray diffraction, Rutherford backscattering, and particle-induced x-ray emission. The film with the highest structural quality had a rocking curve width of 5 arcmin, the lowest reported value for MBE growth to date. copyright 1996 American Institute of Physics

  13. Plasma-assisted molecular beam epitaxy of (11-22)-oriented 3-nitrides

    International Nuclear Information System (INIS)

    This work reports on the molecular-beam epitaxial growth of (1122)-oriented semi-polar nitride semiconductors using m-sapphire substrates. The (1122) crystallographic orientation is predefined by AlN deposition on m-sapphire under N excess. On top of this AlN buffer layer, undoped or Si-doped two-dimensional GaN(1122) films are formed under Ga-rich conditions, with a stabilized Ga-excess ad-layer of about 1.05±0.10 ML. In contrast, Mg tends to segregate on the GaN surface, inhibiting the self-regulated Ga excess film. Nevertheless, uniform Mg incorporation can be obtained, and p-type conductivity was achieved. GaN/AlN quantum wells are synthesized by deposition of the binary compounds under the above-described conditions. In the case of GaN/AlN quantum dots, the three-dimensional transition is induced by a growth interruption under vacuum. The reduction of the internal electric field in GaN/AlN nano-structures is confirmed by the blue shift of the photoluminescence spectrum and by the short photoluminescence decay times measured at low temperature. These results are consistent with theoretical calculations of the electronic structure. (author)

  14. Photoluminescence of localized excitons in ZnCdO thin 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.; Shen, J. L.; Chou, W. C.

    2016-07-01

    We have investigated the luminescence characteristics of Zn1-xCdxO thin films with different Cd contents grown by molecular beam epitaxy system. The temperature-dependent photoluminescence (PL) and excitation power-dependent PL spectra were measured to clarify the luminescence mechanisms of the Zn1-xCdxO thin films. The peak energy of the Zn1-xCdxO thin films with increasing the Cd concentration is observed as redshift and can be fitted by the quadratic function of alloy content. The broadened full-width at half-maximum (FWHM) estimated from the 15 K PL spectra as a function of Cd content shows a larger deviation between the experimental values and theoretical curve, which indicates that experimental FWHM values are affected not only by alloy compositional disorder but also by localized excitons occupying states in the tail of the density of states. The Urbach energy determined from an analysis of the lineshape of the low-energy side of the PL spectrum and the degree of localization effect estimated from the temperature-induced S-shaped PL peak position described an increasing mean exciton-localization effects in ZnCdO films with increasing the Cd content. In addition, the PL intensity and peak position as a function of excitation power are carried out to clarify the types of radiative recombination and the effects of localized exciton in the ZnCdO films with different Cd contents.

  15. Molecular Beam Epitaxial Growth of GaAs on (631) Oriented Substrates

    International Nuclear Information System (INIS)

    In this work, we report the study of the homoepitaxial growth of GaAs on (631) oriented substrates by molecular beam epitaxy (MBE). We observed the spontaneous formation of a high density of large scale features on the surface. The hilly like features are elongated towards the [-5, 9, 3] direction. We show the dependence of these structures with the growth conditions and we present the possibility of to create quantum wires structures on this surface

  16. Gas source molecular beam epitaxy of GaN with hydrazine on spinel substrates

    Science.gov (United States)

    Nikishin, S. A.; Temkin, H.; Antipov, V. G.; Guriev, A. I.; Zubrilov, A. S.; Elyukhin, V. A.; Faleev, N. N.; Kyutt, R. N.; Chin, A. K.

    1998-05-01

    Growth of high quality wurtzite-structure GaN layers on (111) MgAl2O4 by gas source molecular beam epitaxy is described. Hydrazine was used as a source of active nitrogen. In situ reflection high energy electron diffraction was used to monitor the growth mode. Two-dimensional growth was obtained at temperatures above 750 °C on multi-step GaN buffer layers. The resulting GaN films show excellent luminescence properties.

  17. Low phonon energy Nd:LaF3 channel waveguide lasers fabricated by molecular beam epitaxy

    OpenAIRE

    Bhutta, T.; Chardon, A.M.; Shepherd, D. P.; Daran, E.; Serrano, C.; Munoz-Yague, A.

    2001-01-01

    We report the first fabrication and laser operation of channel waveguides based on LaF3 planar thin films grown by molecular beam epitaxy. To our knowledge, this is the lowest phonon energy dielectric material to have shown guided-wave laser operation to date. A full characterization, in terms of spectroscopy, laser results, and propagation losses, is given for the planar thin films upon which the channel waveguides are based. Two channel-fabrication methods are then described, the first invo...

  18. Carrier dynamics in ZnxCd1-xO films grown by molecular beam epitaxy

    Science.gov (United States)

    Cheng, F. J.; Lee, Y. C.; Hu, S. Y.; Lin, Y. C.; Tiong, K. K.; Chou, W. C.

    2016-05-01

    In this work, the carrier dynamics in Zn1-xCdxO thin films with different Cd contents grown by molecular beam epitaxy system have been investigated using photoluminescence and time-resolved photoluminescence measurements. The carrier lifetime can be estimated from the PL decay curve fitted by triple exponential function. The emission energy dependence and temperature dependence of the PL decay time indicate that carrier localization dominate the luminescence mechanism of the ZnCdO alloy semiconductor.

  19. Low-temperature grown graphene films by using molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Meng-Yu [Institute of Electronics, National Taiwan University, Taipei, Taiwan (China); Research Center for Applied Sciences, Academia Sinica, Nankang, Taipei, Taiwan (China); Guo, Wei-Ching; Wang, Pro-Yao [Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, Taiwan (China); Wu, Meng-Hsun [College of Photonics, National Chiao-Tung University, Tainan, Taiwan (China); Liu, Te-Huan; Chang, Chien-Cheng [Institute of Applied Mechanics, National Taiwan University, Taipei, Taiwan (China); Pao, Chun-Wei; Lin, Shih-Yen [Research Center for Applied Sciences, Academia Sinica, Nankang, Taipei, Taiwan (China); Lee, Si-Chen [Institute of Electronics, National Taiwan University, Taipei, Taiwan (China)

    2012-11-26

    Complete graphene film is prepared by depositing carbon atoms directly on Cu foils in a molecular beam epitaxy chamber at 300 Degree-Sign C. The Raman spectrum of the film has indicated that high-quality few-layer graphene is obtained. With back-gated transistor architecture, the characteristic current modulation of graphene transistors is observed. Following the similar growth procedure, graphitization is observed at room temperature, which is consistent with the molecular dynamics simulations of graphene growth.

  20. Transport properties of modulation-doped structures grown by molecular beam epitaxy after focused ion beam implantation

    International Nuclear Information System (INIS)

    Modulation-doped structures are grown by molecular beam epitaxy after focused ion beam writing. The growth and implantation chambers are connected in a high vacuum to minimize the effect of growth interruption. The electron channel is drastically depleted by the buried Be+ implanted region, but only slightly depleted by the buried Au+ and Au2+ implanted regions. This is because Be+ implantation forms a p-type material, while Au+ or Au2+ implantation leaves damage only in the n-type material. Be+ implantation is therefore used to fabricate 0.1 μm-wide wires with electron mobility of 2.1x105 cm2/Vs. (author)

  1. Epitaxial growth of HgCdTe 1.55-um avalanche photodiodes by molecular beam epitaxy

    Science.gov (United States)

    de Lyon, Terence J.; Baumgratz, B.; Chapman, G. R.; Gordon, E.; Hunter, Andrew T.; Jack, Michael D.; Jensen, John E.; Johnson, W.; Johs, Blaine D.; Kosai, K.; Larsen, W.; Olson, G. L.; Sen, M.; Walker, B.

    1999-04-01

    Separate absorption and multiplication avalanche photodiode (SAM-APD) device structures, operating in the 1.1 - 1.6 micrometer spectral range, have been fabricated in the HgCdTe material system by molecular-beam epitaxy. These HgCdTe device structures, which offer an alternative technology to existing III-V APD detectors, were grown on CdZnTe(211)B substrates using CdTe, Te, and Hg sources with in situ In and As doping. The alloy composition of the HgCdTe layers was adjusted to achieve both efficient absorption of IR radiation in the 1.1 - 1.6 micrometer spectral range and low excess-noise avalanche multiplication. To achieve resonant enhancement of hole impact ionization from the split-off valence band, the Hg(subscript 1-x)Cd(subscript x)Te alloy composition in the gain region of the device, x equals 0.73, was chosen to achieve equality between the bandgap energy and spin-orbit splitting. The appropriate value of this alloy composition was determined from analysis of the 300 K bandgap and spin-orbit splitting energies of a set of calibration layers, using a combination of IR transmission and spectroscopic ellipsometry measurements. MBE-grown APD epitaxial wafers were processed into passivated mesa-type discrete device structures and diode mini-arrays using conventional HgCdTe process technology. Device spectral response, dark current density, and avalanche gain measurements were performed on discrete diodes and diode mini- arrays on the processed wafers. Avalanche gains in the range of 30 - 40 at reverse bias of 85 - 90 V and array-median dark current density below 2 X 10(superscript -4) A/cm(superscript 2) at 40 V reverse bias have been demonstrated.

  2. 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.

  3. Epitaxial growth of M-plane GaN on ZnO micro-rods by plasma-assisted molecular beam epitaxy

    OpenAIRE

    Shuo-Ting You; Ikai Lo; Jenn-Kai Tsai; Cheng-Hung Shih

    2015-01-01

    We have studied the GaN grown on ZnO micro-rods by plasma-assisted molecular beam epitaxy. From the analyses of GaN microstructure grown on non-polar M-plane ZnO surface ( 10 1 ̄ 0 ) by scanning transmission electron microscope, we found t...

  4. Growth study of chemical beam epitaxy of GaN xP 1 - x using NH 3 and tertiarybutylphosphine

    Science.gov (United States)

    Li, N. Y.; Wong, W. S.; Tomich, D. H.; Dong, H. K.; Solomon, J. S.; Grant, J. T.; Tu, C. W.

    1996-07-01

    A study in the growth of GaN xP 1 - x epilayers by chemical beam epitaxy using tertiarybutylphosphine (TBP), ammonia (NH 3), and elemental Ga or triethylgallium is reported. Monitoring reflection high-energy electron diffraction (RHEED) intensity oscillations, we observe that both group-III- and group-V-induced incorporation rates are increased when NH 3 is introduced into a single cracker with TBP. From the difference in the periods of group-V-induced RHEED intensity oscillations, a 16% N incorporation is expected, but X-ray rocking curve measurement shows only 0.08% N. Using separate TBP and NH 3 crackers results in no enhancement in incorporation rates. We conclude that the cracking efficiency of TBP is increased with NH 3 co-injection.

  5. Strain-induced properties of epitaxial VOx thin films

    Science.gov (United States)

    Rata, A. D.; Hibma, T.

    2005-01-01

    We have grown VOx thin films on different substrates in order to investigate the influence of epitaxial strain on the transport properties. We found that the electric conductivity is much larger for films grown under compressive strain on SrTiO3 substrates, as compared to bulk material and VOx films grown under tensile strain on MgO substrates. A clear crossover from metallic to semiconducting behavior is observed when increasing the oxygen content x. Apparently, the application of strain induces a Mott-Hubbard insulator-to-metal transition in VOx<1. The VOx/SrTiO3 films show an unexpected large positive magnetoresistance effect at low temperatures, which is not found in the VOx films grown under tensile strain on MgO or on a substrate with a similar lattice parameter.

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

    International Nuclear Information System (INIS)

    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

  7. GaN grown on (1 1 1) single crystal diamond substrate by molecular beam epitaxy

    Science.gov (United States)

    Dussaigne, A.; Malinverni, M.; Martin, D.; Castiglia, A.; Grandjean, N.

    2009-10-01

    GaN epilayers are grown on (1 1 1) oriented single crystal diamond substrate by ammonia-source molecular beam epitaxy. Each step of the growth is monitored in situ by reflection high energy electron diffraction. It is found that a two-dimensional epitaxial wurtzite GaN film is obtained. The surface morphology is smooth: the rms roughness is as low as 1.3 nm for 2×2 μm 2 scan. Photoluminescence measurements reveal pretty good optical properties. The GaN band edge is centred at 3.469 eV with a linewidth of 5 meV. These results demonstrate that GaN heteroepitaxially grown on diamond opens new rooms for high power electronic applications.

  8. 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.

  9. Growth of GaNAs/GaAs multiple quantum well by molecular beam epitaxy using modulated N radical beam source

    International Nuclear Information System (INIS)

    GaNAs/GaAs multiple quantum well (MQW) structures have been grown on GaAs(001) substrates by molecular beam epitaxy (MBE) using modulated N radical beam source under optimized conditions, wherein the amount of N2 gas flow, RF-power and shutter sequence are systematically controlled. Clear and flat GaNAs/GaAs interfaces were observed in the cross-sectional transmission electron microscopy (TEM) measurements. Fine MQW structures originating from the precise control of the modulated N radical beam have been demonstrated as clear satellite peaks from the X-ray diffraction (XRD) measurements and sharp photoluminescence (PL) peaks. The step-like behaviors in the absorption spectra which reflect the density of state in two-dimensional systems, were clearly observed for all MQW samples. (authors)

  10. Electrical properties of scandium nitride epitaxial films grown on (100) magnesium oxide substrates by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Scandium nitride (ScN) films were grown on (100) MgO single crystals by a molecular beam epitaxy method. The effects of growth conditions, including [Sc]/[N] ratio, growth temperature, and nitrogen radical state, on the electrical properties of the ScN films were studied. The ScN films comprised many small columnar grains. Hall coefficient measurements confirmed that the ScN films were highly degenerate n-type semiconductors and that the carrier concentration of the ScN films was sensitive to the growth temperature and the nitrogen radical states during the film growth. The carrier concentrations of the ScN films ranged from 1019–1021 cm−3 while the Hall mobilities ranged from 50–130 cm2·V−1·s−1 for undoped films. The temperature-dependent Hall coefficient measurements showed that the carrier concentration is nearly independent of temperature, indicating that the change in resistivity with temperature is explained by a change in the Hall mobility. The temperature-dependence of the Hall mobility was strongly affected by the growth conditions

  11. 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.

  12. Efficient photo-enhancement of GaP and AlGaP growth in chemical beam epitaxy

    Science.gov (United States)

    Yoshimoto, M.; Ozasa, K.; Matsunami, H.

    1991-11-01

    The growth rate of GaP and AlGaP epitaxial layers was efficiently enhanced by N2-laser irradiation at low substrate temperatures in chemical beam epitaxy. The photo-enhancement efficiency, defined as the ratio of the number of deposited Ga atoms to the number of irradiating photons per unit area per unit time, is estimated to be 7×10-4. The decomposition of triethylaluminum was also enhanced by the irradiation, but less efficiently.

  13. Nanoclusters of CaSe in calcium-doped Bi2Se3 grown by molecular-beam epitaxy

    Science.gov (United States)

    Shang, Panju; Guo, Xin; Zhao, Bao; Dai, Xianqi; Bin, Li; Jia, Jinfeng; Li, Quan; Xie, Maohai

    2016-02-01

    In calcium (Ca) doped Bi2Se3 films grown by molecular beam epitaxy, nanoclusters of CaSe are revealed by high-angle annular dark field imaging and energy dispersive x-ray spectroscopy analysis using a scanning transmission electron microscope. As the interface between the ordinary insulator CaSe and topological insulator, Bi2Se3, can host topological nontrivial interface state, this represents an interesting material system for further studies. We show by first principles total energy calculations that aggregation of Ca atoms in Bi2Se3 is driven by energy minimization and a preferential intercalation of Ca in the van der Waals gap between quintuple layers of Bi2Se3 induces reordering of atomic stacking and causes an increasing amount of stacking faults in film. The above findings also provide an explanation of less-than-expected electrical carrier (hole) concentrations in Ca-doped samples.

  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. Universality and geometry dependence in the class of the nonlinear molecular beam epitaxy equation

    OpenAIRE

    Carrasco, I. S. S.; Oliveira, T. J.

    2016-01-01

    We report extensive numerical simulations of growth models belonging to the nonlinear molecular beam epitaxy (nMBE) class, with flat and curved geometries. In both $d=1+1$ and $2+1$, we find that growth regime height distributions (HDs), spatial and temporal covariances are universal, but geometry-dependent, while the critical exponents are the same for flat and curved interfaces. Therefore the nMBE class does split into subclasses, as also does the Kardar-Parisi-Zhang (KPZ) class. Applying t...

  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. Improved tunneling magnetoresistance at low temperature in manganite junctions grown by molecular beam epitaxy

    OpenAIRE

    Werner, Robert; Petrov, Alexandr Yu.; Mino, Lucero Alvarez; Kleiner, Reinhold; Koelle, Dieter; Davidson, Bruce A.

    2011-01-01

    We report resistance versus magnetic field measurements for a La0.65Sr0.35MnO3/SrTiO3/La0.65Sr0.35MnO3 tunnel junction grown by molecular-beam epitaxy, that show a large field window of extremely high tunneling magnetoresistance (TMR) at low temperature. Scanning the in-plane applied field orientation through 360^/circ, the TMR shows 4-fold symmetry, i.e. biaxial anisotropy, aligned with the crystalline axes but not the junction geometrical long axis. The TMR reaches ~ 1900% at 4K, correspond...

  18. Reflection mass spectrometry technique for monitoring and controlling composition during molecular beam epitaxy

    Science.gov (United States)

    Brennan, Thomas M.; Hammons, B. Eugene; Tsao, Jeffrey Y.

    1992-01-01

    A method for on-line accurate monitoring and precise control of molecular beam epitaxial growth of Groups III-III-V or Groups III-V-V layers in an advanced semiconductor device incorporates reflection mass spectrometry. The reflection mass spectrometry is responsive to intentional perturbations in molecular fluxes incident on a substrate by accurately measuring the molecular fluxes reflected from the substrate. The reflected flux is extremely sensitive to the state of the growing surface and the measurements obtained enable control of newly forming surfaces that are dynamically changing as a result of growth.

  19. Luminescence characterization of CdTe:In grown by molecular beam epitaxy

    Science.gov (United States)

    Bassani, F.; Tatarenko, S.; Saminadayar, K.; Bleuse, J.; Magnea, N.; Pautrat, J. L.

    1991-06-01

    We report on the incorporation of indium as a shallow donor in CdTe by molecular beam epitaxy. Using proper surface stoichiometry conditions, we demonstrate that it is possible to incorporate and activate up to 1018 cm-3 indium impurities. The doped layers have been characterized by secondary-ion mass spectroscopy, capacitance-voltage and Hall-effect measurements. Photoluminescence (PL) and resonant excitation of the PL clearly identify indium as the chemical dopant, acting as an effective mass donor with an energy of 14 meV. Incorrect stoichiometry conditions lead to a poor dopant activity and to complex centers formation.

  20. 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.

  1. Structural Characterization and Ultraviolet Photoresponse of GaN Nanodots Grown by Molecular Beam Epitaxy

    OpenAIRE

    Kumar, Mahesh; Roul, Basanta; Bhat, Thirumaleshwara N; Rajpalke, Mohana K; Krupanidhi, SB

    2012-01-01

    The present work explores the electrical transport and UV photoresponse properties of GaN nanodots (NDs) grown by molecular beam epitaxy (MBE). Single-crystalline wurtzite structure of GaN NDs is verified by X-ray diffraction and transmission electron microscopy (TEM). The interdigitated electrode pattern was created and current-voltage (I-V) characteristics of GaN NDs were studied in a metal-semiconductor-metal configuration. Dark I-V characteristics of lateral grown GaN NDs obeyed the Frenk...

  2. GaN quantum dot density control by rf-plasma molecular beam epitaxy

    OpenAIRE

    Brown, J.; F Wu; Petroff, P. M.; J. S. Speck

    2004-01-01

    We report on the growth of GaN quantum dots and the control of their density in the Stranski-Krastanov mode on AlN (0001) by rf-plasma molecular beam epitaxy at 750 degreesC. After depositing the equivalent of 2-3 ML GaN coverage, as limited by N fluence under Ga-droplet growth conditions, excess Ga was desorbed and Stranski-Krastanov islands formed under vacuum. We present the dependence of island density as a function of GaN coverage (for two growth rates: 0.10 and 0.23 ML/s), as estimated ...

  3. Ferromagnetism in Ge1-xCrxTe epilayers grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    IV-VI ferromagnetic semiconductor Ge1-xCrxTe has been grown on BaF2 (111) by molecular beam epitaxy. The ferromagnetism was clearly established by direct magnetization and Hall measurements. The experimental correlation between the anomalous Hall resistivity ρxy and the resistivity ρxx, ρxy∝ρxx1.76, is understood from the semiclassical nature of the charge carrier dynamics, suggesting that the ferromagnetism gives rise to p-d exchange interaction. The Curie temperature increases systematically from the substrate temperature TS of 300 to 250 to 200 deg. C and with increasing the Cr composition along with each TS

  4. Defect-controlled growth of GaN nanorods on (0001)sapphire by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Transmission electron microscopy is used to reveal threading defects in single crystal c-oriented GaN nanorods grown on (0001)sapphire by molecular beam epitaxy. The defects are shown to be planar faults lying on (1010) planes and bounded by opposite partial screw dislocations with Burgers vectors of 1/2. The faults nucleate, as dislocation half-loops, from points close to the GaN/(0001)sapphire interface. It is proposed that the spiral growth of the partial atomic step joining the emerging dislocations controls nanorod growth and accounts for the growth surface morphology. The significance of these defects for nanorod growth and applications is discussed

  5. 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.)

  6. Growth of GaN with warm ammonia by molecular beam epitaxy

    Science.gov (United States)

    Kawaharazuka, A.; Yoshizaki, T.; Ploog, K. H.; Horikoshi, Y.

    2009-03-01

    We demonstrate the growth of GaN by molecular beam epitaxy with warm ammonia as a nitrogen source. Ammonia gas is heated by the tungsten filament located at the open end of the gas-tube installed in the growth chamber. By using this simple structure, the multiple collisions of molecules within the heater, thus the generation of nitrogen molecule, can be suppressed. The crystalline quality of the grown GaN layer is significantly improved by introducing the warm ammonia. This effect can be explained by the enhancement of the two-dimensional growth due to the active nitrogen species such as radical NH2* generated by cracking ammonia molecule.

  7. Application of ellipsometry to crystal growth by organometallic molecular beam epitaxy

    Science.gov (United States)

    Aspnes, D. E.; Quinn, W. E.; Gregory, S.

    1990-06-01

    We report the first use of ellipsometry as a real-time monitor of III-V semiconductor crystal growth by molecular beam epitaxy, specifically growth of GaAs and AlGaAs from arsine, triethylgallium, and triethylaluminum sources. Our results provide new insight into the oxide desorption process and show a sensitivity of ±0.03 in compositions x>0.2 for 10 Å thickness increments of AlxGa1-xAs during initial deposition on GaAs.

  8. The growth of high-quality AlGaAs by metalorganic molecular-beam epitaxy

    Science.gov (United States)

    Hersee, S. D.; Martin, P. A.; Chin, A.; Ballingall, J. M.

    1991-07-01

    The electrical and optical properties of AlGaAs grown by metalorganic molecular-beam epitaxy using triethylaluminum, tri-isobutylaluminum, and trimethylamine-alane are compared. It is found that tri-isobutylaluminum yields the lowest residual carbon incorporation in the layers (Na - Nd = 4 × 1015 cm-3) and the highest electron and hole mobilities. Photoluminescence spectra for the higher-quality AlGaAs, grown using TiBAl, show excitonic luminescence. However, this luminescence appears to be defect related.

  9. Demonstration of molecular beam epitaxy and a semiconducting band structure for I-Mn-V compounds

    Czech Academy of Sciences Publication Activity Database

    Jungwirth, Tomáš; Novák, Vít; Martí, X.; Cukr, Miroslav; Máca, František; Shick, Alexander; Mašek, Jan; Horodyská, P.; Němec, P.; Holý, V.; Zemek, Josef; Kužel, Petr; Němec, I.; Gallagher, B. L.; Campion, R. P.; Foxon, C. T.; Wunderlich, Joerg

    2011-01-01

    Roč. 83, č. 3 (2011), "035321-1"-"035321-6". ISSN 1098-0121 R&D Projects: GA MŠk LC510; GA AV ČR KAN400100652; GA MŠk(CZ) 7E08087 Grant ostatní: EU FP7- SemiSpinNet(XE) 215368; Seventh Framework Programme - NAMASTE(XE) 214499; ERC(XE) 268066 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z10100521 Keywords : antiferromagnetic semiconductors * spintronics * molecular beam epitaxy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.691, year: 2011

  10. Towards precise defect control in layered oxide structures by using oxide molecular beam epitaxy

    OpenAIRE

    Federico Baiutti; Georg Christiani; Gennady Logvenov

    2014-01-01

    In this paper we present the atomic-layer-by-layer oxide molecular beam epitaxy (ALL-oxide MBE) which has been recently installed in the Max-Planck Institute for Solid State Research and we report on its present status, providing some examples that demonstrate its successful application in the synthesis of different layered oxides, with particular reference to superconducting La2CuO4 and insulator-to-metal La2−xSrxNiO4. We briefly review the ALL-oxide MBE technique and its unique capabilities...

  11. Deep electron traps in CdTe:In films grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Zakrzewski, A.K.; Dobaczewski, L.; Karczewski, G.; Wojtowicz, T.; Kossut, J. [Institute of Physics, Polish Academy of Science, Warsaw (Poland)

    1995-12-31

    N-type indium CdTe grown on n{sup +}-GaAs molecular beam epitaxy has been studied by the standard deep level transient spectroscopy and the isothermal Laplace-transform deep level transient spectroscopy. It was found that the Cd/Te flux ratio strongly influences the deep level transient spectroscopy results. The unusual temperature dependence of the electron emission rate in films grown at nearly stoichiometric conditions may point out that the observed defect is resonant with the conduction band. (author). 5 refs, 1 fig.

  12. Molecular-beam epitaxy of monolayer MoSe2: growth characteristics and domain boundary formation

    Science.gov (United States)

    Jiao, L.; Liu, H. J.; Chen, J. L.; Yi, Y.; Chen, W. G.; Cai, Y.; Wang, J. N.; Dai, X. Q.; Wang, N.; Ho, W. K.; Xie, M. H.

    2015-05-01

    Monolayer (ML) transition metal dichalcogenides (TMDs) are of great research interest due to their potential use in ultrathin electronic and optoelectronic applications. They show promise in new concept devices in spintronics and valleytronics. Here we present a growth study by molecular-beam epitaxy of ML and sub-ML MoSe2, an important member of TMDs, revealing its unique growth characteristics as well as the formation processes of domain boundary (DB) defects. A dramatic effect of growth temperature and post-growth annealing on DB formation is uncovered.

  13. 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.

  14. Perspective: Extremely fine tuning of doping enabled by combinatorial molecular-beam epitaxy

    International Nuclear Information System (INIS)

    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

  15. HgTe and CdTe epitaxial layers and HgTe–CdTe superlattices grown by laser molecular beam epitaxy

    OpenAIRE

    Cheung, J. T.; Niizawa, G.; Moyle, J.; Ong, N. P.; Paine, B. M.; Vreeland, T., Jr.

    1986-01-01

    CdTe and HgTe epilayers and HgTe/CdTe superlattices have been grown by laser molecular beam epitaxy (laser MBE) on CdTe substrates. The power density of the laser radiation used to evaporate source materials was found to be a very important growth parameter. The superlattice structures have been characterized by helium ion backscattering spectrometry, x-ray double crystal diffractometry, and low temperature electrical transport measurements. Results indicate good crystallinity and very strong...

  16. Disorder and defect formation mechanisms in molecular-beam-epitaxy grown silicon epilayers

    Energy Technology Data Exchange (ETDEWEB)

    Akbari-Sharbaf, Arash [Department of Physics and Astronomy, University of Western Ontario, London, ON, Canada N6A 3K7 (Canada); Baribeau, Jean-Marc; Wu, Xiaohua; Lockwood, David J. [Institute for Microstructural Sciences, National Research Council, Ottawa, ON, Canada K1A 0R6 (Canada); Fanchini, Giovanni, E-mail: gfanchin@uwo.ca [Department of Physics and Astronomy, University of Western Ontario, London, ON, Canada N6A 3K7 (Canada); Department of Chemistry, University of Western Ontario, London, ON, Canada N6A 5B7 (Canada)

    2013-01-01

    We investigate the role of disorder, stress and crystallite size in determining the density of defects in disordered and partially ordered silicon thin films deposited at low or moderate temperatures by molecular beam epitaxy. We find that the paramagnetic defect density measured by electron spin resonance (ESR) is strongly dependent on the growth temperature of the films, decreasing from ∼ 2 · 10{sup 19} cm{sup −3} at 98 °C to ∼ 1 · 10{sup 18} cm{sup −3} at 572 °C. The physical nature of the defects is strongly dependent on the range of order in the films: ESR spectra consistent with dangling bonds in an amorphous phase are observed at the lowest temperatures, while the ESR signal gradually becomes more anisotropic as medium-range order improves and the stress level (measured both by X-ray diffraction and Raman spectroscopy) is released in more crystalline films. Anisotropic ESR spectra consistent with paramagnetic defects embedded in an epitaxial phase are observed at the highest growth temperature (572 °C). - Highlights: ► Disordered Si epilayers were grown by molecular beam epitaxy. ► Growth has been carried out at temperatures T = 98 °C–514 °C. ► A correlation between defect density and disorder in the films has been found. ► Lack of medium range order and stress cause the formation of defects at low T. ► At high T, defects are associated to grain boundaries and oriented stacking faults.

  17. Study of structural properties of cubic InN films on GaAs(001) substrates by molecular beam epitaxy and migration enhanced epitaxy

    International Nuclear Information System (INIS)

    InN epitaxial films with cubic phase were grown by rf-plasma-assisted molecular beam epitaxy (RF-MBE) on GaAs(001) substrates employing two methods: migration-enhanced epitaxy (MEE) and conventional MBE technique. The films were synthesized at different growth temperatures ranging from 490 to 550 °C, and different In beam fluxes (BEPIn) ranging from 5.9 × 10−7 to 9.7 × 10−7 Torr. We found the optimum conditions for the nucleation of the cubic phase of the InN using a buffer composed of several thin layers, according to reflection high-energy electron diffraction (RHEED) patterns. Crystallographic analysis by high resolution X-ray diffraction (HR-XRD) and RHEED confirmed the growth of c-InN by the two methods. We achieved with the MEE method a higher crystal quality and higher cubic phase purity. The ratio of cubic to hexagonal components in InN films was estimated from the ratio of the integrated X-ray diffraction intensities of the cubic (002) and hexagonal (1011) planes measured by X-ray reciprocal space mapping (RSM). For MEE samples, the cubic phase of InN increases employing higher In beam fluxes and higher growth temperatures. We have obtained a cubic purity phase of 96.4% for a film grown at 510 °C by MEE.

  18. In situ surface/interface x-ray diffractometer for oxide molecular beam epitaxy

    International Nuclear Information System (INIS)

    In situ studies of oxide molecular beam epitaxy by synchrotron x-ray scattering has been made possible by upgrading an existing UHV/molecular beam epitaxy (MBE) six-circle diffractometer system. For oxide MBE growth, pure ozone delivery to the chamber has been made available, and several new deposition sources have been made available on a new 12 in. CF (ConFlat, a registered trademark of Varian, Inc.) flange. X-ray diffraction has been used as a major probe for film growth and structures for the system. In the original design, electron diffraction was intended for the secondary diagnostics available without the necessity of the x-ray and located at separate positions. Deposition of films was made possible at the two diagnostic positions. And, the aiming of the evaporation sources is fixed to the point between two locations. Ozone can be supplied through two separate nozzles for each location. Also two separate thickness monitors are installed. Additional features of the equipment are also presented together with the data taken during typical oxide film growth to illustrate the depth of information available via in situ x-ray techniques

  19. In situ surface/interface x-ray diffractometer for oxide molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lee, J. H. [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA; Tung, I. C. [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA; Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA; Chang, S. -H. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; Bhattacharya, A. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; Fong, D. D. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA; Freeland, J. W. [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA; Hong, Hawoong [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA

    2016-01-01

    In situ studies of oxide molecular beam epitaxy by synchrotron x-ray scattering has been made possible by upgrading an existing UHV/molecular beam epitaxy (MBE) six-circle diffractometer system. For oxide MBE growth, pure ozone delivery to the chamber has been made available, and several new deposition sources have been made available on a new 12 in. CF (ConFlat, a registered trademark of Varian, Inc.) flange. X-ray diffraction has been used as a major probe for film growth and structures for the system. In the original design, electron diffraction was intended for the secondary diagnostics available without the necessity of the x-ray and located at separate positions. Deposition of films was made possible at the two diagnostic positions. And, the aiming of the evaporation sources is fixed to the point between two locations. Ozone can be supplied through two separate nozzles for each location. Also two separate thickness monitors are installed. Additional features of the equipment are also presented together with the data taken during typical oxide film growth to illustrate the depth of information available via in situ x-ray techniques.

  20. Investigation of the silicon ion density during molecular beam epitaxy growth

    CERN Document Server

    Eifler, G; Ashurov, K; Morozov, S

    2002-01-01

    Ions impinging on a surface during molecular beam epitaxy influence the growth and the properties of the growing layer, for example, suppression of dopant segregation and the generation of crystal defects. The silicon electron gun in the molecular beam epitaxy (MBE) equipment is used as a source for silicon ions. To use the effect of ion bombardment the mechanism of generation and distribution of ions was investigated. A monitoring system was developed and attached at the substrate position in the MBE growth chamber to measure the ion and electron densities towards the substrate. A negative voltage was applied to the substrate to modify the ion energy and density. Furthermore the current caused by charge carriers impinging on the substrate was measured and compared with the results of the monitoring system. The electron and ion densities were measured by varying the emission current of the e-gun achieving silicon growth rates between 0.07 and 0.45 nm/s and by changing the voltage applied to the substrate betw...

  1. In situ surface/interface x-ray diffractometer for oxide molecular beam epitaxy.

    Science.gov (United States)

    Lee, J H; Tung, I C; Chang, S-H; Bhattacharya, A; Fong, D D; Freeland, J W; Hong, Hawoong

    2016-01-01

    In situ studies of oxide molecular beam epitaxy by synchrotron x-ray scattering has been made possible by upgrading an existing UHV/molecular beam epitaxy (MBE) six-circle diffractometer system. For oxide MBE growth, pure ozone delivery to the chamber has been made available, and several new deposition sources have been made available on a new 12 in. CF (ConFlat, a registered trademark of Varian, Inc.) flange. X-ray diffraction has been used as a major probe for film growth and structures for the system. In the original design, electron diffraction was intended for the secondary diagnostics available without the necessity of the x-ray and located at separate positions. Deposition of films was made possible at the two diagnostic positions. And, the aiming of the evaporation sources is fixed to the point between two locations. Ozone can be supplied through two separate nozzles for each location. Also two separate thickness monitors are installed. Additional features of the equipment are also presented together with the data taken during typical oxide film growth to illustrate the depth of information available via in situ x-ray techniques. PMID:26827327

  2. In situ surface/interface x-ray diffractometer for oxide molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lee, J. H.; Freeland, J. W.; Hong, Hawoong, E-mail: hhong@aps.anl.gov [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Tung, I. C. [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (United States); Chang, S.-H.; Bhattacharya, A.; Fong, D. D. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

    2016-01-15

    In situ studies of oxide molecular beam epitaxy by synchrotron x-ray scattering has been made possible by upgrading an existing UHV/molecular beam epitaxy (MBE) six-circle diffractometer system. For oxide MBE growth, pure ozone delivery to the chamber has been made available, and several new deposition sources have been made available on a new 12 in. CF (ConFlat, a registered trademark of Varian, Inc.) flange. X-ray diffraction has been used as a major probe for film growth and structures for the system. In the original design, electron diffraction was intended for the secondary diagnostics available without the necessity of the x-ray and located at separate positions. Deposition of films was made possible at the two diagnostic positions. And, the aiming of the evaporation sources is fixed to the point between two locations. Ozone can be supplied through two separate nozzles for each location. Also two separate thickness monitors are installed. Additional features of the equipment are also presented together with the data taken during typical oxide film growth to illustrate the depth of information available via in situ x-ray techniques.

  3. Residual stress in AlN films grown on sapphire substrates by molecular beam epitaxy

    Science.gov (United States)

    Rong, Xin; Wang, Xinqiang; Chen, Guang; Pan, Jianhai; Wang, Ping; Liu, Huapeng; Xu, Fujun; Tan, Pingheng; Shen, Bo

    2016-05-01

    Residual stress in AlN films grown by molecular beam epitaxy (MBE) has been studied by Raman scattering spectroscopy. A strain-free Raman frequency and a biaxial stress coefficient for E2(high) mode are experimentally determined to be 657.8 ± 0.3 cm-1 and 2.4 ± 0.2 cm-1 / GPa, respectively. By using these parameters, the residual stress of a series of AlN layers grown under different buffer layer conditions has been investigated. The residual compressive stress is found to be obviously decreased by increasing the Al/N beam flux ratio of the buffer layer, indicating the generation of tensile stress due to stronger coalescence of AlN grains, as also confirmed by the in-situ reflection high energy electron diffraction (RHEED) monitoring observation. The stronger coalescence does lead to improved quality of AlN films as expected.

  4. 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.

  5. Investigation of the silicon ion density during molecular beam epitaxy growth

    International Nuclear Information System (INIS)

    Ions impinging on a surface during molecular beam epitaxy influence the growth and the properties of the growing layer, for example, suppression of dopant segregation and the generation of crystal defects. The silicon electron gun in the molecular beam epitaxy (MBE) equipment is used as a source for silicon ions. To use the effect of ion bombardment the mechanism of generation and distribution of ions was investigated. A monitoring system was developed and attached at the substrate position in the MBE growth chamber to measure the ion and electron densities towards the substrate. A negative voltage was applied to the substrate to modify the ion energy and density. Furthermore the current caused by charge carriers impinging on the substrate was measured and compared with the results of the monitoring system. The electron and ion densities were measured by varying the emission current of the e-gun achieving silicon growth rates between 0.07 and 0.45 nm/s and by changing the voltage applied to the substrate between 0 to -1000 V. The dependencies of ion and electron densities were shown and discussed within the framework of a simple model. The charged carrier densities measured with the monitoring system enable to separate the ion part of the substrate current and show its correlation to the generation rate. Comparing the ion density on the whole substrate and in the center gives a hint to the ion beam focusing effect. The maximum ion and electron current densities obtained were 0.40 and 0.61 μA/cm2, respectively

  6. Characterization of CdTe, HgTe, and Hg1-xCdxTe grown by chemical beam epitaxy

    Science.gov (United States)

    Wagner, B. K.; Rajavel, D.; Benz, R. G.; Summers, C. J.

    1991-10-01

    Detailed characterization of chemical beam epitaxially (CBE) grown CdTe and Hg1-xCdxTe layers are reported. These characterizations include photoluminescence, infrared transmission, energy dispersive x-ray analysis, and variable temperature (10-300 K) Hall effect and resistivity measurements. The results indicate that high quality HgCdTe layers can be grown by CBE.

  7. 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

    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...

  8. Growth and properties of GdTiO3 films prepared by hybrid molecular beam epitaxy

    Science.gov (United States)

    Moetakef, Pouya; Ouellette, Daniel G.; Zhang, Jack Y.; Cain, Tyler A.; Allen, S. James; Stemmer, Susanne

    2012-09-01

    The paper reports on the thin film growth of a protoptype Mott insulator, ferrimagnetic GdTiO3, using shuttered molecular beam epitaxy. Substrates were (001) (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT), with and without epitaxial SrTiO3 buffer layers, respectively. It was found that on bare LSAT, the starting monolayer was crucial for stabilizing the GdTiO3 perovskite phase. The quality of the films was evaluated using structural, electric, optical and magnetic characterization. Structural characterization showed that the GdTiO3 layers were free of pyrochlore impurity phases and that the lattice parameter was close to what was expected for coherently strained, stoichiometric GdTiO3. The room temperature film resistivity was 7 Ωcm and increased with decreasing temperature, consistent with Mott insulating characteristics. The Curie temperature was 30 K and a small coercivity was observed at 2 K, in good agreement with bulk GdTiO3 properties reported in the literature.

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

    International Nuclear Information System (INIS)

    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 Fe1−xVx electrodes is shown to significantly increase TMR. Finally, unexpected transport properties in Fe1−XCox/MgO/Fe1−XCox (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

  10. Molecular beam epitaxy of Ge-Sb-Te thin films on Si substrates

    International Nuclear Information System (INIS)

    Owing to their phase-change properties, Ge-Sb-Te thin films, i.e., Ge2Sb2Te5 (GST), are being intensively studied for new concepts of non-volatile memory. The deposition technique commonly employed is sputtering, leading to poly-crystalline layers. Here it is shown that molecular beam epitaxy allows for the preparation of highly ordered Ge-Sb-Te films even on strongly lattice-mismatched substrates like Si. In situ reflection high-energy diffraction and quadrupole mass spectrometry are utilized to monitor the growth process in real time. Ex situ X-ray diffraction, atomic force microscopy and secondary electron microscopy, and X-ray fluorescence are used to investigate the structural properties, the surface morphology, and the stoichiometry of the grown films, respectively. As main result, single crystalline GST layers can be achieved on Si(111) substrates with epitaxial relationships GST[111]//Si[111] and GST//Si in the growth direction and in-plane, respectively. The growth on Si(001) instead produces (111)-oriented films with weak texture. GST thin films with a high structural order are expected to exhibit superior electrical/switching properties to the poly-crystalline layers deposited by sputtering.

  11. MnTe and ZnTe grown on sapphire by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Przezdziecka, E. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland)], E-mail: Ewa.Przezdziecka@ifpan.edu.pl; Dynowska, E.; Paszkowicz, W.; Dobrowolski, W. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Kepa, H. [Institute of Experimental Physics, ul. Hoza 69, 00-681 Warsaw (Poland); Majkrzak, C.F. [Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Giebultowicz, T.M. [Physics Department, Oregon State University, Corvallis, OR 97331 (United States); Janik, E. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Kossut, J. [Institute of Physics, Polish Academy of Sciences, and ERATO Semiconductor Spintronics Project, Al. Lotnikow 32/46, 02-668 Warsaw (Poland)

    2008-06-02

    We report on growth of MnTe layers by molecular beam epitaxy on Al{sub 2}O{sub 3} substrates and of ZnTe layers on hybrid MnTe/Al{sub 2}O{sub 3} substrates. The aim of our work was to prepare hexagonal phases of epitaxial thin films of these two materials. In the case of MnTe, the hexagonal NiAs-type phase was prepared by depositing the film directly on Al{sub 2}O{sub 3} substrates. On the other hand, the crystal structure of ZnTe layers grown on hybrid MnTe/Al{sub 2}O{sub 3} substrates was found to depend on the layer thickness: layers thinner than 0.05 {mu}m grew in a metastable hexagonal wurtzite structure, but with further increases of the thickness, the cubic zinc blende phase of ZnTe tended to appear. The structural properties of MnTe and ZnTe layers were characterized by high energy electron and X-ray diffraction methods. Electrical properties of MnTe films were assessed by the Hall effect measurements. The topography and microstructure were analyzed by atomic force microscope. The Neel temperature and magnetic domains structure of antiferromagnetic hexagonal MnTe layers were obtained from neutron experiments.

  12. 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}.

  13. Hybrid molecular beam epitaxy for the growth of stoichiometric BaSnO3

    International Nuclear Information System (INIS)

    Owing to its high room-temperature electron mobility and wide bandgap, BaSnO3 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 BaSnO3 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. BaSnO3 films were thus grown on SrTiO3 (001) and LaAlO3 (001) substrates. Growth conditions for stoichiometric BaSnO3 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 SrTiO3 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 BaSnO3

  14. Radical-source molecular beam epitaxy of ZnO-based heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Sadofiev, Sergey

    2009-10-27

    This work focuses on the development of the novel growth approaches for the fabrication of Group II-oxide materials in the form of epitaxial films and heterostructures. It is shown that molecular-beam epitaxial growth far from thermal equilibrium allows one to overcome the standard solubility limit and to alloy ZnO with MgO or CdO in strict wurtzite phase up to mole fractions of several 10 %. In this way, a band-gap range from 2.2 to 4.4 eV can be covered. A clear layer-by-layer growth mode controlled by oscillations in reflection high-energy electron diffraction makes it possible to fabricate atomically smooth heterointerfaces and well-defined quantum well structures exhibiting prominent band-gap related light emission in the whole composition range. On appropriately designed structures, laser action from the ultraviolet down to green wavelengths and up to room temperature is achieved. The properties and potential of the ''state-of-the-art'' materials are discussed in relation to the advantages for their applications in various optoelectronic devices. (orig.)

  15. A GaAs/GaInP dual junction solar cell grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    We report the recent result of GaAs/GaInP dual-junction solar cells grown by all solid-state molecular-beam-epitaxy (MBE). The device structure consists of a GaIn0.48P homojunction grown epitaxially upon a GaAs homojunction, with an interconnected GaAs tunnel junction. A photovoltaic conversion efficiency of 27% under the AM1.5 globe light intensity is realized for a GaAs/GaInP dual-junction solar cell, while the efficiencies of 26% and 16.6% are reached for a GaAs bottom cell and a GaInP top cell, respectively. The energy loss mechanism of our GaAs/GaInP tandem dual-junction solar cells is discussed. It is demonstrated that the MBE-grown phosphide-containing III—V compound semiconductor solar cell is very promising for achieving high energy conversion efficiency. (semiconductor devices)

  16. 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.

    2016-01-01

    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. PMID:26928710

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

    International Nuclear Information System (INIS)

    Since the discovery of its superconducting properties in 2001, magnesium diboride has generated terrific scientific and engineering research interest around the world. With a TC of 39K 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.

  18. Improved tunneling magnetoresistance at low temperature in manganite junctions grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    We report resistance versus magnetic field measurements for a La0.65Sr0.35MnO3/SrTiO3/La0.65Sr0.35MnO3 tunnel junction grown by molecular-beam epitaxy, that show a large field window of extremely high tunneling magnetoresistance (TMR) at low temperature. Scanning the in-plane applied field orientation through 360 deg., the TMR shows fourfold symmetry, i.e., biaxial anisotropy, aligned with the crystalline axis but not the junction geometrical long axis. The TMR reaches ∼1900% at 4 K, corresponding to an interfacial spin polarization of >95% assuming identical interfaces. These results show that uniaxial anisotropy is not necessary for large TMR, and lay the groundwork for future improvements in TMR in manganite junctions.

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

    International Nuclear Information System (INIS)

    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. (paper)

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

    International Nuclear Information System (INIS)

    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 AlxGa1-x As and InxGa1-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)

  1. 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)

  2. High electron mobility in Ga(In)NAs films grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    We report the highest mobility values above 2000 cm2/Vs in Si doped GaNAs film grown by molecular beam epitaxy. To understand the feature of the origin which limits the electron mobility in GaNAs, temperature dependences of mobility were measured for high mobility GaNAs and referential low mobility GaInNAs. Temperature dependent mobility for high mobility GaNAs is similar to the GaAs case, while that for low mobility GaInNAs shows large decrease in lower temperature region. The electron mobility of high quality GaNAs can be explained by intrinsic limiting factor of random alloy scattering and extrinsic factor of ionized impurity scattering.

  3. Surface energies for molecular beam epitaxy growth of HgTe and CdTe

    Science.gov (United States)

    Berding, M. A.; Krishnamurthy, Srinivasan; Sher, A.

    1991-10-01

    We present results for the surface binding energies for HgTe and CdTe that will serve as input for molecular beam epitaxy growth models. We have found that the surface binding energies are surface orientation dependent and are not simply proportional to the number of first-neighbor bonds being made to the underlying layer. Moreover, because of the possibility of charge transfer between cation and anion surface states, one may have large differences between the binding energy for the first and the last atom in a given layer, and these differences will be different for the narrow-gap, less ionic materials than for the wide gap, ionic materials. We also find that the surface states associated with an isolated surface atom or vacancy are extended in materials with small gaps and small effective masses, and thus call into question the modeling of surface binding by simple pair interactions.

  4. Characterisation of multiple carrier transport in indium nitride grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Quantitative mobility spectrum analysis (QMSA) was performed on multiple magnetic field Hall effect measurements of indium nitride grown by molecular beam epitaxy. This enables two clearly distinct electron species to be identified, which are attributed to the bulk and a surface accumulation layer. In this material, single magnetic field data corresponds to neither electron species, as both contribute significantly to the total conduction. The bulk electron distribution has an extracted average Hall mobility of 3570 cm2/(Vs) at 300 K with a concentration of 1.5 x 1017 cm-3, while the surface electrons have sheet charge density that is an order of magnitude higher than previously reported surface concentrations. The high quality bulk characteristics revealed emphasise the importance of using multi-carrier analysis when performing transport measurements on InN. (Abstract Copyright [2007], Wiley Periodicals, Inc.)

  5. InAs/GaAs(001) molecular beam epitaxial growth in a scanning tunnelling microscope

    International Nuclear Information System (INIS)

    The growth on InAs on GaAs(001) has attracted great interest and investigation over the past few decades primarily due to the opto-electronic properties of the self-assembled quantum dot (QD) arrays formed. Scanning tunnelling microscopy (STM) has been extensively employed to investigate the complicated and spontaneous mechanism of QD growth via molecular beam epitaxy (MBE). Classically, combined MBE-STM requires quenching the sample after growth and transferring it to an arsenic-free high vacuum chamber which houses the STM system. However, without access to the phenomenon as a dynamic process a basic understanding remains elusive. In order to access surface dynamics, MBE and STM must be combined into a single element. The system herein discussed allows the operation of MBE sources in an STM system relating to InAs/GaAs(001) surfaces.

  6. Accommodation mechanism of InN nanocolumns grown on Si(111) substrates by molecular beam epitaxy

    International Nuclear Information System (INIS)

    High quality InN nanocolumns have been grown by molecular beam epitaxy on bare and AlN-buffered Si(111) substrates. The accommodation mechanism of the InN nanocolumns to the substrate was studied by transmission electron microscopy. Samples grown on AlN-buffered Si(111) show abrupt interfaces between the nanocolumns and the buffer layer, where an array of periodically spaced misfit dislocations develops. Samples grown on bare Si(111) exhibit a thin SixNy at the InN nanocolumn/substrate interface because of Si nitridation. The SixNy thickness and roughness may affect the nanocolumn relative alignment to the substrate. In all cases, InN nanocolumns grow strain- and defect-free

  7. Molecular beam epitaxy growth and magnetic properties of Cr-Co-Ga Heusler alloy films

    International Nuclear Information System (INIS)

    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

  8. High breakdown single-crystal GaN p-n diodes by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Molecular beam epitaxy grown GaN p-n vertical diodes are demonstrated on single-crystal GaN substrates. A low leakage current <3 nA/cm2 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 cm2 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

  9. Photoluminescence characteristics of Pb-doped, molecular-beam-epitaxy grown ZnSe crystal layers

    International Nuclear Information System (INIS)

    The characteristic green photoluminescence emission and related phenomena in Pb-doped, molecular-beam-epitaxy (MBE)-grown ZnSe crystal layers were investigated to explore the nature of the center responsible for the green emission. The intensity of the green emission showed a distinct nonlinear dependence on excitation intensity. Pb-diffused polycrystalline ZnSe was similarly examined for comparison. The characteristic green emission has been observed only in MBE-grown ZnSe crystal layers with moderate Pb doping. The results of the investigations on the growth conditions, luminescence, and related properties of the ZnSe crystal layers suggest that the green emission is due to isolated Pb replacing Zn and surrounded with regular ZnSe lattice with a high perfection

  10. Growth and properties of amorphous silicon films grown using pulsed-flow reactive plasma beam epitaxy

    Science.gov (United States)

    Dalal, Vikram L.; Knox, Ralph; Kandalaft, Nabeeh; Baldwin, Greg

    1991-01-01

    The growth and properties of a-Si:H films grown using a novel deposition technique, reactive plasma beam epitaxy, are discussed. In this technique, a remote H plasma produced in a microwave-ECR reactor is used to grow a-Si:H films at low pressures. The H ions react with SiH4 introduced near the substrate to produce the film. The flow of SiH4 is pulsed on or off, thereby achieving in-situ annealing of the film during growth by H ions and radicals. The films produced by this technique appear to have good electronic quality, and are more stable than the standard glow discharge films.

  11. Growth of semiconductor alloy InGaPBi on InP by molecular beam epitaxy

    International Nuclear Information System (INIS)

    We report the first successful growth of InGaPBi single crystals on InP substrate with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InGaPBi thin films reveal excellent surface and structural qualities, making it a promising new III–V compound family member for heterostructures. The strain can be tuned between tensile and compressive by adjusting Ga and Bi compositions. The maximum achieved Bi concentration is 2.2 ± 0.4% confirmed by Rutherford backscattering spectroscopy. Room temperature photoluminescence shows strong and broad light emission at energy levels much smaller than the InP bandgap. (paper)

  12. Thermal stability of CdZnO thin films grown by molecular-beam epitaxy

    International Nuclear Information System (INIS)

    CdZnO thin films with near-band-edge (NBE) photoluminescence (PL) emission from 2.39 eV to 2.74 eV were grown by plasma-assisted molecular-beam epitaxy on c-plane sapphire substrates with 800 deg. C in situ annealing. CdZnO thin films evolve from pure wurtzite (wz) structure, to mixture of wz and rock-salt (rs) structures confirmed by X-ray diffraction studies. Rapid-thermo-annealing (RTA) was performed on in situ annealed CdZnO samples. Pure wz CdZnO shows insignificant NBE PL peak shift after RTA, while mixture structure CdZnO shows evident blue shifts due to phase change after annealing, indicating the rs phase CdZnO changes to wz phase CdZnO during RTA process.

  13. Microstructure of InxGa1−xN nanorods grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Transmission electron microscopy is used to examine the structure and composition of InxGa1−xN nanorods grown by plasma-assisted molecular beam epitaxy. The results confirm a core–shell structure with an In-rich core and In-poor shell resulting from axial and lateral growth sectors respectively. Atomic resolution mapping by energy-dispersive x-ray microanalysis and high angle annular dark field imaging show that both the core and the shell are decomposed into Ga-rich and In-rich platelets parallel to their respective growth surfaces. It is argued that platelet formation occurs at the surfaces, through the lateral expansion of surface steps. Studies of nanorods with graded composition show that decomposition ceases for x ≥ 0.8 and the ratio of growth rates, shell:core, decreases with increasing In concentration. (paper)

  14. Antimony segregation in stressed SiGe heterostructures grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    The effects of the growth temperature, composition, and elastic strains in separate layers on the segregation of antimony are studied experimentally for stressed SiGe structures grown by molecular beam epitaxy. It is established that the growth conditions and parameters of the structures exert an interrelated influence on the segregation of Sb: the degree of the influence of the composition and elastic stresses in the SiGe layers on Sb segregation depends on the growth temperature. It is shown that usage of a method previously proposed by us for the selective doping of silicon structures with consideration for the obtained dependences of Sb segregation on the growth conditions and parameters of the SiGe layers makes it possible to form SiGe structures selectively doped with antimony

  15. Fe-doped InN layers grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Iron(Fe)-doped InN (InN:Fe) layers have been grown by molecular beam epitaxy. It is found that Fe-doping leads to drastic increase of residual electron concentration, which is different from the semi-insulating property of Fe-doped GaN. However, this heavy n-type doping cannot be fully explained by doped Fe-concentration ([Fe]). Further analysis shows that more unintentionally doped impurities such as hydrogen and oxygen are incorporated with increasing [Fe] and the surface is degraded with high density pits, which probably are the main reasons for electron generation and mobility reduction. Photoluminescence of InN is gradually quenched by Fe-doping. This work shows that Fe-doping is one of good choices to control electron density in InN.

  16. SIMS studies of CI- doped Zn Se epilayers grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Chlorine is one of the most used species to produce n-type zinc selenium epilayers. In this paper, we present secondary ion mass spectrometry profiles of a series of chlorine-doped zinc selenium samples, which were grown in a molecular beam epitaxy chamber. These profiles have been used to examine the limitation of secondary ion mass spectrometry analysis of narrow chlorine-delta layers. In order to covert secondary ion mass spectrometry raw data to quantified data, the depth profile from a chlorine-implanted standard sample has been used to estimate the useful ion yieldof chlorine and thus the instrument sensitivity for chlorine in a zinc selenium matrix. The useful ion yieldand detection limit of chlorine in the zinc selenium host matrix were calculated to be 4.7 X 10-17 atoms/ cm3, respectively

  17. Design and growth of a P N diode by molecular beam epitaxy

    International Nuclear Information System (INIS)

    In this work, design, growth and characterization of a GaAs p-n contact is presented. The contact growth has been performed by Molecular Beam Epitaxy. The n layer with thickness of 1μm and electron concentration of 6 * 1017 cm-3 has been grown on a p-type GaAs substrate with hole concentration of 1 * 1017cm-3. During growth, in situ monitoring of the layer stoichiometry has been made possible by using Reflection High Energy Electron Diffraction technique. After growth characterization was performed by the use of Hall-effect measurement, the results for the carrier concentration was further confirmed by Electrochemical Capacitance-Voltage profiling technique

  18. Growth of high quality AlGaAs by metalorganic molecular beam epitaxy using trimethylamine alane

    Science.gov (United States)

    Abernathy, C. R.; Jordan, A. S.; Pearton, S. J.; Hobson, W. S.; Bohling, D. A.; Muhr, G. T.

    1990-06-01

    AlGaAs grown by metalorganic molecular beam epitaxy (MOMBE) has been problematic due to oxygen and carbon contamination, particularly when triethylaluminum (TEAl) has been used as the aluminum source. Consequently, we have investigated trimethylamine alane (TMAAl) as a potential replacement for the conventional metalorganic Al sources. AlGaAs films with excellent structural and optical properties have been grown with this source. Photoluminescence intensities from AlGaAs grown by MOMBE at 500 °C using TMAAl are comparable to those from material grown by metalorganic chemical vapor deposition at 675 °C using triethylaluminum (TMAl). Carbon and oxygen levels in MOMBE-grown AlGaAs are drastically reduced in comparison to similar films grown with TEAl.

  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

    2016-01-01

    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. PMID:27381641

  20. 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.

  1. Effects of substrate orientation on the growth of InSb nanostructures by molecular beam epitaxy

    Science.gov (United States)

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

    2016-05-01

    In this work, the effects of substrate orientation on InSb quantum structure growth by molecular beam epitaxy (MBE) are presented. Motivated by the observation that (411) evolves naturally as a stable facet during MBE crystal growth, comparison studies have been carried out to investigate the effects of the crystal orientation of the underlying GaSb substrate on the growth of InSb by MBE. By depositing InSb on a number of different substrate orientations, namely: (100), (311), (411), and (511), a higher nanostructure density was observed on the (411) surface compared with the other orientations. This result suggests that the (411) orientation presents a superior surface in MBE growth to develop a super-flat GaSb buffer surface, naturally favorable for nanostructure growth.

  2. Molecular beam epitaxy of SrTiO3 with a growth window

    Science.gov (United States)

    Jalan, Bharat; Moetakef, Pouya; Stemmer, Susanne

    2009-07-01

    Many complex oxides with only nonvolatile constituents do not have a wide growth window in conventional molecular beam epitaxy (MBE) approaches, which makes it difficult to obtain stoichiometric films. Here it is shown that a growth window in which the stoichiometry is self-regulating can be achieved for SrTiO3 films by using a hybrid MBE approach that uses a volatile metal-organic source for Ti, titanium tetra isopropoxide (TTIP). The growth window widens and shifts to higher TTIP/Sr flux ratios with increasing temperature, showing that it is related to the desorption of the volatile TTIP. We demonstrate stoichiometric, highly perfect, insulating SrTiO3 films. The approach can be adapted for the growth of other complex oxides that previously were believed to have no wide MBE growth window.

  3. Hydrogen reduction in GaAsN thin films by flow rate modulated chemical beam epitaxy

    International Nuclear Information System (INIS)

    The amount of residual H in the GaAsN film grown by chemical beam epitaxy (CBE) can be decreased by flow rate modulation growth. Many H atoms in the films grown by CBE exist as N-H or N-H2 structures. Although a higher growth temperature was required for decreasing the H concentration ([H]), it caused a decrease in the N concentration ([N]). A reduction in [H] while keeping [N] constant was necessary. By providing an intermittent supply of Ga source while continuously supplying As and N sources, [H] effectively decreased in comparison with the [H] value in the film grown at the same temperature by conventional CBE without reducing [N

  4. Analysis of carbon in SrTiO3 grown by hybrid molecular beam epitaxy

    International Nuclear Information System (INIS)

    Secondary ion mass spectroscopy (SIMS) was used to investigate carbon impurity concentrations in stoichiometric SrTiO3 films grown by a hybrid molecular beam epitaxy approach that uses an effusion cell to supply strontium, a rf plasma source for oxygen and a metal organic titanium source (titanium tetra isopropoxide). The carbon concentration in the films was measured as a function of growth parameters. At sufficiently high growth temperatures (>800 degree sign C), the films contain a few ppm of carbon. The challenges in accurately quantifying low carbon concentrations are discussed. A carbon-containing contamination layer is detected on the surfaces of SrTiO3 substrates and air-exposed films by SIMS and in scanning transmission electron microscopy. The contamination layer could be removed by high-temperature predeposition oxygen plasma cleaning.

  5. High quality YBCO superconductive thin films fabricated by laser molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    High quality YBa2Cu3O6+x (YBCO) superconductive thin films have been fabricated on the SrTiO3(100) substrate using laser molecular beam epitaxy (laser-MBE).The active oxygen source was used,which made the necessary ambient oxygen pressure be 2-3 orders lower than that in pulsed laser deposition (PLD).Tc0 is 85-87 K,and Jc~1.0×106 A/cm2.Atomic force microscopy (AFM) measurements show that no obvious particulates can be observed and the root mean square roughness is 7.8 nm.High stability DC superconducting quantum interference devices (DC-SQUID) was fabricated using this YBCO thin film.

  6. 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.

  7. Molecular beam epitaxy grown (Ga,Mn)(As,P) with perpendicular to plane magnetic easy axis

    International Nuclear Information System (INIS)

    We present an experimental investigation of the magnetic, electrical, and structural properties of Ga0.94Mn0.06As1-yPy layers grown by molecular beam epitaxy on GaAs substrates for y≤0.3. X-ray diffraction measurements reveal that the layers are under tensile strain, which gives rise to a magnetic easy axis perpendicular to the plane of the layers. The strength of the magnetic anisotropy and the coercive field increases as the phosphorous concentration is increased. The resistivity of all samples shows metallic behavior with the resistivity increasing as y increases. These materials will be useful for studies of micromagnetic phenomena requiring metallic ferromagnetic material with perpendicular magnetic anisotropy

  8. Towards precise defect control in layered oxide structures by using oxide molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Federico Baiutti

    2014-05-01

    Full Text Available In this paper we present the atomic-layer-by-layer oxide molecular beam epitaxy (ALL-oxide MBE which has been recently installed in the Max-Planck Institute for Solid State Research and we report on its present status, providing some examples that demonstrate its successful application in the synthesis of different layered oxides, with particular reference to superconducting La2CuO4 and insulator-to-metal La2−xSrxNiO4. We briefly review the ALL-oxide MBE technique and its unique capabilities in the deposition of atomically smooth single-crystal thin films of various complex oxides, artificial compounds and heterostructures, introducing our goal of pursuing a deep investigation of such systems with particular emphasis on structural defects, with the aim of tailoring their functional properties by precise defects control.

  9. Electrical and optical properties of ZnO films grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Zinc oxide (ZnO) films have been grown on sapphire by molecular beam epitaxy (MBE), and it is found that the grain size of the ZnO films increased with increasing the growth temperature. Photoluminescence (PL) study shows that the intensity ratio of near-band-edge emission to deep-level-related emission (NBE/DL) of the ZnO is significantly enhanced with increasing the growth temperature, and the dependence of the carrier mobility on the growth temperature shows very similar trend, which implies that there is a community factor that determines the optical and electrical properties of ZnO, and this factor is suggested to be the grain boundary. The results obtained in this paper reveal that by reducing the grain boundaries, ZnO films with high optical and electrical properties may be acquired.

  10. The mechanism of sputter-induced epitaxy modification in YBCO (001) films grown on MgO (001) substrates

    International Nuclear Information System (INIS)

    The sputter-induced epitaxy change of in-plane orientation occurring in YBa2Cu3O7-x (001) thin films grown on MgO (001) substrates by pulsed organo-metallic beam epitaxy (POMBE) is investigated by a series of film growth and characterization experiments, including RBS and TEM. The factors influencing the orientation change are systematically studied. The experimental results suggest that the substrate surface morphology change caused by the ion sputtering and the Ar ion implantation in the substrate surface layer are not the major factors that affect the orientation change. Instead, the implantation of W ions, which come from the hot filament of the ion gun, and the initial Ba deposition layer in the YBCO film growth play the most important roles in controlling the epitaxy orientation change. Microstructure studies show that a BaxMg1-xO buffer layer is formed on top of the sputtered substrate surface due to Ba diffusion into the W implanted layer. It is believed that the formation of this buffer layer relieves the large lattice mismatch and changes the YBCO film from the 45 degree oriented growth to the 0 degree oriented growth. copyright 1998 Materials Research Society

  11. Topological insulator Bi2Se3 thin films grown on double-layer graphene by molecular beam epitaxy

    OpenAIRE

    Song, Can-Li; Wang, Yi-Lin; Jiang, Ye-Ping; Zhang, Yi; Chang, Cui-Zu; Wang, Lili; He, Ke; Chen, Xi; Jia, Jin-Feng; Wang, Yayu; Fang, Zhong; Dai, Xi; Xie, Xin-Cheng; Qi, Xiao-Liang; Zhang, Shou-Cheng

    2010-01-01

    Atomically flat thin films of topological insulator Bi2Se3 have been grown on double-layer graphene formed on 6H-SiC(0001) substrate by molecular beam epitaxy. By a combined study of reflection high energy electron diffraction and scanning tunneling microscopy, we identified the Se-rich condition and temperature criterion for layer-by-layer growth of epitaxial Bi2Se3 films. The as-grown films without doping exhibit a low defect density of 1.0\\pm 0.2x1011/cm2, and become a bulk insulator at a ...

  12. Optical control of growth of AlxGa1 - xAs by organometallic molecular beam epitaxy

    Science.gov (United States)

    Aspnes, D. E.; Quinn, W. E.; Gregory, S.

    1990-12-01

    Using spectroellipsometry, we obtain information on the near-surface composition x of epitaxial AlxGa1-xAs layers during crystal growth by organometallic molecular beam epitaxy and use this information to regulate the flow of triethylaluminum to the growth surface. The resulting closed-loop control system maintains the imaginary part of the dielectric response of thick AlxGa1-xAs films constant to an equivalent compositional precision better than ±0.001 over extended periods of time.

  13. Greatly improved interfacial passivation of in-situ high κ dielectric deposition on freshly grown molecule beam epitaxy Ge epitaxial layer on Ge(100)

    Energy Technology Data Exchange (ETDEWEB)

    Chu, R. L. [Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Liu, Y. C.; Lee, W. C.; Huang, M. L.; Kwo, J., E-mail: raynien@phys.nthu.edu.tw, E-mail: mhong@phys.ntu.edu.tw [Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Lin, T. D.; Hong, M., E-mail: raynien@phys.nthu.edu.tw, E-mail: mhong@phys.ntu.edu.tw [Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China); Pi, T. W. [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China)

    2014-05-19

    A high-quality high-κ/Ge interface has been achieved by combining molecule beam epitaxy grown Ge epitaxial layer and in-situ deposited high κ dielectric. The employment of Ge epitaxial layer has sucessfully buried and/or removed the residue of unfavorable carbon and native oxides on the chemically cleaned and ultra-high vacuum annealed Ge(100) wafer surface, as studied using angle-resolved x-ray photoelectron spectroscopy. Moreover, the scanning tunneling microscopy analyses showed the significant improvements in Ge surface roughness from 3.5 Å to 1 Å with the epi-layer growth. Thus, chemically cleaner, atomically more ordered, and morphologically smoother Ge surfaces were obtained for the subsquent deposition of high κ dielectrics, comparing with those substrates without Ge epi-layer. The capacitance-voltage (C-V) characteristics and low extracted interfacial trap density (D{sub it}) reveal the improved high-κ/Ge interface using the Ge epi-layer approach.

  14. Epitaxial growth of Fe3Si/CaF2/Fe3Si magnetic tunnel junction structures on CaF2/Si(111) by molecular beam epitaxy

    International Nuclear Information System (INIS)

    The Fe3Si(24 nm)/CaF2(2 nm)/Fe3Si(12 nm) magnetic tunnel junction (MTJ) structures were grown epitaxially on CaF2/Si(111) by molecular beam epitaxy (MBE). The 12-nm-thick Fe3Si underlayer was grown epitaxially on CaF2/Si(111) at approximately 400 deg. C; however, the surface of the Fe3Si film was very rough, and thus a lot of pinholes are considered to exist in the 2-nm-thick CaF2 barrier layer. The average roughness (Ra) of the CaF2 barrier layer was 7.8 nm. This problem was overcome by low-temperature deposition of Fe and Si at 80 deg. C on CaF2/Si(111), followed by annealing at 250 deg. C for 30 min to form the Fe3Si layer. The Ra roughness was significantly reduced down to approximately 0.26 nm. A hysteresis loop with coercive field Hc of approximately 25 Oe was obtained in the magnetic field dependence of Kerr rotation at room temperature (RT)

  15. Laser Molecular Beam Epitaxy Growth of BaTiO3 in Seven Thousands of Unit-Cell Layers

    Institute of Scientific and Technical Information of China (English)

    HUANG Yan-Hong; YANG Guo-Zhen; HE Meng; ZHAO Kun; TIAN Huan-Fang; L(U) Hui-Bin; JIN Kui-Juan; CHEN Zheng-Hao; ZHOU Yue-Liang; LI Jian-Qi

    2005-01-01

    @@ BaTiO3 thin films in seven thousands of unit-cell layers have been successfully fabricated on SrTiO3 (001)substrates by laser molecular beam epitaxy. The fine streak pattern and the undamping intensity oscillation of reflection high-energy electron diffraction indicate that the BaTiO3 film was layer-by-layer epitaxial growth. The measurements of scanning electron microscopy and atomic force microscopy show that surfaces of the BaTiO3thin film are atomically smooth. The measurements of x-ray diffraction and transmission electron microscopy,as well as selected-area electron diffraction revealthat the BaTiO3 thin film is a c-oriented epitaxial crystalline structure.

  16. High-index Cu2O (113) film on faceted MgO (110) by molecular beam epitaxy

    Science.gov (United States)

    Huo, Wenxing; Shi, Jin'an; Mei, Zengxia; Liu, Lishu; Li, Junqiang; Gu, Lin; Du, Xiaolong; Xue, Qikun

    2015-06-01

    We report the growth of single-oriented Cu2O (113) film on faceted MgO (110) substrate by radio-frequency plasma assisted molecular beam epitaxy. A MgO {100} faceted homoepitaxial layer was introduced beforehand as a template for epitaxy of Cu2O film. The epitaxial relationship is determined to be Cu2O (113)//MgO (110) with a tilt angle of 4.76° and Cu2O [ 1 1 bar 0]//MgO [ 1 1 bar 0] by the combined study of in-situ reflection high-energy electron diffraction and ex-situ X-ray diffraction and transmission electron microscopy. The film demonstrates a good p-type conductivity and excellent optical properties, indicating that this unique approach is potentially applicable for high-index film preparation and device applications.

  17. Ion beam induced crystallization of amorphous Si from NiSi2 precipitates: An in situ study

    International Nuclear Information System (INIS)

    By first growing NiSi2 precipitates in a-Si and then irradiating with a 150 keV Si beam, the authors have studied ion beam induced epitaxial crystallization (IBIEC) of Si initiated at a-Si/NiSi2 precipitate interfaces. The growth shape and its temperature dependence are studied in-beam via in situ transmission electron microscopy. Interface roughening is evidenced. Preliminary results for the Co-Si system are also reported

  18. Strain induced ionic conductivity enhancement in epitaxial Ce0.9Gd0.1O22d

    DEFF Research Database (Denmark)

    Kant, K. Mohan; Esposito, Vincenzo; Pryds, Nini

    2012-01-01

    Strained epitaxial Ce0.9Gd0.1O2d (CGO) thin films are deposited on MgO(001) substrates with SrTiO3 (STO) buffer layers. The strain in CGO epitaxial thin films is induced and controlled by varying the thickness of STO buffer layers. The induced strain is found to significantly enhance the in......-plane ionic conductivity in CGO epitaxial thin films. The ionic conductivity is found to increase with decrease in buffer layer thickness. The tailored ionic conductivity enhancement is explained in terms of close relationships among epitaxy, strain, and ionic conductivity....

  19. In silico carbon molecular beam epitaxial growth of graphene on the h-BN substrate: carbon source effect on van der Waals epitaxy

    Science.gov (United States)

    Lee, Jonghoon; Varshney, Vikas; Park, Jeongho; Farmer, Barry L.; Roy, Ajit K.

    2016-05-01

    Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon molecular beam epitaxy (CMBE) techniques using solid carbon sublimation have reported relatively poor quality of the graphene. In this article, the CMBE growth of graphene on the h-BN substrate is numerically studied in order to identify the effect of the carbon source on the quality of the graphene film. The carbon molecular beam generated by the sublimation of solid carbon source materials such as graphite and glassy carbon is mostly composed of atomic carbon, carbon dimers and carbon trimers. Therefore, the graphene film growth becomes a complex process involving various deposition characteristics of a multitude of carbon entities. Based on the study of surface adsorption and film growth characteristics of these three major carbon entities comprising graphite vapour, we report that carbon trimers convey strong traits of vdW epitaxy prone to high quality graphene growth, while atomic carbon deposition is a surface-reaction limited process accompanied by strong chemisorption. The vdW epitaxial behaviour of carbon trimers is found to be substantial enough to nucleate and develop into graphene like planar films within a nanosecond of high flux growth simulation, while reactive atomic carbons tend to impair the structural integrity of the crystalline h-BN substrate upon deposition to form an amorphous interface between the substrate and the growing carbon film. The content of reactive atomic carbons in the molecular beam is suspected to be the primary cause of low quality graphene reported in the literature. A possible optimization of the molecular beam composition towards the synthesis of better quality graphene films is suggested.Against the presumption that hexagonal boron-nitride (h-BN) should provide an ideal substrate for van der Waals (vdW) epitaxy to grow high quality graphene films, carbon

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

    International Nuclear Information System (INIS)

    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. (topical review)

  1. Surface diffusion effects on growth of nanowires by chemical beam epitaxy

    International Nuclear Information System (INIS)

    Surface processes play a large role in the growth of semiconductor nanowires by chemical beam epitaxy. In particular, for III-V nanowires the surface diffusion of group-III species is important to understand in order to control the nanowire growth. In this paper, we have grown InAs-based nanowires positioned by electron beam lithography and have investigated the dependence of the diffusion of In species on temperature, group-III and -V source pressure and group-V source combinations by measuring nanowire growth rate for different nanowire spacings. We present a model which relates the nanowire growth rate to the migration length of In species. The model is fitted to the experimental data for different growth conditions, using the migration length as fitting parameter. The results show that the migration length increases with decreasing temperature and increasing group-V/group-III source pressure ratio. This will most often lead to an increase in growth rate, but deviations will occur due to incomplete decomposition and changes in sticking coefficient for group-III species. The results also show that the introduction of phosphorous precursor for growth of InAs1-xPx nanowires decreases the migration length of the In species followed by a decrease in nanowire growth rate

  2. Molecular beam epitaxial growth of ferromagnetic Heusler alloys for group-IV semiconductor spintronic devices

    International Nuclear Information System (INIS)

    Our recent progress in low-temperature molecular beam epitaxy of ferromagnetic Heusler alloys on group-IV-semiconductor is reviewed. By optimizing beam flux ratio (Fe:Si = 3:1) and growth temperature (130 oC), a high-quality hybrid structure, i.e., DO3-type Fe3Si on Ge with an atomically flat interface, was achieved. Excellent magnetic properties with a small coercivity (0.9 Oe) and electrical properties with Schottky barrier height of 0.52 eV were obtained. The ratio of the on-current to the off-current of Schottky diode was on the order of 104. In addition, heteroepitaxy of half-metallic alloys (Fe3-XMnxSi(X = 0.6-1.4)) on Ge substrates was demonstrated. These results will be a powerful tool to open up group-IV-semiconductor spin-transistors, consisting of Ge channel with high mobility and ferromagnetic source/drain for spin-injection.

  3. Ion beam induced alignment of semiconductor nanowires

    International Nuclear Information System (INIS)

    Epitaxially grown GaAs nanowires were irradiated with different kinds of energetic ions. The growth substrates were GaAs, and the nanowires grow under an angle of 35 circle. A bending of the nanowires was observed under ion beam irradiation, where the direction and magnitude of the bending depends on the energy, the species, and fluence of the incident ions. By choosing suitable ion beam parameters the nanowires could be realigned towards the ion beam direction. In order to understand the underlying mechanisms, computer simulations of the ion irradiation were done using a special version of TRIM which accounts for the geometry of the nanowires. The simulated distributions indicate vacancy and interstitial formation within the implantation cascade as the key mechanism for bending.

  4. Bi-induced band gap reduction in epitaxial InSbBi alloys

    International Nuclear Information System (INIS)

    The properties of molecular beam epitaxy-grown InSb1−xBix alloys are investigated. Rutherford backscattering spectrometry shows that the Bi content increases from 0.6% for growth at 350 °C to 2.4% at 200 °C. X-ray diffraction indicates Bi-induced lattice dilation and suggests a zinc-blende InBi lattice parameter of 6.626 Å. Scanning electron microscopy reveals surface InSbBi nanostructures on the InSbBi films for the lowest growth temperatures, Bi droplets at intermediate temperatures, and smooth surfaces for the highest temperature. The room temperature optical absorption edge was found to change from 172 meV (7.2 μm) for InSb to ∼88 meV (14.1 μm) for InSb0.976Bi0.024, a reduction of ∼35 meV/%Bi

  5. Bi-induced band gap reduction in epitaxial InSbBi alloys

    Energy Technology Data Exchange (ETDEWEB)

    Rajpalke, M. K.; Linhart, W. M.; Birkett, M.; Alaria, J.; Veal, T. D., E-mail: T.Veal@liverpool.ac.uk [Stephenson Institute for Renewable Energy and Department of Physics, School of Physical Sciences, University of Liverpool, Liverpool L69 7ZF (United Kingdom); Yu, K. M. [Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Bomphrey, J. J.; Jones, T. S.; Ashwin, M. J., E-mail: M.J.Ashwin@warwick.ac.uk [Department of Chemistry, University of Warwick, Coventry CV4 7AL (United Kingdom); Sallis, S.; Piper, L. F. J. [Materials Science and Engineering, Binghamton University, Binghamton, New York 13902 (United States)

    2014-11-24

    The properties of molecular beam epitaxy-grown InSb{sub 1−x}Bi{sub x} alloys are investigated. Rutherford backscattering spectrometry shows that the Bi content increases from 0.6% for growth at 350 °C to 2.4% at 200 °C. X-ray diffraction indicates Bi-induced lattice dilation and suggests a zinc-blende InBi lattice parameter of 6.626 Å. Scanning electron microscopy reveals surface InSbBi nanostructures on the InSbBi films for the lowest growth temperatures, Bi droplets at intermediate temperatures, and smooth surfaces for the highest temperature. The room temperature optical absorption edge was found to change from 172 meV (7.2 μm) for InSb to ∼88 meV (14.1 μm) for InSb{sub 0.976}Bi{sub 0.024}, a reduction of ∼35 meV/%Bi.

  6. Molecular beam epitaxy of GeTe-Sb2Te3 phase change materials studied by X-ray diffraction

    International Nuclear Information System (INIS)

    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

  7. Copper ion implanted aluminum nitride dilute magnetic semiconductors (DMS) prepared by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Highlights: • AlN:Cu dilute magnetic semiconductors were successfully prepared by molecular beam epitaxy followed by Cu+ implantation. • Room temperature ferromagnetism was observed after annealing the samples at appropriate temperature. • XRD and Raman spectrometry excluded the possibility of formation of any secondary phases. • By doping intrinsically nonmagnetic dopants (Cu), it has been proved experimentally that their precipitates do not contribute to ferromagnetism. • The reason for ferromagnetism in Cu-doped AlN as observed was explained on the basis of p–d hybridization mechanism (Wu et al.). - Abstract: Diluted magnetic semiconductor (DMS) AlN:Cu films were fabricated by implanting Cu+ ions into AlN thin films at various ion fluxes. AlN films were deposited on c-plane sapphire by molecular beam epitaxy followed by Cu+ ion implantation. The structural and magnetic characterization of the samples was performed through Rutherford backscattering and channeling spectrometry (RBS/C), X-ray diffraction (XRD), Raman spectroscopy, vibrating sample magnetometer (VSM) and SQUID. Incorporation of copper into the AlN lattice was confirmed by RBS, while XRD revealed that no new phase was formed as a result of ion implantation. RBS also indicated formation of defects as a result of implantation process and the depth and degree of damage increased with an increase in ion fluence. Raman spectra showed only E2 (high) and A1 (LO) modes of wurtzite AlN crystal structure and confirmed that no secondary phases were formed. It was found that both Raman modes shift with Cu+ fluences, indicating that Cu ion may go to interstitial or substitutional sites resulting in distortion or damage of lattice. Although as implanted samples showed no magnetization, annealing of the samples resulted in appearance of room temperature ferromagnetism. The saturation magnetization increased with both the annealing temperature as well as with ion fluence. FC/ZFC measurements indicated

  8. Comparison of Morphology Evolution of Ge(001) Homoepitaxial Films Grown by Pulsed Laser Deposition and Molecular Beam Epitaxy

    OpenAIRE

    McCamy, James W.; Shin, Byungha; Leonard, John P.; Aziz, Michael

    2005-01-01

    Using a dual Molecular Beam Epitaxy (MBE)-Pulsed Laser Deposition (PLD) Ultra-High Vacuum chamber, we have conducted the first experiments under identical thermal, background, and surface preparation conditions to compare Ge(001) homoepitaxial growth morphology in PLD and MBE. We find that in PLD with low kinetic energy and in MBE the film morphology evolves in a similar fashion: initially irregularly shaped mounds form, followed by pyramidal mounds with edges of the square-base along direc...

  9. Carbon doping of GaN with CBr4 in radio-frequency plasma-assisted molecular beam epitaxy

    OpenAIRE

    Green, D S; Mishra, U. K.; Speck, J.S.

    2004-01-01

    Carbon tetrabromide (CBr4) was studied as an intentional dopant during rf plasma molecular beam epitaxy of GaN. Secondary ion mass spectroscopy was used to quantify incorporation behavior. Carbon was found to readily incorporate under Ga-rich and N-rich growth conditions with no detectable bromine incorporation. The carbon incorporation [C] was found to be linearly related to the incident CBr4 flux. Reflection high-energy electron diffraction, atomic force microscopy and x-ray diffraction wer...

  10. Strain-induced magneto-optical anisotropy in epitaxial hcp Co films

    Science.gov (United States)

    Arregi, J. A.; González-Díaz, J. B.; Idigoras, O.; Berger, A.

    2015-11-01

    We investigate the existence and origin of magneto-optical anisotropy in epitaxial hcp Co films. Our results show that a significant magneto-optical anisotropy exists in our samples and, more importantly, they reveal that its amplitude is directly correlated with epitaxial strain. We find a linear coefficient of 16.8 % magneto-optical anisotropy per every 1% epitaxial strain, which is in stark contrast to an isotropic magneto-optical coupling factor Q , a very frequent and common assumption in magneto-optics of metallic thin films and multilayers. In addition, the Co films exhibit a similar strain-induced increase of the magnetocrystalline anisotropy energy, evidencing the fact that both magneto-optical anisotropy and magnetocrystalline anisotropy are dependent on the modification of the spin-orbit coupling introduced by anisotropic lattice distortions.

  11. Orbital angular momentum induced beam shifts

    OpenAIRE

    Hermosa N.; Merano M.; Aiello A.; Woerdman J.P.

    2011-01-01

    We present experiments on Orbital Angular Momentum (OAM) induced beam shifts in optical reflection. Specifically, we observe the spatial Goos-H\\"anchen shift in which the beam is displaced parallel to the plane of incidence and the angular Imbert-Fedorov shift which is a transverse angular deviation from the geometric optics prediction. Experimental results agree well with our theoretical predictions. Both beam shifts increase with the OAM of the beam; we have measured these for OAM indices u...

  12. Room temperature epitaxial growth of Ag on low-index Si surfaces by a partially ionized beam

    Science.gov (United States)

    Nason, T. C.; You, L.; Lu, T.-M.

    1992-07-01

    The room temperature growth of 1000-1500 Å Ag films on HF-dipped Si substrates is studied as a function of self-ion (Ag+) energy during deposition. In all cases the films contained a mixture of epitaxial grains and randomly oriented (111) grains. The orientations observed were Ag(111)/Si(111) with both type A (Ag//Si) and type B (Ag//Si) twins; Ag(110)/Si(110) with Ag//Si; and Ag(100)/Si(100) with Ag//Si. All three constructions match three Si atomic rows with four Ag rows. As judged by the ratio of epitaxial to nonepitaxial grains, the strength of the epitaxy was seen to decrease in the order (111)≳(110)≳(100). Increasing the Ag+ ion energy during the deposition was generally seen to decrease this ratio. Annealing of the Ag/Si(100) films induced preferential (100) grain growth.

  13. Process-Induced Morphological Defects in Epitaxial CVD Silicon Carbide

    Science.gov (United States)

    Powell, J. A.; Larkin, D. J.

    1997-07-01

    Silicon carbide (SiC) semiconductor technology has been advancing rapidly, but there are numerous crystal growth problems that need to be solved before SiC can reach its full potential. Among these problems is a need for an improvement in the surface morphology of epitaxial films that are grown to produce device structures. Various processes before and during epilayer growth lead to the formation of morphological defects observed in SiC epilayers grown on SiC substrates. In studies of both 6H and 4H-SiC epilayers, atomic force microscopy (AFM) and other techniques have been used to characterize SiC epilayer surface morphology. In addition to the well-known micropipe defect, SiC epilayers contain growth pits, triangular features (primarily) in 4H-SiC, and macro step due to step bunching. In work at NASA Lewis, it has been found that factors contributing to the formation of some morphological defects include: defects in the substrate bulk, defects in the substrate surface caused by cutting and polishing the wafer, the tilt angle of the wafer surface relative to the basal plane, and growth conditions. Some of these findings confirm results of other research groups. This paper presents a review of published and unpublished investigations into processes that are relevant to epitaxial film morphology.

  14. Structural and band alignment properties of Al2O3 on epitaxial Ge grown on (100), (110), and (111)A GaAs substrates by molecular beam epitaxy

    Science.gov (United States)

    Hudait, M. K.; Zhu, Y.; Maurya, D.; Priya, S.; Patra, P. K.; Ma, A. W. K.; Aphale, A.; Macwan, I.

    2013-04-01

    Structural and band alignment properties of atomic layer Al2O3 oxide film deposited on crystallographically oriented epitaxial Ge grown in-situ on (100), (110), and (111)A GaAs substrates using two separate molecular beam epitaxy chambers were investigated using cross-sectional transmission microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). High-resolution triple axis x-ray measurement demonstrated pseudomorphic and high-quality Ge epitaxial layer on crystallographically oriented GaAs substrates. The cross-sectional TEM exhibited a sharp interface between the Ge epilayer and each orientation of the GaAs substrate as well as the Al2O3 film and the Ge epilayer. The extracted valence band offset, ΔEv, values of Al2O3 relative to (100), (110), and (111) Ge orientations using XPS measurement were 3.17 eV, 3.34 eV, and 3.10 eV, respectively. Using XPS data, variations in ΔEv related to the crystallographic orientation were ΔEV(110)Ge>ΔEV(100)Ge≥ΔEV(111)Ge and the conduction band offset, ΔEc, related to the crystallographic orientation was ΔEc(111)Ge>ΔEc(110)Ge>ΔEc(100)Ge using the measured ΔEv, bandgap of Al2O3 in each orientation, and well-known Ge bandgap of 0.67 eV. These band offset parameters are important for future application of Ge-based p- and n-channel metal-oxide field-effect transistor design.

  15. Structural properties of In0.53Ga0.47As epitaxial films grown on Si (111) substrates by molecular beam epitaxy

    International Nuclear Information System (INIS)

    In0.53Ga0.47As epitaxial films are grown on 2-inch diameter Si (111) substrates by growing a low-temperature In0.4Ga0.6As buffer layer using molecular beam epitaxy. The effect of the buffer layer thickness on the as-grown In0.53Ga0.47As films is characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy and transmission electron microscopy (TEM). It is revealed that the crystalline quality and surface morphology of as-grown In0.53Ga0.47As epilayer are strongly affected by the thickness of the In0.4Ga0.6As buffer layer. From TEM investigation, we understand that the type and the distribution of dislocations of the buffer layer and the as-grown In0.53Ga0.47As film are different. We have demonstrated that the In0.4Ga0.6As buffer layer with a thickness of 12 nm can advantageously release the lattice mismatch stress between the In0.53Ga0.47As and Si substrate, ultimately leading to a high-quality In0.53Ga0.47As epitaxial film with low surface roughness. - Highlights: • We provide a simple approach to achieve high-quality In0.53Ga0.47As films on Si. • An appropriate thickness of In0.4Ga0.6As buffer layer can release mismatch strain. • High-quality In0.53Ga0.47As film is grown on Si using 12-nm-thick buffer layer. • Smooth surface In0.53Ga0.47As film is grown on Si using 12-nm-thick buffer layer

  16. Characterization of carbon-doped InSb diode grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Carbon-doped p-type InSb layers grown by solid source molecular beam epitaxy are characterized using a p+-n diode structure. Based on the combination of current-voltage, secondary ion mass spectroscopy and x-ray diffraction measurements, carbon is proven to be an effective p-type dopant for InSb with hole concentration reaching the range of 1019 cm-3. It is also proven that the use of the Hall effect to determine the hole concentration in the p-type InSb layer may be unreliable in cases where the leakage current in the p+-n junction is high. A thermal trap-assisted tunnelling model with two trap levels successfully explains the origin of leakage current mechanisms in the carbon-doped InSb samples. Good agreement between measured and calculated dc characteristics of the diodes at reverse bias up to -3 V from 30 to 120 K supports the validity of the current transport model

  17. 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.

  18. 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.

  19. 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.

  20. Molecular-beam epitaxy of CdTe on large area Si(100)

    Science.gov (United States)

    Sporken, R.; Lange, M. D.; Faurie, J. P.; Petruzzello, J.

    1991-10-01

    We have grown CdTe directly on 2- and 5-in. diam Si(100) by molecular-beam epitaxy and characterized the layers by in situ reflection high-energy electron diffraction, double crystal x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and low-temperature photoluminescence. The films are up to 10-μm thick and mirror-like over their entire surface. Even on 5-in. diam wafers, the structural and thickness uniformity is excellent. Two domains, oriented 90° apart, are observed in the CdTe films on oriented Si(100) substrates, whereas single-domain films are grown on Si(100) titled 6° or 8° toward [011]. The layers on misoriented substrates have better morphology than those on oriented Si(100), and the substrate tilt also eliminates twinning in the CdTe layers. First attempts to grow HgCdTe on Si(100 with a CdTe buffer layer have produced up to 10-μm thick layers with cutoff wavelengths between 5 and 10-μm and with an average full width at half-maximum of the double-crystal x-ray diffraction peaks of 200 arc s.

  1. Growth of HfOx thin films by reactive molecular beam epitaxy

    International Nuclear Information System (INIS)

    Thin films of hafnium oxide were grown on single crystal r-cut and c-cut sapphire by reactive molecular beam epitaxy. The conditions for the growth of single oriented hafnium oxide thin films have been established. Hafnium oxide thin films were characterized by X-ray diffraction and optical absorption measurements. It was found that hafnium oxide thin films grown on r-cut sapphire were (00l) oriented whereas, on c-cut sapphire, hafnium oxide films showed different orientations depending on the growth temperature and oxidation conditions. The hafnium oxide films grown at higher temperature and under strong oxidation conditions yielded (001) oriented films on c-cut sapphire whereas slightly weaker oxidation condition leads to (111) oriented hafnium oxide films. The bandgap deducted from optical absorption measurement carried out on hafnium oxide films grown under optimized conditions agreed well with the values reported in literature. A range of oxygen deficient thin films of hafnium oxide were also grown on single crystal sapphire substrates in order to investigate the effect of oxygen vacancies on dielectric properties of hafnium oxide. The oxygen deficient thin films of hafnium oxide show a decrease in bandgap with increase in oxygen deficiency

  2. Structural and morphological evolution of gallium nitride nanorods grown by chemical beam epitaxy

    International Nuclear Information System (INIS)

    The morphological and structural evolution is presented for GaN nanorods grown by chemical beam epitaxy on (0001) Al2O3 substrates. Their structural and optical properties are investigated by x-ray diffraction, scanning and transmission electron microscopy, and temperature-dependent photoluminescence measurements. While increasing the growth temperature and the flow rate of radio-frequency nitrogen radical, the three-dimensional growth mode will be enhanced to form one-dimensional nanostructures. The high density of well-aligned nanorods with a diameter of 30-50 nm formed uniformly over the entire sapphire substrate. The x-ray diffraction patterns and transmission electron microscopic images indicate that the self-assembled GaN nanorods are a pure single crystal and preferentially oriented in the c-axis direction. Particularly, the ''S-shape'' behavior with localization of ∼10 meV observed in the temperature-dependent photoluminescence might be ascribed to the fluctuation in crystallographic defects and composition.

  3. Structural and morphological evolution of gallium nitride nanorods grown by chemical beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kuo, Shou-Yi; Lai, Fang-I; Chen, Wei-Chun; Hsiao, Chien-Nan; Lin, Woei-Tyng [Department of Electronic Engineering, Chang Gung University, Taiwan, Green Technology Research Center, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan, Tao-Yuan 333, Taiwan (China); Department of Electrical Engineering, Yuan-Ze University, Taiwan, 135, Far-East Rd., Chung-Li, Taoyuan, Tao-Yuan, 320, Taiwan (China); Instrument Technology Research Center, National Applied Research Laboratories, Taiwan, 20 R and D Road VI, Hsinchu Science Park, Hsinchu 300, Taiwan (China); Department of Electrical Engineering, Yuan-Ze University, Taiwan, 135, Far-East Road, Chung-Li, Taoyuan, Tao-Yuan, 320, Taiwan (China)

    2009-07-15

    The morphological and structural evolution is presented for GaN nanorods grown by chemical beam epitaxy on (0001) Al{sub 2}O{sub 3} substrates. Their structural and optical properties are investigated by x-ray diffraction, scanning and transmission electron microscopy, and temperature-dependent photoluminescence measurements. While increasing the growth temperature and the flow rate of radio-frequency nitrogen radical, the three-dimensional growth mode will be enhanced to form one-dimensional nanostructures. The high density of well-aligned nanorods with a diameter of 30-50 nm formed uniformly over the entire sapphire substrate. The x-ray diffraction patterns and transmission electron microscopic images indicate that the self-assembled GaN nanorods are a pure single crystal and preferentially oriented in the c-axis direction. Particularly, the ''S-shape'' behavior with localization of {approx}10 meV observed in the temperature-dependent photoluminescence might be ascribed to the fluctuation in crystallographic defects and composition.

  4. 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.

  5. Current transport in ZnO/Si heterostructure grown by laser molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Teng Xiao-Yun; Wu Yan-Hua; Yu Wei; Gao Wei; Fu Guang-Sheng

    2012-01-01

    The n-ZnO/p-Si heterojunction was fabricated by depositing high quality single crystalline aluminium-doped n-type ZnO film on p-type Si using the laser molecular beam epitaxy technique. The heterojunction exhibited a good rectifying behavior.The electrical properties of the heterojunction were investigated by means of temperature dependence current density-voltage measurements.The mechanism of the current transport was proposed based on the band structure of the heterojunction.When the applied bias V is lower than 0.15 V,the current follows the Ohmic behavior.When 0.15 V < V < 0.6 V,the transport property is dominated by diffusion or recombination in the junction space charge region,while at higher voltages (V > 0.6 V),the space charge limited effect becomes the main transport mechanism.The current-voltage characteristic under illumination was also investigated.The photovoltage and the short circuit current density of the heterojunction aproached 270 mV and 2.10 mA/cm2,respectively.

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

    International Nuclear Information System (INIS)

    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-1 is suggested to be the second harmonic mode of the substitutional N, NAs, LVM around 469 cm-1. The absorption peak around 960 cm-1 is suggested to be the wagging mode of the N-H, where the stretch mode is observed around 3098 cm-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

  7. Growth of SrVO3 thin films by hybrid molecular beam epitaxy

    International Nuclear Information System (INIS)

    The authors report the growth of stoichiometric SrVO3 thin films on (LaAlO3)0.3(Sr2AlTaO6)0.7 (001) substrates using hybrid molecular beam epitaxy. This growth approach employs a conventional effusion cell to supply elemental A-site Sr and the metalorganic precursor vanadium oxytriisopropoxide (VTIP) to supply vanadium. Oxygen is supplied in its molecular form through a gas inlet. An optimal VTIP:Sr flux ratio has been identified using reflection high-energy electron-diffraction, x-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy, demonstrating stoichiometric SrVO3 films with atomically flat surface morphology. Away from the optimal VTIP:Sr flux, characteristic changes in the crystalline structure and surface morphology of the films were found, enabling identification of the type of nonstoichiometry. For optimal VTIP:Sr flux ratios, high quality SrVO3 thin films were obtained with smallest deviation of the lattice parameter from the ideal value and with atomically smooth surfaces, indicative of the good cation stoichiometry achieved by this growth technique

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

    International Nuclear Information System (INIS)

    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

  9. Selective area growth of a- and c-plane GaN nanocolumns by molecular beam epitaxy using colloidal nanolithography

    OpenAIRE

    Bengoechea-Encabo, A.; S. Albert; Sanchez-Garcia, M.A.; López, L.L.; Estradé, S.; Rebled, J.M.; Peiró, F.; Nataf, G.; De Mierry, P.; Zuniga-Perez, J.; E. Calleja

    2012-01-01

    Selective area growth of a-plane GaN nanocolumns by molecular beam epitaxy was performed for the first time on a-plane GaN templates. Ti masks with 150 nm diameter nanoholes were fabricated by colloidal lithography, an easy, fast and cheap process capable to handle large areas. Even though colloidal lithography does not provide a perfect geometrical arrangement like e-beam lithography, it produces a very homogeneous mask in terms of nanohole diameter and density, and is used here for the firs...

  10. Laser molecular beam epitaxy growth and properties of SrTiO3 thin films for microelectronic applications

    International Nuclear Information System (INIS)

    Dielectric SrTiO3 thin films were deposited on LaAlO3 and Si substrates using laser molecular beam epitaxy. The correlations between the deposition parameters of SrTiO3 thin films, their structural characteristics, and dielectric properties were studied. The conditions for achieving epitaxial SrTiO3 thin films were found to be limited to deposition conditions such as deposition temperature. We show that the SrTiO3 films with single (110) orientation can be grown directly on Si substrates. The nature of epitaxial growth and interfacial structures of the grown films were examined by various techniques, such as Laue diffraction and X-ray photoelectron spectroscopy. The SrTiO3/Si interface was found to be epitaxially crystallized without any SiO2 layer. Furthermore, we have measured dielectric properties of the grown SrTiO3 multilayer suitable for tunable microwave device. A large tunability of 74.7%, comparable to that of SrTiO3 single-crystal, was observed at cryogenic temperatures. Such STO thin films will be very promising for the development of microelectronic device applications

  11. Controlling the crystal phase and structural quality of epitaxial InAs nanowires by tuning V/III ratio in molecular beam epitaxy

    International Nuclear Information System (INIS)

    In this study, we demonstrated the control of crystal phase and structural quality of Au-catalyzed InAs nanowires grown on the GaAs {1 1 1}B substrates by tuning the V/III ratio in molecular beam epitaxy. It has been found that InAs nanowires can only be grown in a relatively narrow window of the V/III ratio. It is also demonstrated that the V/III ratio can be used to control the structural quality of wurtzite structured and zinc-blende structured InAs nanowires under low V/III ratios, and defect-free wurtzite structured and zinc-blende structured InAs nanowires were successfully achieved. This study provides an insight into the controlled growth of high-quality wurtzite structured and zinc-blende structured InAs nanowires through the V/III ratio engineering

  12. Epitaxial growth of M-plane GaN on ZnO micro-rods by plasma-assisted molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Shuo-Ting You

    2015-12-01

    Full Text Available We have studied the GaN grown on ZnO micro-rods by plasma-assisted molecular beam epitaxy. From the analyses of GaN microstructure grown on non-polar M-plane ZnO surface ( 10 1 ̄ 0 by scanning transmission electron microscope, we found that the ZnGa2O4 compound was formed at the M-plane hetero-interface, which was confirmed by polarization-dependent photoluminescence. We demonstrated that the M-plane ZnO micro-rod surface can be used as an alternative substrate to grow high quality M-plane GaN epi-layers.

  13. Spectroscopic and magnetic properties of Mn doped GaN epitaxial films grown by plasma assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Vidyasagar, R., E-mail: dr.vidyasagar1979@gmail.com [Department of Physics and Centre for Nanoscience and Nanotechnology, National Sun-Yat Sen University, Kaohsiung 80424, Taiwan, ROC (China); Lin, Y.-T.; Tu, L.-W. [Department of Physics and Centre for Nanoscience and Nanotechnology, National Sun-Yat Sen University, Kaohsiung 80424, Taiwan, ROC (China)

    2012-12-15

    Graphical abstract: We report here that micro-Raman scattering spectrum for Mn doped GaN thin film has displayed a new peak manifested at 578 cm{sup −1}, by which it is attributed to interior LVM originated by the incorporation of Mn ions in place of Ga sites. Mn doped GaN thin film also showed the typical negative magnetoresistance up to ∼50 K, revealing that the film showed magnetic ordering of spins below 50 K. Display Omitted Highlights: ► GaN and Mn doped GaN single phase wurtzite structures grown by PAMBE. ► The phase purity of the epilayers investigated by HRXRD, HRSEM and EDX. ► The red shift in near band edge emission has been observed using micro-PL. ► A new peak related LVM at 578 cm{sup −1} in micro-Raman scattering measurements confirmed Mn doped into GaN. ► Negative-magnetoresistance investigations have showed that the film has T{sub c} < 50 K. -- Abstract: Spectroscopic and magnetic properties of Mn doped GaN, and GaN epitaxial films have been investigated by employing micro-photoluminescence, micro-Raman, and temperature dependent magneto-resistance measurements. The HR-XRD profiles have shown that the epitaxial films are in hexagonal wurtzite structures. Morphology and composition of the films have been examined by field emission scanning electron microscopy, and energy-dispersive X-ray analysis. Micro-photoluminescence spectrum displayed a dominant near band edge emission at 362 nm, which is assigned to near band edge transition within the hexagonal structure of GaN. Raman scattering profiles showed a new vibrational mode at 578 cm{sup −1}, which is attributed to the vacancy-related local vibrational mode of Mn occupying the Ga site. Temperature dependent negative magnetoresistance measurements provide a direct evidence of magnetic ordering below 50 K for the Mn doped GaN thin film.

  14. Increase in the diffusion length of minority carriers in AlxGa1–xN alloys (x = 0–0.1) fabricated by ammonia molecular beam epitaxy

    International Nuclear Information System (INIS)

    The room-temperature diffusion length of minority carriers in n-Al0.1Ga0.9N layers grown by ammonia molecular beam epitaxy on sapphire (0001) substrates used in structures for ultraviolet photodetectors is studied. Measurements were performed using the spectral dependence of the photocurrent recorded in a built-in p–n junction for thin samples and using the induced electron-current procedure for films up to 2 µm thick. The results show that the hole diffusion length in n-AlGaN films is 120–150 nm, which is larger than in GaN films grown under similar growth conditions by a factor of 3–4. This result can be associated with the larger lateral sizes characteristic of hexagonal columns in AlGaN layers grown by molecular beam epitaxy. No increase in the hole diffusion length is observed for thicker films

  15. Strain-induced modification of magnetic structure and new magnetic phases in rare-earth epitaxial films

    Indian Academy of Sciences (India)

    C Dufour; K Dumesnil; Ph Mangin

    2006-07-01

    Rare earths exhibit complex magnetic phase diagrams resulting from the competition between various contributions to the magnetic energy: exchange, anisotropy and magnetostriction. The epitaxy of a rare-earth film on a substrate induces (i) a clamping to the substrate and (ii) pseudomorphic strains. Both these effects are shown to lead to modifications of the magnetic properties in (0 0 1)Dy, (0 0 1)Tb and (1 1 0)Eu films. In Dy and Tb films, spectacular variations of the Curie temperature have been evidenced. Additionally, Tb films exhibit a new large wavelength magnetic modulation. In Eu films, one of the helical magnetic domains disappears at low temperature whereas the propagation vectors of the other helices are tilted. The link between structural and magnetic properties is underlined via magnetoelastic models. Moreover, molecular beam epitaxy permits the growth of Sm in a metastable dhcp phase. The magnetic structure of dhcp Sm has been elucidated for the first time. In this review, neutron scattering is shown to be a powerful technique to reveal the magnetic structures of rare-earth films.

  16. Critical thickness and strain relaxation in molecular beam epitaxy-grown SrTiO3 films

    Science.gov (United States)

    Wang, Tianqi; Ganguly, Koustav; Marshall, Patrick; Xu, Peng; Jalan, Bharat

    2013-11-01

    We report on the study of the critical thickness and the strain relaxation in epitaxial SrTiO3 film grown on (La0.3Sr0.7)(Al0.65Ta0.35)O3 (001) (LSAT) substrate using the hybrid molecular beam epitaxy approach. No change in the film's lattice parameter (both the in-plane and the out-of-plane) was observed up to a film thickness of 180 nm, which is in sharp contrast to the theoretical critical thickness of ˜12 nm calculated using the equilibrium theory of strain relaxation. For film thicknesses greater than 180 nm, the out-of-plane lattice parameter was found to decrease hyperbolically in an excellent agreement with the relaxation via forming misfit dislocations. Possible mechanisms are discussed by which the elastic strain energy can be accommodated prior to forming misfit dislocations leading to such anomalously large critical thickness.

  17. Compensation mechanism of undoped GaAs films grown by molecular beam epitaxy using an As-valved cracker cell

    Science.gov (United States)

    Hong, C. U.; Gozu, S.; Okayasu, J.; Koyano, M.; Katayama, S.; Hori, H.; Yamada, S.

    1998-06-01

    We have investigated GaAs films epitaxially grown by molecular beam epitaxy (MBE) using a valved As-cracker source. When the cracking temperature ( Tc) of the As-valved cracker cell is raised, which means the dominant As species changes from As 4 to As 2, the conduction type of the films changed from p - to n -. In order to clarify the origins of the change of compensation mechanism of those GaAs films, estimations were made using electrical (Hall effect) and optical (photoluminescence and far-infrared) measurements. Impurity incorporation behaviors suggested by these estimations are found to give a reasonable explanation for the change of conduction type, that is, the change of compensation mechanism.

  18. Topological insulator Bi2Se3 thin films grown on double-layer graphene by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Atomically flat thin films of topological insulator Bi2Se3 have been grown on double-layer graphene formed on 6H-SiC(0001) substrate by molecular beam epitaxy. By a combined study of reflection high energy electron diffraction and scanning tunneling microscopy, we identified the Se-rich condition and temperature criterion for layer-by-layer growth of epitaxial Bi2Se3 films. The as-grown films without doping exhibit a low defect density of 1.0±0.2x1011/cm2, and become a bulk insulator at a thickness of ten quintuple layers, as revealed by in situ angle resolved photoemission spectroscopy measurement.

  19. X—ray reflectivity measurement of δ—doped erbium profile in silicon molecular—beam epitaxial layer

    Institute of Scientific and Technical Information of China (English)

    JunWan; Q.J.Jia; 等

    1999-01-01

    Synchrontron radiation x-ray reflectivity measurement is used to study the concentration profile of a δ-doped Er layer in Si epitaxial film grown by molecular-beam epitaxy.The oscillation of the reflectivity amplitude as a function of reflection angle is observed in the experiment.By doing a theoretical simulation.the concentration profile of Er atoms could be deried.It is shown that the originally grown δ-doped Er layer changes into an expionentially decayed function due to the Er segregation.The temperature dependence of the 1/e decay length indicates that the segregation is a kinetically limited process.The activation energy is determined to be 0.044±0.005eV.

  20. Size dependent bandgap of molecular beam epitaxy grown InN quantum dots measured by scanning tunneling spectroscopy

    International Nuclear Information System (INIS)

    InN quantum dots (QDs) were grown on Si (111) by epitaxial Stranski-Krastanow growth mode using plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN QDs was verified by the x-ray diffraction and transmission electron microscopy. Scanning tunneling microscopy has been used to probe the structural aspects of QDs. A surface bandgap of InN QDs was estimated from scanning tunneling spectroscopy (STS) I-V curves and found that it is strongly dependent on the size of QDs. The observed size-dependent STS bandgap energy shifts with diameter and height were theoretical explained based on an effective mass approximation with finite-depth square-well potential model.

  1. The growth of III-V nitrides heterostructure on Si substrate by plasma-assisted molecular beam epitaxy

    International Nuclear Information System (INIS)

    This paper reports the growth of InGaN/GaN/AlN epitaxial layer on Si(1 1 1) substrate by utilizing plasma-assisted molecular beam epitaxy (PA-MBE) system. The as-grown film was characterized using high-resolution X-ray diffraction (HR-XRD) and photoluminescence (PL). High work function metals, iridium and gold were deposited on the film as metal contacts and their electrical characteristics at pre- and post-annealing were studied. The structural quality of this film is comparative to the values reported in the literature, and the indium molar fraction is 0.57 by employing Vegard's law. The relatively low yellow band emission signifies the grown film is of high quality. For metal contact studies it was found that the post-annealed sample for 5 min shows good conductivity as compared to the other samples.

  2. Molecular beam epitaxy of thick InGaN(0001) films: Effects of substrate temperature on structural and electronic properties

    Science.gov (United States)

    Papadomanolaki, E.; Bazioti, C.; Kazazis, S. A.; Androulidaki, M.; Dimitrakopulos, G. P.; Iliopoulos, E.

    2016-03-01

    Indium gallium nitride films with compositions close to the middle of the miscibility gap and thickness approximately up to 0.5 μm were epitaxially grown on GaN(0001) by plasma-assisted molecular beam epitaxy at growth temperatures spanning a range of 400-590 °C. Epilayers were characterized by X-ray diffraction, transmission electron microscopy and Hall effect measurements. The effect of substrate temperature during growth, on the structural and electronic properties of the films, was studied. Single phase films, with record high electron mobilities were obtained at lower temperatures. Increased growth temperatures led to epilayers with higher defect densities and phase separation. Strain relaxation through sequestration layering and introduction of multiple basal stacking faults was observed at such temperatures.

  3. Defect reduction in GaN/(0001)sapphire films grown by molecular beam epitaxy using nanocolumn intermediate layers

    International Nuclear Information System (INIS)

    Transmission and scanning electron microscopies are used to examine the epitaxial lateral overgrowth of GaN on GaN nanocolumns grown on AlN/(0001)sapphire by molecular beam epitaxy. Initially, N-rich growth gave a bimodal morphology consisting of defect-free Ga-polar nanocolumns emanating from a compact, highly defective N-polar layer. Under subsequent Ga-rich conditions, the nanocolumns grew laterally to produce continuous Ga-polar overlayers. Threading dislocation (TD) densities in the overlayer were in the range of 108-109 cm-2, up to two orders of magnitude less than in the N-polar underlayer. It is proposed that the change in polarity is a key factor controlling the reduction in TD density

  4. Mid-infrared to ultraviolet optical properties of InSb grown on GaAs by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    D' Costa, Vijay Richard, E-mail: elevrd@nus.edu.sg; Yeo, Yee-Chia, E-mail: eleyeoyc@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583 (Singapore); Tan, Kian Hua; Jia, Bo Wen; Yoon, Soon Fatt [School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore)

    2015-06-14

    Spectroscopic ellipsometry was used to investigate the optical properties of an InSb film grown on a GaAs (100) substrate, and to compare the optical properties of InSb film with those of bulk InSb. The film was grown by molecular beam epitaxy under conditions intended to form 90° misfit dislocations at the InSb-GaAs interface. The complex dielectric function obtained in a wide spectroscopic range from 0.06–4.6 eV shows the critical point transitions E{sub 0}, E{sub 1}, E{sub 1} + Δ{sub 1}, E{sub 0}{sup ′}, and E{sub 2}. The amplitudes, energy transitions, broadenings, and phase angles have been determined using a derivative analysis. Comparing film and bulk critical point results reveal that the epitaxial film is nearly relaxed and has bulk-like optical characteristics.

  5. Molecular beam epitaxy deposition of Gd2O3 thin films on SrTiO3 (100) substrate

    Science.gov (United States)

    Wang, Jinxing; Hao, Jinghua; Zhang, Yangyang; Wei, Hongmei; Mu, Juyi

    2016-06-01

    Gd2O3 thin films are grown on the SrTiO3 (100) substrate by molecular beam epitaxy (MBE) deposition. X-ray diffraction (XRD) analysis, conventional transmission electron microscopy (TEM) and aberration-corrected scanning transmission electron microscopy (STEM) are performed to investigate the microstructure of deposited thin films. It is found that the as-deposited thin film possesses a very uniform thickness of ∼40 nm and is composed of single cubic phase Gd2O3 grains. STEM and TEM observations reveal that Gd2O3 thin film grows epitaxially on the SrTiO3 (100) substrate with (001)Gd2O3//(100)STO and [110]Gd2O3//[001]STO orientations. Furthermore, the Gd atoms are found to diffuse into the SrTiO3 substrate for a depth of one unit cell and substitute for the Sr atoms near the interface.

  6. Molecular beam epitaxial regrowth on diffraction gratings for vertical-cavity, surface-emitting laser-based integrated optoelectronics

    International Nuclear Information System (INIS)

    Epitaxial regrowth techniques, using molecular beam epitaxy, were optimized for the inclusion of submicron diffraction gratings within a vertically resonant structure. Various growth conditions including chemical surface preparation, growth rate, and regrown interfacial structure were studied to determine the quality of the regrown materials and structures. Characteristics such as dislocation density and growth planarity (flatness of the regrown layers) were of particular importance due to the vertical geometry and resonance requirements of the structure. Threading dislocation densities of ≅3x106 cm-2 were measured, by means of transmission electron microscopy, in the regrown structures using optimized regrowth processes. Layer thickness variations, due to growth on nonplanar surfaces (diffraction gratings), were characterized using modeling and optical reflectometry. With these results, inclusion of diffraction gratings has been demonstrated with the accurate control over layer thickness needed for use in vertically oriented devices such as vertical-cavity, surface-emitting lasers, and resonant cavity photodetectors

  7. Patterned growth of InGaN/GaN quantum wells on freestanding GaN grating by molecular beam epitaxy

    OpenAIRE

    Wang Yongjin; Hu Fangren; Hane Kazuhiro

    2011-01-01

    Abstract We report here the epitaxial growth of InGaN/GaN quantum wells on freestanding GaN gratings by molecular beam epitaxy (MBE). Various GaN gratings are defined by electron beam lithography and realized on GaN-on-silicon substrate by fast atom beam etching. Silicon substrate beneath GaN grating region is removed from the backside to form freestanding GaN gratings, and the patterned growth is subsequently performed on the prepared GaN template by MBE. The selective growth takes place wit...

  8. Lattice strain induced phase selection and epitaxial relaxation in crystalline GeTe thin film

    International Nuclear Information System (INIS)

    We report that the lattice strain induced phase selection and epitaxial relaxation in crystalline GeTe thin films by pulsed laser deposition. The single-crystal substrates of MgO and BaF2 are designed to match the lattice of low-temperature α-GeTe phase and high-temperature β-GeTe phase, respectively. The structures of deposited GeTe films show lattice-match dependence rather than temperature dependence. Raman analysis indicates that the α-GeTe to β-GeTe ferroelectric phase transition accompanies an increase of local six-coordinated Ge atoms, which is analogous to the phase transition from amorphous to crystalline for memory application. - Highlights: • Lattice-match dependence in crystalline GeTe growth • The epitaxial relaxation induced by slight misfit strain • Crystalline GeTe is ferroelectric. • The local structure evolution during crystalline GeTe phase transition

  9. 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.)

  10. Self-corrected sensors based on atomic absorption spectroscopy for atom flux measurements in molecular beam epitaxy

    International Nuclear Information System (INIS)

    A high sensitivity atom flux sensor based on atomic absorption spectroscopy has been designed and implemented to control electron beam evaporators and effusion cells in a molecular beam epitaxy system. Using a high-resolution spectrometer and a two-dimensional charge coupled device detector in a double-beam configuration, we employ either a non-resonant line or a resonant line with low cross section from the same hollow cathode lamp as the reference for nearly perfect background correction and baseline drift removal. This setup also significantly shortens the warm-up time needed compared to other sensor technologies and drastically reduces the noise coming from the surrounding environment. In addition, the high-resolution spectrometer allows the most sensitive resonant line to be isolated and used to provide excellent signal-to-noise ratio

  11. Atomic Layer Epitaxy of h-BN(0001) Multilayers on Co(0001) and Molecular Beam Epitaxy Growth of Graphene on h-BN(0001)/Co(0001).

    Science.gov (United States)

    Driver, M Sky; Beatty, John D; Olanipekun, Opeyemi; Reid, Kimberly; Rath, Ashutosh; Voyles, Paul M; Kelber, Jeffry A

    2016-03-22

    The direct growth of hexagonal boron nitride (h-BN) by industrially scalable methods is of broad interest for spintronic and nanoelectronic device applications. Such applications often require atomically precise control of film thickness and azimuthal registry between layers and substrate. We report the formation, by atomic layer epitaxy (ALE), of multilayer h-BN(0001) films (up to 7 monolayers) on Co(0001). The ALE process employs BCl3/NH3 cycles at 600 K substrate temperature. X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) data show that this process yields an increase in h-BN average film thickness linearly proportional to the number of BCl3/NH3 cycles, with BN layers in azimuthal registry with each other and with the Co(0001) substrate. LEED diffraction spot profile data indicate an average BN domain size of at least 1900 Å. Optical microscopy data indicate the presence of some domains as large as ∼20 μm. Transmission electron microscopy (TEM) and ambient exposure studies demonstrate macroscopic and microscopic continuity of the h-BN film, with the h-BN film highly conformal to the Co substrate. Photoemission data show that the h-BN(0001) film is p-type, with band bending near the Co/h-BN interface. Growth of graphene by molecular beam epitaxy (MBE) is observed on the surface of multilayer h-BN(0001) at temperatures of 800 K. LEED data indicate azimuthal graphene alignment with the h-BN and Co(0001) lattices, with domain size similar to BN. The evidence of multilayer BN and graphene azimuthal alignment with the lattice of the Co(0001) substrate demonstrates that this procedure is suitable for scalable production of heterojunctions for spintronic applications. PMID:26940024

  12. Structural and Magnetic Phase Transitions in Manganese Arsenide Thin-Films Grown by Molecular Beam Epitaxy

    Science.gov (United States)

    Jaeckel, Felix Till

    Phase transitions play an important role in many fields of physics and engineering, and their study in bulk materials has a long tradition. Many of the experimental techniques involve measurements of thermodynamically extensive parameters. With the increasing technological importance of thin-film technology there is a pressing need to find new ways to study phase transitions at smaller length-scales, where the traditional methods are insufficient. In this regard, the phase transitions observed in thin-films of MnAs present interesting challenges. As a ferromagnetic material that can be grown epitaxially on a variety of technologically important substrates, MnAs is an interesting material for spintronics applications. In the bulk, the first order transition from the low temperature ferromagnetic alpha-phase to the beta-phase occurs at 313 K. The magnetic state of the beta-phase has remained controversial. A second order transition to the paramagnetic gamma-phase takes place at 398 K. In thin-films, the anisotropic strain imposed by the substrate leads to the interesting phenomenon of coexistence of alpha- and beta-phases in a regular array of stripes over an extended temperature range. In this dissertation these phase transitions are studied in films grown by molecular beam epitaxy on GaAs (001). The films are confirmed to be of high structural quality and almost purely in the A0 orientation. A diverse set of experimental techniques, germane to thin-film technology, is used to probe the properties of the film: Temperature-dependent X-ray diffraction and atomic-force microscopy (AFM), as well as magnetotransport give insights into the structural properties, while the anomalous Hall effect is used as a probe of magnetization during the phase transition. In addition, reflectance difference spectroscopy (RDS) is used as a sensitive probe of electronic structure. Inductively coupled plasma etching with BCl3 is demonstrated to be effective for patterning MnAs. We show

  13. Molecular beam epitaxy growth of indium nitride and indium gallium nitride materials for photovoltaic applications

    Science.gov (United States)

    Trybus, Elaissa

    The objective of the proposed research is to establish the technology for material growth by molecular beam epitaxy (MBE) and fabrication of indium gallium nitride/gallium nitride (InxGa1-xN/GaN) heterojunction solar cells. InxGa1-xN solar cells have the potential to span 90% of the solar spectrum, however there has been no success with high indium (In) incorporation and only limited success with low In incorporation InxGa1-xN. Therefore, this present work focuses on 15--30% In incorporation leading to a bandgap value of 2.3--2.8 eV. This work will exploit the revision of the indium nitride (InN) bandgap value of 0.68 eV, which expands the range of the optical emission of nitride-based devices from ultraviolet to near infrared regions, by developing transparent In xGa1-xN solar cells outside the visible spectrum. Photovoltaic devices with a bandgap greater than 2.0 eV are attractive because over half the available power in the solar spectrum is above the photon energy of 2.0 eV. The ability of InxGa1-xN materials to optimally span the solar spectrum offers a tantalizing solution for high-efficiency photovoltaics. This work presents results confirming the revised bandgap of InN grown on germanium (Ge) substrates and the effects of oxygen contamination on the bandgap. This research adds to the historical discussion of the bandgap value of InN. Using the metal modulated epitaxy (MME) technique in a new, ultra-clean refurbished MBE system, an innovative growth regime is established where In and Ga phase separation is diminished by increasing the growth rate for In xGa1-xN. The MME technique modulates the metal shutters with a fixed duty cycle while maintaining a constant nitrogen flux and proves effective for improving crystal quality and p-type doping. InxGa 1-xN/GaN heterojunction solar cells require p-type doping to create the p-n subcell collecting junction, which facilitates current collection through the electrostatic field created by spatially separated ionized

  14. Direct growth of hexagonal boron nitride/graphene heterostructures on cobalt foil substrates by plasma-assisted molecular beam epitaxy

    Science.gov (United States)

    Xu, Zhongguang; Khanaki, Alireza; Tian, Hao; Zheng, Renjing; Suja, Mohammad; Zheng, Jian-Guo; Liu, Jianlin

    2016-07-01

    Graphene/hexagonal boron nitride (G/h-BN) heterostructures have attracted a great deal of attention because of their exceptional properties and wide variety of potential applications in nanoelectronics. However, direct growth of large-area, high-quality, and stacked structures in a controllable and scalable way remains challenging. In this work, we demonstrate the synthesis of h-BN/graphene (h-BN/G) heterostructures on cobalt (Co) foil by sequential deposition of graphene and h-BN layers using plasma-assisted molecular beam epitaxy. It is found that the coverage of h-BN layers can be readily controlled on the epitaxial graphene by growth time. Large-area, uniform-quality, and multi-layer h-BN films on thin graphite layers were achieved. Based on an h-BN (5-6 nm)/G (26-27 nm) heterostructure, capacitor devices with Co(foil)/G/h-BN/Co(contact) configuration were fabricated to evaluate the dielectric properties of h-BN. The measured breakdown electric field showed a high value of ˜2.5-3.2 MV/cm. Both I-V and C-V characteristics indicate that the epitaxial h-BN film has good insulating characteristics.

  15. Characterization using ion beam analysis of In(Ga)As quantum dots grown by epitaxy on silicon

    International Nuclear Information System (INIS)

    The integration on silicon of direct band gap materials such as some semiconductors from the III-V group is of a rising interest for tomorrow's optoelectronic devices. Although silicon is the raw material for many microelectronic devices, it has a poor light emitting efficiency due to his indirect band gap. Among the III-V family, the In(Ga)As compounds present the advantage of a smaller band gap than silicon, which encourage the confinement of electron-hole pairs. However, the large lattice mismatch between silicon and In(Ga)As is a serious limitation for the epitaxial integration. This PhD work has been focused on the ion beam study of In(Ga)As quantum dots (QDs) grown by epitaxy on silicon and of the QD capping by silicon. Rutherford Backscattering Spectrometry (RBS) has been used to quantify composition of both QDs and cap layer. Exo-diffusion and excess issues of some elements have been pointed out. The epitaxial relation between QDs and substrate have been investigated by ion channelling (RBS-C). Medium Energy Ion Scattering (MEIS) has also been used to obtain high resolution profiles of composition, defects and strain for both the QD plane and the capping layer. Direct space mapping of both crystals has also been achieved by MEIS thanks to the blocking effect. (author)

  16. Evolution of self-assembled InAs/Gas(001) quantum dots grown by growth-interrupted molecular beam epitaxy

    OpenAIRE

    Balzarotti, A.

    2008-01-01

    Self-assembled InAs quantum dots (QDs) grown on GaAs(001) surface by molecular beam epitaxy under continuous and growth-interruption modes exhibit two families of QDs, quasi-3D (Q3D) and 3D QDs, whose volume density evolution is quantitatively described by a rate-equation kinetic model. The volume density of small Q3D QDs decreases exponentially with time during the interruption, while the single-dot mean volume of the large QDs increases by Ostwald ripening. The kinetics of growth involves c...

  17. The thickness-dependent dynamic magnetic property of Co2FeAl films grown by molecular beam epitaxy

    Science.gov (United States)

    Qiao, Shuang; Nie, Shuaihua; Zhao, Jianhua; Zhang, Xinhui

    2014-10-01

    Co2FeAl films with different thickness were prepared at different temperature by molecular beam epitaxy. Their dynamic magnetic property was studied by the time-resolved magneto-optical Kerr effect measurements. It is observed that the intrinsic damping factor of Co2FeAl for [100] orientation is not related to the film's thickness and magnetic anisotropy as well as temperature at high-field regime, but increases with structural disorder of Co2FeAl. The dominant contribution from the inhomogeneous magnetic anisotropy is revealed to be responsible for the observed extremely nonlinear and drastic field-dependent damping factors at low-field regime.

  18. Growth of high-quality SrTiO3 films using a hybrid molecular beam epitaxy

    OpenAIRE

    Jalan, Bharat; Engel-Herbert, Roman; Wright, Nicholas J.; Stemmer, Susanne

    2009-01-01

    A hybrid molecular beam epitaxy approach for atomic-layer controlled growth of high-quality SrTiO3 films with scalable growth rates was developed. The approach uses an effusion cell for Sr, a plasma source for oxygen, and a metal-organic source titanium tetra isopropoxide for Ti. SrTiO3 films were investigated as a function of cation flux ratio on 001 SrTiO3 and LaAlO30.3Sr2AlTaO60.7 LSAT substrates. Growth conditions for stoichiometric insulating films were identified. Persistent 180 oscilla...

  19. Molecular beam epitaxy growth of Si/SiGe bound-to-continuum quantum cascade structures for THz emission

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, M. [Department of Physics, Chemistry and Biology, Linkoeping University, SE-581 83 Linkoeping (Sweden)], E-mail: Ming.Zhao@imec.be; Karim, A.; Hansson, G.V. [Department of Physics, Chemistry and Biology, Linkoeping University, SE-581 83 Linkoeping (Sweden); Ni, W.-X. [Department of Physics, Chemistry and Biology, Linkoeping University, SE-581 83 Linkoeping (Sweden); National Nano Device Laboratories, Hsinchu 30078, Taiwan, ROC (China); Townsend, P.; Lynch, S.A.; Paul, D.J. [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 0HE (United Kingdom)

    2008-11-03

    A Si/SiGe bound-to-continuum quantum cascade design for THz emission was grown using solid-source molecular beam epitaxy on Si{sub 0.8}Ge{sub 0.2} virtual substrates. The growth parameters were carefully studied and several samples with different boron doping concentrations were grown at optimized conditions. Extensive material characterizations revealed a high crystalline quality of the grown structures with an excellent growth control. Layer undulations resulting from a nonuniform strain field, introduced by high doping concentration, were observed. The device characterizations suggested that a modification on the design was needed in order to enhance the THz emission.

  20. Molecular beam epitaxy growth of MgZnSSe/ZnSSe Bragg mirrors controlled by in situ optical reflectometry.

    OpenAIRE

    Hegarty, John

    1995-01-01

    PUBLISHED In situ optical reflectometry at the wavelength of 488 nm was employed to control the growth of MgZnSSe/ZnSSe Bragg mirror stacks for the blue-green spectral region. 10- and 20-period layer structures of MgZnSSe/ZnSSe were grown on GaAs ~100! epilayers by molecular beam epitaxy. A room-temperature peak reflectance of 86% was obtained for the 20-period structure at the central wavelength of 474 nm. The results show that, in general, in situ optical monitoring of growth...

  1. Effect of source chemistry and growth parameters on AlGaAs grown by metalorganic molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Abernathy, C.R.; Pearton, S.J.; Baiocchi, F.A.; Ambrose, T.; Jordan, A.S. (AT and T Bell Labs., Murray Hill, NJ (USA)); Bohling, D.A.; Muhr, G.T. (Air Products and Chemicals, Inc., Allentown, PA (USA))

    1991-03-01

    We have investigated the effect of V/III ratio and substrate temperature on the growth rate, Al composition, crystallinity, and impurity concentration of AlGaAs grown by metalorganic molecular beam epitaxy (MOMBE). The effect of these growth parameters on the deposition rates of both GaAs and AlAs has also been determined. By comparing films grown from various combinations of triethylgallium (TEGa), trimethylgallium (TMGa), triethylaluminium (TEA), and trimethylamine alane (TMAAl), we have been able to further identify the surface reactions which are most important in determining film composition and quality. (orig.).

  2. Transmission electron microscopy study of CdTe(111) grown on GaAs(100) by molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Reno, J.L.; Carr, M.J.; Gourley, P.L. (Sandia National Laboratory, Albuquerque, New Mexico 87185 (USA))

    1990-05-01

    We have used transmission electron microscopy to investigate CdTe(111) grown on GaAs(100) by molecular-beam epitaxy. The loop structure previously observed by photoluminescence microscopy has been identified as the boundary between twinned microcrystallites that extend from the CdTe/GaAs interface to the CdTe surface. When viewed along the growth axis, these boundaries between the columnar twins appear as loops and segments. Surface roughness of the GaAs substrate contributes to the initial growth of twinned material. This leads to competitive growth between the twins and the creation of the observed columnar twins.

  3. Stimulated emission from a CdTe/HgCdTe separate confinement heterostructure grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Mahavadi, K.K.; Bleuse, J.; Sivananthan, S.; Faurie, J.P. (Microphysics Laboratory, Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60680 (USA))

    1990-05-21

    We present the results of low-temperature photoluminescence and stimulated emission experiments performed on a CdTe/Hg{sub 0.45}Cd{sub 0.55}Te/Hg{sub 0.67}Cd{sub 0.33}Te multiquantum well separate confinement heterostructure grown by molecular beam epitaxy. The photoluminescence results suggest that because of the growth conditions, there is a strong interdiffusion in the multiquantum well region. Pulsed stimulated emission was observed from this structure up to 77 K.

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

    International Nuclear Information System (INIS)

    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.

  5. Transition between wurtzite and zinc-blende GaN: An effect of deposition condition of molecular-beam epitaxy

    OpenAIRE

    Xie, MH; Wu, HS; Shi, BM; Wang, N.; Tong, SY

    2006-01-01

    GaN exists in both wurtzite and zinc-blende phases and the growths of the two on its (0001) or (111) surfaces are achieved by choosing proper deposition conditions of molecular-beam epitaxy (MBE). At low substrate temperatures but high gallium fluxes, metastable zinc-blende GaN films are obtained, whereas at high temperatures and/or using high nitrogen fluxes, equilibrium wurtzite phase GaN epilayers resulted. This dependence of crystal structure on substrate temperature and source flux is no...

  6. InN nanorods prepared with CrN nanoislands by plasma-assisted molecular beam epitaxy

    OpenAIRE

    Young Sheng-Joue; Wu Ya-Ling; Chen Yue-Zhang; Hung Hung; Wang Shih-Ming; Chen Kuan-Jen; Liu Kuang-Wei; Chang Shoou-Jinn; Hsueh Tao-Hung; Mai Yu-Chun

    2011-01-01

    Abstract The authors report the influence of CrN nanoisland inserted on growth of baseball-bat InN nanorods by plasma-assisted molecular beam epitaxy under In-rich conditions. By inserting CrN nanoislands between AlN nucleation layer and the Si (111) substrate, it was found that we could reduce strain form Si by inserting CrN nanoisland, FWHM of the x-ray rocking curve measured from InN nanorods from 3,299 reduced to 2,115 arcsec. It is due to the larger strain from lattice miss-match of the ...

  7. (GaMn)As: GaAs-based III?V diluted magnetic semiconductors grown by molecular beam epitaxy

    Science.gov (United States)

    Hayashi, T.; Tanaka, M.; Nishinaga, T.; Shimada, H.; Tsuchiya, H.; Otuka, Y.

    1997-05-01

    We have grown novel III-V diluted magnetic semiconductors, (Ga 1 - xMn x)As, on GaAs substrates by low-temperature molecular beam epitaxy using strong nonequilibrium growth conditions. When the Mn concentration x is relatively low (≲0.08), homogeneous alloy semiconductors, GaMnAs, are grown with zincblende structure and slightly larger lattice constants than that of GaAs, whereas inhomogeneous structures with zincblende GaMnAs (or GaAs) plus hexagonal MnAs are formed when x is relatively high. Magnetization measurements indicate that the homogeneous GaMnAs films have ferromagnetic ordering at low temperature.

  8. Thickness control of molecular beam epitaxy grown layers at the 0.01–0.1 monolayer level

    International Nuclear Information System (INIS)

    Electron tunnelling through semiconductor tunnel barriers is exponentially sensitive to the thickness of the barrier layer, and in the most common system, the AlAs tunnel barrier in GaAs, a one monolayer variation in thickness results in a 300% variation in the tunnelling current for a fixed bias voltage. We use this degree of sensitivity to demonstrate that the level of control at 0.06 monolayer can be achieved in the growth by molecular beam epitaxy, and the geometrical variation of layer thickness across a wafer at the 0.01 monolayer level can be detected. (paper)

  9. Effect of source chemistry and growth parameters on AlGaAs grown by metalorganic molecular beam epitaxy

    Science.gov (United States)

    Abernathy, C. R.; Pearton, S. J.; Baiocchi, F. A.; Ambrose, T.; Jordan, A. S.; Bohling, D. A.; Muhr, G. T.

    1991-03-01

    We have investigated the effect of V/III ratio and substrate temperature on the growth rate, Al composition, crystallinity, and impurity concentration of AlGaAs grown by metalorganic beam epitaxy (MOMBE). The effect of these growth parameters on the deposition rates of both GaAs and AlAs has also been determined. By comparing films grown from various combinations of triethylgallium (TEGa), trimethylgallium (TMGa), triethylaluminum (TEAl), and trimethylamine alane (TMAA1), we have been able to further identity the surface reactions which are most important in determining film composition and quality.

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

    International Nuclear Information System (INIS)

    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.

  11. Enhanced growth of highly lattice-mismatched CdSe on GaAs substrates by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jyh-Shyang, E-mail: jswang@cycu.edu.tw [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Center for Nano-Technology, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Tsai, Yu-Hsuan; Wang, Hsiao-Hua; Ke, Han-Xiang; Tong, Shih-Chang [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Yang, Chu-Shou [Graduate institute of Electro-Optical Engineering, Tatung University, Taipei 10452, Taiwan (China); Wu, Chih-Hung [Institute of Nuclear Energy Research, Longtan 32546, Taiwan (China); Shen, Ji-Lin [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Center for Nano-Technology, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China)

    2013-04-01

    This work demonstrates the improvement of the molecular beam epitaxial growth of zinc-blende CdSe on (0 0 1) GaAs substrate with a large lattice mismatch by introducing a small amount of Te atoms. Exposing the growing surface to Te atoms changes the reflection high-energy electron diffraction pattern from spotty to streaky together with (2 × 1) surface reconstruction, and greatly reduces the full width at half maximum of the X-ray rocking curve and increases the integral intensity of room-temperature photoluminescence by a factor of about nine.

  12. Growth of GaSb1-xBix by molecular beam epitaxy

    DEFF Research Database (Denmark)

    Song, Yuxin; Wang, Shumin; Roy, Ivy Saha;

    2012-01-01

    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......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...

  13. Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

    Science.gov (United States)

    Ahmed, Adam S.; Wen, Hua; Ohta, Taisuke; Pinchuk, Igor V.; Zhu, Tiancong; Beechem, Thomas; Kawakami, Roland K.

    2016-08-01

    We report the successful growth of high-quality SrO films on highly-ordered pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy. The SrO layers have (001) orientation as confirmed by X-ray diffraction (XRD) while atomic force microscopy measurements show continuous pinhole-free films having rms surface roughness of deposition show a strong dependence between the Dirac point and Sr oxidation. Subsequently, the SrO is leveraged as a buffer layer for more complex oxide integration via the demonstration of (001) oriented SrTiO3 grown atop a SrO/HOPG stack.

  14. Room temperature weak ferromagnetism in Sn1-xMnxSe2 2D films grown by molecular beam epitaxy

    Science.gov (United States)

    Dong, Sining; Liu, Xinyu; Li, Xiang; Kanzyuba, Vasily; Yoo, Taehee; Rouvimov, Sergei; Vishwanath, Suresh; Xing, Huili G.; Jena, Debdeep; Dobrowolska, Margaret; Furdyna, Jacek K.

    2016-03-01

    We discuss growth and magnetic properties of high-quality two dimensional (2D) Sn1-xMnxSe2 films. Thin films of this 2D ternary alloy with a wide range of Mn concentrations were successfully grown by molecular beam epitaxy. Mn concentrations up to x ≈ 0.60 were achieved without destroying the crystal structure of the parent SnSe2 2D system. Most important, the specimens show clear weak ferromagnetic behavior above room temperature, which should be of interest for 2D spintronic applications.

  15. 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

  16. Growing high-quality ternary CdMnTe epilayers by molecular beam epitaxy on Si substrates and its mechanism

    International Nuclear Information System (INIS)

    Cd(Mn,Zn)Te-based ternary compound semiconductors with wide band-gaps are important in the detection of radiation and photovoltaic applications. This study characterizes Cd1-xMnxTe epilayers on Si substrates with various Mn compositions grown by molecular beam epitaxy. The surface smoothness, crystallinity and optical quality all are significantly improved with increasing Mn content. The Cd0.61Mn0.39Te epilayer with a thickness of only about 500 nm yields a full width at half maximum of the X-ray rocking curve of 165 arcsec. Photoluminescence spectra at 10 K show that the intensity of defect-related emissions is much lower than that of binary CdTe epilayers, reaching zero from the samples with high Mn content, while the integral intensity of the exciton-related emissions is increased by more than two orders of magnitude. Raman scattering spectra reveal that the intensity of the Te–Te related defect vibration modes falls significantly as the Mn content increase, even disappearing altogether in the samples with high Mn content. This work proposes that incorporating Mn atoms during epitaxial growth can promote the decomposition of Te2 sources, owing to the high sticking coefficient of Mn and the high cohesive energy of the Mn–Te bond, and then reduce the number of Te–Te related stacking fault defects, yielding high-quality CdMnTe epilayers. Our results herein demonstrate that the CdMnTe ternary epilayers are much more promising in terms of material quality than the CdZnTe ternary epilayers. - Highlights: • High-quality ternary CdMnTe were grown on Si substrates by molecular beam epitaxy. • The material qualities were significantly improved with increasing Mn content. • The Te–Te related defects were greatly reduced with increasing Mn content. • We report an enhanced growth of CdTe-based epilayers by the incorporation of Mn atoms

  17. Large array of single, site-controlled InAs quantum dots fabricated by UV-nanoimprint lithography and molecular beam epitaxy

    International Nuclear Information System (INIS)

    We present the growth of single, site-controlled InAs quantum dots on GaAs templates using UV-nanoimprint lithography and molecular beam epitaxy. A large quantum dot array with a period of 1.5 µm was achieved. Single quantum dots were studied by steady-state and time-resolved micro-photoluminescence experiments. We obtained single exciton emission with a linewidth of 45 µeV. In time-resolved experiments, we observed decay times of about 670 ps. Our results underline the potential of nanoimprint lithography and molecular beam epitaxy to create large-scale, single quantum dot arrays. (paper)

  18. Modelling of electron beam induced nanowire attraction

    Science.gov (United States)

    Bitzer, Lucas A.; Speich, Claudia; Schäfer, David; Erni, Daniel; Prost, Werner; Tegude, Franz J.; Benson, Niels; Schmechel, Roland

    2016-04-01

    Scanning electron microscope (SEM) induced nanowire (NW) attraction or bundling is a well known effect, which is mainly ascribed to structural or material dependent properties. However, there have also been recent reports of electron beam induced nanowire bending by SEM imaging, which is not fully explained by the current models, especially when considering the electro-dynamic interaction between NWs. In this article, we contribute to the understanding of this phenomenon, by introducing an electro-dynamic model based on capacitor and Lorentz force interaction, where the active NW bending is stimulated by an electromagnetic force between individual wires. The model includes geometrical, electrical, and mechanical NW parameters, as well as the influence of the electron beam source parameters and is validated using in-situ observations of electron beam induced GaAs nanowire (NW) bending by SEM imaging.

  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

    International Nuclear Information System (INIS)

    An epitaxial L10 FePt thin film grown from an [Fe(10 Å)/Pt(10 Å)]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 L10 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. Patterned growth of InGaN/GaN quantum wells on freestanding GaN grating by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Wang Yongjin

    2011-01-01

    Full Text Available Abstract We report here the epitaxial growth of InGaN/GaN quantum wells on freestanding GaN gratings by molecular beam epitaxy (MBE. Various GaN gratings are defined by electron beam lithography and realized on GaN-on-silicon substrate by fast atom beam etching. Silicon substrate beneath GaN grating region is removed from the backside to form freestanding GaN gratings, and the patterned growth is subsequently performed on the prepared GaN template by MBE. The selective growth takes place with the assistance of nanoscale GaN gratings and depends on the grating period P and the grating width W. Importantly, coalescences between two side facets are realized to generate epitaxial gratings with triangular section. Thin epitaxial gratings produce the promising photoluminescence performance. This work provides a feasible way for further GaN-based integrated optics devices by a combination of GaN micromachining and epitaxial growth on a GaN-on-silicon substrate. PACS 81.05.Ea; 81.65.Cf; 81.15.Hi.

  1. Magnetic properties of Fe films and Fe/Si/Fe trilayers grown on GaAs(001) and MgO(001) by ion-beam sputter epitaxy

    International Nuclear Information System (INIS)

    We grow monocrystalline Fe(001) films and Fe/Si/Fe(001) trilayers by ion-beam sputter epitaxy on GaAs(001) and MgO(001) substrates. Ion-beam sputtering parameters such as substrate presputtering time, substrate temperature, beam voltage, and target angle are optimized for 10-nm-thick Fe(001) films with respect to epitaxial growth and magnetic properties. In situ low-energy electron diffraction patterns confirm the epitaxial and monocrystalline nature of the sputtered films, surprisingly even on untreated and thus oxidized substrates. The magneto-optical Kerr effect and ferromagnetic resonance are employed to investigate the magnetic properties, and the structural properties are characterized by atomic force microscopy and x-ray reflectivity measurements. Using the optimized set of parameters that yields the best magnetic properties for single Fe films on GaAs, we deposit epitaxial Fe/Si/Fe(001) structures and observe antiferromagnetic interlayer exchange coupling for epitaxially sputtered Fe/Si/Fe(001) trilayers on GaAs(001). The total coupling strength reaches values of up to 2 mJ/m2 at a Si thickness of 15 A

  2. 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)

  3. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    International Nuclear Information System (INIS)

    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

  4. 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

  5. Vacancy-type defects in Si-doped InN grown by plasma-assisted molecular-beam epitaxy probed using monoenergetic positron beams

    International Nuclear Information System (INIS)

    High-quality InN layers grown on sapphire substrates by plasma-assisted molecular-beam epitaxy were characterized using monoenergetic positron beams. The carrier concentrations of the films were controlled by Si doping (2.1x1018 to 1.4x1019 cm-3), and the highest obtained Hall mobility was 1300 cm2 V-1 s-1. The Doppler broadening spectra of the annihilation radiation and the lifetime spectra of positrons were measured as a function of the incident positron energy for undoped and Si-doped InN films. The line-shape parameter S increased with increasing carrier concentration, suggesting the introduction of vacancy-type defects by a Fermi-level effect. The major defect species were varied with carrier concentration, and its species were identified as In vacancies (VIn) or their related defects

  6. Beam induced RF cavity transient voltage

    International Nuclear Information System (INIS)

    We calculate the transient voltage induced in a radio frequency (RF) cavity by the injection of a relativistic bunched beam into a circular accelerator. A simplified model of the beam induced voltage, using a single tone current signal, is generated and compared with the voltage induced by a more realistic model of a point-like bunched beam. The high Q limit of the bunched beam model is shown to be related simply to the simplified model. Both models are shown to induce voltages at the resonant frequency ωr of the cavity and at an integer multiple of the bunch revolution frequency (i.e. the accelerating frequency for powered cavity operation) hω0. The presence of two nearby frequencies in the cavity leads to a modulation of the carrier wave exp(jhω0t). A special emphasis is placed in this paper on studying the modulation function. These models prove useful for computing the transient voltage induced in superconducting RF cavities, which was the motivation behind this research. The modulation of the transient cavity voltage discussed in this paper is the physical basis of the recently observed and explained new kind of longitudinal rigid dipole mode which differs from the conventional Robinson mode

  7. Simulation of beam-induced plasma for the mitigation of beam-beam effects

    Energy Technology Data Exchange (ETDEWEB)

    Ma, J.; Wang, G.; Samulyak, R.; Yu, K.; Litvinenko, V.

    2015-05-03

    One of the main challenges in the increase of luminosity of circular colliders is the control of the beam-beam effect. In the process of exploring beam-beam mitigation methods using plasma, we evaluated the possibility of plasma generation via ionization of neutral gas by proton beams, and performed highly resolved simulations of the beam-plasma interaction using SPACE, a 3D electromagnetic particle-in-cell code. The process of plasma generation is modelled using experimentally measured cross-section coefficients and a plasma recombination model that takes into account the presence of neutral gas and beam-induced electromagnetic fields. Numerically simulated plasma oscillations are consistent with theoretical analysis. In the beam-plasma interaction process, high-density neutral gas reduces the mean free path of plasma electrons and their acceleration. A numerical model for the drift speed as a limit of plasma electron velocity was developed. Simulations demonstrate a significant reduction of the beam electric field in the presence of plasma. Preliminary simulations using fully-ionized plasma have also been performed and compared with the case of beam-induced plasma.

  8. 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)

  9. Gas source molecular beam epitaxy of scandium nitride on silicon carbide and gallium nitride surfaces

    International Nuclear Information System (INIS)

    Scandium nitride (ScN) is a group IIIB transition metal nitride semiconductor with numerous potential applications in electronic and optoelectronic devices due to close lattice matching with gallium nitride (GaN). However, prior investigations of ScN have focused primarily on heteroepitaxial growth on substrates with a high lattice mismatch of 7%–20%. In this study, the authors have investigated ammonia (NH3) gas source molecular beam epitaxy (NH3-GSMBE) of ScN on more closely lattice matched silicon carbide (SiC) and GaN surfaces (3-GSMBE conditions of 10−5–10−4 Torr NH3 and 800–1050 °C where selected for initial investigation. In-situ x-ray photoelectron spectroscopy (XPS) and ex-situ Rutherford backscattering measurements showed all ScN films grown using these conditions were stoichiometric. For ScN growth on 3C-SiC (111)-(√3 × √3)R30° carbon rich surfaces, the observed attenuation of the XPS Si 2p and C 1s substrate core levels with increasing ScN thickness indicated growth initiated in a layer-by-layer fashion. This was consistent with scanning electron microscopy (SEM) images of 100–200 nm thick films that revealed featureless surfaces. In contrast, ScN films grown on 3C-SiC (111)-(3 × 3) and 3C-SiC (100)-(3 × 2) silicon rich surfaces were found to exhibit extremely rough surfaces in SEM. ScN films grown on both 3C-SiC (111)-(√3 × √3)R30° and 2H-GaN (0001)-(1 × 1) epilayer surfaces exhibited hexagonal (1 × 1) low energy electron diffraction patterns indicative of (111) oriented ScN. X-ray diffraction ω-2θ rocking curve scans for these same films showed a large full width half maximum of 0.29° (1047 arc sec) consistent with transmission electron microscopy images that revealed the films to be poly-crystalline with columnar grains oriented at ≈15° to the [0001] direction of the 6H-SiC (0001) substrate. In-situ reflection electron energy loss spectroscopy measurements determined the band-gap for

  10. Gas source molecular beam epitaxy of scandium nitride on silicon carbide and gallium nitride surfaces

    Energy Technology Data Exchange (ETDEWEB)

    King, Sean W., E-mail: sean.king@intel.com; Davis, Robert F. [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Nemanich, Robert J. [Department of Physics, North Carolina State University, Raleigh, North Carolina 27695 (United States)

    2014-11-01

    Scandium nitride (ScN) is a group IIIB transition metal nitride semiconductor with numerous potential applications in electronic and optoelectronic devices due to close lattice matching with gallium nitride (GaN). However, prior investigations of ScN have focused primarily on heteroepitaxial growth on substrates with a high lattice mismatch of 7%–20%. In this study, the authors have investigated ammonia (NH{sub 3}) gas source molecular beam epitaxy (NH{sub 3}-GSMBE) of ScN on more closely lattice matched silicon carbide (SiC) and GaN surfaces (<3% mismatch). Based on a thermodynamic analysis of the ScN phase stability window, NH{sub 3}-GSMBE conditions of 10{sup −5}–10{sup −4} Torr NH{sub 3} and 800–1050 °C where selected for initial investigation. In-situ x-ray photoelectron spectroscopy (XPS) and ex-situ Rutherford backscattering measurements showed all ScN films grown using these conditions were stoichiometric. For ScN growth on 3C-SiC (111)-(√3 × √3)R30° carbon rich surfaces, the observed attenuation of the XPS Si 2p and C 1s substrate core levels with increasing ScN thickness indicated growth initiated in a layer-by-layer fashion. This was consistent with scanning electron microscopy (SEM) images of 100–200 nm thick films that revealed featureless surfaces. In contrast, ScN films grown on 3C-SiC (111)-(3 × 3) and 3C-SiC (100)-(3 × 2) silicon rich surfaces were found to exhibit extremely rough surfaces in SEM. ScN films grown on both 3C-SiC (111)-(√3 × √3)R30° and 2H-GaN (0001)-(1 × 1) epilayer surfaces exhibited hexagonal (1 × 1) low energy electron diffraction patterns indicative of (111) oriented ScN. X-ray diffraction ω-2θ rocking curve scans for these same films showed a large full width half maximum of 0.29° (1047 arc sec) consistent with transmission electron microscopy images that revealed the films to be poly-crystalline with columnar grains oriented at ≈15° to the [0001] direction of the

  11. Beam Induced Pressure Rise at RHIC

    CERN Document Server

    Zhang, S Y; Bai, Mei; Blaskiewicz, Michael; Cameron, Peter; Drees, Angelika; Fischer, Wolfram; Gullotta, Justin; He, Ping; Hseuh Hsiao Chaun; Huang, Haixin; Iriso, Ubaldo; Lee, Roger C; Litvinenko, Vladimir N; MacKay, William W; Nicoletti, Tony; Oerter, Brian; Peggs, Steve; Pilat, Fulvia Caterina; Ptitsyn, Vadim; Roser, Thomas; Satogata, Todd; Smart, Loralie; Snydstrup, Louis; Thieberger, Peter; Trbojevic, Dejan; Wang, Lanfa; Wei, Jie; Zeno, Keith

    2005-01-01

    Beam induced pressure rise in RHIC warm sections is currently one of the machine intensity and luminosity limits. This pressure rise is mainly due to electron cloud effects. The RHIC warm section electron cloud is associated with longer bunch spacings compared with other machines, and is distributed non-uniformly around the ring. In addition to the countermeasures for normal electron cloud, such as the NEG coated pipe, solenoids, beam scrubbing, bunch gaps, and larger bunch spacing, other studies and beam tests toward the understanding and counteracting RHIC warm electron cloud are of interest. These include the ion desorption studies and the test of anti-grazing ridges. For high bunch intensities and the shortest bunch spacings, pressure rises at certain locations in the cryogenic region have been observed during the past two runs. Beam studies are planned for the current 2005 run and the results will be reported.

  12. Structural and ferroelectric properties of BaTiO 3/YBa 2Cu 3O 7 heterostructures prepared by laser molecular beam epitaxy

    Science.gov (United States)

    Wang, H. S.; Liu, Y. W.; Ma, K.; Peng, Z. Q.; Cui, D. F.; Lu, H. B.; Zhou, Y. L.; Chen, Z. H.; Li, L.; Yang, G. Z.

    1997-08-01

    Heteroepitaxial BaTiO 3(BTO)/YBa 2Cu 3O 7(YBCO) thin films were grown on (100) SrTiO 3(STO) substrates by ozone assistant laser molecular beam epitaxy (L sbnd MBE). The results show that by using this technique, high quality ferroelectric/superconductor heterostructures with high crystalline quality and desirable device performance can be obtained.

  13. Critical thickness and strain relaxation in molecular beam epitaxy-grown SrTiO{sub 3} films

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Tianqi; Ganguly, Koustav; Marshall, Patrick; Xu, Peng; Jalan, Bharat [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

    2013-11-18

    We report on the study of the critical thickness and the strain relaxation in epitaxial SrTiO{sub 3} film grown on (La{sub 0.3}Sr{sub 0.7})(Al{sub 0.65}Ta{sub 0.35})O{sub 3} (001) (LSAT) substrate using the hybrid molecular beam epitaxy approach. No change in the film's lattice parameter (both the in-plane and the out-of-plane) was observed up to a film thickness of 180 nm, which is in sharp contrast to the theoretical critical thickness of ∼12 nm calculated using the equilibrium theory of strain relaxation. For film thicknesses greater than 180 nm, the out-of-plane lattice parameter was found to decrease hyperbolically in an excellent agreement with the relaxation via forming misfit dislocations. Possible mechanisms are discussed by which the elastic strain energy can be accommodated prior to forming misfit dislocations leading to such anomalously large critical thickness.

  14. Fabrication of GeSn-multiple quantum wells by overgrowth of Sn on Ge by using molecular beam epitaxy

    International Nuclear Information System (INIS)

    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

  15. Epitaxial growth and exchange biasing of PdMn/Fe bilayers grown by ion-beam sputtering

    International Nuclear Information System (INIS)

    Epitaxial PdMn/Fe bilayer structures, in both a-axis PdMn(100)/Fe(001)/MgO(001) and c-axis PdMn(001)/Fe(001)/MgO(001) orientations, were grown by ion-beam sputtering. The a-axis samples were grown at low temperatures (T300 degreeC). Vibrating sample magnetometry measurements show that the as-grown a-axis samples do not have a measurable exchange bias while c-axis samples have an exchange bias field He∼33Oe. However, annealing at 230 degreeC for 40 min results in a measurable exchange (He∼10Oe) for a-axis samples due to chemical ordering. The possible cause for the difference of He in a-axis and c-axis orientations is also discussed. In addition to the normal structure, inverted structures were obtained epitaxially. The exchange biasing for Fe(001)/PdMn(001)/MgO(001) is as big as 68 Oe. [copyright] 2001 American Institute of Physics

  16. Molecular beam epitaxial growth and characterization of GaSb layers on GaAs (0 0 1) substrates

    Science.gov (United States)

    Li, Yanbo; Zhang, Yang; Zhang, Yuwei; Wang, Baoqiang; Zhu, Zhanping; Zeng, Yiping

    2012-06-01

    We report on the growth of GaSb layers on GaAs (0 0 1) substrates by molecular beam epitaxy (MBE). We investigate the influence of the GaAs substrate surface treatment, growth temperature, and V/III flux ratios on the crystal quality and the surface morphology of GaSb epilayers. Comparing to Ga-rich GaAs surface preparation, the Sb-rich GaAs surface preparation can promote the growth of higher-quality GaSb material. It is found that the crystal quality, electrical properties, and surface morphology of the GaSb epilayers are highly dependent on the growth temperature, and Sb/Ga flux ratios. Under the optimized growth conditions, we demonstrate the epitaxial growth of high quality GaSb layers on GaAs substrates. The p-type nature of the unintentionally doped GaSb is studied and from the growth conditions dependence of the hole concentrations of the GaSb, we deduce that the main native acceptor in the GaSb is the Ga antisite (GaSb) defect.

  17. 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.

  18. Influence of complex impact of the picosecond electron beam and volume discharge in atmospheric-pressure air on the electronic properties of MCT epitaxial films surface

    Science.gov (United States)

    Grigoryev, Denis V.; Novikov, Vadim A.; Bezrodnyy, Dmitriy A.; Tarasenko, Viktor F.; Shulepov, Michail A.; Dvoretskii, Sergei A.

    2015-12-01

    In the present report we studied the distribution of surface potential of the HgCdTe epitaxial films grown by molecular beam epitaxy after the impact of picosecond electron beam and volume discharge in atmospheric-pressure air. The surface potential distribution was studied by the Kelvin Force Probe Microscopy. The experimental data obtained for the variation of the contact potential difference (ΔCPD) between the V-defect and the main matrix of the epitaxial film. The investigation of the origin epitaxial films show that variation of the spatial distribution of surface potential in the V-defect region can be related to the variation of the material composition. The experimental data obtained for the irradiated samples show that the mean value of ΔCPD for the original surface differs from the one for the irradiated surface for 55 eV. At the same time the mean value of ΔCPD changes its sign indicating that the original surface of the epitaxial HgCdTe film predominantly contains the grains with increased cadmium content while after the irradiation the grains possess an increased content of mercury. Therefore, during the irradiation process a decrease of the mercury content in the near-surface region of the semiconductor takes place resulting in the alteration of the electrophysical properties in the films near-surface region.

  19. Epitaxy of semiconductor-superconductor nanowires

    DEFF Research Database (Denmark)

    Krogstrup, P.; Ziino, N.L.B.; Chang, W.;

    2015-01-01

    Controlling the properties of semiconductor/metal interfaces is a powerful method for designing functionality and improving the performance of electrical devices. Recently semiconductor/superconductor hybrids have appeared as an important example where the atomic scale uniformity of the interface...... plays a key role in determining the quality of the induced superconducting gap. Here we present epitaxial growth of semiconductor-metal core-shell nanowires by molecular beam epitaxy, a method that provides a conceptually new route to controlled electrical contacting of nanostructures and the design of...... devices for specialized applications such as topological and gate-controlled superconducting electronics. Our materials of choice, InAs/Al grown with epitaxially matched single-plane interfaces, and alternative semiconductor/metal combinations allowing epitaxial interface matching in nanowires are...

  20. Induced focusing and conversion of a Gaussian beam into an elliptic Gaussian beam

    Indian Academy of Sciences (India)

    Manoj Mishra; Swapan Konar

    2005-09-01

    We have presented an investigation of the induced focusing in Kerr media of two laser beams, the pump beam and the probe beam, which could be either Gaussian or elliptic Gaussian or a combination of the two. We have used variational formalism to derive relevant beam-width equations. Among several important findings, the finding that a very week probe beam can be guided and focused when power of both beams are well below their individual threshold for self-focusing, is a noteworthy one. It has been found that induced focusing is not possible for laser beams of any wavelength and beam radius. In case both beams are elliptic Gaussian, we have shown that when power of both beams is above a certain threshold value then the effective radius of both beams collapses and collapse distance depends on power. Moreover, it has been found that induced focusing can be employed to convert a circular Gaussian beam into an elliptic Gaussian beam.

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

    International Nuclear Information System (INIS)

    We report on properties of high quality ∼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.

  2. High Growth Rate Metal-Organic Molecular Beam Epitaxy for the Fabrication of GaAs Space Solar Cells

    Science.gov (United States)

    Freundlich, A.; Newman, F.; Monier, C.; Street, S.; Dargan, P.; Levy, M.

    2005-01-01

    In this work it is shown that high quality GaAs photovoltaic devices can be produced by Molecular Beam Epitaxy (MBE) with growth rates comparable to metal-organic chemical vapor deposition (MOCVD) through the subsitution of group III solid sources by metal-organic compounds. The influence the III/V flux-ratio and growth temperatures in maintaining a two dimensional layer by layer growth mode and achieving high growth rates with low residual background impurities is investigated. Finally subsequent to the study of the optimization of n- and p doping of such high growth rate epilayers, results from a preliminary attempt in the fabrication of GaAs photovoltaic devices such as tunnel diodes and solar cells using the proposed high growth rate approach are reported.

  3. Optical Properties of InGaAs/ GaAs Multi Quantum Wells Structure Grown By Molecular Beam Epitaxy

    International Nuclear Information System (INIS)

    Inclusive analysis on the optical characteristics of InGaAs/ GaAs QW structure for 980 nm semiconductor laser operation is presented from experimental and theoretical point of view. The InGaAs/ GaAs quantum well structure is grown by molecular beam epitaxy at different indium composition and quantum well thickness for optical characteristic comparison. Photoluminescence spectra from the measurement show that the spectrum is in good agreement with the simulation results. Detail simulation on the material gain for the InGaAs/ GaAs quantum well as a function of carrier densities and operating temperature is also performed in order to optimize the semiconductor laser design for device fabrication. (author)

  4. Electrical performance of phase change memory cells with Ge3Sb2Te6 deposited by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Here, we report on the electrical characterization of phase change memory cells containing a Ge3Sb2Te6 (GST) alloy grown in its crystalline form by Molecular Beam Epitaxy (MBE). It is found that the high temperature growth on the amorphous substrate results in a polycrystalline film exhibiting a rough surface with a grain size of approximately 80–150 nm. A detailed electrical characterization has been performed, including I-V characteristic curves, programming curves, set operation performance, crystallization activation at low temperature, and resistance drift, in order to determine the material related parameters. The results indicate very good alignment of the electrical parameters with the current state-of-the-art GST, deposited by physical vapor deposition. Such alignment enables a possible employment of the MBE deposition technique for chalcogenide materials in the phase change memory technology, thus leading to future studies of as-deposited crystalline chalcogenides as integrated in electrical vehicles

  5. 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.

  6. Contactless electroreflectance studies of surface potential barrier for N- and Ga-face epilayers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kudrawiec, R.; Janicki, L.; Gladysiewicz, M.; Misiewicz, J. [Institute of Physics, Wroclaw University of Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław (Poland); Cywinski, G.; Boćkowski, M.; Muzioł, G. [Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw (Poland); Chèze, C. [TopGaN Sp. z o.o., Sokołowska 29/37, 01-142 Warsaw (Poland); Sawicka, M.; Skierbiszewski, C. [Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw (Poland); TopGaN Sp. z o.o., Sokołowska 29/37, 01-142 Warsaw (Poland)

    2013-07-29

    Two series of N- and Ga-face GaN Van Hoof structures were grown by plasma-assisted molecular beam epitaxy to study the surface potential barrier by contactless electroreflectance (CER). A clear CER resonance followed by strong Franz-Keldysh oscillation of period varying with the thickness of undoped GaN layer was observed for these structures. This period was much shorter for N-polar structures that means smaller surface potential barrier in these structures than in Ga-polar structures. From the analysis of built-in electric field it was determined that the Fermi-level is located 0.27 ± 0.05 and 0.60 ± 0.05 eV below the conduction band for N- and Ga-face GaN surface, respectively.

  7. Molecular beam epitaxial growth and characterization of Bi{sub 2}Se{sub 3}/II-VI semiconductor heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Zhiyi, E-mail: zchen2@ccny.cuny.edu; Zhao, Lukas; Krusin-Elbaum, Lia [Department of Physics, The City College of New York, CUNY, New York, New York 10031 (United States); The Graduate Center, CUNY, New York, New York 10016 (United States); Garcia, Thor Axtmann; Tamargo, Maria C. [The Graduate Center, CUNY, New York, New York 10016 (United States); Department of Chemistry, The City College of New York, CUNY, New York, New York 10031 (United States); Hernandez-Mainet, Luis C. [Department of Chemistry, The City College of New York, CUNY, New York, New York 10031 (United States); Deng, Haiming [Department of Physics, The City College of New York, CUNY, New York, New York 10031 (United States)

    2014-12-15

    Surfaces of three-dimensional topological insulators (TIs) have been proposed to host quantum phases at the interfaces with other types of materials, provided that the topological properties of interfacial regions remain unperturbed. Here, we report on the molecular beam epitaxy growth of II-VI semiconductor–TI heterostructures using c-plane sapphire substrates. Our studies demonstrate that Zn{sub 0.49}Cd{sub 0.51}Se and Zn{sub 0.23}Cd{sub 0.25}Mg{sub 0.52}Se layers have improved quality relative to ZnSe. The structures exhibit a large relative upward shift of the TI bulk quantum levels when the TI layers are very thin (∼6nm), consistent with quantum confinement imposed by the wide bandgap II-VI layers. Our transport measurements show that the characteristic topological signatures of the Bi{sub 2}Se{sub 3} layers are preserved.

  8. InGaN nanorod arrays grown by molecular beam epitaxy: Growth mechanism structural and optical properties

    International Nuclear Information System (INIS)

    Vertically c-axis-aligned InGaN nanorod arrays were synthesized on c-plane sapphire substrates by radio-frequency molecular beam epitaxy. In situ reflection high-energy electron diffraction was used to monitor the growth process. X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscope, and photoluminescence were used to investigate the structural and optical properties of the nanorods. The growth mechanism was studied and a growth model was proposed based on the experimental data. A red shift of photoluminescence spectrum of InGaN nanorods with increasing growth time was found and attributed to the partial release of stress in the InGaN nanorods.

  9. Room temperature Ultraviolet B emission from InAlGaN films synthesized by plasma-assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kong, W., E-mail: wei.kong@duke.edu; Jiao, W. Y.; Kim, T. H.; Brown, A. S. [Department of Electrical and Computer Engineering, Duke University, Durham, North Carolina 27708 (United States); Roberts, A. T. [Charles Bowden Laboratory, Army Aviation and Missile RD& E Center, Redstone Arsenal, Alabama 35898 (United States); Fournelle, J. [Department of Geoscience, University of Wisconsin, Madison, Wisconsin 53706 (United States); Losurdo, M. [CNR-NANOTEC, Istituto di Nanotecnologia, via Orabona, 4-70126 Bari (Italy); Everitt, H. O. [Charles Bowden Laboratory, Army Aviation and Missile RD& E Center, Redstone Arsenal, Alabama 35898 (United States); Department of Physics, Duke University, Durham, North Carolina 27708 (United States)

    2015-09-28

    Thin films of the wide bandgap quaternary semiconductor In{sub x}Al{sub y}Ga{sub (1−x−y)}N with low In (x = 0.01–0.05) and high Al composition (y = 0.40–0.49) were synthesized on GaN templates by plasma-assisted molecular beam epitaxy. High-resolution X-ray diffraction was used to correlate the strain accommodation of the films to composition. Room temperature ultraviolet B (280 nm–320 nm) photoluminescence intensity increased with increasing In composition, while the Stokes shift remained relatively constant. The data suggest a competition between radiative and non-radiative recombination occurs for carriers, respectively, localized at centers produced by In incorporation and at dislocations produced by strain relaxation.

  10. Optical characterization of Hg1-xCdxTe/CdTe/GaAs multilayers grown by molecular beam epitaxy

    Science.gov (United States)

    Liu, Weijun; Liu, Pulin; Shi, Guo L.; Zhu, Jing-Bing; He, Li; Xie, Qin X.; Yuan, Shixin

    1991-11-01

    The IR transmission spectra for HgCdTe/CdTe/GaAs multilayers grown by molecular-beam epitaxy were measured in the wavenumber region of 600 cm-1 - 4000 cm-1 at 300 K and 77 K. The transmission spectra were calculated taking the thickness d1 of MCT layer and the thickness d2 of CdTe layer as fitting parameters in the energy range from 600 cm-1 to 300 cm-1 below the energy gap Eg assuming the existence of abrupt interfaces between the neighboring layers. The values of d1 and d2 obtained by fitting the IR transmission spectra are in good agreement with that by transmission electron microscopy (TEM) measurement. The accurate absorption coefficient spectra were obtained and discussed in the energy region equivalent to 0.9 Eg to 4000 cm-1 taking into account the interference effects.

  11. Molecular beam epitaxial growth of ultrathin CdTe-CdMnTe quantum wells and their characterization

    Science.gov (United States)

    Waag, A.; Schmeusser, S.; Bicknell-Tassius, R. N.; Yakovlev, D. R.; Ossau, W.; Landwehr, G.; Uraltsev, I. N.

    1991-12-01

    We report the growth and optical characterization of CdTe/CdMnTe single quantum wells with well thicknesses ranging from 60 down to 6 Å. The single quantum wells were grown by standard molecular beam epitaxy without growth interruption and investigated by reflection, photoluminescence (PL), and excitation PL. All structures including the 6-Å-thick quantum well exhibit extraordinarily narrow photoluminescence lines. From an analysis of linewidth and Stokes shift of the photoluminescence lines informations on the structure of the CdTe/CdMnTe interfaces are derived. The good quality of those structures made it possible to identify for the first time recombination of two-dimensional free exciton magnetic polarons.

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

    Science.gov (United States)

    Nicolaï, J.; Warot-Fonrose, B.; Gatel, C.; Teissier, R.; Baranov, A. N.; Magen, C.; Ponchet, A.

    2015-07-01

    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.

  13. Phase-coherent transport and spin relaxation in InAs nanowires grown by molecule beam epitaxy

    International Nuclear Information System (INIS)

    We report low-temperature magnetotransport studies of individual InAs nanowires grown by molecule beam epitaxy. At low magnetic fields, the magnetoconductance characteristics exhibit a crossover between weak antilocalization and weak localization by changing either the gate voltage or the temperature. The observed crossover behavior can be well described in terms of relative scales of the transport characteristic lengths extracted based on the quasi-one-dimensional theory of weak localization in the presence of spin-orbit interaction. The spin relaxation length extracted from the magnetoconductance data is found to be in the range of 80–100 nm, indicating the presence of strong spin-orbit coupling in the InAs nanowires. Moreover, the amplitude of universal conductance fluctuations in the nanowires is found to be suppressed at low temperatures due to the presence of strong spin-orbit scattering

  14. Growth temperature dependence of the surface segregation of Er atoms in GaAs during molecular beam epitaxy

    International Nuclear Information System (INIS)

    We have quantitatively studied the temperature dependence of the surface segregation of Er atoms in GaAs during molecular beam epitaxy using secondary ion mass spectroscopy. It was found that a significant number of Er atoms segregate to the growing surface at temperatures of 400°C and above and that the segregation decay length is approximately 0.5 µm at 500°C, indicating that the incorporation ratio of Er atoms into GaAs is less than 10-3. In contrast to the growth at higher temperatures, GaAs overlayer growth at a temperature as low as 300°C is effective in suppressing the surface segregation of Er and obtaining δ-doped structures. (author)

  15. Low-temperature growth of GaSb epilayers on GaAs (001) by molecular beam epitaxy

    Science.gov (United States)

    Benyahia, D.; Kubiszyn, Ł.; Michalczewski, K.; Kębłowski, A.; Martyniuk, P.; Piotrowski, J.; Rogalski, A.

    2016-01-01

    Non-intentionally doped GaSb epilayers were grown by molecular beam epitaxy (MBE) on highly mismatched semi-insulating GaAs substrate (001) with 2 offcut towards [110]. The effects of substrate temperature and the Sb/Ga flux ratio on the crystalline quality, surface morphology and electrical properties were investigated by Nomarski optical microscopy, X-ray diffraction (XRD) and Hall measurements, respectively. Besides, differential Hall was used to investigate the hole concentration behaviour along the GaSb epilayer. It is found that the crystal quality, electrical properties and surface morphology are markedly dependent on the growth temperature and the group V/III flux ratio. Under the optimized parameters, we demonstrate a low hole concentration at very low growth temperature. Unfortunately, the layers grown at low temperature are characterized by wide FWHM and low Hall mobility.

  16. Effect of N2 microplasma treatment on initial growth of GaN by metal–organic molecular beam epitaxy

    Science.gov (United States)

    Suzuki, Yohei; Kusakabe, Yasuhiro; Uchiyama, Shota; Maruyama, Takahiro; Naritsuka, Shigeya; Shimizu, Kazuo

    2016-08-01

    N2 atmospheric microplasma was applied to improve the yields and reproducibility of the initial growth of GaN by metal–organic molecular beam epitaxy (MOMBE). The plasma treatment was found to be effective in cleaning the surface, and excellent flat growth was achieved even in the early stage of the growth. The effect of the air exposure after plasma treatment was also studied, and the yield of the growth was found to be largely decreased by the air exposure even after the treatment. Therefore, the oxidation of the substrate is one of main causes of the poor initial growth and the installation of the microplasma equipment in the MBE loading chamber is useful for suppressing the oxidation after the treatment. Atomic force microscopy (AFM) measurement shows that the microplasma treatment is also effective for undoing the surface double steps through etching, which is helpful for a very smooth layer-by-layer growth in the early stage of growth.

  17. Growth morphology of MnAs epilayers on GaAs(1 1 1)-B substrates by molecular beam epitaxy

    Science.gov (United States)

    Etgens, V. H.; Eddrief, M.; Demaille, D.; Zheng, Y. L.; Ouerghi, A.

    2002-04-01

    MnAs epilayers were grown by molecular beam epitaxy on GaAs(1 1 1)B substrates. The morphology of epilayers has been studied by coupling several in situ techniques. Two distinct growth regimes were distinguished as a function of the substrate temperature. For the growth at 320°C, the system shows an intriguing mechanism of relaxation that produces MnAs isolated islands (the so-called "blocks") with constant height. The explanation for this mechanism associates the large mobility of atoms at this temperature with the strain due to the important misfit. At lower temperature (200°C) the surface mobility is greatly reduced which results in a more homogeneous film.

  18. 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.

  19. Electrical, magnetic, and structural properties of Sn1-xMnxTe layers grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Layers of Sn1-xMnxTe (x ≤ 0.1) with thickness 0.2 - 2 μm were grown by molecular beam epitaxy on BaF2 substrates with a 0.01 -1 μm thick SnTe buffer layer. Both SnTe and Sn1-xMnxTe layers show metallic p-type conductivity with conducting hole concentrations (at T = 77 K) p77 7x1019 - 2x1021 cm-3. The layers grown under the conditions of an extra Te flux have a high carrier concentration and exhibit ferromagnetic phase transition at TC ≤ 7 K. The layers grown with no (or very low) additional Te flux show low carrier concentrations (below 1020 cm-3) and remain paramagnetic in the temperature range studied T = 4.5 - 70 K. (author)

  20. (111)-oriented Zn3N2 growth on a-plane sapphire substrates by molecular beam epitaxy

    International Nuclear Information System (INIS)

    (111)-oriented Zn3N2 thin films were grown on a-plane (112-bar0) sapphire substrates by plasma-assisted molecular beam epitaxy. Zn3N2/sapphire exhibits orientational relationships of out-of-plane parallel [112-bar0] and in-plane almost parallel [0001] and parallel [0001]. These specific orientations result from similar surface configurations of N atoms in Zn3N2 and Al atoms in sapphire at the interface. Under the optimum growth conditions, the film showed a full width at half maximum of 185 arcsec for an X-ray (222) diffraction rocking curve and a root-mean-square roughness of 8.5 A in an atomic force microscope image. These results suggest that a-plane sapphire is a suitable heteroepitaxial substrate for high-quality Zn3N2 thin films. (author)

  1. Monolithically integrated InGaAs/InP MSM-FET photoreceiver prepared by chemical beam epitaxy

    International Nuclear Information System (INIS)

    The authors demonstrate the first monolithic integration of a metal-semiconductor-metal (MSM) InGaAs photodetector with an FET and resistors into a high-impedance front-end photoreceiver circuit. The sample was grown in a single step by chemical beam epitaxy, and standard processing steps for making FET's were used to fabricate the receiver circuit. Semi-insulating Fe-doped InP layers were used as the insulating gate of the FET, the barrier enhancement layer in the MSM photodetector, and the electrical isolation layer between the photodetector and the electronic circuit. A bit error rate of less than 10-9 at 200 Mbits/s has been achieved with this preliminary circuit for an optical power of - 17 dBm

  2. Formation of GaN quantum dots by molecular beam epitaxy using NH{sub 3} as nitrogen source

    Energy Technology Data Exchange (ETDEWEB)

    Damilano, B., E-mail: bd@crhea.cnrs.fr; Brault, J.; Massies, J. [CRHEA-CNRS, Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, Rue B. Grégory, Valbonne 06560 (France)

    2015-07-14

    Self-assembled GaN quantum dots (QDs) in Al{sub x}Ga{sub 1−x}N (0.3 ≤ x ≤ 1) were grown on c-plane sapphire and Si (111) substrates by molecular beam epitaxy using ammonia as nitrogen source. The QD formation temperature was varied from 650 °C to 800 °C. Surprisingly, the density and size of QDs formed in this temperature range are very similar. This has been explained by considering together experimental results obtained from reflection high-energy electron diffraction, atomic force microscopy, and photoluminescence to discuss the interplay between thermodynamics and kinetics in the QD formation mechanisms. Finally, possible ways to better control the QD optical properties are proposed.

  3. 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.

  4. Spinel-structured metal oxide on a substrate and method of making same by molecular beam epitaxy

    Science.gov (United States)

    Chambers, Scott A.

    2006-02-21

    A method of making a spinel-structured metal oxide on a substrate by molecular beam epitaxy, comprising the step of supplying activated oxygen, a first metal atom flux, and at least one other metal atom flux to the surface of the substrate, wherein the metal atom fluxes are individually controlled at the substrate so as to grow the spinel-structured metal oxide on the substrate and the metal oxide is substantially in a thermodynamically stable state during the growth of the metal oxide. A particular embodiment of the present invention encompasses a method of making a spinel-structured binary ferrite, including Co ferrite, without the need of a post-growth anneal to obtain the desired equilibrium state.

  5. Growth of ErAs nanodots by molecular beam epitaxy for application to tunneling junctions in multijunction solar cells

    Science.gov (United States)

    Hung, Chao-Yu; Sogabe, Tomah; Miyashita, Naoya; Okada, Yoshitaka

    2016-02-01

    ErAs nanodots (NDs) grown on GaAs(001) substrates by using molecular beam epitaxy (MBE) were investigated. Atomic force microscope images indicate that the size of ErAs NDs increases with deposition time and growth temperature. A calibration was performed to determine the deposition rate of ErAs in order that the size of NDs can be accurately controlled and hence optimized. Local current flow images and surface profiles around ErAs NDs were simultaneously measured to clarify the local conductivity distribution corresponding to a real space profile. Furthermore, we also fabricated and characterized an ErAs-ND-embedded GaAs tunnel junction (TJ), which resulted in a voltage drop of 30 mV for 15 A/cm2 operation current equivalent to 1000 suns concentration, which is less than one-third of that of a conventional heavily doped tunnel junction.

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

    International Nuclear Information System (INIS)

    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.

  7. 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.

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

    International Nuclear Information System (INIS)

    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

  9. Single-crystalline BaTiO3 films grown by gas-source molecular beam epitaxy

    Science.gov (United States)

    Matsubara, Yuya; Takahashi, Kei S.; Tokura, Yoshinori; Kawasaki, Masashi

    2014-12-01

    Thin BaTiO3 films were grown on GdScO3 (110) substrates by metalorganic gas-source molecular beam epitaxy. Titanium tetra-isopropoxide (TTIP) was used as a volatile precursor that provides a wide growth window of the supplied TTIP/Ba ratio for automatic adjustment of the film composition. Within the growth window, compressively strained films can be grown with excellent crystalline quality, whereas films grown outside of the growth window are relaxed with inferior crystallinity. This growth method will provide a way to study the intrinsic properties of ferroelectric BaTiO3 films and their heterostructures by precise control of the stoichiometry, structure, and purity.

  10. CdSe/CdTe type-II superlattices grown on GaSb (001) substrates by molecular beam epitaxy

    International Nuclear Information System (INIS)

    CdSe/CdTe superlattices are grown on GaSb substrates using molecular beam epitaxy. X-ray diffraction measurements and cross-sectional transmission electron microscopy images indicate high crystalline quality. Photoluminescence (PL) measurements show the effective bandgap varies with the superlattice layer thicknesses and confirm the CdSe/CdTe heterostructure has a type-II band edge alignment. The valence band offset between unstrained CdTe and CdSe is determined as 0.63 ± 0.06 eV by fitting the measured PL peak positions using the envelope function approximation and the Kronig-Penney model. These results suggest that CdSe/CdTe superlattices are promising candidates for multi-junction solar cells and other optoelectronic devices based on GaSb substrates.

  11. Abrupt PbTiO3/SrTiO3 superlattices grown by reactive molecular beam epitaxy

    International Nuclear Information System (INIS)

    PbTiO3/SrTiO3 superlattices were grown on (001) SrTiO3 substrates by reactive molecular beam epitaxy (MBE). Sharp superlattice reflections were observed by x-ray diffraction. High-resolution transmission electron microscopy of a [(PbTiO3)10/(SrTiO3)10]15 superlattice revealed that the PbTiO3/SrTiO3 interface structure is atomically sharp. The superlattice interfaces are fully coherent; no misfit dislocations or other crystal defects were observed in the superlattice by transmission electron microscopy. Selected area electron diffraction patterns indicated that the PbTiO3 layers are oriented with the c axis parallel to the growth direction. The dimensional control and interface abruptness achieved in this model system indicate that MBE is a viable method for constructing oxide multilayers on a scale where enhanced dielectric effects are expected. copyright 1999 American Institute of Physics

  12. Low-relaxation spin waves in laser-molecular-beam epitaxy grown nanosized yttrium iron garnet films

    Science.gov (United States)

    Lutsev, L. V.; Korovin, A. M.; Bursian, V. E.; Gastev, S. V.; Fedorov, V. V.; Suturin, S. M.; Sokolov, N. S.

    2016-05-01

    Synthesis of nanosized yttrium iron garnet (Y3Fe5O12, YIG) films followed by the study of ferromagnetic resonance (FMR) and spin wave propagation in these films is reported. The YIG films were grown on gadolinium gallium garnet substrates by laser molecular beam epitaxy. It has been shown that spin waves propagating in YIG deposited at 700 °C have low damping. At the frequency of 3.29 GHz, the spin-wave damping parameter is less than 3.6 × 10-5. Magnetic inhomogeneities of the YIG films give the main contribution to the FMR linewidth. The contribution of the relaxation processes to the FMR linewidth is as low as 1.2%.

  13. Antimony incorporation in InAs quantum dots grown on GaAs substrate by molecular beam epitaxy

    Science.gov (United States)

    Rihani, J.; Sallet, V.; Christophe, H. J.; Oueslati, M.; Chtourou, R.

    2008-01-01

    We have grown InAs(Sb) quantum dots (QDs) on GaAs (0 0 1) substrates by molecular beam epitaxy (MBE) using two different antimony exposures ( ΦSb). Atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy were carried out to investigate the dot size evolution as function of the incorporated antimony content in InAs/GaAs QDs material. Anomalous asymmetric-band feature was observed in room temperature photoluminescence (RTPL) spectra of the investigated QD samples grown at relatively high temperature (490 °C). From the temperature-dependent PL measurements, it was found that the asymmetric-band feature is associated with the ground-states transitions from QDs with bimodal size distribution. The analysis of the pump power dependent PL spectra allows us to suggest a type II band lineup for the InAsSb/GaAs QDs materials system.

  14. Influence of substrate quality on structural properties of AlGaN/GaN superlattices grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Short-period AlGaN/GaN superlattices were established as versatile test structures to investigate the structural properties of molecular beam epitaxy (MBE)-grown GaN and AlGaN layers and their dependence on the GaN substrate quality. X-ray diffractometry data of the investigated superlattices allow access to relevant structural parameters such as aluminum mole fraction and layer thicknesses. The occurrence of theoretically predicted intense high-order satellite peaks and pronounced interface fringes in the diffraction pattern reflects abrupt interfaces and perfect 2-dimensional growth resulting in smooth surfaces. The data unambiguously demonstrate that the structural quality of the MBE grown layers is limited by the structural properties of the GaN substrate

  15. Demonstration of nearly non-degenerate electron conduction in InN grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Electrical characterization of undoped single crystal InN has always exhibited degenerate n-type conductivity. InN layers were grown by molecular beam epitaxy (MBE), and their resistivity and Hall coefficient were measured as a function of magnetic field. The variable magnetic field Hall measurements coupled with multiple-layer modeling allowed the separation of surface, film, and near surface film electrical conduction, and thus was used to remove degenerate conduction associated with surface and interfacial layers. This approach resulted in the measurement of a temperature-dependent mobility and carrier concentration, and constitutes the first detailed measurement of conduction in InN which is only partially degenerate. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Effects of substrate anisotropy and edge diffusion on submonolayer growth during molecular beam epitaxy: A Kinetic Monte Carlo study

    International Nuclear Information System (INIS)

    We have performed Kinetic Monte Carlo simulation work to study the effect of diffusion anisotropy, bonding anisotropy and edge diffusion on island formation at different temperatures during the sub-monolayer film growth in Molecular Beam Epitaxy. We use simple cubic solid on solid model and event based Bortz, Kalos and Labowitch (BKL) algorithm on the Kinetic Monte Carlo method to simulate the physical phenomena. We have found that the island morphology and growth exponent are found to be influenced by substrate anisotropy as well as edge diffusion, however they do not play a significant role in island elongation. The growth exponent and island size distribution are observed to be influenced by substrate anisotropy but are negligibly influenced by edge diffusion. We have found fractal islands when edge diffusion is excluded and compact islands when edge diffusion is included. (author)

  17. Electron beam induced growth of tin whiskers

    International Nuclear Information System (INIS)

    We have investigated the influence of electron irradiation on tin whisker growth. Sputtered tin samples exposed to electron beam of 6 MeV energy exhibited fast whisker growth, while control samples did not grow any whiskers. The statistics of e-beam induced whiskers was found to follow the log-normal distribution. The observed accelerated whisker growth is attributed to electrostatic effects due to charges trapped in an insulating substrate. These results offer promise for establishing whisker-related accelerated life testing protocols

  18. Electron beam induced growth of tin whiskers

    Science.gov (United States)

    Vasko, A. C.; Warrell, G. R.; Parsai, E. I.; Karpov, V. G.; Shvydka, Diana

    2015-09-01

    We have investigated the influence of electron irradiation on tin whisker growth. Sputtered tin samples exposed to electron beam of 6 MeV energy exhibited fast whisker growth, while control samples did not grow any whiskers. The statistics of e-beam induced whiskers was found to follow the log-normal distribution. The observed accelerated whisker growth is attributed to electrostatic effects due to charges trapped in an insulating substrate. These results offer promise for establishing whisker-related accelerated life testing protocols.

  19. Temperature dependence of InGaP, InAlP, and AlGaP growth in metalorganic molecular-beam epitaxy

    Science.gov (United States)

    Ozasa, Kazunari; Yuri, Masaaki; Matsunami, Hiroyuki

    1990-04-01

    Metalorganic molecular-beam epitaxy of InGaP, InAlP, and AlGaP was investigated at various temperatures (290-650°C), using triethylindium (TEIn), triethylgallium (TEGa), triethylaluminum (TEAl), and phosphine. Three distinct stages were observed in the temperature dependence of growth rate and epilayer composition of those ternaries. At lower temperatures below 390°C the incomplete pyrolysis of TEGa and TEAl limits the growth, while TEIn decomposes perfectly as low as 290°C. TEAl decomposition is incomplete at all the temperatures studied, and is enhanced by the existence of TEIn or TEGa. To explain this observation, a co-decomposition mechanism was proposed, in which thermal energy produced by the pyrolysis of TEIn or TEGa induces the decomposition of TEAl; complexes such as TEAl-TEIn and TEAl-TEGa are assumed to be formed by mixing the metalorganics in the vapor phase. In the moderate-temperature region of 390-520°C, the growth is limited by the supply of metalorganics. At higher temperatures above 520°C phosphorus evaporates from the superficial part of epilayers with breaking bonds of In-P, resulting in many indium droplets on the epilayer surfaces. The incorporation of gallium and aluminum atoms into the indium droplets reduces the growth rate of the GaP and AlP constituents in InGaP and InAlP epitaxy. By the absence of In-P bonds, the growth rate of AlGaP does not decrease up to 650°C, and no droplets are formed on the surfaces.

  20. Molecular-beam epitaxy growth and structural characterization of semiconductor-ferromagnet heterostructures by grazing incidence X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Satapathy, D.K.

    2005-12-19

    The present work is devoted to the growth of the ferromagnetic metal MnAs on the semiconductor GaAs by molecular-beam epitaxy (MBE). The MnAs thin films are deposited on GaAs by molecular-beam epitaxy (MBE). Grazing incidence diffraction (GID) and reflection high-energy electron diffraction (RHEED) are used in situ to investigate the nucleation, evolution of strain, morphology and interfacial structure during the MBE growth. Four stages of the nucleation process during growth of MnAs on GaAs(001) are revealed by RHEED azimuthal scans. GID shows that further growth of MnAs films proceed via the formation of relaxed islands at a nominal thickness of 2.5 ML which increase in size and finally coalesce to form a continuous film. Early on, an ordered array of misfit dislocations forms at the interface releasing the misfit strain even before complete coalescence occurs. The fascinating complex nucleation process of MnAs on GaAs(0 0 1) contains elements of both Volmer-Weber and Stranski-Krastanov growth. A nonuniform strain amounting to 0.66%, along the [1 -1 0] direction and 0.54%, along the [1 1 0] direction is demonstrated from x-ray line profile analysis. A high correlation between the defects is found along the GaAs[1 1 0] direction. An extremely periodic array of misfit dislocations with a period of 4.95{+-}0.05 nm is formed at the interface along the [1 1 0] direction which releases the 7.5% of misfit. The inhomogeneous strain due to the periodic dislocations is confined at the interface within a layer of 1.6 nm thickness. The misfit along the [1 -1 0] direction is released by the formation of a coincidence site lattice. (orig.)

  1. Investigation of ZnO thin films deposited on ferromagnetic metallic buffer layer by molecular beam epitaxy toward realization of ZnO-based magnetic tunneling junctions

    International Nuclear Information System (INIS)

    Deposition of ZnO thin films on a ferromagnetic metallic buffer layer (Co3Pt) by molecular beam epitaxy technique was investigated for realization of ZnO-based magnetic tunneling junctions with good quality hexagonal ZnO films as tunnel barriers. For substrate temperature of 600 °C, ZnO films exhibited low oxygen defects and high electrical resistivity of 130 Ω cm. This value exceeded that of hexagonal ZnO films grown by sputtering technique, which are used as tunnel barriers in ZnO-MTJs. Also, the effect of oxygen flow during deposition on epitaxial growth conditions and Co3Pt surface oxidation was discussed.

  2. The study of in situ scanning tunnelling microscope characterization on GaN thin film grown by plasma assisted molecular beam epitaxy

    International Nuclear Information System (INIS)

    The epitaxial growth of GaN by Plasma Assisted Molecular Beam Epitaxy was investigated by Scanning Tunnelling Microscope (STM). The GaN film was grown on initial GaN (0001) and monitored by in situ Reflection High Energy Electron Diffraction and STM during the growth. The STM characterization was carried out on different sub-films with increased thickness. The growth of GaN was achieved in 3D mode, and the hexagonal edge of GaN layers and growth gradient were observed. The final GaN was of Ga polarity and kept as (0001) orientation, without excess Ga adlayers or droplets formed on the surface.

  3. Highly c-axis oriented growth of GaN film on sapphire (0001) by laser molecular beam epitaxy using HVPE grown GaN bulk target

    OpenAIRE

    S. S. Kushvaha; M. Senthil Kumar; K. K. Maurya; Dalai, M. K.; Nita D. Sharma

    2013-01-01

    Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500–750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) ...

  4. Structural, Optical and Electrical Properties of n-type GaN on Si (111) Grown by RF-plasma assisted Molecular Beam Epitaxy

    International Nuclear Information System (INIS)

    In this paper, we present the study of the structural, optical and electrical of n-type GaN grown on silicon (111) by RF plasma-assisted molecular beam epitaxy (RF-MBE). X-ray diffraction (XRD) measurement reveals that the GaN was epitaxially grown on silicon. For the photoluminescence (PL) measurement, a sharp and intense peak at 364.5 nm indicates that the sample is of high optical quality. Hall effect measurement shows that the film has a carrier concentration of 3.28x1019 cm-3. The surface of the n-type GaN was smooth and no any cracks and pits

  5. Growing high-quality ternary CdMnTe epilayers by molecular beam epitaxy on Si substrates and its mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jyh-Shyang, E-mail: jswang@cycu.edu.tw [Department of Physics, Chung Yuan Christian University, Taoyuan City 32023, Taiwan (China); Center for Nano-Technology, Chung Yuan Christian University, Taoyuan City 32023, Taiwan (China); Tong, Shih-Chang; Tsai, Yu-Hsuan; Tsai, Wei-jiun [Department of Physics, Chung Yuan Christian University, Taoyuan City 32023, Taiwan (China); Yang, Chu-Shou; Chang, Yi-Hsin [Graduate Institute of Electro-Optical Engineering, Tatung University, Taipei 10452, Taiwan (China); Cheng, Yung-Chen [Department of Materials Science, National University of Tainan, Tainan 70005, Taiwan (China); Wu, Chih-Hung [Institute of Nuclear Energy Research, Longtan 32546, Taiwan (China); Yuan, Chi-Tsu; Shen, Ji-Lin [Department of Physics, Chung Yuan Christian University, Taoyuan City 32023, Taiwan (China); Center for Nano-Technology, Chung Yuan Christian University, Taoyuan City 32023, Taiwan (China)

    2015-10-15

    Cd(Mn,Zn)Te-based ternary compound semiconductors with wide band-gaps are important in the detection of radiation and photovoltaic applications. This study characterizes Cd{sub 1-x}Mn{sub x}Te epilayers on Si substrates with various Mn compositions grown by molecular beam epitaxy. The surface smoothness, crystallinity and optical quality all are significantly improved with increasing Mn content. The Cd{sub 0.61}Mn{sub 0.39}Te epilayer with a thickness of only about 500 nm yields a full width at half maximum of the X-ray rocking curve of 165 arcsec. Photoluminescence spectra at 10 K show that the intensity of defect-related emissions is much lower than that of binary CdTe epilayers, reaching zero from the samples with high Mn content, while the integral intensity of the exciton-related emissions is increased by more than two orders of magnitude. Raman scattering spectra reveal that the intensity of the Te–Te related defect vibration modes falls significantly as the Mn content increase, even disappearing altogether in the samples with high Mn content. This work proposes that incorporating Mn atoms during epitaxial growth can promote the decomposition of Te{sub 2} sources, owing to the high sticking coefficient of Mn and the high cohesive energy of the Mn–Te bond, and then reduce the number of Te–Te related stacking fault defects, yielding high-quality CdMnTe epilayers. Our results herein demonstrate that the CdMnTe ternary epilayers are much more promising in terms of material quality than the CdZnTe ternary epilayers. - Highlights: • High-quality ternary CdMnTe were grown on Si substrates by molecular beam epitaxy. • The material qualities were significantly improved with increasing Mn content. • The Te–Te related defects were greatly reduced with increasing Mn content. • We report an enhanced growth of CdTe-based epilayers by the incorporation of Mn atoms.

  6. Direct observation of strain in InAs quantum dots and cap layer during molecular beam epitaxial growth using in situ X-ray diffraction

    International Nuclear Information System (INIS)

    Direct measurements on the growth of InAs quantum dots (QDs) and various cap layers during molecular beam epitaxy are performed by in situ X-ray diffraction (XRD). The evolution of strain induced both in the QDs and cap layers during capping is discussed based on the XRD intensity transients obtained at various lattice constants. Transients with different features are observed from those obtained during InGaAs and GaAs capping. The difference observed is attributed to In-Ga intermixing between the QDs and the cap layer under limited supply of In. Photoluminescence (PL) wavelength can be tuned by controlling the intermixing, which affects both the strain induced in the QDs and the barrier heights. The PL wavelength also varies with the cap layer thickness. A large redshift occurs by reducing the cap thickness. The in situ XRD observation reveals that this is a result of reduced strain. We demonstrate how such information about strain can be applied for designing and preparing novel device structures

  7. Beam-induced tensor pressure tokamak equilibria

    International Nuclear Information System (INIS)

    D-shaped tensor pressure tokamak equilibria induced by neutral-beam injection are computed. The beam pressure components are evaluated from the moments of a distribution function that is a solution of the Fokker-Planck equation in which the pitch-angle scattering operator is ignored. The level-psub(perpendicular) contours undergo a significant shift away from the outer edge of the device with respect to the flux surfaces for perpendicular beam injection into broad-pressure-profile equilibria. The psub(parallel) contours undergo a somewhat smaller inward shift with respect to the flux surfaces for both parallel and perpendicular injection into broad-pressure-profile equilibria. For peaked-pressure-profile equilibria, the level pressure contours nearly co-incide with the flux surfaces. (author)

  8. 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)

  9. Local structure and magnetic properties of ferromagnetic GaMnAs made by helium ion induced epitaxial crystallization annealing

    International Nuclear Information System (INIS)

    Highlights: • No observable secondary phases were found in the sample by using IBIEC annealing on Mn-implanted GaAs thin film. It is different from other Mn-implanted GaAs treated with rapid thermal annealing or furnace thermal annealing. • The ferromagnetic dipole moment is correlated with co-doped Mg ions. • We found significant anisotropy in magnetic measurement. - Abstract: In this study we show GaMnAs preparation by Mn implantation in GaAs followed by helium ion beam induced epitaxial crystallization annealing. The characteristics of the Mn-implanted layer were investigated by X-ray diffraction, and transmission electron microscopy. The magnetic nature of the Mn-implanted layer was investigated with a superconducting quantum interference device. Structure analysis showed that Mn ions were incorporated substitutionally into the GaAs lattice without the formation of any detectable secondary phases. The remanent magnetic moment exhibited room temperature ferromagnetism. Additional measurement using X-ray magnetic circular dichroism also revealed that the carriers were spin polarized

  10. Crack healing during molecular-beam-epitaxy growth of GaP/GaAs thin films

    International Nuclear Information System (INIS)

    A crack-healing phenomenon occurring during epitaxial growth of GaP films on a GaAs substrate was studied by transmission electron microscopy. The process is driven by a decrease in the surface energy of the cracked film. The results indicate that the fundamental mechanism operating during healing is the deposition and diffusion of Ga and P atoms onto the crack surface in the GaP lattice, combined with self-diffusion of GaAs within the crack tip in the GaAs substrate. This process is not fully completed in the GaP/GaAs system; unhealed crack tips located in the GaAs substrate always remain in the structure. Development of cracks and subsequent crack healing during film growth lead to a decrease in residual stress in the film. New cracks are formed at an equilibrium spacing which increases with increasing film thickness. A modified expression for predicting the relation between crack spacing and film thickness in epitaxial films is proposed

  11. Magnetic properties of Mn3O4 film under compressive stress grown on MgAl2O4 (001) by molecular beam epitaxy

    International Nuclear Information System (INIS)

    High quality single-crystalline Mn3O4 thin films were grown on MgAl2O4 (001) substrates by plasma-assisted molecular beam epitaxy. It is found that the films are compressed in the (001) plane and elongated in the perpendicular direction via in-situ reflection high-energy electron diffraction and ex-situ X-ray diffraction, which is confirmed by frequency hardening of relevant Raman bands. Different from the bulk, the epitaxial film with a thickness of 65 nm shows more obvious magnetic anisotropy and higher magnetic phase transition temperatures (TN = 50 K, T1 = 40.5 K, and T2 = 36 K) than that of the bulk (TN = 42 K, T1 = 39 K, and T2 = 33 K). The variation of magnetic properties could be attributed to the changes of interplay among spin, orbital, and lattice degrees of freedom owing to the residual strain in the epitaxial film

  12. Superconducting thin films of As-free pnictide LaPd1-xSb2 grown by reactive molecular beam epitaxy

    International Nuclear Information System (INIS)

    We use reactive molecular beam epitaxy as synthesis technique for the search of arsenic free pnictide superconductors. Epitaxial thin films of LaPd1-xSb2 were grown on (100) MgO substrates from elemental sources by simultaneous evaporation of high purity La, Pd and Sb metals by e-gun. LaPd1-xSb2 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 Tc inLaPd1-xSb2 is 3.1 K and does not depend on x. We discuss strategies to increase Tc in this pnictide subfamily.

  13. Characterization of molecular beam epitaxy grown β-Nb2N films and AlN/β-Nb2N heterojunctions on 6H-SiC substrates

    Science.gov (United States)

    Nepal, Neeraj; Katzer, D. Scott; Meyer, David J.; Downey, Brian P.; Wheeler, Virginia D.; Storm, David F.; Hardy, Matthew T.

    2016-02-01

    β-Nb2N films and AlN/β-Nb2N heterojunctions were grown by molecular beam epitaxy (MBE) on 6H-SiC. The epitaxial nature and β-Nb2N phase were determined by symmetric and asymmetric high-resolution X-ray diffraction (HRXRD) measurements, and were confirmed by grazing incidence diffraction measurements using synchrotron photons. Measured lattice parameters and the in-plane stress of β-Nb2N on 6H-SiC were c = 5.0194 Å, a = 3.0558 Å, and 0.2 GPa, respectively. The HRXRD, transmission electron microscopy, and Raman spectroscopy revealing epitaxial growth of AlN/β-Nb2N heterojunctions have identical orientations with the substrate, abrupt interfaces, and bi-axial stress of 0.88 GPa, respectively. The current finding opens up possibilities for the next generation of high-power devices that cannot be fabricated at present.

  14. 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.

  15. Mg incorporation in GaN grown by plasma-assisted molecular beam epitaxy at high temperatures

    Science.gov (United States)

    Yang, W. C.; Lee, P. Y.; Tseng, H. Y.; Lin, C. W.; Tseng, Y. T.; Cheng, K. Y.

    2016-04-01

    The influence of growth conditions on the incorporation and activation of Mg in GaN grown by plasma-assisted molecular beam epitaxy at high growth temperature (>700 °C) is presented. It is found that the highest Mg incorporation with optimized electrical properties is highly sensitive both to the Mg/Ga flux ratio and III/V flux ratio. A maximum Mg activation of ~5% can be achieved at a growth temperature of 750 °C. The lowest resistivity achieved is 0.56 Ω-cm which is associated with a high hole mobility of 6.42 cm2/V-s and a moderately high hole concentration of 1.7×1018 cm-3. Although the highest hole concentration achieved in a sample grown under a low III/V flux ratio and a high Mg/Ga flux ratio reaches 7.5×1018 cm-3, the mobility is suffered due to the formation of defects by the excess Mg. In addition, we show that modulated beam growth methods do not enhance Mg incorporation at high growth temperature in contrast to those grown at a low temperature of 500 °C (Appl. Phys. Lett. 93, 172112, Namkoong et al., 2008 [19]).

  16. Strain Induced Magnetism in SrRuO3 Epitaxial Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Grutter, A.; Wong, F.; Arenholz, E.; Liberati, M.; Suzuki, Y.

    2010-01-10

    Epitaxial SrRuO{sub 3} thin films were grown on SrTiO{sub 3}, (LaAlO{sub 3}){sub 0.3}(SrAlO{sub 3}){sub 0.7} and LaAlO{sub 3} substrates inducing different biaxial compressive strains. Coherently strained SrRuO{sub 3} films exhibit enhanced magnetization compared to previously reported bulk and thin film values of 1.1-1.6 {micro}{sub B} per formula unit. A comparison of (001) and (110) SrRuO{sub 3} films on each substrate indicates that films on (110) oriented have consistently higher saturated moments than corresponding (001) films. These observations indicate the importance of lattice distortions in controlling the magnetic ground state in this transitional metal oxide.

  17. Effect of high temperature thermal treatment of (100) γ-LiAlO2 substrate on epitaxial growth of ZnO films by plasma-assisted molecular beam epitaxy

    International Nuclear Information System (INIS)

    Non-polar ZnO thin films were fabricated on (100) γ-LiAlO2 substrates by plasma-assisted molecular beam epitaxy. The effect of high temperature thermal treatment of substrate on the crystalline orientation and quality of ZnO thin film was investigated. The film grown on (100) γ-LiAlO2 substrate without high temperature thermal treatment consists of domains of both polar and non-polar orientations as identified by the X-ray diffraction pattern. Using high temperature thermal treatment of substrate, the growth of polar ZnO has been suppressed effectively. Besides, high temperature thermal treatment of substrate improves the crystalline quality of epitaxial ZnO thin film, which exhibits a smaller full width at half maximum value of ZnO (101−0) diffraction peak and a weaker deep level emission of photoluminescence. The suppression of polar ZnO growth and the quality improvement of the epitaxial ZnO films are due to the improvement of surface morphology and roughness of the substrate upon high temperature treatment. - Highlights: • ZnO films are grown on (100) γ-LiAlO2 by plasma-assisted molecular beam epitaxy. • ZnO film grown on (100) γ-LiAlO2 without high temperature treatment is dual-oriented. • ZnO film grown on γ-LiAlO2 thermally-treated at 900 °C for 1 h is almost (101−0) oriented. • High-temperature thermal treatment of substrate improves ZnO crystalline quality

  18. Effects of buffer layer preparation and Bi concentration on InGaAsBi epilayers grown by gas source molecular beam epitaxy

    International Nuclear Information System (INIS)

    The effect of using an In0.53Ga0.47As buffer layer on the crystalline quality of InGaAsBi epilayer with Bi concentration up to 3.1% grown by gas source molecular beam epitaxy was investigated. It is found that use of the buffer layer has a dramatic effect on the improvement of surface morphology, structural, electrical and optical properties of InGaAsBi epilayers. Bi incorporation in InGaAs up to a concentration of 3.1% causes no degradation of the electron mobility and induces p-type carriers that compensate the background n-type carriers resulting in mobility enhancement with increasing Bi concentration. With the buffer layer preparation, a maximum electron mobility of 5550 cm2 V–1 s–1 at room temperature is demonstrated in InGaAsBi with x Bi = 3.1%, which is the highest value reported in InGaAsBi with x Bi > 2.5%. (paper)

  19. Growth modes and epitaxy of FeAl thin films on a-cut sapphire prepared by pulsed laser and ion beam assisted deposition

    International Nuclear Information System (INIS)

    FeAl films around equiatomic composition are grown on a-cut (112¯0) sapphire substrates by ion beam assisted deposition (IBAD) and pulsed laser deposition (PLD) at ambient temperature. Subsequent successive annealing is used to establish chemical order and crystallographic orientation of the films with respect to the substrate. We find a strongly [110]-textured growth for both deposition techniques. Pole figures prove the successful preparation of high quality epitaxial films by PLD with a single in-plane orientation. IBAD-grown films, however, exhibit three in-plane orientations, all of them with broad angular distributions. The difference of the two growth modes is attributed to the existence of a metastable intermediate crystalline orientation as concluded from nonassisted sputter depositions at different substrate temperatures. The formation of the chemically ordered crystalline B2 phase is accompanied by the expected transition from ferromagnetic to paramagnetic behavior of the films. In accordance with the different thermally induced structural recovery, we find a step-like magnetic transition to paramagnetic behavior after annealing for 1 h at TA = 300 °C for IBAD deposition, while PLD-grown films show a gradual decrease of ferromagnetic signals with rising annealing temperatures

  20. Annealing studies of heteroepitaxial InSbN on GaAs grown by molecular beam epitaxy for long-wavelength infrared detectors

    Energy Technology Data Exchange (ETDEWEB)

    Patra, Nimai C.; Bharatan, Sudhakar [Electrical and Computer Engineering, North Carolina A and T State University, Greensboro, North Carolina 27411 (United States); Li Jia; Iyer, Shanthi [Electrical and Computer Engineering, North Carolina A and T State University, Greensboro, North Carolina 27411 (United States); Department of Nanoengineering, North Carolina A and T State University, Greensboro, North Carolina 27401 (United States)

    2012-10-15

    We report the effect of annealing on the structural, vibrational, electrical, and optical properties of heteropepitaxially grown InSbN epilayers on GaAs substrate by molecular beam epitaxy for long-wavelength infrared detector applications. As-grown epilayers exhibited high N incorporation in the both substitutional and interstitial sites, with N induced defects as evidenced from high resolution x-ray diffraction, secondary ion mass spectroscopy, and room temperature (RT) micro-Raman studies. The as-grown optical band gap was observed at 0.132 eV ({approx}9.4 {mu}m) and the epilayer exhibited high background carrier concentration at {approx}10{sup 18} cm{sup -3} range with corresponding mobility of {approx}10{sup 3} cm{sup 2}/Vs. Ex situ and in situ annealing at 430 Degree-Sign C though led to the loss of N but improved InSb quality due to effective annihilation of N related defects and other lattice defects attested to enhanced InSb LO phonon modes in the corresponding Raman spectra. Further, annealing resulted in the optical absorption edge red shifting to 0.12 eV ({approx}10.3 {mu}m) and the layers were characterized by reduced background carrier concentration in the {approx}10{sup 16} cm{sup -3} range with enhanced mobility in {approx}10{sup 4} cm{sup 2}/Vs range.

  1. Annealing studies of heteroepitaxial InSbN on GaAs grown by molecular beam epitaxy for long-wavelength infrared detectors

    International Nuclear Information System (INIS)

    We report the effect of annealing on the structural, vibrational, electrical, and optical properties of heteropepitaxially grown InSbN epilayers on GaAs substrate by molecular beam epitaxy for long-wavelength infrared detector applications. As-grown epilayers exhibited high N incorporation in the both substitutional and interstitial sites, with N induced defects as evidenced from high resolution x-ray diffraction, secondary ion mass spectroscopy, and room temperature (RT) micro-Raman studies. The as-grown optical band gap was observed at 0.132 eV (∼9.4 μm) and the epilayer exhibited high background carrier concentration at ∼1018 cm−3 range with corresponding mobility of ∼103 cm2/Vs. Ex situ and in situ annealing at 430 °C though led to the loss of N but improved InSb quality due to effective annihilation of N related defects and other lattice defects attested to enhanced InSb LO phonon modes in the corresponding Raman spectra. Further, annealing resulted in the optical absorption edge red shifting to 0.12 eV (∼10.3 μm) and the layers were characterized by reduced background carrier concentration in the ∼1016 cm−3 range with enhanced mobility in ∼104 cm2/Vs range.

  2. 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

  3. Control over the morphology of AlN during molecular beam epitaxy with the plasma activation of nitrogen on Si (111) substrates

    International Nuclear Information System (INIS)

    The results of studies of the growth kinetics of AlN layers during molecular beam epitaxy with the plasma activation of nitrogen using Si (111) substrates are presented. The possibility of the growth of individual AlN/Si (111) nanocolumns using growth conditions with enrichment of the surface with metal near the formation mode of Al drops, at a substrate temperature close to maximal, during molecular beam epitaxy with the plasma activation of nitrogen (Ts ≈ 850°C) is shown. The possibility of growing smooth AlN layers on a nanocolumnar AlN/Si (111) buffer with the use of Ts ≈ 750°C and growth conditions providing enrichment with metal is shown

  4. Effect of interaction in the Ga-As-O system on the morphology of a GaAs surface during molecular-beam epitaxy

    Science.gov (United States)

    Ageev, O. A.; Balakirev, S. V.; Solodovnik, M. S.; Eremenko, M. M.

    2016-05-01

    A thermodynamic analysis of processes of interphase interaction in the Ga-As-O system has been performed and their theoretical laws have been determined, taking into account nonlinear thermal physical properties of the compounds, the oxide film compositions, and modes of molecular-beam epitaxy of GaAs. The processes of interaction of the native oxide of GaAs with the substrate material and also with Ga and As4 from a vapor gaseous phase have been studied experimentally. The experimental results correlate with the results of the thermodynamic analysis. The laws of influence of the removal of the proper oxide on the evolution of the GaAs surface morphology under conditions of the molecular-beam epitaxy have been proposed.

  5. Growth and characterization of lattice-matched InAlN/GaN Bragg reflectors grown by plasma-assisted Molecular Beam Epitaxy

    OpenAIRE

    Gacevic, Zarko; Fernández-Garrido, Sergio; Calleja Pardo, Enrique; Luna García de la Infanta, Esperanza; Trampert, Achim

    2009-01-01

    We demonstrate six to ten period lattice-matched In(0.18) Al(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, crosssectional analysis by high resolution transmission electron microscopy reveals highly periodic structure with abrupt interfaces. When the number of...

  6. Structural and optical properties of Cd 0.7Hg 0.3Te-CdTe heterostructures grown by molecular beam epitaxy

    Science.gov (United States)

    Lentz, G.; Magnea, N.; Mariette, H.; Tuffigo, H.; Feuillet, G.; Fontenille, J.; Ligeon, E.; Saminadayar, K.

    1990-04-01

    Layers and single quantum wells of Cd xHg 1- xTe with x ⋍ 0.7 have been grown by molecular beam epitaxy. Structural analysis shows that growth free of defects (twins, dislocations) can be achieved on (111)Te Cd 0.96Zn 0.04Te substrates. The Photoluminescence analysis of the layers and the wells reveal that they are efficient light emittors in the 1.3-1.5 μm range.

  7. Growth of high-quality SrTiO{sub 3} films using a hybrid molecular beam epitaxy approach

    Energy Technology Data Exchange (ETDEWEB)

    Jalan, Bharat; Engel-Herbert, Roman; Wright, Nicholas J.; Stemmer, Susanne [Materials Department, University of California, Santa Barbara, California 93106-5050 (United States)

    2009-05-15

    A hybrid molecular beam epitaxy approach for atomic-layer controlled growth of high-quality SrTiO{sub 3} films with scalable growth rates was developed. The approach uses an effusion cell for Sr, a plasma source for oxygen, and a metal-organic source (titanium tetra isopropoxide) for Ti. SrTiO{sub 3} films were investigated as a function of cation flux ratio on (001) SrTiO{sub 3} and (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (LSAT) substrates. Growth conditions for stoichiometric insulating films were identified. Persistent (>180 oscillations) reflection high-energy electron diffraction oscillation characteristic of layer-by-layer growth were observed. The full widths at half maximum of x-ray diffraction rocking curves were similar to those of the substrates, i.e., 34 arc sec on LSAT. The film surfaces were nearly ideal with root mean square surface roughness values of less than 0.1 nm. The relationship between surface reconstructions, growth modes, and stoichiometry is discussed.

  8. Effect of thickness on the microstructure of GaN films on Al203 (0001) by laser molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Liu Ying-Ying; Zhu Jun; Luo Wen-Bo; Hao Lan-Zhong; Zhang Ying; Li Yan-Rong

    2011-01-01

    Heteroepitaxia1l GaN films are grown on sapphire (0001) substrates using laser molecular beam epitaxy.The growth processes are in-situ monitored by reflection high energy electron diffraction.It is revealed that the growth mode of GaN transformed from three-dimensional (3D) island mode to two-dimensional (2D) layer-by-layer mode with the increase of thickness.This paper investigates the interfacial strain relaxation of GaN films by analysing their diffraction patterns.Calculation shows that the strain is completely relaxed when the thickness reaches 15 nm.The surface morphology evolution indicates that island merging and reduction of the island-edge barrier provide an effective way to make GaN films follow a 2D layer-by-layer growth mode.The 110-nm GaN films with a 2D growth mode have smooth regular hexagonal shapes.The X-ray diffraction indicates that thickness has a significant effect on the crystallized quality of GaN thin films.

  9. Influence of annealing conditions on impurity species in arsenic-doped HgCdTe grown by molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Yue Fang-Yu; Chen Lu; Li Ya-Wei; Hu Zhi-Gao; Sun Lin; Yang Ping-Xiong; Chu Jun-Hao

    2010-01-01

    Based on our previous work, the influence of annealing conditions on impurity species in in-situ arsenic (As)doped Hg1-x>Cdx>Te (x≈0.3) grown by molecular beam epitaxy has been systematically investigated by modulated photoluminescence spectra. The results show that (I) the doped-As acting as undesirable shallow/deep levels in as grown can be optimized under proper annealing conditions and the physical mechanism of the disadvantage of high activation temperature, commonly assumed to be more favourable for As activation, has been discussed as compared with the reports in the As-implanted HgCdTe epilayers (x≈0.39), (ii) the density of VHg> has an evident effect on the determination of bandgap (or composition) of epilayers and the excessive introduction of VHg will lead to a short wavelength shift of epilayers, and (iii) the VHg prefers forming the VHg-AsHg complex when the inactivated-As (AsHg>or related) coexists in a certain density, which makes it difficult to annihilate VHg in As-doped epilayers. As a result, the bandedge electronic structures of epilayers under different conditions have been drawn as a brief guideline for preparing extrinsic p-type epilayers or related devices.

  10. Characterization of GaNxAs1-x Alloy Grown on GaAs by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    李联合; 张伟; 潘钟; 林耀望; 吴荣汉

    2000-01-01

    The GaNxAs1-x alloy has been investigated which is grown on GaAs (100) substrate by molecular beam epitaxy with a DC-plasma nitrogen source. The samples are characterized by high resolution X-ray diffraction (HRXRD) and low temperature photoluminescence (PL) measurements. Both HRXRD and PL measurements demonstrate that the crystalline and optical qualities of GaNxAs1-x alloy degrade rapidly with the increase of N composition. The nitrogen composition of 4.5 % can be obtained in GaNxAs1-x/GaAs quantum well by optimizing growth conditions,through which a photoluminescence peak of 1201nm is observed at a low temperature (10 K). The dependence of GaNxAs1-x band gap energy on the nitrogen composition in this investigation corresponds very well with that of the theoretical one based on the dielectric model when considering the effect of the strain. At the same time,we also demonstrate that the bowing parameter of GaNxAs1-x alloy is composition dependent.

  11. Precipitation control and activation enhancement in boron-doped p+-BaSi2 films grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Precipitation free boron (B)-doped as-grown p+-BaSi2 layer is essential for the BaSi2 p-n junction solar cells. In this article, B-doped p-BaSi2 layers were grown by molecular beam epitaxy on Si(111) substrates, and the influence of substrate growth temperature (TS) and B temperature (TB) in the Knudsen cell crucible were investigated on the formation of B precipitates and the activation efficiency. The hole concentration, p, reached 1.0 × 1019 cm−3 at room temperature for TS = 600 and TB = 1550 °C. However, the activation rate of B was only 0.1%. Furthermore, the B precipitates were observed by transmission electron microscopy (TEM). When the TS was raised to 650 °C and the TB was decreased to 1350 °C, the p reached 6.8 × 1019 cm−3, and the activation rate increased to more than 20%. No precipitation of B was also confirmed by TEM.

  12. Semipolar and nonpolar GaN epi-films grown on m-sapphire by plasma assisted molecular beam epitaxy

    International Nuclear Information System (INIS)

    We hereby report the development of non-polar epi-GaN films of usable quality, on an m-plane sapphire. Generally, it is difficult to obtain high-quality nonpolar material due to the planar anisotropic nature of the growth mode. However, we could achieve good quality epi-GaN films by involving controlled steps of nitridation. GaN epilayers were grown on m-plane (10-10) sapphire substrates using plasma assisted molecular beam epitaxy. The films grown on the nitridated surface resulted in a nonpolar (10-10) orientation while without nitridation caused a semipolar (11-22) orientation. Room temperature photoluminescence study showed that nonpolar GaN films have higher value of compressive strain as compared to semipolar GaN films, which was further confirmed by room temperature Raman spectroscopy. The room temperature UV photodetection of both films was investigated by measuring the I-V characteristics under UV light illumination. UV photodetectors fabricated on nonpolar GaN showed better characteristics, including higher external quantum efficiency, compared to photodetectors fabricated on semipolar GaN. X-ray rocking curves confirmed better crystallinity of semipolar as compared to nonpolar GaN which resulted in faster transit response of the device

  13. Molecular beam epitaxy of CdTe and HgCdTe on large-area Si(100)

    Science.gov (United States)

    Sporken, R.; Lange, M. D.; Faurie, Jean-Pierre

    1991-09-01

    The current status of molecular beam epitaxy (MBE) of CdTe and HgCdTe on Si(100) is reviewed. CdTe and HgCdTe grow in the (111)B orientation on Si(100); monocrystalline films with two domains are obtained on most nominal Si(100) substrates, single domain films are grown on misoriented substrates and on nominal Si(100) preheated to 900-950 degree(s)C. Double-crystal x-ray rocking curves (DCRCs) with full-width at half-maximum (FWHM) as low as 110 arcsec are reported for HgCdTe on silicon; these layers are n-type, and electron mobilities higher than 5 X 104 cm2V-2s-1 are measured at 23 K for x equals 0.26. Excellent thickness and composition uniformity is obtained: standard deviation of the CdTe thickness 0.4% of the average thickness on 2-in. and 2.3% on 5-in., standard deviation of the Cd concentration in the HgCdTe layers 0.6% of the average concentration on 3-in. and 2.4% on 5-in. First results regarding growth of CdTe on patterned Si substrates are also reported.

  14. Epitaxial silicon nanowire growth catalyzed by gold dot arrays from electron beam lithography patterning using silane precursors

    Energy Technology Data Exchange (ETDEWEB)

    Hoffmann, Bjoern; Broenstrup, Gerald; Huebner, Uwe; Christiansen, Silke [Institut fuer Photonische Technologien e.V., Abt. Halbleiter Nanostrukturen, Jena (Germany)

    2010-07-01

    Ordered arrays of silicon nanowires (SiNWs) are promising building blocks for a variety of photonic, photovoltaic and sensor applications. In our approach to create SiNWs we use electron beam lithography (EBL) and thermal metal evaporation to create nano-patterned arrays of gold nanodots on a Si(111) wafer. These Au dots are subsequently used to catalyze the bottom-up growth of SiNWs that follow the vapor-liquid-solid (VLS) growth mechanism using silane in a CVD reactor. The grown nanowires are characterized structurally using SEM, TEM and electron backscatter diffraction (EBSD). We observe epitaxial growth of the SiNWs on the Si(111) wafer and we are able to control the growth direction to be either dominated by <111> or <112> directions by just changing the silane partial pressure. The lengths as well as the diameters of the wires are precisely controlled by the EBL Au dot patterning and CVD parameters. To predict wire diameters modelling is carried out that takes into account the EBL- and CVD-parameters and describes the observed experimental results very well. Furthermore we were able to create single crystalline Au-dot arrays which are very promising structures for surface enhanced raman spectroscopy (SERS) substrates.

  15. Magnetic properties of MnSb inclusions formed in GaSb matrix directly during molecular beam epitaxial growth

    International Nuclear Information System (INIS)

    Despite of intensive search for the proper semiconductor base materials for spintronic devices working at room temperature no appropriate material based on ferromagnetic semiconductors has been found so far. We demonstrate that the phase segregated system with MnSb hexagonal inclusions inside the GaSb matrix, formed directly during the molecular beam epitaxial growth reveals the ferromagnetic properties at room temperature and is a good candidate for exploitation in spintronics. Furthermore, the MnSb inclusions with only one crystalline structure were identified in this GaMn:MnSb granular material. The SQUID magnetometry confirmed that this material exhibits ferromagnetic like behavior starting from helium up to room temperature. Moreover, the magnetic anisotropy was found which was present also at room temperature, and it was proved that by choosing a proper substrate it is possible to control the direction of easy axis of inclusions' magnetization moment between in-plane and out-of-plane; the latter is important in view of potential applications in spintronic devices.

  16. Molecular-beam epitaxy growth and in situ arsenic doping of p-on-n HgCdTe heterojunctions

    Science.gov (United States)

    Arias, Jose; Zandian, M.; Pasko, J. G.; Shin, S. H.; Bubulac, L. O.; DeWames, R. E.; Tennant, W. E.

    1991-02-01

    In this paper we present, results on the growth of in situ doped p-on-n heterojunctions on HgCdTe epilayers grown on (211)B GaAs substrates by molecular-beam epitaxy (MBE). Long wavelength infrared (LWIR) photodiodes made with these grown junctions are of high performance. The n-type MBE HgCdTe/GaAs alloy epilayer in these structures was grown at Ts=185 °C and it was doped with indium (high 1014 cm-3 range) atoms. This epilayer was directly followed by the growth, at Ts=165 °C, of an arsenic-doped (1017-1018 cm-3 ) HgTe/CdTe superlattice structure which was necessary to incorporate the arsenic atoms as acceptors. After the structure was grown, a Hg annealing step was needed to interdiffuse the superlattice and obtain the arsenic-doped p-type HgCdTe layer above the indium-doped layer. LWIR mesa diodes made with this material have 77 K R0A values of 5×103, 81, 8.5, and 1.1 Ω cm2 for cutoff wavelengths of 8.0, 10.2, 10.8, and 13.5 μm, respectively; the 77 K quantum efficiency values for these diodes were greater than 55%. These recent results represent a significant step toward the demonstration of MBE as a viable growth technique for the in situ fabrication of large area LWIR focal plane arrays.

  17. Sr flux stability against oxidation in oxide-molecular-beam-epitaxy environment: Flux, geometry, and pressure dependence

    International Nuclear Information System (INIS)

    Maintaining stable fluxes for multiple source elements is a challenging task when the source materials have significantly different oxygen affinities in a complex-oxide molecular-beam-epitaxy (MBE) environment. Considering that Sr is one of the most easily oxidized and widely used elements in various complex oxides, we took Sr as a probe to investigate the flux-stability problem in a number of different conditions. Source oxidation was less for higher flux, extended port geometry, and unmelted source shape. The extended port geometry also eliminated the flux transient after opening a source shutter as observed in the standard port. We also found that the source oxidation occurred more easily on the crucible wall than on the surface of the source material. Atomic oxygen, in spite of its stronger oxidation effectiveness, did not make any difference in source oxidation as compared to molecular oxygen in this geometry. Our results may provide a guide for solutions to the source oxidation problem in oxide-MBE system.

  18. Antimony segregation in Ge and formation of n-type selectively doped Ge films in molecular beam epitaxy

    International Nuclear Information System (INIS)

    Antimony segregation in Ge(001) films grown by molecular beam epitaxy was studied. A quantitative dependence of the Sb segregation ratio in Ge on growth temperature was revealed experimentally and modeled theoretically taking into account both the terrace-mediated and step-edge-mediated segregation mechanisms. A nearly 5-orders-of-magnitude increase in the Sb segregation ratio in a relatively small temperature range of 180–350 °C was obtained, which allowed to form Ge:Sb doped layers with abrupt boundaries and high crystalline quality using the temperature switching method that was proposed earlier for Si-based structures. This technique was employed for fabrication of different kinds of n-type Ge structures which can be useful for practical applications like heavily doped n+-Ge films or δ-doped layers. Estimation of the doping profiles sharpness yielded the values of 2–5 nm per decade for the concentration gradient at the leading edge and 2–3 nm for the full-width-half-maximum of the Ge:Sb δ-layers. Electrical characterization of grown Ge:Sb structures revealed nearly full electrical activation of Sb atoms and the two-dimensional nature of charge carrier transport in δ-layers

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

    International Nuclear Information System (INIS)

    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.)

  20. Growth of high-quality SrTiO3 films using a hybrid molecular beam epitaxy approach

    International Nuclear Information System (INIS)

    A hybrid molecular beam epitaxy approach for atomic-layer controlled growth of high-quality SrTiO3 films with scalable growth rates was developed. The approach uses an effusion cell for Sr, a plasma source for oxygen, and a metal-organic source (titanium tetra isopropoxide) for Ti. SrTiO3 films were investigated as a function of cation flux ratio on (001) SrTiO3 and (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT) substrates. Growth conditions for stoichiometric insulating films were identified. Persistent (>180 oscillations) reflection high-energy electron diffraction oscillation characteristic of layer-by-layer growth were observed. The full widths at half maximum of x-ray diffraction rocking curves were similar to those of the substrates, i.e., 34 arc sec on LSAT. The film surfaces were nearly ideal with root mean square surface roughness values of less than 0.1 nm. The relationship between surface reconstructions, growth modes, and stoichiometry is discussed.

  1. High-Resistivity Semi-insulating AlSb on GaAs Substrates Grown by Molecular Beam Epitaxy

    Science.gov (United States)

    Vaughan, E. I.; Addamane, S.; Shima, D. M.; Balakrishnan, G.; Hecht, A. A.

    2016-04-01

    Thin-film structures containing AlSb were grown using solid-source molecular beam epitaxy and characterized for material quality, carrier transport optimization, and room-temperature radiation detection response. Few surface defects were observed, including screw dislocations resulting from shear strain between lattice-mismatched layers. Strain was also indicated by broadening of the AlSb peak in x-ray diffraction measurements. Threading dislocations and interfacial misfit dislocations were seen with transmission electron microscopy imaging. Doping of the AlSb layer was introduced during growth using GaTe and Be to determine the effect on Hall transport properties. Hall mobility and resistivity were largest for undoped AlSb samples, at 3000 cm2/V s and 106 Ω cm, respectively, and increased doping levels progressively degraded these values. To test for radiation response, p-type/intrinsic/ n-type (PIN) diode structures were grown using undoped AlSb on n-GaAs substrates, with p-GaSb cap layers to protect the AlSb from oxidation. Alpha-particle radiation detection was achieved and spectra were produced for 241Am, 252Cf, and 239Pu sources. Reducing the detector surface area increased the pulse height observed, as expected based on voltage-capacitance relationships for diodes.

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

    Science.gov (United States)

    Kolkovsky, Vl.; Zytkiewicz, Z. R.; Korona, K. P.; Sobanska, M.; Klosek, K.

    2015-12-01

    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 102 and the leakage current of about 10-4 A/cm2 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 SiNx 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 × 1015 cm-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 SiNx 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.

  3. 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.

    2015-09-01

    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 Landé g-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.

  4. Demonstration of isotype GaN/AlN/GaN heterobarrier diodes by NH3-molecular beam epitaxy

    International Nuclear Information System (INIS)

    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 NH3 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

  5. Structural and magnetic characterization of Sm-doped GaN grown by plasma-assisted molecular beam epitaxy

    Science.gov (United States)

    Dehara, Kentaro; Miyazaki, Yuta; Hasegawa, Shigehiko

    2016-05-01

    We have investigated structural, optical and magnetic properties of Sm-doped GaN thin films grown by plasma-assisted molecular beam epitaxy. Reflection high-energy electron diffraction and X-ray diffraction reveal that Ga1- x Sm x N films with a SmN mole fraction of ˜8% or below are grown on GaN templates without segregation of any secondary phases. With increasing SmN mole fraction, the c-axis lattice parameter of the GaSmN films linearly increases. GaSmN films with low Sm concentrations exhibit inner-4f transitions of Sm3+ in photoluminescence spectra. The present findings show that Sm atoms are substituted for some Ga atoms as trivalent ions (Sm3+). The Ga1- x Sm x N films display hysteresis loops in magnetization versus external magnetic field (M-H) curves even at 300 K. We will discuss the origin of these features together with the corresponding temperature dependences of magnetization.

  6. High purity GaAs and Al xGa 1-xAs grown by metalorganic molecular beam epitaxy

    Science.gov (United States)

    Furuhata, Naoki; Okamoto, Akihiko; Hoshino, Hitoshi

    1990-06-01

    High purity GaAs and Al xGa 1- xAs were grown by metalorganic molecular beam epitaxy (MOMBE) using metalorganic sources and arsenic (As 4). In GaAs growth using triethylgallium (TEG) and As 4, carrier concentrations depended on As 4 pressure and substrate temperatures. Below 1.5 x 10 -4 Torr As 4 pressure, the p-type carrier concentrations decreased with an increase in As 4 pressure. Above 1.5 x 10 -4 Torr As 4 pressure, the epilayer converted from p-type to n-type conductivity. Carrier concentrations decreased with a decrease in substrate temperatures. At 500°C and 1.5 x 10 -4 Torr As 4 pressure, the carrier concentration in the p-type GaAs epilayer exhibited 1.5 x 10 14 cm -3 with a room temperature mobility of 400 cm 2/V.s. Al xGa 1-xAs ( x=0.1-0. .2) was also grown using TEG, three different Al sources (triethylaluminum (TEA), trimethylaluminum (TMA) and dimethylaluminum hydride (DMAH) and As 4. Using TEG, TEA and As 4, the Al 0.15Ga 0.85As epilayer showed p-type conduction with carrier concentration of 1.2x10 15 cm -3 and mobility of 117 cm 2/V.s. This carrier concentration is the lowest value ever reported for Al xGa 1- xAs grown by MOMBE.

  7. Gas Source Melecular Beam Epitaxy Growth of High Quality AlGaAs Using Trimethylamine Alane as the Aluminum Source

    Science.gov (United States)

    Okamoto, Naoya; Ando, Hideyasu; Sandhu, Adarsh; Fujii, Toshio

    1991-12-01

    We investigated the dependence of the background impurity incorporation on growth conditions and optical properties of undoped AlGaAs grown by gas source molecular beam epitaxy using trimethylamine alane (TMAAl), triethylgallium, and arsine. The use of TMAAl enabled us to reduce the carbon concentration (7× 1016 cm-3) to over one order of magnitude less than that using triethylaluminum (TEAl). The 77 K photoluminescence spectrum of undoped AlGaAs grown using TMAAl was dominated by excitonic band-edge emission not observable in AlGaAs grown using TEAl. Furthermore, we report for the first time the doping characteristics of n-type AlGaAs grown using disilane (Si2H6) as an n-type gaseous dopant source together with TMAAl. The carrier concentration (5× 1017--3× 1018 cm-3) in n-AlxGa1-xAs (x{=}0.09--0.27) was reliably controlled and showed the same Si2H6 flow rate dependence as that of GaAs. The activation efficiency of silicon was more than 60%. We demonstrated the excellent n-type doping characteristics by uisng TMAAl.

  8. An Effective Approach to Improving Cadmium Telluride (111)A Surface by Molecular-Beam-Epitaxy Growth of Tellurium Monolayer.

    Science.gov (United States)

    Ren, Jie; Fu, Li; Bian, Guang; Su, Jie; Zhang, Hao; Velury, Saavanth; Yukawa, Ryu; Zhang, Longxiang; Wang, Tao; Zha, Gangqiang; Guo, Rongrong; Miller, Tom; Hasan, M Zahid; Chiang, Tai-Chang

    2016-01-13

    The surface cleansing treatment of non-natural cleavage planes of semiconductors is usually performed in vacuum using ion sputtering and subsequent annealing. In this Research Article, we report on the evolution of surface atomic structure caused by different ways of surface treatment as monitored by in situ core-level photoemission measurements of Cd-4d and Te-4d atomic levels and reflection high-energy electron diffraction (RHEED). Sputtering of surface increases the density of the dangling bonds by 50%. This feature and the less than ideal ordering can be detrimental to device applications. An effective approach is employed to improve the quality of this surface. One monolayer (ML) of Te grown by the method of molecular beam epitaxy (MBE) on the target surface with heating at 300 °C effectively improves the surface quality as evidenced by the improved sharpness of RHEED pattern and a reduced diffuse background in the spectra measured by high-resolution ultraviolet photoemission spectroscopy (HRUPS). Calculations have been performed for various atomic geometries by employing first-principles geometry optimization. In conjunction with an analysis of the core level component intensities in terms the layer-attenuation model, we propose a "vacancy site" model of the modified 1 ML-Te/CdTe(111)A (2 × 2) surface. PMID:26672795

  9. 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. PMID:26308470

  10. 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.

  11. 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.

  12. Controllable Growth of Vertical Heterostructure GaTe(x)Se(1-x)/Si by Molecular Beam Epitaxy.

    Science.gov (United States)

    Liu, Shanshan; Yuan, Xiang; Wang, Peng; Chen, Zhi-Gang; Tang, Lei; Zhang, Enze; Zhang, Cheng; Liu, Yanwen; Wang, Weiyi; Liu, Cong; Chen, Chen; Zou, Jin; Hu, Weida; Xiu, Faxian

    2015-08-25

    Two dimensional (2D) alloys, especially transition metal dichalcogenides, have attracted intense attention owing to their band-gap tunability and potential optoelectrical applications. Here, we report the controllable synthesis of wafer-scale, few-layer GaTexSe1-x alloys (0 ≤ x ≤ 1) by molecular beam epitaxy (MBE). We achieve a layer-by-layer growth mode with uniform distribution of Ga, Te, and Se elements across 2 in. wafers. Raman spectroscopy was carried out to explore the composition-dependent vibration frequency of phonons, which matches well with the modified random-element-isodisplacement model. Highly efficient photodiode arrays were also built by depositing few-layer GaTe0.64Se0.36 on n-type Si substrates. These p-n junctions have steady rectification characteristics with a rectifying ratio exceeding 300 and a high external quantum efficiency around 50%. We further measured more devices on MBE-grown GaTexSe1-x/Si heterostructures across the full range to explore the composition-dependent external quantum efficiency. Our study opens a new avenue for the controllable growth of 2D alloys with wafer-scale homogeneity, which is a prominent challenge in 2D material research. PMID:26234804

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

    International Nuclear Information System (INIS)

    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. InN nanorods prepared with CrN nanoislands by plasma-assisted molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Young Sheng-Joue

    2011-01-01

    Full Text Available Abstract The authors report the influence of CrN nanoisland inserted on growth of baseball-bat InN nanorods by plasma-assisted molecular beam epitaxy under In-rich conditions. By inserting CrN nanoislands between AlN nucleation layer and the Si (111 substrate, it was found that we could reduce strain form Si by inserting CrN nanoisland, FWHM of the x-ray rocking curve measured from InN nanorods from 3,299 reduced to 2,115 arcsec. It is due to the larger strain from lattice miss-match of the film-like InN structure; however, the strain from lattice miss-match was obvious reduced owing to CrN nanoisland inserted. The TEM images confirmed the CrN structures and In droplets dissociation from InN, by these results, we can speculate the growth mechanism of baseball-bat-like InN nanorods.

  15. Spectroscopic ellipsometry analysis of GaAs{sub 1-x}N{sub x} layers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Ben Sedrine, N. [Laboratoire de Photovoltaique et de Semiconducteurs, Centre de Recherche et de Technologie de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia)], E-mail: bsnebiha@yahoo.fr; Rihani, J. [Laboratoire de Photovoltaique et de Semiconducteurs, Centre de Recherche et de Technologie de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia); Stehle, J.L. [SOPRA S.A., 26 rue Pierre Joigneaux 92270 Bois Colombes (France); Harmand, J.C. [Laboratoire de Photonique et de Nanostructures, CNRS Route de Nozay 91 460, Marcoussis (France); Chtourou, R. [Laboratoire de Photovoltaique et de Semiconducteurs, Centre de Recherche et de Technologie de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia)

    2008-07-01

    In this work, we present the effect of nitrogen incorporation on the dielectric function of GaAsN samples, grown by molecular beam epitaxy (MBE) followed by a rapid thermal annealing (for 90 s at 680 deg. C). The GaAs{sub 1-x}N{sub x} samples with N content up to 1.5% (x = 0.0%, 0.1%, 0.5%, 1.5%), are investigated using room temperature spectroscopic ellipsometry (SE). The optical transitions in the spectral region around 3 eV are analyzed by fitting analytical critical point line shapes to the second derivative of the dielectric function. It was found that the features associated with E{sub 1} and E{sub 1} + {delta}{sub 1} transitions are blue-shifted and become less sharp with increasing nitrogen incorporation, in contrast to the case of E{sub 0} transition energy in GaAs{sub 1-x}N{sub x}. An increase of the split-off {delta}{sub 1} energy with nitrogen content was also obtained, in agreement to results found with MOVPE GaAs{sub 1-x}N{sub x} grown samples.

  16. Abnormal optical behaviour of InAsSb quantum dots grown on GaAs substrate by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Rihani, J. [Laboratoire de Photovoltaique et de Semiconducteurs, Centre de Recherche des Sciences et Technologies de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia)], E-mail: rihani_jaouher@yahoo.fr; Ben Sedrine, N. [Laboratoire de Photovoltaique et de Semiconducteurs, Centre de Recherche des Sciences et Technologies de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia); Sallet, V.; Harmand, J.C. [Laboratoire de Photonique et de Nanostructures, CNRS Route de Nozay 91 460 Marcoussis (France); Oueslati, M. [Unite nanoelectronique Faculte des Sciences de Tunis, Campus Universitaire, Elmanar 2092 Tunis (Tunisia); Chtourou, R. [Laboratoire de Photovoltaique et de Semiconducteurs, Centre de Recherche des Sciences et Technologies de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia)

    2008-07-01

    InAs(Sb) quantum dots (QDs) samples were grown on GaAs (001) substrate by Molecular Beam Epitaxy (MBE). The structural characterization by Atomic Force Microscopy (AFM) of samples shows that InAsSb islands size increases strongly with antimony incorporation in InAs/GaAs QDs and decreases with reducing the growth temperature from 520 deg. C to 490 deg. C. Abnormal optical behaviour was observed in room temperature (RT) photoluminescence (PL) spectra of samples grown at high temperature (520 deg. C). Temperature dependent PL study was investigated and reveals an anomalous evolution of emission peak energy (EPE) of InAsSb islands, well-known as 'S-inverted curve' and attributed to the release of confined carriers from the InAsSb QDs ground states to the InAsSb wetting layer (WL) states. With only decreasing the growth temperature, the S-inverted shape was suppressed indicating a fulfilled 3D-confinement of carriers in the InAsSb/GaAs QD sample.

  17. 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.

  18. Piezoelectric InAs (211)B quantum dots grown by molecular beam epitaxy: Structural and optical properties

    International Nuclear Information System (INIS)

    The structural and optical properties of piezoelectric (211)B InAs nanostructures grown by molecular beam epitaxy are systematically investigated as a function of the various growth parameters. Depending on the specific growth conditions, we show that the InAs nanostructures take the form of a quantum dot (QD) or a quantum dash, their height ranges between 2 and 20 nm, and their density varies from a few times 108 cm-2 all the way up to a few times 1010 cm-2. The (211)B QDs are characterized by large aspect ratios, which are compatible with a truncated pyramid morphology. By analyzing the QD emission spectrum, we conclude that only small size QDs, with heights less than 3 nm, are optically active. This is consistent with high resolution transmission electron microscopy observations showing that large QDs contain misfit dislocations, whereas small QDs are dislocation-free. The formation of a two-dimensional wetting layer is observed optically, and its thickness is determined to be between 0.30 and 0.39 nm. Finally, the large blueshift in the QD emission observed with increasing excitation power represents a clear evidence of the strong built-in piezoelectric field present in these dots.

  19. Fabrication of Fe3Si/CaF2 heterostructures ferromagnetic resonant tunneling diode by selected-area molecular beam epitaxy

    International Nuclear Information System (INIS)

    We have fabricated 200-nm-diameter ferromagnetic resonant tunneling diodes (FM-RTDs) using CaF2/Fe3Si heterostructures on Si(111) substrates, by selected-area molecular beam epitaxy (MBE) using electron-beam (EB) lithography. Clear negative differential resistances (NDRs) were observed in the current-voltage (I-V) characteristics at room temperature (RT). The reproducibility of the I-V characteristics was greatly improved, and approximately 40% of the FM-RTDs showed clear NDRs at RT.

  20. Fabrication of Fe{sub 3}Si/CaF{sub 2} heterostructures ferromagnetic resonant tunneling diode by selected-area molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Sadakuni-Makabe, Kenji; Suzuno, Mitsushi; Harada, Kazunori [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8573 (Japan); Suemasu, Takashi, E-mail: suemasu@bk.tsukuba.ac.jp [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8573 (Japan); Akinaga, Hiro [Nanodevice Innovation Research Center and Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568 (Japan)

    2011-10-03

    We have fabricated 200-nm-diameter ferromagnetic resonant tunneling diodes (FM-RTDs) using CaF{sub 2}/Fe{sub 3}Si heterostructures on Si(111) substrates, by selected-area molecular beam epitaxy (MBE) using electron-beam (EB) lithography. Clear negative differential resistances (NDRs) were observed in the current-voltage (I-V) characteristics at room temperature (RT). The reproducibility of the I-V characteristics was greatly improved, and approximately 40% of the FM-RTDs showed clear NDRs at RT.

  1. 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.

  2. Quantitative analysis of the epitaxial recrystallization effect induced by swift heavy ions in silicon carbide

    Science.gov (United States)

    Benyagoub, A.

    2015-12-01

    This paper discusses recent results on the recrystallization effect induced by swift heavy ions (SHI) in pre-damaged silicon carbide. The recrystallization kinetics was followed by using increasing SHI fluences and by starting from different levels of initial damage within the SiC samples. The quantitative analysis of the data shows that the recrystallization rate depends drastically on the local amount of crystalline material: it is nil in fully amorphous regions and becomes more significant with increasing amount of crystalline material. For instance, in samples initially nearly half-disordered, the recrystallization rate per incident ion is found to be 3 orders of magnitude higher than what it is observed with the well-known IBIEC process using low energy ions. This high rate can therefore not be accounted for by the existing IBIEC models. Moreover, decreasing the electronic energy loss leads to a drastic reduction of the recrystallization rate. A comprehensive quantitative analysis of all the experimental results shows that the SHI induced high recrystallization rate can only be explained by a mechanism based on the melting of the amorphous zones through a thermal spike process followed by an epitaxial recrystallization initiated from the neighboring crystalline regions if the size of the latter exceeds a certain critical value. This quantitative analysis also reveals that recent molecular dynamics calculations supposed to reproduce this phenomenon are wrong since they overestimated the recrystallization rate by a factor ∼40.

  3. Direct formation of thin films and epitaxial overlayers at low temperatures using a low-energy (10-500 eV) ion beam deposition system

    International Nuclear Information System (INIS)

    A low-energy ion beam deposition system has been developed at Oak Ridge National Laboratory and has been applied successfully to the growth of epitaxial films at low temperatures for a number of different elements. The deposition system utilizes the ion source and optics of a commercial ion implantation accelerator. The 35 keV mass- and energy-analyzed ion beam from the accelerator is decelerated in a four-element electrostatic lens assembly to energies between 10 and 500 eV for direct deposition onto a target under UHV conditions. Current densities on the order of 10 μA/cm2 are achieved with good uniformity over a 1.4 cm diameter spot. The completed films are characterized by Rutherford backscattering, ion channeling, cross-section transmission electron microscopy, and x-ray diffraction. The effects of substrate temperature, ion energy, and substrate cleaning have been studied. Epitaxial overlayers which show good minimum yields by ion channeling (3 to 4%) have been produced at temperatures as low as 3750C for Si on Si(100) and 2500C for Ge on Ge(100) at growth rates that exceed the solid-phase epitaxy rates at these temperatures by more than an order of magnitude

  4. Characterization and density control of GaN nanodots on Si (111) by droplet epitaxy using plasma-assisted molecular beam epitaxy

    OpenAIRE

    Yu, Ing-Song; Chang, Chun-Pu; Yang, Chung-Pei; Lin, Chun-Ting; Ma, Yuan-Ron; Chen, Chun-Chi

    2014-01-01

    In this report, self-organized GaN nanodots have been grown on Si (111) by droplet epitaxy method, and their density can be controlled from 1.1 × 1010 to 1.1 × 1011 cm-2 by various growth parameters, such as substrate temperatures for Ga droplet formation, the pre-nitridation treatment of Si substrate, the nitridation duration for GaN crystallization, and in situ annealing after GaN formation. Based on the characterization of in situ RHEED, we can observe the surface condition of Si and the f...

  5. Layer by layer growth of BaTiO 3 thin films with extremely smooth surfaces by laser molecular beam epitaxy

    Science.gov (United States)

    Wang, H. S.; Ma, K.; Cui, D. F.; Peng, Z. Q.; Zhou, Y. L.; Lu, H. B.; Chen, Z. H.; Li, L.; Yang, G. Z.

    1997-05-01

    Using pure ozone-assisted laser molecular beam epitaxy, we have grown c-axis-oriented single crystal BaTiO 3 thin films on SrTiO 3 substrates at temperatures ( Ts) of 400-750°C and under ambient gas pressures of 5 × 10 -5 to 1 × 10 -1 Pa, respectively. Stripy reflection high-energy electron diffraction (RHEED) patterns and regular RHEED intensity oscillations reveal the smooth surface and layer-by-layer epitaxial growth of the films. Scanning electron microscopy analysis shows that the films are free of pinholes, grain boundaries and outgrowths on the surface. In addition, we found a strong dependence of the film lattice constant c on Ts, which might be related to the strain in the film.

  6. Electron mobility exceeding 160 000 cm2/V s in AlGaN/GaN heterostructures grown by molecular-beam epitaxy

    International Nuclear Information System (INIS)

    We report on the transport properties of a two-dimensional electron gas (2DEG) confined in an AlGaN/GaN heterostructure grown by plasma-assisted molecular-beam epitaxy on a semi-insulating GaN template prepared by hydride vapor phase epitaxy with a threading dislocation density of ∼5x107 cm-2. Using a gated Hall bar structure, the electron density (ne) is varied from 4.1 to 9.1x1011 cm-2. At T=300 mK, the 2DEG displays a maximum mobility of 167 000 cm2/V s at a sheet density of 9.1x1011 cm-2, corresponding to a mean-free-path of ∼3 μm. Shubnikov-de Haas oscillations, typically not observed at magnetic fields below 2 T in GaN, commence at B=0.6 T

  7. 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.

  8. Glancing-angle ion enhanced surface diffusion on gaAs(001) during molecular beam epitaxy.

    Science.gov (United States)

    DeLuca, P M; Ruthe, K C; Barnett, S A

    2001-01-01

    We describe the effects of glancing incidence 3-4 keV Ar ion bombardment on homoepitaxial growth on vicinal GaAs(001). The average adatom lifetime on surface terraces, measured during growth using specular ion scattering, decreased monotonically with increasing ion current density. The results indicated that surface diffusivity was increased by the ions. The ion beam also suppressed growth oscillations and decreased the film surface roughness. This indicates a change from two-dimensional island nucleation to step-flow growth due to increased adatom surface diffusivity. A simple model, involving direct momentum transfer from ions to adatoms, is shown to be consistent with the measured enhanced diffusion. PMID:11177806

  9. Light emission from particle beam induced plasma - An overview

    CERN Document Server

    Ulrich, A

    2015-01-01

    Experiments to study the light emission from plasma produced by particle beams are presented. Fundamental aspects in comparison with discharge plasma formation are discussed. It is shown that the formation of excimer molecules is an important process. This paper summarizes various studies of particle beam induced light emission and presents first results of a direct comparison of light emission induced by electron- and ion beam excitation. Both high energy heavy ion beam and low energy electron beam experiments are described and an overview over applications in the form of light sources, lasers, and ionization devices is given.

  10. Beam induced damage - what is a safe beam?

    CERN Document Server

    Kain, V; Brugger, M; Sapinski, M

    2009-01-01

    The knowledge of damage levels is vital to define protection schemes, beam loss monitor thresholds, safe beam limits for setting up the machines, etc. This talk will try to revisit our present knowledge and assumptions on damage levels in the LHC in terms of lost beam intensity, beam momentum and emittance. It is clear that with the LHC’s unprecedented energy reach, benchmark tests to cross-check energy deposition simulations for all possible energies before LHC start-up have not been possible. Also, the definition of when equipment is damaged is not always straight forward. In view of the obvious limitations to our knowledge of damage levels, operational commissioning and LHC running strategies will be re-discussed, open questions will be highlighted and proposals will be presented where possible.

  11. Growth and stuctural characterization of InGaN layers with controlled In content prepared by plasma-assisted molecular beam epitaxy

    International Nuclear Information System (INIS)

    InGaN layers with controlled In composition up to 30 at.% are grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. By considering the growth rate differences in GaN and InN caused by different vapor pressure and sticking coefficient, factors of the Ga and In source fluxes for the targeted In composition are determined. By applying the factors, InGaN layers with the almost same In compositions are grown. Before the growth the substrates were nitrided by rf-nitrogen plasma, which resulted in the formation of epitaxial AlN layer. The growth of thin GaN on this AlN surface shows strong streaky reflection high energy electron diffraction pattern with a specular spot, however, InGaN layers on the GaN layer show spotty patterns. Surface morphology of the InGaN layers shows island-like granules and the granule-like morphology is getting clear as the In composition and roughness are increased, too. The InGaN layers with In composition up to 30 at.% do not show formation of InN and only InGaN peaks are detected from the X-ray diffraction. Crystal quality of the InGaN layer with In composition of 15 at.% is worse than that of 30 at.%-In layer as addressed by larger broadening of X-ray rocking curves. - Highlights: ► Growth of InGaN epilayers by molecular beam epitaxy ► InGaN epilayers with In content up to 30 at.% without secondary phase formation. ► Controlled In content to the targeted content from the experimental set-up. ► Nitridation process of sapphire substrate to formed epitaxial AlN layer. ► Growth mode and structural characterization of InGaN layers

  12. Electron-beam-induced conduction in polyethylene

    International Nuclear Information System (INIS)

    The electrical conduction in polyethylene induced by the irradiation of the short-pulsed-electron-beam (100 nsec time width) consists of the fast and the slow components. The former is attributed to the carrier transport in the crystalline part and the latter to that in the amorphous part. Logarithmic plot (Scher-Montroll plot) of the slow part of the induced current vs. time gives a knee at time T sub(r), which is thought to be the transit time of the carrier front between electrodes. Simple calculation by the formula μ = L/T sub(r) E gives the apparent slow carrier mobility μ of 5.6 x 10-7 cm2/V.sec and 3.2 x 10-7 cm2/V.sec for the electron and the hole respectively at 343 K under the field E of 1.2 MV/cm for the sample thickness L of 12 μm. These apparent slow carrier mobilities are dependent on both the thickness and the field strength. These behavior are discussed in terms of Scher-Montroll theory on the transport in amorphous substances. The activation energy of the mobility is in good agreement with the apparent trap depth obtained from the TSC measurement. (author)

  13. Growth and characterization of metamorphic InAs/GaSb tunnel heterojunction on GaAs by molecular beam epitaxy

    Science.gov (United States)

    Liu, Jheng-Sin; Clavel, Michael B.; Pandey, Rahul; Datta, Suman; Meeker, Michael; Khodaparast, Giti A.; Hudait, Mantu K.

    2016-06-01

    The structural, morphological, optical, and electrical transport characteristics of a metamorphic, broken-gap InAs/GaSb p-i-n tunnel diode structure, grown by molecular beam epitaxy on GaAs, were demonstrated. Precise shutter sequences were implemented for the strain-balanced InAs/GaSb active layer growth on GaAs, as corroborated by high-resolution X-ray analysis. Cross-sectional transmission electron microscopy and detailed micrograph analysis demonstrated strain relaxation primarily via the formation of 90° Lomer misfit dislocations (MDs) exhibiting a 5.6 nm spacing and intermittent 60° MDs at the GaSb/GaAs heterointerface, which was further supported by a minimal lattice tilt of 180 arc sec observed during X-ray analysis. Selective area diffraction and Fast Fourier Transform patterns confirmed the full relaxation of the GaSb buffer layer and quasi-ideal, strain-balanced InAs/GaSb heteroepitaxy. Temperature-dependent photoluminescence measurements demonstrated the optical band gap of the GaSb layer. Strong optical signal at room temperature from this structure supports a high-quality material synthesis. Current-voltage characteristics of fabricated InAs/GaSb p-i-n tunnel diodes measured at 77 K and 290 K demonstrated two bias-dependent transport mechanisms. The Shockley-Read-Hall generation-recombination mechanism at low bias and band-to-band tunneling transport at high bias confirmed the p-i-n tunnel diode operation. This elucidated the importance of defect control in metamorphic InAs/GaSb tunnel diodes for the implementation of low-voltage and high-performance tunnel field effect transistor applications.

  14. On the quality of molecular-beam epitaxy grown Fe/MgO and Co/MgO(001) interfaces

    International Nuclear Information System (INIS)

    We investigated in detail the structural, chemical, and magnetic properties of Fe at the interface with MgO. The samples were grown by molecular-beam epitaxy and analyzed by using reflection high-energy electron diffraction, scanning tunneling microscopy, Auger electron spectroscopy, x-ray photoemission spectroscopy (XPS), x-ray-absorption spectroscopy (XAS), and x-ray magnetic circular dichroism (XMCD) measurements. We discuss the presence or absence of C and O contaminants at the surface of the metallic film. We actually show that when growing the first Fe layer on the initial MgO substrate, a carbon contamination at the surface of the annealed Fe layer is observed leading to a C(2x2) surface structure. We propose a method to eliminate this carbon contamination and to get interfaces free of carbon. On the other hand, we observed that the reactivity of the Fe surface to oxygen contamination is greatly influenced by the presence of carbon or absence on the surface. The influence of oxygen adsorption at the Fe surface on the MgO growth will also be discussed. Concerning the hybridization between Fe or Co with MgO, XPS, and XAS-XMCD analyses clearly demonstrate that the charge transfer is weak, and that the magnetization at the interface is larger than in bulk (3μB/at for Fe). With such clean interfaces, reproducible magnetoresistance equal to 160% are obtained on Fe/MgO(3 nm)/Fe(001) 100x100 μm2 tunnel junctions at room temperature in our laboratory. Finally, we show that pollution at the bottom Fe/MgO interface modify drastically spin-dependent tunneling properties

  15. Electrical and photovoltaic properties of CdTe/ZnTe n-i-p junctions grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Preliminary studies have been performed on photoelectrical properties of CdTe/ZnTe n-i-p junctions grown using the molecular beam epitaxy technique. Photovoltaic properties of the cells have been investigated by the measurements of current-voltage (I-V) characteristics under 1-sun illumination. I-V characteristics yield efficiencies of the cells varying from 3.4% to 4.9%. The low efficiency can be due to the presence of electrically active defects. In order to study the origin of defects in CdTe/ZnTe photovoltaic junctions, space charge techniques (C-V and deep level transient spectroscopy (DLTS)) have been applied. From the C-V measurements, a doping profile was calculated confirming charge accumulation in the i-CdTe layer. The results of the DLTS studies revealed the presence of four traps within a temperature range from 77–420 K. Three of them with activation energies equal to 0.22 eV, 0.45 eV, and 0.78 eV have been ascribed to the hole traps present in the i-CdTe material and their possible origin has been discussed. The fourth, high-temperature DLTS peak observed at ∼350 K has been attributed to extended defects as its amplitude and temperature position depends on the value of the filling pulse width. It is assumed that the defects related to the trap are either located in the i-CdTe layer or at the i-CdTe/ZnTe interface. However, it was found that the trap exhibits twofold nature: it behaves as a majority or as a minority trap, depending on the filling pulse height, which is a characteristic feature of recombination centers. This trap is presumably responsible for the low efficiency of the cells.

  16. Localized Si enrichment in coherent self-assembled Ge islands grown by molecular beam epitaxy on (001)Si single crystal

    International Nuclear Information System (INIS)

    Transmission electron microscopy (TEM), atomic force microscopy, and Rutherford backscattering spectrometry (RBS) have been used to investigate the morphology, structure, and composition of self-assembled Ge islands grown on Si (001) substrates by molecular beam epitaxy (MBE) at different temperatures. Increasing the temperature from 550 °C to 700 °C causes progressive size and shape uniformity, accompanied by enhanced Si-Ge intermixing within the islands and their wetting layer. Elemental maps obtained by energy filtered-TEM (EF-TEM) clearly show pronounced Si concentration not only in correspondence of island base perimeters, but also along their curved surface boundaries. This phenomenon is strengthened by an increase of the growth temperature, being practically negligible at 550 °C, while very remarkable already at 650 °C. The resulting island shape is affected, since this localized Si enrichment not only provides strain relief near their highly stressed base perimeters but it also influences the cluster surface energy by effective alloying, so as to form Si-enriched SiGe interfaces. Further increase to 700 °C causes a shape transition where more homogenous Si-Ge concentration profiles are observed. The crucial role played by local “flattened” alloyed clusters, similar to truncated pyramids with larger bases and enhanced Si enrichment at coherently stressed interfaces, has been further clarified by EF-TEM analysis of a multi-layered Ge/Si structure containing stacked Ge islands grown at 650 °C. Sharp accumulation of Si has been here observed not only in proximity of the uncapped island surface in the topmost layer but also at the buried Ge/Si interfaces and even in the core of such capped Ge islands.

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

    International Nuclear Information System (INIS)

    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.

  18. Characterization and process effects of HfO2 thin films grown by metal-organic molecular beam epitaxy

    International Nuclear Information System (INIS)

    HfO2 dielectric layers were grown on the p-type Si(1 0 0) substrate by metal-organic molecular beam epitaxy (MOMBE). Hafnium-tetra-butoxide [Hf(O.t-C4H9)4] was used as a Hf precursor and argon gas was used as a carrier gas. The microstructure and thickness of HfO2 films were measured by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The electrical characteristics of the HfO2 layers were evaluated by high frequency (HF) capacitance-voltage (C-V) and current-voltage (I-V) measurements. The surface morphology, crystal structure, and chemical binding states of HfO2 films were also examined by atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) measurements. HF C-V and I-V measurements have shown that HfO2 layer grown by MOMBE has higher dielectric constant (k) of 20-22 and lower leakage current density of ∼10-8 A/cm2 compared with the conventional SiO2. In addition, it has been shown that the HfO2 layer has fixed oxide charge of about 8 x 1011 cm-2 and interfacial state density of about 1 x 1012 eV-1 cm-2. The electrical characteristics and surface morphology of HfO2 films are affected by O2/Ar gas flow ratio. Finally, post-metallization annealing (PMA) was carried out to reduce the interface state density

  19. Persistent ion beam induced conductivity in zinc oxide nanowires

    OpenAIRE

    Johannes, Andreas; Niepelt, Raphael; Gnauck, Martin; Ronning, Carsten

    2015-01-01

    We report persistently increased conduction in ZnO nanowires irradiated by ion beam with various ion energies and species. This effect is shown to be related to the already known persistent photo conduction in ZnO and dubbed persistent ion beam induced conduction. Both effects show similar excitation efficiency, decay rates, and chemical sensitivity. Persistent ion beam induced conduction will potentially allow countable (i.e., single dopant) implantation in ZnO nanostructures and other mater...

  20. Silicon sample holder for molecular beam epitaxy on pre-fabricated integrated circuits

    Science.gov (United States)

    Hoenk, Michael E. (Inventor); Grunthaner, Paula J. (Inventor); Grunthaner, Frank J. (Inventor)

    1994-01-01

    The sample holder of the invention is formed of the same semiconductor crystal as the integrated circuit on which the molecular beam expitaxial process is to be performed. In the preferred embodiment, the sample holder comprises three stacked micro-machined silicon wafers: a silicon base wafer having a square micro-machined center opening corresponding in size and shape to the active area of a CCD imager chip, a silicon center wafer micro-machined as an annulus having radially inwardly pointing fingers whose ends abut the edges of and center the CCD imager chip within the annulus, and a silicon top wafer micro-machined as an annulus having cantilevered membranes which extend over the top of the CCD imager chip. The micro-machined silicon wafers are stacked in the order given above with the CCD imager chip centered in the center wafer and sandwiched between the base and top wafers. The thickness of the center wafer is about 20% less than the thickness of the CCD imager chip. Preferably, four titanium wires, each grasping the edges of the top and base wafers, compress all three wafers together, flexing the cantilever fingers of the top wafer to accommodate the thickness of the CCD imager chip, acting as a spring holding the CCD imager chip in place.

  1. Suppression of planar defects in the molecular beam epitaxy of GaAs/ErAs/GaAs heterostructures

    International Nuclear Information System (INIS)

    We present a growth method that overcomes the mismatch in rotational symmetry of ErAs and conventional III-V semiconductors, allowing for epitaxially integrated semimetal/semiconductor heterostructures. Transmission electron microscopy and reflection high-energy electron diffraction reveal defect-free overgrowth of ErAs layers, consisting of >2x the total amount of ErAs that can be embedded with conventional layer-by-layer growth methods. We utilize epitaxial ErAs nanoparticles, overgrown with GaAs, as a seed to grow full films of ErAs. Growth proceeds by diffusion of erbium atoms through the GaAs spacer, which remains registered to the underlying substrate, preventing planar defect formation during subsequent GaAs growth. This growth method is promising for metal/semiconductor heterostructures that serve as embedded Ohmic contacts to epitaxial layers and epitaxially integrated active plasmonic devices.

  2. Epitaxy physical principles and technical implementation

    CERN Document Server

    Herman, Marian A; Sitter, Helmut

    2004-01-01

    Epitaxy provides readers with a comprehensive treatment of the modern models and modifications of epitaxy, together with the relevant experimental and technological framework. This advanced textbook describes all important aspects of the epitaxial growth processes of solid films on crystalline substrates, including a section on heteroepitaxy. It covers and discusses in details the most important epitaxial growth techniques, which are currently widely used in basic research as well as in manufacturing processes of devices, namely solid-phase epitaxy, liquid-phase epitaxy, vapor-phase epitaxy, including metal-organic vapor-phase epitaxy and molecular-beam epitaxy. Epitaxy’s coverage of science and texhnology thin-film is intended to fill the need for a comprehensive reference and text examining the variety of problems related to the physical foundations and technical implementation of epitaxial crystallization. It is intended for undergraduate students, PhD students, research scientists, lecturers and practic...

  3. Native defect induced charge and ferromagnetic spin ordering and coexisting electronic phases in CoO epitaxial thin film

    Science.gov (United States)

    Negi, D. S.; Loukya, B.; Datta, R.

    2015-12-01

    We report on the observation of Co vacancy (VCo) induced charge ordering and ferromagnetism in CoO epitaxial thin film. The ordering is associated with the coexistence of commensurate, incommensurate, and discommensurate electronic phases. Density functional theory calculation indicates the origin of ordering in Co atoms undergoing high spin to low spin transition immediately surrounding the VCo(16.6 at. %). Electron magnetic chiral dichroism experiment confirms the ferromagnetic signal at uncompensated Co spins. Such a native defects induced coexistence of different electronic phases at room temperature in a simple compound CoO is unique and adds to the richness of the field with the possibility of practical device application.

  4. A six-circle diffractometer system for synchrotron X-ray studies of surfaces and thin film growth by molecular beam epitaxy

    International Nuclear Information System (INIS)

    A new ultrahigh vacuum (UHV) surface diffractometer system equipped with molecular beam epitaxy (MBE) capabilities has been developed. It has a versatile 6-circle configuration for defining the diffraction geometry, and a three-axis translation stage for controlling the sample position. Rugged mechanical components are employed in the design to allow accurate diffraction measurements. Sample cooling is facilitated by passing liquid nitrogen into a reservoir in the base of a sample mount. The sample can be heated to very high temperatures by either direct current heating or electron beam bombardment. During film growth and processing, the sample temperature, monitored by thermocouples, can be continuously and rapidly varied between ∼110 K to above room temperature. A charge coupled device (CCD) camera, attached to the μ circle, allows rapid reciprocal space mapping for real time studies of sample growth and evolution during deposition and annealing. A beam stop and a baffle are implemented to minimize stray scattered radiation

  5. 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.

  6. Surface effects of vapour-liquid-solid driven Bi surface droplets formed during molecular-beam-epitaxy of GaAsBi

    Science.gov (United States)

    Steele, J. A.; Lewis, R. A.; Horvat, J.; Nancarrow, M. J. B.; Henini, M.; Fan, D.; Mazur, Y. I.; Schmidbauer, M.; Ware, M. E.; Yu, S.-Q.; Salamo, G. J.

    2016-01-01

    Herein we investigate a (001)-oriented GaAs1−xBix/GaAs structure possessing Bi surface droplets capable of catalysing the formation of nanostructures during Bi-rich growth, through the vapour-liquid-solid mechanism. Specifically, self-aligned “nanotracks” are found to exist trailing the Bi droplets on the sample surface. Through cross-sectional high-resolution transmission electron microscopy the nanotracks are revealed to in fact be elevated above surface by the formation of a subsurface planar nanowire, a structure initiated mid-way through the molecular-beam-epitaxy growth and embedded into the epilayer, via epitaxial overgrowth. Electron microscopy studies also yield the morphological, structural, and chemical properties of the nanostructures. Through a combination of Bi determination methods the compositional profile of the film is shown to be graded and inhomogeneous. Furthermore, the coherent and pure zincblende phase property of the film is detailed. Optical characterisation of features on the sample surface is carried out using polarised micro-Raman and micro-photoluminescence spectroscopies. The important light producing properties of the surface nanostructures are investigated through pump intensity-dependent micro-PL measurements, whereby relatively large local inhomogeneities are revealed to exist on the epitaxial surface for important optical parameters. We conclude that such surface effects must be considered when designing and fabricating optical devices based on GaAsBi alloys. PMID:27377213

  7. 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

    Science.gov (United States)

    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.

  8. Direct growth of hexagonal InN films on 6H-SiC by radio-frequency metal-organic molecular-beam epitaxy

    International Nuclear Information System (INIS)

    Wurtzite InN films were prepared on a 6H-SiC substrate by a self-designed plasma-assisted metal-organic molecular-beam epitaxy system without a buffer layer. In this article, the authors investigate the structural and optical properties of InN films grown on a 6H-SiC substrate. The crystallinity and microstructure of the thin film were further characterized by x-ray diffraction (XRD), field-emission scanning-electron microscopy, and transmission-electron microscopy. Electrical and optical properties were evaluated by Hall and photoluminescence (PL) measurements. XRD results indicate that InN film grown at 500 deg. C is epitaxially grown along the c-axis orientation. The two-dimensional growth mode is clearly shown in scanning-electron microscope images. Room-temperature PL spectra show that the emission peak is located at ∼0.83 eV due to the Burstein-Moss effect. In addition, the crystalline InN samples crack and peel away from the substrate at elevated growth temperature. This phenomenon may be attributed to lattice mismatch and grain coalescence while increasing the growth temperature. The narrow window of the growth temperature plays an important role in engineering the InN epitaxial growth.

  9. Surface effects of vapour-liquid-solid driven Bi surface droplets formed during molecular-beam-epitaxy of GaAsBi

    Science.gov (United States)

    Steele, J. A.; Lewis, R. A.; Horvat, J.; Nancarrow, M. J. B.; Henini, M.; Fan, D.; Mazur, Y. I.; Schmidbauer, M.; Ware, M. E.; Yu, S.-Q.; Salamo, G. J.

    2016-07-01

    Herein we investigate a (001)-oriented GaAs1‑xBix/GaAs structure possessing Bi surface droplets capable of catalysing the formation of nanostructures during Bi-rich growth, through the vapour-liquid-solid mechanism. Specifically, self-aligned “nanotracks” are found to exist trailing the Bi droplets on the sample surface. Through cross-sectional high-resolution transmission electron microscopy the nanotracks are revealed to in fact be elevated above surface by the formation of a subsurface planar nanowire, a structure initiated mid-way through the molecular-beam-epitaxy growth and embedded into the epilayer, via epitaxial overgrowth. Electron microscopy studies also yield the morphological, structural, and chemical properties of the nanostructures. Through a combination of Bi determination methods the compositional profile of the film is shown to be graded and inhomogeneous. Furthermore, the coherent and pure zincblende phase property of the film is detailed. Optical characterisation of features on the sample surface is carried out using polarised micro-Raman and micro-photoluminescence spectroscopies. The important light producing properties of the surface nanostructures are investigated through pump intensity-dependent micro-PL measurements, whereby relatively large local inhomogeneities are revealed to exist on the epitaxial surface for important optical parameters. We conclude that such surface effects must be considered when designing and fabricating optical devices based on GaAsBi alloys.

  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. New structure of three-terminal GaAs p(+)-n(-)-delta(p+)-n(-)-n(+) switching device prepared by molecular beam epitaxy

    Science.gov (United States)

    Wang, Y. H.; Yarn, K. F.; Chang, C. Y.; Jame, M. S.

    1987-08-01

    A new three-terminal GaAs p(+)-n(-)-delta(p+)-n(-)-n(+), voltage-controlled switching device grown by molecular beam epitaxy is presented. A simple method to contact the third terminal is employed by applying the Au-Zn to the delta(p+) barrier using the B-groove etching technique, in which the delta(p+) barrier height can be directly modulated by the external voltage. The device may be more effective than other voltage-controlled devices due to the direct barrier modulation.

  12. Incorporation model of N into GaInNAs alloys grown by radio-frequency plasma-assisted molecular beam epitaxy

    International Nuclear Information System (INIS)

    We present a Maxwell-Boltzmann electron energy distribution based model for the incorporation rate of nitrogen into GaInNAs grown by molecular beam epitaxy (MBE) using a radio frequency plasma source. Nitrogen concentration is predicted as a function of radio-frequency system primary resistance, N flow, and RF power, and group III growth rate. The semi-empirical model is shown to be repeatable with a maximum error of 6%. The model was validated for two different MBE systems by growing GaInNAs on GaAs(100) with variable nitrogen composition of 0%–6%

  13. Materials and tunneling characteristics of HTSC Y1Ba2Cu3O7-x thin films by molecular beam epitaxy

    International Nuclear Information System (INIS)

    The capability of developing an efficient activated oxygen source in conjunction with molecular beam epitaxy has led to successful thin film synthesis of Y1Ba2Cu3O7-x high temperature superconductors. The smooth morphology and well ordered surface structures of these in-situ grown films allow to conduct superconducting tunneling experiments directly in a planar junction mode. The authors review in this paper in-situ film growth, materials and superconducting properties, and quasi particle tunneling characteristics of Y1Ba2Cu3O7-x/native barrier/Pb junctions

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

    OpenAIRE

    Yuryev Vladimir; Arapkina Larisa

    2011-01-01

    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 temper...

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

    International Nuclear Information System (INIS)

    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 107 cm–2 and a root mean square roughness of less than 1 nm are obtained

  16. 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.

  17. Surface photo-voltage characterization of GaAs/AlGaAs single quantum well laser structures grown by molecular beam epitaxy

    Science.gov (United States)

    Muralidharan, R.; Ramesh, V.; Mishra, Puspashree; Srinivasan, T.

    2014-03-01

    We present surface photo-voltage (SPV) measurements on molecular beam epitaxy (MBE) grown single quantum well (SQW) laser structures. Each layer in the hetero-structure has been identified by measurement of the SPV signal after a controlled sequential chemical etching process. These results have been correlated with high resolution x-ray diffraction and photoluminescence (PL) measurements. Quantum confined Stark effect and the carrier screening of electric field have been taken into consideration both theoretically and experimentally to account for the differences observed in SPV and PL results. It is shown that SPV can be used as a very effective tool for evaluation of hetero-structures involving multiple layers.

  18. Surface photo-voltage characterization of GaAs/AlGaAs single quantum well laser structures grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    We present surface photo-voltage (SPV) measurements on molecular beam epitaxy (MBE) grown single quantum well (SQW) laser structures. Each layer in the hetero-structure has been identified by measurement of the SPV signal after a controlled sequential chemical etching process. These results have been correlated with high resolution x-ray diffraction and photoluminescence (PL) measurements. Quantum confined Stark effect and the carrier screening of electric field have been taken into consideration both theoretically and experimentally to account for the differences observed in SPV and PL results. It is shown that SPV can be used as a very effective tool for evaluation of hetero-structures involving multiple layers. (paper)

  19. High-efficiency GaAs and GaInP solar cells grown by all solid-state molecular-beam-epitaxy

    OpenAIRE

    Lu, Shulong; Ji, Lian; He, Wei; Dai, Pan; Yang, Hui; Arimochi, Masayuki; Yoshida, Hiroshi; Uchida, Shiro; Ikeda, Masao

    2011-01-01

    We report the initial results of GaAs and GaInP solar cells grown by all solid-state molecular-beam-epitaxy (MBE) technique. For GaAs single-junction solar cell, with the application of AlInP as the window layer and GaInP as the back surface field layer, the photovoltaic conversion efficiency of 26% at one sun concentration and air mass 1.5 global (AM1.5G) is realized. The efficiency of 16.4% is also reached for GaInP solar cell. Our results demonstrate that the MBE-grown phosphide-contained ...

  20. Room temperature weak ferromagnetism in Sn1−xMnxSe2 2D films grown by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Sining Dong

    2016-03-01

    Full Text Available We discuss growth and magnetic properties of high-quality two dimensional (2D Sn1−xMnxSe2 films. Thin films of this 2D ternary alloy with a wide range of Mn concentrations were successfully grown by molecular beam epitaxy. Mn concentrations up to x ≈ 0.60 were achieved without destroying the crystal structure of the parent SnSe2 2D system. Most important, the specimens show clear weak ferromagnetic behavior above room temperature, which should be of interest for 2D spintronic applications.

  1. Electron beam induced modification of grafted polyamides

    International Nuclear Information System (INIS)

    It is well known that irradiation, when applied on its own or in combination with other physical and chemical treatments, can manifest in radiation damage to materials. Radiation processing technology focuses upon producing favourable modification of materials through use of relatively high dose and dose rates. Current interest is in modifying the thermal and electrical properties of textured polymers in an effort to improve safety and wear comfort of clothing. No less important is the production of textiles which are safe to use, both in homes and offices. Present investigations provide additional data in support of findings which show that polyamides, a particular class of textured polymer, are amenable to radiation processing. Accelerated electron beam irradiation of sheets of polyamide fibre results in induced grafting of acrylic and methacrylic acids. The degree of grafting is critically dependent upon irradiation dose and the extent of monomers dilution. Of particular importance is the high correlation which is found between degree of grafting and a decrease in the softening rate of the modified polyamide. A systematic modification of electrical conductivity is also observed. (author)

  2. First results for custom-built low-temperature (4.2 K) scanning tunneling microscope/molecular beam epitaxy and pulsed laser epitaxy system designed for spin-polarized measurements

    Science.gov (United States)

    Foley, Andrew; Alam, Khan; Lin, Wenzhi; Wang, Kangkang; Chinchore, Abhijit; Corbett, Joseph; Savage, Alan; Chen, Tianjiao; Shi, Meng; Pak, Jeongihm; Smith, Arthur

    2014-03-01

    A custom low-temperature (4.2 K) scanning tunneling microscope system has been developed which is combined directly with a custom molecular beam epitaxy facility (and also including pulsed laser epitaxy) for the purpose of studying surface nanomagnetism of complex spintronic materials down to the atomic scale. For purposes of carrying out spin-polarized STM measurements, the microscope is built into a split-coil, 4.5 Tesla superconducting magnet system where the magnetic field can be applied normal to the sample surface; since, as a result, the microscope does not include eddy current damping, vibration isolation is achieved using a unique combination of two stages of pneumatic isolators along with an acoustical noise shield, in addition to the use of a highly stable as well as modular `Pan'-style STM design with a high Q factor. First 4.2 K results reveal, with clear atomic resolution, various reconstructions on wurtzite GaN c-plane surfaces grown by MBE, including the c(6x12) on N-polar GaN(0001). Details of the system design and functionality will be presented.

  3. Scrape-off layer-induced beam density fluctuations and their effect on beam emission spectroscopy

    Science.gov (United States)

    Moulton, D.; Marandet, Y.; Tamain, P.; Dif-Pradalier, G.

    2015-07-01

    A statistical model is presented to calculate the magnitude of beam density fluctuations generated by a turbulent scrape-off layer (SOL). It is shown that the SOL can induce neutral beam density fluctuations of a similar magnitude to the plasma density fluctuations in the core, potentially corrupting beam emission spectroscopy measurements. The degree of corruption is quantified by combining simulations of beam and plasma density fluctuations inside a simulated measurement window. A change in pitch angle from the separatrix to the measurement window is found to reduce the effect of beam fluctuations, whose largest effect is to significantly reduce the measured correlation time.

  4. Nanostructure formation during relatively high temperature growth of Mn-doped GaAs by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Del Río-De Santiago, A.; Méndez-García, V.H. [CIACyT-UASLP, Sierra Leona Av. # 550, Lomas 2a Secc, San Luis Potosí, S.L.P. 78210, México (Mexico); Martínez-Velis, I.; Casallas-Moreno, Y.L. [Physics Department, CINVESTAV-IPN, Apdo. Postal 14470 D. F. México, México (Mexico); López-Luna, E. [CIACyT-UASLP, Sierra Leona Av. # 550, Lomas 2a Secc, San Luis Potosí, S.L.P. 78210, México (Mexico); Yu Gorbatchev, A. [IICO-UASLP, Av. Karakorum 1470, Lomas 4a. Sección, San Luis Potosí, S.L.P. 78210, México (Mexico); López-López, M. [Physics Department, CINVESTAV-IPN, Apdo. Postal 14470 D. F. México, México (Mexico); Cruz-Hernández, E., E-mail: esteban.cruz@uaslp.mx [CIACyT-UASLP, Sierra Leona Av. # 550, Lomas 2a Secc, San Luis Potosí, S.L.P. 78210, México (Mexico)

    2015-04-01

    Highlights: • The formation of different kind of nanostructures in GaMnAs layers depending on Mn concentration at relative HT-MBE is reported. In this Mn% range, it is found the formation of nanogrooves, nanoleaves, and nanowires. • It is shown the progressive photoluminescence transitions from purely GaAsMn zinc blende (for Mn% = 0.01) to a mixture of zinc blende and wurtzite GaAsMn (for Mn% = 0.2). • A critical thickness for the Mn catalyst effect was determined by RHEED. - Abstract: In the present work, we report on molecular beam epitaxy growth of Mn-doped GaAs films at the relatively high temperature (HT) of 530 °C. We found that by increasing the Mn atomic percent, Mn%, from 0.01 to 0.2, the surface morphology of the samples is strongly influenced and changes from planar to corrugated for Mn% values from 0.01 to 0.05, corresponding to nanostructures on the surface with dimensions of 200–300 nm and with the shape of leave, to nanowire-like structures for Mn% values above 0.05. From reflection high-energy electron diffraction patterns, we observed the growth mode transition from two- to three-dimensional occurring at a Mn% exceeding 0.05. The optical and electrical properties were obtained from photoluminescence (PL) and Hall effect measurements, respectively. For the higher Mn concentration, besides the Mn related transitions at approximately 1.41 eV, PL spectra sharp peaks are present between 1.43 and 1.49 eV, which we related to the coexistence of zinc blende and wurtzite phases in the nanowire-like structures of this sample. At Mn% of 0.04, an increase of the carrier mobility up to a value of 1.1 × 10{sup 3} cm{sup 2}/Vs at 77 K was found, then decreases as Mn% is further increased due to the strengthening of the ionized impurity scattering.

  5. Sharpness changes of gaussian beams induced by spherically aberrated lenses

    Science.gov (United States)

    Piquero, G.; Mejías, P. M.; Martínez-Herrero, R.

    1994-04-01

    Sharpness changes of the spatial profile of a gaussian beam induced by spherically aberrated lenses are investigated in terms of the so-called kurtosis parameter. It is shown both theoretically and experimentally that, after a single aberrated lens, it is possible to get flatter and sharper beam intensity distributions than the input gaussian beam depending on the plane where the field is observed. Agreement between analytical and experimental results is discussed.

  6. Pile-up reduction by detector-induced beam suppression

    International Nuclear Information System (INIS)

    The technique of detector-induced beam suppression using a beam deflector and a high power pulse generator has been explored. The γ spectra of the 98Mo(α,xn) reactions are presented with and without beam suppression and it is seen that with the pile-up reduction system working, there is a considerable increase in the count rate in the 98Rn 653 keV peak, with almost the same background. (C.F.)

  7. Interfacial Exchange Coupling Induced Anomalous Anisotropic Magnetoresistance in Epitaxial γ′-Fe 4 N/CoN Bilayers

    KAUST Repository

    Li, Zirun

    2015-02-02

    Anisotropic magnetoresistance (AMR) of the facing-target reactively sputtered epitaxial γ′-Fe4N/CoN bilayers is investigated. The phase shift and rectangular-like AMR appears at low temperatures, which can be ascribed to the interfacial exchange coupling. The phase shift comes from the exchange bias (EB) that makes the magnetization lag behind a small field. When the γ′-Fe4N thickness increases, the rectangular-like AMR appears. The rectangular-like AMR should be from the combined contributions including the EB-induced unidirectional anisotropy, intrinsic AMR of γ′-Fe4N layer and interfacial spin scattering.

  8. Mechanistic studies of electron beam induced organic reactions for electron beam resist materials

    International Nuclear Information System (INIS)

    Triphenylsulfonium methanesulfonate in the solid state was irradiated with an electron beam and the radiolytic products were characterized spectroscopically and chromatographically. The electron beam irradiation of the salt offered a new benzene-substituted sulfonium salt, together with methanesulfonic acids, diphenyl sulfides, and 2-, 3- and 4-phenylthiobyphenyls known as photoproducts of triphenylsulfonium salts. The formation of the salt appears to be due to the nature of electron beam induced reactions. (author)

  9. On the use of a O{sub 2}:SF{sub 6} plasma treatment on GaAs processed surfaces for molecular beam epitaxial regrowth

    Energy Technology Data Exchange (ETDEWEB)

    Desplats, O.; Gallo, P.; Doucet, J.B. [LAAS, CNRS, Universite de Toulouse, 7 avenue du Colonel Roche, F-31077 Toulouse Cedex 4 (France); Monier, G.; Bideux, L. [LASMEA, Universite de Clermont II, Campus des Cezeaux-24, Avenue des Landais, F-63177 AUBIERE Cedex (France); Jalabert, L.; Arnoult, A.; Lacoste, G. [LAAS, CNRS, Universite de Toulouse, 7 avenue du Colonel Roche, F-31077 Toulouse Cedex 4 (France); Armand, C.; Voillot, F. [INSA, Universite de Toulouse, Departement de Genie Physique, 135 avenue de Rangueil, F-31077 Toulouse Cedex 4 (France); Fontaine, C. [LAAS, CNRS, Universite de Toulouse, 7 avenue du Colonel Roche, F-31077 Toulouse Cedex 4 (France)], E-mail: fontaine@laas.fr

    2009-01-01

    Preparation of processed GaAs surface cleaning in view of molecular beam epitaxy regrowth by means of a O{sub 2}SF{sub 6} microwave plasma has been investigated. Photoemission, Auger electron spectroscopy, atomic force microscopy and secondary ion mass spectrometry have been used for characterization. The O{sub 2}SF{sub 6} plasma treatment was found to be very efficient for decontaminating the GaAs surface and leads to the formation of an oxide layer that can be taken off by a thermal or low-temperature H-plasma-assisted deoxidation. The levels of oxygen and carbon contaminants at the regrowth interface were measured to be in the range of a standard homoepitaxial layer-epiready substrate interface. Fluorine was observed to be eliminated upon deoxidation while sulphur is present, particularly in the case of low temperature grown layers. This plasma treatment was found to be efficient for preparation of processed GaAs surfaces for molecular beam epitaxial regrowth.

  10. Optimization of VI/II pressure ratio in ZnTe growth on GaAs(0 0 1) by molecular beam epitaxy

    International Nuclear Information System (INIS)

    ZnTe epilayers were grown on GaAs(0 0 1) substrates by molecular beam epitaxy (MBE) at different VI/II beam equivalent pressure (BEP) ratios (RVI/II) in a wide range of 0.96-11 with constant Zn flux. Based on in situ reflection high-energy electron diffraction (RHEED) observation, two-dimensional (2D) growth mode can be formed by increasing the RVI/II to 2.8. The Te/Zn pressure ratios lower than 4.0 correspond to Zn-rich growth state, while the ratios over 6.4 correspond to Te-rich one. The Zn sticking coefficient at various VI/II ratios are derived by the growth rate measurement. The ZnTe epilayer grown at a RVI/II of 6.4 displays the narrowest full-width at half-maximum (FWHM) of double-crystal X-ray rocking curve (DCXRC) for (0 0 4) reflection. Atomic force microscopy (AFM) characterization shows that the grain size enlarges drastically with the RVI/II. The surface root-mean-square (RMS) roughness decreases firstly, attains a minimum of 1.14 nm at a RVI/II of 4.0 and then increases at higher ratios. It is suggested that the most suitable RVI/II be controlled between 4.0 and 6.4 in order to grow high-quality ZnTe epitaxial thin films.

  11. Improving surface smoothness and photoluminescence of CdTe(1 1 1)A on Si(1 1 1) substrates grown by molecular beam epitaxy using Mn atoms

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jyh-Shyang, E-mail: jswang@cycu.edu.tw [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Center for Nano-Technology, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Tsai, Yu-Hsuan; Chen, Chang-Wei; Dai, Zi-Yuan; Tong, Shih-Chang [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Yang, Chu-Shou [Graduate Institute of Electro-Optical Engineering, Tatung University, Taipei 10452, Taiwan (China); Wu, Chih-Hung [Institute of Nuclear Energy Research, Longtan 32546, Taiwan (China); Yuan, Chi-Tsu; Shen, Ji-Lin [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Center for Nano-Technology, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China)

    2014-04-01

    Highlights: • CdTe(1 1 1)A epilayers were grown on Si(1 1 1) substrates by molecular beam epitaxy. • We report an enhanced growth using Mn atoms. • The significant improvements in surface quality and optical properties were found. - Abstract: This work demonstrates an improvement of the molecular beam epitaxial growth of CdTe(1 1 1)A epilayer on Si(1 1 1) substrates using Mn atoms. The reflection high-energy electron diffraction patterns show that the involvement of some Mn atoms in the growth of CdTe(1 1 1)A is even more effective than the use of a buffer layer with a smooth surface for forming good CdTe(1 1 1)A epilayers. 10 K Photoluminescence spectra show that the incorporation of only 2% Mn significantly reduced the intensity of defect-related emissions and considerably increased the integral intensity of exciton-related emissions by a large factor of about 400.

  12. Compensating tune spread induced by space charge in bunched beams

    Energy Technology Data Exchange (ETDEWEB)

    Litvinenko, V.; Wang, G.

    2015-05-03

    The effects of space charge play a significant role in modern-day accelerators, frequently constraining the beam parameters attainable in an accelerator or in an accelerator chain. They also can limit the luminosity of hadron colliders operating either at low energies or with sub-TeV high-brightness hadron beams. The latter is applied for strongly cooled proton and ion beams in eRHIC – the proposed future electron-ion collider at Brookhaven National Laboratory. Using an appropriate electron beam would compensate both the tune shift and the tune spread in the hadron beam in a coasting beam. But these methods cannot compensate space charge tune spread in a bunched hadron beam. In this paper we propose and evaluate a novel idea of using a co-propagating electron bunch with mismatched longitudinal velocity to compensate the space charge induced tune-shift and tune spread.

  13. Helium ion beam induced growth of hammerhead AFM probes

    NARCIS (Netherlands)

    Nanda, G.; Van Veldhoven, E.; Maas, D.; Sadeghian, H.; Alkemade, P.F.A.

    2015-01-01

    The authors report the direct-write growth of hammerhead atomic force microscope(AFM) probes by He+beam induced deposition of platinum-carbon. In order to grow a thin nanoneedle on top of a conventional AFM probe, the authors move a focused He+beam during exposure to a PtC precursor gas. In the fina

  14. Helium ion beam induced growth of hammerhead AFM probes

    NARCIS (Netherlands)

    Nanda, G.; Veldhoven, E. van; Maas, D.J.; Sadeghian Marnani, H.; Alkemade, P.F.A.

    2015-01-01

    The authors report the direct-write growth of hammerhead atomic force microscope (AFM) probes by He+ beam induced deposition of platinum-carbon. In order to grow a thin nanoneedle on top of a conventional AFM probe, the authors move a focused He+ beam during exposure to a PtC precursor gas. In the f

  15. Vacuum ultraviolet laser induced fluorescence on a Si atomic beam

    Science.gov (United States)

    O'Brian, T. R.; Lawler, J. E.

    1991-01-01

    A broadly applicable vacuum ultraviolet experiment is described for measuring radiative lifetimes of neutral and singly-ionized atoms in a beam environment to 5-percent accuracy using laser induced fluorescence. First results for neutral Si are reported.

  16. Hole-induced insulator-to-metal transition in La1-xSrxCrO3 epitaxial films

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Hongliang; Du, Yingge; Sushko, Petr; Bowden, Mark E.; Shutthanandan, V.; Sallis, Shawn; Piper, Louis F. J.; Chambers, Scott A.

    2015-04-01

    We have investigated the evolution of the structural and electronic properties of La1-xSrxCrO3 (0 ≤ x ≤ 1) epitaxial films deposited by molecular beam epitaxy (MBE) using x-ray diffraction, x-ray photoemission spectroscopy, x-ray absorption spectroscopy, electrical transport, and ab initio modeling. LaCrO3 is an antiferromagnetic Mott insulator whereas stoichiometric SrCrO3 is a metal. Substituting Sr2+ for La3+ in LaCrO3 effectively dopes holes into the top of valence band, leading to Cr4+ (3d2) local electron configurations. Core-level and valence-band features monotonically shift to lower binding energy with increasing x, indicating downward movement of the Fermi level toward the valence band maximum. An insulator-to-metal like transition is observed at x ≥ 0. 65 even as the material becomes a p-type semiconductor at lower doping level and eventually becomes degenerately doped. Valence band x-ray photoemission spectroscopy reveals diminution of electronic state density at the top of the valence band while O K-edge x-ray absorption spectroscopy shows the development of a new unoccupied state above the Fermi level as holes are doped into LaCrO3. These results indicate a pronounced redistribution of electronic state density of states upon hole doping, a result that is also obtained by density functional theory with a Hubbard U correction.

  17. Molecular characterization of microbial mutations induced by ion beam irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Ichida, Hiroyuki [Graduate School of Science and Technology, Chiba University, Matsudo, Chiba 271-8510 (Japan); Accelerator Applications Research Group, Nishina Center for Accelerator-Based Science, RIKEN, Wako, Saitama 351-0198 (Japan)], E-mail: ichida@riken.jp; Matsuyama, Tomoki [Cellular Biochemistry Laboratory, Discovery Research Institute, RIKEN, Wako, Saitama 351-0198 (Japan); Ryuto, Hiromichi [Accelerator Operation Group, Nishina Center for Accelerator-Based Science, RIKEN, Wako, Saitama 351-0198 (Japan); Hayashi, Yoriko [Accelerator Applications Research Group, Nishina Center for Accelerator-Based Science, RIKEN, Wako, Saitama 351-0198 (Japan); Fukunishi, Nobuhisa [Accelerator Operation Group, Nishina Center for Accelerator-Based Science, RIKEN, Wako, Saitama 351-0198 (Japan); Abe, Tomoko [Accelerator Applications Research Group, Nishina Center for Accelerator-Based Science, RIKEN, Wako, Saitama 351-0198 (Japan); Koba, Takato [Graduate School of Science and Technology, Chiba University, Matsudo, Chiba 271-8510 (Japan)

    2008-03-01

    A positive selection system for gene disruption using a sucrose-sensitive transgenic rhizobium was established and used for the molecular characterization of mutations induced by ion beam irradiations. Single nucleotide substitutions, insertions, and deletions were found to occur in the sucrose sensitivity gene, sacB, when the reporter line was irradiated with highly accelerated carbon and iron ion beams. In all of the insertion lines, fragments of essentially the same sequence and of approximately 1188 bp in size were identified in the sacB regions. In the deletion lines, iron ions showed a tendency to induce larger deletions than carbon ions, suggesting that higher LET beams cause larger deletions. We found also that ion beams, particularly 'heavier' ion beams, can produce single gene disruptions and may present an effective alternative to transgenic approaches.

  18. The effects of CdCl sub 2 on the electronic properties of molecular-beam epitaxially grown CdTe/CdS heterojunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Ringel, S.A.; Smith, A.W.; MacDougal, M.H.; Rohatgi, A. (School of Electrical Engineering and Microelectronics Research Center, Georgia Institute of Technology, Atlanta, Georgia 30332 (US))

    1991-07-15

    Significant improvements in CdTe/CdS solar cell efficiency are commonly observed as a result of a postdeposition CdCl{sub 2} dip followed by a 400 {degree}C heat treatment during cell processing which increases CdTe grain size. In this paper, we investigate the electronic mechanisms responsible for CdCl{sub 2}-induced improvement in cell performance along with possible performance-limiting defects resulting from this process in molecular-beam epitaxy-grown polycrystalline CdTe/CdS solar cells. Current density-voltage-temperature ({ital J}-{ital V}-{ital T}) analysis revealed that the CdCl{sub 2} treatment changes the dominant current transport mechanism from interface recombination/tunneling to depletion region recombination, suggesting a decrease in the density and dominance of interface states due to the CdCl{sub 2} treatment. It is shown that the change in transport mechanism is associated with (a) an increase in heterojunction barrier height from 0.56 to 0.85 eV, (b) a decrease in dark leakage current from 4.7{times}10{sup {minus}7} A/cm{sup 2} to 2.6{times}10{sup {minus}9} A/cm{sup 2} and, (c) an increase in cell {ital V}{sub oc} from 385 to 720 mV. The CdCl{sub 2} also improved the optical response of the cell. Substantial increases in the surface photovoltage and quantum efficiency accompanied by a decrease in the bias dependence of the spectral response in the CdCl{sub 2}-treated structures indicate that the CdCl{sub 2} treatment improves carrier collection from the bulk as well as across the heterointerface. However, deep level transient spectroscopy measurements detected a hole trap within the CdTe depletion region of the CdCl{sub 2}-treated devices at {ital E}{sub {ital v}} + 0.64 eV which is attributed to the formation of {ital V}{sub Cd}-related defects during the annealing process after the CdCl{sub 2} dip.

  19. The effects of CdCl2 on the electronic properties of molecular-beam epitaxially grown CdTe/CdS heterojunction solar cells

    Science.gov (United States)

    Ringel, S. A.; Smith, A. W.; MacDougal, M. H.; Rohatgi, A.

    1991-07-01

    Significant improvements in CdTe/CdS solar cell efficiency are commonly observed as a result of a postdeposition CdCl2 dip followed by a 400 °C heat treatment during cell processing which increases CdTe grain size. In this paper, we investigate the electronic mechanisms responsible for CdCl2-induced improvement in cell performance along with possible performance-limiting defects resulting from this process in molecular-beam epitaxy-grown polycrystalline CdTe/CdS solar cells. Current density-voltage-temperature (J-V-T) analysis revealed that the CdCl2 treatment changes the dominant current transport mechanism from interface recombination/tunneling to depletion region recombination, suggesting a decrease in the density and dominance of interface states due to the CdCl2 treatment. It is shown that the change in transport mechanism is associated with (a) an increase in heterojunction barrier height from 0.56 to 0.85 eV, (b) a decrease in dark leakage current from 4.7×10-7 A/cm2 to 2.6×10-9 A/cm2 and, (c) an increase in cell Voc from 385 to 720 mV. The CdCl2 also improved the optical response of the cell. Substantial increases in the surface photovoltage and quantum efficiency accompanied by a decrease in the bias dependence of the spectral response in the CdCl2-treated structures indicate that the CdCl2 treatment improves carrier collection from the bulk as well as across the heterointerface. However, deep level transient spectroscopy measurements detected a hole trap within the CdTe depletion region of the CdCl2-treated devices at Ev + 0.64 eV which is attributed to the formation of VCd-related defects during the annealing process after the CdCl2 dip. J-V-T analysis demonstrated that this trap is the probable source of dominant recombination in the CdCl2-treated cells. An inverse correlation was found between the density of the Ev + 0.64 eV trap and cell Voc, suggesting that the heat treatment with CdCl2 may eventually limit the CdTe/CdS cell performance unless the

  20. Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films

    Science.gov (United States)

    Hirai, Kei; Kan, Daisuke; Ichikawa, Noriya; Mibu, Ko; Yoda, Yoshitaka; Andreeva, Marina; Shimakawa, Yuichi

    2015-01-01

    Oxygen coordination of transition metals is a key for functional properties of transition-metal oxides, because hybridization of transition-metal d and oxygen p orbitals determines correlations between charges, spins and lattices. Strain often modifies the oxygen coordination environment and affects such correlations in the oxides, resulting in the emergence of unusual properties and, in some cases, fascinating behaviors. While these strain effects have been studied in many of the fully-oxygenated oxides, such as ABO3 perovskites, those in oxygen-deficient oxides consisting of various oxygen coordination environments like tetrahedra and pyramids as well as octahedra remain unexplored. Here we report on the discovery of a strain-induced significant increase, by 550 K, in the metal-insulator transition temperature of an oxygen-deficient Fe oxide epitaxial thin film. The observed transition at 620 K is ascribed to charge disproportionation of Fe3.66+ into Fe4+ and Fe3+, associated with oxygen-vacancy ordering. The significant increase in the metal-insulator transition temperature, from 70 K in the bulk material, demonstrates that epitaxial growth of oxygen-deficient oxides under substrate-induced strain is a promising route for exploring novel functionality.

  1. Repeatable low-temperature negative-differential resistance from Al0.18Ga0.82N/GaN resonant tunneling diodes grown by molecular-beam epitaxy on free-standing GaN substrates

    Science.gov (United States)

    Li, D.; Tang, L.; Edmunds, C.; Shao, J.; Gardner, G.; Manfra, M. J.; Malis, O.

    2012-06-01

    Low-aluminum composition AlGaN/GaN double-barrier resonant tunneling structures were grown by plasma-assisted molecular-beam-epitaxy on free-standing c-plane GaN substrates grown by hydride-vapor phase epitaxy. Clear, exactly reproducible, negative-differential resistance signatures were observed from 4 × 4 μm2 devices at 1.5 V and 1.7 V at 77 K. The relatively small value of the maximum peak-to-valley ratio (1.03) and the area dependence of the electrical characteristics suggest that charge transport is affected by leakage paths through dislocations. However, the reproducibility of the data indicates that electrical traps play no significant role in the charge transport in resonant tunneling diodes grown by molecular-beam-epitaxy under Ga-rich conditions on free-standing GaN substrates.

  2. Beam-induced quench test of LHC main quadrupole

    CERN Document Server

    Priebe, A; Dehning, B; Effinger, E; Emery, J; Holzer, E B; Kurfuerst, C; Nebot Del Busto, E; Nordt, A; Sapinski, M; Steckert, J; Verweij, A; Zamantzas, C

    2011-01-01

    Unexpected beam loss might lead to a transition of the accelerator superconducting magnet to a normal conducting state. The LHC beam loss monitoring (BLM) system is designed to abort the beam before the energy deposited in the magnet coils reach a quench-provoking level. In order to verify the threshold settings generated by simulation, a series of beam-induced quench tests at various beam energies has been performed. The beam losses are generated by means of an orbital bump peaked in one of main quadrupole magnets (MQ). The analysis includes not only BLM data but also the quench protection system (QPS) and cryogenics data. The measurements are compared to Geant4 simulations of energy deposition inside the coils and corresponding BLM signal outside the cryostat.

  3. Growth of Ge films by cluster beam deposition

    CERN Document Server

    Xu, J L; Feng, J Y

    2002-01-01

    Ge epitaxial layers with reasonable quality were grown on the Si(1 1 1) substrates by cluster beam deposition (CBD) process. The growth temperature plays a dominant role in the epitaxial growth of Ge films. The substrate temperature for epitaxial growth is about 500 deg. C, which is lower than the reported critical temperature of Ge epitaxial growth by MBE and CVD. A stress induced phase transition of Ge lattice from cubic to tetragonal is also observed in the CBD process, and the mechanism is discussed.

  4. Orientational ordering of solution derived epitaxial Gd-doped ceria nanowires induced by nanoscratching

    Energy Technology Data Exchange (ETDEWEB)

    Zabaleta, Jone; Mestres, Narcis; Abellan, Patricia; Gibert, Marta; Sandiumenge, Felip; Puig, Teresa; Obradors, Xavier, E-mail: jzabaleta@icmab.es, E-mail: narcis.mestres@icmab.es [Institut de Ciencia de Materials de Barcelona, ICMAB-CSIC, Campus de la UAB, Bellaterra, 08193 Barcelona, Catalunya (Spain)

    2010-01-15

    When one-dimensional nanostructures are epitaxially grown on a substrate a key goal is to control the nanowire's position and orientation. Nanoscratching of single crystalline (001)- LaAlO{sub 3} substrates is demonstrated to be extraordinarily effective in directing the self-assembly of Ce{sub 0.9}Gd{sub 0.1}O{sub 2-y} epitaxial nanowires grown by chemical solution deposition. The local anisotropic elastic strain field imposed by the indentation lines is responsible for the breaking of the pre-existing orientation energy degeneracy and selects the nanowires' orientation parallel to the lines to an extent that can reach 100%.

  5. Beam induced vacuum measurement error in BEPC II

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    When the beam in BEPCII storage ring aborts suddenly, the measured pressure of cold cathode gauges and ion pumps will drop suddenly and decrease to the base pressure gradually. This shows that there is a beam induced positive error in the pressure measurement during beam operation. The error is the difference between measured and real pressures. Right after the beam aborts, the error will disappear immediately and the measured pressure will then be equal to real pressure. For one gauge, we can fit a non-linear pressure-time curve with its measured pressure data 20 seconds after a sudden beam abortion. From this negative exponential decay pumping-down curve, real pressure at the time when the beam starts aborting is extrapolated. With the data of several sudden beam abortions we have got the errors of that gauge in different beam currents and found that the error is directly proportional to the beam current, as expected. And a linear data-fitting gives the proportion coefficient of the equation, which we derived to evaluate the real pressure all the time when the beam with varied currents is on.

  6. Epitaxial Bi3Fe5O12(001) films grown by pulsed laser deposition and reactive ion beam sputtering techniques

    Science.gov (United States)

    Adachi, N.; Denysenkov, V. P.; Khartsev, S. I.; Grishin, A. M.; Okuda, T.

    2000-09-01

    We report on processing and comparative characterization of epitaxial Bi3Fe5O12 (BIG) films grown onto Gd3(ScGa)5O12[GSGG,(001)] single crystal using pulsed laser deposition (PLD) and reactive ion beam sputtering (RIBS) techniques. A very high deposition rate of about 0.8 μm/h has been achieved in the PLD process. Comprehensive x-ray diffraction analyses reveal epitaxial quality both of the films: they are single phase, exclusively (001) oriented, the full width at half maximum of the rocking curve of (004) Bragg reflection is 0.06 deg for PLD and 0.05 deg for RIBS film, strongly in-plane textured with cube-on-cube film-to-substrate epitaxial relationship. Saturation magnetization 4πMs and Faraday rotation at 635 nm were found to be 1400 Gs and -7.8 deg/μm in PLD-BIG, and 1200 Gs and -6.9 deg/μm in RIBS-BIG. Ferromagnetic resonance (FMR) measurements performed at 9.25 GHz yielded the gyromagnetic ratio γ=1.797×107l/s Oe, 1.826×107 l/s Oe; the constants of uniaxial magnetic anisotropy were Ku*=-8.66×104erg/cm3, -8.60×104 erg/cm3; the cubic magnetic anisotropy K1=-2.7×103 erg/cm3,-3.8×103 erg/cm3; and the FMR linewidth ΔH=25 and 34 Oe for PLD and RIBS films correspondingly. High Faraday rotation, low microwave loss, and low coercive field ⩽40 Oe of BIG/GSGG(001) films promise their use in integrated magneto-optic applications.

  7. Plasma-assisted molecular beam epitaxy of strain-compensated a-plane InGaN/AlGaN superlattices

    International Nuclear Information System (INIS)

    Strain-compensated InGaN/AlGaN structures can enable the growth of thick layers of InGaN epitaxial films far beyond the critical thickness for InGaN grown pseudomorphically to GaN. In this paper, we demonstrate the epitaxial growth of high-quality strain-compensated a-plane In0.12Ga0.88N/Al0.19Ga0.81N superlattices up to 5 times thicker than the critical thickness on free-standing a-plane GaN substrates by plasma-assisted molecular beam epitaxy (PA-MBE). The superlattices consist of 50 to 200 periods of 10 nm thick In0.12Ga0.88N and 6 nm thick Al0.19Ga0.81N layers. The structures are characterized using a double crystal X-ray diffractometer, asymmetric reciprocal space mapping, and atomic force microscopy. We use X-ray diffraction to determine the strain, composition, degree of relaxation, and superlattice period of our samples. The structural characteristics of periodic structures containing from 50 to 200 periods are compared to single layer, uncompensated In0.12Ga0.88N films. A 100 period structure exhibited only 15% relaxation compared to 69% relaxation for the bulk In0.12Ga0.88N film grown with the same total InGaN thickness but without strain-compensating layers. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Experimental results on radiation induced bulk damage effects in float-zone and epitaxial silicon detectors

    Energy Technology Data Exchange (ETDEWEB)

    Dezillie, B. [European Organization for Nuclear Research, Geneva (Switzerland); Lemeilleur, F. [European Organization for Nuclear Research, Geneva (Switzerland); Glaser, M. [European Organization for Nuclear Research, Geneva (Switzerland); Casse, G.-L. [European Organization for Nuclear Research, Geneva (Switzerland); Leroy, C. [Montreal Univ., PQ (Canada)

    1997-02-11

    A comparative study of the radiation hardness of silicon pad detectors, manufactured from float-zone and epitaxial n-type monocrystals and irradiated with protons and neutrons up to fluence of 3.5 x 10{sup 14} cm{sup -2} is presented. The results are compared in terms of their reverse current, depletion voltage, and charge collection as a function of fluence during irradiation and as a function of time after irradiation. (orig.).

  9. Focused-ion-beam induced damage in thin films of complex oxide BiFeO3

    Directory of Open Access Journals (Sweden)

    W. Siemons

    2014-02-01

    Full Text Available An unexpected, strong deterioration of crystal quality is observed in epitaxial perovskite BiFeO3 films in which microscale features have been patterned by focused-ion-beam (FIB milling. Specifically, synchrotron x-ray microdiffraction shows that the damaged region extends to tens of μm, but does not result in measureable changes to morphology or stoichiometry. Therefore, this change would go undetected with standard laboratory equipment, but can significantly influence local material properties and must be taken into account when using a FIB to manufacture nanostructures. The damage is significantly reduced when a thin metallic layer is present on top of the film during the milling process, clearly indicating that the reduced crystallinity is caused by ion beam induced charging.

  10. Al precipitate evolution in epitaxial silicon layers induced by thermal oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Rimini, E.; Galvagno, G.; La Ferla, A. [dell`Universita di Catania (Italy)] [and others

    1996-12-31

    Al, the fastest p-type diffuser in silicon, interacts strongly with oxygen, defects, and precipitates, with a detrimental effect on the electrical activity. Although, substrates with low oxygen content, such as epitaxial layers on FZ grown crystals, can be used, it is practically impossible to avoid oxidation steps and then the amount of oxygen that is introduced into the wafer depends on the oxidation temperature. The present work deals with the behaviour of Al implanted at high energies either in bare epitaxial Si or in pre-oxidized epitaxial Si with a 300 nm thick thermal oxide layer. The subsequent annealings were performed under oxygen or nitrogen atmosphere. The SIMS and the spreading resistance analyses indicate that even the oxygen present in the silicon substrates after the thermal oxidation at temperatures above 1000 {degrees}C causes the precipitation of Al at the depth of the damage peak. The effect has been quantitatively analysed by comparison with thermal processes in nitrogen atmosphere. For the Al implant through the oxide layer, the growth and dissolution of Al-O precipitates has been studied.

  11. Relativistic-electron-beam-induced fusion

    International Nuclear Information System (INIS)

    The interaction of a focussed relativistic electron beam (REB) with a solid target has been investigated. The beam performance of the REB generator ''REIDEN III'' is 500 kV, 80 kA at a focal spot of 1.5 mm diameter, which gives 2X1012Wcm-2. High-temperature dense plasmas are produced at the focal point on the solid target. It expands radially along the target surface. The measured electron temperature (1-2 keV) and the ion energy (approximately 2 keV) endorse the existence of enhanced REB absorption in a dense plasma. The neutrons observed (approximately 109/shot, 2.45 MeV) in the case of a CD2 target are of thermonuclear origin and compatible with the plasma temperature. On the assumption that the electron beam of radius r is stopped at a length Λ and deposits its energy, the energy balance equation is approximately given by πr2Λn1kT=IVtau. On inserting beam current I, voltage V, pulse time tau and density n1, the energy deposition distance Λ can be estimated. For a fusion temperature of 1 keV, the distance Λ must be two orders of magnitude shorter than the simple classical stopping length, which seems to be due to non-linear coupling. A pellet implosion experiment of a multi-structure target has been performed. (author)

  12. Native defect induced charge and ferromagnetic spin ordering and coexisting electronic phases in CoO epitaxial thin film

    Energy Technology Data Exchange (ETDEWEB)

    Negi, D. S., E-mail: devendranegi@jncasr.ac.in, E-mail: ranjan@jncasr.ac.in; Loukya, B.; Datta, R., E-mail: devendranegi@jncasr.ac.in, E-mail: ranjan@jncasr.ac.in [International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064 (India); Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064 (India)

    2015-12-07

    We report on the observation of Co vacancy (V{sub Co}) induced charge ordering and ferromagnetism in CoO epitaxial thin film. The ordering is associated with the coexistence of commensurate, incommensurate, and discommensurate electronic phases. Density functional theory calculation indicates the origin of ordering in Co atoms undergoing high spin to low spin transition immediately surrounding the V{sub Co(16.6 at. %)}. Electron magnetic chiral dichroism experiment confirms the ferromagnetic signal at uncompensated Co spins. Such a native defects induced coexistence of different electronic phases at room temperature in a simple compound CoO is unique and adds to the richness of the field with the possibility of practical device application.

  13. Growth model investigation for AlN/Al(Ga)InN interface growth by plasma-assisted molecular beam epitaxy for high electron mobility transistor applications

    Energy Technology Data Exchange (ETDEWEB)

    Aidam, Rolf; Diwo, Elke; Godejohann, Birte-Julia; Kirste, Lutz; Quay, Ruediger; Ambacher, Oliver [Fraunhofer-Institute for Applied Solid State Physics, Freiburg (Germany)

    2014-12-01

    Heterostructures with lattice matched Al(Ga)InN barriers have been widely investigated as alternative to standard AlGaN/GaN based high electron mobility transistor structures for high power applications. Mostly these heterostructures comprise a thin AlN based spacer between GaN channel and lattice matched barrier. One key issue for high quality plasma-assisted molecular beam epitaxy (PA-MBE) of these structures is the control of the AlN-Al(Ga)InN interface since optimal growth conditions for high quality AlN differ significantly from those for growth of indium containing material. In this paper, a detailed analysis and a deduced model of the interface growth is presented. The Al/N ratio during AlN spacer growth is likely to influence the subsequent growth of quaternary Al(Ga)InN. Ideal Al/N ratio leads to high performance heterostructures, while slightly Al-rich conditions lead to the formation of Al residues on the substrate surface, which hinder subsequent epitaxial growth. Al/N ratios below unity lead to the deposition of ternary AlGaN instead of binary AlN spacers and to increased alloy scattering. An insertion of a thin GaN layer between spacer and barrier can hinder the formation of Al residues and leads to improved wafer homogeneity. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. Influence of growth transients on interface and composition uniformity of ultra thin In(As,P) and (In,Al,Ga)As epilayers grown by chemical beam epitaxy

    International Nuclear Information System (INIS)

    In this work, measurements of epitaxial growth rate transients for multiple quantum wells (MQWs) in chemical beam epitaxy (CBE) have been made. Mass spectrometry measurements of typical growth conditions were made of gas source species of the InAsxP1-x/InP system, while reflection high-energy electron diffraction (RHEED) measurements were made for the GaAs/AlxGa1-xAs and InxGa1-xAs/GaAs systems. The results of these experiments went directly into predicting the transient growth rate of thin layers for multi-quantum well photovoltaic devices. The data obtained using these techniques resulted in an improved growth interruption sequence for MQW structures in the InAsxP1-x/InP system. Improvements in overall material quality have been observed by high resolution X-ray diffraction (HRXRD). HRXRD measurements of the InAsxP1-x/InP structures yield sharp satellite peaks revealing the possibility of achieving nearly perfect interfaces. From low temperature photoluminescence, narrow emission linewidths from quantum wells indicate an enhanced compositional uniformity, and room temperature photocurrent spectroscopy reveals an improvement in device performance

  15. Blue-violet InGaN laser diodes grown on bulk GaN substrates by plasma-assisted molecular-beam epitaxy

    International Nuclear Information System (INIS)

    We report on the InGaN multiquantum laser diodes (LDs) made by rf plasma-assisted molecular beam epitaxy (PAMBE). The laser operation at 408 nm is demonstrated at room temperature with pulsed current injections using 50 ns pulses at 0.25% duty cycle. The threshold current density and voltage for the LDs with cleaved uncoated mirrors are 12 kA/cm2 (900 mA) and 9 V, respectively. High output power of 0.83 W is obtained during pulse operation at 3.6 A and 9.6 V bias with the slope efficiency of 0.35 W/A. The laser structures are deposited on the high-pressure-grown low dislocation bulk GaN substrates taking full advantage of the adlayer enhanced lateral diffusion channel for adatoms below the dynamic metallic cover. Our devices compare very favorably to the early laser diodes fabricated using the metalorganic vapor phase epitaxy technique, providing evidence that the relatively low growth temperatures used in this process pose no intrinsic limitations on the quality of the blue optoelectronic components that can be fabricated using PAMBE

  16. Electron-diffraction and spectroscopical characterisation of ultrathin ZnS films grown by molecular beam epitaxy on GaP(0 0 1)

    International Nuclear Information System (INIS)

    ZnS films were grown by molecular beam epitaxy employing a single compound effusion cell on GaP(0 0 1) substrate at different temperatures, and characterised by means of low energy electron diffraction, X-ray and ultra-violet photoelectron spectroscopy, angle-resolved ultra-violet photoelectron spectroscopy and X-ray emission spectroscopy. The GaP(0 0 1) substrate exhibits a (4x2) reconstruction after Ar ion sputtering and annealing at 370 deg. C. Crystal quality of the ZnS films depends on both film thickness and growth temperature. Thinner films grown at higher temperatures and thicker films grown at lower temperatures have better crystal quality. The layer-by-layer growth mode of the ZnS films at lower (25, 80 and 100 deg. C) temperatures changes to layer-by-layer-plus-island mode at higher temperatures (120, 150 and 180 deg. C). A chemical reaction takes place and is confined to the interface. The valence band offset of the ZnS-GaP heterojunction was determined to be 0.8±0.1 eV. Sulphur L2,3 emission spectra of ZnS powder raw material and the epitaxial ZnS films display the same features, regardless of the existence of the Ga-S bonding in the film samples

  17. Photoelectrical characteristics of metal–insulator–semiconductor structures based on graded-gap HgCdTe grown by molecular-beam epitaxy

    International Nuclear Information System (INIS)

    Metal–insulator–semiconductor structures based on HgCdTe are grown by molecular-beam epitaxy. Near-surface graded-gap layers with high CdTe content are formed on both sides of the epitaxial HgCdTe film. Photoelectrical characteristics of these structures are studied experimentally and theoretically. For structures based on n-Hg1−xCdxTe (x = 0.21–0.23), the formation of a near-surface graded-gap layer leads to an increase in the differential resistance of the space charge region due to the suppression of tunneling. The temperature dependences of the differential resistance calculated with account to different mechanisms of generation of minority charge carriers are similar to the experimental dependences of the photoelectromotive force. - Highlights: • The metal–insulator–semiconductor structures based on HgCdTe were studied. • Photoelectrical properties of such structures were investigated. • Mechanisms of generation of minority carriers were studied. • Creation of near-surface graded-gap layers suppresses tunneling

  18. Preparation of GaAs and Ga1-xAlxAs Multi-Layer Structures by Metalorganic Molecular Beam Epitaxy

    Science.gov (United States)

    Tokumitsu, Eisuke; Katoh, Toshiaki; Kimura, Ryuhei; Konagai, Makoto; Takahashi, Kiyoshi

    1986-08-01

    Metalorganic molecular beam epitaxial (MOMBE) growth of GaAs and (GaAl)As using triethylgallium (TEG) and triethylaluminum (TEA) has been studied. N-GaAs/p-GaAs multi-layer structures were prepared by applying an alternating ionization voltage to hydrogen. Single-crystal Ga1-xAlxAs ternary alloy with good surface mophology was successfully grown by introducing TEA as an Al source. The epitaxial layers typically showed p-type conduction with a carrier concentration of more than 1018 cm-3, this being due to residual carbon. A (GaAl)As/GaAs multiquantum well (MQW) heterostructure was fabricated by switching TEA and it was observed that the photoluminescence peak energies from the MQW structures were shifted to the higher energy position. Furthermore, selective growth of GaAs and (GaAl)As on a partly SiO2 masked GaAs substrate was investigated. In the MOMBE growth of (GaAl)As, polycrystalline film was deposited on the SiO2 masked region, while no deposition took place in the growth of GaAs.

  19. Low temperature p-type doping of (Al)GaN layers using ammonia molecular beam epitaxy for InGaN laser diodes

    International Nuclear Information System (INIS)

    We demonstrate state-of-the-art p-type (Al)GaN layers deposited at low temperature (740 °C) by ammonia molecular beam epitaxy (NH3-MBE) to be used as top cladding of laser diodes (LDs) with the aim of further reducing the thermal budget on the InGaN quantum well active region. Typical p-type GaN resistivities and contact resistances are 0.4 Ω cm and 5 × 10−4 Ω cm2, respectively. As a test bed, we fabricated a hybrid laser structure emitting at 400 nm combining n-type AlGaN cladding and InGaN active region grown by metal-organic vapor phase epitaxy, with the p-doped waveguide and cladding layers grown by NH3-MBE. Single-mode ridge-waveguide LD exhibits a threshold voltage as low as 4.3 V for an 800 × 2 μm2 ridge dimension and a threshold current density of ∼5 kA cm−2 in continuous wave operation. The series resistance of the device is 6 Ω and the resistivity is 1.5 Ω cm, confirming thereby the excellent electrical properties of p-type Al0.06Ga0.94N:Mg despite the low growth temperature

  20. Molecular-beam epitaxy of heterostructures of wide-gap II–VI compounds for low-threshold lasers with optical and electron pumping

    International Nuclear Information System (INIS)

    The paper presents basic approaches in designing and growing by molecular beam epitaxy of (Zn,Mg)(S,Se)-based laser heterostructures with multiple CdSe quantum dot (QD) sheets or ZnCdSe quantum wells (QW). The method of calculation of compensating short-period ZnSSe/ZnSe superlattices (SLs) in both active and waveguide regions of laser heterostructures possessing the different waveguide thickness and different number of active regions is presented. The method allowing reduction of the density of nonequilibrium point defects in the active region of the II–VI laser structures has been proposed. It utilizes the migration enhanced epitaxy mode in growing the ZnSe QW confining the CdSe QD sheet. The threshold power density as low as Pthr ∼ 0.8 kW/cm2 at T = 300 K has been demonstrated for laser heterostructure with single CdSe QD sheet and asymmetric graded-index waveguide with strain-compensating SLs

  1. Epitaxy of semiconductor-superconductor nanowires

    Science.gov (United States)

    Krogstrup, P.; Ziino, N. L. B.; Chang, W.; Albrecht, S. M.; Madsen, M. H.; Johnson, E.; Nygård, J.; Marcus, C. M.; Jespersen, T. S.

    2015-04-01

    Controlling the properties of semiconductor/metal interfaces is a powerful method for designing functionality and improving the performance of electrical devices. Recently semiconductor/superconductor hybrids have appeared as an important example where the atomic scale uniformity of the interface plays a key role in determining the quality of the induced superconducting gap. Here we present epitaxial growth of semiconductor-metal core-shell nanowires by molecular beam epitaxy, a method that provides a conceptually new route to controlled electrical contacting of nanostructures and the design of devices for specialized applications such as topological and gate-controlled superconducting electronics. Our materials of choice, InAs/Al grown with epitaxially matched single-plane interfaces, and alternative semiconductor/metal combinations allowing epitaxial interface matching in nanowires are discussed. We formulate the grain growth kinetics of the metal phase in general terms of continuum parameters and bicrystal symmetries. The method realizes the ultimate limit of uniform interfaces and seems to solve the soft-gap problem in superconducting hybrid structures.

  2. Epitaxy of semiconductor-superconductor nanowires.

    Science.gov (United States)

    Krogstrup, P; Ziino, N L B; Chang, W; Albrecht, S M; Madsen, M H; Johnson, E; Nygård, J; Marcus, C M; Jespersen, T S

    2015-04-01

    Controlling the properties of semiconductor/metal interfaces is a powerful method for designing functionality and improving the performance of electrical devices. Recently semiconductor/superconductor hybrids have appeared as an important example where the atomic scale uniformity of the interface plays a key role in determining the quality of the induced superconducting gap. Here we present epitaxial growth of semiconductor-metal core-shell nanowires by molecular beam epitaxy, a method that provides a conceptually new route to controlled electrical contacting of nanostructures and the design of devices for specialized applications such as topological and gate-controlled superconducting electronics. Our materials of choice, InAs/Al grown with epitaxially matched single-plane interfaces, and alternative semiconductor/metal combinations allowing epitaxial interface matching in nanowires are discussed. We formulate the grain growth kinetics of the metal phase in general terms of continuum parameters and bicrystal symmetries. The method realizes the ultimate limit of uniform interfaces and seems to solve the soft-gap problem in superconducting hybrid structures. PMID:25581626

  3. Two-dimensional streaming flows induced by resonating, thin beams.

    Science.gov (United States)

    Açikalin, Tolga; Raman, Arvind; Garimella, Suresh V

    2003-10-01

    Miniaturized resonating slender beams are finding increased applications as fluidic actuators for portable electronics cooling. Piezoelectric and ultrasonic "fans" drive a flexural mode of the beam into resonance thus inducing a streaming flow, which can be used to cool microelectronic components. This paper presents analytical, computational, and experimental investigations of the incompressible two-dimensional streaming flows induced by resonating thin beams. Closed-form analytical streaming solutions are presented first for an infinite beam. These are used to motivate a computational scheme to predict the streaming flows from a baffled piezoelectric fan. Experiments are conducted to visualize the asymmetric streaming flows from a baffled piezoelectric fan and the experimental results are found to be in close agreement with the predicted results. The findings are expected to be of relevance in the optimal design and positioning of these solid-state devices in cooling applications. PMID:14587580

  4. Effect of using a high-purity Fe source on the transport properties of p-type β-FeSi2 grown by molecular-beam epitaxy

    International Nuclear Information System (INIS)

    Intentionally undoped p-type β-FeSi2 thin films were grown on Si(111) substrates by molecular-beam epitaxy using low-purity (4N) and high-purity (5N) Fe sources to investigate the effect of using a high-purity Fe source on the electrical properties of β-FeSi2. The hole mobility increased and the hole density decreased greatly as the annealing temperature and time were increased, particularly for the β-FeSi2 films produced using 5N-Fe. The observed temperature dependence of the hole mobility was reproduced well by considering various carrier scattering mechanisms due to acoustic-phonon, polar-optical phonon, nonpolar-optical phonon, and ionized impurities

  5. Magnetic properties of Fe0.4Mn0.6/Co2FeAl bilayers grown on GaAs by molecular-beam epitaxy

    Science.gov (United States)

    Meng, K. K.; Nie, S. H.; Yu, X. Z.; Wang, S. L.; Yan, W. S.; Zhao, J. H.

    2011-11-01

    Polycrystalline Fe0.4Mn0.6 layers with the different thickness are deposited on 4-nm-thick single-crystalline Co2FeAl layers, which are grown on GaAs (001) substrates at room temperature by molecular-beam epitaxy. Both the exchange bias and the in-plane magnetic anisotropies of the bilayers are strongly dependent on the thickness of the Fe0.4Mn0.6 layer. The former is described using a granular level model. A modified Stoner-Wohlfarth model is used to explain the in-plane magnetic anisotropies observed at 5 K, while one possible reason for the magnetic anisotropies measured at 300 K is the complex interfacial magnetic properties proved by x-ray magnetic circular dichroism measurements.

  6. 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.

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

    Science.gov (United States)

    Treu, J.; Speckbacher, M.; Saller, K.; Morkötter, S.; Döblinger, M.; Xu, X.; Riedl, H.; Abstreiter, G.; Finley, J. J.; Koblmüller, G.

    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) 0.6) NWs, whereas limitations at intermediate Ga-content (0.4 blue-shifted to red-shifted photoluminescence emission relative to the band edge emission of the bulk ZB InGaAs phase.

  8. Improved tunnel magnetoresistance of magnetic tunnel junctions with Heusler Co2FeAl0.5Si0.5 electrodes fabricated by molecular beam epitaxy

    International Nuclear Information System (INIS)

    The authors have developed a magnetic tunnel junction of Co2FeAl0.5Si0.5 electrodes and a MgO barrier fabricated by molecular beam epitaxy and observed that this device had a tunnel magnetoresistance ratio of 386% at approximately 300 K and 832% at 9 K. The lower Co2FeAl0.5Si0.5 electrode was annealed during and after deposition resulting in a highly ordered structure with small roughness. This highly ordered structure could be obtained by annealing treatment even at low temperatures. Furthermore, a weak temperature dependence of the tunnel magnetoresistance ratio was observed for the developed magnetic tunnel junction.

  9. Molecular-beam epitaxy and lattice parameter of GaNxSb1−x: deviation from Vegard's law for x > 0.02

    International Nuclear Information System (INIS)

    The N content of a series of GaNSb samples grown by molecular-beam epitaxy is investigated using high-resolution x-ray diffraction (HRXRD) and secondary-ion mass spectrometry. The N contents determined by the two methods agree well at lower N compositions (x 0.02). Analysis of the HRXRD-determined lattice constant using Vegard's law, underestimates the N content for high N compositions. The underestimation is found to be up to 24% for x = 0.03. The variation of the lattice parameter with N content is modelled by considering the influence of the density of the interstitial N–Sb complex rising with increasing N content. (paper)

  10. Structural properties of InN films grown on O-face ZnO(0001) by plasma-assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Yong Jin; Brandt, Oliver; Kaganer, Vladimir M.; Ramsteiner, Manfred; Riechert, Henning [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Korytov, Maxim; Albrecht, Martin [Leibniz-Institut fuer Kristallzuechtung, Max-Born-Str. 2, 12489 Berlin (Germany)

    2012-04-09

    We study the impact of substrate temperature and layer thickness on the morphological and structural properties of InN films directly grown on O-face ZnO(0001) substrates by plasma-assisted molecular beam epitaxy. With increasing substrate temperature, an interfacial reaction between InN and ZnO takes place that eventually results in the formation of cubic In{sub 2}O{sub 3} and voids. The properties of the InN films, however, are found to be unaffected by this reaction for substrate temperatures less than 550 deg. C. In fact, both the morphological and the structural quality of InN improve with increasing substrate temperature in the range from 350 to 500 deg. C. High quality films with low threading dislocation densities are demonstrated.

  11. Effect of growth stoichiometry on the electrical activity of screw dislocations in GaN films grown by molecular-beam epitaxy

    International Nuclear Information System (INIS)

    The impact of the Ga/N ratio on the structure and electrical activity of threading dislocations in GaN films grown by molecular-beam epitaxy is reported. Electrical measurements performed on samples grown under Ga-rich conditions show three orders of magnitude higher reverse bias leakage compared with those grown under Ga-lean conditions. Transmission electron microscopy (TEM) studies reveal excess Ga at the surface termination of pure screw dislocations accompanied by a change in the screw dislocation core structure in Ga-rich films. The correlation of transport and TEM results indicates that dislocation electrical activity depends sensitively on dislocation type and growth stoichiometry. [copyright] 2001 American Institute of Physics

  12. Structure of CdTe-Cd1 - xMnxTe multiple quantum wells grown on (001) InSb substrates by molecular beam epitaxy

    Science.gov (United States)

    Williams, G. M.; Cullis, A. G.; Whitehouse, C. R.; Ashenford, D. E.; Lunn, B.

    1989-09-01

    Molecular beam epitaxy has been used to prepare multiple quantum well structures of CdTe/Cd1-xMnxTe on (001) InSb substrates. The growth of such a system on InSb allows the use of particularly low growth temperatures, hence minimizing interdiffusion effects. This study presents the first transmission electron microscope investigation of this multilayer system grown on InSb. The work clearly demonstrates that multiple quantum wells of high structural quality can be grown reproducibly over a wide range of layer thicknesses. The importance of efficient substrate surface cleaning prior to growth is demonstrated. In order to grow high structural quality multilayers, the choice of buffer layer is also important and a possible explanation for this observation is given.

  13. Determination of CdTe bulk carrier lifetime and interface recombination velocity of CdTe/MgCdTe double heterostructures grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    The bulk Shockley-Read-Hall carrier lifetime of CdTe and interface recombination velocity at the CdTe/Mg0.24Cd0.76Te heterointerface are estimated to be around 0.5 μs and (4.7 ± 0.4) × 102 cm/s, respectively, using time-resolved photoluminescence (PL) measurements. Four CdTe/MgCdTe double heterostructures (DHs) with varying CdTe layer thicknesses were grown on nearly lattice-matched InSb (001) substrates using molecular beam epitaxy. The longest lifetime of 179 ns is observed in the DH with a 2 μm thick CdTe layer. It is also shown that the photon recycling effect has a strong influence on the bulk radiative lifetime, and the reabsorption process affects the measured PL spectrum shape and intensity

  14. Two-dimensional weak anti-localization in Bi2Te3 thin film grown on Si(111)-(7 × 7) surface by molecular beam epitaxy

    International Nuclear Information System (INIS)

    We report on low temperature transport studies of Bi2Te3 topological insulator thin films grown on Si(111)-(7 × 7) surface by molecular beam epitaxy. A sharp increase in the magnetoresistance with magnetic field at low temperature indicates the existence of weak anti-localization. The measured weak anti-localization effect agrees well with the Hikami-Larkin-Nagaoka model, and the extracted phase coherence length shows a power-law dependence with temperature indicating the existence of a two-dimensional system. An insulating ground state has also been observed at low temperature showing a logarithmic divergence of the resistance that appears to be the influence of electron-electron interaction in a two-dimensional system.

  15. High density of (pseudo) periodic twin-grain boundaries in molecular beam epitaxy-grown van der Waals heterostructure: MoTe2/MoS2

    Science.gov (United States)

    Diaz, Horacio Coy; Ma, Yujing; Chaghi, Redhouane; Batzill, Matthias

    2016-05-01

    Growth of transition metal dichalcogenide heterostructures by molecular beam epitaxy (MBE) promises synthesis of artificial van der Waals materials with controllable layer compositions and separations. Here, we show that MBE growth of 2H-MoTe2 monolayers on MoS2 substrates results in a high density of mirror-twins within the films. The grain boundaries are tellurium deficient, suggesting that Te-deficiency during growth causes their formation. Scanning tunneling microscopy and spectroscopy reveal that the grain boundaries arrange in a pseudo periodic "wagon wheel" pattern with only ˜2.6 nm repetition length. Defect states from these domain boundaries fill the band gap and thus give the monolayer an almost metallic property. The band gap states pin the Fermi-level in MoTe2 and thus determine the band-alignment in the MoTe2/MoS2 interface.

  16. Structural characterization of InAs quantum dot chains grown by molecular beam epitaxy on nanoimprint lithography patterned GaAs(100)

    International Nuclear Information System (INIS)

    We combine nanoimprint lithography and molecular beam epitaxy for the site-controlled growth of InAs quantum dot chains on GaAs(100) substrates. We study the influence of quantum dot growth temperature and regrowth buffer thickness on the formation of the quantum dot chains. In particular, we show that by carefully tuning the growth conditions we can achieve equal quantum dot densities and photoluminescence ground state peak wavelengths for quantum dot chains grown on patterns oriented along the [011], [011-bar], [011] and [001] directions. Furthermore, we identify the crystal facets that form the sidewalls of the grooves in the differently oriented patterns after capping and show that the existence of (411)A sidewalls causes reduction of the QD density as well as sidewall roughening.

  17. Structural characterization of InAs quantum dot chains grown by molecular beam epitaxy on nanoimprint lithography patterned GaAs(100)

    Energy Technology Data Exchange (ETDEWEB)

    Hakkarainen, T V; Tommila, J; Schramm, A; Tukiainen, A; Ahorinta, R; Dumitrescu, M; Guina, M, E-mail: teemu.hakkarainen@tut.fi [Optoelectronics Research Centre, Tampere University of Technology, PO Box 692, FIN-33101 Tampere (Finland)

    2011-07-22

    We combine nanoimprint lithography and molecular beam epitaxy for the site-controlled growth of InAs quantum dot chains on GaAs(100) substrates. We study the influence of quantum dot growth temperature and regrowth buffer thickness on the formation of the quantum dot chains. In particular, we show that by carefully tuning the growth conditions we can achieve equal quantum dot densities and photoluminescence ground state peak wavelengths for quantum dot chains grown on patterns oriented along the [011], [011-bar], [011] and [001] directions. Furthermore, we identify the crystal facets that form the sidewalls of the grooves in the differently oriented patterns after capping and show that the existence of (411)A sidewalls causes reduction of the QD density as well as sidewall roughening.

  18. 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.

  19. Optical quality improvement of InGaAs/AlAs/AlAsSb coupled double quantum wells grown by molecular beam epitaxy

    Science.gov (United States)

    Kasai, J.; Mozume, T.; Yoshida, H.; Simoyama, T.; Gopal, A. V.; Ishikawa, H.

    2004-02-01

    We have grown InGaAs/AlAs/AlAsSb coupled double quantum wells (C-DQWs) with AlAs diffusion-stopping layers by molecular beam epitaxy. An obtained sample had many cross-hatched lines, suggesting relatively poor structural quality. Optical measurements, however, revealed that the optical quality of the C-DQWs was greatly improved compared to earlier C-DQWs without AlAs diffusion-stopping layers. The intersubband absorption saturation intensity in the present C-DQW sample was extremely low, measuring 34 fJ/m2 at the optical communication wavelength of 1.62 m, while ultrafast response times of about 600 fs were maintained.

  20. 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.

  1. AlN/GaN double-barrier resonant tunneling diodes grown by rf-plasma-assisted molecular-beam epitaxy

    International Nuclear Information System (INIS)

    AlN/GaN double-barrier resonant tunneling diodes (DB-RTDs) were fabricated on (0001) Al2O3 substrates by molecular-beam epitaxy, using a rf-plasma nitrogen source. The AlN/GaN DB-RTDs were designed to have a 3-ML-thick GaN quantum well and 4-ML-thick AlN barrier layers sandwiched by Si-doped n-type GaN contact layers. The current-voltage characteristics of mesa diode samples showed clear negative differential resistance (NDR) at room temperature. The NDR was observed at 2.4 V with a peak current of 2.9 mA, which corresponds to 180 A/cm2. A peak-to-valley current ratio as high as 32 was obtained

  2. 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.

  3. Superconducting nanowires by electron-beam-induced deposition

    Energy Technology Data Exchange (ETDEWEB)

    Sengupta, Shamashis, E-mail: shamashis.sengupta@u-psud.fr [CSNSM, Univ. Paris-Sud, IN2P3, UMR 8609, F-91405 Orsay Cedex (France); LPS, Univ. Paris-Sud, CNRS, UMR 8502, F-91405 Orsay Cedex (France); Li, Chuan; Guéron, S.; Bouchiat, H. [LPS, Univ. Paris-Sud, CNRS, UMR 8502, F-91405 Orsay Cedex (France); Baumier, Cedric; Fortuna, F. [CSNSM, Univ. Paris-Sud, IN2P3, UMR 8609, F-91405 Orsay Cedex (France); Kasumov, Alik [LPS, Univ. Paris-Sud, CNRS, UMR 8502, F-91405 Orsay Cedex (France); Institute of Microelectronics Technology and High Purity Materials, RAS, ac. Ossipyan, 6, Chernogolovka, Moscow Region 142432 (Russian Federation)

    2015-01-26

    Superconducting nanowires can be fabricated by decomposition of an organometallic gas using a focused beam of Ga ions. However, physical damage and unintentional doping often result from the exposure to the ion beam, motivating the search for a means to achieve similar structures with a beam of electrons instead of ions. This has so far remained an experimental challenge. We report the fabrication of superconducting tungsten nanowires by electron-beam-induced-deposition, with critical temperature of 2.0 K and critical magnetic field of 3.7 T, and compare them with superconducting wires made with ions. This work is an important development for the template-free realization of nanoscale superconducting devices, without the requirement of an ion beam column.

  4. Superconducting nanowires by electron-beam-induced deposition

    International Nuclear Information System (INIS)

    Superconducting nanowires can be fabricated by decomposition of an organometallic gas using a focused beam of Ga ions. However, physical damage and unintentional doping often result from the exposure to the ion beam, motivating the search for a means to achieve similar structures with a beam of electrons instead of ions. This has so far remained an experimental challenge. We report the fabrication of superconducting tungsten nanowires by electron-beam-induced-deposition, with critical temperature of 2.0 K and critical magnetic field of 3.7 T, and compare them with superconducting wires made with ions. This work is an important development for the template-free realization of nanoscale superconducting devices, without the requirement of an ion beam column

  5. Relaxation of Blazar Induced Pair Beams in Cosmic Voids

    OpenAIRE

    Miniati, Francesco; Elyiv, Andrii

    2012-01-01

    The stability properties of a low density ultra relativistic pair beam produced in the intergalactic medium by multi-TeV gamma-ray photons from blazars are analyzed. The problem is relevant for probes of magnetic field in cosmic voids through gamma-ray observations. In addition, dissipation of such beams could affect considerably the thermal history of the intergalactic medium and structure formation. We use a Monte Carlo method to quantify the properties of the blazar induced electromagnetic...

  6. Optical beam steering based on electromagnetically induced transparency

    International Nuclear Information System (INIS)

    We propose a scheme that provides all-optically-controlled steering of light beam. The system is based on steep dispersion of a coherently driven medium. Using the eikonal equation, we study the steering angle, the spread of the optical beam, and the limits set by residual absorption of the medium under conditions of electromagnetically induced transparency. Implementation of another scheme for ultrashort pulses is also discussed

  7. Multi-electron beam system for high resolution electron beam induced deposition

    OpenAIRE

    Van Bruggen, M.J.

    2008-01-01

    The development of a multi-electron beam system is described which is dedicated for electron beam induced deposition (EBID) with sub-10 nm resolution. EBID is a promising mask-less nanolithography technique which has the potential to become a viable technique for the fabrication of 20-2 nm structures after 2013, as described by the International Technology Roadmap for Semiconductors (ITRS), or can be used for rapid prototyping in research applications. The key point is to combine the throughp...

  8. Induced radioactivity of the IHEP proton synchrotron beam extraction equipment

    International Nuclear Information System (INIS)

    The measurement results of induced radioactivity of the beam extraction equipment during 1972-1978 are presented. All the values are given to the moment of the accelerator stop. The experimental data permits to predict further possible variations of the induced radioactivity levels of the equipment. Given are the measures required for reduction of the accelerator equipment irradiation, which are the following: 1) compensation of residual distortion of a closed beam orbit in the course of the induction system operation; 2) limitation of the intensity of drop on the internal targets up to the 11 protons per target level over a cycle; 3) putting into operation the program control system for the duration of a current pulse of a linear accelerator to minimize the beam residues at the 70 GeV energy during physical experiments; 4) construction of the system of beam interception and cutting-off to ensure effective energy suppression of uncontrolled beam residues and localization of their radiation effect; 5) extraction of a high-energy beam out of the accelerator during the experiments (e.g., into the neutrino channel for apparatus adjusting) instead of its dropping on the interceptor-target; 6) beam orbit controlling in the case of multiturn injection into the accelerator

  9. Beam-Induced Damage Mechanisms and their Calculation

    CERN Document Server

    Bertarelli, A

    2016-01-01

    The rapid interaction of highly energetic particle beams with matter induces dynamic responses in the impacted component. If the beam pulse is sufficiently intense, extreme conditions can be reached, such as very high pressures, changes of material density, phase transitions, intense stress waves, material fragmentation and explosions. Even at lower intensities and longer time-scales, significant effects may be induced, such as vibrations, large oscillations, and permanent deformation of the impacted components. These lectures provide an introduction to the mechanisms that govern the thermomechanical phenomena induced by the interaction between particle beams and solids and to the analytical and numerical methods that are available for assessing the response of impacted components. An overview of the design principles of such devices is also provided, along with descriptions of material selection guidelines and the experimental tests that are required to validate materials and components exposed to interactio...

  10. Strain-induced stabilization of new magnetic spinel structures in epitaxial oxide heterostructures.

    OpenAIRE

    Rigato, Franco; Estradé Albiol, Sònia; Arbiol i Cobos, Jordi; Peiró Martínez, Francisca; Lüders, Ulrike Anne; Martí, X.; Sánchez Barrera, Florencio; Fontcuberta i Griñó, Josep

    2007-01-01

    We report here on the growth of NiFe2O4 epitaxial thin films of different thickness (3 nm ¿ t ¿ 32 nm) on single crystalline substrates having spinel (MgAl2O4) or perovskite (SrTiO3) structure. Ultrathin films, grown on any of those substrates, display a huge enhancement of the saturation magnetization: we will show that partial cationic inversion may account for this enhancement, although we will argue that suppression of antiparallel collinear spin alignment due to size-effects cannot be ex...

  11. Proximity Effect Induced Electronic Properties of Epitaxial Graphene on Bi2Te2Se

    OpenAIRE

    Lee, Paengro; Jin, Kyung-Hwan; Sung, Si Jin; Kim, Jin Gul; Ryu, Min-Tae; Park, Hee-Min; Jhi, Seung-Hoon; Kim, Namdong; Kim, Yongsam; Yu, Seong Uk; Kim, Kwang S; Noh, Do Young; Chung, Jinwook

    2015-01-01

    We report that the {\\pi}-electrons of graphene can be spin-polarized to create a phase with a significant spin-orbit gap at the Dirac point (DP) using a graphene-interfaced topological insulator hybrid material. We have grown epitaxial Bi2Te2Se (BTS) films on a chemical vapor deposition (CVD) graphene. We observe two linear surface bands both from the CVD graphene notably flattened and BTS coexisting with their DPs separated by 0.53 eV in the photoemission data measured with synchrotron photo...

  12. Flexoelectricity induced increase of critical thickness in epitaxial ferroelectric thin films

    International Nuclear Information System (INIS)

    Flexoelectricity describes the coupling between polarization and strain/stress gradients in insulating crystals. In this paper, using the Landau-Ginsburg-Devonshire phenomenological approach, we found that flexoelectricity could increase the theoretical critical thickness in epitaxial BaTiO3 thin films, below which the switchable spontaneous polarization vanishes. This increase is remarkable in tensile films while trivial in compressive films due to the electrostriction caused decrease of potential barrier, which can be easily destroyed by the flexoelectricity, between the ferroelectric state and the paraelectric state in tensile films. In addition, the films are still in a uni-polar state even below the critical thickness due to the flexoelectric effect.

  13. Electric field-tunable Ba{sub x}Sr{sub 1-x}TiO{sub 3} films with high figures of merit grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Mikheev, Evgeny; Kajdos, Adam P.; Hauser, Adam J.; Stemmer, Susanne [Materials Department, University of California, Santa Barbara, California 93106-5050 (United States)

    2012-12-17

    We report on the dielectric properties of Ba{sub x}Sr{sub 1-x}TiO{sub 3} (BST) films grown by molecular beam epitaxy on epitaxial Pt bottom electrodes. Paraelectric films (x Less-Than-Or-Equivalent-To 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.

  14. Are laser-induced beams spin polarized?

    Energy Technology Data Exchange (ETDEWEB)

    Buescher, Markus; Lehrach, Andreas; Raab, Natascha [Institut fuer Kernphysik (IKP), Juelich Center for Hadron Physics (JCHP), Forschungszentrum Juelich (Germany); Engin, Ilhan; Hessan, Mohammad Aziz [RWTH Aachen (Germany); Institut fuer Kernphysik (IKP), Juelich Center for Hadron Physics (JCHP), Forschungszentrum Juelich (Germany); Gibbon, Paul; Karmakar, Anupam [Juelich Supercomputing Center (JSC), Forschungszentrum Juelich (Germany); Toncian, Monika; Toncian, Toma; Willi, Oswald [Institut fuer Laser-Plasma Physik (ILPP), Heinrich Heine Universitaet, Duesseldorf (Germany)

    2011-07-01

    The physics of laser-plasma interactions has undergone dramatic developments in recent years, both experimentally and in the theoretical understanding of high-brightness light and particle sources. However, it is a yet untouched issue whether the laser-generated particle beams are or can be spin-polarized and, thus, whether laser-based polarized sources are conceivable. A first measurement of the degree of polarization of laser-accelerated protons have recently been carried out at the Duesseldorf Arcturus Laser Facility where proton beams of typically 3 MeV were produced in foil targets. The results have been analysed with the help of particle-in-cell simulations to follow the generation of static magnetic field gradients ({proportional_to}100s of Megagauss per micron) in thin foil targets. As a next step, measurements with unpolarized H{sub 2} (for proton acceleration) and {sup 3}He gas (for {sup 3}He ions) are planned and, finally, pre-polarized {sup 3}He will be used.

  15. Aerosol nucleation induced by a high energy particle beam

    DEFF Research Database (Denmark)

    Enghoff, Martin Andreas Bødker; Pedersen, Jens Olaf Pepke; Uggerhøj, Ulrik I.;

    2011-01-01

    We have studied sulfuric acid aerosol nucleation in an atmospheric pressure reaction chamber using a 580 MeV electron beam to ionize the volume of the reaction chamber. We find a clear contribution from ion-induced nucleation and consider this to be the first unambiguous observation of the ion-effect...... on aerosol nucleation using a particle beam under conditions that resemble the Earth's atmosphere. By comparison with ionization using a gamma source we further show that the nature of the ionizing particles is not important for the ion-induced component of the nucleation. This implies that...

  16. Dilute Nitride GaNP Wide Bandgap Solar Cells Grown by Gas-Source Molecular Beam Epitaxy

    Science.gov (United States)

    Sukrittanon, Supanee

    Integration of III-V semiconductors and Si is a very attractive means to achieve low-cost high-efficiency solar cells. A promising configuration is to utilize a dual-junction solar cell, in which Si is employed as the bottom junction and a wide-bandgap III-V semiconductor as the top junction. The use of a III-V semiconductor as a top junction offers the potential to achieve higher efficiencies than today's best Si solar cell. Dilute nitride GaNP is a promising candidate for the top cell in dual-junction solar cells because it possesses several extremely important attributes: a direct-bandgap that is also tunable as well as easily-attained lattice-match with Si. As a first step towards integration of GaNP solar cells onto Si, the goal of this dissertation is to optimize and demonstrate GaNP solar cells grown by gas-source molecular beam epitaxy (GSMBE) on GaP (001) substrate. The dissertation is divided into three major parts. In the first part, we demonstrate ˜ 2.05 eV ([N]˜ 1.8%) dilute nitride GaNP thin film solar cells, in which the GaNP is closely lattice-matched to Si, on GaP substrates. From transmission electron microscopy (TEM), the device exhibits defects only at the GaNP/GaP interface, and no threading dislocations in an active layer are observed. Our best GaNP solar cell achieved an efficiency of 7.9% with anti-reflection (AR) coating and no window layer. This GaNP solar cell's efficiency is higher than the most efficient GaP solar cell to date and higher than other solar cells with similar direct bandgap (InGaP, GaAsP). Through a systematic study of the structural, electrical, and optical properties of the device, efficient broadband optical absorption and enhanced solar cell performance using GaNP are demonstrated. In the second part, we demonstrate the successful fabrication of GaP/GaNP core/shell microwires utilizing a novel technique: top-down reactive-ion etching (RIE) to create the cores and MBE to create the shells. Systematic studies have been

  17. Strain induced room temperature ferromagnetism in epitaxial magnesium oxide thin films

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Zhenghe; Kim, Ki Wook [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Nori, Sudhakar; Lee, Yi-Fang; Narayan, Jagdish [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Kumar, D. [Department of Mechanical Engineering, North Carolina A & T State University, Greensboro, North Carolina 27411 (United States); Wu, Fan [Princeton Institute for the Science and Technology of Materials (PRISM), Princeton University, Princeton, New Jersey 08540 (United States); Prater, J. T. [Materials Science Division, Army Research Office, Research Triangle Park, North Carolina 27709 (United States)

    2015-10-28

    We report on the epitaxial growth and room-temperature ferromagnetic properties of MgO thin films deposited on hexagonal c-sapphire substrates by pulsed laser deposition. The epitaxial nature of the films has been confirmed by both θ-2θ and φ-scans of X-ray diffraction pattern. Even though bulk MgO is a nonmagnetic insulator, we have found that the MgO films exhibit ferromagnetism and hysteresis loops yielding a maximum saturation magnetization up to 17 emu/cc and large coercivity, H{sub c} = 1200 Oe. We have also found that the saturation magnetization gets enhanced and that the crystallization degraded with decreased growth temperature, suggesting that the origin of our magnetic coupling could be point defects manifested by the strain in the films. X-ray (θ-2θ) diffraction peak shift and strain analysis clearly support the presence of strain in films resulting from the presence of point defects. Based on careful investigations using secondary ion mass spectrometer and X-ray photoelectron spectroscopy studies, we have ruled out the possibility of the presence of any external magnetic impurities. We discuss the critical role of microstructural characteristics and associated strain on the physical properties of the MgO films and establish a correlation between defects and magnetic properties.

  18. Properties of a radiation-induced charge multiplication region in epitaxial silicon diodes

    CERN Document Server

    Lange, Jörn; Fretwurst, Eckhart; Klanner, Robert; Lindström, Gunnar

    2010-01-01

    Charge multiplication (CM) in p$^+$n epitaxial silicon pad diodes of 75, 100 and 150 $\\upmu$m thickness at high voltages after proton irradiation with 1 MeV neutron equivalent fluences in the order of $10^{16}$ cm$^{-2}$ was studied as an option to overcome the strong trapping of charge carriers in the innermost tracking region of future Super-LHC detectors. Charge collection efficiency (CCE) measurements using the Transient Current Technique (TCT) with radiation of different penetration (670, 830, 1060 nm laser light and $\\alpha$-particles with optional absorbers) were used to locate the CM region close to the p$^+$-implantation. The dependence of CM on material, thickness of the epitaxial layer, annealing and temperature was studied. The collected charge in the CM regime was found to be proportional to the deposited charge, uniform over the diode area and stable over a period of several days. Randomly occurring micro discharges at high voltages turned out to be the largest challenge for operation of the dio...

  19. Strain induced room temperature ferromagnetism in epitaxial magnesium oxide thin films

    International Nuclear Information System (INIS)

    We report on the epitaxial growth and room-temperature ferromagnetic properties of MgO thin films deposited on hexagonal c-sapphire substrates by pulsed laser deposition. The epitaxial nature of the films has been confirmed by both θ-2θ and φ-scans of X-ray diffraction pattern. Even though bulk MgO is a nonmagnetic insulator, we have found that the MgO films exhibit ferromagnetism and hysteresis loops yielding a maximum saturation magnetization up to 17 emu/cc and large coercivity, Hc = 1200 Oe. We have also found that the saturation magnetization gets enhanced and that the crystallization degraded with decreased growth temperature, suggesting that the origin of our magnetic coupling could be point defects manifested by the strain in the films. X-ray (θ-2θ) diffraction peak shift and strain analysis clearly support the presence of strain in films resulting from the presence of point defects. Based on careful investigations using secondary ion mass spectrometer and X-ray photoelectron spectroscopy studies, we have ruled out the possibility of the presence of any external magnetic impurities. We discuss the critical role of microstructural characteristics and associated strain on the physical properties of the MgO films and establish a correlation between defects and magnetic properties

  20. Relaxation of Blazar-induced Pair Beams in Cosmic Voids

    Science.gov (United States)

    Miniati, Francesco; Elyiv, Andrii

    2013-06-01

    The stability properties of a low-density ultrarelativistic pair beam produced in the intergalactic medium (IGM) by multi-TeV gamma-ray photons from blazars are analyzed. The problem is relevant for probes of magnetic field in cosmic voids through gamma-ray observations. In addition, dissipation of such beams could considerably affect the thermal history of the IGM and structure formation. We use a Monte Carlo method to quantify the properties of the blazar-induced electromagnetic shower, in particular the bulk Lorentz factor and the angular spread of the pair beam generated by the shower, as a function of distance from the blazar itself. We then use linear and nonlinear kinetic theory to study the stability of the pair beam against the growth of electrostatic plasma waves, employing the Monte Carlo results for our quantitative estimates. We find that the fastest growing mode, like any perturbation mode with even a very modest component perpendicular to the beam direction, cannot be described in the reactive regime. Due to the effect of nonlinear Landau damping, which suppresses the growth of plasma oscillations, the beam relaxation timescale is found to be significantly longer than the inverse Compton loss time. Finally, density inhomogeneities associated with cosmic structure induce loss of resonance between the beam particles and plasma oscillations, strongly inhibiting their growth. We conclude that relativistic pair beams produced by blazars in the IGM are stable on timescales that are long compared with the electromagnetic cascades. There appears to be little or no effect of pair beams on the IGM.