WorldWideScience

Sample records for beam induced epitaxial

  1. 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

  2. Submicron FETs Using Molecular Beam Epitaxy.

    Science.gov (United States)

    1979-08-01

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

  3. Silicon Holder For Molecular-Beam Epitaxy

    Science.gov (United States)

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

    1993-01-01

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

  4. 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.

  5. 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.

  6. 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.

  7. Silicon/Germanium Molecular Beam Epitaxy

    OpenAIRE

    2006-01-01

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

  8. Determination of Kinetic Parameters of Molecular Beam Epitaxy,

    Science.gov (United States)

    1985-04-17

    A kinetic growth model for molecular beam epitaxy (MBE) was discussed. Furthermore, high energy electron diffraction (HEED) was used as a surface...characterization method to provide evidence for this model. GaAs was used as an example to study the growth rate of molecular beam epitaxy . The relation

  9. Infrared Rugates by Molecular Beam Epitaxy

    Science.gov (United States)

    Rona, M.

    1993-01-01

    Rugates are optical structures that have a sinusoidal index of refraction (harmonic gradient-index field). As their discrete high/ low index filter counterparts, they can be used as narrow rejection band filters. However, since rugates do not have abrupt interfaces, they tend to have a smaller absorption, hence deliver a higher in band reflectivity. The absence of sharp interfaces makes rugates even more desirable for high-energy narrow band reflectors. In this application, the lack of a sharp interface at the maximum internal standing wave electric field results in higher breakdown strengths. Our method involves fabricating rugates, with molecular beam epitaxy, on GaAs wafers as an Al(x)Ga(1-x)As single-crystal film.

  10. Applying CLIPS to control of molecular beam epitaxy processing

    Science.gov (United States)

    Rabeau, Arthur A.; Bensaoula, Abdelhak; Jamison, Keith D.; Horton, Charles; Ignatiev, Alex; Glover, John R.

    1990-01-01

    A key element of U.S. industrial competitiveness in the 1990's will be the exploitation of advanced technologies which involve low-volume, high-profit manufacturing. The demands of such manufacture limit participation to a few major entities in the U.S. and elsewhere, and offset the lower manufacturing costs of other countries which have, for example, captured much of the consumer electronics market. One such technology is thin-film epitaxy, a technology which encompasses several techniques such as Molecular Beam Epitaxy (MBE), Chemical Beam Epitaxy (CBE), and Vapor-Phase Epitaxy (VPE). Molecular Beam Epitaxy (MBE) is a technology for creating a variety of electronic and electro-optical materials. Compared to standard microelectronic production techniques (including gaseous diffusion, ion implantation, and chemical vapor deposition), MBE is much more exact, though much slower. Although newer than the standard technologies, MBE is the technology of choice for fabrication of ultraprecise materials for cutting-edge microelectronic devices and for research into the properties of new materials.

  11. Epitaxial growth and new phase of single crystal Dy by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Kai-Yueh; Homma, Hitoshi; Schuller, I.K.

    1987-09-01

    We have grown two novel epitaxial phases of dysprosium (Dy) on vanadium (V) by molecular beam epitaxy technique. Surface and bulk structures are studied by in-situ reflection high energy electron diffraction (RHEED) and x-ray diffraction techniques. The new hcp phases are approx.4% expanded uniformly in-plane (0001), and approx.9% and approx.4% expanded out of plane along the c-axes for non-interrupted and interrupted deposition case, respectively. We also observed (2 x 2), (3 x 3), and (4 x 4) Dy surface reconstruction patterns and a series of transitions as the Dy film thickness increases. 12 refs., 3 figs.

  12. Epitaxial film growth and metastable phases of single crystal Dy by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Yang, K.; Homma, H.; Schuller, I.K.

    1988-04-15

    We have grown two novel epitaxial phases of dysprosium (Dy) on vanadium (V) by the molecular beam epitaxy technique. Surface structures are studied by in situ reflection high-energy electron diffraction, and bulk structures are studied by x-ray diffraction after removal from the growth chamber. The new hcp phases are approx.4% expanded uniformly in the (0001) plane and approx.9% and approx.4% expanded out of plane, along the c axes, for noninterrupted and interrupted deposition cases, respectively. We also observed (2 x 2), (3 x 3), and (4 x 4) Dy surface reconstruction patterns and a series of structural changes as the Dy film thickness increases.

  13. Topological Insulator Film Growth by Molecular Beam Epitaxy: A Review

    OpenAIRE

    2016-01-01

    In this article, we will review recent progress in the growth of topological insulator (TI) thin films by molecular beam epitaxy (MBE). The materials we focus on are the V2-VI3 family of TIs. These materials are ideally bulk insulating with surface states housing Dirac excitations which are spin-momentum locked. These surface states are interesting for fundamental physics studies (such as the search for Majorana fermions) as well as applications in spintronics and other fields. However, the m...

  14. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-08-31

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

  16. Gas source molecular beam epitaxial growth of GaN

    Science.gov (United States)

    Brown, Duncan W.

    1992-11-01

    Aluminum gallium nitride (AlGaN) has long been recognized as a promising radiation hard optoelectronic material. AlGaN has a wide direct band gap and therefore has potential applications in the fabrication of short wave-length devices, e.g., detectors and light-emitting diodes in the visible to ultraviolet region. Additionally, its piezoelectric properties and high acoustic velocities make it attractive for acoustic devices. The technical objective in Phase 1 was to determine if low temperature sources based on covalently bonded Group 3-nitrogen compounds could be used to prepare AlGaN films by gas source molecular beam epitaxy. The program required to investigate low temperature AlGaN source materials was separated into two parts: (1) the synthesis, purification, and pyrolysis of gallium-nitrogen adducts and aluminum-nitrogen adducts; and (2) the growth of GaN by chemical beam epitaxy. We clearly demonstrated under CBE conditions GaN(x)C(y) films could be grown using compounds with pre-existing Ga-N bonds whereas no films were formed using trimethylgallium. Dimethylgallium amide was shown to produce dramatically lower carbon content films in the presence of ammonia than did trimethylgallium in the presence of ammonia.

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

    Directory of Open Access Journals (Sweden)

    A. Lastras-Martínez

    2014-03-01

    Full Text Available We report on real time-resolved Reflectance-difference (RD spectroscopy of GaAs(001 grown by molecular beam epitaxy, with a time-resolution of 500 ms per spectrum within the 2.3–4.0 eV photon energy range. Through the analysis of transient RD spectra we demonstrated that RD line shapes are comprised of two components with different physical origins and determined their evolution during growth. Such components were ascribed to the subsurface strain induced by surface reconstruction and to surface stoichiometry. Results reported in this paper render RD spectroscopy as a powerful tool for the study of fundamental processes during the epitaxial growth of zincblende semiconductors.

  18. Growth of very large InN microcrystals by molecular beam epitaxy using epitaxial lateral overgrowth

    Energy Technology Data Exchange (ETDEWEB)

    Kamimura, J., E-mail: kamimura@pdi-berlin.de [Department of Engineering and Applied Sciences, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo 102-8554 (Japan); Kishino, K.; Kikuchi, A. [Department of Engineering and Applied Sciences, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo 102-8554 (Japan); Sophia Nanotechnology Research Center, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo 102-8554 (Japan)

    2015-02-28

    Very thick InN (∼40 μm) was grown by molecular beam epitaxy using the epitaxial lateral overgrowth (ELO) technique. In some regions, the ELO of InN was observed as expected, indicating an important step toward fabricating quasi-bulk InN substrates. Interestingly, most parts of the sample consist of large flat-topped microcrystals and well-faceted microstructures. This is likely due to local growth condition variations during ELO, which is supported by an experiment where ELO of InN was performed on a substrate with various stripe mask patterns. TEM characterization of a flat top InN microcrystal revealed few stacking faults and only related threading dislocations. Defect-free small faceted microcrystals were also observed. The thick InN crystals show a narrow photoluminescence spectrum with a peak at 0.679 eV and linewidth of 16.8 meV at 4 K.

  19. 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.

  20. Effects of shutter transients in molecular beam epitaxy.

    Science.gov (United States)

    Gozu, Shin-Ichiro; Mozume, Teruo; Kuwatsuka, Haruhiko; Ishikawa, Hiroshi

    2012-11-12

    : We have studied the effects of shutter transients (STs) in molecular beam epitaxy (MBE). Two series of samples were grown by MBE and evaluated by X-ray diffraction (XRD) and X-ray reflectivity (XRR) measurements. The effects of STs were evaluated by growth rate (GR) analysis using a combination of growth time (GT) and thickness evaluated by XRD and XRR measurements. We revealed two opposite effects of STs: (1) overshoot of GR and (2) increase in GR with GT and subsequent saturation. Each effect was consistent with the previous studies; however, the previous studies showed no relationships between these two effects. By considering closing time of the shutter, the two opposite effects were well understood.

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

    Science.gov (United States)

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

    2013-01-03

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

  2. InPBi single crystals grown by molecular beam epitaxy.

    Science.gov (United States)

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

    2014-06-26

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

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

    Directory of Open Access Journals (Sweden)

    Harmand Jean Christophe

    2004-01-01

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

  4. Molecular beam epitaxy for high-efficiency nitride optoelectronics

    Energy Technology Data Exchange (ETDEWEB)

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

    2006-06-15

    We review the significant progress made in the development of nitride laser diodes by molecular beam epitaxy (MBE). We report on our recent result of room temperature continuous-wave operation of InGaN quantum well laser diodes grown by MBE. Ridge waveguide lasers fabricated on freestanding GaN substrates have a continuous-wave threshold current of 125 mA, corresponding to a threshold current density of 5.7 kA cm{sup -2}. The lasers have a threshold voltage of 8.6 V and a lifetime of several minutes. We outline the further technical challenges associated with demonstrating lifetimes of several thousand hours and present an assessment of the potential of MBE as a growth method for commercial quality nitride optoelectronic devices. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Nitrides optoelectronic devices grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

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

    2007-01-15

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

  6. A Study of GaAsSb Nanowires by Molecular Beam Epitaxy for Near IR Applications

    Science.gov (United States)

    2015-09-18

    NWs. Chen et al. [24] reported an InSb NW- based IR photodetector grown by Au catalyst-assisted molecular beam epitaxy (MBE). Recently, GaSb NWs were...these, Be is the commonly used p-type dopant in molecular beam epitaxy as it has a high diffusion coefficient4 and less memory effects5. Additionally...flux. Be is the commonly used p-type dopant in molecular beam epitaxy as it has a high diffusion coefficient [1] and less memory effects [2

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-01-14

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

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

    Science.gov (United States)

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

    2013-01-01

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

  9. 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.

  10. In-situ epitaxial growth of graphene/h-BN van der Waals heterostructures by molecular beam epitaxy.

    Science.gov (United States)

    Zuo, Zheng; Xu, Zhongguang; Zheng, Renjing; Khanaki, Alireza; Zheng, Jian-Guo; Liu, Jianlin

    2015-10-07

    Van der Waals materials have received a great deal of attention for their exceptional layered structures and exotic properties, which can open up various device applications in nanoelectronics. However, in situ epitaxial growth of dissimilar van der Waals materials remains challenging. Here we demonstrate a solution for fabricating van der Waals heterostructures. Graphene/hexagonal boron nitride (h-BN) heterostructures were synthesized on cobalt substrates by using molecular beam epitaxy. Various characterizations were carried out to evaluate the heterostructures. Wafer-scale heterostructures consisting of single-layer/bilayer graphene and multilayer h-BN were achieved. The mismatch angle between graphene and h-BN is below 1°.

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

    Institute of Scientific and Technical Information of China (English)

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

    2007-01-01

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

  12. 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.

  13. Topological Insulator Film Growth by Molecular Beam Epitaxy: A Review

    Directory of Open Access Journals (Sweden)

    Theresa P. Ginley

    2016-11-01

    Full Text Available In this article, we will review recent progress in the growth of topological insulator (TI thin films by molecular beam epitaxy (MBE. The materials we focus on are the V2-VI3 family of TIs. These materials are ideally bulk insulating with surface states housing Dirac excitations which are spin-momentum locked. These surface states are interesting for fundamental physics studies (such as the search for Majorana fermions as well as applications in spintronics and other fields. However, the majority of TI films and bulk crystals exhibit significant bulk conductivity, which obscures these states. In addition, many TI films have a high defect density. This review will discuss progress in reducing the bulk conductivity while increasing the crystal quality. We will describe in detail how growth parameters, substrate choice, and growth technique influence the resulting TI film properties for binary and ternary TIs. We then give an overview of progress in the growth of TI heterostructures. We close by discussing the bright future for TI film growth by MBE.

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

    Institute of Scientific and Technical Information of China (English)

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

    2011-01-01

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

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

    Science.gov (United States)

    Halley, D.; Gilles, B.; Bayle-Guillemaud, P.; Arenal, R.; Marty, A.; Patrat, G.; Samson, Y.

    2004-11-01

    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 L 10 (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 L 10 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 L 10 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.

  16. Epitaxial growth of dilute nitride-arsenide compound semiconductors by molecular beam epitaxy

    Science.gov (United States)

    Adamcyk, Martin

    InyGa1-yAs 1-xNx containing a small amount of nitrogen (x narrow bandgap semiconductor alloy that has advantageous properties for the fabrication of optoelectronic devices. In this thesis, we seek to improve the material quality of InGaAsN and GaAsN by studying how the epitaxial growth conditions affect both the structural and electronic properties of the alloy. We describe a novel RF plasma source based on a helical resonator design that was developed for the incorporation of nitrogen into GaAsN and InGaAsN thin films grown by molecular beam epitaxy. The plasma source is equipped with a baffle apparatus that decreases the ion content of the flux. We show how the structural and electronic properties of InGaAsN epilayers depend on the growth conditions. In situ light scattering measurements and atomic force microscopy show that a faceted surface morphology occurs when growth conditions increase adatom surface diffusion: slow growth rate, high substrate temperature and high V/III ratio. Large nitrogen concentrations also favour the faceted growth mode. The residual strain in relaxed InGaAsN films is found to be higher than in InGaAs epilayers having the same lattice mismatch. In situ substrate curvature measurements were used to monitor the strain state of the sample in real time during the growth. Ex situ transmission electron microscopy and x-ray diffraction measurements agree with the residual strain determined with the in situ monitor. These characterization results also indicate that threading dislocation glide is slower in InGaAsN than in InGaAs. Finally, we find that the electronic properties of InGaAsN are generally degraded with increasing nitrogen content. However, by choosing appropriate growth conditions, we demonstrate InGaAsN quantum wells with room temperature photoluminescence efficiencies that are comparable to InGaAs structures. These photoluminescence results may be related to the faceting transition that was observed during GaAsN growth. In

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

    Science.gov (United States)

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

    2017-02-01

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

  18. Effects of hydrogen during molecular beam epitaxy of GaN

    Energy Technology Data Exchange (ETDEWEB)

    Dong, Y.; Feenstra, R.M. [Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States)

    2005-05-01

    We study the effect of introducing hydrogen gas through the RF plasma source during plasma-assisted molecular beam epitaxy of GaN(0001). The well-known smooth-to-rough transition that occurs for this surface as a function of decreasing Ga flux in the absence of H is found to persist even with H present. But, the critical Ga flux for this transition is increased by the presence of H, and for sufficiently high H pressure a new 2 x 2 surface structure that is believed to be H-terminated is observed. Under Ga-rich conditions, the presence of hydrogen is found to induce step bunching on the surface, from which we argue that H selectively bonds to surface step and/or kink sites. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2006-07-01

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

  20. Formation of GeSn alloy on Si(100) by low-temperature molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Talochkin, A. B., E-mail: tal@isp.nsc.ru [A. V. Rzhanov Institute of Semiconductor Physics, Lavrentyev Avenue 13, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Mashanov, V. I. [A. V. Rzhanov Institute of Semiconductor Physics, Lavrentyev Avenue 13, Novosibirsk 630090 (Russian Federation)

    2014-12-29

    GeSn alloys grown on Si(100) by the low-temperature (100 °C) molecular beam epitaxy are studied using scanning tunneling microscopy and Raman spectroscopy. It is found that the effect of Sn as a surfactant modifies substantially the low-temperature growth mechanism of Ge on Si. Instead of the formation of small Ge islands surrounded by amorphous Ge, in the presence of Sn, the growth of pure Ge islands appears via the Stranski-Krastanov growth mode, and a partially relaxed Ge{sub 1−x}Sn{sub x} alloy layer with the high Sn-fraction up to 40 at. % is formed in the area between them. It is shown that the observed growth mode induced by high surface mobility of Sn and the large strain of the pseudomorphic state of Ge to Si ensures the minimum elastic-strain energy of the structure.

  1. 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.

  2. Epitaxial Growth of Si(111)/Er2O3(111) Structure on Si(111) by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    XU Run; TANG Min-Yan; ZHU Yan-Yan; WANG Lin-Jun

    2011-01-01

    The Si overlayers are grown by molecular beam epitaxy on atomically smllth Er2O3(111) films prepared on Si(111) substrates. Single crystalline Si overlayers are achieved and are evident due to the spot-like reflective high energy electron diffraction(RHEED) patterns and x-ray diffraction patterns. The epitaxial relationship of the Si overlayer along the surface with respect to the orientation of EreO3 and the Si substrate is as follows:overgrown Si(111)//Er2O3(111)//Si(111).The rough surface of Si overlayers, as identified by both RHEED patterns and atomic force microscopy images, indicates a three-dimensional growth mode. The reason for this is based on the interfacial energy argument. Further growth of Er2O3 films on this rough Si overlayer leads to the polycrystalline nature of the topmost Er2O3 layer.

  3. 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.

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

    Science.gov (United States)

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

    1992-08-01

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

  5. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-02-15

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

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

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

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

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

    Science.gov (United States)

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

    2016-08-01

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

  9. 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.

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

    DEFF Research Database (Denmark)

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

    2016-01-01

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

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

    DEFF Research Database (Denmark)

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

    2013-01-01

    Molecular beam epitaxy growth for InSb1−xBix thin films on (100) GaAs substrates is reported. Successful Bi incorporation for 2% is achieved, and up to 70% of the incorporated Bi atoms are at substitutional sites. The effects of growth parameters on Bi incorporation and surface morphology...

  12. Molecular beam epitaxy growth of InSb1-xBix thin films

    DEFF Research Database (Denmark)

    Yuxin Song; Shumin Wang; Saha Roy, Ivy;

    2013-01-01

    Molecular beam epitaxy growth for InSb1-xBix thin films on (100) GaAs substrates is reported. Successful Bi incorporation for 2% is achieved, and up to 70% of the incorporated Bi atoms are at substitutional sites. The effects of growth parameters on Bi incorporation and surface morphology...

  13. 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.

  14. Diffusion of Pt in molecular beam epitaxy grown ZnSe

    Science.gov (United States)

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

    1998-05-01

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

  15. Molecular beam epitaxy of three dimensional topological insulator Bi₂Se₃ thin films

    OpenAIRE

    Guo, Xin; 郭欣

    2013-01-01

    In this thesis, molecular-beam epitaxy (MBE) of three-dimensional (3D) topological insulator (TI) Bi_2 Se_3 thin films on different substrates is presented. The substrates experimented include InP(111)A, GaAs(111)A, InP(001) and GaAs(001). Multiple characterization techniques are employed to investigate the film’s structural, morphological and electrical properties. To facilitate growth of high quality epitaxial Bi_2 Se_3, thermal treatment of the substrate surfaceturnsout to be crucial for b...

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

    OpenAIRE

    Urbańczyk, Adam; NöTZEL, R

    2012-01-01

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

  17. Epitaxial crystallization and nucleation during MeV-ion beam processing of amorphous GaAs surface layers

    Energy Technology Data Exchange (ETDEWEB)

    Bachmann, T. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Glaser, E. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Schulz, R. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Kaiser, U. [Jena Univ. (Germany). Inst. fuer Festkoerperphysik; Safran, G. [Research Institute for Technical Physics, P.O. Box 76, H-1325 Budapest (Hungary)

    1996-06-01

    <100> -GaAs wafers were preamorphized in a thin surface layer using 50 keV {sup 14}N{sup +}-ions. Ion beam induced epitaxial crystallization (IBIEC) and interfacial amorphization (IBIIA) were studied as a function of the target temperature using MeV Ar{sup +}- or Kr{sup +}-ions. Backscattering experiments and electron microscopy show that the IBIEC process is stopped above a critical irradiation temperature due to enhanced ion beam induced nucleation and growth of crystallites. At a fixed dose an optimum irradiation temperature for IBIEC was found, at which the recrystallized layer thickness has a maximum and crystallite formation is negligible. This offers the possibility to crystallize much larger layer thicknesses than {approx}65 nm which stands for the maximum value reported up to now. (orig.).

  18. Fast atom diffraction inside a molecular beam epitaxy chamber, a rich combination

    Science.gov (United States)

    Debiossac, M.; Atkinson, P.; Zugarramurdi, A.; Eddrief, M.; Finocchi, F.; Etgens, V. H.; Momeni, A.; Khemliche, H.; Borisov, A. G.; Roncin, P.

    2017-01-01

    Two aspects of the contribution of grazing incidence fast atom diffraction (GIFAD) to molecular beam epitaxy (MBE) are reviewed here: the ability of GIFAD to provide in-situ a precise description of the atomic-scale surface topology, and its ability to follow larger-scale changes in surface roughness during layer-by-layer growth. Recent experimental and theoretical results obtained for the He atom beam incident along the highly corrugated [ 1 1 bar 0 ] direction of the β2(2 × 4) reconstructed GaAs(001) surface are summarized. We also discuss the measurements and calculations for the beam incidence along the weakly corrugated [010] direction where a periodicity twice smaller than expected is observed. The combination of the experiment, quantum scattering matrix calculations, and semiclassical analysis allows structural characteristics of the surface to be revealed. For the in situ measurements of GIFAD during molecular beam epitaxy of GaAs on GaAs surface we analyze the change in elastic and inelastic contributions in the scattered beam, and the variation of the diffraction pattern in polar angle scattering. This analysis outlines the robustness, the simplicity and the richness of the GIFAD as a technique to monitor the layer-by-layer epitaxial growth.

  19. Structural and magnetic properties of magnetoelectric oxide heterostructures deposited by molecular beam epitaxy

    Science.gov (United States)

    Sterbinsky, George Evan

    There is considerable interest in incorporating magnetic materials into electronic devices to achieve new functions such as nonvolatile memories. Electric field control of magnetism is of much interest for new low power electronic devices because it eliminates the need to apply magnetic fields. One approach to achieving electrical control of magnetism is to exploit magnetoelastic effects in composites of ferromagnetic and ferroelectric materials. Application of an electric field to the composite will induce a strain through the piezo-electric effect, and the strain will alter the magnetization of the ferromagnetic constituent through the magnetoelastic effect. In this work, we examine the relationships between growth, strain, and magnetic properties of epitaxial ferrimagnetic Fe3O4 (magnetite) and ferroelectric BaTiO3 thin film heterostructures. We find that altering the strain state of a magnetite layer deposited on a BaTiO3 substrate has a profound effect on its magnetization. Here, we demonstrate the interaction between strain and magnetization is mediated by magnetic anisotropy and the magnetic domains structure of the films. Epitaxial magnetite films were deposited on MgO, BaTiO3, and SrTiO3 substrates by molecular beam epitaxy between temperatures of 573 and 723 K. Examination of the morphologies of Fe3O 4 films indicates that island growth is favored. Films exhibit in-plane magnetic isotropy and reduced saturation magnetizations with respect to the bulk material, as demonstrated by superconducting quantum interference device magnetometry. Magnetic hysteresis measurements suggest that these differences originate from antiphase boundary defects within the films. The strain in magnetite films deposited on BaTiO3 single crystal substrates was measured by x-ray diffraction. Measurements reveal a dependence of magnetization (M) on strain (epsilon) with discontinuities in magnetization versus temperature curves resulting from changes in the domain structure of the

  20. Adsorption-controlled growth of BiVO4 by molecular-beam epitaxy

    Directory of Open Access Journals (Sweden)

    S. Stoughton

    2013-10-01

    Full Text Available Single-phase epitaxial films of the monoclinic polymorph of BiVO4 were synthesized by reactive molecular-beam epitaxy under adsorption-controlled conditions. The BiVO4 films were grown on (001 yttria-stabilized cubic zirconia (YSZ substrates. Four-circle x-ray diffraction, scanning transmission electron microscopy (STEM, and Raman spectroscopy confirm the epitaxial growth of monoclinic BiVO4 with an atomically abrupt interface and orientation relationship (001BiVO4 ∥ (001YSZ with [100]BiVO4 ∥ [100]YSZ. Spectroscopic ellipsometry, STEM electron energy loss spectroscopy (STEM-EELS, and x-ray absorption spectroscopy indicate that the films have a direct band gap of 2.5 ± 0.1 eV.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-07-01

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

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

    Science.gov (United States)

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

    2015-01-01

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

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

    Science.gov (United States)

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

    2012-12-11

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

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

    Science.gov (United States)

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

    2005-06-01

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

  9. Molecular beam epitaxial growth and structural characterization of ZnS on (001) GaAs

    Science.gov (United States)

    Benz, R. G., II; Huang, P. C.; Stock, S. R.; Summers, C. J.

    1988-01-01

    The effect of surface nucleation processes on the quality of ZnS layers grown on (001) GaAs substrates by molecular beam epitaxy is reported. Reflection high energy electron diffraction indicated that nucleation at high temperatures produced more planar surfaces than nucleation at low temperatures, but the crystalline quality as assessed by X-ray double crystal diffractometry is relatively independent of nucleation temperature. A critical factor in layer quality was the initial roughness of the GaAs surfaces.

  10. ’Molecular Beam Epitaxial Growth, Characterization, and Devices of Modulated Semiconductor Structures’

    Science.gov (United States)

    1990-02-28

    on reverse if necessary and identify by block number) Key Words: Molecular Beam Epitaxv, X-ray diffraction, RHEED, GeSn , AlGaSb, Surface Structure iLb...equipment so far has been used in the study of metastable GeSn alloys grown on InP and GaSb substrates, and in analysis of the (Al, Ga)Sb material system...Homma, "Molecular beam epitaxial 6 growth of metastable GeSn alloys", Sept. 13-15, 1989, North Carolina State University, Raleigh, N.C. Also to be

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

    Science.gov (United States)

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

    2012-08-13

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

  12. Molecular beam epitaxy and metalorganic chemical vapor deposition growth of epitaxial CdTe on (100) GaAs/Si and (111) GaAs/Si substrates

    Science.gov (United States)

    Nouhi, A.; Radhakrishnan, G.; Katz, J.; Koliwad, K.

    1988-01-01

    Epitaxial CdTe has been grown on both (100)GaAs/Si and (111)GaAs/Si substrates. A combination of molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) has been employed for the first time to achieve this growth: the GaAs layers are grown on Si substrates by MBE and the CdTe film is subsequently deposited on GaAs/Si by MOCVD. The grown layers have been characterized by X-ray diffraction, scanning electron microscopy, and photoluminescence.

  13. Molecular beam epitaxy of cubic III-nitrides on GaAs substrates

    Energy Technology Data Exchange (ETDEWEB)

    As, D.J.; Schikora, D.; Lischka, K. [Dept. of Physics, Univ. of Paderborn, Paderborn (Germany)

    2003-07-01

    Molecular beam epitaxy has successfully been used to grow crystalline layers of group III-nitrides (GaN, AlN and InN) with cubic (zinc-blende) structure on GaAs substrates. In this article, we discuss these efforts that, despite inherent difficulties due to the metastability of the c-III nitrides, led to substantial improvements of the structural, electrical and optical quality of these wide gap semiconductors. We review experimental work concerned with the epitaxy of c-GaN and the control of the growth process in-situ, the important issue of p- and n-type doping of c-GaN and investigations of the structural and optical properties of c-InGaN and c-AlGaN. (orig.)

  14. Fabrication of atomically smooth SrRuO3 thin films by laser molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    High-quality SrRuO3 (SRO) thin films and SrTiO3/SRO bilayer were grown epitaxially on SrTiO3 (STO)(001) substrates by laser molecular beam epitaxy. The results of in situ observation of reflection high-energy electron diffraction and ex situ X-ray diffraction θ -2θ scan indicate that the SRO thin films have good crystallinity. The measurements of atomic force microscopy and scan tunneling microscopy reveal that the surface of the SRO thin film is atomically smooth. The resistivity of the SRO thin film is 300 μΩ·cm at room temperature. Furthermore, the transmission electron microscopy study shows that the interfaces of STO/SRO and SRO/STO are very clear and no interfacial reaction layer was observed. The experimental results show that the SRO thin film is an excellent electrode material for devices based on perovskite oxide materials.

  15. Growth of MoO3 films by oxygen plasma assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Altman, Eric I.; Droubay, Timothy C.; Chambers, Scott A.

    2002-07-22

    The growth of MoO₃ films on SrLaAlO₄(0 0 1), a substrate lattice-matched to b-MoO , by oxygen plasma assisted molecular beam epitaxy was characterized using reflection high-energy electron diffraction (RHEED), X-ray photoelectron spectroscopy, Xray diffraction (XRD), and atomic force and scanning tunneling microscopies (AFM and STM).It was found that the flux of reactive oxygen species to the surface was not high enough to maintain the proper stoichiometry, even at the lowest measurable deposition rates. Therefore, the films were grown by depositing Mo in small increments and then allowing the Mo to oxidize. At 675 K, the films grew epitaxially but in a three-dimensional manner. XRD of films grown under these conditions revealed atetragonal structure that has not been previously observed in bulk MoO₃ samples.

  16. Hexagonal Boron Nitride Tunnel Barriers Grown on Graphite by High Temperature Molecular Beam Epitaxy

    Science.gov (United States)

    Cho, Yong-Jin; Summerfield, Alex; Davies, Andrew; Cheng, Tin S.; Smith, Emily F.; Mellor, Christopher J.; Khlobystov, Andrei N.; Foxon, C. Thomas; Eaves, Laurence; Beton, Peter H.; Novikov, Sergei V.

    2016-01-01

    We demonstrate direct epitaxial growth of high-quality hexagonal boron nitride (hBN) layers on graphite using high-temperature plasma-assisted molecular beam epitaxy. Atomic force microscopy reveals mono- and few-layer island growth, while conducting atomic force microscopy shows that the grown hBN has a resistance which increases exponentially with the number of layers, and has electrical properties comparable to exfoliated hBN. X-ray photoelectron spectroscopy, Raman microscopy and spectroscopic ellipsometry measurements on hBN confirm the formation of sp2-bonded hBN and a band gap of 5.9 ± 0.1 eV with no chemical intermixing with graphite. We also observe hexagonal moiré patterns with a period of 15 nm, consistent with the alignment of the hBN lattice and the graphite substrate. PMID:27681943

  17. InAs nanowire growth modes on Si (111) by gas source molecular beam epitaxy

    Science.gov (United States)

    Robson, M. T.; LaPierre, R. R.

    2016-02-01

    InAs nanowires (NWs) were grown on silicon substrates by gas source molecular beam epitaxy using five different growth modes: (1) Au-assisted growth, (2) positioned (patterned) Au-assisted growth, (3) Au-free growth, (4) positioned Au-assisted growth using a patterned oxide mask, and (5) Au-free selective-area epitaxy (SAE) using a patterned oxide mask. Optimal growth conditions (temperature, V/III flux ratio) were identified for each growth mode for control of NW morphology and vertical NW yield. The highest yield (72%) was achieved with the SAE method at a growth temperature of 440 °C and a V/III flux ratio of 4. Growth mechanisms are discussed for each of the growth modes.

  18. Cleaning chemistry of InSb(100) molecular beam epitaxy substrates

    Science.gov (United States)

    Vasquez, R. P.; Lewis, B. F.; Grunthaner, F. J.

    1983-01-01

    InSb has been used as a substrate for molecular beam epitaxy. For good epitaxial growth, a substrate surface which is smooth and clean on an atomic scale is required. Chemical cleaning procedures provide an oxide film to passivate the surface. This film is then desorbed by in situ heating. The material forming the film should, therefore, have a high vapor pressure at some temperature less than the substrate melting temperature. A chloride film appears to satisfy the latter requirement. The present investigation is, therefore, concerned with the formation of a chloride film rather than an oxide film. Carbon contamination has been found to cause problems in chemical cleaning procedures. The level of carbon contamination found in the case of chloride film formation, is therefore compared with the corresponding level observed in procedures using oxide films. It appears that a chloride film grown in connection with a short exposure time to a Cl2 plasma is preferable to other passivation films studied.

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

    Science.gov (United States)

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

    2016-04-13

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-06-15

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

  1. Epitaxial niobium dioxide thin films by reactive-biased target ion beam deposition

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yuhan, E-mail: yw9ep@virginia.edu; Kittiwatanakul, Salinporn; Lu, Jiwei [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Comes, Ryan B. [Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Wolf, Stuart A. [Department of Materials Science and Engineering and Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States)

    2015-03-15

    Epitaxial NbO{sub 2} thin films were synthesized on Al{sub 2}O{sub 3} (0001) substrates via reactive bias target ion beam deposition. X-ray diffraction and Raman spectra were used to confirm the tetragonal phase of pure NbO{sub 2}. Through XPS, it was found that there was a ∼1.3 nm thick Nb{sub 2}O{sub 5} layer on the surface and the bulk of the thin film was NbO{sub 2}. The epitaxial relationship between the NbO{sub 2} film and the substrate was determined. Electrical transport measurement was measured up to 400 K, and the conduction mechanism was discussed.

  2. Growth of CuInSe2 by molecular beam epitaxy

    Science.gov (United States)

    Grindle, S. P.; Clark, A. H.; Rezaie-Serej, S.; Falconer, E.; McNeily, J.; Kazmerski, L. L.

    1980-10-01

    Molecular beam epitaxy was used to grow CuInSe2 layers on CdS (001B) and other substrates. Epitaxial growth is obtained at a substrate temperature of 300 C. The ratio of the arrival rates of copper to indium is the key parameter governing layer stoichiometry. To produce low-resistivity p-type layers, the Cu/In arrival rate ratio must be slightly higher than that used to grow nominally stoichiometric layers. This suggests that a different defect is controlling electrical properties, rather than the copper vacancy complex which dominates bulk material. CuInSe2/CdS heterojunctions were fabricated which show a maximum solar conversion efficiency of about 5%.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-01-15

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-07-22

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

  5. 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.

  6. 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.

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

    Science.gov (United States)

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

    2014-03-17

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-12-15

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

  9. 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.

  10. 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)

  11. An ultra-compact, high-throughput molecular beam epitaxy growth system.

    Science.gov (United States)

    Baker, A A; Braun, W; Gassler, G; Rembold, S; Fischer, A; Hesjedal, T

    2015-04-01

    We present a miniaturized molecular beam epitaxy (miniMBE) system with an outer diameter of 206 mm, optimized for flexible and high-throughput operation. The three-chamber system, used here for oxide growth, consists of a sample loading chamber, a storage chamber, and a growth chamber. The growth chamber is equipped with eight identical effusion cell ports with linear shutters, one larger port for either a multi-pocket electron beam evaporator or an oxygen plasma source, an integrated cryoshroud, retractable beam-flux monitor or quartz-crystal microbalance, reflection high energy electron diffraction, substrate manipulator, main shutter, and quadrupole mass spectrometer. The system can be combined with ultrahigh vacuum (UHV) end stations on synchrotron and neutron beamlines, or equivalently with other complex surface analysis systems, including low-temperature scanning probe microscopy systems. Substrate handling is compatible with most UHV surface characterization systems, as the miniMBE can accommodate standard surface science sample holders. We introduce the design of the system, and its specific capabilities and operational parameters, and we demonstrate the epitaxial thin film growth of magnetoelectric Cr2O3 on c-plane sapphire and ferrimagnetic Fe3O4 on MgO (001).

  12. Cleaning chemistry of GaAs(100) and InSb(100) substrates for molecular beam epitaxy

    Science.gov (United States)

    Vasquez, R. P.; Lewis, B. F.; Grunthaner, F. J.

    1983-01-01

    Ploog (1980) and Bachrach and Krusor (1981) have pointed out the importance of substrate preparation and surface cleaning for obtaining high quality films with the aid of molecular beam epitaxial growth techniques. In the present investigation, high resolution X-ray photoemission (XPS) is used to determine the oxide removal mechanism for GaAs(100) substrates which have undergone a standardized cleaning procedure. Other objectives of the investigation are related to a comparison of different cleaning procedures in order to minimize carbon contamination, the extension of these cleaning techniques to other III-V compound semiconductors such as InSb, and the evaluation of the sensitivity of the compositional results to electron-induced damage effects.

  13. Non-adiabatic ab initio molecular dynamics of supersonic beam epitaxy of silicon carbide at room temperature.

    Science.gov (United States)

    Taioli, Simone; Garberoglio, Giovanni; Simonucci, Stefano; a Beccara, Silvio; Aversa, Lucrezia; Nardi, Marco; Verucchi, Roberto; Iannotta, Salvatore; Dapor, Maurizio; Alfè, Dario

    2013-01-28

    In this work, we investigate the processes leading to the room-temperature growth of silicon carbide thin films by supersonic molecular beam epitaxy technique. We present experimental data showing that the collision of fullerene on a silicon surface induces strong chemical-physical perturbations and, for sufficient velocity, disruption of molecular bonds, and cage breaking with formation of nanostructures with different stoichiometric character. We show that in these out-of-equilibrium conditions, it is necessary to go beyond the standard implementations of density functional theory, as ab initio methods based on the Born-Oppenheimer approximation fail to capture the excited-state dynamics. In particular, we analyse the Si-C(60) collision within the non-adiabatic nuclear dynamics framework, where stochastic hops occur between adiabatic surfaces calculated with time-dependent density functional theory. This theoretical description of the C(60) impact on the Si surface is in good agreement with our experimental findings.

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

    Science.gov (United States)

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

    2001-11-01

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

  15. Growth of CrTe thin films by molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Sreenivasan, M.G. [Data Storage Institute, 5 Engineering Drive 1, Singapore 117608 (Singapore); Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Hou, X.J. [Data Storage Institute, 5 Engineering Drive 1, Singapore 117608 (Singapore); Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Teo, K.L. [Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore)]. E-mail: eleteokl@nus.edu.sg; Jalil, M.B.A. [Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Liew, T. [Data Storage Institute, 5 Engineering Drive 1, Singapore 117608 (Singapore); Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Chong, T.C. [Data Storage Institute, 5 Engineering Drive 1, Singapore 117608 (Singapore)

    2006-05-18

    We report the growth of Cr{sub 1-{delta}}Te films on (100) GaAs substrates using ZnTe buffer layers by solid-source molecular-beam epitaxial technique. RHEED patterns indicate a clear structural change during the initial stages of deposition. Temperature-dependent magnetization results reveal that different NiAs-related phases of Cr{sub 1-{delta}}Te can be obtained at different substrate temperatures. By varying the film thickness, a metastable zinc blende structure of CrTe could be obtained at lower substrate temperature.

  16. A portable molecular beam epitaxy system for in situ x-ray investigations at synchrotron beamlines.

    Science.gov (United States)

    Slobodskyy, T; Schroth, P; Grigoriev, D; Minkevich, A A; Hu, D Z; Schaadt, D M; Baumbach, T

    2012-10-01

    A portable synchrotron molecular beam epitaxy (MBE) system is designed and applied for in situ investigations. The growth chamber is equipped with all the standard MBE components such as effusion cells with shutters, main shutter, cooling shroud, manipulator, reflection high energy electron diffraction setup, and pressure gauges. The characteristic feature of the system is the beryllium windows which are used for in situ x-ray measurements. An UHV sample transfer case allows in vacuo transfer of samples prepared elsewhere. We describe the system design and demonstrate its performance by investigating the annealing process of buried InGaAs self-organized quantum dots.

  17. Crystallographic dependence of photocatalytic activity of WO3 thin films prepared by molecular beam epitaxy.

    Science.gov (United States)

    Li, Guoqiang; Varga, Tamas; Yan, Pengfei; Wang, Zhiguo; Wang, Chongmin; Chambers, Scott A; Du, Yingge

    2015-06-21

    We investigated the impact of crystallographic orientation on the photocatalytic activity of single crystalline WO3 thin films prepared by molecular beam epitaxy on the photodegradation of rhodamine B (RhB). A clear effect is observed, with (111) being the most reactive surface, followed by (110) and (001). Photoreactivity is directly correlated with the surface free energy determined by density functional theory calculations. The RhB photodegradation mechanism is found to involve hydroxyl radicals in solution formed from photo-generated holes and differs from previous studies performed on nanoparticles and composites.

  18. Existence and regularity of weak solutions to a model for coarsening in molecular beam epitaxy

    CERN Document Server

    Zhang, Jun

    2011-01-01

    Taking into account the occurrence of a zero of the surface diffusion current and the requirement of the Ehrlich-Schwoebel effect, Siegert et al \\cite{Siegert94} formulate a model of Langevin type that describes the growth of pyramidlike structures on a surface under conditions of molecular beam epitaxy, and that the slope of these pyramids is selected by the crystalline symmetries of the growing film. In this article, the existence and uniqueness of weak solution to an initial boundary value problem for this model is proved, in the case that the noise is neglected. The regularity of the weak solution to models, with/without slope selection, is also investigated.

  19. 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.)

  20. Growth of layered superconductor β-PdBi2 films using molecular beam epitaxy

    Science.gov (United States)

    Denisov, N. V.; Matetskiy, A. V.; Tupkalo, A. V.; Zotov, A. V.; Saranin, A. A.

    2017-04-01

    Bulk β-PdBi2 layered material exhibits advanced properties and is supposed to be probable topological superconductor. We present a method based on molecular beam epitaxy that allows us to grow β-PdBi2 films from a single β-PdBi2 triple layer up to the dozens of triple layers, using Bi(111) film on Si(111) as a template. The grown films demonstrate structural, electronic and superconducting properties similar to those of bulk β-PdBi2 crystals. Ability to grow the β-PdBi2 films of desired thickness opens the promising possibilities to explore fascinating properties of this advanced material.

  1. 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.

  2. 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.

  3. 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.

  4. Molecular beam epitaxy growth and optical properties of single crystal Zn3N2 films

    Science.gov (United States)

    Wu, Peng; Tiedje, T.; Alimohammadi, H.; Bahrami-Yekta, V.; Masnadi-Shirazi, M.; Wang, Cong

    2016-10-01

    Single crystal Zn3N2 films with (100) orientation have been grown by plasma-assisted molecular beam epitaxy on MgO and A-plane sapphire substrates with in situ optical reflectance monitoring of the growth. The optical bandgap was found to be 1.25-1.28 eV and an electron Hall mobility as high as 395 cm2 V-1 s-1 was measured. The films were n-type with carrier concentrations in the 1018-1019 cm-3 range.

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

    Science.gov (United States)

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

    2016-08-01

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

  6. Silicon sheet with molecular beam epitaxy for high efficiency solar cells

    Science.gov (United States)

    Allen, F. G.

    1983-01-01

    The capabilities of the new technique of Molecular Beam Epitaxy (MBE) are applied to the growth of high efficiency silicon solar cells. Because MBE can provide well controlled doping profiles of any desired arbitrary design, including doping profiles of such complexity as built-in surface fields or tandem junction cells, it would appear to be the ideal method for development of high efficiency solar cells. It was proposed that UCLA grow and characterize silicon films and p-n junctions of MBE to determine whether the high crystal quality needed for solar cells could be achieved.

  7. Growth of (110) GaAs/GaAs by molecular beam epitaxy

    Science.gov (United States)

    Parechanian, L. T.; Weber, E. R.; Hierl, T. L.

    1985-04-01

    The simultaneous molecular beam epitaxy (MBE) growth of (100) and (110) GaAs/GaAs intentionally doped with Si(-1E16/cu cm) was studied as a function of substrate temperature, arsenic overpressure, and epitaxial growth rate. The films were analyzed by scanning electron and optical microscopy, liquid helium photoluminescence (PL), and electronic characterization. For the (110) epitaxial layers, an increase in morphological defect density and degradation of PL signal was observed with a lowering of the substrate temperature from 570 C. Capacitance-voltage (CV) and Hall effect measurements yield room temperature donor concentrations for the (100) films of n-7E15/ cu cm while the (110) layers exhibit electron concentrations of n-2E17/cu cm. Hall measuremtns at 77k on the (100) films show the expected mobility enhancement of Si donors, whereas the (110) epi layers become insulating or greatly compensated. This behavior suggests that room temperature conduction in the (110) films is due to a deeper donor partially compensated by an acceptor level whose concentration is of the smae order of magnitude as that of any electrically active Si. Temperature dependent Hall effect indicates that the activation energy of the deeper donor level lies -145 meV from the conduction band.

  8. Molecular beam epitaxy growth of germanium junctions for multi-junction solar cell applications

    Science.gov (United States)

    Masuda, T.; Faucher, J.; Lee, M. L.

    2016-11-01

    We report on the molecular beam epitaxy (MBE) growth and device characteristics of Ge solar cells. Integrating a Ge bottom cell beneath a lattice-matched triple junction stack grown by MBE could enable ultra-high efficiencies without metamorphic growth or wafer bonding. However, a diffused junction cannot be readily formed in Ge by MBE due to the low sticking coefficient of group-V molecules on Ge surfaces. We therefore realized Ge junctions by growth of homo-epitaxial n-Ge on p-Ge wafers within a standard III-V MBE system. We then fabricated Ge solar cells, finding growth temperature and post-growth annealing to be key factors for achieving high efficiency. Open-circuit voltage and fill factor values of ~0.175 V and ~0.59 without a window layer were obtained, both of which are comparable to diffused Ge junctions formed by metal-organic vapor phase epitaxy. We also demonstrate growth of high-quality, single-domain GaAs on the Ge junction, as needed for subsequent growth of III-V subcells, and that the surface passivation afforded by the GaAs layer slightly improves the Ge cell performance.

  9. Electron beam source molecular beam epitaxial growth of analog graded Al(x)Ga(1-x)As ballistic transistors

    Science.gov (United States)

    Malik, Roger J.; Levi, Anthony F. J.

    1988-01-01

    A new method has been developed for the growth of graded band-gap Al(x)Ga(1-x)As alloys by molecular beam epitaxy which is based upon electron beam evaporation of the group III elements. The metal fluxes are measured and feedback controlled using a modulated ion gauge sensor. The system is computer controlled which allows precise programming of the Ga and Al evaporation rates. The large dynamic response of the metal sources enables growth of variable band-gap III-V alloys with arbitrary composition profiles. This new technique is demonstrated by synthesis of analog graded Al(x)Ga(1-x)As unipolar ballistic electron transistors.

  10. The effect of anharmonicity in epitaxial interfaces. I. Substrate-induced dissociation of finite epitaxial islands

    Science.gov (United States)

    Milchev, Andrey; Markov, Ivan

    1984-01-01

    The behaviour of finite epitaxial islands in the periodic field of the substrate is theoretically investigated whereby the role of anharmonicity in the interatomic forces of the deposit is examined. The harmonic potential, traditionally adopted in the model of Frank and van der Merwe, is replaced by Toda and Morse potentials and sets of difference recursion equations, governing the static properties of such a system, are derived and solved numerically. Thus a new effect of substrate-induced rupture of anharmonic chains migrating on the surface, is found. It is shown that dissociation of migrating clusters is enhanced, if: (i) The substrate potential becomes increasingly modulated, (ii) the natural misfit between deposit and substrate is decreased (in absolute value), (iii) the misfit is negative, rather than positive (with the same absolute value) and (iv) the size of the cluster increases. A relation between dislocations in the chain and rupture appears to exist, suggesting dilatons (enormously stretched interatomic bonds) as the origin for destruction. The influence of anharmonicity on the equilibrium structure of the overgrowth is considered in Part II.

  11. Electron-Beam Detection of Bits Reversibly Recorded on Epitaxial InSe/GaSe/Si Phase-Change Diodes

    Science.gov (United States)

    Chaiken, Alison; Gibson, Gary A.; Chen, John; Yeh, Bao S.; Jasinski, J. B.; Liliental‑Weber, Z.; Nauka, K.; Yang, C. C.; Lindig, D. D.; Subramanian, S.

    2006-04-01

    We demonstrate a data read-back scheme based on electron-beam induced current in a data storage device that utilizes thermal recording onto a phase-change medium. The phase-change medium is part of a heterojunction diode whose local charge-collection efficiency depends on the crystalline or amorphous state of a bit. Current gains up to 65 at 2 keV electron beam energy have been demonstrated using InSe/GaSe/Si epitaxial diodes. Fifteen write-erase cycles are obtained without loss of signal contrast by using a protective cap layer and short write pulses. 100 write-erase cycles have been achieved with some loss of contrast. Erasure times for the bits are longer than in similar polycrystalline In-Se media films. Possible reasons for the long erasure times are discussed in terms of a nucleation- or growth-dominated recrystallization. Prospects for extension to smaller bit sizes using electron-beam writing are considered.

  12. Epitaxial film growth study of single crystal V/Ce prepared by molecular-beam epitaxy on sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Homma, H.; Yang, K.Y.; Schuller, I.K.

    1986-11-01

    The growth of epitaxial films of cerium (Ce)/vanadium (V)/on single crystal sapphires (..cap alpha..-Al/sub 2/O/sub 3/) was studied by in-situ reflection high energy electron diffraction and x-ray scattering. For the first time Ce(111) single crystal films was grown on V(110)/Al/sub 2/O/sub 3/(1120) in the Frank-van der Merwe mode. A new epitaxial orientation, different from the well known Nishiyama-Wasserman or Kurdjumov-Sachs orientations is found in the present study. Subsequent V(110) layers grow epitaxially with three equivalent domains.

  13. High Performance Photocathodes based on Molecular Beam Epitaxy Deposition for Next Generation Photo Detectors and Light Sources

    CERN Document Server

    Xie, Junqi; Wagner, Robert

    2013-01-01

    The development of high-performance photocathodes is a key challenge for future accelerator and particle physics applications. In this paper photocathode growth through molecular beam epitaxy is introduced as a promising technique to obtain robust, highly efficient alkali-antimonide based photocathodes. Recent research shows that the quantum efficiency of photocathodes can be significantly enhanced through control of the photocathode crystallinity. Molecular beam epitaxy allows for cost-effective growth of large-area photocathodes with excellent control of the stoichiometry and crystallinity, making photocathodes with peak quantum efficiencies exceeding 35% routine.

  14. Molecular beam epitaxial growth of tungsten layers embedded in single crystal gallium arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Harbison, J.P.; Hwang, D.M.; Levkoff, J.; Derkits G.E. Jr.

    1985-12-01

    We have been able to fabricate structures which consist of a thin (approx.10 nm) polycrystalline W film embedded in surrounding single crystalline GaAs by molecular beam epitaxy (MBE) using an electron beam evaporation source to deposit W metal in an ultrahigh vacuum MBE growth chamber. The entire deposition sequence can take place at elevated temperature (625--700 /sup 0/C) due to the nonreactive nature of W with respect to GaAs. Reflective high-energy diffraction and transmission electron microscopy indicate that the single crystal GaAs overgrowth proceeds by seeding from the GaAs layer beneath the W through spontaneously occurring perforations in the W layer.

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

    Science.gov (United States)

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

    2016-08-01

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

  16. Stochastic growth theory of molecular beam epitaxy with atom correlation effects: A Monte-Carlo master equation method

    Science.gov (United States)

    Nakayama, Hiroshi; Furuichi, Akihisa; Kita, Takashi; Nishino, Taneo

    1997-04-01

    Structural phase transition of epitaxial growing layer is quite important to understand the atomic scale mechanism of molecular beam epitaxy (MBE). GaAs and related alloy semiconductors are typical systems which show variety of such structural transitions during MBE. Structural evolution of surface reconstruction phases and an order-disorder transition in III-V alloy semiconductors are typical cases where such phase transitions appear during epitaxial processes. In this work, a stochastic theory and the Monte-Carlo simulation have been presented to describe the structural evolution of epitaxial growth in binary system. This method, known here as the 'Monte-Carlo master equation (MCME) method', couples a master equation for epitaxial growth kinetics with an Ising Hamiltonian of growing surface. The Monte-Carlo (MC) simulation of binary growing surface with atom-correlation effects has successfully revealed the evolution of atomic structure and the formation of short-range ordering (SRO) during epitaxy. This demonstrates the usefulness of the MCME method in describing the atomic-structural dynamics as compared with a conventional theory of epitaxy based on a diffusion equation and standard nucleation theory.

  17. 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.

  18. 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.

  19. 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...

  20. 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.

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

    Science.gov (United States)

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

    2016-10-01

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

  2. 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.

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

    Science.gov (United States)

    Eifler, G.; Kasper, E.; Ashurov, Kh.; Morozov, S.

    2002-05-01

    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 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.

  4. X-rays diffraction on a new chromium oxide single-crystal thin film prepared by molecular beam epitaxy

    NARCIS (Netherlands)

    Du, X. S.; Hak, S.; Hibma, T.; Rogojanu, O. C.; Struth, B.

    2006-01-01

    Chromium oxide films were prepared on MgO substrates by molecular beam epitaxy. The crystalline structure of the films was characterized by X-ray diffraction (XRD) with conventional as well as synchrotron X-ray sources. The theta-2 theta spectra showed that the film was a new chromium oxide epitaxia

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

    Science.gov (United States)

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

    2014-11-12

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-05-07

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

  7. 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}.

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

    Science.gov (United States)

    Zhong, Aihua; Hane, Kazuhiro

    2012-12-27

    GaN nanowall network was epitaxially grown on Si (111) substrate by molecular beam epitaxy. GaN nanowalls overlap and interlace with one another, together with large numbers of holes, forming a continuous porous GaN nanowall network. The width of the GaN nanowall can be controlled, ranging from 30 to 200 nm by adjusting the N/Ga ratio. Characterization results of a transmission electron microscope and X-ray diffraction show that the GaN nanowall is well oriented along the C axis. Strong band edge emission centered at 363 nm is observed in the spectrum of room temperature photoluminescence, indicating that the GaN nanowall network is of high quality. The sheet resistance of the Si-doped GaN nanowall network along the lateral direction was 58 Ω/. The conductive porous nanowall network can be useful for integrated gas sensors due to the large surface area-to-volume ratio and electrical conductivity along the lateral direction by combining with Si micromachining.

  9. Molecular Beam Epitaxy Growth of High Crystalline Quality LiNbO3

    Science.gov (United States)

    Tellekamp, M. Brooks; Shank, Joshua C.; Goorsky, Mark S.; Doolittle, W. Alan

    2016-12-01

    Lithium niobate is a multi-functional material with wide reaching applications in acoustics, optics, and electronics. Commercial applications for lithium niobate require high crystalline quality currently limited to bulk and ion sliced material. Thin film lithium niobate is an attractive option for a variety of integrated devices, but the research effort has been stagnant due to poor material quality. Both lattice matched and mismatched lithium niobate are grown by molecular beam epitaxy and studied to understand the role of substrate and temperature on nucleation conditions and material quality. Growth on sapphire produces partially coalesced columnar grains with atomically flat plateaus and no twin planes. A symmetric rocking curve shows a narrow linewidth with a full width at half-maximum (FWHM) of 8.6 arcsec (0.0024°), which is comparable to the 5.8 arcsec rocking curve FWHM of the substrate, while the film asymmetric rocking curve is 510 arcsec FWHM. These values indicate that the individual grains are relatively free of long-range disorder detectable by x-ray diffraction with minimal measurable tilt and twist and represents the highest structural quality epitaxial material grown on lattice mismatched sapphire without twin planes. Lithium niobate is also grown on lithium tantalate producing high quality coalesced material without twin planes and with a symmetric rocking curve of 193 arcsec, which is nearly equal to the substrate rocking curve of 194 arcsec. The surface morphology of lithium niobate on lithium tantalate is shown to be atomically flat by atomic force microscopy.

  10. Formation of Ga droplets on patterned GaAs (100) by molecular beam epitaxy.

    Science.gov (United States)

    Li, Ming-Yu; Hirono, Yusuke; Koukourinkova, Sabina D; Sui, Mao; Song, Sangmin; Kim, Eun-Soo; Lee, Jihoon; Salamo, Gregory J

    2012-10-03

    In this paper, the formation of Ga droplets on photo-lithographically patterned GaAs (100) and the control of the size and density of Ga droplets by droplet epitaxy using molecular beam epitaxy are demonstrated. In extension of our previous result from the journal Physical Status Solidi A, volume 209 in 2012, the sharp contrast of the size and density of Ga droplets is clearly observed by high-resolution scanning electron microscope, atomic force microscope, and energy dispersive X-ray spectrometry. Also, additional monolayer (ML) coverage is added to strength the result. The density of droplets is an order of magnitude higher on the trench area (etched area), while the size of droplets is much larger on the strip top area (un-etched area). A systematic variation of ML coverage results in an establishment of the control of size and density of Ga droplets. The cross-sectional line profile analysis and root mean square roughness analysis show that the trench area (etched area) is approximately six times rougher. The atomic surface roughness is suggested to be the main cause of the sharp contrast of the size and density of Ga droplets and is discussed in terms of surface diffusion.

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

    Science.gov (United States)

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

    2016-03-01

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

  12. The competing oxide and sub-oxide formation in metal-oxide molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Vogt, Patrick; Bierwagen, Oliver [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, D-10117 Berlin (Germany)

    2015-02-23

    The hetero-epitaxial growth of the n-type semiconducting oxides β-Ga{sub 2}O{sub 3}, In{sub 2}O{sub 3}, and SnO{sub 2} on c- and r-plane sapphire was performed by plasma-assisted molecular beam epitaxy. The growth-rate and desorbing flux from the substrate were measured in-situ under various oxygen to metal ratios by laser reflectometry and quadrupole mass spectrometry, respectively. These measurements clarified the role of volatile sub-oxide formation (Ga{sub 2}O, In{sub 2}O, and SnO) during growth, the sub-oxide stoichiometry, and the efficiency of oxide formation for the three oxides. As a result, the formation of the sub-oxides decreased the growth-rate under metal-rich growth conditions and resulted in etching of the oxide film by supplying only metal flux. The flux ratio for the exclusive formation of the sub-oxide (e.g., the p-type semiconductor SnO) was determined, and the efficiency of oxide formation was found to be the highest for SnO{sub 2}, somewhat lower for In{sub 2}O{sub 3}, and the lowest for Ga{sub 2}O{sub 3}. Our findings can be generalized to further oxides that possess related sub-oxides.

  13. 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.)

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

    Institute of Scientific and Technical Information of China (English)

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

    2012-01-01

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

  15. 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)

  16. Synthesis of atomically thin hexagonal boron nitride films on nickel foils by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Nakhaie, S.; Wofford, J. M.; Schumann, T.; Jahn, U.; Ramsteiner, M.; Hanke, M.; Lopes, J. M. J., E-mail: lopes@pdi-berlin.de; Riechert, H. [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2015-05-25

    Hexagonal boron nitride (h-BN) is a layered two-dimensional material with properties that make it promising as a dielectric in various applications. We report the growth of h-BN films on Ni foils from elemental B and N using molecular beam epitaxy. The presence of crystalline h-BN over the entire substrate is confirmed by Raman spectroscopy. Atomic force microscopy is used to examine the morphology and continuity of the synthesized films. A scanning electron microscopy study of films obtained using shorter depositions offers insight into the nucleation and growth behavior of h-BN on the Ni substrate. The morphology of h-BN was found to evolve from dendritic, star-shaped islands to larger, smooth triangular ones with increasing growth temperature.

  17. 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.

  18. 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.

  19. Interfaces in InAs/GaSb Superlattices Grown by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    GUO Jie; SUN Wei-Guo; PENG Zhen-Yu; ZHOU Zhi-Qiang; XU Ying-Qiang; NIU Zhi-Chuan

    2009-01-01

    @@ Short period InAs(4ML)/GaSb(SML) superlattices (SLs) with InSb- and mixed-like (or Ga1-xInxAs1-ySby-like) interfaces (IFs) are grown by molecular-beam epitaxy (MBE) on (001) GaSh substrates at optimized growth temperature. Raman scattering reveals that two kinds of IFs can be formed by controlling shutter sequences. X-ray diffraction (XRD) and atomic force microscopy (AFM) demonstrate that SLs with mixed-like IFs are more sensitive to growth temperature than that with InSb-like IFs. The photoluminescence (PL) spectra of SLs with mixed-like IFs show a stronger intensity and narrower line width than with InSb-like IFs. It is concluded that InAs/GaSb SLs with mixed-like IFs have better crystalline and optical properties.

  20. 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.

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

    Science.gov (United States)

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

    2016-07-06

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

  2. 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.

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

    Directory of Open Access Journals (Sweden)

    Wuwei Feng

    2015-11-01

    Full Text Available We have re-investigated growth and magnetic properties of Cr2CoGa films using molecular beam epitaxy technique. Phase separation and precipitate formation were observed experimentally again in agreement with observation of multiple phases separation in sputtered Cr2CoGa films by M. Meinert et al. However, significant phase separation could be suppressed by proper control of growth conditions. We showed that Cr2CoGa Heusler phase, rather than Co2CrGa phase, constitutes the majority of the sample grown on GaAs(001 at 450 oC. The measured small spin moment of Cr2CoGa is in agreement with predicted HM-FCF nature; however, its Curie temperature is not as high as expected from the theoretical prediction probably due to the off-stoichiometry of Cr2CoGa and the existence of the disorders and phase separation.

  4. 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.

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

    Science.gov (United States)

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

    2017-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Jean-Baptiste Laloë

    2011-01-01

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

  7. Synthesis of long group IV semiconductor nanowires by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Patriarche Gilles

    2011-01-01

    Full Text Available Abstract We report the growth of Si and Ge nanowires (NWs on a Si(111 surface by molecular beam epitaxy. While Si NWs grow perpendicular to the surface, two types of growth axes are found for the Ge NWs. Structural studies of both types of NWs performed with electron microscopies reveal a marked difference between the roughnesses of their respective sidewalls. As the investigation of their length dependence on their diameter indicates that the growth of the NWs predominantly proceeds through the diffusion of adatoms from the substrate up along the sidewalls, difference in the sidewall roughness qualitatively explains the length variation measured between both types of NWs. The formation of atomically flat {111} sidewalls on the <110>-oriented Ge NWs accounts for a larger diffusion length.

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

    Science.gov (United States)

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

    2013-05-01

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

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

    Science.gov (United States)

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

    2013-01-11

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

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

    Science.gov (United States)

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

    2015-01-27

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

  11. Raman measurements of substrate temperature in a molecular beam epitaxy growth chamber.

    Science.gov (United States)

    Hutchins, T; Nazari, M; Eridisoorya, M; Myers, T M; Holtz, M

    2015-01-01

    A method is described for directly measuring the temperature of a substrate in a molecular-beam epitaxy (MBE) growth system. The approach relies on the establishment of the temperature dependence of Raman-active phonons of the substrate material using independently known calibration points across the range of interest. An unknown temperature in this range is then determined based on the Raman peak position with the substrate in situ the MBE chamber. The apparatus relies on conventional optics and Raman components. Shifting and broadening of the Raman spectrum are described based on the effects of thermal expansion and anharmonic decay. The choice of reference temperature is discussed. The method is qualified by examining the substrate temperature dependence, relative to that of a standard thermocouple, during a commonly used ramp procedure. Both temperature difference and time lag are obtained.

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

    Science.gov (United States)

    Baiutti, Federico; Christiani, Georg; Logvenov, Gennady

    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- x Sr x NiO4. 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.

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

    Science.gov (United States)

    Tamura, Yosuke; Hane, Kazuhiro

    2015-12-01

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

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

    Science.gov (United States)

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

    2014-01-13

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

  15. Growth of Inclined GaAs Nanowires by Molecular Beam Epitaxy: Theory and Experiment

    Directory of Open Access Journals (Sweden)

    Tchernycheva M

    2010-01-01

    Full Text Available Abstract The growth of inclined GaAs nanowires (NWs during molecular beam epitaxy (MBE on the rotating substrates is studied. The growth model provides explicitly the NW length as a function of radius, supersaturations, diffusion lengths and the tilt angle. Growth experiments are carried out on the GaAs(211A and GaAs(111B substrates. It is found that 20° inclined NWs are two times longer in average, which is explained by a larger impingement rate on their sidewalls. We find that the effective diffusion length at 550°C amounts to 12 nm for the surface adatoms and is more than 5,000 nm for the sidewall adatoms. Supersaturations of surface and sidewall adatoms are also estimated. The obtained results show the importance of sidewall adatoms in the MBE growth of NWs, neglected in a number of earlier studies.

  16. Raman measurements of substrate temperature in a molecular beam epitaxy growth chamber

    Energy Technology Data Exchange (ETDEWEB)

    Hutchins, T.; Nazari, M.; Eridisoorya, M.; Myers, T. M.; Holtz, M., E-mail: Mark.Holtz@txstate.edu [Department of Physics, Texas State University, San Marcos, Texas 78666 (United States)

    2015-01-15

    A method is described for directly measuring the temperature of a substrate in a molecular-beam epitaxy (MBE) growth system. The approach relies on the establishment of the temperature dependence of Raman-active phonons of the substrate material using independently known calibration points across the range of interest. An unknown temperature in this range is then determined based on the Raman peak position with the substrate in situ the MBE chamber. The apparatus relies on conventional optics and Raman components. Shifting and broadening of the Raman spectrum are described based on the effects of thermal expansion and anharmonic decay. The choice of reference temperature is discussed. The method is qualified by examining the substrate temperature dependence, relative to that of a standard thermocouple, during a commonly used ramp procedure. Both temperature difference and time lag are obtained.

  17. Growth of Inclined GaAs Nanowires by Molecular Beam Epitaxy: Theory and Experiment.

    Science.gov (United States)

    Zhang, X; Dubrovskii, V G; Sibirev, N V; Cirlin, G E; Sartel, C; Tchernycheva, M; Harmand, J C; Glas, F

    2010-07-24

    The growth of inclined GaAs nanowires (NWs) during molecular beam epitaxy (MBE) on the rotating substrates is studied. The growth model provides explicitly the NW length as a function of radius, supersaturations, diffusion lengths and the tilt angle. Growth experiments are carried out on the GaAs(211)A and GaAs(111)B substrates. It is found that 20° inclined NWs are two times longer in average, which is explained by a larger impingement rate on their sidewalls. We find that the effective diffusion length at 550°C amounts to 12 nm for the surface adatoms and is more than 5,000 nm for the sidewall adatoms. Supersaturations of surface and sidewall adatoms are also estimated. The obtained results show the importance of sidewall adatoms in the MBE growth of NWs, neglected in a number of earlier studies.

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

    Science.gov (United States)

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

    1989-10-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-06-15

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

  20. Concentration transient analysis of antimony surface segregation during Si(100) molecular beam epitaxy

    Science.gov (United States)

    Markert, L. C.; Greene, J. E.; Ni, W.-X.; Hansson, G. V.; Sundgren, J.-E.

    1991-01-01

    Antimony surface segregation during Si(100) molecular beam epitaxy (MBE) was investigated at temperatures T(sub s) = 515 - 800 C using concentration transient analysis (CTA). The dopant surface coverage Theta, bulk fraction gamma, and incorporation probability sigma during MBE were determined from secondary-ion mass spectrometry depth profiles of modulation-doped films. Programmed T(sub s) changes during growth were used to trap the surface-segregated dopant overlayer, producing concentration spikes whose integrated area corresponds to Theta. Thermal antimony doping by coevaporation was found to result in segregation strongly dependent on T(sub s) with Theta(sub Sb) values up to 0.9 monolayers (ML): in films doped with Sb(+) ions accelerated by 100 V, Theta(sub Sb) was less than or equal to 4 x 10(exp -3) ML. Surface segregation of coevaporated antimony was kinematically limited for the film growth conditions in these experiments.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-11-15

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-06-24

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

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

    Science.gov (United States)

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

    2014-05-05

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

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

    Science.gov (United States)

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

    2015-12-01

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

  5. Molecular beam epitaxy and characterization of thin Bi2Se3 films on Al2O3 (110)

    Science.gov (United States)

    Tabor, Phillip; Keenan, Cameron; Urazhdin, Sergei; Lederman, David

    2011-07-01

    The structural and electronic properties of thin Bi2Se3 films grown on Al2O3 (110) by molecular beam epitaxy are investigated. The epitaxial films grow in the Frank-van der Merwe mode and are c-axis oriented. They exhibit the highest crystallinity, the lowest carrier concentration, and optimal stoichiometry at a substrate temperature of 200 °C determined by the balance between surface kinetics and desorption of Se. The crystallinity of the films improves with increasing Se/Bi flux ratio. Our results enable studies of thin topological insulator films on inert, non-conducting substrates that allow optical access to both film surfaces.

  6. Influence of substrate orientation on the structural quality of GaAs nanowires in molecular beam epitaxy.

    Science.gov (United States)

    Zhang, Zhi; Shi, Sui-Xing; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2015-01-26

    In this study, the effect of substrate orientation on the structural quality of Au-catalyzed epitaxial GaAs nanowires grown by a molecular beam epitaxy reactor has been investigated. It was found that the substrate orientations can be used to manipulate the nanowire catalyst composition and the catalyst surface energy and, therefore, to alter the structural quality of GaAs nanowires grown on different substrates. Defect-free wurtzite-structured GaAs nanowires grown on the GaAs (110) substrate have been achieved under our growth conditions.

  7. Growth and characterization of GaAs layers on Si substrates by migration-enhanced molecular beam epitaxy

    Science.gov (United States)

    Kim, Jae-Hoon; Liu, John K.; Radhakrishnan, Gouri; Katz, Joseph; Sakai, Shiro

    1988-01-01

    Migration-enhanced molecular beam epitaxial (MEMBE) growth and characterization of the GaAs layer on Si substrates (GaAs/Si) are reported. The MEMBE growth method is described, and material properties are compared with those of normal two-step MBE-grown or in situ annealed layers. Micrographs of cross-section view transmission electron microscopy and scanning surface electron microscopy of MEMBE-grown GaAs/Si showed dislocation densities of 10 to the 7th/sq cm. AlGaAs/GaAs double heterostructures have been successfully grown on MEMBE GaAs/Si by both metalorganic chemical vapor deposition and liquid phase epitaxy.

  8. Top-gate dielectric induced doping and scattering of charge carriers in epitaxial graphene

    Science.gov (United States)

    Puls, Conor P.; Staley, Neal E.; Moon, Jeong-Sun; Robinson, Joshua A.; Campbell, Paul M.; Tedesco, Joseph L.; Myers-Ward, Rachael L.; Eddy, Charles R.; Gaskill, D. Kurt; Liu, Ying

    2011-07-01

    We show that an e-gun deposited dielectric impose severe limits on epitaxial graphene-based device performance based on Raman spectroscopy and low-temperature transport measurements. Specifically, we show from studies of epitaxial graphene Hall bars covered by SiO2 that the measured carrier density is strongly inhomogenous and predominantly induced by charged impurities at the grapheme/dielectric interface that limit mobility via Coulomb interactions. Our work emphasizes that material integration of epitaxial graphene and a gate dielectric is the next major road block towards the realization of graphene-based electronics.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-01-05

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

  10. 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.

  11. 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

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

    Science.gov (United States)

    Ng, Hock Min

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

  13. Avoiding polar catastrophe in the growth of polarly orientated nickel perovskite thin films by reactive oxide molecular beam epitaxy

    Science.gov (United States)

    Yang, H. F.; Liu, Z. T.; Fan, C. C.; Yao, Q.; Xiang, P.; Zhang, K. L.; Li, M. Y.; Liu, J. S.; Shen, D. W.

    2016-08-01

    By means of the state-of-the-art reactive oxide molecular beam epitaxy, we synthesized (001)- and (111)-orientated polar LaNiO3 thin films. In order to avoid the interfacial reconstructions induced by polar catastrophe, screening metallic Nb-doped SrTiO3 and iso-polarity LaAlO3 substrates were chosen to achieve high-quality (001)-orientated films in a layer-by-layer growth mode. For largely polar (111)-orientated films, we showed that iso-polarity LaAlO3 (111) substrate was more suitable than Nb-doped SrTiO3. In situ reflection high-energy electron diffraction, ex situ high-resolution X-ray diffraction, and atomic force microscopy were used to characterize these films. Our results show that special attentions need to be paid to grow high-quality oxide films with polar orientations, which can prompt the explorations of all-oxide electronics and artificial interfacial engineering to pursue intriguing emergent physics like proposed interfacial superconductivity and topological phases in LaNiO3 based superlattices.

  14. Avoiding polar catastrophe in the growth of polarly orientated nickel perovskite thin films by reactive oxide molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    H. F. Yang

    2016-08-01

    Full Text Available By means of the state-of-the-art reactive oxide molecular beam epitaxy, we synthesized (001- and (111-orientated polar LaNiO3 thin films. In order to avoid the interfacial reconstructions induced by polar catastrophe, screening metallic Nb-doped SrTiO3 and iso-polarity LaAlO3 substrates were chosen to achieve high-quality (001-orientated films in a layer-by-layer growth mode. For largely polar (111-orientated films, we showed that iso-polarity LaAlO3 (111 substrate was more suitable than Nb-doped SrTiO3. In situ reflection high-energy electron diffraction, ex situ high-resolution X-ray diffraction, and atomic force microscopy were used to characterize these films. Our results show that special attentions need to be paid to grow high-quality oxide films with polar orientations, which can prompt the explorations of all-oxide electronics and artificial interfacial engineering to pursue intriguing emergent physics like proposed interfacial superconductivity and topological phases in LaNiO3 based superlattices.

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

    Energy Technology Data Exchange (ETDEWEB)

    Shah, A., E-mail: attaullah77@yahoo.com [National Institute of Lasers and Optronics (NILOP), PO Nilore, Islamabad (Pakistan); DMME, Pakistan Institute of Engineering and Applied Science (PIEAS), PO Nilore, Islamabad (Pakistan); Ahmad, Jamil [DMME, Pakistan Institute of Engineering and Applied Science (PIEAS), PO Nilore, Islamabad (Pakistan); Ahmad, Ishaq [Experimental Physics Lab, National Center for Physics (NCP), Islamabad (Pakistan); Mehmood, Mazhar [DMME, Pakistan Institute of Engineering and Applied Science (PIEAS), PO Nilore, Islamabad (Pakistan); Mahmood, Arshad [National Institute of Lasers and Optronics (NILOP), PO Nilore, Islamabad (Pakistan); Rasheed, Muhammad Asim [DMME, Pakistan Institute of Engineering and Applied Science (PIEAS), PO Nilore, Islamabad (Pakistan)

    2014-10-30

    Highlights: • AlN:Cu dilute magnetic semiconductors were successfully prepared by molecular beam epitaxy followed by Cu{sup +} 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{sup +} ions into AlN thin films at various ion fluxes. AlN films were deposited on c-plane sapphire by molecular beam epitaxy followed by Cu{sup +} 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 E{sub 2} (high) and A{sub 1} (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{sup +} 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

  16. Growth instability due to lattice-induced topological currents in limited-mobility epitaxial growth models.

    Science.gov (United States)

    Kanjanaput, Wittawat; Limkumnerd, Surachate; Chatraphorn, Patcha

    2010-10-01

    The energetically driven Ehrlich-Schwoebel barrier had been generally accepted as the primary cause of the growth instability in the form of quasiregular moundlike structures observed on the surface of thin film grown via molecular-beam epitaxy (MBE) technique. Recently the second mechanism of mound formation was proposed in terms of a topologically induced flux of particles originating from the line tension of the step edges which form the contour lines around a mound. Through large-scale simulations of MBE growth on a variety of crystalline lattice planes using limited-mobility, solid-on-solid models introduced by Wolf-Villain and Das Sarma-Tamborenea in 2+1 dimensions, we show that there exists a topological uphill particle current with strong dependence on specific lattice crystalline structure. Without any energetically induced barriers, our simulations produce spectacular mounds very similar, in some cases, to what have been observed in many recent MBE experiments. On a lattice where these currents cease to exist, the surface appears to be scale invariant, statistically rough as predicted by the conventional continuum growth equation.

  17. High electron mobility of modulation doped GaAs after growing InP by solid source molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    SHU Yong-chun; PI Biao; LIN Yao-wang; XING Xiao-dong; YAO Jiang-hong; WANG Zhan-guo; XU Jing-jun

    2005-01-01

    Modulation-doped AlGaAs/GaAs structures were grown on GaAs(100) substrate by solid source molecular beam epitaxy (SSMBE) system. The factors which influence the electron mobility were investigated. After growing InP based materials, growth conditions were deteriorated, but by an appropriate method and using reasonaand growth conditions have been studied and optimized via Hall measurements. For a typical sample, 2.0 K electron served.

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

    OpenAIRE

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

    2004-01-01

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

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

    OpenAIRE

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

    2011-01-01

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

  20. 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...

  1. Plasma-assisted molecular beam epitaxy growth of ZnSnN2

    Science.gov (United States)

    Feldberg, Nathaniel; Aldous, James; Yao, Yuan; Tanveer, Imtiaz; Keen, Benjamin; Linhart, Wojciech; Veal, Tim; Song, Young-Wook; Reeves, Roger; Durbin, Steve

    2012-02-01

    The Zn-IV-nitrides are a promising series of ``earth abundant element'' semiconductors with a predicted band gap range of 0.6 eV to 5.4 eV, which, like the (Al,Ga,In)N family, spans the entire visible solar spectrum. Considering this alternative family has a number of advantages, including the avoidance of indium, the price of which has varied almost an order of magnitude over the past decade, and surface electron accumulation which is present in the In-rich alloys. Not all members of this family have yet been synthesized, in particular ZnSnN2, the most important member for PV with its predicted band gap of approximately 2 eV. We have successfully grown a series of these films using plasma-assisted molecular beam epitaxy using elemental Zn and Sn sources. In this report, we discuss the relationship between process parameters and microstructure, as well as stoichiometry as determined by Rutherford backscattering spectrometry. Additionally, we provide preliminary estimates for its bandgap energy based on photoluminescence and optical absorption.

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

    Science.gov (United States)

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

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

  3. Temperature stabilized effusion cell evaporation source for thin film deposition and molecular-beam epitaxy

    Science.gov (United States)

    Tiedje, H. F.; Brodie, D. E.

    2000-05-01

    A simple effusion cell evaporation source for thin film deposition and molecular-beam epitaxy is described. The source consists of a crucible with a thermocouple temperature sensor heated by a resistive crucible heater. Radiation heat transfer from the crucible to the thermocouple produces a consistent and reproducible thermocouple temperature for a given crucible temperature, without direct contact between the thermocouple and the crucible. The thermocouple temperature is somewhat less than the actual crucible temperature because of heat flow from the thermocouple junction along the thermocouple lead wires. In a typical case, the thermocouple temperature is 1007 °C while the crucible is at 1083 °C. The crucible temperature stability is estimated from the measured sensitivity of the evaporation rate of indium to temperature, and the observed variations in the evaporation rate for a fixed thermocouple temperature. The crucible temperature peak-to-peak variation over a one hour period is 1.2 °C. Machined molybdenum crucibles were used in the indium and copper sources for depositing CuInSe2 thin films for solar cells.

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

    Science.gov (United States)

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

    2016-08-01

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

  5. Molecular beam epitaxy of InN dots on nitrided sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Romanyuk, Yaroslav E.; Dengel, Radu-Gabriel; Stebounova, LarissaV.; Leone, Stephen R.

    2007-04-20

    A series of self-assembled InN dots are grown by radio frequency (RF) plasma-assisted molecular beam epitaxy (MBE) directly on nitrided sapphire. Initial nitridation of the sapphire substrates at 900 C results in the formation of a rough AlN surface layer, which acts as a very thin buffer layer and facilitates the nucleation of the InN dots according to the Stranski-Krastanow growth mode, with a wetting layer of {approx}0.9 nm. Atomic force microscopy (AFM) reveals that well-confined InN nanoislands with the greatest height/width at half-height ratio of 0.64 can be grown at 460 C. Lower substrate temperatures result in a reduced aspect ratio due to a lower diffusion rate of the In adatoms, whereas the thermal decomposition of InN truncates the growth at T>500 C. The densities of separated dots vary between 1.0 x 10{sup 10} cm{sup -2} and 2.5 x 10{sup 10} cm{sup -2} depending on the growth time. Optical response of the InN dots under laser excitation is studied with apertureless near-field scanning optical microscopy and photoluminescence spectroscopy, although no photoluminescence is observed from these samples. In view of the desirable implementation of InN nanostructures into photonic devices, the results indicate that nitrided sapphire is a suitable substrate for growing self-assembled InN nanodots.

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

    Science.gov (United States)

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

    2017-01-01

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

  7. Graphitic platform for self-catalysed InAs nanowires growth by molecular beam epitaxy.

    Science.gov (United States)

    Zhuang, Qian D; Anyebe, Ezekiel A; Sanchez, Ana M; Rajpalke, Mohana K; Veal, Tim D; Zhukov, Alexander; Robinson, Benjamin J; Anderson, Frazer; Kolosov, Oleg; Fal'ko, Vladimir

    2014-01-01

    We report the self-catalysed growth of InAs nanowires (NWs) on graphite thin films using molecular beam epitaxy via a droplet-assisted technique. Through optimising metal droplets, we obtained vertically aligned InAs NWs with highly uniform diameter along their entire length. In comparison with conventional InAs NWs grown on Si (111), the graphite surface led to significant effects on the NWs geometry grown on it, i.e. larger diameter, shorter length with lower number density, which were ascribed to the absence of dangling bonds on the graphite surface. The axial growth rate of the NWs has a strong dependence on growth time, which increases quickly in the beginning then slows down after the NWs reach a length of approximately 0.8 μm. This is attributed to the combined axial growth contributions from the surface impingement and sidewall impingement together with the desorption of adatoms during the diffusion. The growth of InAs NWs on graphite was proposed following a vapour-solid mechanism. High-resolution transmission electron microscopy reveals that the NW has a mixture of pure zinc-blende and wurtzite insertions.

  8. Dynamic layer rearrangement during growth of layered oxide films by molecular beam epitaxy.

    Science.gov (United States)

    Lee, J H; Luo, G; Tung, I C; Chang, S H; Luo, Z; Malshe, M; Gadre, M; Bhattacharya, A; Nakhmanson, S M; Eastman, J A; Hong, H; Jellinek, J; Morgan, D; Fong, D D; Freeland, J W

    2014-09-01

    The A(n+1)B(n)O(3n+1) Ruddlesden-Popper homologous series offers a wide variety of functionalities including dielectric, ferroelectric, magnetic and catalytic properties. Unfortunately, the synthesis of such layered oxides has been a major challenge owing to the occurrence of growth defects that result in poor materials behaviour in the higher-order members. To understand the fundamental physics of layered oxide growth, we have developed an oxide molecular beam epitaxy system with in situ synchrotron X-ray scattering capability. We present results demonstrating that layered oxide films can dynamically rearrange during growth, leading to structures that are highly unexpected on the basis of the intended layer sequencing. Theoretical calculations indicate that rearrangement can occur in many layered oxide systems and suggest a general approach that may be essential for the construction of metastable Ruddlesden-Popper phases. We demonstrate the utility of the new-found growth strategy by performing the first atomically controlled synthesis of single-crystalline La3Ni2O7.

  9. 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.

  10. Growth of SrVO{sub 3} thin films by hybrid molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Eaton, Craig; Brahlek, Matthew; Engel-Herbert, Roman, E-mail: rue2@psu.edu [Department of Material Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Moyer, Jarrett A. [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Alipour, Hamideh M.; Grimley, Everett D.; LeBeau, James M. [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)

    2015-11-15

    The authors report the growth of stoichiometric SrVO{sub 3} thin films on (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 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 SrVO{sub 3} 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 SrVO{sub 3} 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.

  11. Mapping growth windows in quaternary perovskite oxide systems by hybrid molecular beam epitaxy

    Science.gov (United States)

    Brahlek, Matthew; Zhang, Lei; Zhang, Hai-Tian; Lapano, Jason; Dedon, Liv R.; Martin, Lane W.; Engel-Herbert, Roman

    2016-09-01

    Requisite to growing stoichiometric perovskite thin films of the solid-solution A'1-xAxBO3 by hybrid molecular beam epitaxy is understanding how the growth conditions interpolate between the end members A'BO3 and ABO3, which can be grown in a self-regulated fashion, but under different conditions. Using the example of La1-xSrxVO3, the two-dimensional growth parameter space that is spanned by the flux of the metal-organic precursor vanadium oxytriisopropoxide and composition, x, was mapped out. The evolution of the adsorption-controlled growth window was obtained using a combination of X-ray diffraction, atomic force microscopy, reflection high-energy electron-diffraction (RHEED), and Rutherford backscattering spectroscopy. It is found that the stoichiometric growth conditions can be mapped out quickly with a single calibration sample using RHEED. Once stoichiometric conditions have been identified, the out-of-plane lattice parameter can be utilized to precisely determine the composition x. This strategy enables the identification of growth conditions that allow the deposition of stoichiometric perovskite oxide films with random A-site cation mixing, which is relevant to a large number of perovskite materials with interesting properties, e.g., high-temperature superconductivity and colossal magnetoresistance, that emerge in solid solution A'1-xAxBO3.

  12. 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.

  13. Numerical approximations for the molecular beam epitaxial growth model based on the invariant energy quadratization method

    Science.gov (United States)

    Yang, Xiaofeng; Zhao, Jia; Wang, Qi

    2017-03-01

    The Molecular Beam Epitaxial model is derived from the variation of a free energy, that consists of either a fourth order Ginzburg-Landau double well potential or a nonlinear logarithmic potential in terms of the gradient of a height function. One challenge in solving the MBE model numerically is how to develop proper temporal discretization for the nonlinear terms in order to preserve energy stability at the time-discrete level. In this paper, we resolve this issue by developing a first and second order time-stepping scheme based on the "Invariant Energy Quadratization" (IEQ) method. The novelty is that all nonlinear terms are treated semi-explicitly, and the resulted semi-discrete equations form a linear system at each time step. Moreover, the linear operator is symmetric positive definite and thus can be solved efficiently. We then prove that all proposed schemes are unconditionally energy stable. The semi-discrete schemes are further discretized in space using finite difference methods and implemented on GPUs for high-performance computing. Various 2D and 3D numerical examples are presented to demonstrate stability and accuracy of the proposed schemes.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-08-29

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

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

    Science.gov (United States)

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

    2017-02-01

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

  16. InGaN violet laser diodes grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

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

    2004-09-01

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

  17. Formation of Ge-Sn nanodots on Si(100 surfaces by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Yu Ing-Song

    2011-01-01

    Full Text Available Abstract The surface morphology of Ge0.96Sn0.04/Si(100 heterostructures grown at temperatures from 250 to 450°C by atomic force microscopy (AFM and scanning tunnel microscopy (STM ex situ has been studied. The statistical data for the density of Ge0.96Sn0.04 nanodots (ND depending on their lateral size have been obtained. Maximum density of ND (6 × 1011 cm-2 with the average lateral size of 7 nm can be obtained at 250°C. Relying on the reflection of high energy electron diffraction, AFM, and STM, it is concluded that molecular beam growth of Ge1-xSnx heterostructures with the small concentrations of Sn in the range of substrate temperatures from 250 to 450°C follows the Stranski-Krastanow mechanism. Based on the technique of recording diffractometry of high energy electrons during the process of epitaxy, the wetting layer thickness of Ge0.96Sn0.04 films is found to depend on the temperature of the substrate.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-02-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-01-21

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

  20. 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.

  1. Growth of uniform CaGe2 films by alternating layer molecular beam epitaxy

    Science.gov (United States)

    Xu, Jinsong; Katoch, Jyoti; Ahmed, Adam S.; Pinchuk, Igor V.; Young, Justin R.; Johnston-Halperin, Ezekiel; Pelz, Jonathan; Kawakami, Roland K.

    2017-02-01

    Layered Zintl phase van der Waals (vdW) materials are of interest due to their strong spin-orbit coupling and potential for high mobility. Here, we report the successful growth of large area CaGe2 films, as a model of layered Zintl phase materials, on atomically flat Ge(111) substrates by molecular beam epitaxy (MBE) using an alternating layer growth (ALG) protocol. Reflection high energy electron diffraction (RHEED) patterns of the Ge buffer layer and CaGe2 indicate high quality two dimensional surfaces, which is further confirmed by atomic force microscopy (AFM), showing atomically flat and uniform CaGe2 films. The appearance of Laue oscillations in X-ray diffraction (XRD) and Kiessig fringes in the X-ray reflectivity (XRR), which are absent in co-deposited CaGe2, confirms the uniformity of the CaGe2 film and the smoothness of the interface. These results demonstrate a novel method of deposition of CaGe2 that could be also applied to other layered Zintl phase vdW materials. Also, the high quality of the CaGe2 film is promising for the exploration of novel properties of germanane.

  2. 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.

  3. Strain-relaxation in NH{sub 3}-source molecular beam epitaxy of AlN epilayers on GaN epitaxial templates

    Energy Technology Data Exchange (ETDEWEB)

    Koyama, T.; Onuma, T.; Chichibu, S.F. [Institute of Applied Physics and Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573 (Japan); NICP, ERATO, Japan Science and Technology Agency (JST), Kawaguchi 332-0012 (Japan); Sugawara, M.; Uchinuma, Y. [Institute of Applied Physics and Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573 (Japan); Kaeding, J.F.; Sharma, R. [Department of Materials Engineering, University of California, Santa Barbara, CA 93106 (United States); Nakamura, S. [NICP, ERATO, Japan Science and Technology Agency (JST), Kawaguchi 332-0012 (Japan); Department of Materials Engineering, University of California, Santa Barbara, CA 93106 (United States)

    2006-05-15

    Temporal evolution of surface morphology in AlN epilayers grown by NH{sub 3}-source molecular beam epitaxy on the GaN/(0001) Al{sub 2}O{sub 3} epitaxial templates was correlated with changes in the degree of the residual strain and the layer thickness. They began to crack for the thickness as thin as 10 nm. However, atomic-layer step-and-terrace surface structures were maintained for the thickness up to 32 nm. Tensile biaxial stress decreased with further increase in the thickness due to the lattice relaxation, which caused surface roughening. An 1580-nm-thick, nearly strain-compensated AlN epilayer, of which threading dislocation density was reduced down to 6 x 10{sup 9} cm{sup -2}, exhibited excitonic photoluminescence peaks at 6.002 and 6.023 eV at 9 K and a near-band-edge peak at 5.872 eV at 293 K. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

    Science.gov (United States)

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

    2017-03-01

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

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

    Science.gov (United States)

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

    2016-04-26

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

  6. 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.

  7. Epitaxial Fe3Si films on GaAs(100) substrates by means of electron beam evaporation

    Science.gov (United States)

    Thomas, J.; Schumann, J.; Vinzelberg, H.; Arushanov, E.; Engelhard, R.; Schmidt, O. G.; Gemming, T.

    2009-06-01

    This paper presents results on the preparation, structural, electrical and magnetic properties of Fe3Si films as a representative for a Heusler alloy-like compound which are known as half-metallic materials with ferromagnetic behaviour. The films have been prepared by means of ultra-high vacuum (UHV) electron beam evaporation with the aim of achieving epitaxial growth on GaAs(100) substrates. The main focus of this work is the structural characterization of the Fe3Si films grown on GaAs by means of high resolution transmission electron microscopy (TEM) to confirm the epitaxial growth. For Fe3Si with a composition in the vicinity of stoichiometry an almost lattice-matched growth on GaAs(001) has been observed characterized by a high crystalline quality and a good interface perfection. Besides the studies on cross-sectional samples by TEM data from reflection high energy electron diffraction (RHEED) and x-ray diffraction (XRD) were also included into the discussion. The electrical and magnetic parameters of the films studied are found to be in good agreement with data reported for the best Fe3Si molecular beam epitaxy (MBE) layers. As evidenced by x-ray diffraction, transmission electron microscopy, resistivity and magnetic measurements, we find an optimum growth temperature of 280-350 °C to obtain ferromagnetic layers with high crystal and interface perfection as well as a high degree of atomic ordering.

  8. Laser molecular-beam epitaxy and second-order optical nonlinearity of BaTiO3/SrTiO3 superlattices

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A series of c-axis oriented BaTiO3/SrTiO3 superlattices with the atomic-scale precision were epitaxially grown on single-crystal SrTiO3 (100) substrates using laser molecular-beam epitaxy (LMBE). A periodic modulation of the intensity of reflection high-energy electron diffraction (RHEED) in BaTiO3 and SrTiO3 layers was observed and attributed to the lattice-misfit-induced periodic variation of the terrace density in film surface. The relationship between the second-order nonlinear optical susceptibilities and the superlattice structure was systematically studied. The experimental and theoretical fitting results indicate that the second-order nonlinear optical susceptibilities of BaTiO3/SrTiO3 superlattices were greatly enhanced with the maximum value being more than one order of magnitude larger than that of bulk BaTiO3 crystal. The mechanism of the enhancement of the second-order optical nonlinearity was discussed by taking into account the stress-induced lattice distortion and polarization enhancement.

  9. Increase in the diffusion length of minority carriers in Al{sub x}Ga{sub 1–x}N alloys ({sub x} = 0–0.1) fabricated by ammonia molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Malin, T. V., E-mail: mal-tv@mail.ru; Gilinsky, A. M.; Mansurov, V. G.; Protasov, D. Yu.; Kozhuhov, A. S. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Yakimov, E. B. [Russian Academy of Sciences, Institute of Microelectronics Technology and High Purity Materials (Russian Federation); Zhuravlev, K. S. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation)

    2015-10-15

    The room-temperature diffusion length of minority carriers in n-Al{sub 0.1}Ga{sub 0.9}N 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.

  10. Structural properties of SrO thin films grown by molecular beam epitaxy on LaAlO3 substrates

    Science.gov (United States)

    Maksimov, O.; Heydemann, V. D.; Fisher, P.; Skowronski, M.; Salvador, P. A.

    2006-12-01

    SrO films were grown on LaAlO3 substrates by molecular beam epitaxy and characterized using reflection high-energy electron diffraction (RHEED) and x-ray diffraction (XRD). The evolution of the RHEED pattern is discussed as a function of film thickness. 500Å thick SrO films were relaxed and exhibited RHEED patterns indicative of an atomically smooth surface having uniform terrace heights. Films had the epitaxial relationship (001)SrO‖(001)LaAlO3; [010]SrO‖[110]LaAlO3. This 45° in-plane rotation minimizes mismatch and leads to films of high crystalline quality, as verified by Kikuchi lines in the RHEED patterns and narrow rocking curves of the (002) XRD peak.

  11. Molecular beam epitaxial growth of a three-dimensional topological Dirac semimetal Na{sub 3}Bi

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yi, E-mail: YiZhang@lbl.gov [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Stanford Institute of Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Liu, Zhongkai; Shen, Zhi-Xun [Stanford Institute of Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Geballe Laboratory for Advanced Materials, Departments of Physics and Applied Physics, Stanford University, Stanford, California 94305 (United States); Zhou, Bo [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Geballe Laboratory for Advanced Materials, Departments of Physics and Applied Physics, Stanford University, Stanford, California 94305 (United States); Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Kim, Yeongkwan; Hussain, Zahid; Mo, Sung-Kwan, E-mail: SKMo@lbl.gov [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Chen, Yulin [Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom)

    2014-07-21

    We report a molecular beam epitaxial growth of Na{sub 3}Bi single-crystal thin films on two different substrates—epitaxial bilayer graphene terminated 6H-SiC(0001) and Si(111). Using reflection high-energy electron diffraction, we found that the lattice orientation of the grown Na{sub 3}Bi thin film was rotated by 30° respect to the surface lattice orientations of these two substrates. An in-situ angle-resolved photoemission spectroscopy clearly revealed the 3-dimensional Dirac-cone band structure in such thin films. Our approach of growing Na{sub 3}Bi thin film provides a potential route for further studying its intriguing electronic properties and for fabricating it into practical devices in future.

  12. Strain relief and growth optimization of GaSb on GaP by molecular beam epitaxy.

    Science.gov (United States)

    Wang, Y; Ruterana, P; Chen, J; Desplanque, L; El Kazzi, S; Wallart, X

    2012-08-22

    In this paper, the impact of growth parameters on the strain relaxation of highly lattice mismatched (11.8%) GaSb grown on GaP substrate by molecular beam epitaxy has been investigated. The surface morphology, misfit dislocation and strain relaxation of the GaSb islands are shown to be highly related to the initial surface treatment, growth rate and temperature. More specifically, Sb-rich surface treatment is shown to promote the formation of Lomer misfit dislocations. Analysis of the misfit dislocation and strain relaxation as functions of the growth temperature and rate led to an optimal growth window for a high quality GaSb epitaxial layer on (001) GaP. With this demonstrated optimized growth, a high mobility (25,500 cm(2) V (-1) s(-1) at room temperature) AlSb/InAs heterostructure on a semi-insulating (001) GaP substrate has been achieved.

  13. Ion beam induced luminescence from diamond using an MeV ion microprobe

    Energy Technology Data Exchange (ETDEWEB)

    Bettiol, A.A.; Jamieson, D. N.; Prawer, S.; Allen, M.G. [Melbourne Univ., Parkville, VIC (Australia). School of Physics

    1993-12-31

    Analysis of the luminescence induced by a MeV ion beam offers the potential to provide useful information about the chemical properties of atoms in crystals to complement the information provided by more traditional Ion Beam Analysis (IBA) such as Rutherford Backscattering Spectrometry (RBS), ion channeling and Particle Induced X-ray Emission (PIXE). Furthermore, the large penetration depth of the MeV ion beam offers several advantages over the relatively shallow penetration of keV electrons typically employed in cathodoluminescence. An Ion Beam Induced Luminescence (IBIL) detection system was developed for the Melbourne microprobe that allows the spatial mapping of the luminescence signal along with the signals from RBS and PIXE. Homoepitaxial diamond growth has been studied and remarkable shifts in the characteristic blue luminescence of diamond towards the green were observed in the overgrowth. This has been tentatively identified as being due to transition metal inclusions in the epitaxial layers. 8 refs., 2 refs.

  14. 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...

  15. Molecular beam epitaxy of thin HfTe2 semimetal films

    Science.gov (United States)

    Aminalragia-Giamini, S.; Marquez-Velasco, J.; Tsipas, P.; Tsoutsou, D.; Renaud, G.; Dimoulas, A.

    2017-03-01

    Epitaxial thin films of 1T-HfTe2 semimetal are grown by MBE on AlN(0001) substrates. The measured in-plane lattice parameter indicates an unstrained film which is also azimuthally aligned with the AlN substrate, albeit with an in-plane mosaic spread, as it would be expected for van der Waals epitaxy. Angle resolved photoemission spectroscopy combined with first principles electronic band structure calculations show steep linearly dispersing conduction and valence bands which cross near the Brillouin zone center, providing evidence that HfTe2/AlN is an epitaxial topological Dirac semimetal.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-03-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-11-02

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Dheeraj, D.L.

    2010-10-15

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Du, Y., E-mail: yingge.du@pnnl.gov, E-mail: scott.chambers@pnnl.gov; Liyu, A. V. [Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Droubay, T. C.; Chambers, S. A., E-mail: yingge.du@pnnl.gov, E-mail: scott.chambers@pnnl.gov [Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Li, G. [Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)

    2014-04-21

    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.

  20. Self-corrected Sensors Based On Atomic Absorption Spectroscopy For Atom Flux Measurements In Molecular Beam Epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Du, Yingge; Droubay, Timothy C.; Liyu, Andrey V.; Li, Guosheng; Chambers, Scott A.

    2014-04-24

    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 (CCD) detector in a double-beam configuration, we employ a non-resonant line or a resonant line with lower absorbance 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.

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

    Science.gov (United States)

    Du, Y.; Droubay, T. C.; Liyu, A. V.; Li, G.; Chambers, S. A.

    2014-04-01

    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.

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

    Science.gov (United States)

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

    2012-08-01

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

  3. Defect-free zinc-blende structured InAs nanowires realized by in situ two V/III ratio growth in molecular beam epitaxy.

    Science.gov (United States)

    Zhang, Zhi; Lu, Zhen-Yu; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2015-08-07

    In this study, we devised a two-V/III-ratio procedure to control the Au-assisted growth of defect-free InAs nanowires in molecular beam epitaxy. The demonstrated two V/III ratio procedure consists of a first high V/III ratio growth step to prepare the nanowire foundation on the substrate surface, followed by a low V/III ratio step to induce the nanowire growth. By manipulating the V/III ratios in different steps, we have achieved the controlled growth of pure defect-free zinc-blende structured InAs nanowires on the GaAs {1̄1̄1̄} substrates. This study provides an approach to control not only the crystal structure of semiconductor nanowires, but also their structural qualities.

  4. 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.)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-05-20

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

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

    Directory of Open Access Journals (Sweden)

    Zheng Zuo

    2013-03-01

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

  7. Chemical beam epitaxy growth of AlGaAs/GaAs tunnel junctions using trimethyl aluminium for multijunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Paquette, B.; DeVita, M.; Turala, A.; Kolhatkar, G.; Boucherif, A.; Jaouad, A.; Aimez, V.; Arès, R. [Institut Interdisciplinaire d' Innovation Technologique (3IT), Université de Sherbrooke, Sherbrooke, Québec (Canada); Wilkins, M.; Wheeldon, J. F.; Walker, A. W.; Hinzer, K. [Centre for Research in Photonics, University of Ottawa, Ottawa, ON (Canada); Fafard, S. [Cyrium Technologies Inc., Ottawa, ON (Canada)

    2013-09-27

    AlGaAs/GaAs tunnel junctions for use in high concentration multijunction solar cells were designed and grown by chemical beam epitaxy (CBE) using trimethyl aluminium (TMA) as the p-dopant source for the AlGaAs active layer. Controlled hole concentration up to 4⋅10{sup 20} cm{sup −3} was achieved through variation in growth parameters. Fabricated tunnel junctions have a peak tunneling current up to 6140 A/cm{sup 2}. These are suitable for high concentration use and outperform GaAs/GaAs tunnel junctions.

  8. InAsP/InGaAsP Strained Microstructures Grown by Gas Source Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    CHEN Yi-Qiao; CHEN Jian-Xin; ZHANG Yong-Gang; LI Ai-Zhen; K. Frbjdh; B. Stotz

    2000-01-01

    Device quality InAsP/InGaAsP strained multiquantum-well (MQW) structures are successfully grown by using gas source molecular beam epitaxy method. The grown MQW and InGaAsP quanternary alloy are characterized by using x-ray diffraction, room temperature photoluminescence measurements, confirming that optimum growth condition and high quality material have been obtained for device application. The grown laser structures are processed into ridge waveguide lasers. A threshold current as low as 16mA at 250C for 300μm long device has been obtained. Temperature-dependent light-current measurement shows a characteristic temperature of75K.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-03-18

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

  10. Nucleation, Growth, and Bundling of GaN Nanowires in Molecular Beam Epitaxy: Disentangling the Origin of Nanowire Coalescence.

    Science.gov (United States)

    Kaganer, Vladimir M; Fernández-Garrido, Sergio; Dogan, Pinar; Sabelfeld, Karl K; Brandt, Oliver

    2016-06-08

    We investigate the nucleation, growth, and coalescence of spontaneously formed GaN nanowires in molecular beam epitaxy combining the statistical analysis of scanning electron micrographs with Monte Carlo growth models. We find that (i) the nanowire density is limited by the shadowing of the substrate from the impinging fluxes by already existing nanowires, (ii) shortly after the nucleation stage, nanowire radial growth becomes negligible, and (iii) coalescence is caused by bundling of nanowires. The latter phenomenon is driven by the gain of surface energy at the expense of the elastic energy of bending and becomes energetically favorable once the nanowires exceed a certain critical length.

  11. Growth window and effect of substrate symmetry in hybrid molecular beam epitaxy of a Mott insulating rare earth titanate

    Energy Technology Data Exchange (ETDEWEB)

    Moetakef, Pouya; Zhang, Jack Y.; Raghavan, Santosh; Kajdos, Adam P.; Stemmer, Susanne [Materials Department, University of California, Santa Barbara, California, 93106-5050 (United States)

    2013-07-15

    The conditions for the growth of stoichiometric GdTiO{sub 3} thin films by molecular beam epitaxy (MBE) are investigated. It is shown that relatively high growth temperatures (>750 Degree-Sign C) are required to obtain an MBE growth window in which only the stoichiometric film grows for a range of cation flux ratios. This growth window narrows with increasing film thickness. It is also shown that single-domain films are obtained by the growth on a symmetry-matched substrate. The influence of lattice mismatch strain on the electrical and magnetic characteristics of the GdTiO{sub 3} thin film is investigated.

  12. Growth of GaSb1-xBix by molecular beam epitaxy

    DEFF Research Database (Denmark)

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

    2012-01-01

    Molecular beam epitaxy for GaSb1-xBix is investigated in this article. The growth window for incorporation of Bi in GaSb was found. Strategies of avoiding formation of Bi droplets and enhancing Bi incorporation were studied. The Bi incorporation was confirmed by SIMS and RBS measurements. The Bi...... concentration in the samples was found to increase with increasing growth temperature and Bi flux. The position of GaSb1-xBix layer peak in XRD rocking curves is found to be correlated to Bi composition. Surface and structural properties of the samples were also investigated. Samples grown on GaSb and Ga...

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

    OpenAIRE

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

    2004-01-01

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

  14. Integration of carbon nanotubes with semiconductor technology: fabrication of hybrid devices by III–V molecular beam epitaxy

    DEFF Research Database (Denmark)

    Stobbe, Søren; Lindelof, P. E.; Nygård, J.

    2006-01-01

    on incorporation of singlewall nanotubes in III–V semiconductor heterostructures grown by molecular beam epitaxy (MBE). We demonstrate that singlewall carbon nanotubes can be overgrown using MBE; electrical contacts to the nanotubes are obtained by GaMnAs grown at 250 °C. The resulting devices can exhibit field......We review a number of essential issues regarding the integration of carbon nanotubes in semiconductor devices for electronics: material compatibility, electrical contacts, functionalities, circuit architectures and reliability. In the second part of the paper, we present our own recent results...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-09-26

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

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

    Science.gov (United States)

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

    2016-12-01

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

  17. 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.

  18. 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.

  19. 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

  20. High active nitrogen flux growth of GaN by plasma assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    McSkimming, Brian M., E-mail: mcskimming@engineering.ucsb.edu; Speck, James S. [Materials Department, University of California, Santa Barbara, California 93106-5050 (United States); Chaix, Catherine [RIBER S.A., 3a Rue Casimir Périer, BP 70083, 95873 Bezons Cedex (France)

    2015-09-15

    In the present study, the authors report on a modified Riber radio frequency (RF) nitrogen plasma source that provides active nitrogen fluxes more than 30 times higher than those commonly used for plasma assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N{sub 2} gas flow rates between 5 and 25 sccm while varying the plasma source's RF forward power from 200 to 600 W. The highest growth rate, and therefore the highest active nitrogen flux, achieved was ∼7.6 μm/h. For optimized growth conditions, the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 × 3 μm) on the order of 1 nm. Secondary ion mass spectroscopy impurity analysis demonstrates oxygen and hydrogen incorporation of 1 × 10{sup 16} and ∼5 × 10{sup 17}, respectively. In addition, the authors have achieved PAMBE growth of GaN at a substrate temperature more than 150 °C greater than our standard Ga rich GaN growth regime and ∼100 °C greater than any previously reported PAMBE growth of GaN. This growth temperature corresponds to GaN decomposition in vacuum of more than 20 nm/min; a regime previously unattainable with conventional nitrogen plasma sources. Arrhenius analysis of the decomposition rate shows that samples with a flux ratio below stoichiometry have an activation energy greater than decomposition of GaN in vacuum while samples grown at or above stoichiometry have decreased activation energy. The activation energy of decomposition for GaN in vacuum was previously determined to be ∼3.1 eV. For a Ga/N flux ratio of ∼1.5, this activation energy was found to be ∼2.8 eV, while for a Ga/N flux ratio of ∼0.5, it was found to be ∼7.9 eV.

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

    Science.gov (United States)

    Schramm, A; Tommila, J; Strelow, C; Hakkarainen, T V; Tukiainen, A; Dumitrescu, M; Mews, A; Kipp, T; Guina, M

    2012-05-04

    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.

  2. Molecular beam epitaxy of c-plane wurtzite GaN on nitridized a-plane {beta}-Ga{sub 2}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Villora, Encarnacion G. E-mail: villora.garcia@nims.go.jp; Shimamura, Kiyoshi [National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan); Aoki, Kazuo [Koha Co., Ltd., 2-6-8 Kouyama, Nerima-ku, Tokyo 176-0022 (Japan); Kitamura, Kenji [National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan)

    2006-04-03

    Epitaxial growth of GaN on {beta}-Ga{sub 2}O{sub 3} single crystal substrates by the molecular beam epitaxy technique is demonstrated for the first time. Standard and in-plane X-ray diffraction evidence the growth of c-plane wurtzite GaN on a-plane {beta}-Ga{sub 2}O{sub 3}, the epitaxial relationship being <0 1 0>{sub Ga{sub 2}}{sub O{sub 3}}-parallel <1 1 2-bar 0>{sub GaN} and <0 0 1>{sub Ga{sub 2}}{sub O{sub 3}}-parallel <1-bar 1 0 0>{sub GaN}. Epitaxial growth without any buffer layer is achieved after an effective surface nitridation under NH{sub 3} gas.

  3. Substrate-induced magnetism in epitaxial graphene buffer layers.

    Science.gov (United States)

    Ramasubramaniam, A; Medhekar, N V; Shenoy, V B

    2009-07-08

    Magnetism in graphene is of fundamental as well as technological interest, with potential applications in molecular magnets and spintronic devices. While defects and/or adsorbates in freestanding graphene nanoribbons and graphene sheets have been shown to cause itinerant magnetism, controlling the density and distribution of defects and adsorbates is in general difficult. We show from first principles calculations that graphene buffer layers on SiC(0001) can also show intrinsic magnetism. The formation of graphene-substrate chemical bonds disrupts the graphene pi-bonds and causes localization of graphene states near the Fermi level. Exchange interactions between these states lead to itinerant magnetism in the graphene buffer layer. We demonstrate the occurrence of magnetism in graphene buffer layers on both bulk-terminated as well as more realistic adatom-terminated SiC(0001) surfaces. Our calculations show that adatom density has a profound effect on the spin distribution in the graphene buffer layer, thereby providing a means of engineering magnetism in epitaxial graphene.

  4. The structural transition from epitaxial Fe/Pt multilayers to an ordered FePt film using low energy ion beam sputtering deposition with no buffer layer

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Chih-Hao, E-mail: chlee@mx.nthu.edu.tw [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Chen, Yu-Sheng [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Electronics and Optoelectronics Research Laboratories, Industrial Technology Research Institute, Hsinchu 31040, Taiwan (China); Liu, Li-Jung [Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Huang, J.C.A. [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China)

    2014-11-03

    An epitaxial L1{sub 0} FePt thin film grown from an [Fe(10 Å)/Pt(10 Å)]{sub 15} multilayer with the orientation of (001) was prepared by an ion beam sputtering deposition method without buffer layer. From the measurement data of X-ray diffraction and X-ray reflectivity, the multilayer structure was totally disappeared and a uniform FePt alloy thin film was formed at temperatures higher than 600 °C. For the as-deposited thin film grown at 100 °C, the multilayer already possesses an epitaxial structure. The epitaxial relation is FePt(001)[100]//MgO(001)[100] and this epitaxial relation persists after sequential high temperature annealing. An epitaxial L1{sub 0} ordered FePt(001) film with order parameter of 0.95 was obtained when the annealing temperature reached 650 °C. The ordered FePt(001) thin film has a perpendicular magnetic anisotropy with a squareness of 0.95 ± 0.03 on the magnetic hysteresis loop. This experiment demonstrates that the low energy ion beam sputtering deposition will preserve the epitaxial relation with no buffer layer between multilayer and substrate. - Highlights: • The Fe/Pt films using ion sputtering deposition with no buffer layer is epitaxial. • Multilayer structure was totally disappeared at temperatures higher than 600 °C. • Order parameter reach 0.95 after annealing at 650 °C. • Interfacial epitaxial FePt alloy already formed at 100 °C.

  5. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-06-21

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

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

    Science.gov (United States)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R

    2014-04-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  8. 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

  9. 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)

  10. Focused helium-ion-beam-induced deposition

    Energy Technology Data Exchange (ETDEWEB)

    Alkemade, P.F.A.; Miro, H. [Delft University of Technology, Kavli Institute of Nanoscience, Delft (Netherlands)

    2014-12-15

    The recent introduction of the helium ion microscope (HIM) offers new possibilities for materials modification and fabrication with spatial resolution below 10 nm. In particular, the specific interaction of He{sup +} ions in the tens of keV energy range with materials - i.e., minimal deflection and mainly energy loss via electronic excitations - renders the HIM a special tool for ion-beam-induced deposition. In this work, an overview is given of all studies of helium-ion-beam-induced deposition (He-IBID) that appeared in the literature before summer 2014. Continuum models that describe the deposition processes are presented in detail, with emphasis on precursor depletion and replenishment. In addition, a Monte Carlo model is discussed. Basic experimental He-IBID studies are critically examined. They show deposition rates of up to 0.1 nm{sup 3}/ion. Analysis by means of a continuum model yields the precursor diffusion constant and the cross sections for beam-induced precursor decomposition and beam-induced desorption. Moreover, it is shown that deposition takes place only in a small zone around the beam impact point. Furthermore, the characterization of deposited materials is discussed in terms of microstructure and resistivity. It is shown that He-IBID material resembles more electron-beam-induced-deposition (EBID) material than Ga-ion-beam-induced-deposition (Ga-IBID) material. Nevertheless, the spatial resolution for He-IBID is in general better than for EBID and Ga-IBID; in particular, proximity effects are minimal. (orig.)

  11. Development of gallium nitride-based ultraviolet and visible light-emitting diodes using hydride vapor-phase epitaxy and molecular beam epitaxy

    Science.gov (United States)

    Cabalu, Jasper Sicat

    Much of the work done on ultraviolet (UV) and visible III-Nitrides-based light emitting diodes (LEDs) involves growth by metal-organic chemical vapor deposition (MOCVD). In this dissertation, the growth, development, and fabrication of III-Nitrides-based UV and visible LEDs with very high photon conversion and extraction efficiencies using hydride vapor-phase epitaxy (HVPE) and radio frequency (rf) plasma-assisted molecular beam epitaxy (PAMBE) is presented. High-power electrically-pumped UV-LEDs based on GaN/AlGaN multiple quantum wells (MQWs) emitting at 340 nm and 350 nm have been fabricated in a flip-chip configuration and evaluated. Under pulsed operation, UV-LEDs emitting at 340 nm have output powers that saturate, due to device heating, at approximately 3 mW. Devices emitting at 350 nm show DC operation output powers as high as 4.5 mW under 200 mA drive current. These results were found to be equivalent with those of UV-LEDs produced by the MOCVD and HVPE methods. The concept of using textured MQWs on UV-LED structures was tested by optical pumping of GaN/AlGaN MQWs grown on textured GaN templates. Results show highly enhanced (>700 times) blue-shifted photoluminescence (PL) at 360 nm compared to similarly produced MQWs on smooth GaN templates whose PL emission is red-shifted. These results are attributed partly to enhancement in light extraction efficiency (LEE) and partly to enhancement in internal quantum efficiency (IQE). The origin of the increase in IQE is partly due to reduction of the quantum-confined Stark effect (QCSE) on QW-planes not perpendicular to the polarization direction and partly due to charge redistribution in the QWs caused by the polarization component parallel to the planes of the QWs. Similar studies have been done for visible LEDs using InGaN/GaN MQWs. Growth of LED structures on textured GaN templates employing textured MQW-active regions resulted in the production of dichromatic (430 nm and 530 nm) phosphorless white LEDs with

  12. 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.

  13. Geometric continuum mechanics and induced beam theories

    CERN Document Server

    R Eugster, Simon

    2015-01-01

    This research monograph discusses novel approaches to geometric continuum mechanics and introduces beams as constraint continuous bodies. In the coordinate free and metric independent geometric formulation of continuum mechanics as well as for beam theories, the principle of virtual work serves as the fundamental principle of mechanics. Based on the perception of analytical mechanics that forces of a mechanical system are defined as dual quantities to the kinematical description, the virtual work approach is a systematic way to treat arbitrary mechanical systems. Whereas this methodology is very convenient to formulate induced beam theories, it is essential in geometric continuum mechanics when the assumptions on the physical space are relaxed and the space is modeled as a smooth manifold. The book addresses researcher and graduate students in engineering and mathematics interested in recent developments of a geometric formulation of continuum mechanics and a hierarchical development of induced beam theories.

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

    DEFF Research Database (Denmark)

    Gas, Katarzyna; Sadowski, Janusz; Kasama, Takeshi;

    2013-01-01

    Mn-doped GaAs nanowires were grown in the self-catalytic growth mode on the oxidized Si(100) surface by molecular beam epitaxy and characterized by scanning and transmission electron microscopy, Raman scattering, photoluminescence, cathodoluminescence, and electron transport measurements...

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

    OpenAIRE

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

    2001-01-01

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

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

    Science.gov (United States)

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

    2010-11-01

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

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

    Science.gov (United States)

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

    2013-10-01

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

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

    Science.gov (United States)

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

    2013-08-14

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

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

    Science.gov (United States)

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

    2015-05-13

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

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

    Science.gov (United States)

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

    2014-08-13

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

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

    Science.gov (United States)

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

    2016-10-01

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

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

    Science.gov (United States)

    Oliveira, F.; Fischer, I. A.; Benedetti, A.; Zaumseil, P.; Cerqueira, M. F.; Vasilevskiy, M. I.; Stefanov, S.; Chiussi, S.; Schulze, J.

    2015-12-01

    We report on the fabrication and structural characterization of epitaxially grown ultra-thin layers of Sn on Ge virtual substrates (Si buffer layer overgrown by a 50 nm thick Ge epilayer followed by an annealing step). Samples with 1 to 5 monolayers of Sn on Ge virtual substrates were grown using solid source molecular beam epitaxy and characterized by atomic force microscopy. We determined the critical thickness at which the transition from two-dimensional to three-dimensional growth occurs. This transition is due to the large lattice mismatch between Ge and Sn (≈14.7%). By depositing Ge on top of Sn layers, which have thicknesses at or just below the critical thickness, we were able to fabricate ultra-narrow GeSn multi-quantum-well structures that are fully embedded in Ge. We report results on samples with one and ten GeSn wells separated by 5 and 10 nm thick Ge spacer layers that were characterized by high resolution transmission electron microscopy and X-ray diffraction. We discuss the structure and material intermixing observed in the samples.

  3. 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.

  4. Molecular Beam Epitaxial Growth of ZnO on Si Substrate Using Ozone as an Oxygen Source

    Science.gov (United States)

    Fujita, Miki; Kawamoto, Noriaki; Tatsumi, Tomohiko; Yamagishi, Katsumi; Horikoshi, Yoshiji

    2003-01-01

    Epitaxial ZnO films have been grown on Si (111) substrates by molecular beam epitaxy using ozone as an oxygen source. An initial deposition of a Zn layer followed by its oxidation produces a superior template for the subsequent ZnO growth. The reflection high-energy electron diffraction measurement suggests that the initial Zn layer and ZnO film are rotated by 30° with respect to the Si substrate orientation. The X-ray diffraction measurement reveals that the as-grown ZnO films are strongly c-oriented and include no rotational domains. Although there exists a small trace of ZnO (10\\bar{1}1) domains, it easily disappears upon annealing at 1100°C for 1 min after growth. Low-temperature photoluminescence measurements indicate that the emission property is improved significantly after annealing. The bound-exciton emission at 3.354 eV is dominant and its full-width at half maximum is as small as 11 meV.

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

    Science.gov (United States)

    Zandian, Majid

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-02-09

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

  7. 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.

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

    Science.gov (United States)

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

    2005-03-01

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

  9. Molecular beam epitaxial growth and characterization of Al(Ga)N nanowire deep ultraviolet light emitting diodes and lasers

    Science.gov (United States)

    Mi, Z.; Zhao, S.; Woo, S. Y.; Bugnet, M.; Djavid, M.; Liu, X.; Kang, J.; Kong, X.; Ji, W.; Guo, H.; Liu, Z.; Botton, G. A.

    2016-09-01

    We report on the detailed molecular beam epitaxial growth and characterization of Al(Ga)N nanowire heterostructures on Si and their applications for deep ultraviolet light emitting diodes and lasers. The nanowires are formed under nitrogen-rich conditions without using any metal catalyst. Compared to conventional epilayers, Mg-dopant incorporation is significantly enhanced in nearly strain- and defect-free Al(Ga)N nanowire structures, leading to efficient p-type conduction. The resulting Al(Ga)N nanowire LEDs exhibit excellent performance, including a turn-on voltage of ∼5.5 V for an AlN nanowire LED operating at 207 nm. The design, fabrication, and performance of an electrically injected AlGaN nanowire laser operating in the UV-B band is also presented.

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

    Institute of Scientific and Technical Information of China (English)

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

    2011-01-01

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

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

    Science.gov (United States)

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

    2016-11-01

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2009-01-01

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

  13. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-03-11

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

  15. Absorption and emission of (In,Ga)N/GaN quantum wells grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Siozade, L.; Disseix, P.; Vasson, A.; Leymarie, J. [CNRS, Aubiere (France). LASMEA; Damilano, B.; Grandjean, N.; Massies, J. [CNRS, Valbonne (France). CRHEA

    2001-01-01

    Thermally detected optical absorption (TDOA) and photoluminescence experiments are carried out on In{sub 0.16}Ga{sub 0.84}N/GaN multi-quantum wells (MQWs) grown by molecular beam epitaxy on (0001) sapphire substrates. A model proposed to adjust the TDOA line shape, allows to deduce the band-edge energies, the absorption coefficients and the broadening parameters of the (In,Ga)N MQWs for different thicknesses. The Fabry-Perot oscillations, which structure the TDOA spectra, are considered in this modelling to accurately account for the experimental data. The emission, which covers the whole visible spectrum at room temperature, is achieved by varying the thickness from 1.5 to 5 nm. A very large Stokes shift between the emission and absorption energies is deduced at low temperature, for the (In,Ga)N MQWs. (orig.)

  16. 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.

  17. Improved control over spontaneously formed GaN nanowires in molecular beam epitaxy using a two-step growth process.

    Science.gov (United States)

    Zettler, J K; Corfdir, P; Geelhaar, L; Riechert, H; Brandt, O; Fernández-Garrido, S

    2015-11-06

    We investigate the influence of modified growth conditions during the spontaneous formation of GaN nanowires (NWs) on Si(111) in plasma-assisted molecular beam epitaxy. We find that a two-step growth approach, where the substrate temperature is increased during the nucleation stage, is an efficient method to gain control over the area coverage, average diameter, and coalescence degree of GaN NW ensembles. Furthermore, we also demonstrate that the growth conditions employed during the incubation time that precedes nanowire nucleation do not influence the properties of the final nanowire ensemble. Therefore, when growing GaN NWs at elevated temperatures or with low Ga/N ratios, the total growth time can be reduced significantly by using more favorable growth conditions for nanowire nucleation during the incubation time.

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

    Science.gov (United States)

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

    2014-05-30

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

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

    Science.gov (United States)

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

    2015-01-07

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

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

    Science.gov (United States)

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

    2016-03-23

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

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

    Science.gov (United States)

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

    1993-01-01

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

  2. High-performance K-band GaAs power field-effect transistors prepared by molecular beam epitaxy

    Science.gov (United States)

    Saunier, P.; Shih, H. D.

    1983-01-01

    The maturity of the molecular beam epitaxy (MBE) technique for preparing device quality GaAs material for microwave applications is demonstrated by the excellent performance characteristics of K-band GaAs power field-effect transistors (FETs) fabricated on the MBE wafers. An output power of 710 mW with 4.5-dB gain and 17.7 percent power-added efficiency was achieved at 21 GHz with a 1.26-mm gate width pi-gate device. A similar device with a 0.56-mm gate width produced an output power of 320 mW with 5.0-dB gain and 26.6 percent power-added efficiency at 21 GHz. These are the best results yet reported to date for GaAs power FETs operated in the K-band frequency range.

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

    Science.gov (United States)

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

    2016-12-01

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

  4. Molecular beam epitaxy engineered III-V semiconductor structures for low-power optically addressed spatial light modulators

    Science.gov (United States)

    Larsson, Anders G.; Maserjian, Joseph

    1992-01-01

    Device approaches are investigated for optically addressed SLMs based on molecular-beam epitaxy (MBE) engineered III-V materials and structures. Strong photooptic effects can be achieved in periodically delta-doped multiple-quantum-well structures, but are still insufficient for high-contrast modulation with only single- or double-pass absorption through active layers of practical thickness. The asymmetric Fabry-Perot cavity approach is employed to permit extinction of light due to interference of light reflected from the front and back surfaces of the cavity. This approach is realized with an all-MBE-grown structure consisting of GaAs/AlAs quarter-wave stack reflector grown over the GaAs substrate as the high reflectance mirror and the GaAs surface as the low reflectance mirror. High-contrast modulation is achieved using a low-power InGaAs/GaAs quantum well laser for the control signal.

  5. Molecular beam epitaxy of GaN{sub 1-x}Bi{sub x} alloys with high bismuth content

    Energy Technology Data Exchange (ETDEWEB)

    Novikov, S.V.; Kent, A.J.; Foxon, C.T. [School of Physics and Astronomy, University of Nottingham (United Kingdom); Yu, K.M.; Liliental-Weber, Z.; Walukiewicz, W. [Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA (United States); Levander, A.X.; Tseng, A.; Dubon, O.D.; Wu, J. [Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA (United States); Department of Materials Science and Engineering, University of California, Berkeley, CA (United States); Dos Reis, R. [Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA (United States); Instituto de Fisica, UFRGS, Porto Alegre (Brazil); Denlinger, J. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Luckert, F.; Edwards, P.R.; Martin, R.W. [Department of Physics, SUPA, University of Strathclyde, Glasgow (United Kingdom)

    2012-03-15

    We have analysed bismuth incorporation into GaN layers using plasma-assisted molecular beam epitaxy (PA-MBE) at extremely low growth temperatures of less than {proportional_to}100 C under both Ga-rich and N-rich growth conditions. The formation of amorphous GaN{sub 1-x}Bi{sub x} alloys is promoted by growth under Ga-rich conditions. The amorphous matrix has a short-range order resembling random crystalline GaN{sub 1-x}Bi{sub x} alloys. We have observed the formation of small crystalline clusters embedded into amorphous GaN{sub 1-x}Bi{sub x} alloys. Despite the fact that the films are pseudo-amorphous we observe a well defined optical absorption edges that rapidly shift to very low energy of {proportional_to}1 eV. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2006-06-15

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

  7. 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.

  8. 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.

  9. 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.

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

    Science.gov (United States)

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

    1992-01-01

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

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

    OpenAIRE

    2004-01-01

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

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

    Science.gov (United States)

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

    2017-04-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-04-30

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2004-10-01

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

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

    Science.gov (United States)

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

    2013-09-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-07-18

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

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

    Science.gov (United States)

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

    2015-04-28

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

  18. 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.

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

    Science.gov (United States)

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

    2016-12-01

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

  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. Shadowing and mask opening effects during selective-area vapor-liquid-solid growth of InP nanowires by metalorganic molecular beam epitaxy.

    Science.gov (United States)

    Kelrich, A; Calahorra, Y; Greenberg, Y; Gavrilov, A; Cohen, S; Ritter, D

    2013-11-29

    Indium phosphide nanowires were grown by metalorganic molecular beam epitaxy using the selective-area vapor-liquid-solid method. We show experimentally and theoretically that the size of the annular opening around the nanowire has a major impact on nanowire growth rate. In addition, we observed a considerable reduction of the growth rate in dense two-dimensional arrays, in agreement with a calculation of the shadowing of the scattered precursors. Due to the impact of these effects on growth, they should be considered during selective-area vapor-liquid-solid nanowire epitaxy.

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

    Energy Technology Data Exchange (ETDEWEB)

    Shimomura, Kenichi; Ohshita, Yoshio; Kamiya, Itaru, E-mail: kamiya@toyota-ti.ac.jp [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan); Suzuki, Hidetoshi [Faculty of Engineering, University of Miyazaki, 1-1 Gakuen Kibanadai-nishi, Miyazaki 889-2192 (Japan); Sasaki, Takuo; Takahasi, Masamitu [Quantum Beam Science Center, Japan Atomic Energy Agency, Koto 1-1-1, Sayo-cho, Hyogo 679-5148 (Japan)

    2015-11-14

    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.

  3. 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)

  4. Growth of polar and non-polar nitride semiconductor quasi-substrates by hydride vapor phase epitaxy for the development of optoelectronic devices by molecular beam epitaxy

    Science.gov (United States)

    Moldawer, Adam Lyle

    The family of nitride semiconductors has had a profound influence on the development of optoelectronics for a large variety of applications. However, as of yet there are no native substrates commercially available that are grown by liquid phase methods as with Si and GaAs. As a result, the majority of electronic and optoelectronic devices are grown heteroepitaxially on sapphire and SiC. This PhD research addresses both the development of polar and non-polar GaN and AIN templates by Hydride Vapor Phase Epitaxy (HVPE) on sapphire and SiC substrates, as well as the growth and characterization of optoelectronic devices on these templates by molecular beam epitaxy (MBE). Polar and non-polar GaN templates have been grown in a vertical HVPE reactor on the C- and R-planes of sapphire respectively. The growth conditions have been optimized to allow the formation for thick (50um) GaN templates without cracks. These templates were characterized structurally by studying their surface morphologies by SEM and AFM, and their structure through XRD and TEM. The polar C-plane GaN templates were found to be atomically smooth. However, the surface morphology of the non-polar GaN films grown on the R-plane of sapphire were found to have a facetted surface morphology, with the facets intersecting at 120° angles. This surface morphology reflects an equilibrium growth, since the A-plane of GaN grows faster than the M-planes of GaN due to the lower atomic density of the plane. For the development of deep-UV optoelectronics, it is required to grow AIGaN quantum wells on AIN templates. However, since AIN is a high melting point material, such templates have to be grown at higher temperatures, close to half the melting point of the material (1500 °C). As these temperatures cannot be easily obtained by traditional furnace heating, an HVPE reactor has been designed to heat the substrate inductively to these temperatures. This apparatus has been used to grow high-quality, transparent AIN films

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-07-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-07-01

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

  7. Interfacial exchange coupling induced anomalous anisotropic magnetoresistance in epitaxial γ'-Fe₄N/CoN bilayers.

    Science.gov (United States)

    Li, Zirun; Mi, Wenbo; Wang, Xiaocha; Zhang, Xixiang

    2015-02-18

    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. 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. Position-controlled growth of GaN nanowires and nanotubes on diamond by molecular beam epitaxy.

    Science.gov (United States)

    Schuster, Fabian; Hetzl, Martin; Weiszer, Saskia; Garrido, Jose A; de la Mata, María; Magen, Cesar; Arbiol, Jordi; Stutzmann, Martin

    2015-03-11

    In this work the position-controlled growth of GaN nanowires (NWs) on diamond by means of molecular beam epitaxy is investigated. In terms of growth, diamond can be seen as a model substrate, providing information of systematic relevance also for other substrates. Thin Ti masks are structured by electron beam lithography which allows the fabrication of perfectly homogeneous GaN NW arrays with different diameters and distances. While the wurtzite NWs are found to be Ga-polar, N-polar nucleation leads to the formation of tripod structures with a zinc-blende core which can be efficiently suppressed above a substrate temperature of 870 °C. A variation of the III/V flux ratio reveals that both axial and radial growth rates are N-limited despite the globally N-rich growth conditions, which is explained by the different diffusion behavior of Ga and N atoms. Furthermore, it is shown that the hole arrangement has no effect on the selectivity but can be used to force a transition from nanowire to nanotube growth by employing a highly competitive growth regime.

  10. Growth by molecular beam epitaxy and properties of inclined GaN nanowires on Si(001) substrate.

    Science.gov (United States)

    Borysiuk, J; Zytkiewicz, Z R; Sobanska, M; Wierzbicka, A; Klosek, K; Korona, K P; Perkowska, P S; Reszka, A

    2014-04-04

    The growth mode and structural and optical properties of novel type of inclined GaN nanowires (NWs) grown by plasma-assisted MBE on Si(001) substrate were investigated. We show that due to a specific nucleation mechanism the NWs grow epitaxially on the Si substrate without any Si(x)N(y) interlayer, first in the form of zinc-blende islands and then as double wurtzite GaN nanorods with Ga-polarity. X-ray measurements show that orientation of these nanowires is epitaxially linked to the symmetry of the substrate so that [0001] axis of w-GaN nanowire is directed along the [111]Si axis. This is different from commonly observed behavior of self-induced GaN NWs that are N-polar and grow perpendicularly to the surface of nitridized silicon substrate independently on its orientation. The inclined NWs exhibit bright luminescence of bulk donor-bound excitons (D(0)X) at 3.472 eV and exciton-related peak at 3.46 eV having a long lifetime (0.7 ns at 4 K) and observable up to 50 K.

  11. 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.

  12. Epitaxial-strain-induced multiferroicity in SrMnO3 from first principles

    Science.gov (United States)

    Lee, Jun Hee; Rabe, Karin M.

    2010-03-01

    In the first-principles search for new ferromagnetic-ferroelectric multiferroics, one key indicator is the softening of the lowest frequency polar phonon with ferromagnetic ordering from a paraelectric antiferromagnetic bulk state. In a first-principles survey of the phonon dispersions of a wide range of magnetic perovskites, we identified SrMnO3 as a promising candidate system. We find that a ferromagnetic-ferroelectric phase is stabilized by both compressive and tensile epitaxial strain. For compressive strain, there is a sequence of intermediate magnetic transitions, first to C-AFM and then to A-AFM ordering, with an increasing fraction of ferromagnetically aligned nearest neighbor Mn. At each of these, the change in magnetic order is accompanied by a jump in the magnitude of the electric polarization, so, near the A-AFM-FE->FE-FM phase boundary at 3.4% and G-AFM-FE->FE-FM phase boundary at -2.9%, an applied electric field can induce a nonzero magnetization, and the jump in c-lattice constant at -2.9% strain can generate a large piezomagnetic response. The origin of the large phonon softening in SrMnO3 will be examined, which should provide guidance in identifying additional candidate systems for epitaxial-strain-induced multiferroicity.

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

    Science.gov (United States)

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

    2015-06-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Kin Man; Liliental-Weber, Z.

    1991-11-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Kin Man; Liliental-Weber, Z.

    1991-11-01

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

  16. 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

  17. Epitaxial gamma-iron silicide grown on single-crystal Si. A summary of Moessbauer results

    Energy Technology Data Exchange (ETDEWEB)

    Desimoni, J.; Sanchez, F.H

    1998-08-15

    Metastable {gamma}-FeSi{sub 2} grown on or into single-crystals of silicon can be produced by different techniques as molecular beam epitaxy, and ion implantation followed by ion beam induced epitaxial crystallisation. In these investigations, Moessbauer effect has been used to provide short range order information about the system. We present here a summary of these results, which will be compared and discussed.

  18. Growth of Y3Fe5O12/GaN layers by laser molecular-beam epitaxy and characterization of their structural and magnetic properties

    Science.gov (United States)

    Kaveev, A. K.; Bursian, V. E.; Gastev, S. V.; Krichevtsov, B. B.; Suturin, S. M.; Volkov, M. P.; Sokolov, N. S.

    2016-12-01

    Laser molecular-beam epitaxy has been employed to obtain layers of yttrium-iron garnet (YIG) Y3Fe5O12 on gallium nitride substrates. It was found that there exists a polycrystalline YIG phase without admixtures of other structural phases. A magnetic anisotropy of films of the "easy-magnetic plane" type was found. The gyromagnetic ratio and the demagnetizing field 4π M S were calculated.

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

    Institute of Scientific and Technical Information of China (English)

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

    2009-01-01

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

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

    Science.gov (United States)

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

    1987-08-01

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

  1. Reflection High-Energy Electron Diffraction Beam-Induced Structural and Property Changes on WO3 Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Du, Yingge; Zhang, Hongliang; Varga, Tamas; Chambers, Scott A.

    2014-08-08

    Reduction of transition metal oxides can greatly change their physical and chemical properties. Using deposition of WO3 as a case study, we demonstrate that reflection high-energy electron diffraction (RHEED), a surface-sensitive tool widely used to monitor thin-film deposition processes, can significantly affect the cation valence and physical properties of the films through electron-beam induced sample reduction. The RHEED beam is found to increase film smoothness during epitaxial growth of WO3, as well as change the electronic properties of the film through preferential removal of surface oxygen.

  2. Molecular beam epitaxy of large-area SnSe2 with monolayer thickness fluctuation

    Science.gov (United States)

    Park, Young Woon; Jerng, Sahng-Kyoon; Jeon, Jae Ho; Roy, Sanjib Baran; Akbar, Kamran; Kim, Jeong; Sim, Yumin; Seong, Maeng-Je; Kim, Jung Hwa; Lee, Zonghoon; Kim, Minju; Yi, Yeonjin; Kim, Jinwoo; Noh, Do Young; Chun, Seung-Hyun

    2017-03-01

    The interest in layered materials is largely based on the expectation that they will be beneficial for a variety of applications, from low-power-consuming, wearable electronics to energy harvesting. However, the properties of layered materials are highly dependent on thickness, and the difficulty of controlling thickness over a large area has been a bottleneck for commercial applications. Here, we report layer-by-layer growth of SnSe2, a layered semiconducting material, via van der Waals epitaxy. The films were fabricated on insulating mica substrates with substrate temperatures in the range of 210 °C-370 °C. The surface consists of a mixture of N and (N ± 1) layers, showing that the thickness of the film can be defined with monolayer accuracy (±0.6 nm). High-resolution transmission electron microscopy reveals a polycrystalline film with a grain size of ˜100 nm and clear Moiré patterns from overlapped grains with similar thickness. We also report field effect mobility values of 3.7 cm2 V-1 s-1 and 6.7 cm2 V-1 s-1 for 11 and 22 nm thick SnSe2, respectively. SnSe2 films with customizable thickness can provide valuable platforms for industry and academic researchers to fully exploit the potential of layered materials.

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

    Science.gov (United States)

    George, T.; Fathauer, R. W.

    1992-01-01

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

  4. Tuning a strain-induced orbital selective Mott transition in epitaxial VO2

    Science.gov (United States)

    Mukherjee, Shantanu; Quackenbush, N. F.; Paik, H.; Schlueter, C.; Lee, T.-L.; Schlom, D. G.; Piper, L. F. J.; Lee, Wei-Cheng

    2016-06-01

    We present evidence of strain-induced modulation of electron correlation effects and increased orbital anisotropy in the rutile phase of epitaxial VO2/TiO2 films from hard x-ray photoelectron spectroscopy and soft V L-edge x-ray absorption spectroscopy, respectively. By using the U(1) slave spin formalism, we further argue that the observed anisotropic correlation effects can be understood by a model of orbital selective Mott transition at a filling that is noninteger but close to the half filling. Because the overlaps of wave functions between d orbitals are modified by the strain, orbital-dependent renormalizations of the bandwidths and the onsite energy occur. These renormalizations generally result in different occupation numbers in different orbitals. We find that if the system has a noninteger filling number near the half filling such as for VO2, certain orbitals could reach an occupation number closer to half filling under the strain, resulting in a strong reduction in the quasiparticle weight Zα of that orbital. Our work demonstrates that such an orbital selective Mott transition, defined as the case with Zα=0 in some but not all orbitals, could be accessed by epitaxial-strain engineering of correlated electron systems.

  5. Demonstration of isotype GaN/AlN/GaN heterobarrier diodes by NH{sub 3}-molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Fireman, Micha N.; Browne, David A.; Mazumder, Baishakhi; Speck, James S. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Mishra, Umesh K. [Electrical and Computer Engineering Department, University of California, Santa Barbara, California 93106 (United States)

    2015-05-18

    The results of vertical transport through nitride heterobarrier structures grown by ammonia molecular beam epitaxy are presented. Structures are designed with binary layers to avoid the effects of random alloy fluctuations in ternary nitride barriers. The unintentional incorporation of Ga in the AlN growth is investigated by atom probe tomography and is shown to be strongly dependent on both the NH{sub 3} flowrate and substrate temperature growth parameters. Once nominally pure AlN layer growth conditions are achieved, structures consisting of unintentionally doped (UID) GaN spacer layers adjacent to a nominally pure AlN are grown between two layers of n+ GaN, from which isotype diodes are fabricated. Varying the design parameters of AlN layer thickness, UID spacer layer thickness, and threading dislocation density show marked effects on the vertical transport characteristics of these structures. The lack of significant temperature dependence, coupled with Fowler-Nordheim and/or Milliken-Lauritsen analysis, point to a prevalently tunneling field emission mechanism through the AlN barrier. Once flatband conditions in the UID layer are achieved, electrons leave the barrier with significant energy. This transport mechanism is of great interest for applications in hot electron structures.

  6. 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.

  7. GaN layers with different polarities prepared by radio frequency molecular beam epitaxy and characterized by Raman scattering

    Institute of Scientific and Technical Information of China (English)

    Zhong Fei; Li Xin-Hua; Qiu Kai; Yin Zhi-Jun; Ji Chang-Jian; Cao Xian-Cun; Han Qi-Feng; Chen Jia-Rong; Wang Yu-Qi

    2007-01-01

    GaN layers with different polarities have been prepared by radio-frequency molecular beam epitaxy (RF-MBE) and characterized by Raman scattering. Polarity control are realized by controlling Al/N flux ratio during high temperature AlN buffer growth. The Raman results illustrate that the N-polarity GaN films have frequency shifts at A1(LO) mode because of their high carrier density; the forbidden A1 (TO) mode occurs for mixed-polarity GaN films due to the destroyed translation symmetry by inversion domain boundaries (IDBS); Raman spectra for Ga-polarity GaN films show that they have neither frequency shifts mode nor forbidden mode. These results indicate that Ga-polarity GaN films have a better quality, and they are in good agreement with the results obtained from the room temperature Hall mobility. The best values of Ga-polarity GaN films are 1042 cm2/Vs with a carrier density of 1.0×1017 cm-3.

  8. 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.

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

    Science.gov (United States)

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

    2003-07-01

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

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

    Science.gov (United States)

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

    2016-10-01

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

  11. 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.

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

    Science.gov (United States)

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

    2016-04-13

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

  13. 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.

  14. 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.

  15. 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.

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

    Directory of Open Access Journals (Sweden)

    David Adolph

    2016-08-01

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

  17. Growth map for Ga-assisted growth of GaAs nanowires on Si(111) substrates by molecular beam epitaxy.

    Science.gov (United States)

    Bastiman, Faebian; Küpers, Hanno; Somaschini, Claudio; Geelhaar, Lutz

    2016-03-04

    For the Ga-assisted growth of GaAs nanowires on Si(111) substrates by molecular beam epitaxy, growth temperature, As flux, and Ga flux have been systematically varied across the entire window of growth conditions that result in the formation of nanowires. A range of GaAs structures was observed, progressing from pure Ga droplets under negligible As flux through horizontal nanowires, tilted nanowires, vertical nanowires, and nanowires without droplets to crystallites as the As flux was increased. Quantitative analysis of the resulting sample morphology was performed in terms of nanowire number and volume density, number yield and volume yield of vertical nanowires, diameter, length, as well as the number and volume density of parasitic growth. The result is a growth map that comprehensively describes all nanowire and parasitic growth morphologies and hence enables growth of nanowire samples in a predictive manner. Further analysis indicates the combination of global Ga flux and growth temperature determines the total density of all objects, whereas the global As/Ga flux ratio independently determines the resultant sample morphology. Several dependencies observed here imply that all objects present on the substrate surface, i.e. both nanowires and parasitic structures, originate from Ga droplets.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-04-15

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

  19. Nucleation phenomena during molecular beam epitaxy of GaN observed by line-of-sight quadrupole mass spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Koblmueller, G.; Averbeck, R.; Riechert, H. [Infineon Technologies AG, Corporate Research Photonics, Otto-Hahn-Ring 6, 81739 Munich (Germany); Pongratz, P. [Vienna University of Technology, Institute of Solid State Physics, Wiedner Hauptstrasse 8-10, 1040 Vienna (Austria)

    2002-12-16

    We investigate nucleation and growth phenomena during molecular beam epitaxy of GaN on sapphire, 6H-SiC and GaN templates using in situ line-of-sight quadrupole mass spectrometry. Moreover, this method allows the quantitative study of nucleation phenomena by monitoring desorption processes. Heteroepitaxial growth of GaN on sapphire and 6H-SiC faces a high energy barrier to nucleation giving rise to a substantial Ga desorption during the initial phase of nucleation. The amount of initial Ga desorption in heteroepitaxy is independent of the chosen substrate material and is as high as 8 {+-} 1.5 nm equivalent GaN thickness. Once critical-sized islands have nucleated they grow three-dimensional (3D) leading to a quadratic increase of the GaN coverage and finally to a steady growth rate after coalescence, as also determined by Rutherford backscattering and atomic force microscopy. In contrast, homoepitaxy on Ga- and N-face GaN templates is distinguished by immediate nucleation. (Abstract Copyright [2002], Wiley Periodicals, Inc.)

  20. 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.

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

    Institute of Scientific and Technical Information of China (English)

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

    2009-01-01

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

  2. Tailoring of polar and nonpolar ZnO planes on MgO (001) substrates through molecular beam epitaxy.

    Science.gov (United States)

    Zhou, Hua; Wang, Hui-Qiong; Liao, Xia-Xia; Zhang, Yufeng; Zheng, Jin-Cheng; Wang, Jia-Ou; Muhemmed, Emin; Qian, Hai-Jie; Ibrahim, Kurash; Chen, Xiaohang; Zhan, Huahan; Kang, Junyong

    2012-03-09

    Polar and nonpolar ZnO thin films were deposited on MgO (001) substrates under different deposition parameters using oxygen plasma-assisted molecular beam epitaxy (MBE). The orientations of ZnO thin films were investigated by in situ reflection high-energy electron diffraction and ex situ X-ray diffraction (XRD). The film roughness measured by atomic force microscopy evolved as a function of substrate temperature and was correlated with the grain sizes determined by XRD. Synchrotron-based X-ray absorption spectroscopy (XAS) was performed to study the conduction band structures of the ZnO films. The fine structures of the XAS spectra, which were consistent with the results of density functional theory calculation, indicated that the polar and nonpolar ZnO films had different electronic structures. Our work suggests that it is possible to vary ZnO film structures from polar to nonpolar using the MBE growth technique and hence tailoring the electronic structures of the ZnO films.PACS: 81; 81.05.Dz; 81.15.Hi.

  3. Synthesis of semimetal A{sub 3}Bi (A = Na, K) thin films by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Wen, Jing, E-mail: wenj07@126.com [State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China); Guo, Hua [State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China); Yan, Chen-Hui [State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China); Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Wang, Zhen-Yu; Chang, Kai; Deng, Peng; Zhang, Teng [State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China); Zhang, Zhi-Dong [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Ji, Shuai-Hua [State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China); Wang, Li-Li; He, Ke; Ma, Xu-Cun [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Chen, Xi; Xue, Qi-Kun [State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084 (China)

    2015-02-01

    Highlights: • First realization of MBE growth of Na{sub 3}Bi on Si(1 1 1)-7 × 7. • The lattice of Na{sub 3}Bi is rotated 30 degree to substrate. • ARPES reveals multi-linear cone structure near Fermi surface. • K{sub 3}Bi was successfully grown on Na{sub 3}Bi/Si(1 1 1)–7 × 7. - Abstract: Three-dimensional (3D) Dirac cones are predicted to reside in semimetals A{sub 3}Bi (A = Na, K). By using molecular beam epitaxy (MBE) and scanning tunneling microscopy (STM), we have successfully established the growth conditions for Na{sub 3}Bi thin films on Si(1 1 1)-7 × 7, and determined that the lattice of Na{sub 3}Bi is rotated by 30 degree with respect to that of Si(1 1 1)-7 × 7. The Na{sub 3}Bi/Si(1 1 1)-7 × 7 thin film was further used as the substrate for the growth of K{sub 3}Bi. The 3D Dirac-cone-like electronic band structures of Na{sub 3}Bi and K{sub 3}Bi have been clearly revealed by angle resolved photoelectron spectroscopy (ARPES)

  4. 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.

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

    Institute of Scientific and Technical Information of China (English)

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

    2010-01-01

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

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

    Science.gov (United States)

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

    2016-04-01

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

  7. Flux pinning properties of MgB{sub 2} thin films on Ti buffered substrate prepared by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Yonekura, K., E-mail: kenji@st.cs.kumamoto-u.ac.j [Department of Computer Science and Electrical Engineering, Kumamoto University, 2-39-1, Kurokami, Kumamoto 860-8555 (Japan); Kugo, A.; Fujiyoshi, T.; Sueyoshi, T. [Department of Computer Science and Electrical Engineering, Kumamoto University, 2-39-1, Kurokami, Kumamoto 860-8555 (Japan); Harada, Y. [JST Satellite Iwate, 3-35-2, Iiokashinden Morioka, Iwate 020-0852 (Japan); Yoshizawa, M.; Ikeda, T. [Department of Materials Science and Engineering, Iwate University, 4-3-5, Ueda, Morioka, Iwate 020-8551 (Japan); Awaji, S.; Watanabe, K. [Institute for Materials Research, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577 (Japan)

    2010-11-01

    Transport properties of the MgB{sub 2} thin films on Si, MgO and ZnO substrates with Ti buffer layer prepared by molecular beam epitaxy were investigated to clarify effects of the substrates and the Ti buffer layer on flux pinning. The critical current density J{sub c} of each sample shows different dependence on magnetic fields parallel to c-axis. However, the scaling analysis of the macroscopic pinning force for all the measured samples implies that the grain boundaries work as the dominant pinning centers for B//c. The pinning parameter for MgB{sub 2}/Ti/Si estimated from the electric field E vs. the current density J characteristics shows the highest value among all the measured samples. This result is attributed to the high density of grain boundaries caused by the effect of both the Ti buffer and Si substrate in the growth process. Therefore, the selection of substrates and buffer layer strongly affects the flux pining properties of MgB{sub 2} thin films and plays an important role in the determination of performance for superconducting devices and wires.

  8. Isolation and control of voids and void-hillocks during molecular beam epitaxial growth of HgCdTe

    Science.gov (United States)

    Chandra, D.; Aqariden, F.; Frazier, J.; Gutzler, S.; Orent, T.; Shih, H. D.

    2000-06-01

    Formation of small voids and defect complexes involving small voids during the molecular beam epitaxial growth of mercury cadmium telluride on cadmium zinc telluride was investigated. Some of these defects were demonstrated to form away from the substrate-epi interface. Other defects were demonstrated to close before reaching the top surface without leaving any perturbations on the surface, thus remaining completely hidden. The voids, which formed away from the substrate-epifilm fixed interface, nucleated on defects introduced into the film already grown, leading to the formation of defect complexes, unlike the voids which nucleated at the substrate-epifilm fixed interface. These defect complexes are decorated with high density dislocation nests. The voids which closed before reaching the film surface usually also nucleated slightly away from the film-substrate interface, continued to replicate for a while as the growth progressed, but then relatively rapidly closed off at a significant depth from the film surface. These voids also appeared to form defect complexes with other kinds of defects. Correlations between these materials defects and performance of individual vertically integrated photodiode (VIP) devices were demonstrated, where the relative location of these defects with respect to the junction boundary appears to be particularly important. Elimination or reduction of fluctuations in relative flux magnitudes or substrate temperature, more likely during multi-composition layer growth, yielded films with significantly lower defect concentrations.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-05-01

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

  10. Swift Heavy Ion Beam-induced Recrystallisation of Buried Silicon Nitride Layer (Review Paper

    Directory of Open Access Journals (Sweden)

    T. Som

    2009-07-01

    Full Text Available Studies on MeV heavy ion beam-induced epitaxial crystallisation of a buried silicon nitride layer are reported. Transmission electron micrographs and selected area diffraction patterns have been used to study the recrystallisation of an ion beam-synthesised layer. Complete recrystallisation of the silicon nitride layer having good quality interfaces with the top- and the substrate-Si has been obsorved. Recrystallisation is achieved at significantly lower temperatures of 100 and 200OC for oxygen and silver ions, respectively. The fact that recrystallisation is achieved at the lowest temperature for the oxygen ions is discussed on the basis of energy loss processes.Defence Science Journal, 2009, 59(4, pp.351-355, DOI:http://dx.doi.org/10.14429/dsj.59.1533

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

    Science.gov (United States)

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

    2013-02-01

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

  12. 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.

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

    Science.gov (United States)

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

    2017-03-01

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

  14. Analysis of beam loss induced abort kicker instability

    Energy Technology Data Exchange (ETDEWEB)

    Zhang W.; Sandberg, J.; Ahrens, L.; Fischer, W.; Hahn, H.; Mi, J.; Pai, C.; Tan, Y.

    2012-05-20

    Through more than a decade of operation, we have noticed the phenomena of beam loss induced kicker instability in the RHIC beam abort systems. In this study, we analyze the short term beam loss before abort kicker pre-fire events and operation conditions before capacitor failures. Beam loss has caused capacitor failures and elevated radiation level concentrated at failed end of capacitor has been observed. We are interested in beam loss induced radiation and heat dissipation in large oil filled capacitors and beam triggered thyratron conduction. We hope the analysis result would lead to better protection of the abort systems and improved stability of the RHIC operation.

  15. Molecular Beam Epitaxial Growth of Heterostructures to Study Quantum Interference Phenomena

    Science.gov (United States)

    1990-01-01

    MBE growth and regrowth of heterostructures for quantum interference transistors and a detailed study of the physical mechanisms and the limitations imposed by them in such devices. We have investigated in detail the suitability of the MBE regrowth process for such applications. Very encouraging progress has been made. The performance characteristics of dual-channel quantum interference devices grown in our laboratory and defined by e-beam lithography have been measured and reported. From this work it is clear that to achieve enhanced performance and to demonstrate a large

  16. Molecular beam epitaxy and characterization of thin Bi{sub 2}Se{sub 3} films on Al{sub 2}O{sub 3} (110)

    Energy Technology Data Exchange (ETDEWEB)

    Tabor, Phillip; Keenan, Cameron; Urazdhin, Sergei; Lederman, David

    2011-07-04

    The structural and electronic properties of thin Bi{sub 2}Se{sub 3} films grown on Al{sub 2}O{sub 3} (110) by molecular beam epitaxy are investigated. The epitaxial films grow in the Frank-van der Merwe mode and are c-axis oriented. They exhibit the highest crystallinity, the lowest carrier concentration, and optimal stoichiometry at a substrate temperature of 200 deg. C determined by the balance between surface kinetics and desorption of Se. The crystallinity of the films improves with increasing Se/Bi flux ratio. Our results enable studies of thin topological insulator films on inert, non-conducting substrates that allow optical access to both film surfaces.

  17. Preparation of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} epitaxial thin films by pulsed ion-beam evaporation

    Energy Technology Data Exchange (ETDEWEB)

    Sorasit, S.; Yoshida, G.; Suzuki, T.; Suematsu, H.; Jiang, W.; Yatsui, K. [Nagaoka University of Technology, Extreme Energy-Density Research Institute, Nagaoka, Niigata (Japan)

    2001-09-01

    Thin films of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (Y-123) grown epitaxially have been successfully deposited by ion-beam evaporation (IBE). The c-axis oriented YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films were successfully deposited on MgO and SrTiO{sub 3} substrates. The Y-123 thin films which were prepared on the SrTiO{sub 3} substrates were confirmed to be epitaxially grown, by X-ray diffraction analysis. The instantaneous deposition rate of the Y-123 thin films was estimated as high as 4 mm/s. (author)

  18. 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.

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

    Science.gov (United States)

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

    2011-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-12-05

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

  1. Proton and γ-ray Induced Radiation Effects on 1 Gbit LPDDR SDRAM Fabricated on Epitaxial Wafer for Space Applications

    Science.gov (United States)

    Park, Mi Young; Chae, Jang-Soo; Lee, Chol; Lee, Jungsu; Shin, Im Hyu; Kim, Ji Eun

    2016-09-01

    We present proton-induced single event effects (SEEs) and γ-ray-induced total ionizing dose (TID) data for 1 Gbit lowpower double data rate synchronous dynamic random access memory (LPDDR SDRAM) fabricated on a 5 μm epitaxial layer (54 nm complementary metal-oxide-semiconductor (CMOS) technology). We compare our radiation tolerance data for LPDDR SDRAM with those of general DDR SDRAM. The data confirms that our devices under test (DUTs) are potential candidates for space flight applications.

  2. Foreign-catalyst-free growth of InAs/InSb axial heterostructure nanowires on Si (111) by molecular-beam epitaxy.

    Science.gov (United States)

    So, Hyok; Pan, Dong; Li, Lixia; Zhao, Jianhua

    2017-03-01

    Epitaxial high-quality InAs/InSb axial heterostructure nanowires are of great interest due to their distinct advantages in fundamental research as well as applications in semiconductor electronic and quantum devices. Currently, nearly all the growth of InAs/InSb axial heterostructure nanowires is assisted with foreign catalysts such as Au, and work on foreign-catalyst-free growth of InAs/InSb axial heterostructure nanowires is lacking. Here we report on the growth of InAs/InSb axial heterostructure nanowires on Si (111) substrates by molecular-beam epitaxy without using any foreign catalysts. The Sb/In beam equivalent pressure (BEP) ratio is found to have important influence on the heterostructure nanowire morphology, and InSb nanowires can be epitaxially grown on InAs nanowire stems with a hexagonal prism and nanosheet-like shapes when the Sb/In BEP ratio varies from 10 to 20. Transmission electron microscopy studies reveal that the InAs nanowire stems have a mixture of zincblende (ZB) and wurtzite (WZ) crystal structures, while InSb nanowire parts have a pure ZB crystal structure free of stacking faults. Composition analysis of axial heterostructure nanowires provides clear evidence that the InSb nanowires are epitaxially grown on InAs nanowires in an In self-assisted vapor-liquid-solid manner. This study paves a new route for growing narrow-gap semiconductor heterostructures with strong spin-orbit interaction for the study of topological states, and the growth manner presented here is expected to be used to grow other In-based axial heterostructure nanowires.

  3. Growth of single-crystal columns of CoSi2 embedded in epitaxial Si on Si(111) by molecular beam epitaxy

    Science.gov (United States)

    Fathauer, R. W.; Nieh, C. W.; Xiao, Q. F.; Hashimoto, Shin

    1989-01-01

    The codeposition of Si and Co on a heated Si(111) substrate is found to result in epitaxial columns of CoSi2 if the Si:Co ratio is greater than approximately 3:1. These columns are surrounded by an Si matrix which shows bulk-like crystalline quality based on transmission electron microscopy and ion channeling. This phenomenon has been studied as functions of substrate temperature and Si:Co ratio. Samples with columns ranging in average diameter from approximately 25 to 130 nm have been produced.

  4. Growth-Rate Induced Epitaxial Orientation of CeO2 on Al2O3(0001)

    Energy Technology Data Exchange (ETDEWEB)

    Kuchibhatla, Satyanarayana V N T; Nachimuthu, Ponnusamy; Gao, Fei; Jiang, Weilin; Shutthanandan, V.; Engelhard, Mark H.; Seal, Sudipta; Thevuthasan, Suntharampillai

    2009-05-19

    High-quality ceria (CeO2) films were grown on sapphire (Al2O3) (0001) substrates using oxygen plasma-assisted molecular beam epitaxy. The epitaxial orientation of the ceria films has been found to be (100) and (111) at low (< 8 Å/min) and higher growth rates (up to ~30 Å/min), respectively. Evidence shows that CeO2 (100) film grows as three-dimensional islands, while CeO2 (111) proceeds with layered growth. Three in-plane domains at 30° to each other are observed in the CeO2 (100), which is attributed to the close match of the oxygen sub-lattices in the film and substrate that has a three-fold symmetry. Molecular dynamic simulations have further confirmed that the CeO2 film retains (100) orientation on the Al2O3 (0001) substrate.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-07-28

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

  6. 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.

  7. Realization of Cu-Doped p-Type ZnO Thin Films by Molecular Beam Epitaxy.

    Science.gov (United States)

    Suja, Mohammad; Bashar, Sunayna B; Morshed, Muhammad M; Liu, Jianlin

    2015-04-29

    Cu-doped p-type ZnO films are grown on c-sapphire substrates by plasma-assisted molecular beam epitaxy. Photoluminescence (PL) experiments reveal a shallow acceptor state at 0.15 eV above the valence band edge. Hall effect results indicate that a growth condition window is found for the formation of p-type ZnO thin films, and the best conductivity is achieved with a high hole concentration of 1.54 × 10(18) cm(-3), a low resistivity of 0.6 Ω cm, and a moderate mobility of 6.65 cm(2) V(-1) s(-1) at room temperature. Metal oxide semiconductor capacitor devices have been fabricated on the Cu-doped ZnO films, and the characteristics of capacitance-voltage measurements demonstrate that the Cu-doped ZnO thin films under proper growth conditions are p-type. Seebeck measurements on these Cu-doped ZnO samples lead to positive Seebeck coefficients and further confirm the p-type conductivity. Other measurements such as X-ray diffraction, X-ray photoelectron, Raman, and absorption spectroscopies are also performed to elucidate the structural and optical characteristics of the Cu-doped p-type ZnO films. The p-type conductivity is explained to originate from Cu substitution of Zn with a valency of +1 state. However, all p-type samples are converted to n-type over time, which is mostly due to the carrier compensation from extrinsic defects of ZnO.

  8. Preservation of beam loss induced quenches, beam lifetime and beam loss measurements with the HERAp beam-loss-monitor system

    Science.gov (United States)

    Wittenburg, Kay

    1994-06-01

    The beam-loss-monitors (BLMs) in the HERA-proton-ring (HERAp) must fulfill the following requirements: They have to measure losses sensitive and fast enough to prevent the superconducting magnets from beam loss induced quenching; the dynamic range of the monitors must exceed several decades in order to measure losses during beam lifetimes of hundreds of hours as well as the much stronger losses that may quench superconducting magnets; they have to be insensitive to the synchrotron radiation of the adjacent electron-ring (HERAe); and their radiation hardness must allow a monitor-lifetime of a few years of HERA operation. These requirements are well satisfied by the HERAp-BLM-System.

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

    Science.gov (United States)

    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 × 10(10) to 1.1 × 10(11) 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 formation of GaN nanodots on Si. The surface nitridaiton treatment at 600°C provides a-SiNx layer which makes higher density of GaN nanodots. Crystal GaN nanodots can be observed by the HRTEM. The surface composition of GaN nanodots can be analyzed by SPEM and μ-XPS with a synchrotron x-ray source. We can find GaN nanodots form by droplet epitaxy and then in situ annealing make higher-degree nitridation of GaN nanodots.

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

    Directory of Open Access Journals (Sweden)

    M. Agrawal

    2017-01-01

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

  11. Columnar growth of CoSi2 on Si(111), Si(100) and Si(110) by molecular beam epitaxy

    Science.gov (United States)

    Fathauer, R. W.; Nieh, C. W.; Xiao, Q. F.; Hashimoto, Shin

    1990-01-01

    Codeposition of silicon and cobalt on heated silicon substrates in ratios several times the silicide stoichiometry is found to result in epitaxial columns of CoSi2 surrounded by a matrix of epitaxial silicon. For (111)-oriented wafers, nearly cylindrical columns are formed, where both columns and surrounding silicon are defect free, as deduced from transmission electron microscopy. Independent control of the column diameter and separation is possible, and diameters of 27-135 nm have been demonstrated.

  12. Magnetic field induced optical vortex beam rotation

    CERN Document Server

    Shi, Shuai; Zhou, Zhi-Yuan; Li, Yan; Zhang, Wei; Shi, Bao-Sen

    2015-01-01

    Light with orbital angular momentum (OAM) has drawn a great deal of attention for its important applications in the fields of precise optical measurements and high capacity optical communications. Here we adopt a method to study the rotation of a light beam, which is based on magnetic field induced circular birefringence in warm 87Rb atomic vapor. The dependence of the rotation angle to the intensity of the magnetic field makes it appropriate for weak magnetic field measurement. We derive a detail theoretical description that is in well agreement with the experimental observations. The experiment shows here provides a new method for precise measurement of magnetic field intensity and expands the application of OAM-carrying light.

  13. 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.

  14. 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...

  15. The Utility of Droplet Elimination by Thermal Annealing Technique for Fabrication of GaN/AlGaN Terahertz Quantum Cascade Structure by Radio Frequency Molecular Beam Epitaxy

    Science.gov (United States)

    Terashima, Wataru; Hirayama, Hideki

    2010-12-01

    We investigated the utility of a droplet elimination by thermal annealing (DETA) technique during the radio-frequency molecular beam epitaxy growth of a quantum cascade laser (QCL) structure. DETA is a method in which droplets deposited on the surface are eliminated by temporarily increasing the substrate temperature. DETA is a useful method which makes it possible not only to increase the number of periods in the QC structure, but also to improve the surface and structural properties of the QC structure. We could successfully increase the radiant intensity from a QCL sample by increasing the number of periods in the stacked QC structure with the DETA method.

  16. Molecular beam epitaxy of free-standing bulk wurtzite AlxGa1-xN layers using a highly efficient RF plasma source

    OpenAIRE

    2016-01-01

    Recent developments with group III nitrides suggest AlxGa1-xN based LEDs can be new alternative commer-cially viable deep ultra-violet light sources. Due to a sig-nificant difference in the lattice parameters of GaN and AlN, AlxGa1-xN substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free-standing wurtzite AlxGa1-xN bulk crystals by plasma-assisted molecular beam epitaxy (PA-MBE) using a novel RF plasma source. Thick wurtz-i...

  17. 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.

  18. Focused electron beam induced deposition: A perspective

    Directory of Open Access Journals (Sweden)

    Michael Huth

    2012-08-01

    Full Text Available Background: Focused electron beam induced deposition (FEBID is a direct-writing technique with nanometer resolution, which has received strongly increasing attention within the last decade. In FEBID a precursor previously adsorbed on a substrate surface is dissociated in the focus of an electron beam. After 20 years of continuous development FEBID has reached a stage at which this technique is now particularly attractive for several areas in both, basic and applied research. The present topical review addresses selected examples that highlight this development in the areas of charge-transport regimes in nanogranular metals close to an insulator-to-metal transition, the use of these materials for strain- and magnetic-field sensing, and the prospect of extending FEBID to multicomponent systems, such as binary alloys and intermetallic compounds with cooperative ground states.Results: After a brief introduction to the technique, recent work concerning FEBID of Pt–Si alloys and (hard-magnetic Co–Pt intermetallic compounds on the nanometer scale is reviewed. The growth process in the presence of two precursors, whose flux is independently controlled, is analyzed within a continuum model of FEBID that employs rate equations. Predictions are made for the tunability of the composition of the Co–Pt system by simply changing the dwell time of the electron beam during the writing process. The charge-transport regimes of nanogranular metals are reviewed next with a focus on recent theoretical advancements in the field. As a case study the transport properties of Pt–C nanogranular FEBID structures are discussed. It is shown that by means of a post-growth electron-irradiation treatment the electronic intergrain-coupling strength can be continuously tuned over a wide range. This provides unique access to the transport properties of this material close to the insulator-to-metal transition. In the last part of the review, recent developments in mechanical

  19. 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.

  20. Technology basis and perspectives on focused electron beam induced deposition and focused ion beam induced deposition

    Energy Technology Data Exchange (ETDEWEB)

    Rius, Gemma, E-mail: rius.gemma@nitech.ac.jp

    2014-12-15

    The main characteristics of focused electron beam induced deposition (FEBID) and focused ion beam induced deposition (FIBID) are presented. FEBID and FIBID are two nanopatterning techniques that allow the fabrication of submicron patterns with nanometer resolution on selected locations of any kind of substrate, even on highly structured supports. The process consists of mask less serial deposition and can be applied to a wide variety of materials, depending strictly on the precursor material source used. The basic mechanism of FEBID and FIBID is the adsorption of volatile precursor molecules onto the sample surface and decomposition of the molecules induced by the energetic electron and ion focused beams. The essential similarities of the two techniques are presented and especial emphasis is dedicated to highlighting their main differences, such as aspects related to resolution, deposition rate, deposits purity, substrate integrity, etc. In both cases, the factors interplay and complex mechanisms are still understood in a qualitative basis, so much work can still be done in terms of modeling and simulating the processes involved in FEBID and FIBID. Current work on FEBID and FIBID is presented through examples of achievements, interesting results and novel approaches.

  1. 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.

  2. Molecular beam epitaxy of GaN(0001) utilizing NH{sub 3} and/or NH{sup +}{sub {ital x}} ions: Growth kinetics and defect structure

    Energy Technology Data Exchange (ETDEWEB)

    Lee, N.; Powell, R.C.; Kim, Y.; Greene, J.E. [Materials Science Department, the Coordinated Science Laboratory, and the Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 (United States)

    1995-09-01

    Gas-source molecular beam epitaxy (GS-MBE), utilizing Ga and NH{sub 3}, and reactive-ion MBE (RIMBE), incorporating both thermal NH{sub 3} and low-energy NH{sup +}{sub {ital x}} ions, were used to grow single crystal GaN(0001) layers on Al{sub 2}O{sub 3}(0001) at temperatures {ital T}{sub {ital s}} between 700 and 850 {degree}C with deposition rates of 0.2--0.5 {mu}m h{sup {minus}1}. The RIMBE experiments were carried out with incident NH{sup +}{sub {ital x}}/Ga flux ratios {ital J}{sub NH{sup +}{sub {ital x}}}/{ital J}{sub Ga}=1.9--3.2 and NH{sup +}{sub {ital x}} acceleration energies {ital E}{sub NH{sup +}{sub {ital x}}}=45--90 eV. Plan-view and cross-sectional transmission electron microscopy analyses showed that the primary defects in the GS-MBE films were threading dislocations having either pure edge or mixed edge/screw characteristics with Burgers vectors {bar b}=1/3{l_angle}2{bar 1}{bar 1}0{r_angle}, basal-plane stacking faults with displacement vectors {bar R}=1/6{l_angle}02{bar 2}3{r_angle}, and prismatic stacking faults with {bar R}=1/2{l_angle}{bar 1}101{r_angle}. In the case of RIMBE films, no stacking faults or residual ion-induced defects were observed with {ital E}{sub NH{sup +}{sub {ital x}}}=45 eV and {ital T}{sub {ital s}}{ge}800 {degree}C. However, increasing {ital E}{sub NH{sup +}{sub {ital x}}} to {ge}60 eV at {ital T}{sub {ital s}}=800 {degree}C gave rise to the formation of residual ion-induced point-defect clusters observable by transmission electron microscopy (TEM). Increasing {ital T}{sub {ital s}} to 850 {degree}C with {ital E}{sub NH{sup +}{sub {ital x}}}{ge}60 eV resulted in the ion-induced defects aggregating to form interstitial basal and prismatic dislocation loops, whose number densities depended upon the ion flux, with Burgers vectors 1/2{l_angle}0001{r_angle} and 1/3{l_angle}2{bar 1}{bar 1}0{r_angle}, respectively. (Abstract Truncated)

  3. 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.

  4. Impact of N-plasma and Ga-irradiation on MoS2 layer in molecular beam epitaxy

    KAUST Repository

    Mishra, Pawan

    2017-01-03

    Recent interest in two-dimensional materials has resulted in ultra-thin devices based on the transfer of transition metal dichalcogenides (TMDs) onto other TMDs or III-nitride materials. In this investigation, we realized p-type monolayer (ML) MoS2, and intrinsic GaN/p-type MoS2 heterojunction by the GaN overgrowth on ML-MoS2/c-sapphire using the plasma-assisted molecular beam epitaxy. A systematic nitrogen plasma (N∗2N2*) and gallium (Ga) irradiation studies are employed to understand the individual effect on the doping levels of ML-MoS2, which is evaluated by micro-Raman and high-resolution X-Ray photoelectron spectroscopy (HRXPS) measurements. With both methods, p-type doping was attained and was verified by softening and strengthening of characteristics phonon modes E12gE2g1 and A1gA1g from Raman spectroscopy. With adequate N∗2N2*-irradiation (3 min), respective shift of 1.79 cm−1 for A1gA1g and 1.11 cm−1 for E12gE2g1 are obtained while short term Ga-irradiated (30 s) exhibits the shift of 1.51 cm−1 for A1gA1g and 0.93 cm−1 for E12gE2g1. Moreover, in HRXPS valence band spectra analysis, the position of valence band maximum measured with respect to the Fermi level is determined to evaluate the type of doping levels in ML-MoS2. The observed values of valance band maximum are reduced to 0.5, and 0.2 eV from the intrinsic value of ≈1.0 eV for N∗2N2*- and Ga-irradiated MoS2 layers, which confirms the p-type doping of ML-MoS2. Further p-type doping is verified by Hall effect measurements. Thus, by GaN overgrowth, we attained the building block of intrinsic GaN/p-type MoS2 heterojunction. Through this work, we have provided the platform for the realization of dissimilar heterostructure via monolithic approach.

  5. Low-temperature growth of Ge{sub 1} {sub -x}Sn{sub x} thin films with strain control by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lin Hai, E-mail: hailin@stanford.edu [Department of Materials Science and Engineering, Stanford University, Stanford, California, 94305 (United States); Chen, Robert; Huo Yijie; Kamins, Theodore I.; Harris, James S. [Department of Electrical Engineering, Stanford University, Stanford, California, 94305 (United States)

    2012-03-30

    High-quality Ge{sub 1-x}Sn{sub x} thin films on InGaAs buffer layers have been demonstrated using low-temperature growth by molecular beam epitaxy. X-ray diffraction and secondary ion mass spectrometry are used to determine the strain and Sn concentration. Up to 10.5% Sn has been incorporated into the Ge{sub 1-x}Sn{sub x} thin film without Sn precipitation, as verified by transmission electron microscopy. Roughened surfaces are found for tensile strained Ge{sub 1-x}Sn{sub x} layers. - Highlights: Black-Right-Pointing-Pointer GeSn alloys were grown by molecular beam epitaxy with up to 10.5% Sn. Black-Right-Pointing-Pointer Unstrained GeSn alloys have high crystal quality. Black-Right-Pointing-Pointer Consistent Sn concentration was obtained from two different methods. Black-Right-Pointing-Pointer The growth of tensile strained GeSn results in a roughened surface.

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

    OpenAIRE

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

    2015-01-01

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

  7. Laser Molecular Beam Epitaxy of Multilayer Heterostructure SrNb0.05 Ti0.95O3/La0.9Sr0.1MnO3 in 10000 Unit-Cell Layers

    Institute of Scientific and Technical Information of China (English)

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

    2008-01-01

    Ten thousands of unit-cell multilayer heterosturctures, [SrNb0.05 Ti0.95 O3/La0.9Sr0.1MnO3]3 (SNTO/LSMO),have been epitaxial grown on SrTiO3 (001) substrates by laser molecular beam epitaxy. The monitor of insitu reflection high-energy electron diffraction demonstrates that the heterosturctures are layer-by-layer epitaxial growth. Atomic force microscope observation indicates that the surface of the heterosturcture is atomically smooth. The measurements of cross-sectional low magnification and high-resolution transmission electron microscopy as well as the corresponding selected area electron diffraction reveal that the interfaces are of perfect orientation, and the epitaxial crystalline structure shows the orientation relation of SNTO(001)//LSMO(001),and SNTO[100]//LSMO[100].

  8. Photoluminescence studies of epitaxial Si 1- xGe x and Si 1- x-yGe xC y layers on Si formed by ion beam synthesis

    Science.gov (United States)

    Katsumata, H.; Kobayashi, N.; Makita, Y.; Hasegawa, M.; Hayashi, N.; Shibata, H.; Uekusa, S.

    1997-01-01

    Low temperature (2 K) photoluminescence (PL) properties of epitaxial Si 1- xGe x and Si 1- x-yGe xC y layers on Si ( x = 0.13 and y = 0.014 at peak concentration) formed by ion beam synthesis (IBS) have been investigated. Samples were prepared by a high-dose Ge with/without C ion implantation (I 2) at room temperature and by subsequent three different crystallization techniques: (i) furnace annealing (FA) process up to 840°C, (ii) ion beam-induced epitaxial crystallization (IBIEC) process with 400 keV Ge or Ar ions at 300-350°C, and (iii) IBIEC process followed by FA process up to 640°C (IBIEC + FA). Although FA-grown Si 1- x-yGe xC y samples showed G-line (C sSi iC s complex) emission at 0.969 eV, IBIEC-grown samples presented a sharp I 1 non-phonon emission at 1.0193 eV. This indicates that C atoms agglomeration is dominant for FA-grown samples, while a creation of trigonal tetravacancy cluster is dominant for IBIEC-grown samples. On the other hand, (IBIEC with Ge ions + FA)-grown Si 1- x-yGe xC y samples showed neither G-line nor I 1-related emissions, which indicates that good crystalline Si 1- x-yGe xC y layers without C agglomeration were formed by this process. In contrast, (IBIEC with Ar ions + FA)-grown samples exhibited novel successive PL vibronic sidebands at 0.98-1.03 eV. From their excitation power dependence measurements, they were found to be associated with exciton bound to defects levels created by Ar + bombardment.

  9. Effect of lithographically-induced strain relaxation on the magnetic domain configuration in microfabricated epitaxially grown Fe81Ga19

    Science.gov (United States)

    Beardsley, R. P.; Parkes, D. E.; Zemen, J.; Bowe, S.; Edmonds, K. W.; Reardon, C.; Maccherozzi, F.; Isakov, I.; Warburton, P. A.; Campion, R. P.; Gallagher, B. L.; Cavill, S. A.; Rushforth, A. W.

    2017-02-01

    We investigate the role of lithographically-induced strain relaxation in a micron-scaled device fabricated from epitaxial thin films of the magnetostrictive alloy Fe81Ga19. The strain relaxation due to lithographic patterning induces a magnetic anisotropy that competes with the magnetocrystalline and shape induced anisotropies to play a crucial role in stabilising a flux-closing domain pattern. We use magnetic imaging, micromagnetic calculations and linear elastic modelling to investigate a region close to the edges of an etched structure. This highly-strained edge region has a significant influence on the magnetic domain configuration due to an induced magnetic anisotropy resulting from the inverse magnetostriction effect. We investigate the competition between the strain-induced and shape-induced anisotropy energies, and the resultant stable domain configurations, as the width of the bar is reduced to the nanoscale range. Understanding this behaviour will be important when designing hybrid magneto-electric spintronic devices based on highly magnetostrictive materials.

  10. Multi-electron beam system for high resolution electron beam induced deposition

    NARCIS (Netherlands)

    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 structure

  11. 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.

  12. Nanopillar growth by focused helium ion-beam-induced deposition

    NARCIS (Netherlands)

    Chen, P.; Veldhoven, E. van; Sanford, C.A.; Salemink, H.W.M.; Maas, D.J.; Smith, D.A.; Rack, P.D.; Alkemade, P.F.A.

    2010-01-01

    A 25 keV focused helium ion beam has been used to grow PtC nanopillars on a silicon substrate by beam-induced decomposition of a (CH3) 3Pt(CPCH3) precursor gas. The ion beam diameter was about 1 nm. The observed relatively high growth rates suggest that el

  13. Soft beams: When capillarity induces axial compression

    Science.gov (United States)

    Neukirch, S.; Antkowiak, A.; Marigo, J.-J.

    2014-01-01

    We study the interaction of an elastic beam with a liquid drop in the case where bending and extensional effects are both present. We use a variational approach to derive equilibrium equations and constitutive relation for the beam. This relation is shown to include a term due to surface energy in addition to the classical Young's modulus term, leading to a modification of Hooke's law. At the triple point where solid, liquid, and vapor phases meet, we find that the external force applied on the beam is parallel to the liquid-vapor interface. Moreover, in the case where solid-vapor and solid-liquid interface energies do not depend on the extension state of the beam, we show that the extension in the beam is continuous at the triple point and that the wetting angle satisfies the classical Young-Dupré relation.

  14. Testing beam-induced quench levels of LHC superconducting magnets

    Science.gov (United States)

    Auchmann, B.; Baer, T.; Bednarek, M.; Bellodi, G.; Bracco, C.; Bruce, R.; Cerutti, F.; Chetvertkova, V.; Dehning, B.; Granieri, P. P.; Hofle, W.; Holzer, E. B.; Lechner, A.; Nebot Del Busto, E.; Priebe, A.; Redaelli, S.; Salvachua, B.; Sapinski, M.; Schmidt, R.; Shetty, N.; Skordis, E.; Solfaroli, M.; Steckert, J.; Valuch, D.; Verweij, A.; Wenninger, J.; Wollmann, D.; Zerlauth, M.

    2015-06-01

    In the years 2009-2013 the Large Hadron Collider (LHC) has been operated with the top beam energies of 3.5 and 4 TeV per proton (from 2012) instead of the nominal 7 TeV. The currents in the superconducting magnets were reduced accordingly. To date only seventeen beam-induced quenches have occurred; eight of them during specially designed quench tests, the others during injection. There has not been a single beam-induced quench during normal collider operation with stored beam. The conditions, however, are expected to become much more challenging after the long LHC shutdown. The magnets will be operating at near nominal currents, and in the presence of high energy and high intensity beams with a stored energy of up to 362 MJ per beam. In this paper we summarize our efforts to understand the quench levels of LHC superconducting magnets. We describe beam-loss events and dedicated experiments with beam, as well as the simulation methods used to reproduce the observable signals. The simulated energy deposition in the coils is compared to the quench levels predicted by electrothermal models, thus allowing one to validate and improve the models which are used to set beam-dump thresholds on beam-loss monitors for run 2.

  15. 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

  16. Electron beam induced oxidation of Al–Mg alloy surfaces

    NARCIS (Netherlands)

    Palasantzas, G.; Agterveld, D.T.L. van; Hosson, J.Th.M. De

    2002-01-01

    Electron beam currents of a few nanoamperes, currently used in nanometer scale scanning Auger/electron microscopy, induces severe oxidation of Al–Mg alloy surfaces at room temperature. Auger peak-to-peak oxygen curves for Al–Mg surfaces support the hypothesis that the electron beam creates additiona

  17. 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.

  18. Coexistence of epitaxial lattice rotation and twinning tilt induced by surface symmetry mismatch

    Energy Technology Data Exchange (ETDEWEB)

    Qiao, L., E-mail: qiaol@ornl.gov, E-mail: biegalskim@ornl.gov; Biegalski, M. D., E-mail: qiaol@ornl.gov, E-mail: biegalskim@ornl.gov [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Xiao, H. Y. [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Weber, W. J. [Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996 (United States)

    2014-06-02

    Combined x-ray diffraction and first-principles studies of various epitaxial rutile-type metal dioxide films on Al{sub 2}O{sub 3}(0001) substrates reveal an unexpected rectangle-on-parallelogram heteroepitaxy. Unique matching of particular lattice spacings and crystal angles between the oxygen sublattices of Al{sub 2}O{sub 3}(0001) and the film(100) result in coexisted crystal rotation and lattice twinning inside the film. We demonstrate that, besides symmetry and lattice mismatch, angular mismatch along a specific crystal direction is also an important factor determining epitaxy. A generalized theorem has been proposed to explain epitaxial behaviors for tetragonal metal dioxides on Al{sub 2}O{sub 3}(0001).

  19. Ion beam induced luminescence: Relevance to radiation induced bystander effects

    Energy Technology Data Exchange (ETDEWEB)

    Ahmad, S.B., E-mail: ahmad.rabilal@gmail.com [Medical Physics and Applied Radiation Sciences, University of McMaster, Hamilton, Ontario (Canada); McNeill, F.E., E-mail: fmcneill@mcmaster.ca [Medical Physics and Applied Radiation Sciences, University of McMaster, Hamilton, Ontario (Canada); Byun, S.H., E-mail: soohyun@mcmaster.ca [Medical Physics and Applied Radiation Sciences, University of McMaster, Hamilton, Ontario (Canada); Prestwich, W.V., E-mail: prestwic@mcmaster.ca [Medical Physics and Applied Radiation Sciences, University of McMaster, Hamilton, Ontario (Canada); Seymour, C., E-mail: seymouc@mcmaster.ca [Medical Physics and Applied Radiation Sciences, University of McMaster, Hamilton, Ontario (Canada); Mothersill, C.E., E-mail: mothers@mcmaster.ca [Medical Physics and Applied Radiation Sciences, University of McMaster, Hamilton, Ontario (Canada)

    2012-10-01

    The aim of this work is quantify the light emitted as a result of charged particle interaction in materials which may be of relevance to radiation induced 'bystander effects' studies. We have developed a system which employs single photon counting to measure the light emitted from samples irradiated under vacuum by a charged particle beam. The system uses a fast photomultiplier tube with a peak cathode response at 420 nm. It has been tested in a proof-of-principle experiment using polystyrene targets. Light output, as a result of irradiation, was measured. The luminescence yield appears to have a non-linear behavior with the incident ion fluence: it rises exponentially to an asymptotic value. The target was irradiated with beam energies varying from 1 to 2 MeV and showed saturation at or before an incident fluence rate of 3 Multiplication-Sign 10{sup 13} H{sup +}/cm{sup 2} s. The average saturation value for the photon output was found to be 40 Multiplication-Sign 10{sup 6} cps. Some measurements were performed using filters to study the emission at specific wavelengths. In the case of filtered light measurements, the photon output was found to saturate at 28 Multiplication-Sign 10{sup 3}, 10 Multiplication-Sign 10{sup 6}, and 35 Multiplication-Sign 10{sup 6} cps for wavelengths of 280 {+-} 5 nm, 320 {+-} 5 nm and 340 {+-} 5 nm respectively. The light output reaches a maximum value because of damage induced in the polymer. Our measurements indicate a 'damage cross section' of the order of 10{sup -14} cm{sup 2}. The average radiant intensity was found to increase at wavelengths of 280 and 320 nm when the proton energy was increased. This was not found to occur at 340 nm. In conclusion, the light emission at specific wavelengths was found to depend upon the incident proton fluence and the proton energy. The wavelengths of the emitted light measured in this study have significance for the understanding of radiation induced bystander effects.

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

    Directory of Open Access Journals (Sweden)

    Sathiabama Thiru

    2015-02-01

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

  1. Buffer-layer enhanced crystal growth of BaB{sub 6} (1 0 0) thin films on MgO (1 0 0) substrates by laser molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kato, Yushi; Yamauchi, Ryosuke; Arai, Hideki; Tan, Geng [Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259-J2-46, Nagatsuta-cho, Midori-ku, Yokohama 226-8503 (Japan); Tsuchimine, Nobuo; Kobayashi, Susumu [Toshima Manufacturing Company Limited, 1414 Shimonomoto, Higashimatsuyama-shi, Saitama 355-0036 (Japan); Saeki, Kazuhiko; Takezawa, Nobutaka [Department of Materials Technology, Industrial Technology Center of Tochigi Prefecture, 367-1 Karinuma, Utsunomiya-shi, Tochigi 321-3224 (Japan); Mitsuhashi, Masahiko; Kaneko, Satoru [Kanagawa Industrial Technology Center, Kanagawa Prefectural Government, 705-1 Shimo-Imaizumi, Ebina, Kanagawa 243-0435 (Japan); Yoshimoto, Mamoru, E-mail: yoshimoto.m.aa@m.titech.ac.jp [Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259-J2-46, Nagatsuta-cho, Midori-ku, Yokohama 226-8503 (Japan); Patent Attorney, Tokyo Institute of Technology, 4259-J2-46, Nagatsuta-cho, Midori-ku, Yokohama 226-8503 (Japan)

    2012-02-01

    Crystalline BaB{sub 6} (1 0 0) thin films can be fabricated on MgO (1 0 0) substrates by inserting a 2-3 nm-thick epitaxial SrB{sub 6} (1 0 0) buffer layer by pulsed laser deposition (PLD) in ultra-high vacuum (i.e., laser molecular beam epitaxy). Reflection high-energy electron diffraction and X-ray diffraction measurements indicated the heteroepitaxial structure of BaB{sub 6} (1 0 0)/SrB{sub 6} (1 0 0)/MgO (1 0 0) with the single domain of the epitaxial relationship. Conversely, BaB{sub 6} thin films without the buffer layer were not epitaxial instead they developed as polycrystalline films with a random in-plane configuration and some impurity phases. As a result, the buffer layer is considered to greatly affect the initial growth of epitaxial BaB{sub 6} thin films; therefore, in this study, buffering effects have been discussed. From the conventional four-probe measurement, it was observed that BaB{sub 6} epitaxial thin films exhibit n-type semiconducting behavior with a resistivity of 2.90 Multiplication-Sign 10{sup -1} {Omega} cm at room temperature.

  2. 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.

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

    Institute of Scientific and Technical Information of China (English)

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

    2004-01-01

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

  4. Large-area growth of multi-layer hexagonal boron nitride on polished cobalt foils by plasma-assisted molecular beam epitaxy

    Science.gov (United States)

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

    2017-01-01

    Two-dimensional (2D) hexagonal boron nitride (h-BN), which has a similar honeycomb lattice structure to graphene, is promising as a dielectric material for a wide variety of potential applications based on 2D materials. Synthesis of high-quality, large-size and single-crystalline h-BN domains is of vital importance for fundamental research as well as practical applications. In this work, we report the growth of h-BN films on mechanically polished cobalt (Co) foils using plasma-assisted molecular beam epitaxy. Under appropriate growth conditions, the coverage of h-BN layers can be readily controlled by growth time. A large-area, multi-layer h-BN film with a thickness of 5~6 nm is confirmed by Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. In addition, the size of h-BN single domains is 20~100 μm. Dielectric property of as-grown h-BN film is evaluated by characterization of Co(foil)/h-BN/Co(contact) capacitor devices. Breakdown electric field is in the range of 3.0~3.3 MV/cm, which indicates that the epitaxial h-BN film has good insulating characteristics. In addition, the effect of substrate morphology on h-BN growth is discussed regarding different domain density, lateral size, and thickness of the h-BN films grown on unpolished and polished Co foils. PMID:28230178

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

    Science.gov (United States)

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

    2017-04-01

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

  6. Microstructural Properties of Single Crystalline PbTe Thin Films Grown on BaF2(111) by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    SI Jian-Xiao; WU Hui-Zhen; XU Tian-Ning; CAO Chun-Fang; HUANG Zhan-Chao

    2005-01-01

    @@ Single crystal PbTe thin films have been grown on BaF2 (111) by using solid source molecular beam epitaxy.The studies of evolution of the surface morphology with the increasing growth temperature from 375 to 525℃by AFM show that PbTe epilayers exhibit smooth surface morphologies with atomic layer scale roughness and are crack free. It is found that for PbTe grown at 475℃, the morphology is dominated by triangles and the rms roughness is 3.987nm. Compared to the rms roughnesses of 0.432nm and 0.759nm for the samples grown at 375 and 525℃ respectively, the surface of the PbTe layer grown at 475℃ is much rougher. This roughening transition is due to the interaction between the elastic relaxation and the plastic relaxation during the strain relaxation process. In contrast to the result of the morphology that the PbTe epitaxial layer grown at 375℃ has most smooth surface, as observed from the line width of x-ray diffraction curves at higher growth temperature improves the crystal quality of the single-crystalline PbTe layer.

  7. 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.

  8. 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.

  9. Instrumentation for Epitaxial Growth of Complex Oxides

    Science.gov (United States)

    2015-12-17

    P.O. Box 12211 Research Triangle Park, NC 27709-2211 epitaxy, molecular beam epitaxy, oxide heterostructures REPORT DOCUMENTATION PAGE 11. SPONSOR...The installation of this shielding was founded to dramatically increase the beam stability and mitigate intensity fluctuations. The RHEED source has

  10. 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.

  11. 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.

  12. Ion beam induced stress formation and relaxation in germanium

    Energy Technology Data Exchange (ETDEWEB)

    Steinbach, T., E-mail: Tobias.Steinbach@uni-jena.de [Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, D-07743 Jena (Germany); Reupert, A.; Schmidt, E.; Wesch, W. [Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, D-07743 Jena (Germany)

    2013-07-15

    Ion irradiation of crystalline solids leads not only to defect formation and amorphization but also to mechanical stress. In the past, many investigations in various materials were performed focusing on the ion beam induced damage formation but only several experiments were done to investigate the ion beam induced stress evolution. Especially in microelectronic devices, mechanical stress leads to several unwanted effects like cracking and peeling of surface layers as well as changing physical properties and anomalous diffusion of dopants. To study the stress formation and relaxation process in semiconductors, crystalline and amorphous germanium samples were irradiated with 3 MeV iodine ions at different ion fluence rates. The irradiation induced stress evolution was measured in situ with a laser reflection technique as a function of ion fluence, whereas the damage formation was investigated by means of Rutherford backscattering spectrometry. The investigations show that mechanical stress builds up at low ion fluences as a direct consequence of ion beam induced point defect formation. However, further ion irradiation causes a stress relaxation which is attributed to the accumulation of point defects and therefore the creation of amorphous regions. A constant stress state is reached at high ion fluences if a homogeneous amorphous surface layer was formed and no further ion beam induced phase transition took place. Based on the results, we can conclude that the ion beam induced stress evolution seems to be mainly dominated by the creation and accumulation of irradiation induced structural modification.

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

    Science.gov (United States)

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

    2016-11-01

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

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

    Science.gov (United States)

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

    2008-05-01

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2005-01-01

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

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

    Science.gov (United States)

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

    2016-08-01

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

  17. 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.

  18. Alloy formation during molecular beam epitaxy growth of Si-doped InAs nanowires on GaAs[111]B.

    Science.gov (United States)

    Davydok, Anton; Rieger, Torsten; Biermanns, Andreas; Saqib, Muhammad; Grap, Thomas; Lepsa, Mihail Ion; Pietsch, Ullrich

    2013-08-01

    Vertically aligned InAs nanowires (NWs) doped with Si were grown self-assisted by molecular beam epitaxy on GaAs[111]B substrates covered with a thin SiO x layer. Using out-of-plane X-ray diffraction, the influence of Si supply on the growth process and nanostructure formation was studied. It was found that the number of parasitic crystallites grown between the NWs increases with increasing Si flux. In addition, the formation of a Ga0.2In0.8As alloy was observed if the growth was performed on samples covered by a defective oxide layer. This alloy formation is observed within the crystallites and not within the nanowires. The Ga concentration is determined from the lattice mismatch of the crystallites relative to the InAs nanowires. No alloy formation is found for samples with faultless oxide layers.

  19. 1.1-μm InAs/GaAs quantum-dot light-emitting transistors grown by molecular beam epitaxy.

    Science.gov (United States)

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

    2015-08-15

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

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

    Science.gov (United States)

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

    2017-02-01

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

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

    Science.gov (United States)

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

    2016-01-26

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

  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. Molecular beam epitaxy growth of GaAs/InAs core-shell nanowires and fabrication of InAs nanotubes.

    Science.gov (United States)

    Rieger, Torsten; Luysberg, Martina; Schäpers, Thomas; Grützmacher, Detlev; Lepsa, Mihail Ion

    2012-11-14

    We present results about the growth of GaAs/InAs core-shell nanowires (NWs) using molecular beam epitaxy. The core is grown via the Ga droplet-assisted growth mechanism. For a homogeneous growth of the InAs shell, the As(4) flux and substrate temperature are critical. The shell growth starts with InAs islands along the NW core, which increase in time and merge giving finally a continuous and smooth layer. At the top of the NWs, a small part of the core is free of InAs indicating a crystal phase selective growth. This allows a precise measurement of the shell thickness and the fabrication of InAs nanotubes by selective etching. The strain relaxation in the shell occurs mainly via the formation of misfit dislocations and saturates at ~80%. Additionally, other types of defects are observed, namely stacking faults transferred from the core or formed in the shell, and threading dislocations.

  4. Native-oxide-based selective area growth of InP nanowires via metal-organic molecular beam epitaxy mediated by surface diffusion.

    Science.gov (United States)

    Calahorra, Yonatan; Greenberg, Yaakov; Cohen, Shimon; Ritter, Dan

    2012-06-22

    The growth of InP nanowires on an InP(111) B substrate is reported. The substrate native oxide was not removed from the surface prior to growth. Nanowires were grown at 400 °C from gold catalysts in a selective area manner, without bulk growth. Unlike SiO(2)-based metal-organic molecular beam epitaxy selective area growth, the growth reported here is mediated by surface diffusion with a characteristic diffusion length of 4 μm, about an order of magnitude larger than values for diffusion on bare substrates. A pre-growth heating treatment at 450 °C was found to increase the yield of nanowire nucleation from the gold catalysts.

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

    Science.gov (United States)

    Kuyanov, P; LaPierre, R R

    2015-08-07

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

  6. X-ray photoelectron spectroscopic study of the oxide removal mechanism of GaAs /100/ molecular beam epitaxial substrates in in situ heating

    Science.gov (United States)

    Vasquez, R. P.; Lewis, B. F.; Grunthaner, F. J.

    1983-01-01

    A standard cleaning procedure for GaAs (100) molecular beam epitaxial (MBE) substrates is a chemical treatment with a solution of H2SO4/H2O2/H2O, followed by in situ heating prior to MBE growth. X-ray photoelectron spectroscopic (XPS) studies of the surface following the chemical treatment show that the oxidized As is primarily As(+ 5). Upon heating to low temperatures (less than (350 C) the As(+ 5) oxidizes the substrate to form Ga2O3 and elemental As, and the As(+ 5) is reduced to As(+ 3) in the process. At higher temperatures (500 C), the As(+ 3) and elemental As desorb, while the Ga(+ 3) begins desorbing at about 600 C.

  7. 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.

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

    Institute of Scientific and Technical Information of China (English)

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

    2008-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2006-07-15

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

  10. Interfacial structure of molecular beam epitaxial grown cubic-GaN films on GaAs(001) probed by x-ray gazing-angle specular reflection

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    We report on a study of interfacial structure of GaN films grown on GaAs(001) substrates by plasma-assisted molecular beam epitaxy using x-ray grazing-angle specular reflection.We show that interfacial layers with electron densities differing from those of GaN and GaAs were formed upon deposition of GaN.It is also found that the interfacial structure of our systems depends strongly on the course of the initial layer deposition.The phase purity of the GaN films was examined by x-ray reciprocal space mapping.A simple kinetic growth model suggested by our results has been presented.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2002-08-16

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2002-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-06-15

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-07-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-12-01

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

  16. Testing beam-induced quench levels of LHC superconducting magnets

    CERN Document Server

    Auchmann, B; Bednarek, M; Bellodi, G; Bracco, C; Bruce, R; Cerutti, F; Chetvertkova, V; Dehning, B; Granieri, P P; Hofle, W; Holzer, E B; Lechner, A; Del Busto, E Nebot; Priebe, A; Redaelli, S; Salvachua, B; Sapinski, M; Schmidt, R; Shetty, N; Skordis, E; Solfaroli, M; Steckert, J; Valuch, D; Verweij, A; Wenninger, J; Wollmann, D; Zerlauth, M

    2015-01-01

    In the years 2009-2013 the Large Hadron Collider (LHC) has been operated with the top beam energies of 3.5 TeV and 4 TeV per proton (from 2012) instead of the nominal 7 TeV. The currents in the superconducting magnets were reduced accordingly. To date only seventeen beam-induced quenches have occurred; eight of them during specially designed quench tests, the others during injection. There has not been a single beam- induced quench during normal collider operation with stored beam. The conditions, however, are expected to become much more challenging after the long LHC shutdown. The magnets will be operating at near nominal currents, and in the presence of high energy and high intensity beams with a stored energy of up to 362 MJ per beam. In this paper we summarize our efforts to understand the quench levels of LHC superconducting magnets. We describe beam-loss events and dedicated experiments with beam, as well as the simulation methods used to reproduce the observable signals. The simulated energy depositio...

  17. 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...

  18. Two-step growth of high quality Bi{sub 2}Te{sub 3} thin films on Al{sub 2}O{sub 3} (0001) by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Harrison, S. E.; Huo, Y.; Harris, J. S. [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Li, S. [Department of Physics, Stanford University, Stanford, California 94305 (United States); Zhou, B.; Chen, Y. L. [Department of Physics, Stanford University, Stanford, California 94305 (United States); Department of Physics, University of Oxford, Parks Road, OX1 3PU Oxford (United Kingdom); Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2013-04-29

    Large-area topological insulator Bi{sub 2}Te{sub 3} thin films were grown on Al{sub 2}O{sub 3} (0001) using a two-temperature step molecular beam epitaxy growth process. By depositing a low temperature nucleation layer to serve as a template for high temperature epitaxial film growth, a high quality terrace-step surface morphology with a significant reduction in three-dimensional defect structures was achieved. X-ray diffraction measurements indicate that high crystalline quality Bi{sub 2}Te{sub 3} layers were grown incoherently by van der Waals epitaxy using this technique. Angle resolved photoemission spectroscopy measurements verified the integrity of this growth method by confirming the presence of metallic surface states on cleaved two-step Bi{sub 2}Te{sub 3} samples.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-07-14

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

  20. 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%.

  1. Laser Induced Chemical Vapor Phase Epitaxial Growth of III-V semiconductor Films

    Science.gov (United States)

    1991-05-14

    temperatures for the preparation and crystal growth of semiconductors . During the first phase of this program at Southern Methodist University, the epitaxial...approach to the preparation of device-quality 4 semiconductor films of controlled electrical and stru -.tural propierties . The excitation of reaction...temperatures for the preparation and crystal growth of semiconductors . The vapors of essentially all metalorganic compounds and group V hydrides are colorless

  2. 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...

  3. 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 inexpensive...... ionization sources - as opposed to expensive accelerator beams - can be used for investigations of ion-induced nucleation....

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

    Science.gov (United States)

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

    2017-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Jos E. Boschker

    2017-01-01

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

  6. Effects of Ga ion irradiation on growth of GaN on SiN substrates by electron cyclotron resonance-assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Yanagisawa, J. [Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531 (Japan) and Center for Quantum Science and Technology under Extreme Conditions, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531 (Japan) and CREST-JST, Kawaguchi Center Building, 4-1-8, Honcho, Kawaguchi, Saitama 332-0012 (Japan)]. E-mail: yanagisawa@ee.es.osaka-u.ac.jp; Matsumoto, H. [Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531 (Japan); Fukuyama, T. [Department of Electronics, Information and Communication Engineering, Osaka Institute of Technology, 5-16-1 Omiya, Asahi-ku, Osaka 535-8585 (Japan); Shiraishi, Y. [Department of Electronics, Information and Communication Engineering, Osaka Institute of Technology, 5-16-1 Omiya, Asahi-ku, Osaka 535-8585 (Japan); Yodo, T. [Department of Electronics, Information and Communication Engineering, Osaka Institute of Technology, 5-16-1 Omiya, Asahi-ku, Osaka 535-8585 (Japan); Akasaka, Y. [Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531 (Japan)

    2007-04-15

    The possibility of forming GaN layers on Ga-implanted SiN surfaces was investigated using electron cyclotron resonance-assisted molecular beam epitaxy (MBE). It is found that the GaN layer initially formed on the SiN surface by Ga implantation at room temperature was amorphous-like, but become to polycrystalline after annealing at 650 deg. C for 3 min in vacuum. After the MBE growth of GaN, a grain structure of h-GaN was observed on the Ga-implanted SiN surface. The crystallinity of the GaN grown was, however, decreased upon increasing the Ga ion fluence on the SiN surface, which might be due, at least partly, to the formation of Ga clusters by the excess Ga implanted. The present results indicate the possibility of forming patterned GaN layers on SiN by selective Ga implantation on the SiN substrate, using a focused ion beam.

  7. 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.

  8. Joule Heating-Induced Metal-Insulator Transition in Epitaxial VO2/TiO2 Devices.

    Science.gov (United States)

    Li, Dasheng; Sharma, Abhishek A; Gala, Darshil K; Shukla, Nikhil; Paik, Hanjong; Datta, Suman; Schlom, Darrell G; Bain, James A; Skowronski, Marek

    2016-05-25

    DC and pulse voltage-induced metal-insulator transition (MIT) in epitaxial VO2 two terminal devices were measured at various stage temperatures. The power needed to switch the device to the ON-state decrease linearly with increasing stage temperature, which can be explained by the Joule heating effect. During transient voltage induced MIT measurement, the incubation time varied across 6 orders of magnitude. Both DC I-V characteristic and incubation times calculated from the electrothermal simulations show good agreement with measured values, indicating Joule heating effect is the cause of MIT with no evidence of electronic effects. The width of the metallic filament in the ON-state of the device was extracted and simulated within the thermal model.

  9. Interdiffusion in epitaxial ultrathin Co2FeAl/MgO heterostructures with interface-induced perpendicular magnetic anisotropy

    Science.gov (United States)

    Wen, Zhenchao; Hadorn, Jason Paul; Okabayashi, Jun; Sukegawa, Hiroaki; Ohkubo, Tadakatsu; Inomata, Koichiro; Mitani, Seiji; Hono, Kazuhiro

    2017-01-01

    The interfacial atomic structure of epitaxial ultrathin Co2FeAl/MgO(001) heterostructures, which is related to the interface-induced perpendicular magnetic anisotropy (PMA), was investigated using scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray magnetic circular dichroism. Al atoms from the Co2FeAl layer significantly interdiffused into MgO, forming an Al-deficient Co-Fe-Al/Mg-Al-O structure near the Co2FeAl/MgO interface. This atomic replacement may have enhanced the PMA, which is consistent with the observed large perpendicular orbital magnetic moments of Fe atoms at the interface. This work suggests that control of interdiffusion at ferromagnet/barrier interfaces is critical for designing an interface-induced PMA system.

  10. Low temperature p-type doping of (Al)GaN layers using ammonia molecular beam epitaxy for InGaN laser diodes

    Energy Technology Data Exchange (ETDEWEB)

    Malinverni, M., E-mail: marco.malinverni@epfl.ch; Lamy, J.-M.; Martin, D.; Grandjean, N. [ICMP, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland); Feltin, E.; Dorsaz, J. [NOVAGAN AG, CH-1015 Lausanne (Switzerland); Castiglia, A.; Rossetti, M.; Duelk, M.; Vélez, C. [EXALOS AG, CH-8952 Schlieren (Switzerland)

    2014-12-15

    We demonstrate state-of-the-art p-type (Al)GaN layers deposited at low temperature (740 °C) by ammonia molecular beam epitaxy (NH{sub 3}-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{sup −4} Ω cm{sup 2}, 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 NH{sub 3}-MBE. Single-mode ridge-waveguide LD exhibits a threshold voltage as low as 4.3 V for an 800 × 2 μm{sup 2} ridge dimension and a threshold current density of ∼5 kA cm{sup −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 Al{sub 0.06}Ga{sub 0.94}N:Mg despite the low growth temperature.

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

    Energy Technology Data Exchange (ETDEWEB)

    Grabowski, Jan

    2010-12-14

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

  12. Effect of lithographically-induced strain relaxation on the magnetic domain configuration in microfabricated epitaxially grown Fe81Ga19

    Science.gov (United States)

    Beardsley, R. P.; Parkes, D. E.; Zemen, J.; Bowe, S.; Edmonds, K. W.; Reardon, C.; Maccherozzi, F.; Isakov, I.; Warburton, P. A.; Campion, R. P.; Gallagher, B. L.; Cavill, S. A.; Rushforth, A. W.

    2017-01-01

    We investigate the role of lithographically-induced strain relaxation in a micron-scaled device fabricated from epitaxial thin films of the magnetostrictive alloy Fe81Ga19. The strain relaxation due to lithographic patterning induces a magnetic anisotropy that competes with the magnetocrystalline and shape induced anisotropies to play a crucial role in stabilising a flux-closing domain pattern. We use magnetic imaging, micromagnetic calculations and linear elastic modelling to investigate a region close to the edges of an etched structure. This highly-strained edge region has a significant influence on the magnetic domain configuration due to an induced magnetic anisotropy resulting from the inverse magnetostriction effect. We investigate the competition between the strain-induced and shape-induced anisotropy energies, and the resultant stable domain configurations, as the width of the bar is reduced to the nanoscale range. Understanding this behaviour will be important when designing hybrid magneto-electric spintronic devices based on highly magnetostrictive materials. PMID:28186114

  13. Study of ion beam induced depolymerization using positron annihilation techniques

    Energy Technology Data Exchange (ETDEWEB)

    Puglisi, O. E-mail: opuglisi@dipchi.unict.it; Fragala, M.E.; Lynn, K.G.; Petkov, M.; Weber, M.; Somoza, A.; Dupasquier, A.; Quasso, F

    2001-04-01

    Ion beam induced depolymerization of polymers is a special class of ion beam induced chemical reaction which gives rise to catastrophic 'unzipping' of macromolecules with production of large amounts of the monomer, of the order of many hundreds monomer molecules per each macromolecule. The possible modification of the density at microscopic level prompted us to undertake a study of this effect utilizing positron annihilation techniques in Poly(methylmethacrylate) (PMMA) before and after bombardment with He{sup +} 300 keV ions at 200 deg. C. Preliminary results shown here indicate that before bombardment there is a reproducible dependence of nano-hole distribution on the sample history. Moreover at 200 deg. C we do not detect formation of new cavities as a consequence of the strong depolymerization that occurs under the ion beam. The possible correlation of these findings with transport properties of PMMA at temperature higher than the glass transition temperature will be discussed.

  14. Proximity effect in ion-beam-induced deposition of nanopillars

    NARCIS (Netherlands)

    Chen, P.; Salemink, H.W.M.; Alkemade, P.F.A.

    2009-01-01

    Ion-beam-induced deposition (IBID) is a powerful technique for prototyping three-dimensional nanostructures. To study its capability for this purpose, the authors investigate the proximity effect in IBID of nanopillars. In particular, the changes in shape and dimension of pillars are studied when a

  15. Fabrication of plasmonic nanostructures with electron beam induced deposition

    NARCIS (Netherlands)

    Acar, H.

    2013-01-01

    The work described in this thesis was shaped by the goal---coming up new approaches to fabricate plasmonic materials with electron beam induced deposition (EBID). One-step, bottom-up and direct-write are typical adjectives that are used to indicate the advantageous properties of this technique. Thes

  16. Gold ion beams induced desorption studies for Booster Nuclotron

    Science.gov (United States)

    Kuznetsov, A. B.; Tuzikov, A. V.; Philippov, A. V.

    2016-12-01

    Heavy ions induced pressure rise is one of the machine limits. The calculation results of the gold ion beam 197Au31+ losses due to residual gas interaction in view of desorption of adsorbed particles on the Booster Nuclotron vacuum chamber surface are discussed.

  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. Ordering of defects induced by epitaxy in LaCoO3 films

    Science.gov (United States)

    Mehta, Virat; Biskup, Neven; Wong, Franklin; Arenholz, Elke; Varela, Maria; Suzuki, Yuri

    2012-02-01

    In the bulk, LaCoO3 (LCO) undergoes a spin state transition from a diamagnet to a paramagnet with increasing temperature. Recent studies of epitaxial LCO thin films have resulted in the stabilization of a higher spin state and ferromagnetic ordering at low temperatures. Here, we explore the effects of epitaxy on the electronic structure of LCO films with X-ray absorption spectroscopy (XAS) and scanning transmission electron microscopy (STEM). We find differences in XAS spectra in coherently strained thinner films compared to the thicker partially relaxed films which may be due to differences in Co valence and bonding. STEM and electron energy loss spectroscopy of thinner LCO films reveal ordered defect planes that appear to be associated with a change in the O and Co bonding environments. In films on LaAlO3 strained in compression periodic planes occur parallel to the substrate-film interface, while films on SrTiO3 strained in tension have perpendicular defect planes. Correlation with magnetic data suggests that defect rich regions may exhibit greater ferromagnetism.

  19. Equilibrium nano-shape changes induced by epitaxial stress (generalised Wulf Kaishew theorem)

    Science.gov (United States)

    Müller, P.; Kern, R.

    2000-06-01

    A generalised Wulf-Kaishew theorem is given describing the equilibrium shape (ES) of an isolated 3D crystal A deposited coherently onto a lattice mismatched planar substrate. For this purpose a free polyhedral crystal is formed then homogeneously strained to be accommodated onto the lattice mismatched substrate. During its elastic inhomogeneous relaxation the epitaxial contact remains coherent so that the 3D crystal drags the atoms of the contact area and produces a strain field in the substrate. The ES of the deposit is obtained by minimising at constant volume the total energy (bulk and surface energies) taking into account the bulk elastic relaxation. Our main results are as follows. (1) Epitaxial strain acts against wetting (adhesion) so that globally it leads to a thickening of the ES. (2) Owing to strain the ES changes with size. More precisely the various facets extension changes, some facets decreasing, some others increasing. (3) Each dislocation entrance, necessary for relaxing plastically too large crystals abruptly modifies the ES and thus the different facets extension in a jerky way. (4) In all cases the usual self-similarity with size is lost when misfit is considered. We illustrate these points for box-shaped and truncated pyramidal crystals. Some experimental evidence is discussed.

  20. Optimizing Electromagnetically Induced Transparency Signals with Laguerre-Gaussian Beams

    Science.gov (United States)

    Holtfrerich, Matthew; Akin, Tom; Krzyzewski, Sean; Marino, Alberto; Abraham, Eric

    2016-05-01

    We have performed electromagnetically induced transparency in ultracold Rubidium atoms using a Laguerre-Gaussian laser mode as the control beam. Laguerre-Gaussian modes are characterized by a ring type transverse intensity profile and carry intrinsic orbital angular momentum. This angular momentum carried by the control beam can be utilized in optical computing applications which is unavailable to the more common Gaussian laser field. Specifically, we use a Laguerre-Gaussian control beam with a Gaussian probe to show that the linewidth of the transmission spectrum can be narrowed when compared to a Gaussian control beam that has the same peak intensity. We present data extending this work to compare control fields in both the Gaussian and Laguerre-Gaussian modes with constant total power. We have made efforts to find the optical overlap that best minimizes the transmission linewidth while also maintaining signal contrast. This was done by changing the waist size of the control beam with respect to the probe. The best results were obtained when the waist of a Laguerre-Gaussian control beam is equal to the waist of the Gaussian probe resulting in narrow linewidth features.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-01-13

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-02-01

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

  3. Effects of in situ annealing of GaAs(100) substrates on the subsequent growth of InAs quantum dots by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Morales-Cortes, H; Mejia-Garcia, C [Escuela Superior de Fisica y Matematicas del IPN, UPALM, Edif. 9, Col. Lindavista, Mexico DF 07738 (Mexico); Mendez-GarcIa, V H; Vazquez-Cortes, D [Coordinacion para la Innovacion y la Aplicacion de la Ciencia y la TecnologIa, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, San Luis PotosI, S L P 78000 (Mexico); Rojas-Ramirez, J S; Contreras-Guerrero, R; RamIrez-Lopez, M; Martinez-Velis, I; Lopez-Lopez, M, E-mail: mlopez@fis.cinvestav.mx [Physics Department, Centro de Investigacion y de Estudios Avanzados del IPN, Apartado Postal 14-740, Mexico DF 07000 (Mexico)

    2010-04-02

    In the present work, we study the growth by molecular beam epitaxy of InAs self-assembling quantum dots (SAQDs) on GaAs(100) substrates subjected to an in situ annealing treatment. The annealing process consists of the exposition of the GaAs buffer layer surface to high temperatures for a few seconds with the shutter of an arsenic Knudsen cell closed. The purpose of the annealing is to obtain a better uniformity of the SAQD sizes. In our study we prepared different samples using the Stranski-Krastanov growth method to obtain InAs/GaAs(100) quantum dot samples with different annealing times and temperatures. Their structural and optical properties were studied by reflection high-energy electron diffraction (RHEED), high-resolution scanning electron microscopy (HRSEM), atomic force microscopy (AFM), and photoreflectance spectroscopy (PR). According to the results of AFM and HRSEM, by the thermal treatment we obtained a better distribution of quantum dot sizes in comparison with a reference sample with no treatment. The PR spectra from 0.9 to 1.35 eV presented two transitions associated with SAQDs. The energy transitions were obtained by fitting the PR spectra using the third derivative model.

  4. Reflectance-anisotropy study of the dynamics of molecular beam epitaxy growth of GaAs and InGaAs on GaAs(001)

    Energy Technology Data Exchange (ETDEWEB)

    Ortega-Gallegos, J.; Lastras-Martinez, A.; Lastras-Martinez, L.F. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, San Luis Potosi (Mexico); Balderas-Navarro, R.E. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, San Luis Potosi (Mexico); Facultad de Ciencias, Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, San Luis Potosi (Mexico)

    2008-07-01

    Reflectance-Anisotropy (RA) observations during the Molecular Beam Epitaxy (MBE) growth of zincblende semiconductors films were carried out using the E{sub 1} optical transition as a probe. We follow the kinetics of the deposition of GaAs and In{sub 0.3}Ga{sub 0.7}As on GaAs(001) at growth rates of 0.2 and 0.25 ML/s, respectively. During growth we used a constant As{sub 4} or As{sub 2} flux pressure of 5 x 10{sup -6} Torr. Clear RA-oscillations were observed during growth with a period that nearly coincides with the growth period for a Ga-As bilayer. RHEED was used as an auxiliary technique in order to obtain a correlation between RHEED and RA oscillations. On the basis of our results, we argue that RAS oscillations are mainly associated to periodic changes in surface atomic structure. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Effects of growth temperature on high-quality In0.2Ga0.8N layers by plasma-assisted molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Zhang Dongyan; Zheng Xinhe; Li Xuefei; Wu Yuanyuan; Wang Jianfeng; Yang Hui

    2012-01-01

    High-quality In0.2Ga0.8N epilayers were grown on a GaN template at temperatures of 520 and 580 ℃ via plasma-assisted molecular beam epitaxy.The X-ray rocking curve full widths at half maximum (FWHM) of (10.2)reflections is 936 arcsec for the 50-nm-thick InGaN layers at the lower temperature.When the growth temperature increases to 580 ℃,the FWHM of (00.2) reflections for these samples is very narrow and keeps similar,while significant improvement of(10.2) reflections with an FWHM value of 612 arcsec has been observed.This improved quality in InGaN layers grown at 580 ℃ is also reflected by the much larger size of the crystalline column from the AFM results,stronger emission intensity as well as a decreased FWHM of room temperature PL from 136 to 93.9 meV.

  6. On the optical and microstrain analysis of graded InGaN/GaN MQWs based on plasma assisted molecular beam epitaxy

    KAUST Repository

    Mishra, Pawan

    2016-05-23

    In this paper, c-plane stepped- and graded- InGaN/GaN multiple quantum wells (MQWs) are grown using plasma assisted molecular beam epitaxy (PAMBE) by in situ surface stoichiometry monitoring (i-SSM). Such a technique considerably reduces the strain build-up due to indium clustering within and across graded-MQWs; especially for QW closer to the top which results in mitigation of the quantum-confined Stark effect (QCSE). This is validated by a reduced power dependent photoluminescence blueshift of 10 meV in graded-MQWs as compared to a blueshift of 17 meV for stepped-MQWs. We further analyze microstrain within the MQWs, using Raman spectroscopy and geometrical phase analysis (GPA) on high-angle annular dark-field (HAADF)-scanning transmission electron microscope (STEM) images of stepped- and graded-MQWs, highlighting the reduction of ~1% strain in graded-MQWs over stepped-MQWs. Our analysis provides direct evidence of the advantage of graded-MQWs for the commercially viable c-plane light-emitting and laser diodes. © 2016 Optical Society of America.

  7. Design of an ultrahigh vacuum transfer mechanism to interconnect an oxide molecular beam epitaxy growth chamber and an x-ray photoemission spectroscopy analysis system.

    Science.gov (United States)

    Rutkowski, M M; McNicholas, K M; Zeng, Zhaoquan; Brillson, L J

    2013-06-01

    We designed a mechanism and the accompanying sample holders to transfer between a VEECO 930 oxide molecular beam epitaxy (MBE) and a PHI Versa Probe X-ray photoemission spectroscopy (XPS) chamber within a multiple station growth, processing, and analysis system through ultrahigh vacuum (UHV). The mechanism consists of four parts: (1) a platen compatible with the MBE growth stage, (2) a platen compatible with the XPS analysis stage, (3) a sample coupon that is transferred between the two platens, and (4) the accompanying UHV transfer line. The mechanism offers a robust design that enables transfer back and forth between the growth chamber and the analysis chamber, and yet is flexible enough to allow transfer between standard sample holders for thin film growth and masked sample holders for making electrical contacts and Schottky junctions, all without breaking vacuum. We used this mechanism to transfer a barium strontium titanate thin film into the XPS analysis chamber and performed XPS measurements before and after exposing the sample to the air. After air exposure, a thin overlayer of carbon was found to form and a significant shift (~1 eV) in the core level binding energies was observed.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-01-28

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-12-15

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2008-01-01

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

  11. Effects of RF plasma parameters on the growth of InGaN/GaN heterostructures using plasma-assisted molecular beam epitaxy

    CERN Document Server

    Shim Kyu Ha; Kim, K H; Hong, S U; Cho, K I; Lee, H G; Kim, J

    1999-01-01

    The effects of rf plasma power on the structural/optical properties of GaN-based nitride epilayers grown by plasma-assisted molecular beam epitaxy have been investigated. Atomic force microscopy and high-resolution x-ray diffraction analyses revealed that the sharp interface of In sub 0 sub . sub 2 Ga sub 0 sub . sub 8 N/GaN heterostructures could be obtained by suppressing the surface roughening at high rf power. photoluminescence data suggest that the formation of damaged subsurface due to energetic particles was alleviated in the InGaN growth in comparison with the GaN growth. In our experimental set-up, the rf power of 400 W appeared to properly suppress the 3D island formation without causing defects at the subsurface of In sub 0 sub . sub 2 Ga sub 0 sub . sub 8 N. The phenomena associated with the indium incorporation could be explained by an inequality with two kinetic processes of the surface diffusion and the plasma stimulated desorption.

  12. High-Temperature Characteristics of GaInNAs/GaAs Single-Quantum-Well Lasers Grown by Plasma-Assisted Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    PAN Zhong; LI Lian-He; DU Yun; LIN Yao-Wang; WU Rong-Han

    2001-01-01

    GaInNAs/GaAs single-quantum-well (SQW) lasers have been grown by solid-source molecular beam epitaxy. N is introduced by a home-made dc-active plasma source. Incorporation of N into InGaAs decreases the bandgap significantly. The highest N concentration of 2.6% in a GalnNAs/GaAs QW is obtained, corresponding to the photoluminescence (PL) peak wavelength of 1.57μm at 10 K. The PL peak intensity decreases rapidly and the PL full width at half maximum increases with the increasing N concentrations. Rapid thermal annealing at 850°C could significantly improve the crystal quality of the QWs. An optimum annealing time of 5s at 850°C was obtained. The GaInNAs/GaAs SQW laser emitting at 1.2μm exhibits a high characteristic temperature of 115 K in the temperature range of 20° C- 75° C.

  13. Molecular beam epitaxy of ZnSSe/CdSe short-period superlattices for III–V/II–VI multijunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Sorokin, S. V., E-mail: sorokin@beam.ioffe.ru; Gronin, S. V.; Sedova, I. V.; Klimko, G. V.; Evropeitsev, E. A.; Baidakova, M. V.; Sitnikova, A. A.; Toropov, A. A.; Ivanov, S. V. [Russian Academy of Sciences, Ioffe Institute (Russian Federation)

    2015-08-15

    Results on the molecular-beam epitaxy growth of short-period alternately-strained ZnS{sub x}Se{sub 1−x}/CdSe superlattices which are pseudomorphic to GaAs (001) substrates and possess effective band-gap values within the range of E{sub g} ≈ 2.5–2.7 eV are presented. Oscillations of the specular-spot intensity in reflection high-energy electron diffraction are used for in situ control of the superlattice parameters. A method to determine the SL parameters (compositions and thicknesses of the constituent layers) based on combined analysis of the grown structures by low-temperature photoluminescence and X-ray diffractometry is developed. It is found that the parameters of the grown ZnS{sub x}Se{sub 1−x}/CdSe superlattices are close to their design values and the density of extended defects in the structures is low even though the structure thickness (∼300 nm) considerably exceeds the critical thickness for bulk II–VI layers with the same lattice-constant mismatch.

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

    Science.gov (United States)

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

    2017-02-01

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

  15. Design of an ultrahigh vacuum transfer mechanism to interconnect an oxide molecular beam epitaxy growth chamber and an x-ray photoemission spectroscopy analysis system

    Science.gov (United States)

    Rutkowski, M. M.; McNicholas, K. M.; Zeng, Zhaoquan; Brillson, L. J.

    2013-06-01

    We designed a mechanism and the accompanying sample holders to transfer between a VEECO 930 oxide molecular beam epitaxy (MBE) and a PHI Versa Probe X-ray photoemission spectroscopy (XPS) chamber within a multiple station growth, processing, and analysis system through ultrahigh vacuum (UHV). The mechanism consists of four parts: (1) a platen compatible with the MBE growth stage, (2) a platen compatible with the XPS analysis stage, (3) a sample coupon that is transferred between the two platens, and (4) the accompanying UHV transfer line. The mechanism offers a robust design that enables transfer back and forth between the growth chamber and the analysis chamber, and yet is flexible enough to allow transfer between standard sample holders for thin film growth and masked sample holders for making electrical contacts and Schottky junctions, all without breaking vacuum. We used this mechanism to transfer a barium strontium titanate thin film into the XPS analysis chamber and performed XPS measurements before and after exposing the sample to the air. After air exposure, a thin overlayer of carbon was found to form and a significant shift (˜1 eV) in the core level binding energies was observed.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-28

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

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

    Directory of Open Access Journals (Sweden)

    Yuryev Vladimir

    2011-01-01

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

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

    Science.gov (United States)

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

    2017-03-01

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

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

    Science.gov (United States)

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

    2016-09-01

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

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

    Science.gov (United States)

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

    2010-09-08

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

  1. Molecular beam epitaxy and superconductivity of stoichiometric FeSe and KxFe2-ySe2 crystalline films

    Institute of Scientific and Technical Information of China (English)

    Wang Li-Li; Ma Xu-Cun; Chen Xi; Xue Qi-Kun

    2013-01-01

    Our recent progress in the fabrication of FeSe and KxFe2-ySe2 ultra thin films and the understanding of their superconductivity properties is reviewed.The growth of high-quality FeSe and KxFe2-ySe2 films is achieved in a well controlled manner by molecular beam epitaxy.The high-quality stoichiometric and superconducting crystalline thin films allow us to investigate the intrinsic superconductivity properties and the interplay between the superconductivity and the film thickness,the local structure,the substrate,and magnetism.In situ low-temperature scanning tunneling spectra reveal the nodes and the twofold symmetry in FeSe,high-temperature superconductivity at the FeSe/SrTiO3 interface,phase separation and magnetic order in KxFe2-ySe2,and the suppression of superconductivity by twin boundaries and Fe vacancies.Our findings not only provide fundamental information for understanding the mechanism of unconventional superconductivity,but also demonstrate a powerful way of engineering superconductors and raising the transition temperature.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-03-15

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

  3. Selective area growth of In(Ga)N/GaN nanocolumns by molecular beam epitaxy on GaN-buffered Si(111): from ultraviolet to infrared emission.

    Science.gov (United States)

    Albert, S; Bengoechea-Encabo, A; Sánchez-García, M A; Kong, X; Trampert, A; Calleja, E

    2013-05-03

    Selective area growth of In(Ga)N/GaN nanocolumns was performed on GaN-buffered Si(111) substrates by plasma-assisted molecular beam epitaxy. Undoped and Si-doped GaN buffer layers were first grown on Si(111) substrates, showing photoluminescence excitonic emission without traces of other low energy contributions, in particular, the yellow band. The GaN buffer surface roughness (between 10 and 14 nm, the rms value in a 10 × 10 μm(2) area) was low enough to allow the fabrication of a thin (7 nm thick) well defined Ti nanohole mask, for the selective area growth. Ordered In(Ga)N/GaN nanocolumns emitting from the ultraviolet (3.2 eV) to the infrared (0.78 eV) were obtained. The morphology and the emission efficiency of the In(Ga)N/GaN nanocolumns emitting at a given wavelength could be substantially improved by tuning the In/Ga and total III/N ratios. An estimated internal quantum efficiency of 36% was derived from photoluminescence data for green emitting nanocolumns.

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

    Science.gov (United States)

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

    2013-08-21

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

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

    Directory of Open Access Journals (Sweden)

    R. Sarmiento

    2003-06-01

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

  6. Impact of P/In flux ratio and epilayer thickness on faceting for nanoscale selective area growth of InP by molecular beam epitaxy.

    Science.gov (United States)

    Fahed, M; Desplanque, L; Coinon, C; Troadec, D; Wallart, X

    2015-07-24

    The impact of the P/In flux ratio and the deposited thickness on the faceting of InP nanostructures selectively grown by molecular beam epitaxy (MBE) is reported. Homoepitaxial growth of InP is performed inside 200 nm wide stripe openings oriented either along a [110] or [1-10] azimuth in a 10 nm thick SiO2 film deposited on an InP(001) substrate. When varying the P/In flux ratio, no major shape differences are observed for [1-10]-oriented apertures. On the other hand, the InP nanostructure cross sections strongly evolve for [110]-oriented apertures for which (111)B facets are more prominent and (001) ones shrink for large P/In flux ratio values. These results show that the growth conditions allow tailoring the nanocrystal shape. They are discussed in the framework of the equilibrium crystal shape model using existing theoretical calculations of the surface energies of different low-index InP surfaces as a function of the phosphorus chemical potential, directly related to the P/In ratio. Experimental observations strongly suggest that the relative (111)A surface energy is probably smaller than the calculated value. We also discuss the evolution of the nanostructure shape with the InP-deposited thickness.

  7. The isotype ZnO/SiC heterojunction prepared by molecular beam epitaxy--A chemical inert interface with significant band discontinuities.

    Science.gov (United States)

    Zhang, Yufeng; Lin, Nanying; Li, Yaping; Wang, Xiaodan; Wang, Huiqiong; Kang, Junyong; Wilks, Regan; Bär, Marcus; Mu, Rui

    2016-03-15

    ZnO/SiC heterojunctions show great potential for various optoelectronic applications (e.g., ultraviolet light emitting diodes, photodetectors, and solar cells). However, the lack of a detailed understanding of the ZnO/SiC interface prevents an efficient and rapid optimization of these devices. Here, intrinsic (but inherently n-type) ZnO were deposited via molecular beam epitaxy on n-type 6H-SiC single crystalline substrates. The chemical and electronic structure of the ZnO/SiC interfaces were characterized by ultraviolet/x-ray photoelectron spectroscopy and x-ray excited Auger electron spectroscopy. In contrast to the ZnO/SiC interface prepared by radio frequency magnetron sputtering, no willemite-like zinc silicate interface species is present at the MBE-ZnO/SiC interface. Furthermore, the valence band offset at the abrupt ZnO/SiC interface is experimentally determined to be (1.2 ± 0.3) eV, suggesting a conduction band offset of approximately 0.8 eV, thus explaining the reported excellent rectifying characteristics of isotype ZnO/SiC heterojunctions. These insights lead to a better comprehension of the ZnO/SiC interface and show that the choice of deposition route might offer a powerful means to tailor the chemical and electronic structures of the ZnO/SiC interface, which can eventually be utilized to optimize related devices.

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

    Science.gov (United States)

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

    2017-01-01

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

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

    Science.gov (United States)

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

    2014-08-13

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

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

    Science.gov (United States)

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

    2014-02-21

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

  11. Self-assembled GaInNAs/GaAsN quantum dot lasers: solid source molecular beam epitaxy growth and high-temperature operation

    Directory of Open Access Journals (Sweden)

    Yoon SF

    2006-01-01

    Full Text Available AbstractSelf-assembled GaInNAs quantum dots (QDs were grown on GaAs (001 substrate using solid-source molecular-beam epitaxy (SSMBE equipped with a radio-frequency nitrogen plasma source. The GaInNAs QD growth characteristics were extensively investigated using atomic-force microscopy (AFM, photoluminescence (PL, and transmission electron microscopy (TEM measurements. Self-assembled GaInNAs/GaAsN single layer QD lasers grown using SSMBE have been fabricated and characterized. The laser worked under continuous wave (CW operation at room temperature (RT with emission wavelength of 1175.86 nm. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. The lowest obtained threshold current density in this work is ∼1.05 kA/cm2from a GaInNAs QD laser (50 × 1,700 µm2 at 10 °C. High-temperature operation up to 65 °C was demonstrated from an unbonded GaInNAs QD laser (50 × 1,060 µm2, with high characteristic temperature of 79.4 K in the temperature range of 10–60 °C.

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

    Science.gov (United States)

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

    2016-12-01

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

  13. Direct growth of GaN on off-oriented SiC (0001) by molecular-beam epitaxy for GaN/SiC heterojunction bipolar transistor

    Energy Technology Data Exchange (ETDEWEB)

    Nakano, Y.; Kimoto, T. [Department of Electronic Science and Engineering, Kyoto University Katsura Campus, Nishikyo-ku, Kyoto, 615-8510 (Japan); Suda, J. [Department of Electronic Science and Engineering, Kyoto University Katsura Campus, Nishikyo-ku, Kyoto, 615-8510 (Japan); PRESTO, Japan Science and Technology Agency (JST) Kawaguchi, Saitama 332-0012 (Japan)

    2005-05-01

    Direct growth of GaN on misoriented 4H- and 6H-SiC (0001) Si-face substrates and electrical characteristics of n-GaN/p-SiC heterojunction mesa diodes are presented. GaN was grown by molecular-beam epitaxy (MBE) using elemental Ga and rf plasma-excited active nitrogen. SiC substrates misoriented 8 toward the [11-20] direction were used in this study. The surfaces of MBE-grown GaN layers have wavy features with peak-to-valley height of 30 nm. These features originated from the substrate misorientation. It was found that step bunching and large faceting along [01-10] and [10-10] directions occurred during the growth of GaN. Lowering the growth temperature suppresses large faceting, and results in reduction of the peak-to-valley height to 3 nm. However, the surface still has the same undulating features (on a smaller length scale). Mesa diodes were fabricated from the grown GaN layers. The correlation between the diode electrical characteristics and GaN growth conditions is discussed. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Effects of N2 Pressure on the Structural and Electrical Properties of TiN Films Deposited by Laser Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    FU Yueehun; XIE Shangsheng; MENG Xianghai; He Huan; SHEN Xiaoming

    2011-01-01

    Titanium nitride (TiN) films were deposited on Si(100) substrates by laser molecular beam epitaxy(LMBE),and their properties of structure and resistivity with varying N2 pressure were investigated.The results showed that atomically flat TiN films with layer-by-layer growth mode were successfully grown on Si(100) substrates,and (200) was the preferred orientation.With the increasing of N2 pressure,the N/Ti ratio gradually increased and the diffraction peak progressively shifted towards lower diffraction angle.At pressure of 0.1 Pa,stoichiometric TiN film was formed which exhibited the characteristic diffraction angle of (200) plane.All films showed high reflectance to infrared spectrum and the films with overstoichiometry and understoichiometry had a higher resistivity owing to the surface particles and lattice distortion,while the stoichiometric TiN film depicted the minimum resistivity,around 19 μΩ · cm.

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

    Science.gov (United States)

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

    2017-01-01

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

  16. Self-catalyzed growth of dilute nitride GaAs/GaAsSbN/GaAs core-shell nanowires by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kasanaboina, Pavan Kumar [Department of Electrical and Computer Engineering, North Carolina A& T State University, Greensboro, North Carolina 27411 (United States); Ahmad, Estiak [Nanoengineering, Joint School of Nanoscience and Nanoengineering, NCA& T State University, Greensboro, North Carolina 27401 (United States); Li, Jia; Iyer, Shanthi [Department of Electrical and Computer Engineering, North Carolina A& T State University, Greensboro, North Carolina 27411 (United States); Nanoengineering, Joint School of Nanoscience and Nanoengineering, NCA& T State University, Greensboro, North Carolina 27401 (United States); Reynolds, C. Lewis; Liu, Yang [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)

    2015-09-07

    Bandgap tuning up to 1.3 μm in GaAsSb based nanowires by incorporation of dilute amount of N is reported. Highly vertical GaAs/GaAsSbN/GaAs core-shell configured nanowires were grown for different N contents on Si (111) substrates using plasma assisted molecular beam epitaxy. X-ray diffraction analysis revealed close lattice matching of GaAsSbN with GaAs. Micro-photoluminescence (μ-PL) revealed red shift as well as broadening of the spectra attesting to N incorporation in the nanowires. Replication of the 4K PL spectra for several different single nanowires compared to the corresponding nanowire array suggests good compositional homogeneity amongst the nanowires. A large red shift of the Raman spectrum and associated symmetric line shape in these nanowires have been attributed to phonon localization at point defects. Transmission electron microscopy reveals the dominance of stacking faults and twins in these nanowires. The lower strain present in these dilute nitride nanowires, as opposed to GaAsSb nanowires having the same PL emission wavelength, and the observation of room temperature PL demonstrate the advantage of the dilute nitride system offers in the nanowire configuration, providing a pathway for realizing nanoscale optoelectronic devices in the telecommunication wavelength region.

  17. Electrical performance of phase change memory cells with Ge{sub 3}Sb{sub 2}Te{sub 6} deposited by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Boschker, Jos E.; Riechert, Henning; Calarco, Raffaella [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Boniardi, Mattia; Redaelli, Andrea [Micron Semiconductor Italia S.r.l., Via C. Olivetti, 2, 20864, Agrate Brianza, MB (Italy)

    2015-01-12

    Here, we report on the electrical characterization of phase change memory cells containing a Ge{sub 3}Sb{sub 2}Te{sub 6} (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.

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

    Science.gov (United States)

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

    2007-09-01

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

  19. Molecular Beam Epitaxy Growth of Superconducting Ba1-xKxFe2As2 and SmFeAs(O,F) Films

    Science.gov (United States)

    Ueda, Shinya; Takeda, Soichiro; Takano, Shiro; Mitsuda, Akihiro; Naito, Michio

    2012-01-01

    We report the molecular beam epitaxy (MBE) growth of the iron-based superconductors, Ba1-xKxFe2As2 and SmFeAs(O,F). In the growth of Ba1-xKxFe2As2 films, the key to incorporating volatile K in films is low-temperature (≤350 °C) growth in reduced As flux. The highest Tc thus far obtained is Tcon (Tcend) = 38.0 K (35.8 K). In the growth of superconducting SmFeAs(O,F), we adopted two methods. In the first method, we first grew pristine SmFeAsO films, and subsequently introduced F into the films by diffusion from an overlayer of SmF3. In the second method, we grew as-grown superconducting SmFeAs(O,F) films by coevaporating Sm, SmF3, Fe, and As. Thus far, better results have been obtained by the first F diffusion method. The films prepared by F diffusion showed Tcon (Tcend) = 56.5 K (55.3 K), whereas the as-grown films showed Tcon (Tcend) = 51.5 K (48.0 K).

  20. Optimization of nitrogen plasma source parameters by measurements of emitted light intensity for growth of GaN by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Klosek, K.; Sobanska, M.; Tchutchulashvili, G.; Zytkiewicz, Z.R., E-mail: zytkie@ifpan.edu.pl; Teisseyre, H.; Klopotowski, L.

    2013-05-01

    A comprehensive analysis of operating parameters of Addon RF nitrogen plasma source was made in order to determine how a ratio of different active nitrogen species depends on operating parameters of the source such as supplied power and nitrogen flow. We show that output signal of the optical sensor that measures intensity of the light emitted by the plasma is a direct measure of the amount of active nitrogen available for growth. Results of optical emission spectroscopy and measurements of growth kinetics show that nitrogen excited metastable molecules are the species mainly contributing to the growth of GaN under Ga-rich conditions. A procedure is presented allowing to find an optimal conditions of the plasma cell for high-quality GaN growth. Under these conditions the nitrogen flux contains maximum amount of excited metastable molecules and minimal amount of ionic and atomic nitrogen species to minimize GaN lattice damage, even at high growth rates. - Highlights: ► Operating parameters of Addon radio-frequency nitrogen plasma source studied ► Their influence on molecular beam epitaxy (MBE) growth of GaN analyzed ► MBE growth rate of GaN well correlates with output of the plasma emission sensor. ► Optical emission spectroscopy measurements of the nitrogen plasma made ► Nitrogen excited molecules mainly contribute to plasma-assisted MBE growth of GaN.