The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Yoshiji Horikoshi - One of the best experts on this subject based on the ideXlab platform.
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Successful growth of Cu2Se-free CuGaSe2 by Migration-Enhanced Epitaxy
Journal of Vacuum Science & Technology. B. Nanotechnology and Microelectronics: Materials Processing Measurement and Phenomena, 2012Co-Authors: Miki Fujita, Tomohiro Sato, Tsuyoshi Kitada, Atsushi Kawaharazuka, Yoshiji HorikoshiAbstract:CuGaSe2 films were grown on GaAs (001) substrates by migration enhanced Epitaxy, where Cu + Ga and Se are alternately deposited. The in situ reflection high energy electron diffraction observation during growth revealed that the segregation of Cu2Se on CuGaSe2 can be detected by anomalous diffraction patterns. When the Cu2Se segregation takes place, a distorted pattern appears in both Cu + Ga and Se deposition periods. By optimizing the flux ratios, the anomalous diffraction disappears, and we succeeded in growing high quality CuGaSe2 single crystal layers free from Cu2Se segregation on GaAs (001) substrates. The authors also found that, in the CuGaSe2/GaAs wafers with Cu2Se segregation, a high density of voids is often observed at the substrate surface. These voids disappeared when the Cu2Se-free growth conditions were employed. Ga atoms near the GaAs substrate surface were probably drawn out by excess Cu atoms in the growing layer to form CuGaSe2, leading to the creation of voids with fairly large size.
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Growth of CuGaSe2 Layers on Closely Lattice-Matched GaAs Substrates by Migration-Enhanced Epitaxy
Japanese Journal of Applied Physics, 2011Co-Authors: Miki Fujita, Atsushi Kawaharazuka, Jiro Nishinaga, Klaus Ploog, Yoshiji HorikoshiAbstract:CuGaSe2 single-crystal films are grown on the As-stabilized (2×4) surface of (001) GaAs by Migration-Enhanced Epitaxy (MEE), where Cu+Ga and Se are alternately deposited. The growth process is monitored by refraction high-energy electron diffraction (RHEED) in the [110] azimuth. Under the Cu-enriched growth condition, a deformed 4-fold pattern is observed in both Cu+Ga and Se deposition periods. The deformed 4-fold pattern is found to be related to the segregation of Cu2Se on the CuGaSe2 surface as confirmed by the results of X-ray diffraction (XRD) measurement. By reducing the beam equivalent pressure of Cu (Cu-BEP), clear 4-fold patterns appear in both Cu+Ga and Se deposition periods instead of deformed 4-fold patterns. Further reduction of Cu-BEP results in clear 4- and 2-fold patterns for Cu+Ga and Se deposition periods. Under these growth conditions, Cu2Se-segregation-free CGS growth is achieved. Thus, the CuGaSe2 single-crystal layers without Cu2Se-segregation are successfully grown on GaAs(001) substrates by optimizing the Cu-BEP.
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Area-selective Epitaxy of GaAs by Migration-Enhanced Epitaxy with As2 and As4 arsenic sources
Applied Surface Science, 2008Co-Authors: Atsushi Kawaharazuka, Ippei Yoshiba, Yoshiji HorikoshiAbstract:Abstract We demonstrate area-selective Epitaxy by Migration-Enhanced Epitaxy with As2 and As4 as arsenic sources. The distinct whisker structure growing in [1 1 1]B direction is obtained when employing As2 as an arsenic source, while (1 1 1)B facet is formed with As4. The difference in the facet formation can be explained by the formation of As-trimer, which significantly reduces the growth rate of the (1 1 1)B surface. With As2, area-selective Epitaxy can be achieved at lower arsenic pressure condition, where less As-trimers are formed. Therefore, growth in the [1 1 1]B direction is enhanced.
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Application of migration‐enhanced Epitaxy to novel semiconductor structures
AIP Conference Proceedings, 2008Co-Authors: Yoshiji Horikoshi, Hiroshi Yamaguchi, S. Ramesh, Naoki KobayashiAbstract:Abstract : Enhanced surface migration is essential to the growth of high quality epitaxial layers. In the growth of III-V compound semiconductors, surface migration is effectively enhanced by supplying group Ill atoms to the growing surface in the absence of group V atoms or molecules. In this situation, the lifetime of isolated group Ill atoms, which are quite mobile on the growing surface, is greatly increased resulting in these atoms migrating a large distance during growth. Migration-Enhanced Epitaxy (MEE) is based on this characteristic. MEE has proved useful for growing flat heterojunctions and for lowering the epitaxial growth temperature of III-V compound semiconductors. This paper describes the principle of MEE and its application to the growth of novel semiconductor structures such as GaAs/AlAs horizontal superlattices, ZnSe/GaAs superlattices, and (GaAs)l-x(Si2)x,/GaAs superlattices.
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Characterization of heavily Sn-doped GaAs grown by Migration-Enhanced Epitaxy
Journal of Crystal Growth, 2007Co-Authors: Tosaporn Chavanapranee, Yoshiji HorikoshiAbstract:Abstract The saturation of electron concentration and mobility at high doping concentration observed in the samples grown by low-temperature Migration-Enhanced Epitaxy (MEE) is found to be strongly related to the morphology change in the film. The structural characteristics of the heavily Sn-doped GaAs have been further investigated by means of X-ray diffraction (XRD) measurement and transmission electron microscopy (TEM). The results indicate that the (GaAs) 1– x (Sn 2 ) x alloy is formed in the Sn-doped GaAs with the doping concentration higher than 1×10 19 cm −3 . However, when the Sn concentration exceeds 1×10 21 cm −3 , the formation of Sn-rich clusters becomes dominant. This formation of (GaAs) 1– x (Sn 2 ) x alloy and Sn clusters is found to be responsible for the saturation of the electron concentration and mobility in the heavily doped samples.
Won Jun Choi - One of the best experts on this subject based on the ideXlab platform.
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Carrier dynamics in the wetting layer of InGaAs/GaAs quantum dots grown by using Migration-Enhanced Epitaxy
Journal of the Korean Physical Society, 2013Co-Authors: Chengshou An, Y. D. Jang, Jin Dong Song, Won Jun ChoiAbstract:We have investigated the effects of carrier localization on the migration-enhancing time in a wetting layer (WL) of quantum dots (QDs) grown by using the Migration-Enhanced Epitaxy (MEE) growth technique. The WL photoluminescence (PL) intensity of QD sample grown with a longer migration-enhancing time remained strong even at low excitation densities. The PL decay time at the WL peak was longer for the MEE-grown QD with a longer migration-enhancing time. Moreover, the decay times of MEE-grown QDs across the WL’s PL band were longer at longer wavelengths. We conclude that the localization effect in the WL intensifies as the migration-enhancing time is increased.
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Delayed emission from InGaAs/GaAs quantum dots grown by Migration-Enhanced Epitaxy due to carrier localization in a wetting layer
Journal of Applied Physics, 2013Co-Authors: C. S. An, Jin Dong Song, Y. D. Jang, Won Jun ChoiAbstract:Wetting layer (WL) photoluminescence (PL) at 10 K dominated the PL spectra of low-density quantum dots (QDs) grown by Migration-Enhanced Epitaxy (MEE), even at very low excitation powers. Long PL rise time at the ground state (GS) of QDs was observed, when carriers are generated in the WL, indicating suppressed carrier capture from the WL into the QDs. Fluctuations in the WL thickness due to WL thinning in the MEE-grown QDs produced strong localization effects. Temperature dependence of the WL PL intensity and the GS PL rise time agreed well with this interpretation.
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Effect of different strain reducing layers on InAs quantum dots grown by migration enhanced Epitaxy
Physica E-low-dimensional Systems & Nanostructures, 2010Co-Authors: Won Jun Choi, J. D. Song, Chan Gyung ParkAbstract:We investigated the effect of InGaAs and AlGaAs combination strain reducing layers on InAs quantum dots (QDs) grown by migration enhanced Epitaxy. The samples were examined by cross-sectional transmission electron microscopy, low-temperature and power dependent photoluminescence (PL). We observed three different size distributions of QDs in the atomic force microscopy image. We found that PL peak 1, 2, and 3 came from three different size distributions, and the energy level of QDs could be modified by changing strain reducing layers irrelevantly to controlling QD height in our samples. Furthermore, we elucidated the role of InGaAs and AlGaAs layer on the energy level modification and related cross-sectional morphology of the QDs.
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Effect of Growth Interruption in Migration Enhanced Epitaxy on InAs/GaAs Quantum Dots
Japanese Journal of Applied Physics, 2009Co-Authors: Won Jun Choi, Jin Dong SongAbstract:In this study, we investigated the effect of growth interruption time (tGI) during migration enhanced Epitaxy (MEE) growth of self-assembled InAs/GaAs quantum dots (QDs) to control the density of the QDs without any substrate rotation stop during QD formation. By manipulating the growth factor (tGI), the control of QD density in the range of 3.4 ×109–3.5 ×1010 dots/cm2, as well as the QD shape, was demonstrated. We concluded that three phenomena occur during growth interruption: 1) In re-evaporation, 2) In segregation, and 3) the redistribution of InAs QDs. From photoluminescence (PL), it is found that the emission wavelength of samples increased from 967.7 to 1151.7 nm as tGI increased due to redistribution. In addition, we confirmed PL peak emissions from QDs, quasi-three-dimensional (Q3D) clusters, and wetting layer. As a result, the manipulation of tGI in the MEE method can control the density, uniformity, size, and wavelength of QDs.
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Influence of arsenic during indium deposition on the formation of the wetting layers of InAs quantum dots grown by migration enhanced Epitaxy
Journal of Applied Physics, 2004Co-Authors: J. D. Song, Won Jun Choi, Yoon-soo Park, Jae Cheol Shin, Youn-ho Park, Chan Gyung ParkAbstract:We compared the structural and optical properties of InAs∕GaAs quantum dots grown by migration enhanced Epitaxy, with and without arsenic, during indium deposition. The uniformity and size of the quantum dots are enhanced in a sample without arsenic. As a result, narrower and longer wavelength photoluminescence is observed in this sample. Furthermore, the thickness of the wetting layers is reduced by ∼20% in the sample without arsenic, and this result agrees well with the speculation that metallic indium has a smaller driving force for corrugating the InAs wetting layers before they are transformed from two-dimensional to three-dimensional layers. Additionally, the photoluminescence linewidth of the sample without arsenic is insensitive to the cryostat temperature due to two major factors: the reduced thickness of the wetting layers and the enhanced uniformity. In the sample with arsenic, however, the photoluminescence linewidth shows typical anomalies.
Shun-ichi Gonda - One of the best experts on this subject based on the ideXlab platform.
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Gas source molecular beam Epitaxy/migration enhanced Epitaxy growth of InAs/AlSb superlattices
Journal of Applied Physics, 1993Co-Authors: Masumichi Seta, Hajime Asahi, Kumiko Asami, Shun-ichi GondaAbstract:We report on the gas source molecular beam Epitaxy/migration enhanced Epitaxy (MEE) growth of InAs/AlSb superlattices. The incorporation behavior of constituent group III and group V atoms during growth is investigated in detail using reflection high energy electron diffraction. In and Sb atoms are found to move towards the surface during MEE growth, although the movement of In atoms can be reduced by lowering the growth temperature. Raman scattering measurement of InAs/AlSb superlattices shows that the formation of atomically controlled heterointerfaces (InSb‐ or AlAs‐type interfaces in InAs/AlSb superlattices) is difficult. However, photoluminescence (PL) measurement shows that the optical properties of quantum well structures are strongly dependent on the shutter sequence at the interfaces. 77 K PL from InAs/AlSb quantum well structures with an InSb‐type interface shutter sequence is one order of magnitude stronger than that of the AlAs‐type interface.
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Atomically controlled InGaAs/InP superlattices grown by gas source MEE (migration enhanced Epitaxy)
Journal of Crystal Growth, 1993Co-Authors: Hajime Asahi, Kumiko Asami, Teruaki Kohara, R.k. Soni, Shuichi Emura, Shun-ichi GondaAbstract:Abstract Atomically controlled InGaAs/InP SL structures having different types of heterointerfaces are grown on (001)InP substrates at 350°C gas source MEE (migration enhanced Epitaxy). RHEED intensity traces exhibit the same shape at the positions of the same type of heterointerfaces, indicating the formation of the desired heterointerfaces. The Raman spectrum from the SL, having only the InAs-type heterointerfaces, is characterized by the absence of GaP-like LO phonon clearly suggesting the formation of only the InAs-type heterointerfaces, while the SL having InGaP-type interfaces indeed shows the presence of GaP-like LO phonon peak. 4.2 K photoluminescence (PL) spectra for the InGaAs/InP quantum well (QW) structures show a very narrow line width comparable to the narrowest line width reported so far. Furthermore, the PL peak energy variation with well thickness clearly depends on the heterointerface type.
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Influence of hydrogen on the step flow growth of GaAs on vicinal surfaces by gas‐source migration enhanced Epitaxy
Applied Physics Letters, 1992Co-Authors: Hajime Asahi, Soon Jae Yu, Tadaaki Kaneko, T. Hisaka, Yasutoshi Okuno, Shun-ichi GondaAbstract:Step flow growth of GaAs on the vicinal surfaces by gas‐source migration enhanced Epitaxy (MEE), the combination of gas‐source molecular beam Epitaxy and MEE, is studied with the reflection high‐energy electron diffraction (RHEED) intensity oscillation. It is found that the use of the thermally cracked AsH3 instead of solid As (As4) as an As source enhances step flow growth of GaAs on the (001) surface misoriented toward the [110] direction. The same tendency is also observed in the MEE growth using As4 under the hydrogen supply. It is considered that the enhancement of step flow growth in the gas‐source MEE is caused by the hydrogen atoms terminated at the steps.
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Gas source MEE (migration enhanced Epitaxy) growth of InP
Journal of Crystal Growth, 1991Co-Authors: Nobuyuki Takeyasu, Hajime Asahi, Soon Jae Yu, Kumiko Asami, Tadaaki Kaneko, Shun-ichi GondaAbstract:Abstract High-quality InP layers are grown by gas source MEE (migration enhanced Epitaxy) method at 350°C. It is found that even at a substrate temperature as low as 350°C, the desorption of some amount of phosphorus from the InP surface occurs when the PH 3 flow is interrupted, although the RHEED pattern is still showing the (2×4) reconstructions. As a result, the perfectly alternating supply of indium and phosphorus can be achieved only when PH 3 is supplied with a proper interruption time before the supply of In. It is also found that InP layers grown by gas source MEE at 350°C have optical properties equal to or better than those grown by conventional gas source MBE (molecular beam Epitaxy) at 470°C.
J. Singh - One of the best experts on this subject based on the ideXlab platform.
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Comparison of growth front profile of strained layers grown by migration‐enhanced Epitaxy and molecular‐beam Epitaxy using reflection high‐energy electron diffraction
Journal of Vacuum Science & Technology B, 1992Co-Authors: Y. C. Chen, P. K. Bhattacharya, J. SinghAbstract:We have compared the growth front smoothness of strained layers grown by migration‐enhanced Epitaxy and molecular‐beam Epitaxy by looking at the oscillation maxima of reflection high‐energy electron diffraction intensities. We find that for growth of InxGa1−xAs on GaAs with x less than ∼0.15, migration‐enhanced Epitaxy improves the surface quality, while for larger amounts of mismatch (x≳0.15) the surface profile during migration enhanced Epitaxy growth is worse than during conventional As‐stabilized molecular‐beam epitaxial growth. Results of Hall mobility, photoluminescence measurements, and modulation‐doped transistor characteristics are consistent with the diffraction intensity studies.
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Strained layer Epitaxy of InGaAs by MBE and migration enhanced Epitaxy — comparison of growth modes and surface quality
Journal of Crystal Growth, 1991Co-Authors: Y. C. Chen, P. K. Bhattacharya, J. SinghAbstract:Our measurements on a series of pseudomorphic n-type modulation doped field effect transistors have shown that the mobility of the two-dimensional carriers appears to suffer from increased interface roughness as the strain increases. Reflection high energy electron diffraction oscillation studies in InxGa1-xAs grown by molecular beam Epitaxy show that as the strain in the overlayer increases, the growth modes change from layer-by-layer to three-dimensional island growth. However, in migration enhanced Epitaxy, we find that the growth remains in the layer-by-layer mode even for high strain. Reflection high energy electron diffraction oscillations also show that surface roughness in strained layers grown by molecular beam Epitaxy can be smoothed by just a few monolayers grown by migration enhanced Epitaxy. This suggests that for pseudomorphic devices most of the strained active layer might be grown by molecular beam Epitaxy but just a few monolayers before interface formation by migration enhanced Epitaxy to produce an abrupt interface. Our device results validate this observation
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Reflection high‐energy electron diffraction studies of the growth of strained InxGa1−xAs on GaAs substrate by migration‐enhanced Epitaxy
Applied Physics Letters, 1990Co-Authors: Yu-cheng Chen, P. K. Bhattacharya, J. SinghAbstract:Reflection high‐energy electron diffraction oscillations have been studied during the growth of strained InxGa1−xAs on GaAs by molecular beam Epitaxy and migration‐enhanced Epitaxy. The oscillations decay rapidly for x≳0.2 during molecular beam Epitaxy, while they persist for a long while during migration‐enhanced Epitaxy. We believe that the altered surface reconstruction pattern in the latter case changes the growth mode from three‐dimensional to a near perfect two‐dimensional mode for high strain values. Using migration‐enhanced Epitaxy, we demonstrate improved channel mobility and performance of GaAs‐based modulation‐doped field‐effect transistors and narrower linewidths in the low‐temperature excitonic photoluminescence of In0.1Ga0.9As/Al0.3Ga0.7As quantum wells.
D. L. Miller - One of the best experts on this subject based on the ideXlab platform.
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Electrical properties of low-temperature GaAs grown by molecular beam Epitaxy and migration enhanced Epitaxy
Journal of Electronic Materials, 1993Co-Authors: Kai Zhang, D. L. MillerAbstract:Measurements on low-temperature GaAs epitaxial layers (LT-GaAs) grown by molecular beam Epitaxy and migration enhanced Epitaxy showed that the excess arsenic incorporated during growth played a crucial role in determining their electrical properties. The electrical transport in LT-GaAs grown by a standard molecular beam Epitaxy proceeded mainly via a hopping process, which showed a higher activation energy and onset temperature than those usually observed in lightly doped semiconductors. Using migration enhanced Epitaxy to grow LT-GaAs, we were able to substantially reduce the density of As-rich defects and to achieve a good Hall mobility in Be-doped LT-GaAs. The study presented here indicates that, with controlled excess arsenic incorporation during growth, LT-GaAs can vary in a range of conduction properties and thus can be engineered for different device applications.
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Low‐temperature migration enhanced Epitaxy of base material for AlGaAs/GaAs heterojunction bipolar transistors
Applied Physics Letters, 1993Co-Authors: Kai Zhang, D. L. Miller, Jianming Fu, Der-woei Wu, Mike Fukuda, Stephen SchauerAbstract:Migration enhanced Epitaxy (MEE) was used in this work to grow p+‐GaAs at the substrate temperature of 300 °C for the base of AlGaAs/GaAs heterojunction bipolar transistors. The results indicated that the low‐temperature MEE‐grown p+‐GaAs epitaxial layers (p=1×1019–1×1020 cm−3) exhibited a crystalline quality comparable to those grown by standard MBE at a substrate temperature of 570 °C. AlGaAs/GaAs HBTs with low‐temperature MEE‐grown bases doped at p≊2×1019 cm−3 were fabricated by using a self‐alignment technique. For the devices with the conventional MBE‐grown base, secondary ion mass spectroscopy depth profiles showed a significant Be diffusion into the AlGaAs emitter and as a consequence, the devices showed no current gain. For the devices with the low‐temperature MBE‐grown base, there was a negligible Be penetration into the emitter and the devices exhibited a common‐emitter dc current gain of 13.
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Scanning tunneling microscope study of GaAs(001) surfaces grown by migration enhanced Epitaxy
Journal of Vacuum Science & Technology B, 1993Co-Authors: M. C. Gallagher, Jianming Fu, Roy F. Willis, D. L. MillerAbstract:We report an investigation of the morphology of p‐type GaAs(001) surfaces using scanning tunneling microscopy (STM). The substrates were prepared using two methods: migration enhanced Epitaxy (MEE) and standard molecular‐beam Epitaxy (MBE). The STM measurements were performed ex situ using As decapping. Analysis indicates that the overall step density of the MEE samples decreases as the growth temperature is increased. Nominally flat samples grown at 300 °C exhibited step densities of 10.5 steps/1000 A along [110] dropping to 2.5 steps at 580 °C. MEE samples exhibited a lower step density than MBE samples. However as‐grown surfaces exhibited a larger distribution of step heights. Annealing the samples reduced the step height distribution exposing fewer atomic layers. Samples grown by MEE at 580 °C and annealed for 2 min displayed the lowest step density and the narrowest step height distribution. All samples displayed an anisotropic step density. We found a ratio of A‐type to B‐type steps of between 2 and...
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Migration‐enhanced Epitaxy of doped GaAs on (111)B and (100)GaAs substrates
Journal of Vacuum Science & Technology B, 1992Co-Authors: Jianming Fu, Kai Zhang, D. L. MillerAbstract:Si‐doped n‐type GaAs and Be‐doped p‐type GaAs have been grown on (111)B oriented GaAs substrates using the migration‐enhanced Epitaxy (MEE) technique, in which arsenic and gallium are deposited separately. The mobilities and carrier densities have been compared with GaAs grown by MEE and conventional Epitaxy on GaAs (100) substrates. Under migration enhanced conditions, the range of substrate temperatures and arsenic fluxes to obtain smooth surfaces and good mobilities is wider than for conventional molecular‐beam Epitaxy, for both substrate orientations. High‐quality doped GaAs material was obtained at substrate temperature as low as 400–450 °C on (111)B substrates.
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Be doped GaAs grown by migration enhanced Epitaxy at low substrate temperature
Journal of Electronic Materials, 1992Co-Authors: Kai Zhang, S. S. Bose, D. L. MillerAbstract:Conductive Be doped GaAs grown by molecular beam Epitaxy at low substrate temperatures (300° C) was obtained for the first time by using migration enhanced Epitaxy (MEE) without subsequent annealing. The layers were characterized using Hall effect, double crystal x-ray diffraction, and photoluminescence. With low arsenic exposure, the low temperature MEE layers doped with Be had the same carrier density and similar luminescent efficiency as layers grown by conventional MBE at 580° C. Mobility at 77 K was reduced somewhat for layers doped at 2 × 10^17cm^−3, which also exhibited hopping conductivity below 40 K. Double crystal x-ray diffraction showed that low temperature MEE samples grown at low As exposure had the narrow linewidth associated with conventional MBE material grown at 580° C, unlike layers grown by conventional MBE at low temperatures, which exhibit an expansion in lattice parameter.