Chemical beam epitaxy and laser-modified chemical beam epitaxy of InGaAs using tris-dimethylaminoarsenic

The growth of In_xGaj_1−xAs (x = 0.13–0.25) on GaAs by chemical beam epitaxy (CBE) and laser-modified CBE using trimethylindium (TMIn), triethylgallium (TEGa), and tris-dimethylaminoarsenic (TDMAAs) has been studied. Reflection high-energy electron diffraction measurements were used to investigate the growth behavior of InGaAs at different conditions. X-ray rocking curve and lowtemperature photoluminescence (PL) measurements were used to characterize the InGaAs/GaAs pseudomorphic strained quantum well structures. Good InGaAs/GaAs interface and optical property were obtained by optimizing the growth condition. As determined by the x-ray simulation, laser irradiation during the InGaAs quantum well growth was found to enhance the InGaAs growth rate and reduce the indium composition in the substrate temperature range studied, 440–500°C, where good interfaces can be achieved. These changes, which are believed to be caused by laser-enhanced decomposition of TEGa and laser-enhanced desorption of TDMAAs, were found to depend on the laser power density as well. With laser irradiation, lateral variation of PL exciton peaks was observed, and the PL peaks became narrower.     

Mechanism of doping gallium arsenide with carbon tetrachloride during organometallic vapor-phase epitaxy

The rates of decomposition of carbon tetrachloride (CCl₄), triethylgallium (TEGa), and tertiarybutylarsine (TBAs), and the rate of GaAs film growth, were measured as a function of the process conditions during organometallic vapor phase epitaxy. In addition, the reaction of CCl₄ with the GaAs(001) surface was monitored in ultrahigh vacuum using infrared spectroscopy, temperature-programmed desorption, and scanning tunneling microscopy. These experiments have revealed that CCl₄ adsorbs onto Ga sites, and decomposes by transferring chlorine ligands to other Ga atoms on the surface. Chlorine and gallium desorb from the surface as GaCl, while the carbon incorporates into the lattice. Triethylgallium is consumed by two competing reactions: GaAs film growth and GaCl etching. Depending on the V/III and IV/III ratios and temperature, the etch rate can be high enough to prevent any GaAs deposition.     

Thermodynamic and kinetic aspects of reconstruction transitions at the GaAs(001) surface

A kinetic and thermodynamic analysis is carried out for reconstruction transitions on the GaAs(001) surface. It is shown that the transition from the As-stabilized (2×4)β2 to the Ga-stabilized (4×2)β2 structures under As₄ flux is a nonequilibrium phase transition and occurs if a certain steady concentration of arsenic adatoms is attained on the surface. The transition is continuous and can be approximated by a three-parameter isotherm. The moving force of an adsorbate-induced transition is the stabilization energy for the (2×4)β2 phase accompanying the formation of arsenic dimers from arsenic adatoms. This energy is estimated. The features of the phase transitions occurring under the As₄ flux and under desorption conditions for an amorphous-arsenic film are discussed.     

Growth of ZnSe films on GaAs(100) substrate by x-ray-enhanced, vapor-phase epitaxy

Epitaxial films of ZnSe deposited on a GaAs(100) substrate are grown by x-ray-enhanced, vaporphase epitaxy (XEVPE) using a URS-55a source (CuKα emission, λ=1.542 Å, P～1–3 mW/cm²) from powdered raw material in a purified hydrogen flow. The differences in the photoluminescence and exciton reflection spectra are investigated for single-crystal ZnSe films on GaAs(100) at T=4.5 K, which are subjected to compressive strain and are grown by x-ray enhanced and conventional VPE. The results indicate an improvement of the crystallographic structure of the epitaxial layer prepared by XEVPE. This is further corroborated by data from x-ray diffraction analysis. The observed phenomena are attributed to x-ray activated adsorption and desorption processes and to a change in the surface mobility of adsorbed atoms.     

Quantum-chemical study of adsorption of 2-propanol molecule on a GaAs (100) surface

Quantum-chemical cluster calculations employing density functional theory are used to study the adsorption mechanism of 2-propanol molecules on a Ga-rich GaAs (100) surface. It is shown that 2-propanol molecules can be adsorbed either molecularly or dissociatively. Dissociation of 2-propanol molecules at the GaAs(100) surface can proceed with the rupture of an O-H or C-OH bond. The state with the rupture of the C-OH bond has the lowest energy among all possible adsorption states. However, for transition into this state, a very high barrier should be overcome, which is possible only at the semiconductor/liquid interface. The calculated adsorption path agrees well with the available experimental data on the interaction of 2-propanol with the GaAs (100) surface.     

Hybrid neural network modeling of anion exchange at the interfaces of mixed anion III-V heterostructures grown by molecular beam epitaxy

A hybrid neural network model is constructed by characterizing the growth of GaAs/sub 1-y/P/sub y/-GaAs superlattices (SLs) grown on [001] GaAs substrates by molecular beam epitaxy. These heterostructures are formed by the P/sub 2/ exposure of an As-stabilized GaAs surface, and ex situ high-resolution X-ray diffraction (HRXRD) is performed to determine the phosphorus composition at the interfaces. A first-order kinetic model is then developed to describe the mechanisms of anion exchange, surface desorption, and diffusion. A semi-empirical hybrid neural network is used to estimate the parameters of the kinetic model and analyze the microscopic processes occurring at the interfaces of the mixed anion III-V heterostructures. The phosphorus diffusion process in GaAs is estimated to have a diffusion coefficient of D=1.4/spl times/10/sup -14/exp(-0.11 eV/k/sub B/T/sub s/) cm/sup 2//spl middot/s/sup -1/ for samples with P/sub As4/=4/spl times/10/sup -6/ torr and exhibits enhanced phosphorus intermixing for samples with lower As-stabilizing fluxes.     

近红外激光诱导InP（100）表面蚀刻反应

采用超声氯分子束和时间分辨质谱研究了由１０６４ｎｍ近红外激光诱导ＩｎＰ（１００）表面蚀刻反应的产物质量分，入射Ｃｌ＿２分子束的平动能效应，激光能量密度和表面温度的影响，并讨论了反应机理。     

Dependence of electrical properties on the crystallographic orientation of CBr4-doped GaAs epilayers grown on GaAs substrates by atmospheric pressure metalorganic chemical vapor deposition

Carbon incorporation into GaAs epilayers has been performed by atmospheric pressure metalorganic chemical vapor deposition using CBr4. The electrical properties of CBr₄-doped GaAs epilayers grown on the GaAs substrates with various surface crystallographic orientations between (100) and (111)A were investigated. The electrical properties of the epilayers showed a strong crystallographic orientation dependence. On increasing the surface offset angle, the hole concentration of CBr4-doped GaAs epilayers rapidly decreased with a hump at (311)A. The lower hole concentration at the high offset angle can be explained by its higher desorption rate than that of the (100) surface. This hole concentration dependence on the offset angle was not changed in spite of the growth temperature and the V/III ratio variation given in this work. The above behaviors indicate that the surface kinetics plays an important role in the C incorporation into the non-planar GaAs epilayers.     

Electron auger spectroscopy and reflectance anisotropy spectroscopy of monolayer nitride films on (001) surfaces of GaAs and GaSb crystals

The methods of electron Auger spectroscopy and reflectance anisotropy spectroscopy are used to study monolayer films of gallium nitride formed on the (001) surface of GaAs by chemical nitridization in hydrazine-sulfide solutions. It is found that the Auger signal for nitrogen N KLL from the nitride film is shifted to higher kinetic energies by ??17.2 eV in comparison with its position for the same signal for a bulk GaN crystal. The observed shift is caused by the specific configuration of the valence orbitals of nitrogen atoms terminating the nitridized GaAs (001) surface. One of the valence orbitals for these atoms does not form a chemical bond and is occupied by an uncoupled pair of electrons. The suggested configuration is confirmed by the results of an analysis of the spectra of anisotropic reflectance from the nitridized GaAs (001) surface. Experiments with chemical nitridization of a GaSb surface have been performed for the first time. The Auger spectra for a nitridized GaSb (001) surface are found to be similar to those for a nitridized GaAs (001) surface. This is indicative of the similar character of chemical processes on these surfaces and the formation of a monolayer nitride film on the GaSb surface.     

UHV/CVD外延生长SiGe/Si表面反应动力学

利用 Si H4 和 Ge H4 作为源气体 ,对 UHV/CVD生长 Si1- x Gex/Si外延层的表面反应机理进行了研究 ,通过 TPD、RHEED等实验观察了 Si( 1 0 0 )表面 Si H4 的饱和吸附、热脱附过程 ,得出 Si H4 的分解应该是每个 Si H4 分子的 4个 H原子全部都吸附到了 Si表面 ,Si H4 的吸附率正比于表面空位的 4次方 ,并分析了 Ge H4 的表面吸附机制 .在此基础上建立了 UHV/CVD生长Si1- x Gex/Si的表面反应动力学模型 ,利用模型对实验结果进行了模拟 ,二者符合得很好     

砷化镓表面自旋极化光电子发射

本文详细地介绍了在圆偏振光作用下,NEA GaAs表面发射目旋极化光电子的原理,及NEA GaAs表面的制备和装置。介绍了表面Cs-O激活的方法。在用此法激活的NEA GaAs(100)表面上可得到灵敏度为8A/mW,极化度约用35%以上的光电子束。发现清洁的GaAs表面覆盖以50%60%Cs单原子层时,光电子的发射出现第一个极大值,同时发现稳定的发射取决于铯吸附量。     

Terahertz-radiation generation and detection in low-temperature-grown GaAs epitaxial films on GaAs (100) and (111)A substrates

The efficiency of the generation and detection of terahertz radiation in the range up to 3 THz by LT-GaAs films containing equidistant Si doping δ layers and grown by molecular beam epitaxy on GaAs (100) and (111)Ga substrates is studied by terahertz spectroscopy. Microstrip photoconductive antennas are fabricated on the film surface. Terahertz radiation is generated by exposure of the antenna gap to femtosecond optical laser pulses. It is shown that the intensity of terahertz radiation from the photoconductive antenna on LT-GaAs/GaAs (111)Ga is twice as large as the intensity of a similar antenna on LT-GaAs/GaAs(100) and the sensitivity of the antenna on LT-GaAs/GaAs (111)Ga as a terahertz-radiation detector exceeds that of the antenna on LT-GaAs/GaAs(100) by a factor of 1.4.     

Growth optimization and optical properties of GaAs-(Ga,Al)As quantum well structures on UV-ozone prepared nominal (111)B GaAs surfaces

GaAs and (Ga,Al)As---GaAs quantum well (QW) structures have been grown by molecular beam epitaxy on nominal (111)B oriented GaAs substrates. The substrate preparation technique involving UV-ozone oxidation was observed to lead to a rough surface after oxide desorption. Mirror-like layer surfaces have nevertheless been achieved by applying a careful procedure during the first stages of growth in order to recover surface flatness. New evidence of planarization is presented, based on the frequency analysis of reflection high-energy electron diffraction (RHEED) intensity oscillations during growth. QWs grown at a moderate substrate temperature (about 610°C) have been obtained with sharp excitonic transitions whose photoluminescence (PL) emission linewidths are comparable to those obtained on misoriented (111)B substrates. In contrast, the use of higher substrate temperatures was found to provide rougher interfaces due to GaAs sublimation during growth interruption at each interface, as revealed by continuous wave and time-resolved PL measurements.     

LaB_6/GaAs(100)表面及界面的角分辨俄歇研究(英文)

The film of LaB6 on GaAs(100) was deposited by ion sputtering. The LaBe/GaAs(100) interface was investigated by Auger electron spectroscopy. Results show the composition of the film is almost the same as that of LaB6 source Adhesion of the film to GaAs(100) surface is very good. AES measurements of the change of LaBe coverage versus time do not exhibit a saturation. We think that LaBe does not grow in layer by layer, but forms islands on the GaAs(100) surface with ununiform thickness.     

Monitoring of CdTe atomic layer epitaxy using in-situ spectroscopic ellipsometry

Atomic layer epitaxy or ALE has proven to be useful for the growth of epitaxial layers of high uniformity, good quality, and well-controlled thickness. In this study, we have carried out in-situ monitoring during the atmospheric pressure ALE of CdTe on GaAs (100) substrates using spectroscopic ellipsometry (SE). The susceptor temperature, reactant partial pressures, as well as the flow and flush duration for each precursor are crucial process variables for ALE growth. Growth was carried out for 20–25 cycles under different sets of these process conditions during the experiment and in-situ SE was used to verify the presence of layer-by-layer growth, which enabled the quick determination of the process window. We observed ALE growth of CdTe at 300°C, supporting the explanation that the growth of CdTe occurs via a surface catalyzed decomposition of the Te precursor di-isopropyltelluride (DIPTe). Investigation of ALE mode growth behavior for different susceptor temperatures and DIPTe flush times indicated that the growth was limited by competition between desorption and reaction of the adsorbed DIPTe species on the Cd terminated surface.     

Low-pressure pyrolysis studies of a new phosphorus precursor: Tertiarybutylbis(dimethylamino)phosphine

The low pressure decomposition of tertiarybutylbis(dimethylamino) phosphine, (t-Bu)P(NMe₂)₂, (TBBDMAP), has been studied on quartz and deposited GaP and InP surfaces. This new phosphorus precursor has been found to pyrolyze on quartz surfaces at much lower temperatures than the related compounds tertiarybutylphosphine, (t-Bu)PH₂, (TBP) and tris(dimethylamino)phosphorus, P(NMe₂)₃, (TDMAP). In contrast to the results obtained for TDMAP, GaP and InP surfaces decrease the decomposition temperature of TBBDMAP only slightly. The TBBDMAP reaction products were dimethylamine, methylmethyleneimine, and isobutylene, consistent with previous pyrolysis studies of TBP and TDMAP.     

Growth of GaAs1−x Sbx by organometallic vapor phase epitaxy

Conditions for growth of GaAsQ_1?x Sb_1?x layers with x as high as 0.7 on GaAs substrates are described for temperatures between 580 and 650°C. Effects of substrate orientation on growth characteristics are noted, and comparisons of growth on (511)- and (100)-GaAs faces are made. The experimental results indicate growth is being controlled by surface reaction kinetics. A simple model based on kinetic control is presented and at least qualitatively explains the results.     

用ARUPS研究Al_x Ga_(1-x)As(100)表面态(英文)

The surface states of Al0.7Ga0.3As(100) were studied by angle resolved ultraviolet photoelectron spectroscopy. It is first found that there exist two surface states on Al0.7Ga0.3As(100) surface, which can be removed by the adsorption of 1500L hydrogen. The evolution of these two surface states with thermal annealing was investigated. These two surface states were well developed by the annealing at 450℃. The ARUP spectra were measured to study their energy dispersions in k space. These results are discussed and compared with those of the GaAs(100)c(4×2) surface.     

Incorporation behaviour of carbon and silicon on (100) and (111) surfaces during growth of GaAs/GaAs and Ga0.47In0.53As/InP by molecular beam epitaxy

Silicon and carbontetrabromide were used as dopant sources in the growth of GaAs/GaAs and Ga_0.47In_0.53As/InP structures. We studied the incorporation behaviour of these group IV atoms on (100) and {111} surfaces as a function of growth temperature. The free carver concentrations determined by Hall measurements for Si-doped GaAs and Ga_0.47In_0.53As layers are independent of growth temperature on all surface orientations studied. Silicon acts fundamentally as a donor except, as expected, for doped layers on (111)A GaAs substrates, where it acts as an acceptor. Carbon incorporation in GaAs and Ga_0.47In_0.53As always results in a p-type conduction independent of the surface orientations (100)/{111} or the growth temperatures we used. In contrast to the results on GaAs, carbon shows a strong temperature-dependent activation in Ga_0.47In_0.53As grown on (100) and (111)B surfaces. Carbon-doped Ga_0.47In_0.53As on (111)A and carbon-doped GaAs layers on (100)/{111} GaAs surfaces exhibit only a very weak dependence of the carrier concentration on the growth temperature. A significant amphoteric behaviour of carbon was not observed in any of the materials investigated.     

A mathematical model for epitaxial growth on nonplanar substrates

A new mathematical model devised to simulate growth on patterned substrates is described. Its aim is not to predict the evolution of the shape of any substrate during epitaxy, but to determine the value of the different kinetic parameters involved in the growth (mean lifetime before incorporation or desorption, surface diffusion length and diffusion coefficient of group III adatoms on the various crystalline facets), just by fitting the output of the program to the experimental epitaxial growth results. A simulation of GaAs MBE growth on a patterned substrate is included as an illustration of its operation.