Electron microscopy investigation of GaAs(100)-(Ga2Se3)-GaAs nanostructures

The GaAs(100)-Ga₂Se₃ heterostructures have been investigated by transmission and scanning electron microscopy. The sequence of structural transformations at the GaAs(100) surface during treatment in selenium vapor has been determined. It has been found that the preliminary treatment of the GaAs(100) surface in selenium vapor increases the orienting effect of the GaAs(100) substrate on the GaAs film growth.     

Heterostructures with InGaAs/GaAs quantum dots doped by transition elements. Part I: Photoluminescence properties

The optical properties of InGaAs/GaAs quantum dot heterostructures that are doped by manganese and chromium during growth by Metal-organic vapor phase epitaxy have been studied. Surface topography photoluminescence spectra measurements have demonstrated the possibility of controlling the spectral characteristics of the structure by varying quantum well growth conditions and sizes in the presence of impurity atoms. Research results are explained by the peculiarities of InAs nanoclusters formation on the GaAs surface in the presence of Mn and Cr atoms.     

Morphological anisotropy during migration enhanced epitaxy of GaAs(0 0 1)

The GaAs(0 0 1) surface morphology and structure during growth by migration enhanced epitaxy (MEE) has been studied by reflection high energy electron diffraction and scanning tunneling microscopy. Changes induced by varying the incident As/Ga flux ratio, growth temperature and the total amount of material deposited in each cycle have been studied and the results compared with GaAs(0 0 1) growth by conventional molecular beam epitaxy (MBE). Comparison of the surface morphology at the end of the Ga and As cycles indicates no clear evidence for any enhancement in the Ga adatom diffusion length during the Ga cycle. However, the morphological anisotropy of the growth front does change significantly and it is proposed that this changing anisotropy during MEE enables Ga adatom diffusion along both azimuths. The surface anisotropy during MEE growth is found to increase with the Ga/As ratio. Although there is a clear correlation between composition and morphology, we have also found that highly ordered and flat surfaces are not necessarily an indication of stoichiometric material. We also attempt to clarify a recent controversy on the structure of the c(4 × 4) reconstruction by studying the surface structure at the end of the As cycle as a function of the As/Ga ratio.     

Surface chemistry and growth mechanisms studies of homo epitaxial (1 0 0) GaAs by laser molecular beam epitaxy

In this paper, GaAs thin film has been deposited on thermally desorbed (1 0 0) GaAs substrate using laser molecular beam epitaxy. Scanning electron microscopy, in situ reflection high energy electron diffraction and in situ X-ray photoelectron spectroscopy are applied for evaluation of the surface morphology and chemistry during growth process. The results show that a high density of pits is formed on the surface of GaAs substrate after thermal treatment and the epitaxial thin film heals itself by a step flow growth, resulting in a smoother surface morphology. Moreover, it is found that the incorporation of As species into GaAs epilayer is more efficient in laser molecular beam epitaxy than conventional molecular beam epitaxy. We suggest the growth process is impacted by surface chemistry and morphology of GaAs substrate after thermal treatment and the growth mechanisms are discussed in details.     

Dynamic RHEED observations of the MBE growth of GaAs

Detailed measurements have been made of the specular beam intensity in RHEED patterns from static and growing GaAs surfaces. The basic parameters investigated were substrate temperature and electron beam azimuth. The results have provided further understanding of growth dynamics and surface disorder, respectively. There is a significant trend away from two-dimensional growth at the higher temperatures, which also correspond to more Ga-rich surface structures. Conversely, surface disorder is apparently greater during growth at the lower temperatures, where the structure is As-rich. The static As-stable 2×4 surface is, however, the most ordered and the most closely two-dimensional. It has also been shown that ordered, two-dimensional growth can be initiated from excess Ga adatom populations.     

Molecular beam epitaxy growth of GaAs on an offcut Ge substrate

Molecular beam epitaxy growth of GaAs on an offcut Ge (100) substrate has been systemically investigated. A high quality GaAs/Ge interface and GaAs film on Ge have been achieved. High temperature annealing before GaAs deposition is found to be indispensable to avoid anti-phase domains. The quality of the GaAs film is found to strongly depend on the GaAs/Ge interface and the beginning of GaAs deposition. The reason why both high temperature annealing and GaAs growth temperature can affect epitaxial GaAs film quality is discussed. High quality In_0.17Ga_0.83As/GaAs strained quantum wells have also been achieved on a Ge substrate. Samples show flat surface morphology and narrow photoluminescence line width compared with the same structure sample grown on a GaAs substrate. These results indicate a large application potential for III--V compound semiconductor optoelectronic devices on Ge substrates.     

关于RHEED振荡技术优化GaAs(110)量子阱生长的研究

在GaAs(110)衬底上生长的半导体材料有诸多优良性能，使得在非极性GaAs(110)衬底上获得高质量各类异质结材料，成为近年来分子束外延生长关注的课题.考虑GaAs(110)表面是Ga和As共面，最佳生长温度窗口很小；反射式高能电子衍射的(1×1)再构图案对生长温度和V/Ⅲ束流比不敏感，难于通过观察再构图案的变化，准确地找到最佳生长条件.作者在制备GaAs(110)量子阱过程中，观察到反射式高能电子衍射强度振荡呈现出的单双周期变化.这意味着不同工艺条件下，在 GaAs(110)衬底上量子阱有单层和双层两种生长模式.透射电子显微镜和室温光致荧光光谱测量结果表明：在双层生长模式下量子阱样品光学性能较差，而在单层生长模式下量子阱光学性能较好，但是界面会变粗糙.利用这一特点，我们采用反射式高能电子衍射强度振荡技术，找到了一种在GaAs(110)衬底上生长高质量量子阱的可行方法. 关键词： 反射高能电子衍射 量子阱 分子束外延     

Surface reconstructions of MnAs grown on GaAs(001)

During epitaxial growth of MnAs on GaAs(001) by molecular-beam epitaxy (MBE) the surface exhibits various reconstructions depending on the growth conditions. These reconstructions have been studied during growth by reflection high-energy electron diffraction (RHEED) and reflectance difference spectroscopy (RDS). A feature sensitive to the surface structure was identified in the RD spectra. After growth, the (1×2) and (1×1) reconstructions were cooled down to room temperature and imaged in ultrahigh vacuum with a conventional scanning tunneling microscope (STM). Atomic-scale images of these surfaces are presented.     

Dynamics of film growth of GaAs by MBE from Rheed observations

Detailed observations have been made of the intensity oscillations in the specularly reflected and various diffracted beams in the RHEED pattern during MBE growth of GaAs, Ga _x Al_1–x As and Ge. The results indicate that growth occurs predominantly in a two-dimensional layer-by-layer mode, but there is some roughening, which is enhanced by deviations from stoichiometry and the presence of impurities. In the case of the GaAs (001) –2×4 reconstructed surface a combination of dynamic and static RHEED measurements has provided firm evidence for the presence of one-dimensional disorder features as well as surface steps.     

Surface processes during growth of InAs/GaAs quantum dot structures monitored by reflectance anisotropy spectroscopy

The time resolved reflectance anisotropy spectroscopy (RAS) measurement at 4.2 eV was used for the optimization of technological parameters for Stranski–Krastanow quantum dot (QD) formation. TMIn dosage and waiting time following InAs deposition during which QD formation takes place were optimized.RAS measurement helps us to study the MOVPE surface processes such as QD formation, dissolution of In from InAs QDs during the growth of GaAs capping layer or recovery of epitaxial surface from As deficiency, when As partial pressure is increased. We have shown, that the recovery of epitaxial surface from As deficiency is rather a slow process of the order of tens of seconds.We have for the first time observed in situ the mechanism of In atoms migration from QDs during GaAs capping layer growth. First the GaAs layer is formed and then the In migration from QDs follows. These two processes do not start at the same time, the In dissolution is delayed. Conclusions extracted from RAS measurement are in agreement with photoluminescence results.     

Studies on nucleation kinetics of In1−xGaxP/GaAs by Liquid-Phase Epitaxy

Summary Nucleation kinetics during the Liquid-Phase Epitaxial (LPE) growth of In_1−xGa_xP on GaAs substrate have been studied. The behaviour of non-equilibrium solid-liquid interface between In-Ga-P solution and GaAs substrate has been analysed and hence the expression derived for the stress-induced supercooling has been incorporated in the classical heterogeneous nucleation theory. The condition for the growth of good-quality GaInP layer on GaAs substrate has been shown theoretically.     

Direct evidence for the step density model in the initial stages of the layer-by-layer homoepitaxial growth of GaAs(111)A

Scanning tunnelling microscopy (STM) has been used to investigate the morphological basis of the specular beam intensity oscillations observed in reflection high-energy electron diffraction (RHEED) studies during the initial stages of GaAs(111)A homoepitaxy. Analysis of STM images after the deposition of controlled amounts of GaAs up to a coverage of 2 monolayers show a strong relationship between the step density and the RHEED specular beam intensity. It is shown that the RHEED oscillations observed during the initial stages of growth reflect the temporal variation in surface step density.     

Surfactant properties of cesium in molecular beam epitaxy of GaAs(100)

The experimental and ab initio investigations of the effect of a decrease in the binding energy of surface arsenic atoms under the cesium adsorption on an As-stabilized GaAs(001)-(2 × 4) surface have been performed. The cesium-induced redistribution of the charge on the surface atoms reduces the electron density in the As-Ga bond of the upper layer of the GaAs(001) surface; thus, the As-Ga binding energy decreases and, as a result, the diffusion activation energy, as well as the arsenic atom desorption, decreases. An increase in the diffusion coefficient of surface atoms, along with the property of Cs to segregate on the surface of a growing semiconductor film, makes it possible to use cesium as a surfactant in the low-temperature growth of GaAs by molecular beam epitaxy.     

金辅助催化方法制备GaAs和GaAs/InGaAs纳米线结构的形貌表征及生长机理研究

利用金（Au）辅助催化的方法,通过金属有机化学气相沉积技术制备了GaAs纳米线及GaAs/InGaAs纳米线异质结构.通过对扫描电子显微镜（SEM）测试结果分析,发现温度会改变纳米线的生长机理,进而影响形貌特征.在GaAs纳米线的基础上制备了高质量的纳米线轴、径向异质结构,并对生长机理进行分析.SEM测试显示,GaAs/InGaAs异质结构呈现明显的“柱状”形貌与衬底垂直,InGaAs与GaAs段之间的界面清晰可见.通过X射线能谱对异质结样品进行了线分析,结果表明在GaAs/InGaAs轴向纳米线异质结构样品中,未发现明显的径向生长.从生长机理出发分析了在GaAs/InGaAs径向纳米线结构制备过程中伴随有少许轴向生长的现象.     

基于MOCVD三步生长的GaAs/Si外延技术EI北大核心CSCD

在硅(Si)上外延生长高质量的砷化镓(GaAs)薄膜是实现硅基光源单片集成的关键因素。但是,Si材料与GaAs材料之间较大的晶格失配、热失配等问题对获得高质量的GaAs薄膜造成了严重影响。本文利用金属有机化学气相沉积(MOCVD)技术开展Si基GaAs生长研究。通过采用三步生长法,运用低温成核层、高温GaAs层与循环热退火等结合的方式,进一步降低Si基GaAs材料的表面粗糙度和穿透位错密度。并利用X射线衍射(XRD)ω-2θ扫描追踪采用不同方法生长的样品中残余应力的变化。最终,在GaAs低温成核层生长时间62 min(生长厚度约25 nm)时,采用三步生长、循环热退火等结合的方式获得GaAs(004)XRD摇摆曲线峰值半高宽(FWHM)为401″、缺陷密度为6.8×10^(7) cm^(-2)、5μm×5μm区域表面粗糙度为6.71 nm的GaAs外延材料,在材料中表现出张应力。     

GaAs/Al_xGa_(1-x)As多量子阱外延结构及其LP-MOCVD生长工艺研究

在低压金属有机化学气相沉积生长工艺中,对用于制作850nm垂直腔面发射激光器件的GaAs/Al_xGa_(1-x)As多量子阱外延结构的生长温度、反应室压力、总载气流量以及生长速度等主要工艺参量进行优化,并进行了完整外延结构的生长.实验结果表明:在700℃条件下,得到多种组分的GaAs/Al_xGa_(1-x)As多量子阱结构,通过光致发光谱对比测试得到的最佳组分x为0.24,同时得到良好的表面形貌,最终确定的最佳生长速度为0.34~0.511nm/s.     

Influence of the structural surface state on the formation of a relief and morphology of GaAs(001) layers during molecular-beam epitaxy and vacuum annealing

Methods of reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM) are used to investigate the special features of morphological changes on the GaAs(001) surface during the molecular-beam epitaxy (MBE) growth and vacuum annealing. A relationship is revealed between the superstructural state of the surface and the character of these changes. Thermodynamic conditions of epitaxial GaAs(001) growth with the most structurally perfect surface are established. The characteristics of the processes causing evolution of the relief during MBE growth in states with reconstruction (2 × 4) are determined. A new technique that allows the efficiency of smoothing of the GaAs(001) surface to be increased considerably by annealing in an arsenic flow is suggested and tested. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 5–13, September, 2008.     

Epitaxial relationships between Al,Ag and GaAs{001} surfaces

Detailed results concerning the orientation of Al and Ag layers grown by MBE onto GaAs{001} surfaces are reported. The observed crystallographic relationships have been found to depend only on the growth temperature in the case of Ag, while for Al the situation is more complex. Possible effects of other parameters such as structure and stoichiometry of the starting GaAs surface and growth rate, are discussed and compared with other results recently reported.     

In/GaAs(111)界面形成过程的电子能谱研究

用光电子能谱结合LEED图样分析的方法研究了In在非解理的GaAs(111)面上的界面形成过程。观察到在这一过程中三维In集团的生长起支配作用。发现对于所有研究过的n型样品,包括Ga终止的GaAs(111)-A面和As终止的GaAs(111)-B面,淀积In之前的表面费密能级均在VBM上面0.75±0.05eV处,在淀积过程中迅速移至VBM上面0.90±0.05eV处。 关键词：     

Oscillations in the surface structure of Sn-doped GaAs during growth by MBE

The presence of predeposited or surface-accumulated Sn during MBE growth modifies the reconstruction of the (001)GaAs surface, as observed by RHEED, at coverages as low as 0.025 monolayer. If growth is initiated on such a surface, oscillation in the intensity modulation of some of the RHEED streaks occurs, with a period equal to the monolayer deposition time of the GaAs. This oscillation decays away at a rate determined by the substrate temperature and Ga flux.