High-quality CdTe(100)/GaAs(100) grown by hot-wall epitaxy using gold tube radiation shield

High-quality CdTe(100) layers grown on GaAs(100) substrates by hot-wall epitaxy using a gold tube radiation shield are reported for the first time. From the investigation of thermal properties, we find that the gold tube radiation shield is more effective in heat confinement and temperature stability than a stainless steel tube radiation shield. The CdTe lattice parameters perpendicular to the interface decrease as the layer thickness increases by strain relaxation. We obtain 89 arc sec full width at half maximum of the X-ray double-crystal rocking curve for a 15 μm thick CdTe layer which is the smallest value reported to date. Exciton emission and donor-acceptor pair emission along with longitudinal optical (LO) phonon replicas are obtained from PL measurements, confirming the good quality of the crystal.     

In situ AFM investigation of 2D nucleation on the (100) face of KDP

Surface morphology of the (100) face of potassium dihydrogen phosphate (KDP) crystals which were grown at different supersaturations at 25 °C was investigated by in situ atomic force microscopy (AFM). Various AFM images of 2D nucleation under different growth conditions were presented. It is found that the growth of KDP is controlled by polynuclear nucleation mechanism at the high supersaturation. With reduction of the supersaturation, the growth velocity of 2D nuclei becomes very slow and shows typical anisotropy. It is found that the process of coalescence of 2D nuclei does not lead to defect. The experiments show that the growth mechanism for KDP at 25 °C changes between step flow and 2D nucleation in the supersaturation range of 4.5‐5%. The triangular nuclei which are close to equilateral triangle are observed in the experiment at the supersaturation σ = 6% for the first time, showing typical anisotropic growth. Through observing the dissolution of 2D nuclei, the dissolving process can be regarded as the reverse process of growth. We also find that the microcrystals landing on the surface at σ = 9% would grow and coalesce with each other and there is no observable defect in the coalescence. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

In-situ and ex-situ characterization of GaAs/AlAs quantum well structures using spectroscopic ellipsometry

Spectroscopic ellipsometer is used to monitor the MBE growth of quantum well structures. Real time monitoring of the growth enabled the measurement of growth rate and correlation with RHEED oscillations. The growth of a single GaAs/AlAs quantum well is also monitored in real time using multiple wavelengths. Interface roughness of the interrupted “inverted” AlAs/GaAs interface was also monitored with SE. Under our growth conditions, we measure approximately a 2 ML interfacial region at the inverted interface. A correlation with photoluminescence is also discussed.     

High-resolution photoluminescence studies of (211) CdTe grown on (211)B GaAs substrate

Sharp and rich photoluminescence lines accociated with free exciton (FE), excitons bound to neutral acceptors (A⁰X) and donors (D⁰X) in molecular beam epitaxially (MBE) grown (211) CdTe/(211)B GaAs have been reported for the first time. The results show that the (211) CdTe/(211)B GaAs grown under optimized conditions could have as high a crystal perfection as those grown on lattice-matched substrates.     

Effects of surface reconstruction on CdTe/GaAs(001) interface structure

CdTe/GaAs(001) heterostructures were fabricated by molecular beam epitaxy on chemically etched and thermally deoxidized GaAs(001) substrates, as well as GaAs(001) (3×1) buffer layers grown in situ by molecular beam epitaxy. Different growth protocols were also explored, leading to Te-induced (6×1) or (2×1) surface reconstructions during the early growth stage. High-resolution cross-sectional transmission electron microscopy was used to examine the final interface structure resulting from the different substrate preparations, and surface reconstructions. The (2×1) surface reconstruction led to pure (001) growth, while the (6×1) reconstruction led to an interface which included small (111)-oriented inclusions. In addition, deposition on etched and deoxidized GaAs(001) wafers led to preferential CdTe growth within etch pits and resulted in a macroscopically rough interface region.     

Surface chemical studies of the influence of In and Al on the decomposition of TEG on GaAs(100)

The interaction of triethylgallium (TEG) with the Ga-stabilized GaAs(100) surface in the presence of In and Al has been investigated using AES (Auger electron spectroscopy), HREELS (high resolution electron energy loss spectroscopy) and TDS (thermal desorption spectroscopy) techniques. Al is shown to greatly increase the saturation surface coverage of TEG on the surface and to suppress the desorption of TEG and diethylgallium (DEG). Etching of the surface Al by TEG is observed, resulting in the formation of gas phase Al organic species. Alkyl migration from GA to Al centres occurs, and the presence of Al substantially enhances the irreversible deposition of C. In is found to enhance DEG desorption and to lower the temperature at which absorbed ethyl groups decompose to gas phase ethene. Computer modelling has been carried out to extract kinetic parameters from measured thermal desorption spectra. These parameters are then used to calculate expected partial growth rates of GaAs during the growth of Ga_xAl_1−xAs and Ga_xIn_1−xAs using TEG. The data provide a molecular level understanding of the GaAs pa rtial growth rate variations arising during the deposition of III–V ternary materials.     

采用MOCVD方法在GaAs衬底上生长ZnO(002)和ZnO(100)薄膜

采用金属有机化学汽相沉积生长法（MOCVD）,在不同的衬底表面处理条件和生长温度下,在GaAs衬底上生长出了ZnO薄膜。随着化学腐蚀条件的不同,可生长出优先定位不同的ZnO（100）和ZnO（002）薄膜。该薄膜的晶体结构特性是由X光衍射谱仪（XRD）所获得的,而其光学特性是由光荧光谱仪（PL）来测的。与ZnO（002）相比,ZnO（100）薄膜具有更优越的晶体结构特性,并且在同样的生长温度下都具有相似的光学特性。对于腐蚀条件不同的GaAs衬底所进行的XPS分析结果表明,ZnO薄膜优先定位变化的主要原因在于腐蚀过程中形成的富As层。     

Transmission electron microscopy study of hexagonal GaN film grown on GaAs (0 0 1) substrate by using AlAs nucleation layer

Hexagonal gallium nitride (h-GaN) films have been grown on AlAs nucleation layer by using radio frequency (RF) plasma source-assisted molecular beam epitaxy on GaAs (0 0 1) substrate. Transmission electron microscopy (TEM) techniques are used to characterize such h-GaN epilayers. TEM results show that (0 0 0 1) atom planes of h-GaN are parallel to (0 0 1) atom planes of the GaAs substrate. Defects, such as stacking faults and dislocations, have also been observed.     

Heavily carbon-doped p-type (In)GaAs grown by gas-source molecular beam epitaxy using diiodomethane

Heavily carbon-doped p-type In_xGa_1−xAs (0≤x<0.49) was successfully grown by gas-source molecular beam epitaxy using diiodomethane (CH₂I₂), triethylindium (TEIn), triethylgallium (TEGa) and AsH₃. Hole concentrations as high as 2.1×10²⁰ cm⁻³ were achieved in GaAs at an electrical activation efficiency of 100%. For In_xGa_1−xAs, both the hole and the atomic carbon concentrations gradually decreased as the InAs mole fraction, x, increased from 0.41 to 0.49. Hole concentrations of 5.1×10¹⁸ and 1.5×10¹⁹ cm⁻³ for x = 0.49 and x = 0.41, respectively, were obtained by a preliminary experiment. After post-growth annealing (500°C, 5 min under As₄ pressure), the hole concentration increased to 6.2×10¹⁸ cm⁻³ for x = 0.49, probably due to the activation of hydrogen-passivated carbon accepters.     

Si和GaAs衬底上的ZnTe、CdTe分子束外延材料的晶向倾角

本文采用X射线双晶衍射二次测量法对φ76mm Si(211)和GaAs(211)B衬底上生长的ZnTe和CdTe外延层的晶向倾角进行了测量,发现对于Si和GaAs衬底,外延层的[211]均绕外延层与衬底的[0-11]复合轴朝[111]倾斜,其晶向倾角与晶格失配呈线性关系;通过实际测量验证了在外延层探测到的[133]峰代表[211]关于[111]旋转180°的[255]孪晶向.     

Molecular dynamics simulation of (100)InGaAs/GaAs strained-layer relaxation processes

Molecular dynamics simulations on In_1−xGa_xAs/GaAs(100) systems are performed showing the dynamics of threading dislocations in the overlayers and the formation of misfit dislocations at the heterojunction interface. The developed code, using a modified Tersoff potential, simulates the threading dislocation dynamics in the InGaAs overlayer, and also the formation of interface misfit dislocations. Values for critical thicknesses are predicted and the atomic structure of the dislocation cores are determined.     

X-ray Diffraction Analysis of the Structure In0.53Ga0.47As Films Grown on (100) and (111)A GaAs Substrates with a Metamorphic Buffer

Crystallography Reports - Epitaxial In0.53Ga0.47As films, grown on GaAs substrates with the (100) and (111)А crystallographic orientations in the standard high-temperature and low-temperature...     

Surface diffusion length of Ga adatoms in molecular-beam epitaxy on GaAs(100)-(110) facet structures

By the molecular-beam epitaxial (MBE) growth of GaAs on [001]-mesa stripes patterned on GaAs(100) substrates, (110) facets were formed on the mesa edges defining (100)-(110) facet structures. The surface diffusion length of Ga adatoms along the [010] direction on the mesa stripes was obtained for a variety of growth conditions by in-situ scanning microprobe reflection high-energy electron diffraction (μ-RHEED). Using these values and the corresponding growth rate on the GaAs(110) facets, the diffusion length on the (110) plane was estimated. We found that the Ga diffusion length on the (110) plane is longer than that on the (100) and (111)B planes. The long diffusion length on the (110) plane is discussed in terms of the particular surface reconstruction on this plane.     

基于液滴外延法的Al(In)纳米结构在GaAs(001)的形成机制

采用液滴外延法在GaAs(001)衬底上同时沉积In、Al液滴形成纳米结构,利用原子力显微镜(AFM)对实验样品进行形貌表征,并通过X射线光电子能谱(XPS)与扫描电子显微镜分析In、Al组分比样品表面元素分布。实验结果显示,混合沉积后的表面InAlAs纳米结构密度随着In组分的降低而降低,而单个纳米结构的尺寸变大。SEM与XPS测试结果证明表面的In并没有因为衬底温度过高而全部偏析。根据实验结果推测,In&Al液滴同时沉积到表面形成InAl混合液滴。当液滴完全晶化后纳米结构中心出现孔洞,而产生这一现象的主要原因是液滴向下刻蚀。     

In situ monitoring of cyclic butylene terephtalate polymerization by dielectric sensing

The in situ monitoring of the polymerization of cyclic butylene terephtalate (CBT) oligomers by dielectric sensing has been investigated under isothermal conditions at different processing temperatures. The change in conductivity depends on the increase of molecular weight but is also influenced by crystallization of the obtained c-PBT during or after polymerization. Dielectric sensing investigations are in good agreement with SEC and DSC analysis which confirm the observation of polymerization and crystallization kinetics. Unfortunately, the conductivity signal could not distinguish between the polymerization and crystallization when they occur simultaneously at lower temperatures (<210 °C) but the crystallization remains detectable by the MWS relaxation which is related to the crystalline/amorphous interface.     

Molecular beam epitaxy growth and properties of GaAs/(AlGa)As p-type heterostructures on (100), (011), (111)B, (211)B, (311)B, and (311)A oriented GaAs

We report on a series of Be-doped GaAs/AlGaAs two-dimensional hole gas (2DHG) structures grown on (110), (111)B, (211)B and (311)B oriented substrates and compare their properties with high-mobility samples grown on (311)A using Si doping. The samples were prepared and grown under the same conditions so as to render them comparable. They are found to have mobilities which are strongly anisotropic within the plane. The highest mobility is found on the (110) surface with 100,000 cm² V⁻¹ s⁻¹, while the (211) surface gave the lowest values 10,000 cm² V⁻¹ s⁻¹. However, the later samples are found to have quantum Hall effect critical currents of >70 μA: an exceptionally high value for a hole gas which makes them suitable for metrology. All the samples show strong low-field positive magnetoresistance with resistance increases of up to 30% at magnetic fields of only 0.1 T. The presence of this feature on all the different planes shows that it does not depend upon the details of the band structure. It is identified with the lifting of the degeneracy of the spin sub-bands by the asymmetrical potential giving rise to a classical two-band magnetoreresistance.     

Auger electron spectroscopic studies of the water vapour adsorption on the (100) surface of austenitic chromium-nickel steel

The water vapour adsorption on the (100) surface of chromium-nickel steel was studied by Auger electron spectroscopy (AES) in the temperature range of 300 K to 700 K at water vapour pressures of 13.3 μPa to 133 mPa. The water vapour adsorption goes on more slowly than the oxygen adsorption under the same conditions. The measured kinetic isotherms may be described by logarithmic time laws as they are typical of the adsorption on inhomogeneous surfaces. With rising temperature of the samples the rate of adsorption as well as the quantity of fragments of the water molecule adsorbed during saturation state increases, i.e. the adsorption is activated. By means of the measured adsorption isotherms it may be concluded that a dissociative adsorption takes place.     

Aspects of low heterostructure symmetry in (311)A (In,Ga)As/GaAs

We investigate the structural and optical properties of (In,Ga)As/GaAs heterostructures induced by the low symmetry of the [311]A orientation. High-resolution X-ray diffraction (HRDXD) measurements reveal the existence of a shear-strained unit cell. The onset of relaxation in heavily strained structures leads to pronounced anisotropies and to satellite splittings in the X-ray diffraction patterns. Optical investigations indicate that the impact of the piezoelectric fields on the ground state energy is compensated for by In segregation. Nevertheless these fields cause a pronounced reduction of the excitonic binding energy in the (311)A structures.