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.     

MOVPE生长GaN薄膜的表面吸附和扩散研究

利用量子化学计算方法,对MOVPE生长GaN薄膜的表面反应进行研究.特别针对反应前体GaCH3(简称MMG)在理想、H覆盖和NH2覆盖GaN(0001)面的吸附和扩散进行计算分析.通过建立3×3 超晶胞模型,优化计算了MMG在三种不同覆盖表面的稳定吸附位、吸附能和电子布居,搜寻了MMG在稳定吸附位之间的扩散能垒.计算结果表明:对于三种表面,MMG的稳定吸附位均为T4位和H3位,H3位比T4位略微稳定.MMG在NH2覆盖表面吸附能最大,在H覆盖表面吸附能最小,在理想表面吸附能居中.MMG中的Ga与不同的表面原子形成的化学键的键强的大小顺序为:Ga-N>Ga-Ga>Ga-H.相比于理想表面和H覆盖表面,MMG在NH2覆盖表面的扩散能垒最大,因此表面过量的NH2会抑制MMG的扩散.     

Influence of Enhanced Gravitation on the Growth of Ammonium Oxalate Monohydrate Crystals from Aqueous Solutions

The growth behaviour of ammonium oxalate monohydrate crystals on seeds from aqueous solutions under terrestrial and enhanced gravity conditions has been investigated. It was found that all types of faces on the crystals revealed growth layers on them. The faces of the crystals obtained under both terrestrial and enhanced gravity conditions on seeds hung on nylon threads show cracks, trapped inclusions and macrospirals, while the faces of the crystals grown on seeds in fixed holders under enhanced gravity conditions are devoid of cracks, inclusions and macrospirals.     

AlGaN epitaxial lateral overgrowth on Ti-evaporated GaN/sapphire substrate

AlGaN growth using epitaxial lateral overgrowth (ELO) by metalorganic chemical vapor deposition on striped Ti, evaporated GaN on sapphire, has been investigated. AlGaN/AlN films growth on GaN/AlGaN superlattices (SLs) structure on the Ti masks, with various SLs growth temperature (1030, 1060 and 1090 °C) were grown. With increasing the growth temperature, AlGaN surface became flat. The AlGaN film had a cathodoluminescence peak around 345 nm. However, in secondary ion mass spectrometry (SIMS) measurement, Ti signal was detected on the top of AlGaN surface when GaN/AlGaN SLs was grown on Ti striped masks. By inserting the AlN blocking layer on SLs, Ti diffusion was stopped at the AlN layer, and the AlGaN crystalline quality was improved.     

The Growth Kinetics and Surface Morphology of GaN Epitaxial Layers on Sapphire

The growth kinetics of GaN on Sapphire was analyed on the base of some experimental data such as: the growth rate temperature depandence, on the base of some experimental data such as: the growth rate temperature dependence, the grwoth rate dependence on the gas flow velocity, the growth rate depandence on the crystallographic and spatial orientation of the substrate. The limiting stage of the epitaxy process was established at different growth conditions. The morphology of GaN epitaxial layers obtained at these conditions is described.     

Heteroepitaxial growth of ZnS on GaP by the close-spaced technique

Heteroepitaxial growth of ZnS on GaP substrates was achieved with high growth rate by the close-spaced technique. Source temperatures were between 900 and 1150° C. The apparent enthalpy change of 36.6 kcal/mol obtained from the temperature dependence of the evaporation rate of source ZnS powder suggests that the material transport is carried out via the reaction between the source and hydrogen by diffusion and convection. The dependence of the growth rate on the substrate orientation is (100) > (111)Ga > (111)P, and the growth rates on these faces at a source temperature of 1000° C are about 1.6, 0.85, and 0.4 μm/min, respectively. The growth kinetics on the (111)Ga face are close to the mass transport limited case. The growth kinetics on the (111)P face are close to the surface reaction limited case, and that on the (100) face are almost the mass transport limited case. The surface morphology and X-ray analysis show that the crystal structure depends on the orientation of the substrate. The (0001) oriented α (hexagonal) modification of ZnS is obtained on the (111)Ga face, the (111) oriented β (cubic) modification on the (111)P face, and the (100) oriented β modification on the (100) face in the studied range of temperature.     

多晶硅晶体生长中固-液界面研究进展

论述了多晶硅晶体生长技术的研究现状,探讨了多晶硅在定向凝固过程中的生长机制,重点阐述了多晶硅定向生长中固-液界面的形貌、杂质分布、数学模型、数值模拟以及外场对界面调控的影响,归纳总结目前国内外多晶硅生长界面的研究现状,展望了多晶硅晶体生长过程中固-液界面调控技术的发展前景.     

Compliant substrate technology: Integration of mismatched materials for opto-electronic applications

A critical review of the literature on compliant substrates, together with our own findings, is presented. Fabrication of various compliant substrate types are compared and the difficulties are discussed, with the main focus on the twist-bonded compliant substrates. Water bonding, which is the key technology to prepare compliant substrates, either directly or using an intermediate layer, will be specifically overviewed. Since compliant substrates are generally used for the growth of device-quality highly mismatched materials on dissimilar substrates, the different models extending the critical thickness are discussed. Our work, which focuses on twist-bonded GaAs compliant substrates prepared by MOVPE (Metal Organic Vapor Phase Epitaxy), will be presented and the results will be interpreted and compared with the current knowledge on compliant substrates. Finally, preliminary photodetector and laser diode devices realized on compliant substrates results, will be presented.     

PECVD法制备不同衬底微晶硅薄膜的研究

采用等离子体增强化学气相沉积(PECVD)法分别在玻璃衬底和p型薄膜硅衬底上制备了微晶硅薄膜。使用拉曼谱仪、紫外-可见分光光度计、傅里叶红外光谱仪等对微晶硅薄膜进行检测,重点研究了硅烷浓度、衬底温度对薄膜沉积速率和晶化率的影响。实验结果表明:两种衬底上薄膜的沉积速率均随硅烷浓度的增大、衬底温度的升高而变大。硅烷浓度对两种衬底的薄膜晶化率影响规律相同,即均随其升高而降低;但两种衬底的衬底温度影响规律存在差别:对玻璃衬底而言,温度升高,样品晶化率减小;而p型薄膜硅衬底则在温度升高时,样品晶化率先增大后减小。此外还发现,晶化率与薄膜光学性能及含氧量存在较密切关联。     

Halide glasses based on chlorides, bromides and iodides

There is relatively little information on glasses based on chlorides, bromides and iodides. Because of the recent interest in fluoride it is the objective of this paper to evaluate the potential for preparing new halide glasses and to offer some predictions on the properties of glasses based on chlorides, bromides and iodides. The predictions of glass-forming tendency, viscosity, chemical durability and structures are discussed.     

离子轰击增强金刚石膜与Si衬底结合力的进一步研究

由于金刚石与Si有较大的表面能差,利用化学气相沉积(CVD)制备金刚石膜时,金刚石在镜面光滑的Si表面上成核困难,而负衬底偏压能够增强金刚石在镜面光滑Si表面上的成核,表明金刚石核与Si表面的结合力也得到增强.本文分析衬底负偏压引起的离子轰击对Si表面产生的影响之后,基于离子轰击使得Si衬底表面产生了微缺陷(凹坑)增大了金刚石膜与Si衬底结合的面积,理论研究了离子轰击对金刚石膜与Si衬底结合力的影响.     

Inline deposited thin-film silicon solar cells on imprinted foil using linear PECVD sources

The standard way to improve the light management of thin film solar cells is to introduce a light scattering structure, either on the front window or at the back reflector. Usually, growth conditions of TCO layers are adjusted to get random surface roughness on the front window. In this paper we present an alternative method, which can be applied both on the front window and at the back reflector. It involves imprinting a UV curable coating layer allowing full control on the texture (random or periodic) to fully optimise the light trapping. Light trapping is even more important for microcrystalline Si solar cells. We have fabricated thin film nip Si solar cells with sputtered Ag/ZnO back contacts on embossed barrier layers on steel foil. We show that the UV curable coating is well-suited as imprintable barrier layer between the steel foil and the active layers. For nip a-Si cells we can obtain light trapping, as measured by the short-circuit current, that is almost as good as that of nip a-Si cells made on Asahi U-type glass, covered with a Ag/ZnO back reflector. Furthermore, we show that dynamically processed a-Si nip cells on foil realised efficiencies of over 7%, which are only slightly less than for cells made in a UHV lab-scale cluster tool in static processing. Finally, a-Si/a-Si tandems and μc-Si/a-Si tandems have been fabricated. Initial efficiencies of around 8% on textured barrier layer on steel foil have been achieved.     

Controllable cubic and hexagonal GaN growth on GaAs(0 0 1) substrates by molecular beam epitaxy

Two kinds of GaN samples were grown on GaAs(0 0 1) substrates. One is grown on nitridized GaAs surface, the other is grown on nitridized AlAs buffer GaAs substrate. X-ray diffraction and photoluminescence measurements find that the GaN sample directly grown on GaAs substrate is pure cubic phase and those grown on AlAs buffer is pure hexagonal phase. The present study shows that the phase of GaN samples grown on GaAs substrates can be controlled using different buffer layers.     

The fracture behaviour of Chromium- and Titanium-doped sapphire monocrystals

The influence of chromium and titanium on the fracture behaviour of sapphire crystals was analysed by means of crack indentation pattern, and the critical stress intensity factors for the easiest spalling planes of the sapphire were measured from the crack lengths at the indents. Together with information on the room temperature plasticity of sapphire the results allow conclusions on the influence of the dopants on crystallographic and glass-like fracture features, respectively.     

Selective area growth of GaN nanorods on patterned W/SiO2/Si substrates by RF-MBE

We report on the selective area growth (SAG) of GaN nanorods on Si substrates masked with W or SiO₂ and also on bare Si substrates by RF plasma-assisted molecular beam epitaxy (RF-MBE). The growth of GaN (i.e. irradiation of Ga and RF plasma-activated N₂) on the W mask layer results in the appearance of a ring reflection high-energy electron diffraction (RHEED) pattern coming from α-W. In contrast, broken ring RHEED patterns from GaN nanorods are clearly observed on SiO₂ and Si surfaces. Ex-situ scanning Auger microscopy analysis confirms that no growth of GaN takes place on W. Utilizing this phenomenon, we have demonstrated the SAG of GaN nanorods on Si substrates partly masked with W. We will discuss this phenomenon in terms of the difference in the desorption energy of Ga on W, SiO₂, and Si.     

Si3N4陶瓷轴承内圈NCD膜制备中的热流耦合分析

本文设计了一套用于HFCVD系统中轴承内圈NCD涂层制备的电极装置,同时在热交换过程的分析基础上对该系统进行了热流耦合分析.对进气参数进行优化后,衬底温度场及气体流场分布均匀.在数值分析的基础上,在氮化硅陶瓷内圈上成功制备了NCD膜.     

Crystal growth and transport rates of GeSe and GeTe in micro-gravity environment

Six vapor transport experiments on the systems GeSe-GeI₄ and GeTe-GeI₄ were performed on Skylab to determine the effects of micro-gravity on crystal growth and transport rates. Based on a direct comparison of crystals and transport data obtained on earth and in space, employing X-ray diffraction, microscopic and etching techniques, the results demonstrate a considerable improvement of the space grown crystals in terms of growth morphology and bulk perfection. The observation of greater mass transport rates than expected in micro-gravity for diffusion-controlled transport could indicate the existence of other transport modes in a reactive solid-gas phase system. The combined results show that the interference of gravity-driven convection with the transport process causes negative effects on crystal growth as observed on earth for otherwise identical conditions. This points to the unique environment of weightlessness for the observation of basic transport phenomena.     

立方氮化硼薄膜的气相沉积及过渡层对其附着性能的影响

本文采用非平衡磁控溅射物理气相沉积工艺,在单晶硅基片上合成了立方氮化硼薄膜,并且通过采用过渡层提高了立方氮化硼薄膜的附着力,过渡层分别是碳化硼(B4C)薄膜以及碳化硼(B4C)薄膜与B-C—N梯度层的复合层(B4C／B—C—N)。同时,不同过渡层的存在使立方氮化硼薄膜的剥落机理产生变化。     

Heterogeneous versus bulk nucleation of lysozyme crystals

Heterogeneous (on‐glass) protein crystal nucleation was separated from the bulk one in systems of thin protein solution layers, confined between two glass plates of custom made quasi two‐dimensional all‐glass cells, as well as by applying forced protein solution flow. Two commercial samples of hen‐egg‐white lysozyme, Seikagaku and Sigma were used as model proteins. Applying the classical technique of separation in time of nucleation and growth stages with protein solution layers of thickness 0.05 cm we found that the on‐glass crystal nucleation prevailed highly with Seikagaku HEWL, while on the opposite, bulk nucleated crystals represented the main crystal fraction in Sigma solution. Also using 0.05 cm solution layers nucleation rates were measured separately for the on‐glass and bulk protein crystals. The process was investigated by varying solution layer thicknesses as well, from 0.05 down to 0.01, 0.0065 and 0.002 cm. Studying the influence of the forced protein solution flow on HEWL crystal nucleation the classical double‐pulse technique was modified by separating the nucleation and growth stages not only in time, but simultaneously also in place. In this case we found that the ratio of on‐glass formed crystal nuclei to bulk nuclei depended on the flow velocity, but in different manner with Seikagaku HEWL and Sigma HEWL. A plausible explanation of our experimental results is that the bulk crystal nucleation occurs on foreign surfaces as well, e.g. on rests of source biomaterial, which are always present in the protein solutions. Moreover, biomaterial seems to be more active nucleant than glass. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)