Substrate temperature dependence of ZnTe epilayers grown on GaAs(001) by molecular beam epitaxy

ZnTe thin films have been grown on GaAs(0 0 1) substrates at different temperatures with constant Zn and Te beam equivalent pressures (BEPs) by molecular beam epitaxy (MBE). In situ reflection high-energy electron diffraction (RHEED) observation indicates that two-dimensional (2D) growth mode can be established after around one-minute three-dimensional (3D) nucleation by increasing the substrate temperature to 340 degrees C. We found that Zn desorption from the ZnTe surface is much greater than that of Te at higher temperatures, and estimated the Zn sticking coefficient by the evolution of growth rate. The Zn sticking coefficient decreases from 0.93 to 0.58 as the temperature is elevated from 320 to 400 degrees C. The ZnTe epilayer grown at 360 degrees C displays the narrowest full-width at half-maximum (FWHM) of 660 arcsec from (0 0 4) reflection in double-crystal X-ray rocking curve (DCXRC) measurements. The surface morphology of ZnTe epilayers is strongly dependent on the substrate temperature, and the root-mean-square (RMS) roughness diminishes drastically with the increase in temperature.

Preparation and optical property of a novel hydrophobic anti-reflection coating for KDP crystal

A novel inorganic-organic hybrid hydrophobic anti-reflection silica film used for laser crystal was obtained by sol-gel process. The film consisted of silica sols mixed with a small amount of polymethyl methacrylate (PMMA) or polystyrene (PS). The optical transparency, hydrophobic property and surface morphology of the film were characterized by UV-VIS-NIR spectrophotometer; contact angle instrument and Scanning Electron Microscopy (SEM), respectively. The results showed that the anti-reflection coating had good hydrophobility and optical transparency from 400 nm to 1200 nm. The contact angle reached to 130-140 degrees. SEM images indicated the hydrophobic films modified with PMMA or PS had compact structure compared to the pure silica sol film. (C) 2008 Elsevier B.V. All rights reserved.

聚合物超分子薄膜表面形貌及性质研究

与本体和溶液中的相行为相比，在薄膜状态下，分子链的运动是在其内在因素和外场的共同作用下进行的。微相分离的最终结构形态除了与超分子的组成，分子量，相分离强度有关外，还与薄膜厚度，表面和界面对组分的选择性亲和作用等因素有关。因此，所提出的问题就是如何利用这些影响薄膜结构的因素，构建具有新颖结构和有序结构的薄膜，以及如何实现薄膜形貌及结构尺寸的调控。另外一个重要方面就是如何利用聚合物超分子本身特殊性质，实现超分子薄膜表面结构随外界条件下的响应性变化。在薄膜的功能性方面，薄膜结构以及组成与薄膜性质有着怎样的关系，如何通过调节薄膜的结构以及组成，来优化薄膜的性质。 本论文利用高分子之间，以及高分子与无机金属离子之间的的非共价键相互作用（静电相互作用，氢键，络合作用）得到聚合物超分子体系。研究其自组装形成纳米结构的影响因素和机理，掌握调控纳米结构的形态、尺寸、以及薄膜光学性质的规律，实现通过调控薄膜微结构来优化薄膜性质的目的。 首先，本论文对聚合物超分子薄膜表面形貌的构建和调控方面进行了研究。利用两种嵌段共聚物之间的氢键作用，实现聚合物超分子络合体溶解性在共溶剂中的下降。在动力学控制的条件下，体系中未形成氢键的组分充当了“桥梁”作用，使形成的纳米球状聚集体发生在一维方向的聚集，得到柱状纳米聚集体。当两种聚合物之间全部形成氢键时，发生柱状纳米聚集体到球状胶束聚集体的转变。研究了溶剂挥发速度，聚合物溶液粘度等对形成纳米结构薄膜的影响。利用静电相互作用，得到聚合物超分子结构。实现了具有规则纳米孔洞结构的聚合物超分子薄膜的制备。研究了溶剂性质，溶剂挥发速度，聚合物溶液粘度，环境温度等对形成规则孔洞的影响，以及薄膜表面结构随外界条件的响应性变化， 并提出了孔洞形成及演变机理。 基于对薄膜表面形貌和结构的调控，我们对薄膜结构与薄膜的光学性质之间的关系进行了研究。利用两种均聚物之间的氢键相互作用，得到超分子嵌段共聚物。超分子嵌段共聚物发生微观相分离可得到自组装薄膜，利用氢键是一种弱的相互作用，使用选择性溶剂将某一组分除去，得到具有纳米孔洞的薄膜。薄膜表现出很好的抗反射性，在可见光区实现了98.00%的单波长高透过。在近红外区实现了宽波抗反射效果，透光率可达到99.00%以上，而且波段可调。深入研究了薄膜的厚度，刻蚀时间对薄膜透光率的影响。利用金属和聚合物之间的络合相互作用，得到被聚合物稳定的银纳米粒子。受聚合物与银纳米粒子之间的电子转移吸收的影响，复合纳米材料在薄膜状态下表现出很好的光致发光性质。研究了材料之间的配比，溶液的浓度，聚合物的分子量对形成的复合纳米粒子的尺寸及光致发光性能的影响。

高分子混合物薄膜表面形态的形成与稳定性

本工作主要从实验上探索了组分的分子量、薄膜厚度、混合物的组成等因素对不相容高分子混合物薄膜表面形态的形成和稳定性的影响规律。在此基础上，利用软印刷的方法对基底表面进行图案化，来控制高分子混合物的相分离行为，以制备规则排列的有序图案。用原子力显微镜（AFM）、偏光显微镜（OM）、X-射线光电子能谱（XPS）等手段，系统研究了PS护MMA混合物薄膜的初始形态及其在退火过程中的形态演变规律。（1）随着PS分子量的增加，研究发现其形态的变化存在一过渡区域并予以合理解释；即：薄膜的初始形态由纳米尺度的相分离向宏观相分离的表面形态过渡；高温下退火时，其形态的演变存在两种过程。（2）对不同厚度的PS／PMMA混合物薄膜，在退火过程中观察到两种能长时间存在的新的表面形态，并阐明其稳定存在的原因；对PS护MMA混合物超薄膜，长时间退火时，在薄膜表面观察到二次相分离。（3）首次提出了利用混合物薄膜的相分离抑制去润湿的方法，即低浓度的PMMA可以抑制PS薄膜的去润湿行为，其稳定机理归结为PMMA优先向基底的表面分离而形成的厚度为少L个纳米的PMMA富相层。（4）研究了PS／P MMA混合物薄膜在OTS图案化基底上的形态变化，结果表明，薄膜的形态演变主要由横向受限和基底的表面自由能决定。通过控制受限程度和退火时间，可得到多种形态。以PS／P 4VP夕昆合体系为例，探索了如何利用高分子混合物薄膜的相分离制备具有规则排列的有序结构。研究表明，只有当PS的分子量相对较小时，在SAM图案化的基底表面，才比较容易形成规则排列的相分离图案。该规则排列的相分离图案具有良好的热稳定性。为深刻理解在旋涂过程中高分子聚集结构的变化情况，以SESS为例，用DFM研究了旋涂高分子薄膜的形成过程。当溶液浓度较低时，首次观察到了条状取向结构并提出该结构的形成机理，说明在旋涂过程中其复杂的剪切拉伸场可以引起柔顺性高分子线团或聚集体的取向。

聚合物薄膜的表面形态结构及相关纳米材料制备

本工作主要从实验上探索了基板、溶液浓度、溶剂性质、组成对均聚物、嵌段共聚物以及嵌段共聚物与均聚物共混薄膜表面形态结构的影响。在此基础上，又以嵌段共聚物薄膜为模板，制备了多种纳米粒子。用原子力显微镜（AFM）研究了超稀PS溶液在固体基板上的表面形貌、表面粗糙度及其润湿性质。研究发现：在所用PS分子量范围内（1）随分子量的增加，退火前PS微区的平均直径增加，而平均高度减小。退火后PS微区的平均直径减小，而平均高度增加。（2）首次观察到：薄膜的表面粗糙度（Ra）除了与溶剂的蒸汽压及所用基板有关外，还和溶剂的偶极矩有关。无论在Si片还是mica上，当l所用溶剂具粼目近的偶极矩不同的蒸汽压时，蒸汽压越小，表面Ra也越小；当所用溶剂具有相近的蒸汽压不同的偶极矩时，偶极矩越大，表面Ra就越小。对所用的每一种溶剂，Si片上薄膜的Ra均大于mica上薄膜的Ra，这可能是由Si片表面的粗糙度大于mica表面的粗糙度引起的。以PS-b-P4VP嵌段共聚物为研究对象，探索了共聚物组成、基板、溶液浓度和溶剂对薄膜表面形貌的影响，并对非对称PS-b-P4VP薄膜在甲醇蒸气下表面形貌随时间的演变过程进行了观察。首次观察到：本体为柱状结构的Ps-b-P4VP薄膜，随着在甲醇蒸气中处理时间的增加，形貌从无特征表面、凹陷结构和条带共存的杂化形貌、条状微区、六方排列的凹陷结构、再到条状微区的转变。不同膜厚其形貌转变程度亦不同，膜越厚观察到的形貌转变就越多。而对于厚度约为18.6nm本体为球状结构的PS-b-P4VP薄膜，当在甲醇蒸气中退火时，只观察到了六方排列的凹陷结构并且这种结构不随退火时间的增加而改变。通过对不同组成PS-b-P4VP／hPS混合物薄膜在云母和石墨上表面形貌的研究，首次观察到：在云母基板上随混合物中Φps的增加，表面形貌经历着由六方有序的球状微区向条状结构再向球状微区最后到宏观相分离结构的转变；而在石墨基板上，随Φps的增加，表面形貌逐渐由条带结构向球状结构转变，未观察到明显的宏观相分离。以PS-b-P4vP胶束薄膜为模板合成了Ag-Pd及ZnO纳米结构，并对不同表面活性剂包裹的CdSe在PS-b-P4VP薄膜中的选择性分布进行了探索。 以PS-b-P4VP胶束薄膜为研究对象研究了溶剂蒸气及酸溶液对其表面形貌的影响。实验结果表明，除了甲醇蒸气，用一元酸处理薄膜也能得到纳米孔结构。

Molecular beam epitaxy of GaSb on GaAs substrates with AlSb/GaSb compound buffer layers

GaSb films with AlSb/GaSb compound buffer layers were grown by molecular beam epitaxy on GaAs (001) substrates. The crystal quality and optical properties were studied by high resolution transition electron microscopy and low temperature photoluminescence spectra (PL), respectively. It was found that the AlSb/GaSb compound buffer layers can restrict the dislocations into GaSb epilayers. The intensity of PL spectra of GaSb layer becomes large with the increasing the periods of AlSb/GaSb superlattices, indicating that the optical quality of GaSb films is improved.

LIQUID-PHASE EPITAXY GROWTH AND PROPERTIES OF GAINASSB/ALGAASSB/GASB HETEROSTRUCTURES

The GaInAsSb/AlGaAsSb/GaSb heterostructures were grown by the liquid phase epitaxy (LPE) technique. The materials were characterized by means of optical microscopy, electroprobe microanalysis (EPMA), double-crystal X-ray diffraction, capacitance-voltage (C-V) and Van der Pauw measurments, infrared absorption spectra, photoluminescence and laser Raman scattering. The results show that the materials have fine surface morphology, low lattice mismatch and good homogeneity. Room-temperature light-emitting diodes with an emission wavelength of 2.2-mu-m were obtained by using the GaInAsSb/AlGaAsSb DH structures.

Lateral periodicity in highly-strained (GaIn)As/Ga(PAs) superlattices investigated by X-ray scattering techniques

In this work we investigate the lateral periodicity of symmetrically strained (GaIn)As/GaAs/Ga(PAs)/GaAs superlattices by means of X-ray scattering techniques. The multilayers were grown by metalorganic Vapour phase epitaxy on (001)GaAs substrates, which were intentionally off-oriented towards the [011]-direction. The substrate off-orientation and the strain distribution was found to affect the structural properties of the superlattices inducing the generation of laterally ordered macrosteps. Several high-resolution triple-crystal reciprocal space maps, which were recorded for different azimuth angles in the vicinity of the (004) Bragg diffraction and contour maps of the specular reflected beam collected in the vicinity of the (000) reciprocal lattice point, are reported and discussed. The reciprocal space maps clearly show a two-dimensional periodicity of the X-ray peak intensity distribution which can be ascribed to the superlattice periodicity in the direction of the surface normal and to a lateral periodicity in a crystallographic direction coinciding with the miscut orientation. The distribution and correlation of the vertical as well as of the lateral interface roughness was investigated by specular reflectivity and diffuse scattering measurements. Our results show that the morphology of the roughness is influenced by the off-orientation angle and can be described by a 2-dimensional waviness.

Growth of GaAs on Si by using a thin Si film as buffer layer

We report a novel technique for growing high-quality GaAs on Si substrate. The process involves deposition of a thin amorphous Si film prior to the conventional two-step growth. The GaAs layers grown on Si by this technique using metalorganic chemical vapor deposition exhibit a better surface morphology and higher crystallinity as compared to the samples gown by conventional two-step method. The full width at half maximum (FWHM) of the x-ray (004) rocking curve for 2.2 mu m thick GaAs/Si epilayer grown by using this new method is 160arcsec. The FWHM of the photoluminescence spectrum main peak for this sample is 2.1 meV. These are among the best results reported so far. In addition, the mechanism of this new growth method was studied using high-resolution transmission electron microscopy.

Epitaxial growth on 4H-SiC by TCS as a silicon precursor

Epitaxial growth on n-type 4H-SiC 8°off-oriented substrates with a size of 10 × 10 mm~2 at different tem-peratures with various gas flow rates has been performed in a horizontal hot wall CVD reactor, using trichlorosilane (TCS) as a silicon precursor source together with ethylene as a carbon precursor source. The growth rate reached 23 μm/h and the optimal epilayer was obtained at 1600 ℃ with a TCS flow rate of 12 sccm in C/Si of 0.42, which has a good surface morphology with a low RMS of 0.64 nm in an area of 10 × 10μm~2. The homoepitaxial layer was oh-tained at 1500 ℃ with low growth rate (< 5μm/h) and the 3C-SiC epilayers were obtained at 1650 ℃ with a growth rate of 60-70μm/h. It is estimated that the structural properties of the epilayers have a relationship with the growth temperature and growth rate. Silicon droplets with different sizes are observed on the surface of the homoepitaxial layer in a low C/Si ratio of 0.32.

NiO removal of Ni/Au Ohmic contact to p-GaN after annealing

The Ni/Au contact was treated with oxalic acid after annealing in O_2 ambient, and its I-V characteristic showed the property of contact has been obviously improved. An Auger electron spectroscopy (AES) depth pro-file of the contact as-annealed showed that the top layer was highly resistive NiO, while an X-ray photo-electron spectroscopy (XPS) of oxalic acid treated samples indicated that the NiO has been removed effectively. A scanning electron microscope (SEM) was used to observe the surface morphology of the contacts, and it was found that the lacunaris surface right after annealing became quite smooth with lots of small Au exposed areas after oxalic acid treatment. When the test probe or the subsequently deposited Ti/Au was directly in contact with these small Au areas, they worked as low resistive current paths and thus decrease the specific contact resistance.

Smaller Ge Quantum Dots Obtained by ArF Excimer Laser Annealing

Ge self-assembled quantum dots (SAQDs) are grown with a self-assembled UHV/CVD epitaxy system. Then,the as-grown Ge quantum dots are annealed by ArF excimer laser. In the ultra-shot laser pulse duration,～20ns, bulk diffusion is forbidden, and only surface diffusion occurs, resulting in a laser induced quantum dot (LIQD). The diameter of the LIQD is 20～25nm which is much smaller than the as-grown dot and the LIQD has a higher density of about 6 × 10~(10)cm~(-2). The surface morphology evolution is investigated by AFM.

Effects of Thickness on Properties of ZnO Films Grown on Si by MOCVD

High quality ZnO films are successfully grown on Si（100） substrates by metal-organic chemical vapor deposition at 300℃. The effects of the thickness of the ZnO films on crystal structure, surface morphology,and optical properties are investigated using X-ray diffraction, scanning probe microscopy,and photoluminescence spectra, respectively. It is shown that the ZnO films grown on Si substrates have a highly-preferential C-axis orientation,but it is difficult to obtain the better structural and optical properties of the ZnO films with the increasing of thickness. It is maybe due to that the grain size and the growth model are changed in the growth process.

Preparation of 50mm 3C-SiC/Si(111) as Substrates Suited for Ⅲ-Nitrides

50mm SiC films with high electrical uniformity are grown on Si(111) by a newly developed vertical low-pressure chemical vapor deposition (LPCVD) reactor.Both in-situ n- and p-type doping of 3C-SiC are achieved by intentional introduction of ammonia and boron into the precursor gases.The dependence of growth rate and surface morphology on the C/Si ratio and optimized growth conditions is obtained.The best electrical uniformity of 50mm 3C-SiC films obtained by non-contact sheet resistance measurement is ±2.58%.GaN films are grown atop the as-grown 3C-SiC/Si(111) layers using molecular beam epitaxy (MBE).The data of both X-ray diffraction and low temperature photoluminescence of GaN/3C-SiC/Si(111) show that 3C-SiC is an appropriate substrate or buffer layer for the growth of Ⅲ-nitrides on Si substrates with no cracks.