Defect analysis in Czochralski-grown Yb : FAP crystal

Growth-induced defects in Yb:FAP crystals grown by the Czochralski method have been investigated by optical microscopy, chemical etching, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Anisotropic etching features have been observed on two FAP crystal planes: (0001) and (1010). The shape of etch pits on the (0001) plane is hexagonal, while the etch pits on the (1010) plane have a variety of irregular shapes. It is also found that the density of etch pit varies along the boule. Based on the experimental observations, the formation mechanisnis of growth defects are discussed, and methods for reducing the growth-induced defect concentration is proposed. (c) 2005 Elsevier B.V. All rights reserved.

Yb：Ca5（PO4）3F激光晶体的生长缺陷

采用提拉法生长了质量优异的Yb：Ca5（PO4）2F（Yb：FAP）晶体。运用化学腐蚀，光学显微镜、扫描电子显微镜以及能量散射光谱仪观察了该晶体中的生长条纹和包裹物等宏观缺陷，以及晶体的位错腐蚀形貌、位错密度及其分布情况，同时观察了晶体中亚晶界的形态。由晶体中位错的径向变化以及生长条纹可知：晶体在生长过程中为微凸界面生长。高温下CaF2的挥发造成了在晶体生长后期熔体中组分偏离化学计量比，出现组分过冷，形成包裹物。且位错密度显著增加。Yb：FAP晶体的各向异性使得晶体在（10 10）面的位错蚀坑形状、大小以

提拉法Ti:LiAlO_2晶体的生长、缺陷及N_2退火研究

本文采用提拉法成功地生长了钛掺杂浓度为0.1%原子分数的LiAlO2单晶体,借助光学显微镜,结合化学腐蚀法,对Ti:LiAlO2晶体(100)面空气退火前后的缺陷特征进行了研究,用AFM观测了(100)面晶片在不同温度下流动N2气氛退火过的表面形貌。结果表明:Ti:LiAlO2晶体(100)面的位错腐蚀坑是底面为平行四边形的锥形坑,位错密度约为5.0×104cm-2,900℃空气退火后晶片表面的位错腐蚀坑变大;N2退火能显著影响晶片的表面形貌,当退火温度为900℃时,晶片的均方根粗糙度(RMS)达到最低值

ScAlMgO_4晶体的生长缺陷

采用提拉法生长出φ30 mm×55 mm的ScAlMgO4晶体。在晶体生长过程中有轻微的挥发,粉末X射线衍射分析表明:挥发物质为MgO单相。运用扫描电镜、光学显微镜以及高分辨X射线衍射仪对晶体中的包裹物、开裂、生长条纹和小角晶界缺陷进行了研究。结果表明:温度梯度和热应力是形成晶体中缺陷的主要原因。通过合理设计温场,控制固-液界面的形状及冷却过程的降温速率,可以提高晶体的完整性。

导模法和温度梯度法生长r面蓝宝石(英文)

r面(0112)蓝宝石晶体可用作制备非极性GaN薄膜的衬底。采用温度梯度法(temperature gradient technique,TGT)和导模法(edge-defined film-fed crystal growth,EFG)生长了质量良好的r面蓝宝石晶体。利用双晶衍射、光学显微镜、光谱仪观察和分析了晶体的结构和缺陷。结果表明:TGT法生长的r蓝宝石晶体的双晶摇摆曲线对称性好,半高宽值仅为18 rad.s,位错密度为4×103 cm-2,透过率达83%,晶体质量好。与TGT法相比,EFG法生长的r面蓝宝石晶体的结构完整性较差,位错密度为5×105 cm-2,透过率仅为75%。但是EFG法具有晶体生长速度快,后期加工成本低的优点。

离子束溅射法薄膜生长中结瘤微缺陷的生长机理

用离子束溅射法制备了锆单层薄膜．用设计新型夹具和预置种子方法，对薄膜中结瘤微缺陷的生长过程进行了研究．在高分辨率光学显微镜和扫描电子显微镜下观察发现，结瘤在其生长初期呈现出分形的特征．用分子动力学和薄膜生长的扩散限制聚集模型，薄膜中结瘤微缺陷成核时的分形现象得到了很好的解释．

Effect of SiO2 protective layer on the femtosecond laser-induced damage of HfO2/SiO2 multilayer high-reflective coatings

Two kinds of HfO2/SiO2 800 nm high-reflective (HR) coatings, with and without SiO2 protective layer were deposited by electron beam evaporation. Laser-induced damage thresholds (LIDT) were measured for all samples with femtosecond laser pulses. The surface morphologies and the depth information of all samples were observed by Leica optical microscopy and WYKO surface profiler, respectively. It is found that SiO2 protective layer had no positive effect on improving the LIDT of HR coating. A simple model including the conduction band electron production via multiphoton ionization and impact ionization is used to explain this phenomenon. Theoretical calculations show that the damage occurs first in the SiO2 protective layer for HfO2/SiO2 HR coating with SiO2 protective layer. The relation of LIDT for two kinds of HfO2/SiO2 HR coatings in calculation agrees with the experiment result. (c) 2006 Elsevier B.V. All rights reserved.

单脉冲飞秒脉冲激光对单层和高反光学薄膜的损伤

用电子柬蒸发的方法在BK7玻璃上制备了ZrO2单层膜和ZrO2／SiO2高反膜，利用掺Ti：sapphire飞秒激光系统输出的中心波长为800nm，脉宽为50fs的激光脉冲对这两种样品进行了激光损伤阈值测试．实验结果表明，ZrO2单层膜的阂值比ZrO2／SiO2高反膜的高；这与传统的纳秒脉冲激光的损伤情况相反．利用光离化和碰撞离化激发电子到导带，形成电子等离子体基本模型并对此现象进行了解释．同时，用显微镜对样品的损伤形貌进行了观测，对损伤的特点进行了表征．

Influence of AlN buffer layer thickness on structural properties of GaN epilayer grown on Si (111) substrate with AlGaN interlayer

We present the growth of GaN epilayer on Si (111) substrate with a single AlGaN interlayer sandwiched between the GaN epilayer and AlN buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an AlN buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.

The effect of low temperature AlN interlayers on the growth of GaN epilayer on Si (111) by MOCVD

Low temperature (LT) AlN interlayers were used to effectively reduce the tension stress and micro-cracks on the surface of the GaN epilayer grown on Si (111) substrate. Optical Microscopy (OM), Atomic Force Microscopy (AFM), Surface Electron Microscopy (SEM) and X-Ray Diffraction (XRD) were employed to characterize these samples grown by metal-organic chemical vapor deposition (MOCVD). In addition, wet etching method was used to evaluate the defect of the GaN epilayer. The results demonstrate that the morphology and crystalline properties of the GaN epilayer strongly depend on the thickness, interlayer number and growth temperature of the LT AlN interlayer. With the optimized LT AlN interlayer structures, high quality GaN epilayers with a low crack density can be obtained. (C) 2008 Elsevier Ltd. All rights reserved.

Influence of AlN buffer layer thickness on the properties of GaN epilayer on Si(111) by MOCVD

The effect of thickness of the high-temperature (HT) AlN buffer layer on the properties of GaN grown on Si(111) has been investigated. Optical microscopy (OM), atomic force microscopy (AFM) and X-ray diffraction (XRD) are employed to characterize these samples grown by metal-organic chemical vapor deposition (MOCVD). The results demonstrate that the morphology and crystalline properties of the GaN epilayer strongly depend on the thickness of HT AlN buffer layer, and the optimized thickness of the HT AlN buffer layer is about 110 nm. Together with the low-temperature (LT) AlN interlayer, high-quality GaN epilayer with low crack density can be obtained. (C) 2008 Elsevier Ltd. All rights reserved.

The effect of single AlGaN interlayer on the structural properties of GaN epilayers grown on Si (111) substrates

High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single AlGaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si (111) substrate by metalorganic chemical vapor deposition. This paper investigates the effect of AlGaN interlayer on the structural proper-ties of the resulting GaN epilayer. It confirms from the optical microscopy and Raman scattering spectroscopy that the AlGaN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy analysis reveal that a significant reduction in both screw and edge threading dislocations is achieved in GaN epilayer by the insertion of AlGaN interlayer. The process of threading dislocation reduction in both AlGaN interlayer and GaN epilayer is demonstrated.

Morphological defects and uniformity issues of 4H-SiC homoepitaxial layers grown on off-oriented (0001)Si faces

The morphological defects and uniformity of 4H-SiC epilayers grown by hot wall CVD at 1500 degrees C on off-oriented (0001) Si faces are characterized by atomic force microscope, Nomarski optical microscopy, and Micro-Raman spectroscopy. Typical morphological defects including triangular defects, wavy steps, round pits, and groove defects are observed in mirror-like SiC epilayers. The preparation of the substrate surface is necessary for the growth of high-quality 4H-SiC epitaxial layers with low-surface defect density under optimized growth conditions. (c) 2006 Elsevier Ltd. All rights reserved.

Microdefects and electrical uniformity of InP annealed in phosphorus and iron phosphide ambiances

Microdefects originating from impurity-dislocation interactions in undoped InP that had been annealed in phosphorus and iron phosphide ambiances have been studied using optical microscopy. The electrical uniformity of the annealed wafer is improved by removing impurity aggregation around dislocations and by eliminating impurity striations in the annealing process. Compared to as-grown Fe-doped semi-insulating (SI) material, SI wafers obtained by annealing undoped InP in iron phosphide ambiances have better uniformity. This is attributed to the avoidance of Fe aggregation around dislocations and dislocation clusters, Fe precipitation and impurity striations, and is related to the use of a low concentration of Fe in the annealed material. The influence of Fe diffusion on the migration of dislocations in the annealing process has been studied and reviewed. (C) 2003 Elsevier B.V. All rights reserved.

Epitaxial growth of SiC on complex substrates

Epitaxial growth of SiC on complex substrates was carried out at substrate temperature from 1200 degreesC to 1400 degreesC. Three kinds of new complex substrates, c-plane sapphire, AlN/sapphire, and GaN/AlN/sapphire, were used in this study. We obtained a growth rate in the range of 1-6 mum/h. Thick (6 mum) SIC epitaxial layers with no cracks were successfully obtained on AlN/sapphire and GaN/AlN/sapphire substrates. X-ray diffraction patterns have confirmed that single-crystal SiC was obtained on these complex substrates. Analysis of optical transmission spectra of the SIC grown on sapphire substrates shows the lowest-energy gap near 2.2 eV, which is the value for cubic SiC. The undoped SIC showed n-type electrical conductivity. (C) 2001 Elsevier Science B.V. All rights reserved.