Screw misfit dislocations in soft substrates of epitaxial heterostructures

We derive compact analytical formulae for the elastic field induced by an anti-plane mismatch deformation in a heterostructure with different elastic moduli of the constituents. Unlike previous studies, we consider the possibility that the misfit dislocations may appear in the substrate, not in the epilayer. We show that this situation can be realized in heterostructures where the substrate is softer than the epilayer. In order to avoid cumbersome calculations, we consider screw misfit dislocations. The misfit dislocations emerge with zero density away from the interface in the body of the substrate when the epilayer reaches its critical thickness. Thus the epilayer remains free from dislocations if it is grown on a softer substrate. This property, which was recently observed experimentally, may find numerous applications in electronics, where epilayers are widely used as active elements.     

半导体异质外延薄膜质量的X射线衍射检测方法

本文介绍了一种使用X射线宽角测角仪和双晶测角仪相配合的检测半导体异质外延薄膜的方法.其特点是快速且不损伤样品,特别适合大失配度的外延生长的条件试验检测,也可用于器件生产过程中的外延质量的监控.此法还可用于各种超晶格结构参数的测量.     

Emergent rotational symmetries in disordered magnetic domain patterns

Uniaxial systems often form labyrinthine domains that exhibit short-range order but are macroscopically isotropic and would not be expected to exhibit precise symmetries. However, their underlying frustration results in a multitude of metastable configurations of comparable energy, and driving such a system externally might lead to pattern formation. We find that soft x-ray speckle diffraction patterns of the labyrinthine domains in CoPd/IrMn heterostructures reveal a diverse array of hidden rotational symmetries about the magnetization axis, thereby suggesting an unusual form of emergent order in an otherwise disordered system. These symmetries depend on applied magnetic field, magnetization history, and scattering wave vector. Maps of rotational symmetry exhibit intriguing structures that can be controlled by manipulating the applied magnetic field in concert with the exchange bias condition.     

Stress evolution influenced by oxide charges on GaN metal–organic chemical vapor deposition on silicon-on-insulator substrate

GaN epilayers have been deposited on silicon-on-insulator (SOI) and bulk silicon substrates. The stress transition thickness and the initial compressive stress of a GaN epilayer on the SOI substrate are larger than those on the bulk silicon substrate, as shown in in situ stress measurement results. It is mainly due to the difference of the three-dimensional island density and the threading dislocation density in the GaN layer. It can increase the compressive stress in the initial stage of growth of the GaN layer, and helps to offset the tensile stress generated by the lattice mismatch. PACS 81.15.Gh     

Comparing light-induced colloidal quasicrystals with different rotational symmetries

Quasicrystals are aperiodic structures with long-range orientational order. Unlike crystals, quasicrystals can, in principle, possess any non-crystallographic rotational symmetry. However, only a few of these rotational symmetries have been observed. By using Monte Carlo simulations of colloidal particles in laser interference patterns with quasicrystalline symmetry, we compare the onset of quasicrystalline order for different rotational symmetries in two dimensions. We find that quasicrystals with 5-, 8-, 10-, and 12-fold rotational axes can be induced with lower laser intensities than quasicrystals with other non-crystallographic rotational symmetries. We relate this finding to the number of local symmetry centers in the respective interference patterns.     

Effect of the thickness of InGaN interlayer on a-plane GaN epilayer

In this paper,we use the a-plane InGaN interlayer to improve the property of a-plane GaN.Based on the a-InGaN interlayer,a template exhibits that a regular,porous structure,which acts as a compliant effect,can be obtained to release the strain caused by the lattice and thermal mismatch between a-GaN and r-sapphire.We find that the thickness of InGaN has a great influence on the growth of a-GaN.The surface morphology and crystalline quality both are first improved and then deteriorated with increasing the thickness of the InGaN interlayer.When the InGaN thickness exceeds a critical point,the a-GaN epilayer peels off in the process of cooling down to room temperature.This is an attractive way of lifting off a-GaN films from the sapphire substrate.     

失配应力引起的Ga_xIn_（1－x）P外延层能带隙的移动

本文首次观察了用ＭＯＣＶＤ方法生长的ＧａｘＩｎ１－ｘＰ外延层的能带隙移动，并给出了ＧａｘＩｎ１－ｘＰ外延层光荧光（ＰＬ）峰能量随组分ｘ的变化关系，结果表明ＰＬ是探测混晶组分的简单而有效的方法之一。     

Thickness measurement of GaN epilayer using high resolution X-ray diffraction technique

In this paper we propose a new method for measuring the thickness of the GaN epilayer, by using the ratio of the integrated intensity of the GaN epilayer X-ray diffraction peaks to that of the sapphire substrate ones. This ratio shows a linear dependence on the GaN epilayer thickness up to 2 μm. The new method is more accurate and convenient than those of using the relationship between the integrated intensity of GaN epilayer diffraction peaks and the GaN thickness. Besides, it can eliminate the absorption effect of the GaN epilayer.     

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.     

Ag/Cu(111)与Au/Cu(111)体系异质外延岛演化过程中的应变释放及其对Moiré结构形成的影响

采用嵌入原子方法的原子间相互作用势，利用分子动力学模拟方法研究了Au/Cu(111)和Ag/Cu (111)体系的异质外延结构特征以及外延岛形貌和应变释放的演化过程. 通过对比Au/Cu(111)和Ag/Cu (111)体系的异质外延结构及外延岛演化行为，揭示了导致Ag/Cu (111)体系中异质外延层形成Moiré结构的微观物理机理及其与外延体系的宏观物理特性之间的关系. 研究结果显示，外延岛原子与基体表面原子之间的界面结合强度是形成Moiré结构的重要因素，异质外延体系的界面结合强度取决于二者的合金熔解热. 当异质外延体系的合金熔解热为正值时，界面结合强度较弱，有利于Moiré结构的形成. 同时，外延岛原子之间的相互作用决定着外延岛的面内弛豫行为，对Moiré结构的形成有一定的影响. 外延岛的面内弛豫行为与外延层和基体之间的相对刚度有关，弹性模量较大的外延层具有较强的延展能力，对Moiré结构的形成有利. 此外，Moiré结构的形成与外延岛的尺度有关，主要是外延岛边界原子的钉扎作用对外延岛内原子弛豫行为的约束作用的影响.     

GaAs/Ge的MOCVD生长研究

用常压MOCVD在Ge衬底上外延生长了GaAs单晶层,研究了GaAs和6e的极性与非极性材料异质外延生长,获得了质量优良的GaAs/Ge外延片,GaAs外延层X射线双晶衍射回摆曲线半高宽达16弧秒.10K下PL谱半峰宽为7meV.讨论了极性与非极性外延的界面反相畴问题和GaAs-Ge界面的Ga、Ge原子互扩散问题.     

Structural and electrical properties of single crystalline and bi-crystalline ZnO thin films grown by molecular beam epitaxy

C-oriented ZnO epitaxial thin films are grown separately on the a-plane and c-plane sapphire substrates by using a molecular-beam epitaxy technique. In contrast to single crystalline ZnO films grown on a-plane sapphire, the films grown on c-plane sapphire are found to be bi-crystalline; some domains have a 30o rotation to reduce the large mismatch between the film and the substrate. The presence of these rotation domains in the bi-crystalline ZnO thin film causes much more carrier scatterings at the boundaries, leading to much lower mobility and smaller mean free path of the mobile carriers than those of the single crystalline one. In addition, the complex impedance spectra are also studied to identify relaxation mechanisms due to the domains and/or domain boundaries in both the single crystalline and bi-crystalline ZnO thin films.     

ZnO的激光分子束外延法制备及X射线研究

利用激光分子束外延(L-MBE)技术在α-Al2O3(0001)衬底上生长出了沿C轴高度择优取向的ZnO外延薄膜,并采用Philips四晶高分辨X射线衍射仪(Philip′s X′Pert HR-MRD)对ZnO薄膜的表面及结构特性进行了研究.应用小角度X射线分析方法(GIXA)对ZnO薄膜的表面以及ZnO/Al2O3界面状况进行了定量表征.X射线反射率(XRR)曲线出现了清晰的源于良好表面及界面特性的Kiessig干涉振荡峰,通过对其精确拟合求得ZnO薄膜的表面及界面粗糙度分别为0.34 nm和1.12 nm.ZnO薄膜与α-Al2O3(0001)衬底的XRD在面(in-plane) Φ扫描结果表明形成了单一的平行畴(Aligned in-plane Oriented Domains),其在面外延关系为ZnO［1010］ ||Al2O3［1120］.XRD ω-2θ 扫描以及ω 摇摆曲线半峰宽分别为0.12度和1.27度,这一结果表明通过形成平行畴及晶格驰豫过程,ZnO薄膜中的应力得到了有效的释放,但同时也引入了螺位错.     

Fixed equilibria of point vortices in symmetric multiply connected domains

The paper provides symmetric fixed configurations of point vortices in multiply connected domains in the unit circle with many circular obstacles. When the circular domain is invariant with respect to rotation around the origin by a degree of 2π/M, a regular M-polygonal ring configuration of identical point vortices becomes a fixed equilibrium. On the other hand, when we assume a special symmetry, called the folding symmetry, on the circular domain, we find a fixed equilibrium in which M point vortices with the positive unit strength and M point vortices with the negative unit strength are arranged alternately at the vertices of a 2M-polygon. We also investigate the stability of these fixed equilibria and their bifurcation for a special circular domain with the rotational symmetry as well as the folding symmetry. Furthermore, we discuss fixed equilibria in non-circular multiply connected domains with the same symmetries. We give sufficient conditions for the conformal mappings, by which fixed equilibria in the circular domains are mapped to those in the general multiply connected domains. Some examples of such conformal mappings are also provided.     

采用AlSb缓冲层生长2.3μm InGaAsSb/AlGaAsSb多量子阱结构

针对常见的GaSb衬底的InGaAsSb/AlGaAsSb多量子阱结构进行了设计和外延生长。样品通过X-射线测试,有多级衍射卫星峰出现,表明量子阱结构的均匀性和界面质量较好,引入AlSb缓冲层可以降低衬底与外延层之间的界面自由能,使AlSb起到了一个滤板的作用,抑制了位错的扩散。光荧光谱测试表明,室温下量子阱结构中心发光波长在2.3μm附近。     

相对论性转动变质量系统的Lie对称性与守恒量

给出相对论性转动变质量系统的d’Alembert原理和运动微分方程.利用运动微分方程在无限小变换下的不变性,建立相对论性转动变质量系统的Lie对称确定方程,得到结构方程和守恒量.并举例说明结果的应用 关键词： 相对论 转动 变质量 Lie对称     

Vertically coupled GaInAsP--InP microring resonators

Vertically coupled microring resonator channel-dropping filters are demonstrated in the GaInAsP-InP material system. These devices were fabricated without regrowth. In this method, low-loss single-mode waveguides are removed from the growth substrate and bonded to a GaAs transfer substrate with benzocyclobutene. This permits fabrication of vertically coupled waveguides on both sides of the epilayer. Optical quality facets are obtained by cleaving through the transfer substrate. Operation of single-mode, single-ring optical channel-dropping filters is demonstrated.     

高能电子衍射研究H钝化偏角Si衬底上Si,GexSi1-x的分子束外延生长模式

用高能电子衍射(RHEED)研究H钝化偏角Si衬底上Si,Ge_xSi_1-x材料的分子束外延(MBE)生长模式,发现经低温处理的H钝化Si衬底上要经过10nm左右的Si生长才能获得比较平整的表面.Si,Ge_xSi_1-x外延时的稳定表面均以双原子台阶为主,双原子台阶与单原子台阶并存的结构.Si双原子台阶上的Si二聚体列(dimerrow)取向垂直于台阶边缘,而Ge_xSi_1-x双原 关键词：     

太赫兹GaAs肖特基混频二极管高频特性分析

在太赫兹波段,存在几种新的高频效应会限制混频二极管的高频特性.应用热电子发射理论和隧道理论,研究了外延层肖特基二极管的高频特性,并以截止频率为品质因数对二极管进行优化设计.研究表明,当二极管工作频率大于等离子频率时,二极管相当于一个电容,失去了混频性能;提高基底掺杂浓度可以减小基底等离子共振效应;外延层等离子频率非常重要并且在研究外延层等离子共振效应时必须考虑传输时间效应;减小阳极直径、减小外延层厚度、提高外延层掺杂浓度可以提高二极管的工作频率.这对太赫兹波段室温混频器件的研制具有重要的参考价值.     

Triphenylene adsorption on Cu(111) and relevant graphene self-assembly

Investigations on adsorption behavior of triphenylene(TP) and subsequent graphene self-assembly on Cu(111) were carried out mainly by using scanning tunneling microscopy(STM).At monolayer coverage,TP molecules formed a longrange ordered adsorption structure on Cu(111) with an uniform orientation.Graphene self-assembly on the Cu(111) substrate with TP molecules as precursor was achieved by annealing the sample,and a large-scale graphene overlayer was successfully captured after the sample annealing up to 1000 K.Three different Moire patterns generated from relative rotational disorders between the graphene overlayer and the Cu(111) substrate were observed,one with 40 rotation between the graphene overlayer and the Cu(111) substrate with a periodicity of 2.93 nm,another with 70 rotation and 2.15 nm of the size of the Moire supercell,and the third with 100 rotation with a periodicity of 1.35 nm.