面心立方晶体外延膜沉积生长中失配位错的结构与形成过程

用分子动力学方法对5%负失配条件下面心立方晶体铝薄膜的原子沉积外延生长进行了三维模拟.铝原子间的相互作用采用嵌入原子法(EAM)多体势计算.模拟结果再现了失配位错的形成现象.分析表明，失配位错在形成之初即呈现为Shockley扩展位错，即由两个伯格斯矢量为〈211〉/6的部分位错和其间的堆垛层错组成，两个部分位错的间距、即层错宽度为1.8 nm,与理论计算结果一致；外延晶体薄膜沉积生长中，位错对会发生滑移，但其间距保持稳定.进一步观察发现，该扩展位错产生于一种类似于“局部熔融-重结晶”的表层局部无序紊乱- 关键词： 失配位错 外延生长 薄膜 分子动力学 铝     

外延生长薄膜中失配位错形成条件的分子动力学模拟研究

运用分子动力学方法对负失配条件下的外延铝簿膜中失配位错的形成进行了模拟研究.所采 用的原子间相互作用势为嵌入原子法(EAM)多体势.模拟结果显示：在500K下长时间静态弛豫 ，表面和内部结构完整的外延膜在9—80原子层厚度范围内(约为其热力学临界厚度的3—40 倍)均不形成失配位错，而在薄膜表面预置一个单原子层厚、三个原子直径大小的凸台或凹 坑时，失配位错则能够在15个原子层厚的外延膜上迅速形成：在动态沉积生长条件下，表面 自然形成凹凸，初始厚度为9个原子层厚的外延膜在沉积生长中迅速形成失配位错.在三种条 件下，所形成的位错均为伯格斯矢量与失配方向平行的全刃位错.分析发现：在压应力作用 下，表面微凸台诱发了其侧薄膜内部原子的挤出，造成位错形核；而表面微凹坑则直接因压 应力作用形成了一个表面半位错环核. 关键词： 外延薄膜 失配位错 分子动力学 铝     

HgCdTe外延薄膜临界厚度的理论分析

基于在任意坐标系内应力与应变的关系、晶体弹性理论和位错滑移理论，研究了生长方向分别为［111］和［211］晶向，HgCdTe外延薄膜临界厚度与CdZnTe衬底中Zn组分和HgCdTe外延层中Cd组分的关系. 结果表明，HgCdTe外延薄膜临界厚度依赖于CdZnTe衬底中Zn组分和HgCdTe外延层中Cd组分的变化. 对于厚度为10μm，生长方向为［111］晶向的液相外延HgCdTe薄膜，要确保HgCdTe/CdZnTe无界面失配位错的前提条件，是CdZnTe衬底中Zn组分和HgCdTe外延层中Cd组分的波动必须分别在±0.225‰和±5‰范围内；而对于相同厚度，生长方向为［211］晶向的分子束外延HgCdTe薄膜，CdZnTe衬底中Zn组分和HgCdTe外延层中Cd组分的波动范围分别为±0.2‰和±4‰. 关键词： HgCdTe/CdZnTe 临界厚度 位错滑移理论 失配位错     

晶体相场法模拟异质外延过程中界面形态演化与晶向倾侧

采用晶体相场模型研究了异质外延过程中失配应变与应力弛豫对外延层界面形态演化的影响, 并对由衬底倾角引起的外延层晶向倾侧进行了分析.研究结果表明: 在有一定倾角的衬底晶体上进行外延生长时,若衬底和外延层之间失配度较大 (ε>0.08),外延层中弹性畸变能会以失配位错的形式释放, 最终薄膜以稳定的流动台阶形式生长且外延层的晶向倾角与衬底倾角呈近似线性关系. 而当衬底和外延层之间失配度较小(ε<0.04)不足以形成失配位错时, 外延层中弹性畸变能会以表面能的形式释放,最终使薄膜以岛状形态生长. 在高过冷度条件下,衬底倾角和失配度较大时,衬底和外延层之间会形成由大量位错规则排列而成的小角度晶界从而显著改变外延层的生长位向.     

Au/Cu(001)异质外延岛演化的分子动力学研究

利用分子动力学弛豫方法模拟了Au/Cu(001)异质外延生长初期Au异质外延岛的形貌演化，分析了Au外延岛演化过程中的局域应力及与基体结合能随表面岛尺寸的变化. 研究结果表明：当异质外延岛小于7×7时，外延岛原子分布呈现赝Cu点阵形貌；当外延岛达到8×8后，外延岛内开始出现失配位错，失配位错数量随外延岛尺寸的增加而增加. 局域压力分析指出，外延岛上原子之间的近邻环境不同导致了所受应力的差异，而外延岛的形变则是由外延岛原子的应力分布所决定. 研究还发现，失配位错的产生导致错位原子与基体原子之间的结合强度减弱，但相对增加了非错位原子与基体原子之间的结合强度. 关键词： 异质外延 表面形貌 局域压力 分子动力学模拟     

[111]晶向银纳米杆结构稳定性的分子动力学研究

采用三维分子动力学模拟方法和Finnis-Sinclair型多体势,以[111]晶向银纳米杆为研究对象,模拟研究不同尺寸纳米杆在不同温度弛豫过程中的动态平衡变化过程,分析研究弛豫后银纳米杆的稳态结构变化、平均势能的变化及其在不同时刻结构的演变过程.结果表明,温度对银纳米杆结构稳定性将产生重大影响,银纳米杆存在一临界失稳温度,当温度小于临界失稳温度时,体系保持完好线状晶态,当温度大于临界失稳温度小于熔点时,体系坍塌熔化后发生重结晶,体系形成由(111)和(100)面围成的多面体;随银纳米杆截面尺寸增大,其临界失稳温度、熔点均增大,当截面尺寸大于2 nm时,临界失稳温度趋近于熔点,失稳现象只在一很窄温度区域内存在.     

GaN衬底的腐蚀程度对ZnO纳米棒阵列光学性能的调控

研究了在湿法腐蚀Ga N衬底上生长的Zn O纳米棒阵列的微结构和光学性能。相比于未经腐蚀及腐蚀5 min、10 min的Ga N上生长的Zn O纳米棒阵列,在腐蚀8 min的Ga N上生长的Zn O纳米棒阵列最细密,光学性能最好,其相应PL光谱峰强积分比IUV/Ivis最大(70.92)。因为此时Ga N衬底中的位错基本全部在表面露头,Zn O容易附着而形成更多的形核种子,并且衬底的位错在表面的边缘有助于诱导Zn O晶体的外延生长,所以Zn O棒更加细密,晶体质量更高,从而光学性能更好。     

温度对Si上MOCVD-ZnO成核与薄膜生长特性的影响

采用金属有机化学气相沉积(MOCVD)方法在Si衬底上进行了ZnO的成核与薄膜生长研究。ZnO薄膜的形貌和结晶特性由成核和后期生长过程共同决定,初期成核温度决定了其尺寸和密度,进而影响后期ZnO主层的生长行为,但由于高温对后期ZnO纳米柱横向生长的抑制,纳米柱的尺寸并没有因为成核尺寸的增大而变大,因此在560℃得到了晶柱尺寸最大、密度最小的ZnO薄膜。最后通过改变成核温度,优化了ZnO外延膜的结晶质量。     

晶格失配对异质外延超薄膜生长中成核特性的影响

利用动力学蒙特卡罗方法模拟了异质外延超薄膜生长中的成核过程.研究了薄膜与衬底的晶格失配对超薄膜生长中成核密度、平均核尺寸、标度关系及生长模式的影响.结果发现产生压（张）应变的晶格负（正）失配使生长过程更早（迟）从成核区进入过渡区，失配越大，这一效应越明显.在相同的沉积条件下，负失配导致超薄膜形成较低的成核密度与较大的平均核尺寸，而正失配则相反.成核密度满足标度关系Ns≈(F/D)χ，随着失配度从-0.04增加到0.02，标度系数χ从0.37逐渐减小到0.33，对应超薄膜生长过程从包含二聚体扩散模式转变到无 关键词： 薄膜生长 成核 晶格失配 蒙特卡罗模拟     

异质薄膜外延生长中温度对失配位错出现厚度的影响

采用三维分子动力学模拟方法,使用Ercolessi和Adams建立的嵌入原子法（EAM）多体势函数,模拟了二维晶格失配铝膜晶体中失配位错的形成过程,通过体系结构和能量曲线两种方法研究了温度对位错出现厚度的影响。结果显示：温度对于失配位错的形成有影响。同等条件下,随着温度的增大,失配位错的出现厚度变薄。     

Structure of epitaxial crystal interfaces

Theoretical work on the structural influences of misfit, bonding and crystal dimension in epitaxial bicrystals is reviewed. The main contents relate to the model in which the inter-action between the crystal halves is represented by a periodic force acting at the interface, the crystals are approximated by elastic continua and the structure is assumed to be governed by lowest energy principles. In this model the misfit is accommodated by sequences of misfit dislocations located at the interface and/or overall lattice strains. The degree to which one or the other mechanism dominates depends on the size and shape of the crystal in addition to the elastic and bonding properties. Realistic approximations for various special cases, e.g. monolayers, thick crystals and intermediate thicknesses, are considered. An exact solution covering the entire spectrum of interest does not exist.     

Ordered step arrays on evaporated As (0001) vicinal surfaces

A computational procedure dealing with a one-dimensional epitaxial monolayer model was developed in part I. In this part it is extended and applied to the two-dimensional case, allowing for misfit along two perpendicular interfacial directions. The model employed differs slightly from that used by van der Merwe in that the overgrowth film is simulated by a plane of atoms linked to each other by elastic springs. This allows for an exact determination of the equilibrium boundary conditions. The results show (i) that the rectangular boundary edge is slightly deformed, lateral contractions occurring where the misfit dislocations intersect the boundary edge, (ii) that the dependence of stable structures on misfit is in good agreement with the analytical results of van der Merwe, (iii) that misfit dislocations are introduced alternately at the mutually perpendicular edges of a system having quadratic symmetry, (iv) that a segmented dependence of lowest energy on crystal size is obtained, one segment for each additional dislocation, (v) that a saw-toothed dependence of average strain on crystal size, in qualitative agreement with the experimental work of Vincent, results and (vi) that a fine structure in the energy curves results from discrete adatom peripheral growth.     

GaAs/AlGaAs分子束外延材料的X射线双晶形貌观察

本文介绍了用非平行非对称(+、-)双晶X射线形貌术研究Ⅲ—Ⅴ族化合物外延晶体的设置和原理。分析了外延后形成的弯曲样品造成的衍射效应。对分子束外延(MBE)法生长的GaAs/AlGaAs衬底和外延层分别进行了X射线形貌术观察。讨论了外延层中存在的失配位错、生长小丘、沾污和局部微差取向等缺陷。对位错的组态和来源进行了初步分析。本实验结果也表明,有应变超晶格过渡层的MBE法对生长优质的GaAs/AlGaAs外延片是有利的。     

Faceting transitions in crystal growth and heteroepitaxial growth in the anisotropic phase-field crystal model

We modify the anisotropic phase-field crystal model(APFC),and present a semi-implicit spectral method to numerically solve the dynamic equation of the APFC model.The process results in the acceleration of computations by orders of magnitude relative to the conventional explicit finite-difference scheme,thereby,allowing us to work on a large system and for a long time.The faceting transitions introduced by the increasing anisotropy in crystal growth are then discussed.In particular,we investigate the morphological evolution in heteroepitaxial growth of our model.A new formation mechanism of misfit dislocations caused by vacancy trapping is found.The regular array of misfit dislocations produces a small-angle grain boundary under the right conditions,and it could significantly change the growth orientation of epitaxial layers.     

Generation and evolution of partial misfit dislocations and stacking faults in thin-film heterostructures

An analysis is made of the specific features in the generation and evolution of partial misfit dislocations at the vertices of V-shaped configurations of stacking fault bands, which terminate in the bulk of the growing film at 90° partial Shockley dislocations. The critical thicknesses h _c of an epitaxial film, at which generation of such defect configurations becomes energetically favorable, are calculated. It is shown that at small misfits, the first to be generated are perfect misfit dislocations and at large misfits, partial ones, which are located at the vertices of V-shaped stacking-fault band configurations emerging onto the film surface. Possible further evolution of stacking-fault band configurations with increasing film thickness are studied.     

Modeling elasticity in crystal growth

A new model of crystal growth is presented that describes the phenomena on atomic length and diffusive time scales. The former incorporates elastic and plastic deformation in a natural manner, and the latter enables access to time scales much larger than conventional atomic methods. The model is shown to be consistent with the predictions of Read and Shockley for grain boundary energy, and Matthews and Blakeslee for misfit dislocations in epitaxial growth.     

The size dependence of equilibrium elastic strain in finite epitaxial islands

The equilibrium elastic strain in epitaxial islands of small size is shown to have a sawtooth dependence on island width by minimizing the systems energy as calculated from a periodic interaction potential between substrate and overgrowth. Such a sawtooth variation is consistent with Vincent's observations and idea that a given misfit between island and substrate may not be entirely accommodated by an integral number of identical misfit dislocations, and hence, the remaining misfit, which depends in part on island width, will be accommodated by residual elastic strain. The present calculations of mechanical equilibrium support these ideas and further reveal that in some cases misfit dislocations may over compensate for the misfit, thereby introducing an elastic strain of opposite sign to that normally expected. Other results of the calculations are in agreement with earlier theoretical and experimental observations.