在(100)GaAs衬底上低温液相外延晶格匹配的In1-xGaxAs1-yPy层及其特性研究

介绍一种低温液相外延技术,可在650℃在GaAs衬底上生长晶格匹配和组份可重复的In1-xGaxAs1-yPy层。给出对外延层进行场发射扫描电镜观察、电子探针、X光双晶衍射、俄歇电子谱和光荧光测量得到的结果。结果表明外延层具有平坦的异质结界面和良好的晶体特性。同时研究了异质结界面的粗糙度和组份梯度变化区域的宽度和晶格失配率的关系。     

In1-xGaxAsyP1-y/InP异质界面晶格失配对外延晶体质量的影响

用X-射线双晶衍射,双晶形貌术和光致发光方法综合研究了In1-xGaxAsyP1-y/InP异质界面晶格失配对LPE晶体质量的影响。实验表明,异质界面晶格失配是导致外延层中位错和缺陷增多,杂质凝聚和辐射复合深中心增多的重要因素。     

p型Ga0.47In0.53AS接触层的生长

用过冷法在632-630℃生长了掺Zn的p型Ga0.47In0.53As接触层.研究了液相中Ga组分和Zn组分对GaxIn1-xAs/InP异质结晶格失配的影响,用一次外延技术生长了GaxIn1-xAs作接触层的GaInAsP/InP双异质结.     

MOCVD生长InP/GaInAsP DBR结构及相关材料特性

采用金属有机化学气相沉积(MOCVD)法InP衬底上成功地制备了GaxIn1-xAsyP1-y/InP交替生长的分布布喇格反射镜(DBR)结构以及与之相关的四元合金GaxIn1-xAsyP1-y和InP外延层。利用X射线衍射、扫描电子显微镜(SEM)、低温光致发光(PL)光谱等测量手段对材料的物理特性进行了表征。结果表明,在InP衬底上生长的InP外延层和四元合金GaxIn1-xAsyP1-y外延层77K光致发光(PL)谱线半峰全宽(FWHM)分别为9.3meV和32meV,说明形成DBRs结构的交替层均具有良好的光学质量。X射线衍射测量结果表明,四元合金GaxIn1-xAsyP1-y外延层与InP衬底之间的相对晶格失配仅为1×10-3。GaxIn1-xAsyP1-y/InP交替生长的DBR结构每层膜的光学厚度约为λ/4n(λ=1.55/μm)。根据多层膜增反原理计算得出当膜的周期数为23时,反射率可达90％。     

两步生长法生长的Inx Ga1-x As/GaAs材料及性质

利用LP-MOCVD技术,采用两步生长法在GaAs(100)单晶衬底上外延生长InxGa1-xAs材料。通过扫描电子显微镜( SEM)与原子力显微镜( AFM)观察了缓冲层厚度对外延层表面形貌、表面粗糙度的影响;利用X射线衍射( XRD)分析了缓冲层厚度对外延层结晶质量的影响;利用拉曼光谱分析了缓冲层厚度对外延层材料合金有序度的影响;通过透射电子显微镜( TEM)观察了外延层材料位错的分布状态,计算了外延层的位错密度。实验结果表明,两步生长法生长的Inx Ga1-x As/GaAs异质结材料的缓冲层厚度存在一个最优值。     

SiGe/Si异质结缺陷的光致发光研究

本文用光致发光(PL)光谱对Si0.87Ge0.13/Si异质结的缺陷进行了研究。对PL光谱中与SiGe外延层应变驰豫产生的失配位错相关的D-Band进行了分析,发现应变驰豫同时在SiGe层和Si衬底中诱生了位错。由于在PL光谱中观察到了D1而没有观察到D2,因此D1,D2很可能并不对应于相同的位错。通过进一步的分析,我们推测引起SiGe/Si异质结的PL光谱中D-Band的位错的微观结构很可能和Si-Si相关。     

光吸收法检测GaxIn1-xAsyP1-y/InP双异质结液相外延片的室温禁带宽度

用双光束分光光度计测定了GaxIn1-xAsyP1-y/InP双异质结外延片中四元层的禁带宽度,并和制得的发光管发射波长及计算值进行比较。部分样品用电子探针阴极荧光法对照。说明光吸收法简便、迅速、可靠。可对液相外延质量提供一定的评价。     

晶格失配对GaInP/In_xGa_(1-x)As/In_yGa_(1-y)As倒装三结太阳电池性能影响的分析

传统GaInP/(In)GaAs/Ge三结太阳电池因受其带隙组合的限制,转换效率再提升空间不大.倒装结构三结太阳电池因其更优的带隙组合期望可以得到更高的效率.基于细致平衡原理,结合P-N结形成机理,应用MATLAB语言对双晶格失配GaInP(1.90 eV)/In_xGa_(1-x)As/In_yGa_(1-y)As倒装结构三结太阳电池底、中电池的不同带隙组合进行模拟优化.模拟结果表明在AM1.5D,500倍聚光(500 suns)下,禁带宽度组合为1.90/1.38/0.94 eV的带隙最优,综合材料成本与试验条件,当顶、中电池最优厚度组合为4μm和3.2μm时理论转化效率高达51.22%,此时两个异质结的晶格失配度分别为0.17%和2.36%.忽略渐变缓冲层生长后底电池位错的影响,通过计算0.17%的晶格失配引入1.70×105cm~(-2)的插入位错密度,对比单晶格失配GaInP/GaAs/In_(0.32)Ga_(0.68)As(0.99 eV)倒装结构三结太阳电池光电转化效率仍提高了0.3%.     

1.3μm InGaAsP/InP双异质结发光管的特性研究

用液相外延技术生长的三层和四层InGaAsP/InP双异质结材料,制成了1.3μm InGaAsP/InP双异质结发光管。光功率输出(100mA)>1.0mW,最高2mW,尾纤输出功率(N.A.0.23,芯径60μ)>50μW。文中描述了器件的特性参数,还讨论了光功率的饱和特性和退化特性。     

电容-电压法研究AlxGa1-xN/GaN异质结压电极化效应

制备了基于调制掺杂Al0.22Ga0.78N/GaN异质结的Pt/Al0.22Ga0.78N/GaN肖特基二极管.由于Al0.22Ga0.78N势垒层中的极化场不同,不同Al0.22Ga0.78N势垒层厚度的二极管的电容-电压特性显著不同.根据对样品电容-电压特性的数值模拟,在Al0.22Ga0.78N势垒层厚度为30nm和45nm的样品中,异质界面的极化电荷面密度为6.78×1012cm-2.在Al0.22Ga0.78N势垒层厚度为75nm的样品中,极化电荷面密度降为1.30×1012cm-2.这种极化电荷面密度的降低是由于GaN上Al0.22Ga0.78N势垒层由于厚度增加而产生应变的部分弛豫.本工作也提供了一种定量表征AlxGa1-xN/GaN异质结中极化电荷面密度的方法.     

Nanoelectronic devices---resonant tunnelling diodes grown on InP substrates by molecular beam epitaxy with peak to valley current ratio of 17 at room temperature

This paper reports that InAs/In$_{0.53}$Ga$_{0.47}$As/AlAs resonant tunnelling diodes have been grown on InP substrates by molecular beam epitaxy. Peak to valley current ratio of these devices is 17 at 300K. A peak current density of 3kA/cm$^{2}$ has been obtained for diodes with AlAs barriers of ten monolayers, and an In$_{0.53}$Ga$_{0.47}$As well of eight monolayers with four monolayers of InAs insert layer. The effects of growth interruption for smoothing potential barrier interfaces have been investigated by high resolution transmission electron microscope.     

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.     

Mismatch and electron mobility in MBE GaxIn1−xas epitaxial layers on InP substrates

Composition inhomogeneity in nearly matched epilayers of the ternary semiconductor alloy Ga_xIn_1–xAs (x close to 0.47), grown by molecular beam epitaxy (MBE) on (001) InP substrates is correlated to variation of the lattice mismatch by x-ray imaging and local diffractometry. Misfit dislocations are shown to develop in areas of large misfit (above 2 × 10^–3) and are at the origin of a severe degradation of the electron mobility: an increase by a factor of about 4 in the intrinsic misfit (2.3 × 10^–3 compared to 0.6 × 10^–3) results in a 35 % reduction of the 77 K electron mobility.Part of this work has been done while this author was with Thomson-CSF Central Research Laboratory, Orsay, France     

采用纳米晶柱阵列衬底抑制失配位错形成的分子动力学模拟研究

运用分子动力学方法对纳米晶柱阵列衬底上铝簿膜的外延生长进行了模拟研究.所采用的原子间相互作用势为嵌入原子法(EAM)多体势.模拟结果表明：采用纳米晶柱阵列衬底可以在不形成失配位错的条件下释放其上生长的外延薄膜晶体中的失配应变,有效地抑制其中失配位错的形成,获得高质量的外延薄膜晶体;这种纳米晶柱阵列的几何设计应满足两个基本条件：1) 晶柱的横截面尺寸应大于对应温度下的晶柱热失稳临界尺寸,以克服纳米结构的热失稳,模拟显示700K下铝的热失稳临界尺寸为19nm;2) 晶柱的高度与间距之比应大于076,以保证 关键词： 失配位错 分子动力学 纳米晶柱 铝     

Formation of Ge self-assembled quantum dots on a SixGe1−x buffer layer

Ge self-assembled quantum dots (SAQDs) grown on a relaxed Si_0.75Ge_0.25 buffer layer were observed using an atomic force microscopy (AFM) and a transmission electron microscopy (TEM). The effect of buried misfit dislocations on the formation and the distribution of Ge SAQDs was extensively investigated. The Burgers vector determination of each buried dislocation using the g·b = 0 invisibility criterion with plane-view TEM micrographs shows that Ge SAQDs grow at specific positions related to the Burgers vectors of buried dislocations. The measurement of the lateral distance between a SAQD and the corresponding misfit dislocation with plane-view and cross-sectional TEM images reveals that SAQDs form at the intersections of the top surface with the slip planes of misfit dislocations. The stress field on the top surface due to misfit dislocations is computed, and it is found that the strain energy of the misfit dislocations provides the preferential formation sites for Ge SAQDs nucleation.     

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.     

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.     

Nano-islands on a composite substrate with misfit dislocations

Spatial arrangements of nano-islands (quantum dots) on the free surface of a composite two-layer substrate containing misfit dislocations of edge type are theoretically examined. It is shown that the elastic interaction between misfit dislocations and nano-islands is capable of causing coagulation of nano-islands. The coagulation of nano-islands is shown to be favourable when the upper-layer thickness is smaller than a critical thickness, H₀. An analytical form of H₀ is presented for the partial case with four-to-one correspondence between nano-islands and cells of the misfit dislocation network. Received: 5 December 2000 / Accepted: 29 March 2001 / Published online: 20 June 2001     

Misfit dislocations in nanocomposites with quantum dots,nanowires and their ensembles

We review theoretical concepts and experimental results on the physics of misfit dislocations in nanocomposite solids with quantum dots (QDs) and nanowires (quantum wires). Special attention is paid to thermodynamic theoretical models of formation of misfit dislocations in QDs and nanowires, including composite core–shell nanowires. The effects of misfit dislocations on the film growth mode during heteroepitaxy and phase transitions in QD systems are analysed. Experimental results and theoretical models of the ordered spatial arrangement of QDs growing on composite substrates with misfit dislocation networks are discussed. The influence of subsurface dislocations in composite substrates on the nucleation of QDs and nanowires on the substrate surface is considered. Models of misfit strain relaxation and dislocation formation in nanofilms on compliant substrates are also reviewed.     

Gax In1-xP缓冲层组分对InP自组装形貌影响的研究

应用缓冲层对自组装结构的作用能Er和自组装结构表面能E8 的协同作用分析了InP自组装结构在GaxIn1-xP缓冲层表面的形貌变化.计算发现缓冲层组分影响自组装结构的形貌.随着缓冲层与InP自组装结构之间应力的增加,InP岛倾向于拉长.理论计算还发现随着自组装结构体积的增大,自组装结构也随之拉长.而且缓冲层的参数决定了自组装结构最小能量状态时的体积大小.应用金属有机物化学气相沉积技术在GaAs衬底上生长了不同的InP/GaInP体系,并对实验得到的自组装体系形貌进行了分析.实验结果证实了以上的理论分析.