X射线三轴晶衍射法测量半绝缘GaAs单晶的化学配比

采用X射线三轴晶衍射法,根据As间隙原子对作为过量As在GaAs单晶材料中存在的主要形式的模型,可以无损、高精度测量半绝缘GaAs单晶的化学配比.并探讨了引起晶格变化的原因及其与熔体组分的关系,对于制备高质量GaAs单晶及其光电器件具有重要的意义.     

高压液封原位合成直拉半绝缘GaAs单晶

<正>近年来国际上对场效应器件及集成电路用半绝缘GaAs单晶开展了大量研究工作,取得了一定的进展.目前采用下述几种方法生长GaAs单晶:(1)高压液封原位合成直拉法,(2)低压液封直拉法(预合成多晶料),(3)低压液封直接合成直拉法,(4)水平三温区法.其中方法(1)是一种液Ga和液As反应合成GaAs后直拉得到单晶的方法.其余均为液Ga和As蒸气缓慢反应合成GaAs后再生长单晶的方法.     

GaAs单晶外延层薄膜厚度的X射线测定法

利用X射线动力学衍射的结果,通过GaAs单晶Ga、As的K-吸收限特性在带有单晶附件的X射线衍射仪上测定GaAs单晶外延层薄膜厚度。     

用LE—VB法生长大直径低位错半绝缘GaAs单晶

<正>LEC法要求有适当的轴向和径向的温度梯度来控制GaAs晶体的直径,但为了降低GaAs单晶的位错密度,又需要降低它们的温度梯度.对大直径GaAs单晶的生长,上述矛盾更为突出.HB法虽然能生长低位错GaAs单晶,但对大直径圆形晶体的生长却无能为力.通常采用VGF(垂直梯度凝固)法来解决大直径和低位错的矛盾.但由于VGF法中要有As源来     

制备均匀半绝缘GaAs单晶新工艺As注入熔体法(AI-LEC法)

日立公司最近研究出一种制备均匀半绝缘GaAs单晶的新方法.方法是在一般LEC拉晶装置的坩埚上方装一个石英储As器,储As器外绕辅助加热器,加热器和储As器均可上、下移动将大约1公斤的Ga、As混合物置于坩埚内,高压原位直接合成GaAs后,立即将储As器中As(30～50g)徐徐注入GaAs熔体,直至拉晶过程结束.这种方法可使拉晶过程中熔体组成保持化学计量比(0.497～0.501).最后获得的结果是:     

水平法生长GaAs单晶中砷微沉淀及碳微夹杂的研究

做为衬底材料的各种掺杂和不掺杂的GaAs单晶材料中的微沉淀及微夹杂,都影响GaAs器件及集成电路的性能。我们用JEM-1000超高压电镜,采用选区电子衍射技术,研究了掺Si、掺Cr及纯度水平法生长(HB)低位错GaAs单晶中的As和C微小第二相的形态及结构。采用约化胞法、借助电子计算机计算约化胞数据表,来分析标定电子衍射花样确定结构。经电子衍射分析表明,掺Si、掺Cr及纯度水平法生(?)GaAs单晶中有二种结构类型As沉淀、一种为六方晶系As(a_0=3.76埃,c=10.55埃),另一种为正交晶系As(a_0=3.63埃,b_0=4.45埃,C_0=10.96埃),而且它们往往与α-方石英微沉淀(或微夹杂)或c微夹杂、或Cr_n As微沉淀共存(照片1)。电子衍射分析还表明,GaAs单晶中c的微夹杂是简单立方结构(a_0=5.55埃)。为了进一步验证水平法生长GaAs单晶中有c微夹杂存在,用JXA—50A扫描电子探针分析观察了,刚刚做好的电镜样品。     

半绝缘GaAs单晶的研制

本文介绍原位合成生长半绝缘GaAs单晶研究与杂质分析结果。Ga、As比的控制,坩埚材料,热处理等条件均对单晶质量产生影响。制得直径75mm、重2.2kg的半绝缘GaAs单晶。典型电参数为:ρ300K≥10~7Ω·cm,μ300K=5380cm~2/V·s。经850℃热处理15分钟,Rs>10~7/□。利用本实验制得的半绝缘GaAs单晶,经外延、离子注入后制成的场效应管性能良好。     

VB-GaAs单晶生长技术

半导体GaAs单晶材料通常用于制作激光二极管和高亮度发光二极管.对于激光二极管而言,特别需要低位错材料.简要阐述了垂直布里奇曼(VB)法生长GaAs单晶材料的动力学原理及VB-GaAs单晶的生长技术.本技术可实现低位错GaAs单晶材料的生长,拉制的50 mm掺硅GaAs单晶的平均位错密度为500 cm-2,最大为1000 cm-2.     

用X射线衍射研究缓冲层对GaInAs材料的影响

用分子束外延方法制备了具有GaInAs组分渐变缓冲层和不具有GaInAs组分渐变缓冲层的Ga0.9In0.1As/GaAs结构的外延材料。利用高分辨率X射线衍射法(HRXRD)对制备的两种样品分别进行了测试分析。实验结果表明,GaInAs组分渐变缓冲层对外延生长在GaAs衬底上的Ga0.9In0.1As外延材料的晶体质量具有显著的改善作用,极大降低了由于外延层与衬底晶格不匹配所带来的影响。从X射线倒易空间衍射(RSM)二维图谱结果来看,具有GaInAs组分渐变缓冲层结构的样品,其Ga0.9In0.1As外延层与GaInAs组分渐变缓冲层接近完全弛豫,Ga0.9In0.1As外延层的应变降低,表面残留应力小于0.06%,同时,GaAs衬底与Ga0.9In0.1As外延层之间的偏移夹角明显变小。     

注S-SI GaAs晶体中的缺陷

对注S-SI GaAs单晶作光致发光测试,确定了两个缺陷能级.1.239eV峰可能是镓空位(V_(Ga))与S的络合物;1.408eV峰是由注S引起SI-GaAs衬底中残留杂质Si发生迁移,增加了Si受主(Si_(As))密度,部份Si_(As)与砷空位(V_(As))相互作用形成V_(As)-Si_(As)络合物而产生的.     

短周期AlGaAs/GaAs超晶格的MOCVD生长及X射线衍射研究

生长了短周期 Al Ga As/ Ga As超晶格 ,并通过双晶 X射线衍射谱 ,对 MOCVD超薄层Al Ga As、Ga As的生长进行了研究。从衍射谱卫星峰的级数及 Pendellosong干涉条纹的出现 ,定性地对晶格结构及界面作出评价。 X光衍射测量结果与 HEMT结构电学性能测试结果有较好的对应关系。     

分子束外延ZnSe/ZnSxSe1-x超晶格光学特性

用分子束外延方法在GaAs(100)衬底上生长了高质量的ZnSe/ZnSxSe1-x(x=0.12)超晶格结构，通过X射线衍射谱和光致发光谱，对其结构特性和光学特性进行了研究。结果表明：在4．4K温度下，超晶格样品显示较强的蓝光发射，主发光峰对应于阱层ZnSe的基态电子到重空穴基态的自由激子跃迁，而且其峰位相对于ZnSe薄膜的自由激子峰有明显蓝移。从理论上分析计算了由变就和量子限制效应引起的自由激妇峰位移动，理论和实验结果相吻合。     

分子束外延ZnSe/ZnS_xSe_(1-x)超晶格光学特性

用分子束外延方法在 Ga As(10 0 )衬底上生长了高质量的 Zn Se/ Zn Sx Se1 - x(x=0 .12 )超晶格结构 ,通过 X射线衍射谱和光致发光谱 ,对其结构特性和光学特性进行了研究 .结果表明 :在 4 .4 K温度下 ,超晶格样品显示较强的蓝光发射 ,主发光峰对应于阱层 Zn Se的基态电子到重空穴基态的自由激子跃迁 ,而且其峰位相对于 Zn Se薄膜的自由激子峰有明显蓝移 .从理论上分析计算了由应变和量子限制效应引起的自由激子峰位移动 ,理论和实验结果相吻合     

低压MOCVD生长ZnO单晶薄膜的制备与性质

利用 LP-MOCVD生长技术 ,采用 Zn(C2 H5) 2 作 Zn源和 CO2 作氧源 ,在 (0 0 0 2 )蓝宝石衬底上获得了沿 c轴取向高度一致的 Zn O单晶薄膜。通过对其吸收谱的曲线拟合 ,得到室温下 Zn O薄膜的光学带隙为 3 .2 45e V。在样品的室温光荧光谱 (PL)中观察到对应于带边发射的较强的发光峰 ,对样品中蓝带的产生原因进行了讨论     

AlGaAs／AlAs体系DBR的MOCVD生长及表征

设计并利用MOCVD在（311）GaAs衬底上生长了12．5个周期的Al0．6Ga0．4As／AlAs黄绿光分布式Bragg反射（DBR）体系，测量了白光反光谱及其外延片峰值波长分布，反射率90％以上，波长不均匀性在1．0％以下；利用了X射线双晶衍射对其进行结构表征，580nm波长DBR结构周期为84．5nm。     

Interfacial Strain‐Induced Oxygen Disorder as the Cause of Enhanced Critical Current Density in Superconducting Thin Films

To understand the origin of the increase in critical current density of rare earth barium cuprate superconductor thin films with decreasing thickness, a series of sub‐300‐nm EuBa₂Cu₃O_7?δ thin films deposited on SrTiO₃ substrates are studied by X‐ray diffraction and electrical transport measurements. The out‐of‐plane crystallographic mosaic tilt and the out‐of‐plane microstrain both increase with decreasing film thickness. The calculated density of c‐axis threading dislocations matches the extent of the observed low‐field enhancement in critical current density for fields applied parallel to c. The in‐plane mosaic twist and in‐plane microstrain are both around twice the magnitude of the out‐of‐plane values, and both increase with decreasing film thickness. The results are consistent with the observed stronger field enhancement in critical current density for fields applied parallel to ab. The lattice parameter variation with thickness is not as expected from consideration of the biaxial strain with the substrate, indicative of in‐plane microstrain accommodation by oxygen disorder. Collectively, the results point to an enhancement of critical current by interfacial strain induced oxygen disorder which is greatest closest to the film‐substrate interface. The findings of this study have important implications for other thin functional oxide perovskite films and nanostructures where surface and interfacial strains dominate the properties.     

X射线衍射、X射线光电子能谱对PtSi薄膜形成机理的研究

促使物相尽可能地向Pt2Si和PtSi 转化,是PtSi薄膜工艺研究中的重要工作。文中通过用X射线衍射（ XRD）、X射线光电子能谱（XPS）微观分析手段对PtSi薄膜形成物相分步观察,研究了长时间变温退火、真空退火以及真空和保护气体（N2和H2）退火等工艺条件对溅射PtSi薄膜物相形成的影响。结果表明,氢气气氛退火能提高薄膜质量;真空退火可以减少氧元素对成膜的影响。     

GaAs高温退火过程中热应力对晶体缺陷的影响

用X射线衍射技术分析在高温退火过程中GaAs晶片和石墨接触区域的热应力对晶体缺陷的影响.结果表明:在高温退火条件下,GaAs晶体与石墨接触区域散热不均匀造成的热应力,致使该区域范性形变,从而产生高密度的位错.GaAs晶体中的刃型位错受热应力作用向垂直滑移面的平面移动,聚集后可形成小角晶界,从而导致GaAs晶体的晶格参数和取向均发生变化     

Direct Evidence of Cation Disorder in Thermoelectric Lead Chalcogenides PbTe and PbS

The extraordinary thermoelectric properties of lead chalcogenides have attracted huge interest in part due to their unexpected low thermal conductivity. Here, it is shown that anharmonicity and large cation disorder are present in both PbTe and PbS, based on elaborate charge density visualization using synchrotron powder X‐ray diffraction (SPXRD) data analyzed with the maximum entropy method (MEM). In both systems, the cation disorder increases with increasing temperature, whereas the Te/S anions appear to be centered on the expected lattice positions. Even at the lowest temperatures of 105 K, the lead ion is on average displaced by ≈0.2 Å from the rock‐salt lattice position, creating a strong phonon scattering mechanism. These findings provide a clue to understanding the excellent thermoelectric performance of crystals with atomic disorder. The SPXRD–MEM approach can be applied in general opening up for widespread characterization of subtle structural features in crystals with unusual properties.     

Stoichiometry Controlled,Single‐Crystalline Bi2Te3 Nanowires for Transport in the Basal Plane

Thermoelectric Bi₂Te₃ based bulk materials are widely used for solid‐state refrigeration and power‐generation at room temperature. For low‐dimensional and nanostructured thermoelectric materials an increase of the thermoelectric figure of merit ZT is predicted due to quantum confinement and phonon scattering at interfaces. Therefore, the fabrication of Bi₂Te₃ nanowires, thin films, and nanostructured bulk materials has become an important and active field of research. Stoichiometric Bi₂Te₃ nanowires with diameters of 50–80 nm and a length of 56 μm are grown by a potential‐pulsed electrochemical deposition in a nanostructured Al₂O₃ matrix. By transmission electron microscopy (TEM), dark‐field images together with electron diffraction reveal single‐crystalline wires, no grain boundaries can be detected. The stoichiometry control of the wires by high‐accuracy, quantitative enegy‐dispersive X‐ray spectroscopy (EDX) in the TEM instrument is of paramount importance for successfully implementing the growth technology. Combined electron diffraction and EDX spectroscopy in the TEM unambiguously prove the correct crystal structure and stoichiometry of the Bi₂Te₃ nanowires. X‐ray and electron diffraction reveal growth along the [110] and [210] directions and the c axis of the Bi₂Te₃ structure lies perpendicular to the wire axis. For the first time single crystalline, stoichiometric Bi₂Te₃ nanowires are grown that allow transport in the basal plane without being affected by grain boundaries.