基于GaAs/AlGaAs量子阱材料的光致折射率分析

初步分析了基于GaAs/AlGaAs量子阱材料的光致折射率变化规律,利用自洽方法计算了光生载流子浓度对传输光的折射率改变量。当805nm的控制光注入强度为6×103W/cm2(8×103W/cm2)时,在垂直材料表面内1μm深度处,对1.55μm(1.31μm)的传输光可以达到-1-0 2的折射率变化量级。与GaAs体材料相比,量子阱材料所需控制光强度能够减少约20%,有助于降低全光开关与全光调制器的功耗。     

852 nm半导体激光器量子阱设计与外延生长

设计并外延生长了具有高温度稳定性的InAlGaAs/AlGaAs应变量子阱激光器,用于解决852 nm半导体激光器在高温环境下工作时的波长漂移问题.基于理论模型,计算并模拟对比了InAlGaAs,InGaAsP,InGaAs和GaAs量子阱的增益及其增益峰值波长随温度的漂移,结果显示,采用In0.15Al0.11Ga0.74As作为852 nm半导体激光器的量子阱可以使器件同时具有较高的增益峰值和良好的波长温漂稳定性.使用金属有机化合物气相淀积(MOCVD)外延生长了In0.15Al0.11Ga0.74As/Al03Ga07As有源区,通过反射各向异性谱(RAS)在线监测和PL谱研究了InAlGaAs/AlGaAs界面的外延质量,实验证明了通过降低生长温度和在InAlGaAs/AlGaAs界面处使用中断时间,可以有效抑制In析出,从而获得InAlGaAs/AlGaAs陡峭界面.最后,采用优化后的外延生长条件,研制出了InAlGaAs/AlGaAs应变量子阱激光器.实验测试结果显示,其光谱半高宽为1.1 nm,斜率效率为0.64 W/A,激射波长随温度漂移为0.256 nm/K.理论计算结果与实验测试结果相吻合,证明器件性能满足在高温环境下工作的要求.     

PL Mapping在SI-GaAs材料与器件性能关系研究中的应用

本文详细研究了扫描光荧光谱(PL Mapping)在半绝缘砷化镓(SI-GaAs)材料与器件性能关系中的应用,实验结果表明SI-GaAs单晶的 PL Mapping均匀性对器件性能有着至关重要的影响,所以在为制备器件选择优质的SI-GaAs材料时,除了电阻率、迁移率、位错密度、碳含量、EL2浓度及其均匀性外,PL Mapping也是表征材料质量的一个重要参数。     

Si(111)和Si(100)衬底上AlN薄膜的激光分子束外延生长特征

采用激光分子束外延技术在Si(111)和Si(100)衬底上制备了AlN薄膜,研究了衬底温度和激光能量对薄膜物相结构和形貌的影响。结果表明:低的激光能量和高的衬底温度有益于薄膜的取向度和表面质量;激光能量为100mJ时,Si(111)衬底上的AlN薄膜呈单一的h-AlN(002)取向,Si(100)衬底上的薄膜在600℃时出现小的h-AlN(100)衍射峰,在700℃时呈微弱的h-AlN(002)取向;在Si(111)衬底上更易生长出取向度高的AlN薄膜。     

应用L-MBE方法制备ZnO薄膜的结构和光学特性

用激光分子束外延(Laser Molecular Beam Epitaxy,L-MBE)设备在p型Si(111)衬底上制备了不同衬底温度和不同氧压的ZnO薄膜,用X射线衍射仪(XRD)和原子力显微镜(AFM)分别对薄膜的结构和形貌进行了分析,用He-Cd激光(325nm)激发的光致发光测试系统对薄膜进行了荧光光谱分析。研究发现,在衬底温度为400℃,氧压1Pa左右所制备的ZnO薄膜表面比较均匀致密,晶粒生长较充分,有较高的结晶质量和发光强度。ZnO薄膜的近带边发射与薄膜的结晶质量和化学配比均有关系。     

Na_2S钝化的GaAs表面光荧光特性的研究

本文用RPM2050型快速扫描光荧光谱仪(PL Mapper)研究经过Na2S.9H2O醇饱 和溶液钝化处理后GaAs表面的光荧光特性。结果表明,GaAs表面经过硫钝化处理后,可 大大降低复合速度改善发光效率。     

1024×1024GaAs量子阱红外光电探测器成像列阵

美国哥达德空间飞行中心、陆军研究实验室及喷气推进实验室的研究人员通过合作，已研制出一种1024像素×1024像素8．4pm～9．0pm红外焦平面列阵。这个具有1M像素的探测器列阵是一个混成器件，它是通过用点焊方法将洛克韦尔公司出品的TCM8050硅读出集成电路焊接在一个GaAs量子阱红外光电探测器列阵上制备而成的。研究人员将该列阵装入一个成像系统，     

多层复杂结构GaAs基光电阴极的光学性能和量子效率

为了更好地了解这两种结构对光电发射性能的影响,设计和生长了两种结构的光电阴极样品,对其光电发射性能进行比较,并利用薄膜光学的矩阵法推导的光学性能公式以及通过求解一维连续性方程推导的量子效率模型,对比研究了光电阴极发射层、缓冲层厚度变化以及AlxGa1-xAs缓冲层中Al组分变化对两种结构光电阴极光学性能和量子效率的影响。这两种结构对光电发射性能的影响机理并不相同,因此作用效果也大不一样。渐变带隙结构的光电阴极通过引入内建电场和减少界面复合从而提升光电发射性能,而DBR结构则通过形成法布里-罗伯共振腔,使得特定波长的入射光在共振腔内来回反射进而被多次吸收,从而加强光电发射。激活实验结果表明,DBR结构样品的发射效率与渐变带隙结构相比具有明显优势,尤其是在755,808和880 nm处有更高的发射效率峰值,可分别提升37.5%,38.9%和47.0%。最后利用模型拟合了量子效率曲线,验证了光学性能参量对复杂结构光电阴极的重要影响及理论模型的合理性。     

Voltage-dependent imaging of antimony on the GaAs(110) surface

Using a scanning tunnelling microscope, voltage-dependent imaging of antimony on the GaAs(110) surface has been performed. For negative sample voltages, the images reflect surface dangling bonds. Depending on the magnitude of the voltage, either one or both of the Sb atoms in the surface unit cell are seen. At positive voltage the density of surface-states is observed to be greatly reduced compared to negative voltages. The results are analysed within the context of a simple tight-binding model for a one-dimensional biatomic chain.     

TEM characterization of self-organized CdSe/ZnSe quantum dots

CdSe quantum dots (QDs) grown on ZnSe were investigated by various transmission electron microscopy (TEM) techniques including diffraction contrast imaging, high-resolution and analytical transmission electron microscopy both of plan-view as well as cross-section specimens. The size of the QDs ranges from about 5–50 nm, where from the contrast features in plan-view imaging two classes can be differentiated. In the features of the smaller dots there is no inner fine structure resolvable. The larger ones exhibit contrast features of fourfold symmetry as expected for pyramid-like islands. Corresponding simulations of diffraction contrast images of truncated CdSe pyramids with the edges of the basal plane orientated parallel to <100> are in relatively good agreement with this assumption. In TEM diffraction contrast imaging of cross-section samples the locations of the quantum dots are visualized by additional dark contrast features. The QDs have a distinct larger extension in growth direction compared to the almost uniformly thick CdSe wetting layer. The presence of the CdSe QDs was also confirmed by energy-dispersive X-ray spectroscopy.     

Defect formation in self-assembling quantum dots of InGaAs on GaAs: a case study of direct measurements of local strain from HREM

The growth and defect structures in free-standing self-assembled In_0.6Ga_0.4As quantum dots (QDs) grown on (001) GaAs by solid source molecular beam epitaxy has been investigated. The QDs are elongated along [1¯ 1 0]. At a nominal thickness of eight monolayers defect complexes, associated with intrinsic stacking faults, have been generally observed on both sides of a QD in (1¯ 1 0) cross-section. The total defect vector of such defect complexes is a /3 <111>. Local strain components on {111} slip planes in the QDs without defects have been measured directly from digitized high-resolution electron microscopy images. The distortion on the two sets of {111} planes of a (1¯ 1 0) cross-section is different owing to elastic relaxation. The results of strain measurements suggest that a 60° dislocation nucleates first on the set of {111} planes of higher contractive shear strain, i.e. (111) planes on the right side of the QDs, and (1¯ 1¯ 1) planes on the left side. A 30° partial dislocation forms subsequently on the other set of {111} planes, i.e. (1¯ 1¯ 1) planes on the right side of the QDs and (111) planes on the left side, when the 60° dislocation glides down towards the In_0.6Ga_0.4As/GaAs interface, as a result of the additional strain field of the 60° dislocation. The efficiency of the defect complexes in strain relaxation of the QDs has been shown by strain measurements in QDs with the presence of defects.     

The preparation of plan-view TEM samples of ZnSe epilayers on GaAs (100) substrates by selective photoelectrochemical etching

Selective photoelectrochemical etching has been employed in order to thin samples of ZnSe epilayers grown on GaAs (100) substrates by metal organic vapour phase epitaxy (MOVPE). The difference in band-gap between the epilayer and substrate was exploited such that only the substrate material was subject to the etching procedure. Samples prepared in this way have been studied by transmission electron microscopy (TEM) and the results of these studies are compared to results obtained by alternative cross-sectional analysis.     

Electron tomography of III‐V quantum dots using dark field 002 imaging conditions

We present an evaluation of electron tomography of buried InAs quantum dots using dark field 002 imaging conditions. The compositional sensitivity of this imaging condition gives strong contrast among III‐V materials of differing compositions and, in principle, should allow an accurate 3D model of the buried structures to be produced. The large extinction distance allows specimens several hundred nanometres in thickness to be examined and reduces the effect of strain contrast in the images, with the advantage that it can be performed using conventional transmission electron microscopy techniques. A two‐beam condition must be maintained for all images, and the presence of other strong diffraction effects at certain specimen orientation results reduces the number of orientations available for tomography by approximately 10%. The data presented here are limited due to a lack of angular range in the data set but we find that an acceptable 3D model of a buried quantum dot may be produced by imposing cylindrical symmetry on the data set.     

Sectional voltage contrast topography of quantum well diodes

Detailed scanning electron microscopy (SEM) of an operational quantum well laser was performed using the differential voltage contrast (DVC) method. Quantitative measurements of Fermi energies in an operational device at high magnifications were possible due to a new calibration procedure described in this study. Precise tailoring of digitized DVC images of an operational laser taken at high and low magnifications is described. The ability to record and to analyze very detailed quasi‐Fermi energy (QFE) profiles across an operational laser or transistor with 30‐Angstrom features improved the DVC technique. A layered GaAs/Ga_xAl_1?xAs/In_yGa_1?y As quantum well light emitter was tested through various operational steps, that is, inverse population, threshold, and full emission. The detailed QFE profile allowed us to analyze collective electron behavior at various steps of operation of the laser.     

VO2/GaAs异质结的制备及其光电特性研究

采用直流磁控溅射和后退火氧化工艺在p型GaAs单晶衬底上成功制备了n-VO_2/pGaAs异质结,研究了不同退火温度和退火时间对VO_2/GaAs异质结性能的影响,并分析其结晶取向、化学组分、膜层质量以及光电特性。结果表明,在退火时间2 h和退火温度693 K下能得到相变性能最佳的VO_2薄膜,相变前后电阻变化约2个数量级。VO_2/GaAs异质结在308 K、318 K和328 K温度下具有较好的整流特性,对应温度下的阈值跳变电压分别为6.9 V、6.6 V和6.2 V,该结果为基于VO_2相变特性的异质结光电器件的设计与应用提供了可行性。     

油酸与亚油酸在Fe(110)面上吸附和剪切的分子动力学模拟

为了揭示植物油主要成分油酸和亚油酸对润滑作用的影响,采用分子动力学模拟的方法,对不同比例油酸和亚油酸在Fe(110)面上进行吸附和剪切计算。构建油酸、亚油酸和Fe模型,并对所构建模型进行几何优化,选择Fe(110)面为吸附面,定义了结合能,进行吸附计算得到不同比例油酸和亚油酸的结合能。构建四层的剪切模型,加载COMPASS力场,采用Forcite-Confined Shear模块进行剪切模拟,得到摩擦表面3个方向的力,进而计算出摩擦因数。结果表明:金属基底对油酸的吸附能比亚油酸大,剪切性比亚油酸好;虽然油酸比亚油酸的吸附性和剪切性更好,但吸附能和剪切性能并不是随着油酸含量的增加而增加,而是在油酸和亚油酸的体积比为3∶1时吸附能最大,剪切性能最好。