Influence of nitrogen and magnesium doping on the properties of ZnO films

Undoped ZnO and doped ZnO films were deposited on the MgO(111) substrates using oxygen plasma-assisted molecular beam expitaxy. The orientations of the grown ZnO thin film were investigated by in situ reflection high-energy electron diffraction and ex situ x-ray diffraction(XRD). The film roughness was measured by atomic force microscopy, which was correlated with the grain sizes determined by XRD. Synchrotron-based x-ray absorption spectroscopy was performed to study the doping effect on the electronic properties of the ZnO films, compared with density functional theory calculations.It is found that, nitrogen doping would hinder the growth of thin film, and generate the NOdefect, while magnesium doping promotes the quality of nitrogen-doped ZnO films, inhibiting(N_2)Oproduction and increasing nitrogen content.     

Strong anti-strain capacity of CoFeB/MgO interface on electronic structure and state coupling

Electronic structure and spin-related state coupling at ferromagnetic material(FM)/MgO(FM = Fe, CoFe, CoFeB)interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO interface, which is superior to the Fe/MgO and CoFe/MgO interfaces, can markedly maintain stable and effective coupling channels for majorityspin ?_1 state under large biaxial strain. Bonding interactions between Fe, Co, and B atoms and the electron transfer between Bloch states are responsible for the redistribution of the majority-spin ?_1 state, directly influencing the coupling effect for the strained interfaces. Layer-projected wave function of the majority-spin ?_1 state suggests slower decay rate and more stable transport property in the CoFeB/MgO interface, which is expected to maintain a higher tunneling magnetoresistance(TMR) value under large biaxial strain. This work reveals the internal mechanism for the state coupling at strained FM/MgO interfaces. This study may provide some references to the design and manufacturing of magnetic tunnel junctions with high tunneling magnetoresistance effect.     

Ⅱ-Ⅵ比对分子束外延生长的ZnO/ZnMgO超晶格的相结构调控

在Zn_1-xMg_xO中,x=0.4~0.6仍为一个岩盐矿和纤锌矿共存的结构,影响了其晶格质量。本文利用等离子体辅助的分子束外延设备在c面蓝宝石衬底上外延生长了ZnO/ZnMgO超晶格,并改变其生长过程中的Ⅱ-Ⅵ比,利用原子力显微镜、X射线衍射、透射谱和X射线光电子能谱对样品进行了表征分析。发现在较低氧分压下制备的样品结构以岩盐矿为主导,而在较高氧分压下两相共存并以纤锌矿为主。这种相分离现象与裂解氧原子的密度有关。     

基于LabVIEW的外延片光致发光扫描系统

概述了一套基于LabVIEW而搭建的半导体光致发光扫描系统.充分考虑扫描过程中由于外延片荧光信号过于微弱、不均匀背景光噪音可能产生的光谱采集失真以及随后分析谱图所存在的物理参量读取误差等因素,通过扣除背光源、隔离样品、高斯拟合等方式对测量过程进行优化.同时依托LabVIEW自身强大的仪器控制能力,如调用动态链接库与ActiveX控件实现了对光谱仪和平移台的通信与控制,结合其良好的数据分析及显示能力,实现了对外延片测量、读取、分析处理以及实时显示等过程的自动化整合,准确高效地提取出样品空间分辨的光致发光特性如峰位、光强等.最后初步分析了所用外延片的发光均匀性,得出波长分布与生长温度分布基本一致,肯定了保持生长腔内温度均匀一致的重要性.该系统不仅界面友好、简单易操作、实时性强、智能化高且搭建简单易行,极大地降低了成本,方便研究人员进行快捷准确的测试.     

GaAsP混晶中的DX中心

用高分辨率深能级瞬态谱、光照深能级瞬态谱及光电容谱方法,对不同组份的掺Te的GaAsP混晶进行了实验研究,结果表明,所有被测样品中同时存在三种施主深能级,其热发射激活能各为0.18,0.28,0.38eV.通过仔细测量与分析它们的电学和光学性质后,认为它们是由Te施主杂质形成的三种类DX中心,可能对应于Te运动会替位施主的不同原子构形. 关键词：     

GaN外延层中的缺陷研究

采用阴极射线致发光法观察金属有机物汽相外延法生长的具有不同表面形貌的GaN外延层中黄色发光带的强度分布.结果表明六角金字塔形表面形貌对发光强度分布的测量有很大影响.测量和比较表面镜面加工样品的黄色发光带强度分布、原子序数衬度和X射线波谱发现,黄色发光带的强度在含有O和C等杂质缺陷附近较强.高分辨透射电子显微镜观察表明,杂质缺陷区的晶格结构不同于GaN基质,以及位错和裂缝等由应力引起的缺陷.认为此类缺陷可能是生长过程中,杂质在结晶小丘合并处的V形凹角中的沉积所产生. 关键词：     

紫外及深紫外光子晶体微腔特性研究

运用平面波展开法并结合有限时域差分法仿真计算了紫外及深紫外波段光子晶体微腔能带和品质特性.结果表明:四角晶格结构的光子晶体相应能带中的光子禁带宽度较窄,不利于形成对紫外波段光子的局域和限制;通过调控和改变二维光子晶体的晶格类型和晶格常量以及设计单一甚至多缺陷的晶格,所形成的局域电场明显增强.优化填充因子,获得了品质因数可高达6 107的多缺陷光子晶体微腔结构.     

单层GaSe表面Fe原子吸附体系电子自旋性质调控

Ⅲ族金属单硫化物因其优越的光电和自旋电子特性而备受关注,实现对其自旋性质的有效调控是发展器件应用的关键.本文采用密度泛函理论系统地研究了GaSe表面Fe原子吸附体系的几何构型及自旋电子特性.Fe/GaSe体系中Fe吸附原子与最近邻Ga,Se原子存在较强的轨道耦合效应,使体系呈现100%自旋极化的半金属性.其自旋极化贡献主要来源于Fe-3d电子的转移及Fe-3d,Se-4p和Ga-4p轨道杂化效应.对于Fe双原子吸附体系,两Fe原子之间的自旋局域导致原本从Fe转移至GaSe的自旋极化电荷量减少,从而费米能级附近的单自旋通道转变为双自旋通道,费米能级处的自旋极化率转变为0.研究结果揭示了Fe_n/GaSe吸附体系自旋极化特性的形成和转变机制,可为未来二维自旋纳米器件的设计与构建提供参考.     

AlGaN量子结构及其紫外光源应用

AlGaN量子结构是实现高光效、高稳定紫外固态光源的核心.近年来,AlGaN半导体材料及其紫外光源应用研究取得了较大的进展.然而,AlGaN材料的生长制备只能在非平衡条件下完成,涉及的生长动力学问题十分复杂,制约了量子阱等结构品质的提高;材料带隙宽,p型掺杂难度大,激活效率低,限制了载流子注入;光学各向异性显著,不利于光从器件正面出射.因此,AlGaN基紫外、特别是深紫外波段器件性能还有待提高.本文梳理了AlGaN量子结构与紫外光源效率之间的关系,详细阐述和总结了有源区量子结构、p型掺杂量子结构以及光学各向异性调控等方面所面临的挑战及近年来的重要研究进展.     

AlGaN-Based Deep-Ultraviolet Light Emitting Diodes Fabricated on AlN/sapphire Template

We report on the growth and fabrication of deep ultraviolet （DUV） light emitting diodes （LEDs） on an AIN template which was grown on a pulsed atomic-layer epitaxial buffer layer. Threading dislocation densities in the AlN layer are greatly decreased with the introduction of this buffer layer. The crystalline quality of the AlGaN epilayer is further improved by using a low-temperature GaN interlayer between AlGaN and AlN. Electroluminescences of different DUV-LED devices at a wavelength of between 262 and 317nm are demonstrated. To improve the hole concentration of p-type AlGaN, Mg-doping with trimethylindium assistance approach is performed. It is found that the serial resistance of DUV-LED decreases and the performance of DUV-LED such as EL properties is improved.