Scattering behaviours to the two-dimensional electron gasinduced by the Al composition fluctuation in AlxGa1-xNbarrier in AlxGa1-xN/GaN heterostructures

<正>This paper reports that cathodoluminescence（CL） measurements have been done to study the alloy fluctuation of the Al_0.3Ga_0.7N layer in Al_0.3Ga_0.7N/GaN heterostructures.The CL images and linescanning results demonstrate the existence of compositional fluctuation of Al in the Al_0.3Ga_0.7N barrier.A model using aδ-shape perturbation Hamilton function has been proposed to simulate the scattering probability of the two dimensional electron gases （2DEG） induced by Al composition fluctuation.Two factors,including conduction band fluctuation and polarization electric field variation,induced by the Al composition fluctuation have been taken into account.The scattering relaxation time induced by both factors has been estimated to be 0.31 ns and 0.0078 ns,respectively,indicating that the variation of the piezoelectric field is dominant in the scattering of the 2DEG induced by Al fluctuation.     

用Mg离子注入提高p型GaN的空穴浓度

研究了离子注入对金属有机化学气相淀积法生长的Mg掺杂GaN性质的影响.样品在800℃退火1小时后,我们获得了空穴浓度达8.28×1017cm-3的p型GaN.这一结果可以用于GaN基器件的p型层的欧姆接触.     

大气压交流辉光放电等离子体气—液相化学反应器

本文介绍一种大报压交流辉光放电等离子体气－液相化学反应器的结构，放电实验及应用结果。该反应器在气－液混合和大气压条件下顺利地产生了氢等离子体，并在常温，常压和无催化剂作用下，对液相Ｃ１８烯酸进行了选择性加氢。     

Strain Effect on Photoluminescences from InGaN MQWs with Different Barriers Grown by MOCVD

InGaN/GaN MQWs, InGaN/AlGaN MQWs and InGaN/AlInGaN MQWs are grown on （0001） sapphire substrates by MOCVD. Membrane samples are fabricated by laser lift-off technology. The photoluminescence spec-ra of membranes show a blue shift of peak positions in InGaN/GaN MQWs, a red shift of peak positions in InGaN/AlGaN MQWs and no shift of peak positions in InGaN/AIlnGaN MQWs from those of samples with substrates. Different changes in Raman scattering spectra and HR-XRD （0002） profile of InGaN/AlInGaN MQWs, from those of InGaN/GaN MQWs and InGaN/AlGaN MQWs, are observed. The fact that the strain changes differently among InGaN MQWs with different barriers is confirmed. The AIlnGaN barrier could adjust the residual stress for the least strain-induced electric field in InGaN/AIlnGaN quantum wells.     

In0.5(Ga1-xAlx)0.5P合金的掺杂生长特性

利用LP-MOCVD分别生长Zn和S掺杂的In0.5(Ga1-xAlx)0 5P外延层,研究生长温度、掺杂源流量、V/Ⅲ比、Al组分以及衬底晶向偏离等生长条件对外延层掺杂浓度的影响.实验结果表明:降低生长温度和Al含量、增加DEZn流量、选择由(100)向(111)A偏6～15的衬底都有利于增加IRGaAlP合金中Zn的掺杂浓度;提高生长温度和增加SIH4流量、减小Al含量和V/Ⅲ比,都有助于增加Si掺杂浓度,而衬底晶向对Si掺杂浓度无影响.     

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.     

GaN发光二极管的负电容现象

采用串联等效电路分析了较大正向电压下半导体二极管的交流电学特性．由此可以同时测量结电容和串联电阻,并能判断二极管是否有界面层。首次发现了在较低的测试频率和较大的正向电压下,GaN二极管的结电容具有负值,并且测试频率越低,正向偏压越大,负电容现象越显著。这种负电容效应可能与大正向电压下强注入造成的电子-空穴复合发光有关。     

MOCVD侧向外延GaN的结构特性

侧向外延（EL0）GaN的原子力显微镜（AFM）表面形貌图像表明,ELO—GaN相当平整,而掩膜区中央有线状分布的小丘群,这是由ELO—GaN在掩膜区中央接合时晶向不一致而产生的缺陷造成的。观察ELO—GaN扫描电子显微镜（SEM）截面图,侧向接合处存在着三角空洞,并且侧向接合导致上述小丘群。X射线衍射（XRD）曲线表明,掩膜边界处的GaN晶面有倾斜。拉曼散射谱表明,掩膜区GaN质量相对于窗口区大为提高。ELO—GaN和普通外延GaN的拉曼散射谱比较表明,ELO—GaN中的应力较小,晶体质量较高。     

Effects of Dislocation on High Temperature Transport Characteristics of Unintentionally Doped GaN

High temperature transport characteristics of unintentionally doped GaN have been investigated by means of high temperature Hall measurements from room temperature to 500^o C. The increment of electron concentration from room temperature to 500^o C is found to vary largely for different samples. The dispersion of temperature dependence of electron concentration is found to be directly proportional to the density of dislocations in GaN layers calculated by fitting the FWHM of the rocking curves in x-ray diffraction measurements （XRD）. The buildup levels in persistent photoconductivity （PPC） are also shown to be directly proportionM to the density of dislocations. The correlation of XRD, Hall and PPC results indicate that the high temperature dependence of electron density in unintentional doped GaN is directly dislocation related.     

中国东海及南海近海4采样点海水可培养细菌的多样性研究

采用不同的培养方法从中国东海和南海近海海水样品中分离得到105株细菌,探讨了不同海区可培养细菌的物种多样性和群落组成特点.16SrDNA序列分析结果表明,东海分离菌株分属于2个细菌门的14个种,南海分离菌株分属于3个细菌门的19个种.其中,东海分离菌株中α-变形菌占33.3%,γ-变形菌占57.2%,厚壁菌门细菌占9.5%.南海分离菌株中α-变形菌占41.9%,γ-变形菌占35.5%,拟杆菌门细菌占17.7%,厚壁菌门细菌占4.8%.东海和南海样品的分离菌株在种属水平上的多样性差异明显,后者的多样性指数高于前者.