ELECTRONIC AND OPTICAL PROPERTIES OF STRAINED WURTZITE GaN

Band structures of wurtzite GaN (α-GaN) under strains in the region -5%—5% are calculated in a tight-binding framework. The empirical scaling rule has been used for considering the effects of hydroatatic strains. The scaling indexes are determined by fitting the deformation-potential constants with other theoretical values. The band gap at Γ point increases with the absolute value of strains. GaN turns to be of indirect band gap when strains reach 5 %. The density of states and the imaginary part of dialectic function (ε₂(ω)) are studied. Both the shape and energy position of the highest peak in the ε₂(ω) spectrum successively change with the strains. The real part of dielectric/unction, refractive index and the effects of the strains on them are also shown.     

分子束外延生长GaN薄膜中的一种早期位错结构

利用高分辨电子显微术，对在GaP基体上由分子束外延生长六角GaN晶体薄膜中的晶体缺陷结构进行了研究．实验中发现了GaN薄膜外延生长过程中产生的一种典型早期刃型位错结构．此晶体缺陷位于一大块GaN晶粒内部，其外观类似于一段（1120）晶界．它由一条（1120）高能孤立晶界段及其两端的两个1/6［1120］不完全刃型位错组成．从大晶格失配材料之间分子束外延生长的机理上对这种缺陷结构的形成进行了解释． 关键词：     

三螺旋核酸polyU*polyA*polyU的喇曼光谱和晶格动力学研究

由于三螺旋核酸在医疗、诊断和生物技术应用中的重要性 ,越来越受到人们的关注 .对溶于 0 .2 5mol/ L的 Na Cl磷酸缓冲液的三螺旋核酸 poly U· poly A· poly U的喇曼光谱进行了测量 ,在 750～ 1 2 50 cm- 1范围内获得了高信噪比的光谱图 .利用晶格动力学方法计算了Anott模型的主链振动模式 .根据势能分布矩阵对每一个喇曼谱线进行了指定 .结果表明poly U· poly A· poly U的三条单链具有相似的简正模式 ,没有一条喇曼线独属于某个单链 .理论同实验符合的事实说明溶液中的 poly U· poly A· poly U采用了 A型结构     

NUMERICAL STUDIES ON THE DYNAMICS OF DISORDERED VORTEX LATTICE

Flow behavior of the driven two-dimensional vortex lattice is numerically studied with different densities of randomly distributed pointlike pinning centers. Different features in the curves of velocity-force dependence are found between the elastic and plastic regimes. Scaling fit between force and velocity above the critical driving force can be obtained in the elastic regime but fails in the plastic regime. Transition from the lastic to plastic regimes is accompanied by maximum peaks in the differential curves of velocity-force dependence in the disordered vortex lattice.     

三螺旋核酸polyU·polyA·polyU的喇曼光谱和晶格动力学研究

由于三螺旋核酸在医疗、诊断和生物技术应用中的重要性,越来越受到人们的关注.对溶于0.25mol/L的NaCl磷酸缓冲液的三螺旋核酸polyU·polyA·polyU的喇曼光谱进行了测量,在750～1250cm^-1范围内获得了高信噪比的光谱图.利用晶格动力学方法计算了Anott模型的主链振动模式.根据势能分布矩阵对每一个喇曼谱线进行了指定.结果表明polyU·polyA·polyU的三条单链具有相似的简正模式,没有一条喇曼线独属于某个单链.理论同实验符合的事实说明溶液中的polyU·polyA·polyU采用了A型结构.     

半导体物理效应与光电子高技术产业

阐述了能带理论和晶格动力学的创建对半导体科学技术发展发展的历史意义，重点介绍了若干关键半导体物理效应的内涵及其对光电子器件与技术发展所作出的源头性贡献，描绘了以半导体激光器为代表的现代光电子高科技产业的发展现状与趋势，指出了光电子高科技持续发展的主要方向。     

非晶半导体中杂质和缺陷态的电子统计理论

本文应用统计物理的方法,讨论了非晶半导体的掺杂效应,特别是在低温下的特性。在荷电的悬挂键模型下,计算了各种情况下的费密能级和电子浓度。并对两类不同的非晶半导体作了详细的讨论。 关键词：     

Electrostriction in GaN/AlN heterostructures

A one-dimensional model accounting for electrostriction, lattice mismatch, piezoelectricity, and strain is presented with special emphasis on GaN/AlN heterostructures recently examined extensively in the literature. It is shown that electrostriction, being a second-order effect in the strain–electric field relation, plays a significant, sometimes dominant contribution subject to DC voltage conditions and externally imposed hydrostatic pressure. Model results are based on experimentally reported values for electrostriction coefficients in GaN.     

Vertical electron transport study in GaN/AlN/GaN heterostructures

In this work, we investigate the electronic structure and vertical electron transport through GaN/AlN/GaN single-barrier structures with different AlN thickness, grown by plasma-assisted molecular beam epitaxy. Conductive and capacitive characterization has been performed, and the experimental results are interpreted by comparison with 1D self-consistent simulations. Capacitive measurements reveal a complete depletion of the top GaN layer, and the formation of a two-dimensional electron gas at the bottom interface of the AlN barrier, even for barrier thicknesses of 0.5 nm (2 monolayers of AlN). Conductive atomic force microscopy reveals discrete leakage current locations with a density of 10⁷ cm⁻², more than one order of magnitude lower than the dislocation density in these samples. These results are promising for the fabrication of resonant tunnelling diodes using the GaN/AlN material system.     

AlN/蓝宝石模板上生长的GaN研究

研究了在分子束外延制备的AlN/蓝宝石模板上采用金属有机物化学气相外延生长的非故意掺杂GaN的材料性质.采用X射线衍射(XRD)、透射电镜(TEM)和原子力显微镜研究了AlN模板的晶体质量和表面相貌对GaN的影响.结果表明,当AlN的表面粗糙度较小时,尽管AlN模板的位错密度较高((102)面XRD ω扫描半高全宽900—1500 arcsec),但生长得到的GaN依然具有和在蓝宝石衬底上采用"二步法"生长的GaN可比拟的晶体质量((002)面XRD ω扫描半高全宽200—30 关键词： 氮化镓 氮化铝 金属有机物化学气相外延     

Crystal structure refinement of AlN and GaN

We have refined the structure parameters of AlN and GaN using X-ray intensities from single crystals collected with an automatic single crystal diffractometer. The lattice constants and the u values are a = 3.110 Å, c = 4.980Å, u = 0.3821 for AlN and a = 3.190Å, c = 5.189 Å, u = 0.377 for GaN. The final R-values for anisotropic temperature factors are equal to 0.015 for AlN and 0.026 for GaN. The effective atomic charges in these compounds are estimated.     

光脉冲在半导体中非线性传输特性的时域和频域分析

本文从理论上研究了半导体非共振透明区光脉冲非线性传输的时域和频域行为,并对应用自由载流子非线性折射效应来构造非线性方向耦合器的可能性进行了分析。     

Effects of GaN cap layer thickness on an AlN/GaN heterostructure

In this study, we investigate the effects of GaN cap layer thickness on the two-dimensional electron gas (2DEG) electron density and 2DEG electron mobility of AlN/GaN heterostructures by using the temperature-dependent Hall measurement and theoretical fitting method. The results of our analysis clearly indicate that the GaN cap layer thickness of an AlN/GaN heterostructure has influences on the 2DEG electron density and the electron mobility. For the AlN/GaN heterostructures with a 3-nm AlN barrier layer, the optimized thickness of the GaN cap layer is around 4 nm and the strained a-axis lattice constant of the AlN barrier layer is less than that of GaN.     

纳米晶体微观畸变与弹性模量的模拟研究

采用分子动力学方法模拟纳米晶体铜原子的结构,又对纳米晶体铜原子进行了X射线衍射模拟．计算了晶粒尺寸和点阵畸变,还计算了能量分布和弹性模量等．结果表明不但晶界产生很大的应力场,而且晶粒内部的畸变也起着与晶界相似的重要作用．由于原子半径的增加,导致弹性模量的减少. 关键词：     

格子Boltzmann方法模拟微尺度流动和传热

本文采用格子Boltzmann方法(LBM)对微尺度Couette流的流动及传热进行了模拟.为了获得壁面边界的速度滑移和温度阶跃,在含有粘性热耗散的热格子模型的基础上,提出了一种新的直接基于宏观量的边界处理格式.模拟得到的速度场和温度分布与解析解吻合得相当好,充分说明了本文采用的模型和边界处理的合理性同时在模拟中还发现:对于不同的Kn数,均存在使得其上壁面的温度阶跃为零的临界Ec数,并且其临界值均在3.0附近.     

磁性薄膜的晶格结构和磁性

采用Monte-Carlo模拟方法对六边形、正方形和三角形晶格结构磁性薄膜的磁学特性及磁畴结构进行了模拟,结果表明,磁性薄膜的磁性特征及其磁相变温度和薄膜结构密切相关并存在临界膜厚,当薄膜厚度大于临界膜厚时薄膜磁性特征稳定.在低温区,不同结构磁性薄膜的磁滞回线均出现台阶现象,结果同相关实验一致.     

Analysis of GaN epilayers on sapphire substrates with GaN and AlN sublayers

The features and results of X-ray diffraction analysis of GaN films are presented. The films are grown by metalorganic vapor-phase epitaxy on c-plane sapphire substrates using GaN or AlN nucleation layers deposited at a low temperature. Measurements of the twist angle and concentrations of Al _x Ga_1-x N solid solutions are discussed in detail.     

炸药爆炸冲击波合成纤锌矿型氮化硼

 本文报道了用国产石墨型氮化硼（gBN）为原料在炸药爆炸产生的冲击波作用下合成纤锌矿型氮化硼（wBN）的技术。对冲击波作用后的回收产物进行化学分离，得到杂质含量低于0.5%的wBN产品；回收产物的wBN的转化率高于50%；单发试验产量达11~12 g。目前已利用这一技术生产出少量wBN产品。在相同的冲击波条件下，对四种不同来源的gBN进行了合成试验。发现wBN的转化率强烈地依赖于原始gBN的结晶特性。比表面积测量及X射线衍射观察表明，冲击波合成的wBN是一种多晶微粉，平均颗粒度约0.1 μm，平均晶粒度约17.5 nm。差热分析显示放热反应起始温度为1 055 K，峰顶温度1 238 K。