Study of the Optical Processes in Nitride Alloy Semiconductors

1. 用相干电位近似（CPA）研究了二元合金半导体A_<1-x>B_x的光吸收光谱。对存在对角线随机性和非对角线随机性的Frenkel激子采用了紧密结合模型。随机效应分别包含在势部Σ (E)和幅部Γ(E)中，它们与Shiba （Prog.）的相干定位器L (E)有关。定理。物理学报，1971,77)为L(E) = (E-Σ(E)) /Γ(E)。具有Σ (E)和Γ (E)的平均Green函数是自洽确定的。将得到的CPA方程应用于3dim。体积系统具有简单的能带结构，也适用于量子阱系统。利用扩展x射线吸收精细结构光谱研究了GaInNAsSb合金的局部原子构型。由于Sb的成分较少，对实验数据的分析存在困难。对后台可移除技术进行升级，成功解决了这一难题。用从头算法对拉曼散射模拟的预测进行了初步研究。定量计算结果与实验结果吻合较好。研究了[0001]、<11-2-2>、<11-20>取向的In_xGa_<1-x>多量子阱在不同铟成分x和光激发强度下的发光特性。对于成分x较大的样品，在ns脉冲的强激发下，在GaN带间跃迁过程中，除了阱结构的特征红色发射外，蓝色区域周围还出现了明显的附加发射带。该发射初步归因于过量光载流子引起的氮化镓层缺陷的发射。还证实了脉冲后两种发射都衰减了几微秒，但没有发现瞬态ESR信号。

1. The optical absorption spectrum of a binary alloy semiconductor A_<1-x>B_x were studied by coherent potential approximation (CPA) . A tight binding model is used for a Frenkel exciton in the presence of the diagonal and off-diagonal randomness. The effects of the randomness are respectively included as the potential part Σ (E) and the amplitude part Γ(E), which are shown to relate to the coherent locator L (E) by Shiba (Prog. Theor. Phys. 46, 1971, 77) as L(E) = (E-Σ(E)) /Γ(E) . The average Green's function with Σ (E) and Γ (E) , is self-consistently determined. The obtained CPA equations were applied to a 3dim. bulk system with a simple band structure and also to quantum well systems.2. Local atomic configurations of GaInNAsSb alloys has been investigated using extended X-ray absorption fine structure spectroscopy. Due to its small composition of Sb, there was a difficulty in the analysis of the experimental data. Upgrading the background removable technique, the difficulty has been successfully solved. A first trial of a prediction of Raman scattering simulation has been also investigated using ab initio calculations. The results quantatively agree well with the experimental results.3. Luminescence properties of In_xGa_<1-x> multiple quantum wells with [0001], <11-2-2>, <11-20> orientation were studied for the variety of indium composition x and photo excitation intensity. For a sample with relatively large composition x, besides a characteristic red emission from the well structures, an additional emission band appeared remarkably around blue region under intensive excitation with ns-pulses into GaN band-to-band transition. The emission was tentatively attributed to the emission from defects in GaN layer induced by excess photo-carriers. It was also confirmed that both emissions decayed by a few microseconds after pulses, however, no transient ESR signal had been found.