Study of the Optical Processes in Nitride Alloy Semiconductors

1.用相干势近似方法研究了二元合金半导体A_ B_x的光吸收谱<1-x>。紧束缚模型用于Frenkel激子的存在下的对角和非对角随机性。随机性的影响分别被包括为势部分Γ（E）和幅度部分Γ（E），其由Shiba（Prog. Theor. Phys.46，1971，77）作为L（E）=（E-E（E））/Γ（E）。平均的绿色函数是自洽确定的。将得到的CPA方程应用于3dim。具有简单能带结构的体系统以及量子阱系统.用扩展X射线吸收精细结构谱研究了GaInNAsSb合金的局域原子组态。由于锑的组成少，实验数据的分析存在困难。通过对后台移除技术的改进，成功地解决了这一难题.首次尝试预测的拉曼散射模拟也进行了研究，使用从头计算。计算结果与实验结果吻合较好.研究了In_xGa_（1-x）<1-x>[0001]取向多量子威尔斯阱<11-2-2>的发光特性<11-20>随In组分x和光激发强度的变化。对于具有相对大的组分x的样品，除了来自阱结构的特征红光发射之外，在ns脉冲到GaN带-带跃迁的强烈激发下，在蓝色区域周围显著地出现了额外的发射带。这种发光初步归因于GaN层中过量光生载流子引起的缺陷发光。还证实了两种发射在脉冲后几微秒衰减，然而，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.