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_&lt；1-x&gt；B_x的光学吸收光谱。对于存在对角线和非对角线随机性的Frenkel激子，采用紧束缚模型。这些随机性的影响分别作为位势部分Σ(E)和幅度部分Γ(E)被Shiba(Prog.西奥。太棒了。46,1971，77)，如L(E)=(E-Σ(E))/Γ(E)。Σ(E)和Γ(E)的平均格林函数是自洽确定的。将所得到的CPA方程应用于三维空间。具有简单能带结构的大块系统和量子井系统。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Sb的组成较小，给实验数据的分析带来了困难。升级了背景可拆卸技术，成功解决了这一难题。还利用从头计算对拉曼散射模拟的预测进行了初步尝试。计算结果与实验结果有较好的一致性。研究了[0001]，&lt；11-2-2&gt；，&lt；11-20&gt；取向的In_xGa_&lt；1-x&gt；多量子阱的发光特性。对于成分x相对较大的样品，在ns脉冲到GaN带间跃迁的强激发下，除了势垒结构的特征红光发射外，蓝区附近还显著地出现了一个额外的发射带。初步认为这是由于GaN层中的缺陷由过量的光载流子引起的发射。还证实，这两种发射都在脉冲后几微秒内衰减，然而，没有发现瞬时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.