Study on the Optical Properties of Superlattices formed by Alloy Semiconductors

用相干电位近似（CPA）研究了由二元合金半导体A_<1-x>B_x构成的量子阱（QW）的电子结构。在由N_xx N_yx N_z位矩形阵列组成的阱中，对单个粒子（电子、空穴、Frenkel激子）采用了紧密结合模型。对角线随机性的影响被包括在相干势Σ(E)中，它被认为对所有站点都是相同的，并且是由平均格林函数自一致地确定的。计算了不同井径和不同维数下，由弗伦克尔激子产生的态能量密度ρ(E)和吸收谱I(E)。对于slab（∞,∞,N_z）和wire（∞,N_y,N_z）结构，ρ(E)和I(E)由N_z（或N_yx N_z）子带组成，并保留了二（一）维van-Hove奇点。当x（或1-x）较小时，B (a)杂质带总是出现在最低（最高）主子带的较低（较高）能量侧。利用荧光扩展x射线吸收精细结构（EXAFS）光谱研究了In和Sb原子周围GaInNAs和GaInNAsSb薄膜的局部原子构型。由于热退火，GaInNAs中in - n键和Ga-Sb键的数量增加。这种变化可以解释为这些合金的总能量的减少。实验结果与ab-initio计算结果一致。

Electronic structures of a quantum well (QW) constructed from a binary alloy semiconductor A_<1-x>B_x are studied in the coherent potential approximation (CPA). A tight binding model is used for a single particle (electron, hole, Frenkel exciton) in the well composed by a rectangular array of N_xx N_yx N_z sites. The effects of the diagonal randomness are included as the coherent potential Σ(E), which is assumed to be the same for all sites, and is selfconsistently determined with the average Green's function. The energy density of states ρ(E) and the absorption spectrum I(E) due to a creation of a Frenkel exciton are calculated for various well-size and the dimensionality. For slab (∞,∞,N_z) and wire (∞,N_y,N_z) structures, ρ(E) and I(E) are composed of N_z (or N_yx N_z) subbands with remains of two (one)-dimensional van-Hove singularity. When x (or 1-x) is small, a B (A) impurity-band always appears at the lower (higher) energy side of the lowest (highest) host-subband.Local atomic configurations of GaInNAs and GaInNAsSb thin films around In and Sb atoms was investigated using fluorescence extended X-ray absorption fine structure (EXAFS) spectroscopy. The increase of the number of In-N bonds in GaInNAs and the number of Ga-Sb bonds in GaInNAsSb were observed due to the thermal annealing. The change would be interpreted as the reduction of the total energy of these alloys. The experimental results were consistent with the results of ab-initio calculations.