Study on the Optical Properties of Superlattices formed by Alloy Semiconductors

在相干势近似下研究了二元合金半导体A_ B_x量子阱的电子结构<1-x>。采用紧束缚模型，研究了N_xN_yxN_z矩形点阵势阱中的单粒子（电子、空穴、Frenkel激子）。对角随机性的影响被包括在相干势ε（E）中，它被假设为对于所有站点都是相同的，并且是用平均绿色函数自洽地确定的。计算了不同阱尺寸和维数下Frenkel激子产生的态密度ρ（E）和吸收谱I（E）。对于板状（∞，∞，Nz）和线状（∞，Ny，Nz）结构，ρ（E）和I（E）是由Nz（或Nyx Nz）个子带组成，并保留了二维van-Hove奇异性。当x（或1-x）较小时，杂质带B（A）总是出现在最低（最高）主体子带的低（高）能侧.用荧光扩展X射线吸收精细结构（EXAFS）谱研究了GaInNAs和GaInNAsSb薄膜中In和Sb原子周围的局域原子组态.由于热退火，观察到GaInNAs中的In-N键数和GaInNAsSb中的Ga-Sb键数的增加。这种变化可以解释为这些合金的总能量的减少。实验结果与从头计算结果一致。

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.