Study on the Optical Properties of Superlattices formed by Alloy Semiconductors

在相干势近似(CPA)下研究了二元合金半导体A&lt；1-x&gt；Bx构成的量子阱的电子结构。用紧束缚模型研究了由N_xx N_yx N_z位组成的势垒中的单个粒子(电子、空穴、Frenkel激子)。对角随机性的影响被包括在相干势Σ(E)中，该相干势对所有位置都是相同的，并由平均格林函数自洽地确定。计算了不同尺寸和维度的Frenkel激子产生的态能量密度ρ(E)和吸收光谱I(E)。对于板条(∞，∞，N_z)和线(∞，N_y，N_z)结构，ρ(E)和I(E)是由N_z(或N_yx N_z)子带组成的，保留了两(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In和Sb原子周围的GaInNAs和GaInNAsSb薄膜的局域原子构型。热处理增加了GaInNAs中In-N键的数目和GaInNAsSb中的Ga-Sb键数目。这种变化将被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.