Research on Optical Transitions of Indirect Semiconductors with Novel Superstructures

系统地研究了邻接约束结构（NCS）的光学性质，这是一种很有前途的基于间接半导体的光发射器。NCS由一对电子量子阱（QW）和嵌入势垒层之间的空穴量子阱（QW）组成。在基于SiGe和algap的半导体材料的NCS中，可以观察到强烈的非声子（NP）线增强的PL。通过改变阱宽，可以明显地观察到量子约束效应，表明增强的NP谱线来自于NCS的预期跃迁。与其横向光学声子副本相比，发现生长后退火导致NP线选择性猝灭。时间分辨PL研究表明，退火样品的辐射寿命随着温度的升高而增加，而生长样品的辐射寿命在低温下没有明显变化。考虑到激子在异质界面的局域化是NCS低温下观察到的NP增强的控制机制，这些结果得到了合理的解释。当井宽在孤岛生长的临界厚度附近时，井宽波动被认为是显著的，激子离域临界温度的增加支持了这一观点。

Optical properties of Neighboring Confinement Structure (NCS), a promising candidate for light emitter based on indirect semiconductors, were systematically investigated. NCS consists of a single pair of a quantum well (QW) for electrons and a QW for holes embedded between barrier layrs. Intense PL with enhanced no-phonon (NP) line was clealy observed from NCS based on SiGe- and AlGaP-based semiconductors. Quantum confinement effect was clearly observed by varying the well width, showing that the enhanced NP lines come from the expected transitions of the NCS.Post growth annealing was found to lead to selective quenching of the NP line compared to its transverse optical phonon replica. Time-resolved PL study clarified that the radiative lifetime of the annealed sample increases with increasing temperature, while that of the as-grown sample shows no significant change at low temperatures. These results were reasonably explained by considering that the exciton localization at the heterointerface is the controlling mechanism for the NP enhancement observed at low temperatures in NCS.The idea was supported by the increase of the critical temperature of the exciton delocalization in the sample with well width of around critical thickness for islanded growth where well width fluctuation is considered to be significant.