碲化鋅/硒化鎂鋅量子點之磊晶成長與光學特性分析

Abstract

本研究利用分子束磊晶系統以Stranski Krastanov成長模式在硒化鎂鋅上成長碲化鋅量子點。並利用光激發螢光譜、變功率光激螢光譜與時間解析光譜等實驗技術來探討其物理特性。 碲化鋅/硒化鎂鋅量子點的晶格不匹配度可由改變鎂濃度做調控。由光激螢光譜我們發現峰值能量隨量子點厚度增加呈現兩個不同斜率的紅位移。當碲化鋅的覆蓋厚度小於臨界厚度時,低溫的光激螢光譜峰值能量隨覆蓋厚度增加而快速的減小。當覆蓋厚度大於臨界厚度時,光激螢光譜 峰值能量趨於緩慢減小。 由改變入射功率的螢光光譜中，觀察到能量位置隨雷射功率呈現藍位移，以及利用兩個複合時間擬合的時間解析光譜所得之長複合時間，可證實碲化鋅/硒化鎂鋅量子點為第二型的能階型態。

ZnTe quantum dots (QDs) were grown on Zn1-xMgxSe by molecular beam epitaxy using the Stranski Krastanov (SK) growth mode. The photoluminescence (PL), power dependent PL and time-resolved PL spectra were used to investigate the interesting physical properties. The tuning of the lattice mismatch by varying Mg concentration was demonstrated in the ZnTe/ Zn1-xMgxSe QDs. The critical thickness of wetting layer was estimated by the observation of abrupt change of photoluminescence (PL) emission energy with the ZnTe coverage. Two different red-shift slopes are observed for the PL peak energy. The peak energy of low temperature PL decreases promptly when the ZnTe coverage is less than the critical thickness and gently when the ZnTe coverage exceeds critical thickness. The PL bands blue-shift as excitation power increases. The decay profiles could be well fitted by two components lifetime. The long decay time measured from TRPL and PL bands blue-shift with increasing excitation power confirm that the ZnTe/ Zn1-xMgxSe QDs has a type II band alignment.