自聚性碲化鋅/硒化鎘鋅量子點之成長與光學特性研究

Abstract

本論文主要利用分子束磊晶法成長硒化鎘鋅薄膜與第二型能帶排列的自聚性碲化鋅/硒化鎘鋅量子點，並且利用光激螢光譜、變溫光激螢光光譜、時間解析光譜等技術探究其光學特性與載子復合機制。此外亦比較硒化鎘鋅與硒化鋅作為能障層對於光學特性的差異。首先藉由調變二六族的分子束流量比，以控制鎘在硒化鎘鋅薄膜的組成，並且改變晶格常數與能隙大小。比較碲化鋅/硒化鎘鋅量子點與碲化鋅/硒化鋅量子點，發現增加摻入鎘的濃度會造成形成量子點的臨界厚度由2.2原子層增為3.2原子層厚。藉由量測不同激發功率下的光激發螢光光譜，由於能帶彎曲現象發現量子點發光訊號有明顯藍移，確認其為第二型態量子點。形成量子點的臨界厚度增加也造成平均量子點尺寸增大。

In this work, ZnCdSe thin films and the type-II self-assembled ZnTe/ZnCdSe quantum dots (QDs) were grown by molecular beam epitaxy (MBE). The photoluminescence (PL), temperature dependent PL, and the time-resolved PL were used to investigate the optical properties and the carrier relaxation dynamics. By optimizing the growth parameters, the beam equivalent pressure (BEP) of the Zn, Cd and Se cell, high quality ZnCdSe epilayers with controllable Cd composition could be achieved to adjust the energy band gap and lattice constant. For the ZnTe/ZnCdSe QDs, the peak energies of the photoluminescence (PL) spectra show a decrease with the increasing ZnTe coverage. An abrupt variation with coverage was observed, which implies the existence of wetting layer of 3.2 MLs. A significant blue-shift of PL peak energy with the excitation power was investigated due to the carrier-induced band-bending effect, which is a signature of type-II band alignment.