砷化銦單量子點光激螢光之研究

Abstract

本論文整合了特殊的長晶技巧和簡易的製程處理，以顯微光激螢光系統成功的量測出自聚型砷化銦單量子點的光激螢光譜線。藉由雷射激發功率的變化，和綜合比較多顆單量子點的螢光譜線位置後，我們可以分辨出負激子(X^-)、激子(X)、雙激子(XX)和正激子(X^+)的螢光譜線，得知在此實驗的量子點中電子和電洞波函數為不均勻分布，由於電洞波函數的空間分布較電子集中，使雙激子的束縛能為負值。將實驗結果和強侷限量子點模型比較，可得相符一致的結果。 在變溫量測方面，我們觀察到單量子點螢光譜線的紅移量和位能障塊材的能隙縮減量相同，顯示在(4.3K~70K)的溫度範圍內，激子複合物螢光譜線的紅移主要還是由能障材料(GaAs, 砷化鎵)的紅移機制來決定，和量子點的尺寸較不相關；隨著溫度的上升，我們也觀察到激子螢光譜線藉由聲子的交互作用而寬化的現象。 經由線偏振極化螢光光譜的量測，我們在激子和雙激子的螢光譜線中觀察到了由電子電洞交換能所產生的精細結構，以及帶電激子因為多餘的載子存在，使交換能為零而使精細結構消失。 最後，我們在時間解析光譜中觀察到單量子點激子複合物螢光的串聯特性，顯示這些譜線確實屬於同一顆量子點，再次驗證了我們的實驗分析。

We’ve integrate special epitaxial technique and simple post-epitaxial process to measure the photoluminescence of single self-assemble InAs quantum dots with a typical micro-photoluminescence(μ-PL) setup. With varying laser excitation power and comparing different single quantum dots spectrum, we can identify different exciton complex luminescence, and find out the different “spreading-out” of the electron and hole wavefunctions. In comparison with strong confined quantum dots model, we can get a matchable picture with our experiment results. In temperature dependent μ-PL experiment, we found out that the exciton complex luminescence energy show characteristic red shift related to the shrinkage of the GaAs barrier band gap at the temperature between 4.3K and 70K. It reveals that the mechanisms of exciton energy red shift are dominant by the coupling of the barrier bulk phonon system, whereas QD size seem to be minor important. In addition to exciton energy red shift, we also observed linewidth broadening caused by exciton-phonon interactions. With linear polarized μ-PL experiment, we have observed the electron-hole exchange energy induced fine structures in exciton and biexciton luminescence spectrum. For charged excitons, the luminescence finestructures vanish due to additional carrier injection. Finally, in time-resolved μ-PL experiment, we observed the single quantum dots cascade luminescence property, which support our analysis in this work.