單一砷化銦鎵雙耦合量子點之光學特性量測分析

Abstract

本論文討論雙層砷化銦鎵量子點堆疊而成的單一垂直耦合雙量子點的螢光光譜。藉由改變功率和偏振方向分析，觀察譜線強度隨功率的變化以及其精細結構分裂，可分辨出直接單激子和間接單激子及雙激子。透過改變激發光的能量，則進一步辨認出帶負電激子。在變溫的過程中，由強度的消長發現了直接單激子態和間接單激子態之間具有單一方向的能量轉換。為了解釋這個現象，我們提出速率方程式模型來模擬實驗結果，藉由擬合的參數判斷此轉換是源自於聲子協助的電洞非共振穿隧效應。透過變功率螢光量測，高溫下譜線強度比值會隨著激發功率而改變，可得到此非共振的電洞穿隧效應的輔助證據。由時間解析光譜量測結果，得到激子態的半衰期不隨溫度改變，代表著激子態佔據量子點分子的機率確實因為溫度的不同而有消長。

The photoluminescence (PL) of single quantum dot molecules (QDMs) formed by two closely stacked In0.5Ga0.5As layers is observed. Similar pattern of photoluminescence were investigated in different QDMs. They can be identified as direct exciton, indirect exciton and biexciton by power dependent and polarization resolved micro-PL measurements. We also confirmed negative charged exciton by the spectra of different excitation energy. With the increasing temperature, we found that the intensity varied with a crossing between driect exciton and indirection exciton. It indicated a directional transfer of hole between the two adjacent dots. We support a rate-equation model to simulate experiment data and inferred that the phenomenon comes from phonon-assisted nonresonant tunneling of the hole by fitting parameters. Power-dependent PL at different temperature implied such nonresornant tunneling.