利用DLTS量測以及缺陷放射模型探討量子點充電效應

Abstract

本論文主要探討利用分子束磊晶成長厚度2.2ML InAs/GaAs單一量子點樣品中缺陷的放射行為。首先我們利用光激發螢光光頻譜(PL)以及低溫77K下電容電壓(C-V)量測中確定樣品中量子點基本特性，由前人研究中知道在外加光源1.32eV照射下以及升溫的過程將會激發能隙中某一產生復合中心(generation center)，進而產生電流對量子點進行充電造成跨壓回推以及電容值抬升等特性，並在深層能階暫態頻譜(DLTS)量測中外加光源條件下，也會發現缺陷將從大偏壓量測訊號回復到小偏壓時所對應的訊號大小。因此為了更進一步了解量子點充電的效應以及其對缺陷放射是如何影響，本論文由DLTS量測分析為主，並建立缺陷放射理論模型與實驗結果做比較，由理論基礎知道缺陷的放射行為不僅與放射速率有關也和其感受到偏壓非常有關係，而在樣品中便存在一個能影響蕭基接面端跨壓的元素，量子點在DLTS量測系統升溫的過程將造成不同程度的充電結果進而對改變不同速率窗、不同偏壓條件、線性擬合求活化能以及缺陷濃度換算等實驗結果上皆會造成影響。

In this study, we focus on the defect which is formed as growing capping layer at low temperature. Frist of all, the photoluminescence (PL) and capacitance-voltage measurements (C-V) at 77 K can help us to know the optical and electrical properties of quantum dots (QDs). According to the previous researches, our sample exists generation centers, which can provide current sources under illumination by the light and thermal excitation. Electrons accumulated in QDs, called charging effect, will produce a potential drop across the QDs layer and cause the depletion region suppression. We also observe this phenomenon in DLTS measurement. So we build a defect model which not only consider defect emission rate but also voltage circumstances. The analytical expression for DLTS has been deduced and used to fit experimental data.