砷化銦量子點載子動力學之溫度相依性

Abstract

本論文探討成長於砷化鎵基板上之砷化銦量子點中，載子動態行為對溫度的相依性。依據量測變溫的時間解析光譜，在一個小範圍的溫度區間，隨著溫度升高，我們觀察到某些樣品中的光譜從兩段轉變成單一指數衰減的特殊現象，擬合的載子生命期則在某個溫度劇烈的變長爾後又隨著溫度再升高而下降。透過包含了暗能態之三能態速率方程式模擬，我們推測在低溫時，載子被暗能態緩慢的態鬆弛時間所限制而使光譜呈現兩段指數衰減；當溫度升高，額外且速率快的路徑主導了載子傳輸使暗激子快速鬆弛並發光，此時光譜的行為呈現單一指數衰減。此現象說明了欲高溫操作自旋儲存之相關元件，我們必須考慮在高溫時載子藉由額外路徑被快速消耗的機制。

This work focuses on the temperature-dependent carrier dynamics of InAs/GaAs quantum dots. We present an abnormal observation of low-temperature spike on carrier lifetimes caused by the change of decay curves from bi-exponential to mono-exponential decay. Theoretically, we then propose a three-level system containing a dark excitonic state and calculate it with rate equations; we find that at low temperature, the curves behave bi-exponentially due to the slow rate of the spin-flip relaxation of dark excitons; however at higher temperature, carriers are able to relax through an additional path with a much faster rate and the process becomes dominating, leading to the mono-exponential decay curves. The study suggests that to realize high-temperature operation spin storage taking the advantage of dark excitons in QDs, one must consider the fast relaxation through the extra mechanisms favored by thermal energy.