以超快量測技術探討在量子點與量子井結構中載子鬆弛過程

Abstract

在本論文中，我們利用超快量測系統來探討量子點中的 載子動態行為。 我們使用up-conversion量測系統，透過改變激發強度，可以發現對載子捕捉機制的影響。溫度從78K至235K的變溫量測，顯示了不同捕捉機制對溫度有不同的相依性。 在載子填滿率探討方面，我們加上一CW綠光雷射光源的方式達成調控樣品中載子填滿率的目的，再同時以脈衝雷射進行動態實驗的量測。從光激螢光的頻譜中，在高強度光激發時，可發現能帶填滿效應的產生，可對應到不同填滿率時基態載子捕捉時間的上升。 我們對量子井與量子點複合結構做時間解析，以砷化銦量子點應力子，來改變銻砷化鎵量子井能帶結構，形成類似量子點的能帶分布，使得量子井中載子動態特性發生改變。另外，在量子點與量子井結構間砷化鎵間隔層厚度不同的樣品中，有載子由量子點捕捉後穿隧至量子井的現象發生。

In this thesis, we use ultrafast measurement system to study quantum dots carrier dynamics in quantum dots. The influence of excitation power on capture mechanisms is studied by using an up-conversion measurement system. From the measurement at temperatures varying from 78 K to 235 K, we show that the different capture mechanisms have different temperature dependencies. To study the effect of carrier occupation probability, a CW green laser light source, serving the purpose of controlling the carrier occupation probability, is used in conjunction with femto-second optical pulse excitation to determine the relations between the occupation probability and carrier dynamics. From the photoluminescence spectrum, under high-intensity excitation, we can find the band filling effect that corresponds to carrier capture time increase with increasing carrier occupation probability. Using InAs quantum dots as a stressor changes the GaAsSb quantum well band structure which forms a similar band structure as quantum dots, and alters the carrier dynamics behavior in the quantum well. In different GaAs spacer thickness samples, we discover the phenomenon that carriers, captured by quantum dots, tunnel into quantum wells.