砷化銦/砷化鎵量子點與量子環的載子動力學

Abstract

由於量子環擁有特殊的環狀結構，因此存在著許多有趣的物理性質。本篇論文總共分成三個主題來探討量子點及量子環之間的載子動態差異，我們藉由超快時間解析光譜的技術，來探討以下的主題。 第一部分是利用螢光上轉換的技術去探討載子捕捉進入量子點及量子環基態中的速率，在此我改變了不同的激發功率，並且觀察不同激發功率對於載子捕捉速率的影響。 第二部份是利用時間相關單光子計數器的技術，在不同溫度下，比較量子點及量子環基態的載子鬆弛生命期。我們也觀察到量子點與量子環在高溫時呈現出截然不同的趨勢，當溫度高於150K時，量子環呈現出逐漸變長的載子生命期。經由計算，可以發現量子環內將存在著一些 l States，我們認為這些 l States可能形成Dark States而使得載子生命期變長。 第三部份則是針對同一製程條件下，探討量子點演變至量子環過程的幾種奈米結構的載子動力學。實驗中也清楚地觀察到螢光生命期會隨著量子環的形成而有變長的趨勢，我們認為這是由於 l States的數目會隨著量子環的形成而變多，且能量差也會逐漸變小所造成的結果。

The nanoscale ring structure, due to its unique rotational symmetry, exhibits many interesting physical properties. The thesis introduced three themes to discuss the carrier dynamics in the quantum dots and the quantum rings. By using the ultrafast time-resolved photoluminescence technology, it allows us to study the following researches. In the first part of the thesis, we used the fluorescence up-conversion technology to study the carrier capture rate in the dots and the rings. We injected different carrier densities in the samples and discussed the mechanisms that affect the capture rate. In the second part, we used the time correlated single photon counting technique to study the ground state carrier decay lifetime in the dots and the rings at various temperatures, and we also observed the different phenomenon between dots and rings at high temperature. At temperatures above 150K, the rings show increasing lifetime as the temperature is increased. From the calculation results, the longer lifetime observed in quantum rings is attributed to the dark states which resulted from the different l states. In the third part, we investigated the carrier dynamics with the structures evolved from the dot to the ring shape. In the experimental results, the carrier lifetime increases as the structures evolved from the dot to the ring shape. This is due to the increasing numbers of the dark states during the quantum rings formation.