型態Ⅱ銻化鎵/砷化鎵量子環之特性分析及其發光元件應用

Abstract

本論文主要是探討型態Ⅱ砷化銻/砷化鎵量子環的表面形貌、發光特性及相關的元件應用。藉由在執行成長後銻原子浸潤時 (Sb post soaking) 時改變銻與背景砷原子的比例，我們可控制量子點或是量子環的形成。相較於量子點結構，量子環較強的螢光強度，其原因是由於擁有較大的電子電洞波函數覆蓋及較多圍繞在量子環周遭的電子數目。為了要更進一步的強化型態Ⅱ量子環的螢光強度、我們提出具有薄砷化鎵間隔層的耦合量子環概念。當隔離層降低到五奈米時、耦合量子環結構呈現了更強的光致發光強度與較大的波峰藍移量，其原因在於此結構改善了電子的侷限效果進而使得較多的電子累積在薄砷化鎵隔離層中。若再更進一步的降低隔離層的厚度到兩奈米時，樣品的螢光強度甚至超過了單層的型態Ⅰ砷化銦/砷化鎵量子點樣品。由此可知，型態Ⅱ耦合量子環結構可在複合發光強度上的增進同時保持其本身型態Ⅱ的特點，這些結果對於型態Ⅱ奈米結構在具有特殊表現的發光元件上的應用將有很大的幫助。

In this thesis, the surface morphologies and optical characteristics of type-II GaSb quantum-ring (QR) structures and its optical device applications are investigated. By changing Sb/background As flux ratios during the post-growth Sb soaking procedure, either fully quantum-dot (QD) or QR morphologies can be obtained. The intense luminescence of GaSb QR structures is observed due to the increasing electron-hole wave function overlapping and more surrounding electron shells over the QRs. To further improve the luminescence intensities of the type-II QRs, coupled QRs separated by thin GaAs spacer layers are proposed. With 5 nm GaAs spacer layers, both stronger photoluminescence (PL) intensity and larger PL blue shift are observed, which are attributed to the larger number of electrons accumulated in the thin GaAs spacer layer resulted from improved electron confinement. With further reducing the GaAs spacer layer to 2 nm, the PL intensity of the sample is even more intense than a single-period type-I InAs QDs. The demonstration of intense luminescence of the type-II coupled-QR structure is advantageous for their application in optical devices with the unique characteristics.