砷化銦自聚式量子點內點缺陷與電子量子能階之交互作用

Abstract

近年來，砷化銦/砷化鎵自聚式成長量子點的技術漸趨成熟，並大量應用在科技上， 引起理論及實驗的廣泛研究，尤其在判定量子點電子能帶結構方面，如何經由分析量子 點的電子躍遷行為來確認之，是許多團隊目前專注的課題之一。然而，電子躍遷時間太 短，加上顯著穿隧效應的影響之下，對實驗量測與分析都是一大挑戰。另一方面，已知 改變深層陷阱的周圍環境條件，對其載子激發皆會造成影響，因此文獻提出，可利用具 有強侷限波函數的深層陷阱(deep trap)，做為分析電子能帶結構的工具；為了達到此目 標，首先此類缺陷需具有高規律性：其電容-時間暫態頻譜必須為指數函數，進而得知 正確的載子激發能量數值。過去的幾年中，我們研究過許多缺陷陷阱，已發現一些合適 的缺陷，譬如與應力鬆弛所誘發之錯位(misfit)有關聯的電子缺陷，此缺陷固定侷限在特 定區域，且其電子激發特性強烈地受環境變因所影響。 因此，在此三年提案中，我們計劃深入探索此類缺陷，以應用在建立量子點電 子能帶結構方面。第一年，我們將使用分子束磊晶(molecular beam epitaxy, MBE)成長樣 品， 將一些缺陷能階佈值在量子點內部或是其周圍， 首先利用光激螢光技術 (photoluminescence, PL) 與穿透式電子顯微鏡(cross-sectional transmission electron microscopy, TEM)，對樣品進行初步研究；電性量測方面，將結合導納頻譜(admittance spectroscopy)、深層能階展態頻譜(deep-level transient spectroscopy, DLTS)以及電容-時間 暫態頻譜(capacitance-time C(t) transience)等分析技術，期望能獲得缺陷與量子點能階， 其激發訊號對應溫度之曲線藍圖。除了MBE 磊晶之外，我們也會利用離子佈值後熱退 火的方式來製造缺陷；第二年期間，藉由了解缺陷及量子點能階的激發特性，可建立缺 陷與量子點能階之間的交互作用模型並規範量子點電特性；至於第三年計畫中，我們則 將著重在缺陷對於熱退火之效應。本研究計畫極具前瞻性，且對於基本科學研究及未來 科技應用上，皆有相當的成效。

InAs/GaAs self-assembled quantum dots (QDs) have recently attracted considerable attention for both theoretical and experimental studies due to promising technological applications. Many works have focused on experimentally determining the electronic band structure of the QD by analyzing electron emission from the QD. However, this emission time is very short and difficult to resolve due to the presence of significant tunneling. On the other hand, deep traps with their strongly localized wave functions have been proposed as local probes for characterizing electronic band structure. The change of the surrounding environment around the defect traps is expected to affect the emission parameters of the defect traps. However, in order to achieve this purpose, there are some requirements for the traps. For one thing, the trap has a high regularity: its capacitance-time transience for electron emission is exponential so that its emission energy can be accurately obtained. In the past years, we have studied many defect traps and found some suitable traps. One example is a trap associated with misfits induced by strain relaxation. This trap is well confined in certain region and its electron-emission properties are strongly affected by their surrounding environment. Thus, in this three year proposal, we intend to explore the possibility of using these traps as local probes for the electronic band structure of the QD. In the first year, we will use molecular beam epitaxy (MBE) to incorporate some defect states inside and near the QDs. The effect of these defects on the QDs will first be investigated by photoluminescence (PL) and cross-sectional transmission electron microscopy (TEM). In the electrical characterizations, we intend to combine admittance spectroscopy, deep-level transient spectroscopy (DLTS) and capacitance-time C(t) transience to obtain a wide temperature spectrum of the emission parameters of the defect states and the QD states. Beside the MBE growth, we will also induce defects in the QDs by implantation of such as N followed by thermal annealing. During the second year, the properties of electron emission from these defect states and from the QD confinement state will be thoroughly characterized. The interaction between the defect state and QD quantum state will be established. This study may provide another method for the modification of the electrical properties of the QDs. During the third year, we will focus on the effect of post-growth annealing on the defect states. This study is pioneering and is expected to be fruitful both in scientific studies and future applications.