規則化量子點晶格及半導體量子環之研究

Abstract

本論文由兩個部分組成，規則化量子點晶格成長與量子環結構之研究。有關第一部份，我們提出了利用格式化基板之選擇性成長方法來達成控制量子點之位置和數目並以實驗證明﹔在另一部份中，自組式半導體量子環結構之成長與特性是討論的主題。 關於量子點之選擇性成長，本論文使用兩種不同之格式化基板方法。首先，我們使用電子束微影和溼式蝕刻形成不同之圖案，並利用原子在不同晶面上所展現之特性，來製作出具有完整晶格結構和長程規則排列之一維量子點陣列。尤有甚者，我們更發展出一種利用應變累積方式，來達成單一量子點之成長。利用這種技術，我們成功地製作出二維規則排列之單一量子點晶格。 接著，我們詳細地探討了在(100)砷化鎵基板上自組式半導體砷化銦鎵量子環的研究與成長。利用AFM量測，我們個別探討了四個主要長晶參數，砷化鎵覆蓋層之長晶速率，砷化鎵覆蓋層之基板溫度，退火溫度與退火時間。我們發現dewetting過程是量子環形成之主要原因，而擴散作用則嚴重地影響量子環之表面型態和組成分怖。此外，為了解決以傳統方式成長量子環，須仔細考慮成長條件之缺失，我們提出了以擴散位障為基礎之方法，藉由額外加入一層AlAs來阻止鎵原子向內擴散而和銦原子形成合金，因而可以在較為寬鬆之成長條件之下製作出量子環。

This dissertation consists of two parts: ordered quantum dots lattice growth and semiconductor quantum rings structures. In the first part, selective growth methods on patterned substrates to achieve position- and number-controlled self-assembled quantum dots were proposed and demonstrated experimentally. In the second part, the growth and characterization of self-assembled semiconductor quantum rings were discussed. As regards QDs selective growth, two approaches of patterned substrates were used in this dissertation. First of all, a high quality crystalline and long-range ordering of QDs array was obtained by making use of different migration behaviors on the faceted surface generating by e-beam nanolithography and wet chemical etching. Besides, a new technique based on strain accumulation was developed for achieving single QDs fabrication. Using this method, 2D ordered single QDs lattice have been demonstrated. In the following, studies and fabrication of self-assembled semiconductor In(Ga)As quantum rings on (100) GaAs substrate were discussed in detail. Using AFM measurements, four main growth parameters, GaAs capped growth rate, GaAs capped temperature, annealing temperature and annealing time, have been studied and discussed respectively. We found that the dewetting process is the dominant mechanism in the formation of quantum rings, and the diffusion-driven transformation greatly influences the surface morphology and composition distribution. Furthermore, a new growth technique based on the diffusion barrier method was developed to solve the problem that the fabrication of quantum rings is strongly dependent on the growth conditions traditionally. An additional AlAs layer impedes the inward diffusion of the Ga and Al atoms and results in nano-ring formation with a more relaxed growth condition.