量子點負微分電容特性研究

Abstract

近年來，由於它們的特異性，零維量子結構或量子點引起許多優秀研究群的注意； 因為其能態密度如delta-函數的緣故，零維系統被認為具有獨特的物理性質，可用於改 善現存半導體元件的性能，或具有現存材料或元件所無法提供之功能。自從1990 年代 自組式砷化銦/砷化鎵量子點成長被發展出來以後，許多研究群已成功地利用MBE 或 MOCVD 成長出高品質幾無缺陷之量子點，元件如量子點雷射與量子點紅外線偵測器也 製作出來，為能充分利用這種量子點，對它們的物理性質的了解就極為重要。 研究這些零維系統的量子能態的論文極多極廣，其中一種主要的方法是光學特性量 測，光學方法的重要性在於它們在量子點的光電元件應用是十分有效的；可是，在僅使 用一種載子的元件中(如量子點紅外線偵測器)，因為在量子點中的載子-載子交互作用， 量子點的特性與光學量測並不相同，但這些特性對於元件設計與最佳化卻相當重要；要 研究僅有電子或電洞的量子點性質，我們必須轉而使用電性量測的方法，目前在這方面 主要有兩種方法，電流-電壓與電容-電壓特性量測；在此計畫的第一年中，我們將專注 在使用包含量子點之Schottky 二極體進行電容-電壓分析，基於負微分電阻的觀察與所 建立的模型，我們將著手進行砷化銦與銻化鎵量子點之溫度及頻率相關的捕捉/逃脫特性 研究；在第二年中，利用反轉之高電子遷移率電晶體內含單層量子點結構，我們將製作 可研究量子點充放電行為研究之元件，該元件也是一個量子點記憶元件，同樣的結構也 將用來探討紅外線光偵測器應用的可能性。

In recent years, 0-D semiconductor quantum structures or quantum dots have attracted much attention from many excellent research groups, because of their novel properties. Due to the delta-function-like density of states, zero dimensional system is believed to hold unique physical properties which can be used to improve the performance of existing semiconductor devices and to have functions not able to be provided by conventional materials and/or devices. Since the InAs/GaAs self-assembled growth of quantum dots was developed in 1990s, very high-quality, nearly defect-free quantum dots have been grown successfully in many groups by using MBE or MOCVD. Devices like quantum-dots lasers or quantum-dot infrared photodetectors (QDIP) also demonstrated. To get the most of these self-assembled quantum dots, understandings on their physical properties are essential. Studies on the quantum states in these zero-dimensional quantum structures are extensive. One of the major methods is optical characterization. The optical way is important because of their usefulness in optoelectronic device application of quantum dots. However, in the devices using only one kind of carriers (or unipolar devices, e.g., quantum dot infrared photodetectors), their properties are different from the optical measurement because the carrier-carrier interaction inside the quantum dots but important for device design and optimization. To study the quantum dots occupying only with electrons or holes, we have to turn to electrical ways instead. Currently, there are two main methods in this direction, current-voltage (I-V) and capacitance-voltage (C-V) characterizations. In the first year of this project, we shall focus on the later (C-V) one by using a Schottky diode structure contained layer(s) of self-assembled quantum dots. Based on the observation of negative differential capacitance and the established simple model, we shall study the temperature- and frequency-dependent capture/escape properties in InAs and GaSb quantum dots. In the second year, by using an inverted-HEMT structure with a single layer of quantum dots, we are going to fabricate devices to study the charging-discharging behavior of dots and they can also work as memory devices. We shall also apply the same structure to explore the possibility of application for infrared photo-detection.