一維暨二維氧化鋅奈米光電特性及結構研究

Abstract

氧化鋅因為具有獨特的物理特性使它成為最有希望的光電元件材料.其主要原因是他具有直接寬能隙以及很高的激子結合能,在室溫以上時就可以產生激子復合的條件. 也由於他的這些獨特性質,使得氧化鋅的研究潮流得以持續數十年. 早期的研究大多集中在三維及二維氧化鋅材料的基礎物理特性上,例如:晶格參數,晶體振動特性,以及光學性質. 隨著長晶科技的進展,使得科學家們有更多的機會去製造出高品質的氧化鋅材料進而能更加深入的探討其特性.在最近的十年裡,阻礙氧化鋅發展的主要因數就是:如何成功的產出再現性高以及低電阻率的p型氧化鋅材料.目前有很多的研究團隊都開始往這兩個瓶頸點突破,並且其中有些團隊宣稱他們已經成功的完成部份的目標. 而在另一方面,理論學家也對這個領域很有興趣,他們提出很多有關本質缺陷以及摻雜物在電學行為上的預測. 另外,近年來關於奈米級氧化鋅材料的合成也吸引了很多人的目光. 這是由於一維氧化鋅奈米結構在基礎量子化的領域上提供了一個吸引人的研究系統並且在化學感測以及生物醫學應用提供了低維電子傳輸的研究. 這本論文主要是研究p型氧化鋅薄膜以及一維氧化鋅奈米結構的製備並且探討他們的物理特性. 第一章,我們將先以氧化鋅材料的簡介概論做出發,其中並探討其本質特性,摻雜行為以及缺陷模式.第二章將簡介一維,二維氧化鋅材料的製造方法,以及相關的奈米科學基礎理論.在這個章節中我們會詳細敘述如何製造高品質的氧化鋅薄膜與奈米柱,以及如何量測到它們極佳的物理特性.關於單根奈米元件的量測方法也將在此章節做介紹. 在第三章中我們將討論有關氧化鋅薄膜的缺陷工程.在氧化鋅中本質缺陷的躍遷研究上我們將以光激發光光譜來檢閱.不同的成長介面層可以改變本質缺陷的濃度並且能改善氧化鋅的物理性質. 所以,我們將對在氧化鋅薄膜中主要缺陷以及光學發光特性上的關係做一系列的討論. 並且在第四章中我們將研究有關五族元素參雜入氧化鋅薄膜後的電學及光學性質變化.我們利用氮離子佈值配合氮化矽介面層的影響並在攝氏850oC氮氣氣氛下退火之後製造出具有再現性並有高電洞濃度的p型氧化鋅薄膜. 到目前為止,最常被使用來成長一維氧化鋅奈米柱的方法是氣相固態法.然而這個方法通常都需要經過高溫製程並且爐管的大小會限制試片的大小.因此,在第五章我們將提出一個方便簡單的製程可以用來製作大面積氧化鋅奈米柱並且此製程相容於有機或無機系統之中.在本章節中我們將以高解析度穿透式電子顯微鏡來研究其成長機制以及熱效應對氧化鋅奈米柱的影響.在下個章節我們將進一步以電漿處理的方法來改善氧化鋅奈米柱的發光及電學特性. 經由適當的電漿氣氛處理不但可以提升n型氧化鋅奈米柱的導電率,也可以製作出具有整流行為的p型奈米柱.最後在第七章,我們將介紹有關單根氧化鋅奈米柱及單壁奈米碳管混合物元件的電子傳輸特性.

Zinc oxide (ZnO) has unique physical properties that make it a most promising material for optoelectronic device. The main reasons are a direct band gap of 3.3 eV and a large exciton binding energy (60 meV), which permits exciton recombination even above room temperature. Owing to its distinctive characteristics the research trend on ZnO has continued for many decades. The former studies are focused on the basic physical properties of three- and two-dimensional ZnO materials, such as lattice parameter, vibrational properties, and optical studies. As improving the technology of materials growth, scientists have more opportunities to produce high-quality ZnO materials and then can do deeply research in it. In this nearly decade, the main obstacle to the development of ZnO has been the lack of reproducible and low-resistivity p-type ZnO. For the moment, many groups have attacked this problem and several have been successful to solve some problems of them [64-67]. Moreover, theoreticians have also been active in this area, and have predicted the electrical activities of various dopants and native defects [68-70]. In addition to ZnO thin films, significant interest has emerged in the synthesis of nanoscale ZnO materials, in recent years. It is due to the one-dimensional ZnO nanostructures provide an attractive candidate system for fundamental quantization and low-dimensional transport studies for chemical sensing and biomedical applications. This thesis outlines the process of fabricating p-type ZnO thin films and one-dimensional ZnO nanostructures, as well as the study of their physical properties. In chapter 1 we will present an introductory overview to ZnO materials. It is devoted, respectively, fundamental, doping, and defects properties in ZnO. Chapter 2 will discuss the fabrication of one- and two-dimensional ZnO materials and basic theoretical concepts of nanoscience. This chapter also includes how we developed high-quality ZnO films and nanorods and measured their excellent physical properties. The individual nanorod measurement setup for electrical transport is also shown in this chapter. Chapter 3 discusses the defects engineering on ZnO thin films. The transitions of native defects in ZnO are inspected by photoluminescence (PL) spectroscopy, in this study. Different buffer-layers could change the concentration of native defects and improve the physical properties of ZnO. We will, therefore, discuss the relationship between the predominant defects and PL emissions in the ZnO films. In chapter 4, we will present the results for the electrical and optical properties of group-V elements doping in ZnO films. Reproducible p-type ZnO films with high carrier concentration (7.3 1017 cm-3) are fabricated by nitrogen-implanted on nitride layer and then annealed at 850 oC in N2 ambient. To date, the most popular method to grow ZnO nanorods is vapor-solid process. However, this method is usually operated under high temperature and it has also locked the size of the sample due to the size of the furnace. In chapter 5, we will show a convenient method to produce large scale ZnO nanorods on organic and inorganic substrates. The growth mechanism and thermal annealed effect of ZnO nanorods will be investigated by high-resolution transmission electron microscopy. The plasma treatments are used to improve the luminescent and electrical properties in ZnO nanorods. The high conductivity n-type and rectifying behavior p-type ZnO nanorods are revealed in chapter 6. The electrical transport of individual ZnO nanorods and single-walled carbon nanotubes composite will be discussed in chapter 7.