以貼靶濺鍍法製備含ZnO量子點之SiO2及SiOxNy

Abstract

本論文研究以貼靶濺鍍法（Target-attached Sputtering Method）製備含氧化鋅量子點（ZnO Quantum Dots，ZnO QDs）之二氧化矽（SiO2）與矽氮氧化物（SiOxNy）奈米複合薄膜（Nanocomposite Thin Films）；實驗結果顯示，此ㄧ間單的物理沉積（Physical Vapor Deposition，PVD）方法確可成長ZnO QDs於介電質（Dielectric）中，並能控制其粒子大小及分布，對微觀結構、光學與發光特性、導電與介電特性之分析，佐以理論計算與實驗結果比對，證實介電質種類對ZnO QDs表面所發生之交互作用及對ZnO QDs本質特性有重要之影響。 貼靶濺鍍法成長之ZnO QDs在此兩種介電質中均形成微結晶之量子點並具有相同的微觀形態，但ZnO QDs-SiOxNy系統由於氮原子的摻入，在ZnO QDs表面形成了不同於其在SiO2中的鍵結組態，使得ZnO QDs於SiOxNy中具有較強的表面極化（Surface Polarization）作用，此抑制了ZnO QD表面之氧離子缺陷化學反應，進而影響了兩種奈米複合薄膜之光穿透率（Transmittance）、折射係數（Refractive Index）與室溫之光激發光（Photoluminance，PL）光譜；藉由量子點空乏區（Depletion Region）與介電侷限能量（Dielectric Confinement Energy）之理論計算比對實驗數據，驗證了介電質種類對ZnO QDs之發光特性之影響。本研究同時建立了一個多層雙電子系統模型（Multi-shell Two-electron System Model）計算半導體量子點-介電質系統之電子基態能量（Ground-state Energy），以解釋ZnO QDs-SiO2系統中所受到之量子化侷限（Quantum Confinement）與介電侷限能量之影響。 在ZnO QDs-SiO2與ZnO QDs-SiOxNy奈米複合薄膜之直流（dc）與交流（ac）導電與介電量測中，對複數平面之各種特性表徵之分析顯示了兩種不同介質之奈米複合薄膜的導電性對ZnO QDs含量有不同的依存關係，對於頻率響應（Frequency Response）也表現了不同的反應及敏感度，此驗證了介電質種類亦影響導電性質，與先前光學性質之研究有一致的結果。雖然複數平面之特性表徵顯示兩系統的介電能力均未臻理想，需改善實驗設計以進行更進一步的分析，但驗證了以改變介電質種類之方法調變ZnO QDs導電性質之可行性。

This thesis prepares the nanocomposite thin films containing ZnO quantum dots (QDs) in SiO2 and SiOxNy dielectric matrices by using the target-attached sputtering method. The optical and electrical properties of nanocomposite thin films as well as the effects of dielectric types on the characteristics of ZnO QDs are also investigated. Experiemental results indicate that such a simple physical deposition (PVD) method can effectively grow the ZnO QDs inside the dielectric material within good control on dot sizes and distribution. Via the analyses including microstructure, optical, and electrical properties in conjunction with theoretical modeling and calculation, the interactions of dielectric matrices on ZnO QD surface and the effects of dielectric types on optical ane electrical properties of ZnO QDs are explored. Transmission electron microscopy (TEM) analysis revealed similar microstructure in both nanocomposite films and the ZnO QDs produced by target-attached sputtering method are crystalline rather then amorphous. In ZnO QDs-SiOxNy system, the incorporation of N atoms generates a distinct bonding configuration on ZnO dot surface and induces a stronger surface polarization in comparison with ZnO QDs-SiO2 system. This suppresses the defect chemical reactions relating to oxygen ions on ZnO dot and further affects the transmittance, refractive index and photoluminance properties of nanocomposite films. We also calculated the width of depletion region and dielectric confinement energy for the nanocomposite films and, in corelated with experimental data, the results evidenced the dielectric matrix type indeed affects the optical properties of ZnO QDs. We also built up a multi-shell two-electron system model to calculate the electron ground-state energy of a semiconductor QDs-dielectric matrix system. The calculated results enabled us to clarify the occurrence of quantum confinement and dielectric confinement effects in the ZnO QDs-SiO2 films. In the dc and ac conductivity measurements of ZnO QDs-SiO2 and ZnO QDs-SiOxNy systems, the complex-plane analysis revealed that the ZnO QD content on affects the conduction properties of nanocomposite films. Furthermore, the two nanocomposite systems exhibited different response powers and sensitivities to the frequency dispersion relationship. Though both systems exhibited poor capacitance properties and a new design of sample structure and further investigations are required, the results above cleary demonstrated the feasibility to manipulate the electrical properties of ZnO QDs via the modification of dielectric matrix type.