以水浴法製作規則排列氧化鋅奈米柱及其於發光二極體之應用

Abstract

在本論文中，我們實現了一種能有效控制並成長出規則排列氧化鋅奈米柱的方法。我們結合奈米壓印技術以氮化矽薄膜為遮罩製作圖案氮化鎵基板，然後使用水浴法成長規則排列之氧化鋅奈米柱。在本研究中，我們改變水浴法成長條件，包含溶液濃度、成長溫度、成長時間以及基板圖案的成長區域面積，並歸納出水浴法在不同條件下的成長機制。我們發現在不同水浴法的成長條件下，規則排列氧化鋅奈米柱的型態變化幅度相當大。為了提升氧化鋅奈米柱的材料品質以及光學特性，我們適量摻雜鎵元素成分形成n型氧化鋅(電子濃度2.57×10^19 每立方公分)，並調變熱退火的條件。我們也利用光激發螢光量測以及穿隧式電子顯微鏡來分析氧化鋅奈米柱的光學特性以及材料品質。我們發現當氧化鋅奈米柱適量摻雜鎵成分並於300℃的氧氣環境下熱退火一個小時，能夠有效改善氧化鋅奈米柱的光學特性。 我們將氧化鋅奈米柱應用於發光二極體之製作，我們製作出n型氧化鋅奈米柱/p型氮化鎵的發光二極體以及n型氧化鋅奈米柱/氧化鎘鋅/氧化鋅三層量子井/p型氮化鎵發光二極體。我們發現這兩種發光二極體元件在施加順向偏壓以及逆向偏壓時均會發光，並進一步研究不同偏壓下的發光機制。由於n型氧化鋅奈米柱以及p型氮化鎵的能帶偏移相當大，加上兩者材料不同，容易在介面處形成缺陷能帶，使得在逆向偏壓時載子容易藉由缺陷能帶穿隧產生電流。比較這兩種發光二極體，n型氧化鋅奈米柱/氧化鎘鋅/氧化鋅三層量子井/p型氮化鎵發光二極體所量測到電激發光的發光強度在逆向偏壓時較強。我們發現當注入不同電流時，量測到的頻譜峰值會逐漸藍移，並且在順向偏壓以及逆向偏壓的發光波長有些微的不同。我們用量子侷限史塔克效應以其載子屏蔽效應來解釋頻譜峰值藍移的現象。

We have developed an effective approach to the controlled growth of regularly patterned ZnO nanorod (NR) arrays with the hydrothermal method based on the nano-imprint lithography on the patterned GaN template. The concentration of growth solution, growth temperature, growth duration, and the geometry of pattern are varied to compare the growth results. The diameter and length of the individual ZnO NRs can be potentially tuned over a wide range. The ZnO NR arrays are highly uniform in diameter and height with a perfect alignment along [0001] direction. We have also successfully fabricated Ga-doped ZnO NR arrays (n-ZnO with an electron density of 2.57×10^19 cm-3) and investigated their material properties. The optical characteristics can be improved by appropriate Ga doping and thermal annealing at 300℃ with ambient O2. The n-ZnO NR arrays are applied to the fabrications of a n-ZnO NRs/p-GaN heterojunction light-emitting diode (LED) and a n-ZnO NRs/CdZnO/ZnO QW/p-GaN LED. Different electroluminescence (EL) spectra under forward and reverse biases are observed. A systematic mechanism is proposed to explain the EL behaviors under forward and reverse biases. Under reverse bias, the current created by the tunneling effect is attributed to the devices emission. It is found that the emission bands of the n-ZnO NRs/p-GaN LED under both forward and reverse biases originated from the p-GaN layer rather than the ZnO layer. The yellow band of the n-ZnO NRs/p-GaN LED originates from the interface defects. While the n-ZnO NRs/p-GaN heterojunction LED exhibits relatively lower EL intensity, LED with the CdZnO/ZnO QWs shows quite strong EL intensity. In the LED with QWs, the emission spectra peak is blue-shifted in increasing injection current in the n-ZnO NRs/CdZnO QW/p-GaN LED. This result can be explained by the carrier screening of the quantum-confined Stark effect (QCSE).