斜向射頻磁控濺鍍氧化鋅奈米線結構之材料特性與於紫外光二極體之應用

Abstract

本論文利用斜向射頻磁控濺鍍系統(glancing-angle radio-frequency magnetron sputtering system)來製備氧化鋅(Zinc oxide, ZnO)薄膜，系統性地分析氧化鋅薄膜其型態分布、材料品質、以及光電特性。再進一步將斜向氧化鋅薄膜成長於氮化鎵材料，最終製作成紫外光發光二極體元件(ultraviolet light-emitting diodes, UV LEDs)，並與傳統正向成長之氧化鋅/氮化鎵異質接面比較。我們發現，斜向氧化鋅薄膜其電阻率可大幅度降低到10-3等級，載子濃度和載子遷移率分別為n = 5.14×109 cm-3 以及n =63.46 cm2/V•s 。由XRD 特性光譜發現斜向氧化鋅薄膜在 (002)晶向位置有明顯的繞射強度，其X-Ray繞射峰約在 = 34.52o。其光激發螢光光譜(Photoluminescence, PL) 波長為=380nm，主要對應於近氧化鋅能隙之發光光譜位置(Near Band-Edge , NBE)。此外，我們也發現隨著快速熱退火(rapid thermal annealing, RTA)溫度的提升，斜向氧化鋅薄膜晶格將重新排列，此將大幅地改善其結晶品質以及PL發光強度。將斜向氧化鋅薄膜成長於p型氮化鎵，並製作成異質接面發光二極體元件後，就電流電壓特性曲線(I-V curves) 而言，斜向氧化鋅UV LED呈現極佳的整流特性，其開通電壓(turn-on voltage)約為4.8V,而漏電流則為4.4 ×10-3A。最重要的是，我們所製做出的斜向氧化鋅UV LED，其電致發光光譜(Electroluminescence, EL) 在我們的量測區間(I = 0–60mA)，都是以NBE (=380nm)發光光譜為主導。隨著注入電流增加，發光強度隨之增強，而其半高全寬(Full Width Half Maximum, FWHM)，則隨之下降。我們的研究說明斜向成長氧化鋅薄膜與氮化鎵材料上(type-II band-alignment)，會產生高載子注入效率，造成氧化鋅缺陷複合飽和，增強近氧化鋅能隙之複合發光效率，其將可廣泛用於 pure UV-emission 之應用。

Both of oblique angle deposition and conventional deposition techniques were used by a RF sputtering system to grown the slanted and planar n-ZnO films on p-GaN, respectively. These two kinds of n-ZnO/p-GaN heterojunctions were then fabricated the light-emitting diodes (LEDs). The electrical and optical properties of these two kinds of LEDs were investigated systematically. The results show that the slanted n-ZnO/p-GaN LEDs have a lower turn-on voltage and less leakage current than that of planar n-ZnO/p-GaN LEDs. Moreover, different from the planar n-ZnO/p-GaN LEDs which emitting colors changes with injection current, the slanted n-ZnO/p-GaN LEDs retains UV emissions (385-400 nm) under the entire range of injection currents we applied. The dominant UV luminescence of slanted n-ZnO/p-GaN LEDs is attributed to the ZnO near band edge transitions, indicating the high quality of slanted ZnO films and exhibiting the essential property dedicated to nano-sized heterojunctions. Hence, we have demonstrated that the slanted n-ZnO/p-GaN LEDs fabricated by oblique angle deposition have better performance than the planar n-ZnO/p-GaN LEDs fabricated by convention deposition means.