臺灣博碩士論文加值系統

發光二極體為光電工業的重要元件，它們的優點包括：實用性高、可靠度及元件的重現度高、對溫度較不敏感、低成本及對眼睛無傷害作用。藍色發光二極體之磊晶材料有三種：氮化鎵、硒化鋅及碳化矽，目前藍色發光二極體相關之研究則多注目於氮化鎵相關之寬能隙材料發光二極體。寬能隙材料之氮化鎵相關材料可發光於綠光至紫光之波段，因此相當適合於全彩之發光元件的應用。一般而言外部量子效應乃是定義為輻射至空氣中之光子與注入之電子電洞對之比例。這個量值可由輻射性復合過程所產生之內部量子效應及由元件所萃取之光子的效率(萃取效率)兩者之乘積來決定。萃取效率乃定義為由元件所萃取之光通量與經由半導體之電子電洞復合後所產生之總光通量的比值，這個比值與內部反射效應及Fresnel 損失來決定。氮化鎵藍色發光二極體在高電流注入時，電流會集中在N-PAD附近產生電流擁擠效應（current crowding），進而產生熱效應(thermal effect) 降低發光效率。
因此我們首先針對了藍色發光二極體之金屬電極層作不同圖形做研究，以不同的金屬電極層圖形形成不同注入電流路徑，以確認金屬電極圖形對整體注入效率與發光效率之影響，進而提出最佳化之電極圖形，有效提升藍色發光二極體之整體電流注入效率與其發光之光強度，其12mil中可提升70%，40mil依照圖形之不同至多可差距118%之多。為了有效提升二極體之發光效率，我們必需要提升氮化鎵藍色發光二極體之萃取效率及內部量子效應。許多光源尤其是利用半導體材料之電子電洞對復合所輻射的光子，其萃取效率並不高，這主要是受到內部全反射所影響。由於氮相關之磊晶層(相對折射係數為2.5)與空氣(相對折射係數為1)具較高之相對折射係數差，由氮化銦鎵/氮化鎵多重量子井所發出的光經p型摻雜之氮化鎵後之出光角並不夠大[sin-1(空氣之折射率/氮化鎵折射率)=23o]，其外部量子效應會因此而減少。對此，我們預計以氧化鋅薄膜做為緩衝層以改善出光角不夠大的問題，因此我們使用PE-MOCVD成長出最低電阻率為8.42×10-03 Ωcm，載子濃度、移動率最高為-2.0×1021 cm−3與6.1×104 cm2/Vs之氧化鋅薄膜。

Light emitting diodes (LEDs) are the key components in the optoelectronics industry. They have several advantages including robustness, reliability, low temperature sensitivity, low cost and eye safety. There are three kinds of material for blue LEDs including GaN, ZnSe, and SiC and many literatures have reported on the wide-bandgap GaN-based material light emitting diodes. The external quantum efficiency is a quality of how many photons can be generated and then emitted to the medium by the injected electrons. It is given by the production of internal quantum efficiency of the radiative recombination process and the subsequent efficiency of photon extraction from the device (i.e. extraction efficiency). The extraction efficiency is defined as the ratio of the flux of the photon extracted from the device and the overall flux of photons emitted in the semiconductor, and is affected by both total internal reflection and Fresnel losses. Under high injection, the current crowded which the current will concentrate in a narrow region between n-pad mental and n-pad metal will occur and then the external quantum efficiency will be worse due to Joule heating.
In this thesis, we first investigate the effect of p-metal pattern. With different pattern of metal, the path of injection current will change because of the distribution of electric field. In order to realize the relationship of designed metal pattern and the path of injection current, we will design the different metal pattern as the p-metal pattern for blue LEDs. Finally, the optimum metal pattern will present by the optical and electric characteristics. There are two kinds of metal pattern as the p-metal pattern for 12mil size blue LEDs and five kinds of 40mil size blue LEDs. In 12mil size chips, the light output power enhances above 70% with comparing to the conventional chip. In 40mil size chip, the output power will be improved by the well-designed pattern. Most of the light sources especially light emitting diodes generated in the semiconductor are not extracted because of the total internal reflection. The refractive indexes of GaN and air are 2.5 and 1.0, respectively. Thus, the critical angle at which light generated in the InGaN-GaN active region can escape approximately [θc =sin-1 (nair/nGaN)] ~23o, which limits the external quantum efficiency of conventional GaN-based LEDs to only a few percent. For this reason, we will introduce the ZnO intermediate layer to improve the critical angle. The ZnO film was grown by plasma enhanced metal organic chemical vapor deposition (PEMOCVD). The resistivity, carrier concentrate, and mobility are 8.42×10-03 Ωcm, 2.0×1021 cm−3, and 6.1×104 cm2/Vs, respectively.

摘 要...........................................i
Abstract........................................ii
表目錄..........................................vi
圖目錄..........................................vii
第一章 導論.....................................1
1-1. 前言.......................................1
1-2. 簡介.......................................3
1-3. 氮化鎵發光二極體目前發展狀況...............5
第二章 發光二極體原理介紹......................10
2-1. 發光二極體原理.............................10
2-2. 氮化鎵發光二極體電流散佈與電流壅塞效應.....14
2-3. 使用不同電極圖形之目的.....................16
2-4. 金屬電極之圖形.............................17
2-5. 氮化鎵藍色發光二極體製作流程...............25
第三章 不同金屬電極圖形電流分佈實驗量測結果.....30
3-1. 12mil氮化鎵藍色發光二極體之特性量測........30
3-1-1. 12mil氮化鎵藍色發光二極體之電學特性量測..30
3-1-2. 12mil氮化鎵藍色發光二極體之光學特性量測..35
3-2. 40mil氮化鎵藍色發光二極體之特性量測........38
3-2-1. 40mil氮化鎵藍色發光二極體電學之特性量測..38
3-2-2. 40mil氮化鎵藍色發光二極體光學之特性量測..45
第四章 結論.....................................49
第五章 未來工作.................................52
參考文獻........................................53
附錄： 以PE-MOVCD沉積氧化鋅薄膜.................56
一、 研究動機...................................56
二、 氧化鋅薄膜介紹.............................57
三、 氧化鋅相關成長技術.........................59
1. N型氧化鋅相關成長技術........................59
2. P型氧化鋅相關成長技術........................61
三、 以PE-MOVCD沉積氧化鋅薄膜與量測.............63
四、 薄膜特性分析...............................66
英文論文大綱(Extended Abstract).................75
簡 歷.......................................78

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