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研究生： 陳揚
Chen, Yang
論文名稱： 利用電極設計與非等向性蝕刻提升氮化鎵發光二極體光輸出之研究
Enhancing Light Output of GaN-Based VLED Via Electrode Pattern Design and Anisotropic Surface Etching
指導教授： 王水進
Wang, Shui-Jinn
學位類別： 碩士
Master
系所名稱： 電機資訊學院 - 微電子工程研究所
Institute of Microelectronics
論文出版年： 2014
畢業學年度： 102
語文別： 中文
論文頁數： 60
中文關鍵詞： 發光二極體 、電流擴散 、電極設計 、非等向性蝕刻
外文關鍵詞： Light-Emitting Diodes, Current Spreading, Electrode Designs, Anisotropic Surface Etching
相關次數： 點閱：88  下載：4 
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    • 現階段GaN-基藍光發光二極體(light emitting diode, LED)，因受惠於有機金屬化學氣相磊晶(MOCVD)技術提升及垂直LED(vertical structure LED, VLED)製程技術開發，其磊晶品質與光電轉換效率(wall plug efficiency, WPE)皆獲顯著改善。於GaN-基VLED元件結構中，陽極為與p-GaN呈歐姆接觸之導電基板，n-GaN為出光面，其上之陰極電極，基於降低接觸電阻與減少遮蔽出光的考量，必須進行電極圖案最佳化設計。
    VLED結構與一般結構相比雖可有效降低串聯電阻，增加元件WPE，然操作於大電流(>1 A)下，仍易發生電流擁擠效應，導致WPE下降。本論文提出一種利用非等向性乾蝕刻製程製備具階梯狀n-GaN表面再搭配適當電極設計，藉由垂直與與側向串聯電阻之調變，使分佈於VLED電流密度趨於一致，有效改善電流擴散、串聯電阻與WPE並利用模擬軟體Crosslight進行驗證。
    實驗結果顯示，在蝕刻深度為200 nm時，具有電極設計之氮化鎵發光二極體元件於注入電流350mA時，與一般氮化鎵發光二極體相較，其光輸出效率增加19.2%。此光電特性結果證實本實驗利用電極設計與階梯蝕刻結構，確實能改善電流分佈並提升光輸出效率。

    Nowadays, the crystal quality and wall plug efficiency (WPE) of GaN-based blue light-emitting diodes have been significantly improved, because of the continuous advances in metal organic chemical vapor deposition technology and VLED chip processing. For vertical structure GaN-based LEDs (VLEDs), light emission from the n-GaN surface is strongly affected by the cathode electrode pattern which should keep both the contact resistance and light shielding ratio as small as possible.
    The advantages of VLED structure are series resistance reduction and WPE increment as compared with the conventional LED structure, however, the current crowding effect would severely decrease the WPE especially at high current condition (>1 A). In this study, to alleviate the current crowding in VLEDs, a two-step ladder surface morphology using inductive coupled plasma (ICP) etching depth and cathode electrode pattern optimization of top n-GaN layer of VLEDs are proposed to improve the current spreading and the light emission uniformity. The same structure is simulated by the Crosslight simulation tool for verification as well.
    The use of inductively coupled plasma (ICP) 2-step mesa etching on the n-GaN layer and optimized cathode electrode pattern were examined both theoretically and experimentally. Good agreements between simulation and experiments are obtained. Our experimental results show that, as compared to regular VLED with flat n-GaN structure and regular electrode, the proposed VLEDs in this paper shows the highest increase in light output power (Lop) by 19.2% at 350 mA. It is expected that the proposed 2-step mesa scheme to improve current spreading in this work could offer potential applications in optoelectronics in the near future.

    目錄 摘 要 I Abstract III 誌 謝 V 第一章 緒論 1 1-1 發光二極體之原理與發展 1 1-2 研究動機 7 第二章 GaN元件結構及其挑戰議題 9 2-1 藍光二極體之發展 9 2-2 水平式與垂直式結構LED 11 2-3 發光二極體之發光效率與提升發光效率之方法 12 2-3-1、發光二極體之發光效率 13 2-3-2提升發光效率之方法 14 第三章 電流分佈理論 25 3-1 電流擴散長度之理論 25 第四章 實驗流程、分析方法與設備 29 4-1 實驗流程 29 4-2 分析方法與實驗設備 29 第五章 非等向性階梯蝕刻與電極設計於LED元件製作 38 5-1 非等向性階梯蝕刻的機制與原理 38 5-2階梯蝕刻電流分佈之模擬 40 5-3 因應非等向性階梯蝕刻設計電極圖案 42 5-4 非等向性階梯蝕刻的製作流程 44 第六章 實驗結果與討論 46 6-1 非等向性蝕刻深度光電特性比較 46 6-2 電極設計光電特性比較 48 6-3 整合電極設計與階梯蝕刻光電特性比較 50 第七章 結論與未來研究之建議 54 7-1 結論 54 7-2 未來研究之建議 54 參考文獻 56 表 目 錄 表1-1 高功率LED與一般照明光源之發展里程碑[7] 5 表1-2 合成白光LED各技術發展分析[8] 6 表6-1 不同深度之階梯蝕刻於VLED其Lop-I-V特性 47 表6-2 不同電極圖案於VLED其Lop-I-V特性 49 表6-3 整合電極設計與階梯蝕刻於VLED其Lop-I-V特性 52 表6-4 整合電極設計與階梯蝕刻於VLED其WPE特性 53 圖 目 錄 圖1-1 直接能隙半導體能帶圖 2 圖1-2 GaN-基藍光LED (a)熱平衡時及 (b)順向偏壓時之能帶示意圖[1] 3 圖1-3 LED照明應用趨勢[5] 4 圖1-4 各種不同光源效率提升Road map[6] 5 圖1-5 三種白光LED發光型式[8] 6 圖2-1 室溫下元素與二元化合物半導體的能隙與晶格常數[37] 11 圖2-2 水平結構LED示意圖 12 圖2-3 垂直結構LED示意圖 12 圖2-4 試片經過KOH蝕刻之SEM圖 (a)10 (b)60 (c)90與 (d)120秒[17] 16 圖2-5 利用微影蝕刻在透明導電層上製作網狀結構 (a)剖面示意圖 (b)俯視示意圖[18] 16 圖2-6 (a)利用準分子雷射照射並且浸泡HCl (b)利用準分子雷射照射並且浸泡HCl與KOH [19] 17 圖2-7 (a)結構示意圖 (b)光強度電流曲線圖[20] 18 圖2-8 (a)六角形結構之側視圖 (b)LED with ZnO rod示意圖 (c)奈米柱增加光萃取效率機制示意圖[21] 18 圖2-9 (a)與(c)為氧化鋅奈米線陣列結構 (b)與(d)為二氧化矽包覆奈米線陣列結構[22] 19 圖2-10 具IZO透明導電層增加電流分佈示意圖 20 圖2-11 Flip Chip結構示意圖[10] 21 圖2-12光子晶體之SEM圖[11] 22 圖2-13 (a)二維光子晶體結構 (b)實驗量測結果[12] 23 圖2-14 TIP-LED結構[41] 24 圖2-15 TIP-LED結構光子逃逸示意圖[42] 24 圖3-1 電流從條狀電極擴散後電流密度分佈圖[43] 25 圖3-2 電流從圓形電極擴散後電流密度分佈圖[43] 27 圖4-1 實驗流程圖 29 圖4-2 高解析掃描式電子顯微鏡 30 圖4-3 電子顯微鏡主體結構示意圖[44] 31 圖4-4 電子束與試片之交互作用。[44] 32 圖4-5 光罩對準曝光機 33 圖4-6 微影製程流程圖 34 圖4-7 感應耦合離子電漿系統(ICP system) 35 圖4-8 LED測試機與測試平台 36 圖4-9 積分球示意圖 37 圖4-10 光形分佈量測儀示意圖 37 圖5-1一般VLED與製備階梯蝕刻VLED其內部等效串聯電阻示意圖 38 圖5-2 Crosslight模擬軟體之階梯蝕刻VLED模組圖 40 圖5-3 Crosslight模擬軟體之階梯蝕刻VLED電流分佈圖 41 圖5-4 Crosslight模擬軟體之階梯蝕刻VLED其MQW電流分佈圖 41 圖5-5 原始電極與樹枝狀電極圖案 42 圖5-6 增加電極線數量改善電流分佈 43 圖5-7 GaN-LED 垂直結構與原始電極圖案 44 圖5-8 GaN-LED 非等向性階梯蝕刻實驗流程圖 45 圖6-1 GaN-VLED 非等向性階梯蝕刻實驗參數 46 圖6-2 不同深度之階梯蝕刻於VLED其Lop-I-V特性比較圖 47 圖6-3 不同深度之階梯蝕刻於VLED其光強度分佈比較圖 47 圖6-4 電極設計參數比較圖 48 圖6-5 不同電極圖案於VLED其Lop-I-V特性比較圖 49 圖6-6 不同電極圖案於VLED其光強度分佈比較圖 49 圖6-7 柵欄式電極不同深度之階梯蝕刻於VLED其Lop-I-V特性比較圖 51 圖6-8 樹枝狀電極不同深度之階梯蝕刻於VLED其Lop-I-V特性比較圖 51 圖6-9 柵欄式電極不同深度之階梯蝕刻於VLED其WPE特性比較圖 52 圖6-10 樹枝狀電極不同深度之階梯蝕刻於VLED其WPE特性比較圖 53

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