InGaN Light-Emitting Diodes with Embedded Nanoporous GaN Distributed Bragg Reflectors

In this thesis, InGaN-based light emitting diodes (LED) with embedded conductive nanoporous-GaN/undoped-GaN (NP-GaN/u-GaN) distributed Bragg reflectors (DBR) have been demonstrated. The nanoporous GaN DBR structures were fabricated through a pulse 355nm laser scribing process and an electrochemical etching (EC) process. Si-heavy doped GaN:Si layers (n+-GaN) in the 8-period n+-GaN/u-GaN stack structure were transformed into a low refractive index and a conductive nanoporous GaN structure. 8-period DBR structure consisted of a quarter-wavelength (1/4λ) NP-GaN layer and a five-quarter-wavelength (3/4λ) u-GaN layer. The center wavelength, peak reflectivity, and stop-band width of the nanoporous GaN DBR structure were measured at 417 nm, 96.3%, and 25.6 nm, respectively. The reflectivity of active layer was 92.6% at 410 nm. The region of EC-LED by EC etching process had high EL intensity that corresponded with beam profile. The resonance cavity modes of the PL spectra were observed by 266 nm pulse laser source in the EC-LED structure with the nanoporous DBR structure. InGaN LED structure with embedded NP-GaN/u-GaN DBR structure had been fabricated that have potential for the high efficiency and the resonant-cavity optoelectronic device applications.本論文研究主要探討埋入具奈米多孔隙之氮化鎵布拉格反射鏡結構於氮化鎵發光二極體，由設計8對高矽濃度摻雜與未摻雜氮化鎵薄膜堆疊結構，係利用Nd:YVO4 355 nm雷射切割系統與選擇性電化學蝕刻製程，使高矽濃度摻雜之氮化鎵層轉變為奈米多孔隙結構，而此結構擁有低折射率與導電之特性，並與未摻雜氮化鎵薄膜交互堆疊為具奈米多孔隙之氮化鎵布拉格反射鏡結構。 此布拉格反射鏡結構分別由8對光學長度1/4λ奈米多孔隙結構(nanoporous GaN:Si)與3/4λ未摻雜(u-GaN)之氮化鎵薄膜所組成，其中心反射波長為417 nm，反射率為96.3%且截止帶(stop-band)寬為25.6 nm，此結構於410 nm主動層發光波長之反射率為92.6%，使EC-LED電化學側蝕區域擁有高電激發光強度，與光強度分佈圖相符，並透過266 nm脈衝雷射觀察共振腔現象，此元件極具有高效率共振腔發光元件(Resonant-cavity optoelectronic device )之應用潛力。中文摘要 I Abstract II 目錄 III 圖目錄 V 第一章 序論 1 1-1 發光二極體介紹 2 1-2 布拉格反射鏡介紹 4 1-3 共振腔發光二極體介紹 6 1-4 雷射二極體介紹 7 1-5 研究動機 9 第二章 文獻回顧 10 2-1布拉格反射鏡(DBR) 10 2-2共振腔發光二極體(RCLED) 14 2-3垂直共振腔面射型雷射(VCSEL) 20 2-4雷射切割製程(Laser scribing processing) 26 2-5電化學蝕刻多孔隙機制(Mechanism of electrochemical etching process) 28 第三章 實驗步驟與方法 32 3-1 實驗設計與流程 32 3-2 試片製備流程 34 3-3實驗設備儀器介紹 37 3-3.1雷射切割系統 37 3-3.2電化學蝕刻 38 3-4分析儀器 39 3-4.1 光學顯微鏡(Optical microscope, OM) 39 3-4.2 多功能聚焦離子束系統(Focused Ion Beam, FIB) 40 3-4.3 電激發螢光光譜(Electroluminescence, EL) 41 3-4.4 光激發螢光光譜(Photoluminescence, PL) 42 3-4.5 發散角量測(Radiation pattern measurement) 43 第四章 實驗結果與討論 44 4-1發光二極體元件之光學顯微鏡表面形貌分析 44 4-2發光二極體元件之場發掃描式電子顯微鏡截面分析 46 4-3發光二極體元件之布拉格反射鏡量測 47 4-4發光二極體元件之光強度分布均勻性分析 48 4-5發光二極體元件之電激發螢光光譜量測 50 4-6發光二極體元件之電激發光遠場光輻射圖形特性 51 4-7發光二極體元件之光激發光光譜量測 52 4-8發光二極體元件之電性分析量測 53 第五章 結論與未來展望 54 5-1 實驗結論 54 5-2 未來展望 55 參考文獻 5