Functional embedded structures in InGaN light-emitting diodes

本論文中，利用雷射處理與電化學濕式蝕刻技術，製作具有奈米孔洞與空隙結構增加光取出效率的發光二極體元件，經由雷射處理與電化學濕式蝕刻後，在元件底部n型氮化鎵層與高濃度摻雜n型氮化鎵層分別形成奈米孔洞與空隙結構，利用草酸選擇性蝕刻之特性，設計不同矽摻雜濃度之n型氮化鎵層之發光二極體元件，並對側蝕結構之元件電性與光性加以探討。本實驗將探討具奈米孔洞與空隙結構之側向蝕刻發光二極體元件(Lateral etching light emitting diode, LE-LED) 與化學剝離發光二極體元件(Chamical lift off, LO-LED) 兩者相對於傳統發光二極體(Standard LED, ST-LED) 之特性研究，分別研究兩種氮化鎵發光元件對於發光特性之影響。 實驗一，LE-LED 在未摻雜之氮化鎵層間埋入一高矽摻雜濃度之n型氮化鎵層，經草酸電化學濕式蝕刻後，由於不同矽摻雜濃度之n型氮化鎵層側蝕速率不同，而在元件底部形成奈米孔洞與空隙(nanoporous/Air) 結構，具奈米孔洞與空隙層的發光元件光取出效率相較於ST-LED 有58% 的提升，其主要是由於側向蝕刻形成之奈米孔洞結構散射所造成，而在LE-LED 元件中觀察到光激發波長出現藍移的現象，主要是由於應力釋放的結果，在0°~35°角度間則發現LE-LED 則發現螢光在420nm~500nm 的波長範圍間有一高光穿透之特性，而在波段520nm~700nm 處則有抑制的現象，可藉此推測LE-LED 之奈米孔洞結構，具有一類似於帶通濾波器之光學性質。 實驗二，LO-LED 結構的製備如同LE-LED，利用草酸選擇性蝕刻，增加反應時間，使高濃度摻雜之n型氮化鎵層完全側蝕，可成功製備出剝離之發光二極體元件，量測其光取出效率相較於ST-LED 有215%提升，光激發波長出現藍移的現象，其主要來自應力釋放所造成之結果，而隨著注入電流增加，電激發光波長 LO-LED藍移量則相對於ST-LED有減少的趨勢，其主要是因為InGaN發光層壓縮應變所導致的壓電場有減少的趨勢。 透過雷射處理與電化學濕式蝕刻技術，可製備出側向蝕刻之奈米孔洞與空隙層結構，能有效提升元件之光取出效率，亦研究出化學剝離元件與基板再利用的可能性。In this paper, the InGaN-based light emitting diodes (LEDs) with nanoporous and air gap structures were fabricated through the laser treatment and the Electrochemical (EC) wet etching process to increase light extraction efficiency. After laser treatment and the EC wet etching process, the nanoporous structure was formed at the GaN:Si layer, and the air gap structures were formed at the heavily doped GaN:Si layer. In this study, we analyzed optical and electrical of these two kinds of LEDs, the lateral etching light emitting diode (LE-LED) and chemical lift off light emitting diode (LO-LED), compared to the standard LED (ST-LED). In the first experiment, the LE-LED structure with the GaN:Si nanoporous and the air-gap structures were fabricated through the EC wet etching process on the GaN:Si layers. The light output power of the LE-LED structure had a 58% enhancement compared with the ST-LED structure that had a high light scattering process occurred on the lateral etched nanoporous structure. The light transmittance ratios of the LE-LED were measured as values of 2.56 times for blue light region (420 to 500nm) and at 0.43 time for yellow light region (520 to 700nm), respectively, compared with the ST-LED structure at lateral 35o detected angle. The transmittance spectrum of the nanoporous GaN:Si structure was similar like a band-pass filter to enhance the light extraction efficiency in InGaN LEDs. In the second experiment, the LO-LED had the same epitaxial structure with the LE-LED. By increasing the reaction time, the GaN:Si nanoporous structure and let the heavily doped GaN:Si layer were etched completely through the EC wet etching process. The light output power of the LO-LED structure had a 215% enhancement compared with a ST-LED structure that had a high light scattering process occurred on the lateral etched nanoporous and completely etched air gap structures. The photoluminescence wavelength blueshift phenomenon of the LO-LED was caused by partial stress release. By increasing the injection current, the peak wavelength blueshift phenomenon of the LO-LED was smaller than the ST-LED that indicated the compress strain induced piezoelectric field of the InGaN active layer was slightly reduced in the LO-LED The nanoporous and the air gap structures of the GaN:Si layers were fabricated through the EC wet etching process with different reaction times on the InGaN LED structures to enhance the light extraction efficiency and lift off LEDs, that can be applied to the high efficiency nitride-based LED and the reusable substrate technology.中文摘要 I ABSTRACT II 目錄 III 圖目錄 V 第一章 序論 1 1.1照明技術的發展 1 1.2 半導體發光二極體簡介 3 1.3 Ⅲ-Ⅴ族半導體 3 1.4研究動機 4 第二章 原理與文獻回顧 5 2-1發光二極體之發光原理 5 2-2發光二極體之光取出效率 7 2-2.1內部量子效率 7 2-2.2外部量子效率 9 2-2.3提升外部量子效率之文獻 10 2.3 壓電場(PIEZOELECTRIC FIELD) 16 2.3.1應變(Strain)的產生 16 2-4 雷射處理 23 2.5多孔隙結構之氮化鎵文獻回顧 24 2.5.1多孔隙重新磊晶成長發光二極體結構 24 2.5.2蝕刻多孔隙結構剝離之應用 25 2.6氮化鎵選擇性電化學蝕刻機制文獻回顧 27 2.6.1能帶與電化學蝕刻之關係 27 2.6.2電化學蝕刻多孔形貌機制 29 2.6.3不同電解液之影響 31 2.6.4施加不同偏壓之影響 32 2.6.5不同電化學反應時間之影響 33 2.6.6不同摻雜濃度對側蝕結構之影響 34 第三章 實驗步驟與方法 35 3-1實驗設計與流程 35 3-2試片製備流程 35 3-3 雷射處理裝置系統 41 3-4 電化學溼式蝕刻裝置 42 3-5分析儀器 43 3-5.1光學顯微鏡(OM) 43 3-5.2場發射掃描式電子顯微鏡(FE-SEM) 43 3-5.3電激螢光光譜(Electroluminescence, EL) 44 3-5.4光激螢光光譜(Photoluminescence, PL) 45 3-5.5發散角量測(Radiation Pattern Measurement) 47 第四章 實驗結果與討論 49 4-1具空氣與多孔(AIR/POROUS)結構之側向蝕刻發光二極體元件(LE-LED) 49 4-1.1 LE-LED之光學顯微鏡(OM)表面形貌分析 49 4-1.2 LE-LED之場發掃描式電子顯微鏡(FE-SEM)形貌分析 51 4-1.3 LE-LED之光強度分布均勻性分析(Beam profile) 53 4-1.4 LE-LED之光激發螢光光譜量測 55 4-1.5 LE-LED之電激發螢光光譜量測 57 4-1.6 LE-LED之電激發光遠場光輻射圖形特性(Far-field Radiation Patterns) 58 4-1.7 LE-LED之光激發光遠場光輻射圖形特性(Far-field Radiation Patterns) 60 4-2溼式電化學剝離發光二極體元件(LO-LED) 63 4-2.1 LO-LED之光學顯微鏡(OM)表面形貌分析 63 4-2.2 LO-LED之場發掃描式電子顯微鏡(FE-SEM) 形貌分析 66 4-2.3 LO-LED 之光強度分布均勻性分析(Beam profile) 68 4-2.4 LO-LED 之微區光激發螢光光譜量測 69 4-2.5 LO-LED 之電激發螢光光譜量測 70 4-3電化學濕式蝕刻機制探討 72 4-3.1 穿透式電子顯微鏡分析 72 4-3.2 蝕刻反應機制探討 75 第五章 結論 76 5-1 實驗結論 76 5-2 未來展望 77 參考文獻 7

Separating InGaN membranes from GaN/sapphire templates through a crystallographic-etch-limited process

InGaN membranes with light-emitting diode (LED) structures were separated from an undoped GaN nanorod structure on sapphire substrates through a chemical lift-off (CLO) process. The CLO processes consisted of a reducing diameter process on the GaN nanorods structure and a crystallographic wet-etching process on an N-face GaN surface. The N-face crystallographic-etching process was limited by the boundary of the GaN nanorods, where a InGaN active layer can prevent etching damage in a hot potassium hydroxide solution. The light output power of the lift-off LED membrane had a 2.28 times enhancement compared with a non-treated LED. A pyramidal-roughened structure was formed on the lift-off GaN surface to increase the light extraction efficiency. The free-standing InGaN LED membranes were realized through a crystallographic-etch-limited CLO process, which has the potential to replace the traditional laser lift-off process for vertical LEDs and be applied to flexible optoelectronic membrane applications

Fabricated InGaN Membranes through a Wet Lateral Etching Process

Epitaxial layers of InGaN light-emitting diodes (LED) were separated from undoped GaN/sapphire structures through a wet lift-off process. A 0.1-µm-thick Si-heavy-doped GaN:Si (n+-GaN) layer was inserted in the InGaN LED structure that acted as a sacrificial layer for a lateral wet etching process. The lateral etching rate of the n+-GaN sacrificial layer was 315 µm/h. The Fabry–Pérot interferences of the lift-off InGaN LED membranes were observed in the angle-resolved photoluminescence spectra that indicated that the lift-off InGaN membranes had a flat etched surface. High light extraction efficiency, narrow divergent angle, and flat wet-etched GaN surface were observed on the lift-off InGaN membrane

InGaN Light-Emitting Diode with a Nanoporous/Air-Channel Structure

High-efficiency InGaN light-emitting diode (LED) with an air-channel structure and a nanoporous structure was fabricated. The air-channel structure was formed through an epitaxial regrowth process on a dry-etched undoped GaN nanorod structure. The GaN:Si nanoporous structure embedded in treated LED structures was fabricated through a photoelectrochemical wet etching process in an oxalic acid solution. Light output powers were enhanced 1.48- and 1.75-fold for the LEDs with an air-channel structure and with a nanoporous/air-channel structure, respectively, in comparison with that of a conventional LED structure. The air-channel structure and the nanoporous GaN:Si structure in the treated LED structures provided high-light-extraction structures