臺灣博碩士論文加值系統

本論文分為二個部分，分別利用背面粗化結構與埋入式奈米孔洞結構，來提升發光二極體之外部量子效率。
第一部分是利用雷射背面掃描及化學側向蝕刻技術，在N-face 氮化鎵底部製作具倒立六角錐的晶格蝕刻面之發光二極體，對此發光元件的光電特性加以探討。將氮化銦鎵發光二極體磊晶片經由雷射做背面掃描熔融氮化鎵/藍寶石基板界面之低溫緩衝層，再藉由加熱氫氧化鉀溶液進行側向蝕刻，形成氮化鎵{101 ̅1 ̅ }穩定蝕刻晶格面。氮化鎵緩衝層所扮演的角色為犧牲層，用於雷射的熔融及側向蝕刻，蝕刻速率約為26μm/min。具倒立六角錐N-face 氮化鎵表面結構之發光二極體，於接近氮化鎵/藍寶石基板界面相較於一般傳統發光二極體擁有較大之光散射效應，且在發光強度量測上有47%提升。接著，我們再用相同技術不同雷射掃描線間距，製作不同粗化面積對發光二極體亮度提升之影響，當增加粗化面積，其穿透光譜之截止波常與光伏效率之波常皆有紅移現象，是由於在主動層中之光吸收增加所導致的。再來，我們依然用此技術做整面元件雷射掃描，量測其發光強度有70%提升，並對此標準與處理過結構量測光伏電池特性與外部量子效率分別為38.3% (at 392 nm) 與 70.5% (at 396 nm)。最後，我們將其技術應用於具圖案化藍寶石基板之發光二極體(pattern sapphire substrate-LED, PS-LED)，來探討其倒立六角錐結構在此種基板上之影響效應。PS-LED強度本身較傳統LED要來的強，是由於圖案化的藍寶石基板，此種基板可增加光散射強度，實驗結論為BRPS-LED其光取出強度較PS-LED高21.4%，所以BRPS-LED整體強度提升效應是存在的。在發散角部份，BRPS-LED具有較大的發散角，是由於倒立六角錐結構造成光散射影響。且在背面取光部分，其PS-LED因圖案化之關係將光反射到正面取光，所以背面取光較弱，而做過處理之BRPS-LED其正面取光不但可提升，亦可提升背面光取出效率。
第二部分在LED結構與藍寶石基板中間設計一0.75um厚度之n+-GaN:Si磊晶層，藉由雷射正面掃描給予通道並進行電化學側向蝕刻技術，製備具有管狀孔洞微結構氮化鎵結構的氮化銦鎵發光二極體，在稀釋過的硝酸水溶液中施一正偏壓10V，n+-GaN:Si磊晶層形成奈米管狀結構。受外加偏壓電場方向影響奈米管狀結構的方向垂直於雷射切割線。寬度560um中尺寸氮化銦鎵元件蝕刻速率高達9.3um/min。埋入式奈米管狀結構具有低折射率的特性，提升LED發光強度，在發散角量測中留有明顯Fabry-Pérot干涉。嵌入式奈米管狀氮化鎵結構有良好取光特性，一次磊晶成長製程，且在低電壓之下能快速進行選擇性電化學蝕刻側蝕，未來具有製備出大尺寸高功率氮化鎵發光二極體之潛力。

The dissertation consisted of the backside roughing process and the embedded nanoporous structure in the InGaN-based light-emitting diodes (LEDs) to increase the external quantum efficiency.
The first part isthe InGaN-based with a roughened patterned backside on the N-ace GaN surface were fabricated through a crystallographic etching process to increase light extraction efficiency. After laser decomposition, laser scribing, and a lateral crystallographic wet etching process at the GaN/Al2O3 interface, stable crystallographic etching planes were formed as the GaN {101 ̅1 ̅ } planes that included an angle with the top GaN (0001) plane measured at 58o. The GaN buffer layer acted as the sacrificial layer for the laser decomposition process and the lateral wet etching process with a 26μm/min etching rate. The LED with the inverted pyramidal N-face GaN surface close to the GaN/Al2O3 interface has a larger light scattering process than the conventional LED. The light output power of the LED with the backside roughened surface had a 47% enhancement when measured in LED chip form.Next, the different backside roughened-area ratios were fabricated through the sametechniqueon different laser-scribe spacing. By increasing the backside roughened area, the cutoff wavelength of the transmittance spectra and the wavelength of the peak photovoltaic efficiency had a redshift phenomenon that could be caused by increasing the light absorption at InGaN active layer.Then, the LED with overall backside roughened-area was realized in the InGaN LED structure.The light output power of the treated LED structure had a 70% enhancement. The peak external quantum efficiency (EQE) and peak wavelengths of the photovoltaic properties were measured at 38.3% (at 392 nm) and 70.5% (at 396 nm) for the conventional and the treated structures, respectively. Final, this technique was used on the InGaN-based LED structure grown on a patterned-sapphire substrate (PS-LED) to form the hexagonal inverted pyramid structures. The light output power of the BRPS-LED with the backside roughened surface had a 21.4% enhancement compared to aconventional PS-LED in chip form. The larger divergent angle of BRPS-LED could be caused by light-scattering process from the inverted pyramidal-shaped structures on the roughened patterned backside surface at the GaN/Al2O3 interface. The high light intensity at the normal direction of the PS-LED caused by the higher light scattering process on the triangle-shaped patterned sapphire structure. In the BRPS-LED structure, the high light intensity was observed at the normal direction and the backside direction that was caused by the higher light scattering process on the inversed cone-shaped structure and the patterned sapphire substrate.
The second part, InGaN light-emitting diodes (LEDs) with directional nano-pipe GaN structures were fabricated through a selectively electrochemical (EC) etching process. A 0.85μm-thick n+-GaN:Si epitaxial layer inserted between LED structure and sapphire substrate was transformed into the nano-pipe structure in diluted nitric acid solution with +10V bias voltage. The directional nano-pipe structure was perpendicular to the laser scribing lines and guided by the external bias electric field. Wide etching width (560μm) and high lateral etching rate (9.3μm/min) were achieved in the middle size of InGaN LED chip (560×910 μm2). High light emission intensity and clear Fabry-Pérot interferences were observed in the treated LED structure, caused by low effective refractive index in the nano-pipe GaN structure. Embedded nano-pipe GaN structure with high light extraction property has been demonstrated with one step epitaxial growth process and the selective EC etching process that have a potential for the large-size high efficiency nitride-based LED applications.

Acknowledgements i
Abstract (in Chinese) ii
Abstract iv
Contents vi
List of Figures ix

Chapter 1 Introduction 1
1.1 Background of Light-Emitting Diodes 1
1.2 Ⅲ-ⅤSemiconductor 2
1.3 Review of Wet Etching Process 3
1.4 The External Quantum Efficiency 4
1.5 Organization of This Dissertation 8
Chapter 2 Experiment 10
2.1 MOCVD Growth InGaN Light-Emitting Diodes 10
2.2 Device Fabrication 11
2.3 Laser-Scribe (LS) process 11
2.4 Wet Etching and Electrochemical Wet Etching Processes 11
2.5 Characterization Techniques 12
2.5.1 The Optical Microscopy (OM) 12
2.5.2 The Cold Field Emission Scanning Electron Microscopy (FE-SEM) 12
2.5.3 The Focused Ion Beam (FIB) 13
2.5.4 The Micro-Photoluminescence Spectroscopy (μ-PL) 13
2.5.5 The Electroluminescence (EL) 14
2.5.6 The Beam Profiler 14
2.5.7 The Radiation Pattern Measurement 15
Chapter 3 Blue Light-Emitting Diodes with a Roughened Backside Fabricated by Wet Etching 18
3.1 General Introduction 18
3.2 Device Fabrication of Blue Light-Emitting Diodes with a Roughened Backside Fabricated by Wet Etching 18
3.3 Characteristics of Blue Light-Emitting Diodes with a Roughened Backside Fabricated by Wet Etching 19
3.4 Summary 22
Chapter 4 InGaN Light Emitting Diodes with a Laser-treated Tapered GaN Structure 26
4.1 General Introduction 26
4.2 Device Fabrication of InGaN Light Emitting Diodes with a Laser-treated Tapered GaN Structure 26
4.3 Characteristics of InGaN Light Emitting Diodes with a Laser-treated Tapered GaN Structure 29
4.4 Summary 36
Chapter 5 InGaN Light Emitting Diodes with Embedded Roughened Structure in the GaN/Sapphire Interface formed using Laser Decomposition Process 43
5.1 General Introduction 43
5.2 Device Fabrication of InGaN Light-Emitting Diodes with Embedded Roughened Structure in the GaN/Sapphire Interface formed using Laser Decomposition Process 43
5.3 Characteristics of InGaN Light-Emitting Diodes with Embedded Roughened Structure in the GaN/Sapphire Interface formed using Laser Decomposition Process 45
5.4 Summary 49
Chapter 6 InGaN Light-Emitting Diodes with Directional Nano-pipe Structures 55
6.1 General Introduction 55
6.2 Device Fabrication of InGaN Light-Emitting Diodes with Directional Nano-pipe Structures 55
6.3 Characteristics of InGaN Light-Emitting Diodes with Directional Nano-pipe Structures 57
6.4 Summary 63
Chapter 7 Conclusions 72
References 74
About the Author 81
Publication Lists 82

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