本論文之研究主題係旨在進行一種具折射係數漸變(從氮化鎵折射係數2.5到氮化矽折射係數1.9~2.0再到空氣折射係數1)奈米結構(氮化鎵奈米線)之氮化鎵發光二極體結構之理論模擬元件製備與光電特性分析，以期製備出最佳發光效率之氮化鎵發光二極體。
本論文研究架構主要分為兩個部分，第一部分以理論模擬分析為主，係透過光學模擬軟體(TracePro)以分析氮化鎵奈米線長度及沉積氮化矽厚度對發光二極體表面之光析出效率影響。由光學模擬軟體顯示，具氮化鎵奈米線於長度800 nm及沉積氮化矽厚度250 nm 的結構，有最佳之光析出效率(與傳統氮化鎵發光二極體比較)。第二部分則著重於實驗之進行，先利用氧化鋅奈米線當作ICP蝕刻之遮罩，製備出表面具氮化鎵奈米結構之發光二極體，再進行PECVD沉積氮化矽薄膜，即完成具折射係數漸變及奈米結構之氮化鎵發光二極體元件。此元件亦藉由掃描式電子顯微鏡(SEM)、能量散射光譜儀(EDS)與積分球…等等儀器，來進行表面形貌、成分、及GaN-基VLED光電特性分析。
實驗結果顯示，具折射係數漸變及奈米結構之氮化鎵發光二極體元件於注入電流350 mA時，與傳統氮化鎵發光二極體(已進行KOH表面粗化)相較，其光析出效率增加28.7%。此光電特性結果證實本研究提出之新穎結構，確實可藉由表面粗化(氮化鎵奈米結構)及折射係數漸變薄膜(沉積氮化矽)來降低全反射效應與菲涅耳損耗，大幅提升光析出效率。

In this thesis, the improvement in light output power of vertical light emitting diodes (VLEDs) is studied. The surface-texturing of VLEDs with Si3N4/GaN nanowire arrays (NWAs) which provides a surface roughening scheme with the refractive index varying from 2.5 (GaN) to 1.9~2.0 (Si3N4) to 1 (air) to effectively maximize light extraction efficiency through releasing total internal reflection (TIR) and minimize Fresnel loss was proposed and demonstrated.
There are two parts comprised in the present thesis. The first part focuses on the simulation and design of Si3N4/GaN NWAs for VLEDs. An optical simulation software, TracePro, was used to simulate the size effects of Si3N4/GaN NWAs (with different lengths and coating thickness) on the light output efficiency of VLEDs. An better design for Si3N4/GaN NWAs with a length of 800 nm and a deposited thickness of 250 nm has been obtained.
The second part of the present study aims at the preparation of VLEDs with Si3N4/GaN NWAs. With ZnO NWAs as a mask, a dry etching using an inductively coupled plasma (ICP) reactive ion etching (RIE) process was conducted to the n-GaN surface with a depth of 800 nm NWAs. A 250-nm-thick Si3N4 layer with a typical refractive index of 1.9~2.0 was coating on the GaN NW using a plasma-enhanced CVD system. Material analysis including surface morphology, components, and photoelectrical properties of the prepared VLEDs are examined and results are presented and discussed.
In summary, the effectiveness of refractive-index-matched (RIM) Si3N4/GaN NWAs surface roughening scheme in improving Lop of VLEDs has been demonstrated. A considerable improvement in Lop of proposed VLEDs by 28.7% at 350 mA, as compared with that of the regular VLEDs, has been achieved, which could be attributed to the RIM Si3N4/GaN NWAs structure can effectively release TIR and minimize the Fresnel loss.

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