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標題: 氮化鎵磊晶模板之缺陷特性研究與發光二極體元件應用
Defect Characterization of GaN Epilayer Template for LED Applications
作者: 凃任鴻
Tu, Jen-Hung
關鍵字: Defect
light-emitting diode
patterned sapphire substrate
efficiency droop
quantum efficiency
出版社: 材料科學與工程學系所
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摘要: 在本論文中我們提出一個有效率降低貫穿式差排密度並且增加內部量子效率應用在氮化銦鎵近紫外光波段(~400 nm)發光二極體元件。氮化鎵選擇性蝕刻缺陷加上圖案化藍寶石基板技術的組合,在成長磊晶層時成為貫穿式差排的遮罩阻止差排成長延伸。這種選擇性蝕刻氮化鎵/圖案化藍寶石基板結構能夠有效將缺陷集中並且將缺陷密度下降約105 cm-2。而再成長的氮化鎵磊晶層使用X-ray雙晶繞射、冷陰極螢光量測、穿透式電子顯微鏡分析其結構特性。在350 mA電流注入下,使用選擇性蝕刻二氧化矽阻擋層/圖案化藍寶石基板結構的LED量測其光輸出功率比傳統使用藍寶石基板效率提高約46%,光輸出功率不只是因為降低缺陷密度,並且利用擇性蝕刻二氧化矽阻擋層/圖案化藍寶石基板結構增加其光取出效率。 另外,我們將使用模擬軟體SiLENS來模擬InGaN多量子井結構於不同缺陷密度下對LED的效率影響,並使用模組模擬在近紫外光波段的(~400 nm) InGaN/GaN發光二極體於不同缺陷密度成長在藍寶石基板上,並改變電流值得到光功率輸出,並且在細節討論元件能帶圖、載子分佈、輻射復合效率、光電特性曲線、和外部量子效率。然而,低缺陷密度元件隨著電流密度注入增加效率跟著下降,然而高缺陷密度的效率衰退反而較小。而模擬結果認為降低缺陷在高電流密度注入下增加光電特性主要還是因為增加直接輻射復合率所造成的。
In this thesis, we report an approach for efficiently improving the threading dislocation (TD) density and internal quantum efficiency of InGaN-based near-ultraviolet (~400 nm) light-emitting diodes (LEDs). A combination of selective etching of GaN defects and patterned sapphire substrate (PSS) techniques forms a growth mask of TDs in GaN epitaxial layers. This selective etched-GaN/PSS structure can efficiently achieve defect centralization and the defect density can be reduced to 105 cm-2. The structural properties of the regrown GaN epilayers were investigated in details using double-crystal X-ray diffraction, cathodeluminescence, and secondary ion mass spectroscopy. Under a 350-mA injection current, the output power of the SiO2-block/PSS LED is enhanced by 46% compared with that of the conventional GaN/sapphire one. The improvement of the output power is not only due to the decrease in dislocation density, but also to the enhancement of extraction efficiency using PSS. In addition, we investigate the characteristics of near-ultraviolet (~400 nm) InGaN multiple-quantum well based LED using a SiLENS simulation program. Simulations of light-output power versus current are performed for GaInN/GaN light-emitting diodes grown on GaN-on-sapphire templates with different threading dislocation densities. The energy band diagrams, carrier concentrations, radiative recombination efficiency, light-current curves, and external quantum efficiency are taken into account in detail. Low-defect-density devices exhibit a efficiency peak followed by droop as current increases. However, the high-defect-density devices show low peak efficiencies and little droop. The simulation results suggest that improvement of internal quantum efficiency is mainly due to the increase of radiative recombination at high current injection.
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