成長於圖案化藍寶石基板之氮化鎵發光二極體特性分析

InGaN Ultraviolet Light-Emitting Diodes Grown on Patterned Sapphire Substrates

謝奇勳(Chi-Hsun Hsieh)

指導教授 ： 綦振瀛

國立中央大學/資訊電機學院/電機工程學系/碩士(2007年)

摘要

本文成功地成長近紫外光發光二極體結構於圖案化藍寶石基板上，並且由基板蝕刻方向、蝕刻深度與晶體之缺陷密度的角度，深入地分析此具有圖案化藍寶石基板的發光二極體 ( Light Emitting Diode Grown on Patterned Sapphire Substrate, PSS-LED ) 與傳統平面基板之發光二極體之差異。
在基板製備方面，我們有系統地描述了於不同酸性蝕刻溶液配比與蝕刻溫度條件下，蝕刻溶液對藍寶石基板的蝕刻測試，並且提出了一個最佳的蝕刻條件；接著分別沿著藍寶石<1-100>與<11-20>方向，蝕刻製備出具對稱與非對稱輪廓之一維條紋圖案化藍寶石基板，並明確地說明相關的蝕刻輪廓與其形成原因。
在具有圖案化基板之發光二極體光電特性探討方面，<11-20> PSS-LED於基板蝕刻深度分別為0.2、0.5與0.9 μm之元件，與傳統平面基板的發光二極體相較之下，光強度依序有著21%、44%與87%之提升；相對地，在具有相同條紋蝕刻深度之<1-100> PSS-LED，於光強度上也有37%、72%與163%的提昇。並且我們也利用遠場光型的量測 ( Far-Field Pattern ) 證明了 <11-20> PSS-LED與<1-100> PSS-LED之發光散角 ( Radiation Pattern ) 會隨著蝕刻圖案深度的增加而縮小，當蝕刻深度由0到0.9 μm時，其發光散角由148o縮小至120o。於元件電特性分析上，在成長氮化鎵緩衝層時，利用類似FIELO成長技術使得緩衝層的差排密度有將近3倍以上之改善，這使得元件具有較少的漏電路徑，也將元件之逆向偏壓特性延伸至-23.85V@-10uA以上。
利用濕式蝕刻技術以製備圖案化藍寶石基板，不但符合可大量生產的條件外，也減少了製程所需之成本與時間；同時成長氮化鎵材料於此圖案化藍寶石基板上，不僅可具有較優越的晶體品質，同時也有效地提升了發光二極體之光萃取率，使得發光二極體有更好的光電特性表現。

關鍵字

發光二極體 ； 氮化鎵 ； 圖案化基板

並列摘要

Near ultraviolet GaN/InGaN multi-quantum-well light-emitting diodes (LEDs) have been grown on stripe-patterned sapphire substrates (PSSs) and investigated. The correlation between the stripe orientation, etching depth, dislocation density, and the electrical and optical properties of the 400 nm LEDs are examined and compared with the LEDs grown on planar sapphire substrates.
Etching conditions have been systemically studied by varying the composition of etching solutions and etching temperatures. Symmetric and asymmetric etching profiles are observed as the stripe patterns are defined along the <1-100>sapphire and <11-20>sapphire direction, respectively. Based on the etch pits density experiments, dislocation density of GaN can be reduced by over 3 times as the patterned sapphire substrates are used. The output power of <11-20> PSS-LEDs is enhanced by 21%, 44% and 87% as the etching depth is 0.2, 0.5 and 0.9 μm, respectively. On the other hand, the output power of <1-100> PSS-LEDs is enhanced by 37%, 72% and 163% as the etching depth is 0.2, 0.5 and 0.9 μm, respectively. The radiation angle of LEDs is also found to decrease from 148o to 120o with increasing groove depth from 0 to 0.9 μm while similar radiation angle is observed for the LEDs grown on PSS with stripes along different directions.

並列關鍵字

GaN ； light-emitting diode ； patterned sapphire substrate

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