氮化銦鎵發光二極體成長於圖案化藍寶石基板之研究

Growth and Characterization of InGaN LEDs Grown on Patterned Sapphire Substrates

林素慧(Shu-hei Lin)

國立虎尾科技大學/電機資訊學院/光電與材料科技研究所/碩士(2006年)

摘要

中文摘要

由於氮化鎵磊晶成長一直缺少晶格常數匹配的基板，因此如何降低氮化鎵磊晶薄膜的缺陷密度已成為目前重要的研究方向。本論文係以感應式耦合電漿蝕刻系統將藍寶石基板蝕刻出規則重複排列的圓形圖案，直徑3 μm、間距3 μm、深度為0、0.5、1和1.5 μm，製作成圖案化藍寶石基板。隨後在圖案化藍寶石基板上利用有機金屬化學氣相沉積系統成長氮化鎵發光二極體結構，也將其應用於覆晶型式發光二極體，並探討其元件特性。經由實驗結果顯示，使用圖案化藍寶石基板且發光波長分別為380、400和470 nm之發光二極體，其光輸出功率較傳統藍寶石基板結構發光二極體分別高出36、13和5 %。這結果顯示說明了圖案化藍寶石基板應用在470 nm氮化鎵發光二極體上，差排密度的降低對發光效率並不會有太大的影響，但對短波長(380 nm)的發光二極體元件，因量子井中銦元素含量少，而造成侷限載子的能力較差，導致差排缺陷產生非輻射再結合，而降低發光效率，因此減少差排密度可大幅增加光輸出功率。最後我們將圖案化藍寶石基板應用在覆晶結構之發光二極體(波長425 nm)，我們發現光輸出功率可提升59%，元件光輸出功率的提升可以歸因於氮化鎵薄膜成長於圖案化藍寶石基板上會產生橫向磊晶的效果，可以降低缺陷密度進而改善氮化鎵磊晶薄膜品質，同時藍寶石基板上的凹凸圖案會產生光散射的效果，因而增加光的取出率。

關鍵字: 氮化鎵、氮化銦鎵、發光二極體、圖案化藍寶石基板

並列摘要

Abstract

In this study, the use of conventional and patterned sapphire substrates (PSSs) to fabricate GaN light-emitting diodes (LEDs) was demonstrated. The PSS was prepared using a periodic hole pattern (diameter: 3mm; spacing: 3mm) on the (0001) sapphire with different etching depths. From transmission-electron-microscopy and etch-pit-density studies, the PSS with an optimum pattern etching depth (1.5 μm) was confirmed to be an efficient way to reduce the thread dislocations in the GaN microstructure. For a typical lamp-form 380 nm near-ultraviolet (UV) PSS LED, the output power (@20 mA) increased from 3.75 to 5.06 mW, corresponding to about 36% increases in the external quantum efficiency. In contrast, the 470 nm blue PSS LED shows a slight increase (5%) in the light output power. This indicates that the dislocation density has a large effect on the performance of UV LEDs. Moreover, the flip-chip technology was applied to the near-UV LEDs with a PSS structure. When the PSS flip-chip LED operated at a forward current 350 mA, the output power increased 59% as compared with that of the standard flip-chip LED. The achieved improvement of the output power is not only due to the improvement of the internal quantum efficiency upon decreasing the dislocation density, but also due to the enhancement of the extraction efficiency using the PSS.

Index Terms: GaN, InGaN, light-emitting diode (LED), patterned sapphire substrate (PSS)

參考文獻

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