利用蝕刻孔洞法研究圖案化藍寶石基板上近紫外光 發光二極體的內部量子效率

Abstract

內部量子效率(IQE)的提升對於近紫外光發光二極體(NUV-LED)之發光效率影響極為重要。目前之NUV-LED主動層材料為氮化鋁鎵，其IQE對於穿隧差排密度之敏感度較高。而其中材料晶體品質直接影響元件的內部量子效率(IQE)，因此對於材料晶體品質的分析與增進變得十分重要。 在本篇論文中，我們首先改善了用於分析晶體品質的蝕刻孔洞法(EPD)，使之能確切地計算出穿隧差排密度(TDD)，並實際應用於分析近紫外光發光二極體(NUV-LED)之緩衝層(Buffer layer)氮化鎵薄膜之缺陷密度。本研究利用圖案化藍寶石基板技術來提升磊晶晶體品質，在優化後的蝕刻孔洞法分析下，我們發現螺旋形差排與混和型差排密度，由2.09*106成功的減少至1.66*106 (cm-2)，整體減少了20.5%的缺陷密度。 該結果最終與鄭文逸同學的拉曼分析模型互相印證，成功證明利用圖案化藍寶石基板(Patterned Sapphire Substrates, PSSs) 可以大幅減少氮化鎵薄膜的穿隧差排密度(Threading Dislocation Density)以增加發光二極體主動層之磊晶品質。

The improvement of internal quantum efficiency (IQE) is significant for the luminous efficiency of near-ultraviolet light-emitting diodes (NUV-LEDs). Recently, the active layer material of NUV-LEDs is AlGaN, whose IQE is highly sensitive to the threading dislocation density. Since the IQE is strongly affected by the crystal quality, it is very important to improve and analyze the crystal quality of materials In this thesis, we first modified the etch pits density (EPD) method for crystal quality analyzation, which made the calculation of the threading dislocation density (TDD) more precise. The method then directly applied to analyze the defect density of the NUV-LEDs buffer layer. In this study, we improve the crystal quality with pattern sapphire substrates, and analyze its crystal quality with the modified EPD method. The results show that the screw and mixed type dislocation density were successfully decreased from 2.09*106 to 1.66*106 (cm-2), totally 20.5% reduced. Finally, the results have compared to the investigation through Raman spectrum analyzation, which is executed by Wen-yi Zheng. The decrease of threading dislocation density of NUV-LEDs buffer layer with PSSs is cross-confirmed successfully.