於圖案化藍寶石基板上磊晶成長氮化鎵發光二極體

Abstract

本研究為改善氮化鎵發光二極體之性質，使用圖案化藍寶石基板使發光二極體磊晶層的品質提升。進而達成高外部量子效率，使整體發光強度增加。在本研究中，利用溼式蝕刻技術製備出兩種形貌的圖案化藍寶石基板，分別為平頂圖案化藍寶石基板和角錐藍寶石基板。 氮化鎵在磊晶時由於和藍寶石基板間有15％的晶格不匹配(Lattice mismatch)，因此將產生貫穿差排(Threading dislocations)，這些缺陷會影響發光二極體的光電特性，虛耗電流，並且產生多餘熱能。根據文獻，C-plane和R-plane兩種藍寶石晶面其磊晶速度不一樣，因此使用溼式蝕刻在C-plane藍寶石基板上製作圖案，形成平面為C-plane、斜面為R-plane的結構，利用磊晶速度差異達成側向磊晶成長(Epitaxial lateral overgrowth，ELOG)。使貫穿差排數量降低，角錐圖案化藍寶石基板由於C-plane面積較少，導致磊晶品質較好。在發光強度(Intensity)較平頂圖案化藍寶石基板提升了54％。但經過特殊處理後的平頂圖案化藍寶石基板，其C-plane平頂不會有氮化鎵磊晶，經TEM觀察後，貫穿差排數量明顯降低，其發光強度(Intensity)超越同組實驗的角錐圖案化藍寶石基板試片。

This study is to improve the design of patterned sapphire substrate. Using the wet-etching technique , it will minimize c-plane area which is the top of pyramid and the shape of pyramid is variable spires from the flattened. In the GaN epitaxial growth, threading dislocations will generate from the interface between the GaN and c-plane, These defects will affect the device performance. Observed by TEM, compared to a flat-top patterned sapphire substrate, the pyramid patterned sapphire substrate can be more effective in reducing the dislocation density. No dislocation can penetrate the LED structure and most of dislocations are confined to the slope on the pyramid. In Iv (Intensity), compared with flat-top LED, the sample of pyramid LED raise 54%. And the flat-top LED with modification of top is better than pyramid LED.