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標題: | 優化基板奈米結構間距改善磊晶品質與氮化鎵類發光二極體效率衰減 Improve Epitaxy and Efficiency Droop of GaN-based LEDs on Nano-Patterned Substrates with Spacing Optimization |
作者: | Zheng-Hung Hung 洪振紘 |
指導教授: | 管傑雄 |
關鍵字: | 氮化鎵類發光二極體,奈米圖案化藍寶石基板,磊晶成長模型,電子束微影,效率衰減, GaN-based Light-emitting diodes,Nano-Pattered Sapphire Substrates,Epitaxial Model,Electron-beam Lithography,Efficiency Droop, |
出版年 : | 2015 |
學位: | 碩士 |
摘要: | 成長在藍寶石基板上的氮化鎵類發光二極體,因磊晶層與藍寶石基板間的晶格常數不匹配以及熱膨脹係數的差異,使得元件產生大量穿隧差排;若通過改變基板表面形貌,在基板上製作奈米結構,將可抑制磊晶層差排的產生。為探究基板形貌與磊晶之交互關係,本篇論文將藉由製作奈米圖案化藍寶石基板,改變方陣型結構週期與大小,探討對氮化鎵類磊晶體薄膜的影響。吾人使用電子束微影系統搭配乾式蝕刻技術,製作出一系列不同週期、結構大小,但相同深度的奈米結構於藍寶石基板上,並使用有機金屬化學氣相沉積系統進行氮化鎵類材料磊晶。其後,將使用非破壞性的光學顯微鏡、光致螢光量測系統、拉曼光譜系統等分析磊晶變化以及觀察缺陷密度,據斯提出氮化鎵成長模型。本研究發現到結構間距小於600nm時會出現磊晶方式的轉變,可同時降低穿隧差排密度與薄膜應力,相似於free-standing GaN材料。接著將上述觀測結果應用在發光二極體上並以電致發光檢測元件發光效率,同時探討效率衰減之原因並指出應該為穿隧差排。 GaN-based Light-Emitting Diodes (LEDs) are typically grown on c-plane sapphire substrates. Due to the large lattice mismatch between GaN and the substrate, GaN on sapphire exhibits lots of threading dislocations (TDs), and as to control them, one can change the surface morphology of substrate, i.e. patterned sapphire substrates (PSSs). For further understanding on GaN epitaxy on nano-scaled PSSs, we fabricated a series of square-array PSSs in this research, providing various period and structure size but the same in depth. We exploited E-beam lithography system accompanied with dry etching method for precise pattern design. After that, GaN-based LED structure was developed on the fabricated PSSs via MOCVD system. A non-destructive analysis over epitaxial revolution was conducted with optical microscopy, micro-PL, and micro-Raman system, whereas a GaN epitaxial model was then proposed. In this research we observed that the epitaxial alteration was associated with spacing between structures, especially below 600nm, and can produce free-standing-like GaN, which is characterized with low defect density and strain simultaneously. For application, devices are capsulated and under electroluminescence (EL) measurement. And from it, a detailed research on device performance containing efficiency droop was discussed. We identified TDs as the main cause. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/53938 |
全文授權: | 有償授權 |
顯示於系所單位: | 光電工程學研究所 |
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