臺灣博碩士論文加值系統

　　高亮度發光二極體(LED)近年來蓬勃發展並且廣泛地被應用在路燈、汽車頭燈、螢幕背光板以及投影機等日常生活用品上。但功率與亮度都得再進一步提升才足以符合現今固態照明的需求。目前常用氮化鎵(GaN)來做發光二極體的材料，並使用藍寶石基板做為基板來磊晶氮化鎵，不過由於兩材料間的晶格不匹配與熱膨脹系數差異，因此會造成許多缺陷，使得內部量子效率(IQE)下降。解決的方法是圖型化藍寶石基板(PSS)，可以讓差排彎曲，並增加表面粗糙度以改變光線路徑，同時提高了光取出效率(LEE)與內部量子效率。
　　本實驗為在圖型化藍寶石基板上以物理氣相沉積(PVD)濺鍍一層氮化鋁(AlN)緩衝層之後再去磊晶氮化鎵，並製作成發光二極體。藉由改變氮化鋁的成長溫度去探討緩衝層對氮化鎵成長機制的影響。材料分析結果為以300°C成長的氮化鋁緩衝層磊晶品質最好，而電性分析結果為600°C的最好，其原因為雖然低溫的緩衝層在退火時較容易結晶化，但也因為結構較鬆散會在磊晶過程時被氫氣所蝕刻而降低磊晶品質。實驗結果證實了氮化鋁緩衝層的圖形化藍寶石基板大幅提升了氮化鎵的磊晶品質，而且可藉由控制氮化鋁緩衝層的成長溫度使其達到最佳化。

　　High brightness light emitting diodes(LEDs) have been highly demand in various fields like using on road light, car headlight, backlight and projector. For the purpose of next-generation application of solid-state lighting, LEDs with higher internal and external quantum efficiency are required. The common material of LEDs is gallium nitride(GaN). We usually use sapphire as substrate to epitaxy GaN. There are still many problems between sapphire and GaN such as lattice mismatch and thermal expansion coefficient difference, which will make defects and degrade internal quantum efficiency(IQE). The solution we use is pattern sapphire substrate(PSS) which can make dislocation bending and change the optical path. It will improve both light extraction efficiency(LEE) and IQE.
　　This experiment is use physical vapor deposition(PVD) to sputter a buffer layer of Aluminium Nitride(AlN) on PSS and epitaxy GaN to analysis. By changing the growth temperature of AlN to investigate the effect of the GaN properties. The growth temperature of 300°C is better in material analysis; the growth temperature of 600°C is better on optoelectronic characteristics. Because the low temperature buffer layer recrystallized easier when annealing but etched by hydrogen when grown GaN. The improvement of GaN quality was attributed to the AlN buffer layer of PSS, and the optimization could controlled by growth temperature of AlN buffer layer.

摘要 i
Abstract ii
目錄 v
圖目錄 vii
表目錄 x
一、 緒論 1
1.1 前言 1
1.2 研究動機 3
二、文獻回顧與理論背景 6
2.1 發光二極體理論 6
2.1.1 發光原理 6
2.1.2 發光二極體發光機制 8
2.1.3 發光二極體轉換效率 9
2.1.4 藍寶石基板 10
2.1.5 藍寶石與氮化鎵晶體結構以及特性簡介 13
2.2 圖形化藍寶石基板介紹及其優點 16
2.2.1 乾蝕刻簡介 17
2.2.2 濕蝕刻簡介 18
2.3 緩衝層(buffer layer)介紹 21
三、實驗方法 24
四、結果與討論 25
4.1 掃描式電子顯微鏡(scanning electron microscope, SEM) 25
4.2 發光度-電流-電壓量測(L-I-V curve) 28
4.3 X光繞射分析(X-ray diffraction, XRD) 31
4.4 光激發螢光光譜分析(Photoluminescence, PL) 33
4.5 原子力顯微鏡(atomic force microscope, AFM) 35
4.6 討論 36
五、結論與未來實驗規劃 39
5.1 結論 39
5.2 未來實驗規劃 40
六、參考文獻 41

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