臺灣博碩士論文加值系統

發光二極體(light emitting diodes ,LEDs)近年來逐漸取代傳統的日熾燈泡，主要是因為LED的體積小、壽命長及發光效率高等優點，常見於汽車頭燈、螢幕面板、交通號誌燈等日常用品。而目前最常被使用來做LED的材料為氮化鎵(GaN)，但由於氮化鎵缺乏本身基板因此多半利用藍寶石基板來磊晶氮化鎵，不過由於兩者之間存在著晶格不匹配與熱膨脹係數差異，因此常在磊晶的過程中產生許多缺陷使得內部量子效率(IQE)下降。常用的改善方法有讓藍寶石基板圖形化使差排彎曲並增加表面粗糙度改變光線路徑，可使內部量子效率與光取出率(LEE)提高，或是利用緩衝層來降低晶格不匹配。 而在本實驗中利用濺鍍氮化鋁做為緩衝層，並利用KOH去進行蝕刻，再磊晶氮化鎵並做分析，在實驗中發現直接用KOH進行蝕刻的試片，氮化鎵的磊晶品質會隨著蝕刻時間增加而下降，這主要是因為底部氮化鋁緩衝層的厚度會隨著蝕刻時間的增加而減少，當底部的氮化鋁緩衝層越薄時，氮化鎵越容易成長於PSS的側壁，導致磊晶品質變差。
因此我們又設計了另一實驗，保護底部的氮化鋁緩衝層不受KOH的蝕刻，實驗的結果也順利的得到了只從底部成長，側壁幾乎沒有氮化鎵成長的試片，而磊晶品質也因而得到改善，這也符合了我們預期的利用改變氮化鋁緩衝層位置可以改善
II
氮化鎵磊晶品質，同時我們也利用聚焦離子束系統(Focus Ion Bean, FIB)來觀察不同位置的氮化鎵之磊晶速率，並加以探討。

Light emitting diodes(LEDs) have been replaced incandescent-filament lamp due to their advantages of small size、long lifetime and high efficiency. There are a lot of applications such as car headlight, screen panel and traffic lights. The material of LEDs is GaN, but GaN is lack of own’s substrate. As a result, 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 duing epitaxial growth and degrade internal quantumefficiency(IQE). So the solution we use is pattern sapphire substrate(PSS) which can make dislocation bending and change optical path. It will improve IQE and light extraction efficiency(LEE). Another solution is using buffer layer to decrease lattice mismatch.
In this experiment we use sputter AlN buffer layer and etch directly with KOH. Then, we epitaxy GaN and analysis. In the experiment, we discover that the quality of GaN become worse while we increase the KOH etching time. This is because the thickness of bottom AlN buffer layer become thinner while we increase the KOH etching time. As the thickness of bottom AlN buffer layer become thinner, the GaN
IV
grow on sidewall of PSS became easier. Then the quality of GaN become worse. We design another experiment to protect bottom AlN buffer layer from KOH etching. In this experiment we grow GaN on bottom of PSS successfully with a little GaN on sidewall. This result adjust to our expectation that changing sputter AlN buffer layer place on PSS can improve GaN quality,and we also useFocus Ion Bean (FIB) to observe GaN epitaxy rate.

摘要.................................................................................................................................I
Abstract........................................................................................................................III
致謝..............................................................................................................................V
目錄............................................................................................................................VII
圖目錄..........................................................................................................................IX
表目錄..........................................................................................................................XI

一、 序論........................................................................................................................1
1.1 LED簡介..............................................................................................................1
1.2 LED理論..............................................................................................................2
1.2.1 LED發光原理............................................................................................2
1.2.2 LED發光機制............................................................................................3
1.2.3 LED轉換效率............................................................................................4
1.3 藍寶石基板..........................................................................................................5
1.3.1圖形化藍寶石基板.....................................................................................9
1.4緩衝層(buffer layer)介紹...................................................................................11
二、 利用氫氧化鉀蝕刻圖形化藍寶石基板上的氮化鋁之研究..............................13
2.1研究動機............................................................................................................13
2.2 Etch AlN on PSS................................................................................................15
2.2.1直接利用氫氧化鉀蝕刻圖形化藍寶石基板上的氮化鋁(directly etch AlN on PSS) ................................................................................................................15
2.2.2利用氫氧化鉀製作底部氮化鋁在圖形化藍寶石基板(Bottom AlN on PSS etched by KOH) ...................................................................................................16
2.3結果與討論........................................................................................................17

2.3.1磊晶短時間...............................................................................................17
2.3.2磊晶LED全結構.......................................................................................30
2.3.3LED chip....................................................................................................30
2.4光電性分析........................................................................................................30
2.5結論..............................................................................................................34
三、總結........................................................................................................................35
四、未來工作..............................................................................................................36
五、參考文獻..............................................................................................................37

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