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研究生： 呂育聰
Lu, Yu-Tsung
論文名稱： 利用電流阻隔層及鈍化層的研究來改善氮化鎵藍光二極體的發光效率
Improvement in light-output efficiency of InGaN/GaN blue LED by current blocking layer and surface passivation layer
指導教授： 洪茂峰
Houng, Mau-Phon
王永和
Wang, Yeong-Her
學位類別： 碩士
Master
系所名稱： 電機資訊學院 - 微電子工程研究所
Institute of Microelectronics
論文出版年： 2003
畢業學年度： 91
語文別： 英文
論文頁數： 102
中文關鍵詞： 氮化鎵，電流阻隔層，鈍化層，藍光二極體
外文關鍵詞： AR coatings, blue LED, surface passivation layer, current blocking layer, InGaN, GaN
相關次數： 點閱：97  下載：2 
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    • 由於磊晶成長技術的成熟及相關製程的改善使得以氮化鎵做為基材的發光二極體，量子效率大幅地提升。然而，和以砷化鎵做為基材的發光二極體比較起來，在外部量子效率方面，它還是顯得不足。其中一個原因可能是電流非均勻分佈的關係，另外一個原因則是因為半導體材料高折射係數及半導體裡一些缺陷的緣故導致光不容易發射至外界而被半導體本身所吸收。
    本論文主要是針對以氮化鎵為基材的發光二極體，在亮度輸出效率方面做一系列地探討及改善。我們提出幾種不同的製程方法來改善以氮化鎵為基材發光二極體的光輸出效率，包括增加抗反射層，阻隔電流層，以及一種新穎的結構(諾亞方舟)。在我們的實驗結果當中，二氧化矽和氮化矽這兩種材料是用來做為發光二極體的抗反射層。以提升光輸出為用途，它們的最佳厚度分別是800埃及300埃，對於光輸出的貢獻則分別有18.5%和11.6%的表現。根據實驗結果和理論的推演，二氧化矽是最適合做為以氮化鎵為基材發光二極體抗反射層的材料。
    基於電流均勻擴散的理論，我們創造出一種新式結構的氮化鎵系列發光二極體，取決於它的設計概念我們把它命名為諾亞方舟。設計此結構的目的是為了讓電流在發光二極體裡能均勻地擴散開來，以致於提升亮度的增加。此外，我們也製作出在p-pad底下具有電流阻隔層的氮化鎵系列發光二極體。我們發現到具有電流阻隔層的氮化鎵系列發光二極體，並不如我們預期地，在光輸出強度及外部量子效率方面，比傳統氮化鎵系列發光二極體有明顯地改善。歸咎其原因可能是由於穿透接觸層的導電度過佳、氮化鎵系列為大能隙材料及以透明基板做為氮化鎵系列發光二極體基板的緣故。

    Because of improved epitaxial growth and advanced process technology, the quantum efficiencies of GaN-based LEDs are increased. However, the external quantum efficiencies are less significantly than that based on GaAs. One of the reasons is that non-uniform current spreading and the other is that light could be re-absorbed by material as a result of the high refractive indices of semiconductor materials and defects.
    In this thesis, we will discuss improvement of light-output efficiency for GaN-based LED. We have proposed some methods to improve in light-output efficiency of GaN-based LED, including AR coatings, current blocking layer, and a novel structure (Noah structure). In our experiments, the optimum thickness of SiO2 and SiNx coatings for GaN-based LED are 800Å and 300Å and the enhancement of light-output intensity of them are 18.5% and 11.6%, respectively. According to being proven by theory and experiment, SiO2 is the most appropriate material as AR coating for GaN-based LED.
    Based on the theory of uniform current spreading, we created a novel structure of GaN-based LED named after Noah structure according to its feature. Our goal is want to make current spreading uniformly and increase the light-output intensity. Besides, we fabricated GaN-based LED with SiO2 as current blocking layer inserted under p-pad. We found that the light-output intensity and external quantum efficiency for the GaN-based LED with a current blocking layer were not as significantly increased as our expectation compared to those for the conventional GaN-based LED. The reasons maybe were due to its good conductivity of transparent contact layer and its wide band-gap of GaN and its alloy and transparent substrate of GaN-based LED.

    Contents 摘 要 I Abstract III Contents V Table captions VIII Figure captions IX Chapter 1. Introduction 1 1.1 Background 1 1.2 Organization 3 Chapter 2. Fabrication InGaN/GaN blue LED with current blocking layer and equipments 5 2.1 Flowchart of processes 5 2.2 Preparation of InGaN/GaN blue LED wafer 9 2.3 Process procedures of blue LED 10 2.3.1 wafer cleaning 10 2.3.2 Mg-activated 10 2.3.3 deposit TCL 10 2.3.4 p-ohmic contact 11 2.3.5 define mesa 11 2.3.6 deposit current blocking layer (CBL) 12 2.3.7 deposit n-metal 12 2.3.8 n-ohmic contact 13 2.3.9 deposit p-pad 13 2.3.10 grow surface passivation (antireflection) layer 13 2.4 The obstacles we have met 14 2.5 Equipments 15 2.5.1 ICP system 15 2.5.2 PECVD system 16 Chapter 3. Enhancement of light-extraction of InGaN/GaN blue LED by surface passivaiton layer 17 3.1 Loss mechanisms 17 3.2 Anti-reflection coatings 21 3.3 Simulation 22 3.4 Results and discussion 23 3.4.1 SiO2/SiNx coatings 23 3.4.2 Optimum thickness of SiO2/SiNx coatings 24 3.4.3 Effect of PECVD parameters on the refractive index25 3.4.4 Device characteristics 26 Chapter 4. Improvement in light output efficiency of InGaN/GaN blue LED by current blocking layer 27 4.1 Lateral current spreading of GaN-based LED 28 4.2 Uniform current spreading of GaN-based LED 29 4.3 GaN LED of Noah structure 32 4.3.1 Light output intensity of Noah structure 32 4.3.2 Device Characteristics 33 4.3.3 Discussion 34 4.4 GaN LED with current blocking layer 35 4.4.1 Light output intensity of GaN LED with CBL 36 4.4.2 Device characteristics 37 4.4.3 Discussion 38 Chapter 5. Conclusion and future work 41 5.1 Conclusion 41 5.2 Future work 42 References 43

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