臺灣博碩士論文加值系統

目前為止，由於磊晶成長技術突破，可得到優良品質的結晶，因此發光亮度急速提升，已被用來生產高亮度的發光二極體。雖然四元系列的發光二極體內部量子效率可達 99% 以上，但外部量子效率還是很低。本論文將設計與製作形狀化發光二極體以增加光取出，進而增加發光二極體發光效率。
本論文設計一些新的發光二極體製作方法以提高發光效率。首先，利用濕蝕刻的方式蝕刻GaAs基板側面部分，藉由對GaAs基板側面進行蝕刻的動作，可以有效減低元件外圍缺陷造成的非輻射複合(non-radiative center)的影響，改善布拉格反射層(Distributed Bragg reflector, DBR)反射的限制形，透過蝕刻部分使得布拉格反射層無法反射的光可以穿透出來，進而提高發光效率。蝕刻的時間越長，對亮度提升越有幫助，但亮度的提昇有一極限值，於本研究中由數值計算來驗證，在蝕刻面積對元件面積比例超過13.4%之後，光強度會有衰減的情形產生。在 20毫安培驅動電流下，9mil及12mil發光二極體元件最高可分別提高 10.9%及18.7%的發光效率。
接著，利用CH4和BCl3的混和氣體以電感耦合電漿蝕刻(ICP)對磷化鎵窗口層(GaP window layer)進行乾式蝕刻，在磷化鎵窗口層上形成67°的斜邊，透過斜邊的設計可以減少全反射現象(Total intertal reflection, TIR)並增加光透射的機會。研究發現：蝕刻時間越久對亮度提升有一定的幫助，但操作電壓會有些微上升的趨勢。與傳統發光二極體比較，於20毫安培操作下，9mil的元件亮度可提升10.4%。

Recently, for the advance high brightness light emitting diodes (LEDs) has been obtained of epitaxy technology. The internal quantum efficiency of AlGaInP LED is up to 99% for a good quality crystalline, the external quantum efficiency is still very poor. Therefore, the output power of LED is still low compared to conventional light sources for high-flux lighting systems, requiring further improvements on LED light-output efficiency. The purpose of this thesis is by using various chip shapes of LEDs to improve the external quantum efficiency and light extraction.
In this thesis, we design some methods of fabrication-process to improve light-output. At first, remove partial of the GaAs sidewall substrate by wet etching technique. By etching GaAs sidewall substrate, the non-radiative center caused by defects around the optical devices would be reduced. Besides, the reflected photons comes from Distributed Bragg reflector (DBR) would be improved. The light out of the reflection angle of DBRs could pass through by the sidewall etching region, and enhanced the Luminous intensity. Longer etching time led to higher luminous intensity. However, the improvement was limited to the proportion of sidewall etching to chip size is being 13.4%, confined by numerical calculation. Efficiency was raised by 10.9% and 18.7% at an operation current of 20mA for chip size 9mil and 12mil sizes, respectively.
Followed, the fabrication process was dry etching on GaP window layer, which is implemented by inductively coupled plasma (ICP) employing the mixture of CH4 and BCl3 gases. The slanted sidewall angle was about 67°. The oblique sidewall could reduce total internal reflection and enhance the light extraction. It was found that the longer etching time led to higher luminous intensity at the cost of poor the electrical property, i.e., the forward voltage was slightly increased. Under the operation current of 20mA, the brightness of the shaped 9 mil AlGaInP LEDs was increased to 1.104 times as compared with the conventional LED.

Contents
Abstract (In Chinese) ----------------------------------- I
Abstract (In English) --------------------------------- III
Acknowledge (In Chinese) ---------------------------------V
Contents ------------------------------------------------VI
Table Captions ----------------------------------------- IX
Figure Captions ----------------------------------------- X
Chapter 1 Introduction ---------------------------------- 1
1-1 A Brief History of Light-Emitting Diodes （LED） -----1
1-2 Background of this Research and Motivation ---------- 4
1-2-1 Quantum efficiency -------------------------------- 4
1-3 Organization of this Thesis ------------------------- 6
Chapter 2 Principles of Light-emitting Diodes ----------- 9
2-1 Light Extraction ------------------------------------ 9
2-1-1 Introduction -------------------------------------- 9
2-1-2 Critical angle and Fresnel loss ------------------ 10
2-1-3 Design to improve extraction efficiency ---------- 12
2-2 Brief Principle of Etching ------------------------- 13
2-2-1 Liquid-Phase Etching ----------------------------- 14
2-2-2 Gas-Phase Etching -------------------------------- 16
Chapter 3 Fabrication Method and Process --------------- 27
3-1 Truncated-Tree shaped AlGaInP LED ------------------ 27
3-1-1 Motivation --------------------------------------- 27
3-1-2 Experimental details ----------------------------- 28
3-1-2-1 Etching solution ------------------------------- 28
3-1-2-2 Process of sidewall etching -------------------- 29
3-1-2-3 Process of Novel structure --------------------- 30
3-2 AlGaInP LED with a trapezoid window layer ---------- 31
3-2-1 Motivation --------------------------------------- 31
3-2-2 Experimental details ----------------------------- 32
3-2-2-1 Dry etching of Gap layer ----------------------- 32
3-2-2-2 Process of Novel structure --------------------- 34
Chapter 4 Result and Discussion ------------------------ 50
4-1 Truncated-Tree shaped AlGaInP LED ------------------ 50
4-1-1 Device Analysis ---------------------------------- 50
4-1-1-1 Optical Characteristics ------------------------ 50
4-1-1-2 Electrical Characteristics --------------------- 52
4-1-2 Summary ------------------------------------------ 53
4-2 AlGaInP LED with a trapezoid window layer ---------- 53
4-2-1 Device Analysis ---------------------------------- 53
4-2-1-1 Electrical Characteristics --------------------- 54
4-2-1-2 Optical Characteristics ------------------------ 56
4-2-2 Summary ------------------------------------------ 57
Chapter 5 Conclusion and Future Prospect --------------- 69
5-1 Conclusion ----------------------------------------- 69
5-2 Proscept ------------------------------------------- 70
Reference ---------------------------------------------- 72

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