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研究生：	黃湘彥 Huang, Xiang-Yan
論文名稱：	利用偏壓式輔助光電化學反應粗糙化p型氮化鎵以增加LED之出光效率 Increasing light emitting efficiency of LED by roughing p-GaN with bias-assisted PEC method
指導教授：	李清庭 Lee, Ching-Ting
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：	2007
畢業學年度：	95
語文別：	英文
論文頁數：	62
中文關鍵詞：	氮化鎵、光電化學
外文關鍵詞：	GaN, PEC
相關次數：	點閱：76 下載：2
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本論文主要分為兩個部份，第一個部份是利用偏壓式輔助光電化學反應對p型氮化鎵進行蝕刻。我們知道光電化學反應已經能夠成功應用於n型氮化鎵，但由於p型氮化鎵功函數較高，導致其必須額外加一偏壓，改變其內建電場方向，才能夠有反應進行，這也是p型氮化鎵難以利用光電化學反應蝕刻之原因。本論文成功的對p型氮化鎵產生蝕刻反應，並計算其蝕刻速率，以及在不同偏壓不同時間下所蝕刻的情形。我們也對經過光電化學反應蝕刻後p型氮化鎵製作TLM元件，以了解蝕刻後的p型氮化鎵歐姆接觸特性。另外，由於光電化學反應，其蝕刻機制為一非等向性之濕性蝕刻，因此對於p型氮化鎵表面會有粗糙化的效果，也利用原子力顯微鏡來量測蝕刻後的p型氮化鎵，證明蝕刻後粗糙化的現象。
第二部份則是針對光電化學反應對p型氮化鎵蝕刻後表面粗糙化之應用，我們知道發光二極體之光輸出效率與試片表面粗糙程度有相對的關係，當試片表面粗糙而非一平整的表面，可以增加發光二極體由量子井所散射出試片表面的光子量，主要原因即為若試片表面過於平整，易將來自於量子井的光反射回去，因此粗糙化試片表面可以降低光全反射的機會，大大提高發光效率。由於p型氮化鎵離子鍵結很強，所以一般利用乾性蝕刻來對p型氮化鎵進行蝕刻，而利用乾性蝕刻來蝕刻p型氮化鎵的同時，也會對氮化鎵表面造成損害，降低元件的特性。由於本論文可以成功對p型氮化鎵進行濕性蝕刻，且在蝕刻的同時又能夠對試片表面進行粗糙化之效果，因此光電化學反應之機制應用於LED製程上，將能提高發光二極體的發光效率。

The research in this paper is made up by two parts. The first part is to etch p-type GaN. It is known that we can use Photoelectrochemical (PEC) etching method to etch or oxidize n-type GaN. Due to the high work function of p-type GaN, it is hard to etch or oxidize p-type GaN. We must apply extra voltage to p-type GaN, and change it’s build-in electrical field. Then we can etch p-type GaN. In this paper , we calculate the etching rate of p-type GaN, and discuss the theory and phenomenon of etching p-type GaN. We also change bias and reaction time for the treated sample, then we discuss the phenomenon. After etching p-type GaN, we make transmission line model (TLM) pattern to analyze the ohmic contact of p-type GaN. In addition, PEC is an anisotropic wet etching method, we can use bias-assisted PEC method to roughen p-type GaN surface.
The other part, we increase light emitting efficiency of light emitting diode (LED) by roughening p-type GaN with bias-assisted PEC method. It is known that the relation between surface roughness and light emitting efficiency. Due to the characteristic of p-type GaN, we can only use dry etching for p-type GaN. But dry etching will make surface damage and reduce electrical characteristic of devices. Wet etching usually provided lower damage than dry etching. In this paper, we can use bias-assisted PEC method to etch and roughen p-type GaN surface, and we also increase light emitting efficiency of LED by roughening p-type GaN with bias-assisted PEC method.

Contents
Abstract (in Chinese)                                         I
Abstract (in English)                                        III
Acknowledgement                                          V
Contents                                                  VI
Table Captions                                           VIII
Figure Captions                                             IX
Chapter 1 Introduction 
1-1 The background of GaN-based LEDs                         1
1-2 Selective etch using photoelectrochemical etching               2 
1-3 Consideration                                           3
Reference                                                  5
Chapter 2 Experimental Theory 
2-1 Light Loss Mechanisms (ηFr)                               7
2-2 Relation between surface roughness and light emitting efficiency   9
2-3 Light scattering                                         10
2-4 Photoelectrochemical wet etching theory                     11
2-5 Bias-assisted photoelectrochemical etching for p-type GaN      12
2-6 Structure of LEDs                                          13
Reference                                                 19
Chapter 3 The Process of p-GaN Etching and Data Analysis
3-1 Sample structure                                        21
3-2 Experiment procedure                                    21
3-2-1 Make metal electrode                                21
3-2-2 The process of p-GaN etching                         22
3-3 Data analysis                                           23
Reference                                                 33
Chapter 4 Transmission Line Model (TLM) Device and Data    Analysis
4-1 Fabrication of TLM Device                                35
4-2 Data Measurement and Analysis                            38
Reference                                                 47
Chapter 5 Fabrication of the Light Emitting Diodes and data analysis
5-1 The growth of GaN-based light emitting diodes (LEDs) devices   48
5-2 The Fabrications of LEDs Chips                            48
    5-2-1 Activiation                                       48
    5-2-2 Cleaning Wafer                                   48
    5-2-3 Roughen surface of LED structure by bias-assisted photoelectrochemical etching method                  　 　49
    5-2-4 Etching Mesa                                     49
    5-2-5 N-type ohmic contact                               50
    5-2-6 P-type ohmic contact                               51

5-3 Data measurement and analysis                            52
    5-3-1 Current-Voltage Characteristics                       52
    5-3-2 Light Output Power versus Current (L-I) Characteristics   53
Reference                                                 60
Chapter 6 Conclusions  
6-1 Conclusions                                            61
                                    

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校內：2009-09-04公開
校外：2012-09-04公開

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