臺灣博碩士論文加值系統

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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