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研究生：	黃楷文 Huang, Kai-Wen
論文名稱：	以凹狀奈米級圖案化藍寶石基板改善氮化鎵發光二極體 Improvement of GaN based LEDs by using concave nano patterned sapphire substrate
指導教授：	蘇炎坤 Su, Yan-Kuin
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：	2013
畢業學年度：	101
語文別：	英文
論文頁數：	84
中文關鍵詞：	奈米壓印技術、圖案化藍寶石基板、發光二極體
外文關鍵詞：	nano imprimt lithography, patterned sapphire substrate, light emitting diode
相關次數：	點閱：97 下載：0
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氮化物發光二極體技術不斷的發展，已成為未來固態照明的明日之星，但整體的外部量子效率還不足，因此提升外部量子效率是目前重要的議題。影響內部量子效率的主要原因在於磊晶品質，而影響光萃取效率的主要原因之一是由於平坦的表面造成光在氮化鎵中產生全反射的現象，使得光溢出的比例下降。
本論文以奈米壓印的技術製作圖案化的蝕刻阻擋層，再以乾式蝕刻的方式製作出凹狀圖案化的藍寶石基板，藉以提升GaN的磊晶品質以及增加LEDs的光萃取效率，選用奈米壓印的技術原因是奈米壓印出的圖案線寬可以很小、製程速度快、成本低，符合業界的需求。
本研究成功地以奈米壓印技術製做出圖案為圓形且直徑約為400 nm的奈米級圖案化藍寶石基板，並且將氮化鎵發光二極體結構成長於圖案化藍寶石基板上，深入地研究具有不同深度奈米級圖案化藍寶石基板的發光二極體之差異，除此之外，試著將二氧化矽應用於圖形化藍寶石基板阻止差排成長來改善二極體的發光效率。
不同深度奈米級圖案化藍寶石基板應用於氮化鎵發光二極體之研究結果顯示，以深度為500 nm的奈米級圖形化基板所成長的發光二極體與傳統平面基板的發光二極體相較之下，外部量子效率5.29％提升到6.28％，此提升是由於內部量子效率及光萃取效率的改善。接著進一步將二氧化矽應用在深度為500 nm的奈米級圖形化基板上，外部量子效率從6.28％提升到11.43％，然而此提升僅由於內部量子效率的改善。

The technique of nitride-based light emitting diodes (LEDs) has been developed for many years. And nitride-based LEDs have become the most promising candidate for solid state lighting in the future. However, the external quantum efficiency is not sufficient yet, so enhancing the external quantum efficiency is the most important issue at present. The main effect on internal quantum efficiency is the epitaxial quality and one of the main effects on light extraction efficiency is that the planar surface leads to total internal reflection of light in the GaN layer. This phenomenon will make the percentage of light transmission decrease.
In this article, the patterned resin was used as etching mask by nano imprint lithography and then the concave patterned sapphire substrate was fabricated by dry etching. By doing this, we hoped to improve epitaxial quality and increase the light extraction efficiency of LEDs. Nano imprint lithography was chosen because of its minimum dimension, high throughput and low cost. These advantages met the needs of the industry.
Nano imprint lithography was successfully applied to manufacture nano patterned sapphire substrates and the size of pattern was about 400 nm. Then LED structures were grown on nano patterned sapphire substrate. And the differences between LEDs with different depths of patterned sapphire substrates were analyzed. Furthermore, we also applied SiO2 as the blocking layer preventing GaN growing from sidewall to further improve crystal quality and enhance LED performance.
In this study, nano patterned sapphire substrates with different etching depths were used. The LED with a concave patterned sapphire substrate in depth of 500 nm was compared with the conventional LED. The external quantum efficiency of the LED with nano patterned sapphire substrate was increased from 5.29 to 6.28％. The increase was due to the improvement of internal quantum efficiency and light extraction efficiency. And when we further applied SiO2, the external quantum efficiency was increased from 6.28 to 11.43％. However, the increase was only by improving internal quantum efficiency.

Contents
Abstract (in Chinese)	I
Abstract (in English)	III
Acknowledgement	V
Contents	VI 
Table Captions	VIII 
Figure Captions	IX
Chapter 1 Introduction	1
1-1 The introduction of GaN-based light-emitting diodes	1
1-2 Motivation	4
Chapter 2 Experimental instruments	9
2-1 Metal organic Chemical Vapor Deposition Systems	9
2-2 Inductively coupled plasma etching (ICP)	10
2-3 Atomic Force Microscopy (AFM)	11
2-4 Scanning Electron Microscope (SEM)	12
2-5 High Resolution X-Ray Diffraction (HRXRD)	13
2-6 Temperature-Dependent Photoluminescence (TDPL)	14
2-7 Transmission electron microscope (TEM)	15
Chapter 3 Enhancement of etching selectivity between resin and sapphire	25
3-1 Preparation of patterned resin as etching mask	25
3-2 Optimal parameters for high etching selectivity	26
3-2-1 Change proportion of BCl3 to Cl2	27
3-2-2 Change UV exposure intensity in imprint process	27
3-2-3 Change bias power	28
3-3 Improvement of etching selectivity	28
3-4 Summary	29
Chapter 4 Investigation of GaN growth mechanism and crystal quality	42
4-1 The introduction of GaN growth mechanism	42
4-2 Decrease the threading dislocations by nano patterned sapphire	43
4-2-1 GaN growth mechanism on nano scale patterned sapphire	43
4-2-2 Analysis for crystal quality of GaN on nano patterned sapphire	44
4-3 summary	45
Chapter 5 GaN based LEDs grown on nano-patterned sapphire substrate	53
5-1 GaN based LEDs grown on various depths patterned substrate	53
5-1-1 Fabrication process of LEDs	53
5-1-2 Material analyses of GaN based LEDs with various nano-patterned sapphire substrates	55
5-1-3 Characteristics of GaN based LEDs with various nano-patterned substrates	56
5-1-4 Summary	57
5-2 Improvement of the performance of LED	58
5-2-1 Sapphire substrates with various depths of pattern	58
5-2-2 Material analyses of GaN based LEDs with various nano-patterned substrates	58
5-2-3 Characteristics of GaN based LEDs with various nano-patterned sapphire substrates	59
5-2-4 Summary	60
Chapter 6 Conclusion and future work	75
6-1 Conclusion	75
6-2 Future work	76
Reference	78

Table Captions

Table 1-1 Approaches to improve light extraction efficiency	8
Table 1-2 Summary of various nanolithographies to fabricate nanoscale patterned sapphire substrates	8
Table 3-1 The ICP parameters 	39
Table 3-2 Etching rate of four kinds of resins 	39
Table 3-3 Summary of etching selectivities, etching rates and AFM images for different gas flow rates and UV exposure intensities 	40
Table 3-4 Summary of etching selectivities, etching rates and AFM images for different bias powers 	40
Table 3-5 Etching selectivity, etching rate and SEM image by using Ni as etching mask 	41
Table 4-1 FWHM (002) (102), screw dislocation density and edge dislocation density of GaN on planar and nano patterned sapphire substrate 	52
Table 5-1 FWHM (002) (102) of GaN on planar sapphire and patterned sapphire with depth from 200 nm to 500 nm 	71
Table 5-2 Leakage current under -5 volts of planar sapphire and patterned sapphire with depth from 200 nm to 500 nm 	71
Table 5-3 Comparison of IQE, LEE and EQE of planar sapphire and patterned sapphire with depth from 200 nm to 500 nm 	72
Table 5-4 Comparison of characteristics for planar sapphire and patterned sapphire with depth from 200 nm to 500 nm 	72
Table 5-5 FWHM of GaN on planar sapphire and patterned sapphire with SiO2 and depth from 200 nm to 500 nm 	73
Table 5-6 Leakage current under -5 volts of planar sapphire and patterned sapphire with SiO2 and depth from 200 nm to 500 nm 	73
Table 5-7 Comparison of IQE, LEE and EQE of planar sapphire and patterned sapphire with SiO2 and depth from 200 nm to 500 nm 	74
Table 5-8 Comparison of characteristics for planar sapphire and patterned sapphire with SiO2 and depth from 200 nm to 500 nm 	74
Table 6-1 Comparison of IQE, LEE and EQE 	77

Figure Captions
Fig. 1-1 Relationship between the lumen per package and year; relationship between the price of light: lumen per dollar and year	6
Fig. 1-2 Trapped light in a planar GaN layer unable to escape for emission angles greater than 23° due to total internal reflection	6
Fig. 1-3 Three parameters of patterned sapphire substrate	7
Fig. 1-4 Relationship between the light output enhancement and diameter of pattern on sapphire substrate 	7
Fig. 2-1 (a) The diagram and (b) the side view of AIXTRON 200RF MOCVD System 	17
Fig. 2-2 The constant temperature tank system 	18
Fig. 2-3 The picture of gas mixing system of MOCVD 	18
Fig. 2-4 The picture of gas mixing system of MOCVD system 	19
Fig. 2-5 The picture of gas vacuum system of MOCVD 	19
Fig. 2-6 The picture of scrubber system of MOCVD 	20
Fig. 2-7 The picture of electronic control system of MOCVD 	20
Fig. 2-8 The schematic of ICP chamber 	21
Fig. 2-9 The different AFM operation modes by the interaction force resulted from the varying distance between the tip and sample surface	 	22
Fig. 2-10 The block diagram of an AFM system 	22
Fig. 2-11 The schematic diagram shows the Bragg diffraction from planes of atoms in a crystal and (b) shows part of (a) in detail. 	23
Fig. 2-12 The schematic diagram of Bede D1 HRXRD 	23
Fig. 2-13 The set up of temperature-dependent PL system 	24
Fig. 2-14 The schematic of TEM equipment 	24
Fig. 3-1 Relationship between resin thickness and etching time for four kinds of resins 	31
Fig. 3-2 Fabrication process of patterned resin on sapphire 	32
Fig. 3-3 Tilted view SEM image of TOX resin after imprinting 	33
Fig. 3-4 Tilted view SEM image of TOK resin after imprinting 	33
Fig. 3-5 (a) Tilted and (b) cross-sectional view SEM images after imprinting 	34
Fig. 3-6 Cross-sectional view SEM images of sapphire after ICP etching 	35
Fig. 3-7 Fabrication process of patterned sapphire	36
Fig. 3-8 (a) Top view SEM images of sapphire which is shrunk and (b) enlarged after ICP etching 	37
Fig. 3-9 (a) Cross-sectional view SEM images of sapphire which is shrunk and (b) enlarged after ICP etching 	38
Fig. 4-1 (a) Tilted view SEM image and (b) cross-sectional TEM image of micro scale patterned sapphire substrate 	46
Fig. 4-2 GaN growth mechanism on micro scale patterned sapphire substrate 	47
Fig. 4-3 Top view SEM image of nano scale patterned sapphire substrate 	48
Fig. 4-4 Top view SEM images of GaN growth on nano scale patterned sapphire substrate for (c) 15min and (d) 20min 	49
Fig. 4-5 cross-sectional TEM image of nano scale patterned sapphire substrate 	50
Fig. 4-6 Room temperature PL spectra of GaN on planar and nano patterned sapphire substrate 	51
Fig. 5-1 Room-temperature Raman spectra of planar sapphire and patterned sapphire with depth from 200 nm to 500 nm 	51
Fig. 5-2 Room temperature PL spectra of planar sapphire and patterned sapphire with depth from 200nm to 500nm 	62
Fig. 5-3 (a) Forward I-V characteristics and (b) reverse I-V characteristics of planar sapphire and patterned sapphire with depth from 200 nm to 500 nm.	62
Fig. 5-4 L-I curves of planar sapphire and patterned sapphire with depth from 200 nm to 500 nm		63
Fig. 5-5 EQE-I curves of planar sapphire and patterned sapphire with depth from 200 nm to 500 nm 	64
Fig. 5-6 Cross-sectional view SEM image of GaN on nano patterned sapphire substrate 	64
Fig. 5-7 Prediction of the threading distribution in GaN on nano patterned sapphire (a) with and (b) without SiO2	65
Fig. 5-8 Fabrication process of patterned sapphire with SiO2 	66
Fig. 5-9 Room-temperature Raman spectra of planar sapphire and patterned sapphire with SiO2 and depth from 200 nm to 500 nm 	67
Fig. 5-10 Room temperature PL spectra of planar sapphire and patternedsapphire with SiO2 and depth from 200 nm to 500 nm 	68
Fig. 5-11 (a) Forward I-V characteristics and (b) reverse I-V characteristics of planar sapphire and patterned sapphire with SiO2 and depth from 200 nm to 500 nm 	68
Fig. 5-12 L-I curves of planar sapphire and patterned sapphire with SiO2 and depth from 200 nm to 500 nm 	70
Fig. 5-13 EQE-I curves of planar sapphire and patterned sapphire with SiO2 and depth from 200 nm to 500 nm 	70


                                    

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校內：2023-12-31公開
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