표면 나노 패터닝을 이용한 통한 수직형 발광 다이오드의 광추출 효율향상에 관한 연구
The study on enhancement of Light extraction efficiency in vertical light emitting diode by surface nano-patterning
- 주제(키워드) 표면 나노 패터닝 , 수직형 발광다이오드 , 광추출 효율
- 발행기관 고려대학교 대학원
- 지도교수 김태근
- 발행년도 2011
- 학위수여년월 2011. 8
- 학위구분 석사
- 학과 일반대학원 전자전기공학과
- 원문페이지 77 p
- 실제URI http://www.dcollection.net/handler/korea/000000026790
- 본문언어 한국어
- 제출원본 000045671711
초록/요약
GaN-based light emitting diodes (LEDs) have attracted considerable interest in variety of applications, such as in traffic lights, full color displays, and general lighting. However, the luminous efficiency of GaN-based white LEDs needs further improvement in order to expand their proliferation in the emerging market. The overall efficiency of these LEDs is mostly limited by their low light extraction whereas their light extraction efficiency is limited by the total internal reflection at the interface between the semiconductor and air. Due to the large difference in the refractive index between the semiconductor and air, only a small fraction of the light can escape to the surrounding air. Therefore, there is still a great need for an improvement in the light extraction efficiency, as well as in the internal quantum efficiency. Nanometer scale patterns have been introduced on the top (or bottom) surface of LEDs by using laser holography, electron-beam lithography, and nano-imprinting techniques for the purpose of increasing the light extraction. These techniques are advantageous in that they achieve nanometer scale patterns with a high resolution; however they are not suitable for exposing large areas of the substrate economically. Nanosphere lithography (NSL), which is capable of producing well-ordered, two-dimensional (2D) periodic bead arrays on the substrate, has been proposed for the fabrication of nano-scale patterns. In a typical procedure, the fabrication of the nano-scale patterns is achieved by coating a self-assembled single layer of nanospheres from a colloidal suspension. Nanospheres are commercially available with diameters from 20-nm to 3-µm, which makes it possible to vary the size and pitch of the patterns. In this study, the light extraction in GaN-based Vertical LEDs was improved by using NSL techniques. Double layered PS nanospheres were coated onto the n-GaN layer by a simple spin-coating method. Oxygen (O2) plasma ashing was employed to shrink the size of the PS spheres. For making patterns, a Ni layer was deposited on the sample using electron-beam evaporation. This layer acted as a mask after removing the PS nanospheres. Inductively coupled plasma reactive ion etching (ICP-RIE) was then used to make patterns using BCl3 and Cl2 gases. Structural properties of pillar patterned n-GaN surfaces were investigated by Scanning Electron Microscope (SEM). In order to the enhancement of light extraction efficiency, the n-GaN patterned Vertical LEDs was investigated. The electroluminescence intensity and light output power of the Vertical LED with pillar and hole patterned n-GaN layer shows much higher than those of the conventional Vertical LED, at an injection current of 350 mA. It was also found that the optical power of the Vertical LED with pillar and hole patterned n-GaN layer was enhanced by 3.1~3.2 times, compared with that of the conventional Vertical LED, due to a reduced total internal reflection at the n-GaN/air interface and increased light scattering at the patterned surface. The light extraction for the n-GaN layer patterns were also calculated by using a ray-tracing simulation, which clearly revealed pillar patterns on the n-GaN layer would serve as the light scattering source inside the Vertical LEDs and enhance the light output power.
more목차
영문 요약
....................................................................................
ⅰ
그림 목차
....................................................................................
ⅶ
표 목 차
....................................................................................
ⅺ
제1장 서론......................................................................................
1
제2장 이론적 고찰..........................................................................
5
2.1 LED(Light Emitting Diode) 개요..........................................
5
2.2 GaN LED의 광학적 특성 ......................................................
9
2.2.1 광추출 효율 (Light Extraction Efficiency) ...................
9
2.2.2 탈출원뿔 (Light escape cone) ......................................
11
2.2.3 Lambertian Emission Pattern ........................................
15
2.3 LED 광추출효율 개선 방안 .................................................
17
2.3.1 Surface texturing..............................................................
17
2.3.2 2차원 광결정 (2 Dimensional Photonic Crystal).............
19
2.4 나노스피어 리소그라피 (Nanosphere lithography) ..............
22
2.4.1 Nanosphere lithography의 개요 .....................................
22
2.4.2 Self-assembled Polystyrene nanosphere array.............
23
2.4.3 Polystyrene nanosphere lithography 방법 ....................
24
2.5 Vertical type LED ...............................................................
26
제 3 장 연구 내용 및 결과............................................................
29
3.1 Polystyrene sphere를 이용한 Nanosphere lithography .......
29
3.1.1 실험개요 .........................................................................
29
3.1.2 실험방법 .........................................................................
30
3.1.3 실험결과 .........................................................................
31
3.2 NSL을 적용한 n-GaN 표면 패터닝 연구..............................
36
3.2.1 실험개요 .........................................................................
36
3.2.2 실험방법 .........................................................................
36
3.2.3 실험결과 .........................................................................
39
3.3 NSL을 적용한 Vertical 구조의 GaN LED 의 n-GaN 표면 패터닝을 통한 광추출효율 향상 연구 ...........................................
42
3.3.1 실험개요 .........................................................................
42
3.3.2 실험방법 .........................................................................
43
3.3.3 실험결과 .........................................................................
45
3.4 시뮬레이션을 통한 Vertical LED의 특성 분석......................
52
3.4.1 시뮬레이션개요 ...............................................................
52
3.4.2 Vertical LED의 광학적 특성 분석 .................................
52
3.4.3 시뮬레이션결과................................................................
55
제 4 장 결론.................................................................................
57
참고 문헌........................................................................................
59
감사의 글........................................................................................
61
