Improved crystal quality of GaN epitaxial layer using GaN nano-island in the buffer layer
완충층 내 GaN nano-island를 이용한 GaN 에피층의 결정품질 향상

DC Field Value Language
dc.description학위논문 (석사)-- 서울대학교 대학원 : 재료공학부(하이브리드 재료), 2012. 8. 윤의준.-
dc.description.abstract최근, GaN 은 광전자 재료로서 매우 우수한 물질로서, 그 결정질의 품질을 높이고자 많은 연구가 되어 왔다. 여기서 성장 초기 단계에서 3D 성장을 하여 결정 결함을 줄이는 연구들이 연구되어 왔다[1,2].Gibart 등의 연구결과에 따르면, 사일렌과 암모니아를 통하여 SiNx 마스킹이나 사파이어 기판에 Si/N 처리를 행하는 것이 nucleation site 의 숫자를 줄여 island 의 크기를 키워, 결과적으로 관통 전위의 수를 줄이는 것을 확인 할 수 있었다. 그 외에도 수많은 그룹이 사일렌과 암모니아를 사파이어 기판에 처리하여 grain 크기를 키워 관통전위를 키우는 연구에 성공하였다.[3,4,5]
그러한 GaN 의 품질을 향상시키는 방법은 기판에 nano-island를 형성하는 것 이다. 우리는 GaN film을 고온에서 etching 하여 GaN nano-island를 성장시켰다. 그리고 이 nano-island를 버퍼층에 적용하여 전위가 GaN 성장방향으로 전파하여 나가는 것을 막았다.
그리고 성장시킨 GaN 결정을 x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) 그리고 high resolution transmission electron microscopy (HR-TEM) 방법으로 측정하였다. 그 결과, 우리는 epi layer 의 crystal quality 와 physical properties 가 개선된 것을 확인 할 수 있었다. 비록 crystal quality 가 향상되는 이유는 알아내지 못하였지만, 이 연구 결과가 GaN 성장이나 MOCVD를 통한 다른 원소의 성장에도 도움이 될 것이다.
dc.description.abstractDue to the potentialities of GaN and related alloys for the optoelectronic devies emitting in the green-ultra-violet range important efforts have been made to improve the crystal quality.
The use of a three dimensional (3D) mode at the first stage of GaN growth has been reported a major role in the reduction of defect density [1,2]. One solution to improve the crystal quality of GaN is GaN nano-island formation on substrate. It is well known that GaN nano-island reduces dislocation density in GaN epitaxial layer. As proposed by Gibart and co-workers, in situ SiNx masking or Si/N treatment of sapphire substrate with silane and ammonia reduces the density of nucleation sites prior to GaN epitaxial layer growth, and hence increases the average grain size leading to films with TD densities below 10-10 cm-2. Several research groups reported exposure of the sapphire substrate, prior to the deposition of a GaN nucleation layer, under silane and ammonia flows. [3,4,5] Another method to similarly reduce the TD density is by intentionally delaying the coalescence of individual GaN islands by starting the growth of the epilayer proper at a reduced V/III ratio.
So, we proposed GaN nano-island formation technique in buffer layer, which prevents propagation of dislocation at very early stage of the growth. We formed GaN nano-islands in buffer layer intentionally by thermal etching, then grew GaN epitaxial layer on nano-islands.
The crystal quality and morphologies of the GaN were examined using x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and high resolution transmission electron microscopy (HR-TEM).
We confirmed that crystal quality and physical properties of GaN layer was improved. Despite the fact that the mechanism for crystal quality improvement is not well understood, we believe this method could prove useful to the MOCVD growth in variety of ways. However, further studies are necessary to confirm the exact reason of crystal quality improvement.
dc.description.tableofcontentsAbstract.…………… I
Contents....................... III
List of figures............................................................ VI

Chapter 1 Introduction 1
1.1 Introduction 1

1.2 Growth techniques of GaN 7
1.2.1 General methods 7
1.2.2 GaN nano-island in buffer layer by Si/N treatment 8

1.3 GaN epitaxial layer using nano-island in buffer layer 9

Chapter 2 Experiments and analysis 14
2.1 Growth equipment 14
2.1.1 MOCVD system 14

2.2 Analysis tools 16
2.2.1 Scanning electron microscopy (SEM) 16
2.2.2 Transmission electron microscopy (TEM) 16
2.2.3 X-ray diffractometry (XRD) 16
2.2.4 Atomic force microscopy (AFM) 17

2.3 Experimental details 17
2.3.1 Sample preparation 17
2.3.2 Growth procedure 17

Chapter 3 Results and disccusion 20

3.1 Nano-island in buffer layer (NB) GaN 20
3.1.1 Growth of NB GaN 20
3.1.2 GaN nano-islands 21

3.2 Characteristics of NB GaN 26
3.2.1 Physical properties of NB GaN 26
3.2.2 Dislocations of NB GaN 27

Chapter 4 Conclusions 33

References 34
Abstract 36
dc.format.extent4977603 bytes-
dc.publisher서울대학교 대학원-
dc.titleImproved crystal quality of GaN epitaxial layer using GaN nano-island in the buffer layer-
dc.title.alternative완충층 내 GaN nano-island를 이용한 GaN 에피층의 결정품질 향상-
dc.contributor.AlternativeAuthorYu HyoSang-
dc.citation.pagesxxxvii, 37-
dc.contributor.affiliation공과대학 재료공학부(하이브리드 재료)-
Appears in Collections:
College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Material Science and Engineering (재료공학부) Theses (Master's Degree_재료공학부)
Files in This Item:
  • mendeley

Items in S-Space are protected by copyright, with all rights reserved, unless otherwise indicated.