| 학회 | 한국재료학회 |
| 학술대회 | 2017년 가을 (11/15 ~ 11/17, 경주 현대호텔) |
| 권호 | 23권 2호 |
| 발표분야 | F. 광기능/디스플레이 재료 분과 |
| 제목 | Growth of GaN on nanocrystalline γ-Al2O3 cavity patterned sapphire substrate |
| 초록 | Recently, we have proposed a new growth scheme of using a cavity engineered sapphire substrate (CES), in which well-defined air-cavity patterns were arrayed on a sapphire, to fabricate highly efficient and less strained GaN-based light emitting diodes (LEDs). By incorporating the air-cavities into GaN layers using the CES, we confirmed that the output power of InGaN/GaN blue LEDs grown on CES was improved up to 9% in the wall-plug efficiency compared to that on state-of-the-art, patterned-sapphire-substrate. Also, the stress in the GaN film was reduced by 32% compared to that on a planar sapphire substrate. However, we have found that during the growth of GaN on CES, undesired GaN crystal was deposited on the top area of the cavity patterns, generating the additional threading dislocations during the coalescence of GaN layer and probably limiting the further improvement of the LED performance. The parasitic growth of GaN on the top is caused by the fact that the cavity top area was (0001) plane of the fully crystallized single crystalline α-phase (sapphire) by solid-phase epitaxy. In this research, in order to suppress the growth of the parasitic GaN, we investigated partially crystallized CES (PCCES) in which the cavity shell is remained in nanocrystalline γ-phase, another phase of alumina, rather than α-phase. By carefully controlling the crystallization process, we successfully obtained nanocrystalline γ-phase cavity shell, while the area between the cavities were crystallized into single crystalline α-phase for the GaN growth. Compared to the GaN grown on fully crystallized CES (FCCES) with single crystalline α-phase cavity shell, the parasitic GaN growth on top of the cavity patterns was successfully suppressed for the PCCES. Transmission electron microscopy analysis revealed that the GaN layer from the planar area was coalesced on top of the pattern without generating additional dislocations. The plan-view cathodoluminescence images of the GaN layer grown on the FCCES showed that a number of dark spots in the GaN layer on FCCES was localized in the specific positions corresponding to the location of cavity patterns. In contrast, the localization of dark spots was not observed for the GaN layer grown on the PCCES. As a result, reverse leakage current for the GaN Schottky diode on PCCES was reduced by one order of magnitude compared to that on FCCES. |
| 저자 | 장정환1, 최대한2, 이승민1, 금대명2, 김종명1, 박용조2, 윤의준1 |
| 소속 | 1Department of Materials Science and Engineering, 2Seoul National Univ. |
| 키워드 | GaN; Light emitting diode; threading dislocation |
