| 학회 | 한국재료학회 |
| 학술대회 | 2017년 봄 (05/17 ~ 05/19, 목포 현대호텔) |
| 권호 | 23권 1호 |
| 발표분야 | F. 광기능/디스플레이 재료 분과 |
| 제목 | Selective area growth of GaN layer on partially crystallized alumina cavity pattern on sapphire substrate |
| 초록 | In order to enhance the efficiency of LEDs and to lower the fabrication cost, solutions to technical issues such as high density of threading dislocations in the epitaxial layer, low light extraction efficiency, and severe wafer bow are strongly required. 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 overcome these problems. An FDTD simulation showed that the emitted light was effectively extracted outside by strong-diffraction at the high-index-contrast air-cavity patterns, and we confirmed that the output power of InGaN/GaN blue light-emitting diodes 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 incorporation of cavities was found to reduce the stress in the GaN film by 32% and the wafer bow by 31%. 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. We speculate that the parasitic growth of GaN on the top is because the cavity shell including the top area was fully crystallized into single crystalline alpha-phase, the phase of sapphire substrate, by solid-phase epitaxy. In this research, in order to suppress the growth of the parasitic GaN, we investigated selective area growth of GaN layer on partially crystallized CES (PCCES) in which the cavity shell is remained in gamma-phase, another phase of alumina, rather than alpha-phase. By carefully controlling the crystallization process, we were successful obtaining gamma-phase cavity shell while the area between the cavities were crystallized into alpha-phase for the GaN growth. Transmission electron microscopy analysis revealed that the parasitic GaN growth on top of the cavity patterns was successfully suppressed and the GaN layer from the planar area was coalesced on top of the pattern without generating additional dislocations. As a result, it was found that threading dislocation density in the GaN layer grown on the PCCES was reduced up to ~ 30 % compared to that on CES with alpha-phase cavity shell. More details of the growth behavior of GaN layer on PCCES and its optical and structural characteristics will be discussed in the presentation. |
| 저자 | 장정환1, 이승민1, 박용조2, 윤의준1 |
| 소속 | 1서울대, 2차세대융합기술(연) |
| 키워드 | <P>GaN; LED; ELO; cavity engineered sapphire substrate; selective area growth</P> |
