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질화갈륨 기반 광다이오드에서 우수한 오믹 거동을 위한 새로운 투명전도막 개발에 관한 연구

Title
질화갈륨 기반 광다이오드에서 우수한 오믹 거동을 위한 새로운 투명전도막 개발에 관한 연구
Other Titles
A study on the development of novel transparent-conducting films for excellent ohmic behavior in GaN-based light emitting diodes
Author
김원
Alternative Author(s)
Kim, Won
Advisor(s)
박진석
Issue Date
2009-02
Publisher
한양대학교
Degree
Master
Abstract
질화갈륨(GaN) 반도체는 넓은 직접천이 밴드갭과 높은 열적 안정성, 화학적 안정성을 가지고 있기 때문에, 단파장 광전자소자, 고온 전자소자 등에 응용이 되고 있다. 특히, LED(light-emitting diode), LD(laser diode), PD(photodetector)와 같은 광전자소자에 많은 응용이 되고 있지만, p형 GaN의 높은 저항과 큰 일함수로 인하여 LED 응용에 있어서 유익한 오믹(ohmic) 특성을 보이지 못하고 있다. 오믹 특성을 이루기 위하여, 일반적으로 p-GaN층 상부에 금속전극을 사용하지만, 광추출효율(external ohmic efficiency)을 저하시키는 문제가 있다. 오믹 특성과 광추출효율의 향상을 모두 만족시키기 위하여 많은 연구그룹에서 다양한 연구들이 시도되고 있다. 본 연구에서는 광추출효율을 향상 시키기 위해 RF 마그네트론 스퍼터링(magnetron sputtering) 방법에 의한 ITO 투명전극을 증착하였으며, ITO 투명전극 증착시 인가한 타겟의 전력 및 기판의 온도 변화, O₂:Ar 분압비, 증착두께, RTA 후처리 조건(온도 및 시간) 등이 ITO의 광학적, 전기적 특성에 미치는 상관관계를 규명하였으며, 마그네트론 스퍼터링 방법으로 ZnO/Mg 계면층(interlayer)을 삽입한 후 ITO/p-GaN간에 오믹 특성 및 투과율 특성에 주는 변화를 관찰하였다. 또한, RTA 후처리 이후 계면층의 원자가 이동하는 현상을 SIMS 분석을 통해 규명하였다.; Ⅲ-Ⅴ nitrides are semiconductors with wide direct bandgap, high thermal conductivity and high chemical stability. Therefore, they have attracted interest as materials for use in short wavelength optoelectronics and high-temperature electronic applications, such as light-emitting diodes (LEDs), laser diodes (LDs) and photodetectors (PDs). However, p-type GaN has a high resistance and a large work function and so can not easily form a good ohmic contact in LED applications. Hence, various solutions have been proposed to reduce the contact resistance. Most conventional nitridebased LEDs use semitransparent Ni/Au on p-type GaN as the p-contact material. However, the transmittance of such a semitransparent Ni/Au contact is only around 60~70% for light of the desired wavelength, 450~550nm. This problem can be solved using transparent indium tin oxide (ITO) as the contact material. But, direct ohmic contact between ITO and p-GaN has not made. Zinc oxide (ZnO) has unique characteristics, including a wide bandgap, a large exciton binding energy and a look of GaN lattice constant. Also, Mg is Ⅱ group element with high conductivity and using p-type dopant of GaN. Therefore, we present experimental results that regard currentvoltage characteristics of ZnO/Mg interlayer for GaN LED. ZnO and Mg are successfully deposited on a p-GaN using the radio-frequency magnetron sputtering method. Effects of thin ZnO/Mg interlayers on electrical and optical properties between p-GaN and ITO were characterized for its application to GaN-LEDs. The ZnO and Mg layers were deposited to have various thicknesses (1~6nm for ZnO and 1~2nm for Mg) by sputtering. After RTA process, the atomic migration between Mg and ZnO and the formation of Ga vacancy were observed from SIMS depth profile, resulting in the increase of hole concentration and the reduction of band bending at the surface region of p-GaN. The sample using ZnO(2nm)/Mg(2nm) interlayer produced the lowest contact resistance with SBH (Schottky barrier height) of 0.576 eV and the transmittance higher than 83% at a wavelength of 460nm when annealed at 500℃ for 3min in air ambient.
URI
https://repository.hanyang.ac.kr/handle/20.500.11754/144728http://hanyang.dcollection.net/common/orgView/200000411653
Appears in Collections:
GRADUATE SCHOOL[S](대학원) > ELECTRONIC,ELECTRICAL,CONTROL & INSTRUMENTATION ENGINEERING(전자전기제어계측공학과) > Theses (Master)
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