GaN 기반의 자외선 발광다이오드를 위한 은 나노와이어 투명전극 연구

Abstract

GaN-based ultraviolet light emitting diodes (UV LEDs) have attracted much attention for applications in curing, water/air purification, fluorescence-based chemical sensing, sterilization, and high-density optical data storage. In addition, UV LEDs can be used as high-color rendering index white light source which is one of the most promising candidates for solid-state lighting. However, the luminous efficiency of InGaN based or AlGaN based UV LEDs is still low for practical application becasue the efficiency of InGaN based or AlGaN based UV LEDs is lower than that of blue LEDs owing to the lack of indium-rich regions that act as localized recombination sites. In addition, one of the problems associated with conventional UV LEDs is the use of non-conductive sapphire as the substrate because it causes the current crowding effect near the p-contact by lateral carrier injection due to low hole concentration and mobility in p-layer. To solve these problems, indium tin oxide (ITO) usually have been widely used as the transparent conducting electrode(TCE) in GaN-based LEDs with advantage in high electrical conductivity and high optical transparency, but ITO is costly, and shows the poor transparency in the ultraviolet range and instability in the presence of acids or base. Promising candidates for ITO replacement in UV LEDs include silver nanowires, carbon nanotubes (CNTs), and graphene. Among these candidates, the silver nanowire (Ag NW) is especially promising because its conductivity (σAg=6.3×107S·m-1) is higher than that of carbon-based CNTs and graphenes and the work function is high (ΦAg=4.74eV) compared to several metals commonly used as electrode materials for LEDs. In this study, we demonstrate an UV LED with a Ag NW-based TCE deposited by the simple solution based coating method. Then, we compare it with UV LEDswith ITO based TCE and without TCE.