| AVS 60th International Symposium and Exhibition | |
| Transparent Conductors and Printable Electronics Focus Topic | Tuesday Sessions |
| Session TC-TuP |
| Session: | Transparent Conductors and Printable Electronics Poster Session |
| Presenter: | K.H. Kim, Korea University, Republic of Korea |
| Authors: | H.D. Kim, Korea University, Republic of Korea S.W. Kim, Korea University, Republic of Korea K.H. Kim, Korea University, Republic of Korea S.J. Kim, Korea University, Republic of Korea M.D. Kim, Chungnam National University, Republic of Korea T.G. Kim, Korea University, Republic of Korea |
| Correspondent: | Click to Email |
Indium-doped tin oxide (ITO) is the most popular transparent conductive electrodes (TCEs) used in flat screen displays and lighting technologies for decades. However, due to indium's limited supply and increasing cost, there has been a big push for many years to find alternatives or replacements of ITO (i.e., indium-free TCEs); many scientist and engineers have been working with zinc oxide and other metal-oxide materials but this area still remains quite challenging. Here we worked towards something different, developing new ways to give a current path between the TCEs using ordinary wide-bandgap materials and p-(Al)GaN layers via conducting filaments (CFs), which can be formed using electrical breakdown (or forming) processes, for ultraviolet light-emitting diodes (UV LEDs).
UV LED is one of the eco-friendly optical sources for different wavelengths in the UV A to C regimes (200–400 nm), useful for various applications including sterilization and high color rendering index lighting. However, currently, the external quantum efficiency of the UV LED, particularly in UV-C bands, is extremely low (3-11%). One of the primary reasons for this low efficiency is a large absorption in narrow-bandgap contact layers for ohmic contact. To fundamentally solve this problem, we should obtain a direct ohmic contact to the p-AlGaN layers using UV-transparent conductive electrodes, as depicted in the right figure below. However, with conventional ohmic methods, it is almost impossible to make such contact and therefore no report has been made so far. In this article, we present a universal method of producing transparent electrodes with high conductivity and high optical transmittance in the UV A to C regimes (as well as visible-to-infrared regimes) using electrical breakdown to form CFs providing a current path between the TCEs and the semiconductor, which leads to a large reduction in their contact resistance. As a result, we found the contact resistance between the TCEs and the p-GaN layers (or p-AlGaN layers) to be on the order of 10-5 Ω·cm2 (or 10-3 Ω·cm2) while optical transmittance was maintained at up to 95% for the AlN-based TCEs at 250 nm.