Recent progress in AlGaN UV-C LEDs grown on SiC

Abstract

Growth of high quality AlGaN is essential to develop efficient UV-C LEDs. However, growth of AlGaN is challenging due to the lack of native substrates, low surface mobility of Aluminum adatoms and low doping efficiency for p-AlGaN. In this work, we illustrate our approach to develop UV-C LED on SiC starting with MOCVD growth of high-quality AlN buffer layer with TDD $\sim 8\times 10^{8}/\text{cm}^{2}$ as measured by TEM, followed by growth of AlGaN UV-C LED structure and then fabricated into Thin-Film Flip-Chip (TFFC) devices via novel epi-transfer process and nondestructive removal of SiC by ICP-RIE. We investigated the effects of Indium, growth rate and Ammonia to improve the conductivity of n-AlGaN. As a result, the free electron concentration as measured by RT Hall effect increases to 3.2×1019/cm3, which facilitates a formation of a direct ohmic contact to 66% AlGaN using Vanadium-based metal stack V/Al/V/Au. Finally, we report on the development of AlGaN UV-C LED on SiC with high $\text{EQE}>2\%$ and output power of 2 mW at DC current of 20mA with an emission wavelength of 262 nm. Therefore, we conclude that SiC is well-suited to be utilized as a substrate for high-power AlGaN UV-C LEDs.