Study of Double-Layer Passivation Effects in InGaN-based Blue Micro LEDs

Abstract

Recently, as the demand for AR/VR devices has increased due to the 4th industrial revolution, ultra-high-resolution Micro LED has emerged as an essential light source for implementing VR/AR displays. However, the decrease in efficiency and stability due to the decrease in the size of the subpixel of Micro LED is becoming a significant problem in commercialization. As the subpixel size becomes smaller, the sidewall damage areas that inevitably occur during the ICP-RIE process relatively increase. Shockley-Read Hall (SRH) recombination, a non-radiative recombination, increases in the surface states formed on the sidewall. Therefore, it was reported that the overall device’s internal and external quantum efficiency was reduced. This decrease in efficiency causes a decrease in the performance and stability of the device and is considered a problem that must be solved. In this study, the unstable sidewall of an InGaN-based blue Micro LED that occurs during plasma etching was thinly and uniformly first passivated with Al2O3 using ALD. Afterward, SiO2 and SiNx were used as a second passivation layer through PECVD to secure thickness and productivity. Micro LEDs of various sizes (10 / 20 / 50 / 100 / 300 um) were manufactured, and a double passivation process was performed. The passivation effect of the Micro LED produced in this way was observed through device electrical and optical measurements. In the case of a device passivated with ALD (Al2O3) + PECVD (SiNx), the leakage current was reduced by 95.8 % compared to the reference device in a 10 um device. It also showed the best electrical characteristics in light emission at low current densities and ideality factor. In terms of optical characteristics, the optical output decreased compared to the reference device, but it was confirmed that the reduction rate decreased as the device size decreased. Through this study, in implementing ultra-high resolution Micro LED, it is expected that the decrease in efficiency and stability due to the miniaturization of subpixels can be solved through double-layer passivation using Al2O3 and SiNx.