Suppressing optical crosstalk for GaN/InGaN based flip-chip micro light-emitting diodes by using an air-cavity patterned sapphire substrate as a light filter

Abstract

In this work, by using three-dimensional finite-difference time-domain (3D FDTD) method, the effect of conventional nano-patterned sapphire substrate (NPSS) on the optical crosstalk and the light extraction efficiency (LEE) for InGaN/GaN-based flip-chip micro light-emitting diodes (µ-LEDs) are systematically studied. We find that the conventional NPSS is not suitable for µ-LEDs. It is because the inclined mesa sidewall for µ-LEDs possesses a good scattering effect for µ-LEDs, but the introduced conventional NPSS causes part of the light be off escape cone between sapphire and air and become the guided light. To suppress the guided light and improve the optical crosstalk, a thick air layer between the n-GaN layer and the sapphire substrate can be used as a light filter to prevent the guided light from propagating into the sapphire. However, in reality, it is challenging to make the aforementioned air layer from point of fabrication view. Therefore, we propose the air-cavity patterned sapphire substrate (AC-PSS) as the light filter. Our results show that the crosstalk ratio can be decreased to the value even lower than 10%. The LEE can also be enhanced simultaneously due to combination effects of the filtering effect of the AC-PSS and the scattering effect of the inclined mesa sidewall.

Recent Advances on GaN-Based Micro-LEDs

“…Due to the excellent scattering ability of the tilted countertop sidewall of µLEDs, and the certain thickness of the air layer between the n-GaN layer and the sapphire substrate, this can be utilized. Jia et al propose the air-cavity patterned sapphire substrate (AC-PSS) as the light filter [ 114 ]. By combining the filtering effect of AC-PSS and the scattering effect of the tilted countertop sidewall, LEE can be enhanced while also improving optical crosstalk.…”

Recent Advances on GaN-Based Micro-LEDs

“…Due to the excellent scattering ability of the tilted countertop sidewall of µLEDs, and the certain thickness of the air layer between the n-GaN layer and the sapphire substrate that can be utilized. Jia at al propose the air-cavity patterned sapphire substrate (AC-PSS) as the light filter [100]. By combining the filtering effect of AC-PSS and the scattering effect of the tilted countertop sidewall, LEE can be enhanced while also improving optical crosstalk.…”