Enhancement of light extraction efficiency in sub-300 nm nitride thin-film flip-chip light-emitting diodes

Abstract

We report on the improved light extraction efficiency of 287nm small periphery AlGaN/AlGaN thin-film flip-chip (TFFC) light-emitting diodes (LEDs) fabricated using the laser lift-off technique. After sapphire substrate removal, the exposed AlN N-face was etched in a KOH solution. The result was a 1.5-fold increase in the TFFC device output power at 20mA dc current injection, which was attributed to the AlN surface texturing. TFFC die encapsulation process produced an additional 1.34-fold enhancement of the emitted light power. More importantly, the encapsulated thin-film LEDs exhibited a similar reliability performance compared to encapsulated conventional FC LEDs processed from the same epiwafer, and with no noticeable degradation of the encapsulating material optical properties.