Enhancement of wall-plug efficiency in AlGaN deep-ultraviolet light-emitting diodes by micro-mesh p-electrode and scattering nanostructures

Abstract

We report an enhancement of the wall-plug efficiency (WPE) of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs). This enhancement was achieved through fabrication of a micro-mesh p-electrode (p-GaN/metals) and scattering nanostructures on the p-side of the device to obtain both high electrical efficiency and enhanced light extraction efficiency (LEE). The micro-mesh p-electrode structure minimizes DUV light absorption by removing a part of the p-GaN layer while maintaining good electrical conduction. The scattering nanostructures, which consist of truncated HfO2 cones, redirect guided light effectively into the escape cone, thus improving the LEE significantly. As a result, the WPE reached 9.1% at an injection current of 12 mA and an emission wavelength of 275 nm. This efficiency was enhanced by approximately 1.7 times when compared with that of conventional DUV-LEDs, in which a p-electrode structure covers the entire mesa. Although the micro-mesh p-electrode was used to reduce DUV light absorption, high electrical efficiency of 90% was demonstrated, with a drive voltage of as low as 4.8 V at 12 mA. These experimental results show good agreement with the results of three-dimensional finite-difference time-domain simulations.