Highly transparent structure for nitride ultraviolet light emitting diodes

We report the merits of the transparent structure for the nitride semiconductor ultraviolet light emitting diodes. The ultraviolet light emitting diodes consisting of AlGaN-based active layers provide a wide spectral range from 200 to 360nm in the ultraviolet range. To produce a transparent device structure at the emission wavelength, we used sapphire substrates, AIN-template layers, AlGaN alloy buffer layers, and p-type contact layers consisting of a short period alloy superlattice, all of which are transparent to the emission. We confirmed the transparency of the device structure from the transmission spectra. The output power characteristic is improved by a factor of four due to the transparent structure. We also demonstrate an efficient ultraviolet light emitting diode grown on an AlGaN buffer layer of low dislocation density. The external quantum efficiency is 1.4%, which is superior to that of the ultraviolet light emitting diode grown on bulk GaN substrate.