UV Light-Emitting Diodes at 340 nm Fabricated on a Bulk GaN Substrate

We demonstrate an ultra-violet light-emitting diode (UV-LED) fabricated on a bulk GaN substrate with electroluminescence (EL) emission centered at about 340 nm. The UV-LED exhibits low reverse leakage current on the order of 10(-9) A under -5 V at room temperature, which can be explained by the low defect density in the epi-structure. The evolution of EL spectra as a function of injection current levels reveals the improved heat dissipation of the LEDs with vertical geometry on the bulk GaN substrate. The unusual increase of EL intensity at elevated temperatures can be explained by thermally assisted p-dopant ionization.