AlGaN -based 280nm light-emitting diodes with continuous wave powers in excess of 1.5mW

Abstract
We report on AlGaN -based light-emitting diodes over sapphire with peak emission at 280 nm . A modified active layer structure consisting of four multiple quantum wells, addition of an electron blocking magnesium doped p - AlGaN layer, improved contacts along with flip-chip packaging resulted in a cw power of 0.7 mW at 230 mA for a single 200 μ m × 200 μ m device. Flip-chipping four 100 μ m × 100 μ m devices in a parallel configuration improved the dc saturation current and enabled us to obtain a cw power of 1.53 mW (at 450 mA ) and a pulse power as high as 24 mW (at 1.5 A ). These powers translate to values of 0.36 % and 0.12 % for the external quantum efficiency and the wall plug efficiency.