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

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 mum x 200 mum device. Flip-chipping four 100 mum x 100 mum 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. (C) 2004 American Institute of Physics.