Low dark current GaN avalanche photodiodes

We report the fabrication and characterization of GaN avalanche photodiodes grown on sapphire by metalorganic chemical vapor deposition. Current-volta ge characteristics indicate a gain higher than 23. The photoresponse is ind ependent of the bias voltage prior to the onset of avalanche gain which occ urs at an electric field of similar to4 MV/cm. Near avalanche breakdown, th e dark current of a 30-mum diameter device is less than 100 pA. The breakdo wn shows a positive temperature coefficient of 0.03 V/K that is characteris tic of avalanche breakdown.