GaN ultraviolet avalanche photodiodes with optical gain greater than 1000 grown on GaN substrates by metal-organic chemical vapor deposition
We report the performance of GaN p-i-n ultraviolet avalanche photodiodes grown on bulk GaN substrates by metal-organic chemical vapor deposition. The low dislocation density in the devices enables low reverse-bias dark currents prior to avalanche breakdown for similar to 30 mu m diameter mesa photodetectors. The photoresponse is relatively independent of the bias voltage prior to the onset of avalanche gain which occurs at an electric field of similar to 2.8 MV/cm. The magnitude of the reverse-bias breakdown voltage shows a positive temperature coefficient of similar to 0.05 V/K, confirming that the avalanche breakdown mechanism dominates. With ultraviolet illumination at lambda similar to 360 nm, devices with mesa diameters of similar to 50 mu m achieve stable maximum optical gains greater than 1000. To the best of our knowledge, this is the highest optical gain achieved for GaN-based avalanche photodiodes and the largest area III-N avalance photodetectors yet reported. (c) 2006 American Institute of Physics.