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 $∼30μm$ 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 $∼2.8MV∕cm$⁠. The magnitude of the reverse-bias breakdown voltage shows a positive temperature coefficient of $∼0.05V∕K$⁠, confirming that the avalanche breakdown mechanism dominates. With ultraviolet illumination at $λ∼360nm$⁠, devices with mesa diameters of $∼50μm$ 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.