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 $p\text{-}i\text{-}n$ 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 $\sim 30\mu \mathrm{m}$ 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 $\sim 2.8\mathrm{MV}∕\mathrm{cm}$ . The magnitude of the reverse-bias breakdown voltage shows a positive temperature coefficient of $\sim 0.05\mathrm{V}∕\mathrm{K}$ , confirming that the avalanche breakdown mechanism dominates. With ultraviolet illumination at $\lambda \sim 360\mathrm{nm}$ , devices with mesa diameters of $\sim 50\mu \mathrm{m}$ 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.