Very high-speed metal-semiconductor-metal ultraviolet photodetectors fabricated on GaN

Abstract
We report on the temporal and the frequency response of metal-semiconductor-metal ultraviolet photodetectors fabricated on single-crystal GaN. The best devices show a fast 10%–90% rise time of ∼23 ps implying a bandwidth of >15 GHz. These time domain data have been corroborated by direct measurement of the power spectral content. From this a cutoff frequency, f3 dB, of ∼16 GHz has been obtained. Analysis in terms of reverse bias and geometric scaling indicates that the photodetectors are transit-time limited. Modeling of the temporal behavior indicates that a slow component in the time and frequency response data is a consequence of the hole drift velocity.