Picosecond response of gallium-nitride metal–semiconductor–metal photodetectors

Metal–semiconductor–metal ultraviolet photodiodes fabricated on GaN were tested in the picosecond regime with an electro-optic sampling system. A device with a feature size of 1 μm showed a response with 1.4 ps rise time and 3.5 ps full width at half maximum. The derived electron velocity, 1.43×107 cm/s, is in good agreement with independent photoexcitation measurements. A slower impulse response was observed in a device with smaller feature size of 0.5 μm.