Very fast metal-semiconductor-metal ultraviolet photodetectors on GaN with submicron finger width

We measured in the time domain fast metal-semiconductor-metal ultraviolet photodetectors fabricated on GaN with finger width and pitch ranging from 0.3 to 5 (mu)m. A broad-band circuit was designed to couple out the short electrical pulse. The minimum temporal resolution between consecutive optical pulses was 26 ps. At low illumination levels, the bandwidth of the response was limited by the measurement system, not the device. At high illuminations, recovery of diode became slower, consistent with the space-charge screening effect caused by the photogenerated carriers.