Enhanced Responsivity of ZnSe-Based Metal-Semiconductor-Metal Near-Ultraviolet Photodetector via Impact Ionization

We report on high-responsivity, fast near-ultraviolet photodetectors based on bulk ZnSe employing a metal-semiconductor-metal structure with and without interdigital contacts. A very high responsivity of 2.42 and 4.44AW(-1) at 20V bias voltage and high rejection rate of 7900 and 4810 for the light with a wavelength of 325nm is obtained for photodetectors without and with interdigital contacts, which indicates an internal gain. The mechanism of internal gain is attributed to the impact ionization of ZnSe atoms under high internal electric field strength of 133kVcm(-1). Also a low dark current of approximate to 3.4nA and high detectivity of approximate to 1.4x10(11)cmHz(1/2)W(-1) at a voltage of 20V is achieved for the device with interdigital contacts at room temperature.