Abstract
We have simulated a double barrier metal semiconductor metal (MSM) UV photo-detector based on a wide band-gap GaN layer deposited on a wider-gap AlGaN layer. Both M-S contacts were of Schottky barrier type. In order to perform the simulation the Poisson equation and the time dependent transport equations were numerically solved in a self-consistent way for the electrostatic potential, carrier concentrations, energy and photo current. Electron and hole transport as well as circuit elements are included. An examination was carried out of the response time of the photo diode when illuminated with the ultra-short pulses of UV radiation (2 picoseconds). The MSM structure was operated under DC bias when the UV pulse was absorbed in GaN in the region between the electrodes. The active area defined by the electrode spacing was chosen to be 0.5 and 1.5 microns. Co-axial cable was used. The current blocking AlGaN substrate layer was used to prevent photon generation far away from the electrodes. The results of simulation indicate that there is a very rapid response of the analyzed structure to pulsed UV radiation. At the DC small background a sharp spike of photo current appears. The influence of the between-electrode gap width on the MSM photo diode response was analyzed.
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