We have developed a two-dimensional theoretical model. This model allowed us to characterize the MSM photodetector based ZnO. It also allowed us to simulate the dark current and photocurrent of the device with different dimensions of the metal contact of structure. The simulation results were agreed with those of the experiment. We have identified the influence of geometry parameters of the metal contact on the dark current and also on the photocurrent. Calculating the ratio (photocurrent / dark current), allowed us to find the best values of finger width w and finger spacing s of the metal structure leading to a low dark current and at the same time a better absorption of the incident light. The best performance of MSM PD are obtained for the following values s = 14 μm, w = 12 microns. These values have enabled us to obtain a dark current of 25nA and a photocurrent equal to 0.78 μA at a 3V bias.
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