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The epilayer thickness and doping density variation effects on the (I-V) characteristics of n-GaN schottky diode are determined numerically. In this work the epilayer thickness of n-GaN schottky diode are varied from 3 mum -11 mum while doping density are varied from 1times10 12cm-3 ~ 1times10 17cm-3. The simulation work is conducted using Atlas/Blaze developed by Silvaco. The various models such as Srh (Shockley-Read Hall), Cvt (Lombardi model), Auger, Impact (Grants model), Bgn (Band gap narrowing), Conmob (concentration dependent mobility) is used to get optimum (I-V) characteristics of n-GaN schottky diode. We find that in forward biased as the epilayer thickness varied from 3 mum ~ 11 mum at constant doping density 1times10 12cm-3 the forward current decreases due to the increase in series resistance, on the other hand the forward current increased by lowering the epilayer thickness up to 3 mum and increasing the doping density ~ 1times10 17cm-3. In reverse biased the selection of doping density and epilayer thickness directly determined the target reverse breakdown voltage of the device. As the epilayer thickness varied from 3 mum ~ 11 mum at constant doping density 1times10 12cm-3, the breakdown voltage increased due to increased in the depletion width, while the breakdown voltage reduced as doping density varied from 1times10 12cm-3 ~ 1times10 17cm-3 at constant epilayer thickness of 3 mum. Hence we conclude that forward current and breakdown voltage have strong, inverse relation between epilayer thickness and doping density.