Two-dimensional theoretical simulations have been carried out to investigate the effect of an ion-implanted high-resistivity guard ring structure on the performance of n-GaN Schottky diode rectifiers for high-power applications. The guard ring, made of p-type implantation, exhibited a Gaussian profile. Calculated forward current-voltage characteristics, reverse breakdown voltage, and leakage current as functions of the peak implant doping and of the characteristic length of the implanted doping in the lateral x direction give a good estimate of the influence of guard ring on the device performance. A judiciously formed guard ring can yield a room-temperature reverse breakdown voltage as high as 3000 V and a reverse leakage current as low as similar to 10(-8) A. However, the reverse leakage current, for example, for an applied bias of -50 V, increases to similar to 10(-5) A at 400 K. One crucial feature of the present study is the investigation of the optimal distance between the metal edge and the edge of the implanted region, which tends to significantly dictate the quality of the diode rectifiers. (c) 2006 American Vacuum Society.