The fabrication of GaN merged p-i-n/Schottky (MPS) diodes using Si+ ion implantation into p-epi layers on bulk, free-standing GaN substrates is reported. Diode diameters from 50 to 500 mum were investigated. These initial NIPS diodes show larger turn-on voltage (similar to30 V) than the unimplanted p-i-n diodes (similar to10 V) fabricated on the same wafer but lower reverse leakage current density. The Si+ implant activation efficiency is similar to25% for 1150 degreesC anneals, reaching similar to30% for 1200 degreesC anneals. (C) 2003 Elsevier Ltd. All rights reserved.