15 MeV proton damage in NiO/& beta;-Ga2O3 vertical rectifiers

15 MeV proton irradiation of vertical geometry NiO/& beta;-Ga2O3 heterojunction rectifiers produced reductions in reverse breakdown voltage from 4.3 kV to 3.7 kV for a fluence of 10(13)ions & BULL;cm(-2) and 1.93 kV for 10(14) ions & BULL;cm(-2). The forward current density was also decreased by 1-2 orders of magnitude under these conditions, with associated increase in on-state resistance R (ON). These changes are due to a reduction in carrier density and mobility in the drift region. The reverse leakage current increased by a factor of & SIM;2 for the higher fluence. Subsequent annealing up to 400 & DEG;C further increased reverse leakage due to deterioration of the contacts, but the initial carrier density of 2.2 x 10(16) cm(-3) was almost fully restored by this annealing in the lower fluence samples and by more than 50% in the 10(14) cm(-2) irradiated devices. Carrier removal rates in the Ga2O3 were in the range 190-1200 for the fluence range employed, similar to Schottky rectifiers without the NiO.