  In this paper, we present the effects of high-energy Ni++ ion irradiation on
the structural and optical properties of GaN films. Three different irradiation
doses of 1013, 1014, and 1015 ions/cm2 were used while keeping the ion energy
at 700keV. The irradiation induced structural and optical changes in GaN films
were measured using X-ray diffraction (XRD) and UV-Vis spectroscopy. The XRD
measurements on irradiated films discovered several extra peaks in the XRD
spectrum compared with the as-grown GaN film indicating the formation of new
phases or defects in the GaN film due to the ion irradiation. The intensity of
these extra peaks increases with increasing ion dose, suggesting that the
density of defects in the GaN film also increases with increasing ion dosage.
The UV-Vis measurements revealed a decrease in the bandgap of the irradiated
GaN films from 3.40 eV for the pristine GaN film to 3.26 eV for the film
irradiated with highest dose of 1015 ions/cm2. The decrease in bandgap can be
attributed to the creation of defects and/or the formation of new phases in the
GaN film due to the ion irradiation.
