An investigation on the variations in properties of Ni+ irradiated ZnO thin films

ZnO thin films, irradiated by 80 MeV Ni⁺ ions, were analysed with the help of different characterization techniques like X-ray diffraction, optical absorption, transmission, photoluminescence (PL), electrical resistivity, photosensitivity (PS) and thermally stimulated current (TSC) measurements. Crystallinity and absorption edge were hardly affected by irradiation. PL spectrum of pristine sample showed a broad peak at 517 nm, whereas irradiated film had two emissions at 517 and 590 nm. Intensity ratio between these two emissions (I₅₁₇/I₅₉₀) decreased with the fluence, and finally at a fluence of 3×10¹³ ions/cm², the emission at 517 nm completely disappeared. Electrical resistivity of the sample irradiated with a fluence of 1×10¹³ ions/cm² drastically increased. However, on increasing the fluence to 3×10¹³ ions/cm², resistivity decreased, probably due the onset of hopping conduction through defects. PS also decreased due to irradiation. TSC measurements on pristine sample could reveal only one defect level at 0.6 eV, due to interstitia1 zinc (Zn_I). But, irradiation at a fluence of 1×10¹² ions/cm², resulted in three different defect levels as per TSC studies. Interestingly, the sample irradiated at a fluence of 3×10¹³ ions/cm² had only one defect level corresponding to a deep donor. The possible origin of these defect levels is also discussed in the paper.