Effect of 120 MeV Ag ion irradiation on the structural and electrical properties of NiO/ZnO heterojunction

Abstract

NiO/ZnO heterojunction deposited on Si(100) substrate by evaporation method were irradiated with 120 MeV Ag ions. The effects of ion irradiation on various properties of the heterojunction were studied. Crystallinity of NiO layer improved due to irradiation at the fluence of 3 × 1011 ions cm-2 as revealed by the increase in grazing incidence X-ray diffraction (GIXRD) peak intensity. Further irradiation reduced the intensity of GIXRD peaks but could not suppress it completely even at the highest fluence (1 × 1013 ions cm-2), where the whole bilayer is expected to be covered with ion tracks. This observation indicated that the columnar region around the ion path is not completely amorphized, but its crystallinity is reduced. Evolution of the area under GIXRD peaks with ion fluence gave radius of this modified columnar region as ∼4.9 nm. The peaks of ZnO were not clearly evident in the GIXRD pattern. However a weak peak due to ZnO could be seen in the Raman spectra, which also did not completely vanish even at the highest fluence of irradiation. The bilayer sample irradiated at a fluence of 1 × 1012 ions cm-2 showed the highest switching ratio, which could be due to the thermal spike induced diffusion of ions across the NiO/ZnO junction.