Defects in 700Â keV oxygen ion irradiated ZnO

It is well known that energetic oxygen ions induce heavy crystalline disorder in ZnO, however, systematic study on this regard is very much limited. Here, we present photoluminescence (PL), optical absorption and sheet resistance measurements on poly and single crystalline ZnO samples irradiated with 700 keV O ions. Results have been compared with the effects of 1.2 MeV Ar irradiation on similar ZnO target. Colour change of the samples with increasing O irradiation fluence has also been noted. Non-monotonic variation of room temperature sheet resistance with the increase of fluence has been observed for polycrystalline ZnO. Such an outcome has been understood as point defects transforming to bigger size clusters. Near band edge (NBE) PL emission is largely reduced due to O ion irradiation. However, at 10 K NBE emission can be observed for irradiated polycrystalline samples. Irradiated ZnO single crystal does not show any band to band transition even at 10 K. It is evident that dynamic recovery of defects is more effective in polycrystalline samples. Ultraviolet-visible absorption spectrum of the irradiated ZnO crystal show pronounced sub-band gap absorption. Oxygen irradiation generated new absorption band in ZnO is at 3.05 eV. In the light of earlier reports, this particular band can be ascribed to absorption by neutral oxygen vacancy defects.