Defect-induced photoluminescence from gallium-doped zinc oxide thin films: influence of doping and energetic ion irradiation

Herein, we present defect-induced photoluminescence behavior of Ga-doped ZnO (GZO) thin films with varying doping (Ga) concentrations and energetic ion irradiation. The Ga-doped ZnO thin films were prepared by a sol-gel spin-coating method. Micro-photoluminescence (mu-PL) was carried out to investigate the defect-related emission with the variation of doping concentration and ion irradiation. The PL spectra revealed that all films showed near-band-edge (NBE) emission along with a broad visible emission band, consisting of violet, blue, green, and yellow emission bands. The intensity of these emission bands was found to be strongly dependent on the Ga doping concentration and ion irradiation. Interestingly, a pronounced violet emission band around 2.99 eV (415 nm) was observed for the Ga-doped ZnO thin films with high Ga doping concentration, whereas an irradiated film with high ion fluence exhibited a strong green emission around 2.39 eV (519 nm); however, we concluded that the violet emission might have originated from zinc interstitial defects (Zn-i), and the concentration of Zn-i increased with the increasing doping concentration. The green emission is ascribed to the oxygen vacancies (V-O), and the concentration of the V-O defects increases with the increasing ion fluence. Thus, the m-PL spectra of the irradiated films with emission dominating in the blue and green regions could be attributed to the formation of extended defects such as clusters and ionizing centers of Zn-i and V-O. Herein, an in-depth understanding of the variation in defects related to the emission bands from these films is reported and correlated with the transport properties of these films for their possible optoelectronic applications.