Enhanced UV emission of Li–Y co-doped ZnO thin films via spray pyrolysis

Abstract

Pure ZnO and ZnO: 2%Y: x%Li (x = 0, 3, 5 and 7 at.%) thin films have been successfully prepared onto glass substrates under optimized conditions by spray pyrolysis technique at 450 °C and their suitability for the fabrication of efficient optoelectronic devices is demonstrated. The samples have been characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV–Visible absorption spectroscopy photoluminescence (PL) and Raman spectroscopy (RS), in order to investigate the effect of Y–Li co-doping on the structure, surface morphology, and optical features of the thin films. The films crystallized into a hexagonal structure, with a preferred orientation along the c-axis. No additional phases have been observed. SEM micrographs showed that Y and Li co-doping plays a key role in the grain size and morphology of the films. The optical study via transmittance and absorption measurements within the UV–vis region revealed that the films are highly transparent (82–90%). The optical bandgap (Eg) depends on the concentration of lithium added, which is explained by the Burstein-Moss (BM) effect. The PL measurements at room temperature under excitation with 325 nm wavelength, showed an appreciable improvement of ultraviolet emission by increasing the Li co-doping concentration. This enhancement reaches a maximum at 5 at.% Li content, and decreases after further increase in Li content. Raman scattering spectra were also carried out and revealed the presence of the wurtzite phase of ZnO exclusively.