The effect of Mg doping concentration and annealing on the structure and luminescence properties of ZnO thin films

In order to gain a deeper understanding of the relationship between defects and luminescent properties in thin films, ZnO films containing 0 to 8 at % Mg were prepared on amorphous quartz substrates by room temperature radio-frequency (RF) magnetron sputtering, followed by annealing in air at 400 °C. X-ray diffraction (XRD) results indicate that the ZnMgO film is a solid solution with a hexagonal close-packed wurtzite structure and preferential c-axis growth direction. With the increase in Mg concentration, the intensity of the (002) diffraction peak gradually decreases. Field emission scanning electron microscopy (FESEM) observations reveal a transition in surface particle shapes from approximately circular to a mixture of circular and irregular polygonal shapes. The optical bandgap (Eg), obtained from optical transmittance measured using a UV–visible spectrophotometer, decreases first and then increases with increasing Mg concentration. Photoluminescence (PL) spectra show a strong violet peak and a weak near-infrared (NIR) peak. Gaussian fitting of the two peaks reveals that the violet peak mainly originates from the radiative recombination of electrons bound to shallow donor interstitial zinc (Zn_i) with holes in the valence band. The NIR peak primarily arises from the radiative recombination of electrons captured by shallow donor interstitial zinc (Zn_i) with holes captured by deep-level acceptor interstitial oxygen (O_i).