Effect of thermal annealing on microstructure and optical properties of Zn1−xMgxO thin films grown by hydrothermal method

Abstract

Zn1−xMgxO films were prepared by hydrothermal method to investigate the effect of thermal annealing on the microstructure and optical properties. The results show that the films exhibit mixed cubic-hexagonal phases. With increasing of calcination temperature from 500 to 1000 °C, the peak intensities of MgO (200) and ZnO in the XRD patterns increases, the absorption edge shows a blue shift. And the band gap broadens from 3.43 to 4.03 eV while the average transmittance from 450 to 750 nm decreases from 88 to 79 at.%. The first-principles calculations reveal that the Zn1−xMgxO is direct band gap semiconductor. When the Mg content in the Zn1–xMgxO films increases with rising the calcination temperature, the CBM determined by the Zn-4s and Mg-2p states shifts significantly to the high energy range and the VBM determined by the O-2p state holds constant at Gamma point. This is the main reason for the band gap broadening of the films with increasing the calcination temperature.