Influence of hydrogen on electrical and optical properties of ZnO films

Abstract

AbstractElectrical and optical properties of H doped ZnO films have been studied experimentally for different H concentrations before and after annealing, as well as theoretically by first‐principles calculations. It is found that electrical resistivity of the H doped ZnO increases when increasing the substrate temperature in the range 25–300 °C. Carrier concentration and mobility measured by Hall method in as‐grown samples are larger than those of annealed ones. The short‐wavelength edge of the transmission spectrum of annealed ZnO is found to shift toward lower energies compared to as‐grown samples. The band gap estimated from the measured transmission spectra of as grown ZnO increases with increasing H concentration, thus demonstrating the Burstein–Moss effect. However, it decreases in samples annealed at 300 °C showing suppression of the Burstein–Moss effect. Possible defect models explaining the reason for the suppression are discussed. The results can be explained by formation of H2 molecules in annealed ZnO.