Comparative study on effects of H2 flux on structure and properties of Al-doped ZnO films by RF sputtering in Ar+H2 ambient at two substrate temperatures

Al-doped ZnO (AZO) thin films were prepared by radio frequency magnetron sputtering with and without H2 flux at substrate temperatures of 200 and 250 °C. The effects of H2 flux on structure and properties of the AZO films were investigated by X-ray diffraction, scanning electron microscopy, Hall Effect measurement, UV-visible spectroscopy, and photoluminescence (PL) spectroscopy. At a substrate temperature of 200 °C, the crystallinity, electrical conductivity, and conductive stability in air of the films increase with the increase in H2 flux to 2 sccm and then remain almost unchanged with further increase in H2 flux, the PL spectra for the films deposited in Ar suggest the existence of three emission peaks, i.e., a UV, a violet and a blue emission peak, and all of these emission peaks show a blue shift and an additional green emission peak appears in the spectra for the films deposited under H2 flux. At a substrate temperature of 250 °C, the crystallinity and conductive stability in air of the films show little dependence on H2 flux; the electrical conductivity is initially unaffected as H2 flux increases, but reduced with further increase in H2 flux. The PL spectra for the films deposited in Ar also indicate the existence of a violet, a blue and a green emission peak, but unlike these for the films deposited at 200 °C, such PL characteristic is unaffected by the H2 flux. For all the films deposited at the two substrate temperatures, the surface roughness increases with H2 flux, but the transmittance in the visible region remains over 80%. The value of Eg increases with carrier concentration, which is attributed to the Burstein-Moss effect. The possible roles of hydrogen for the variation in structures and properties of AZO films deposited at the two substrate temperatures are discussed.