Tailoring of composition, band-gap, and structural phase in ZnMgO films by simply controlling growth temperature and oxygen partial pressure during sputter deposition

It has been suggested in this study that the Mg content, band-gap energy, and structural phase in the sputter deposited ZnMgO films could be tailored in a wide range by simply controlling the growth temperature and sputtering ambient. The Mg content in film and the band-gap energy showed a strong dependence on the growth temperature and sputtering ambient, increasing with the growth temperature or decreasing by an oxygen addition into the plasma ambient. In this work, the wurtzite ZnMgO film with a wide band gap of 4.53 eV and a high Mg content of XMg = 0.53 could be realized for the first time by sputtering the Zn0.7Mg0.3O alloy targets with Mg contents of 0.3–0.35 below 200 °C and under pure Ar ambient. From the dependence of the structural phase on the growth temperature, the solubility limit of Mg in the wurtzite ZnMgO single phase without phase segregation was estimated to be about 0.53–0.56 and confirmed to reduce with the growth temperature, possibly due to the lower formation Gibbs free energy of MgO than ZnO and the difference in growth condition.