Tuning material properties of amorphous zinc oxynitride thin films by magnesium addition

The amorphous n-type multi-cation and multi-anion compound zinc magnesium oxynitride was fabricated by reactive long-throw magnetron co-sputtering from a metallic zinc and a metallic magnesium target. We achieved magnesium cation compositions in the thin films between 1 at. % and 7.5 at. % by varying the magnesium target power (variable-power approach) and compared this approach to a continuous composition spread. Both approaches lead to a reduction in Zn2+, an addition of Mg2+ cations, and a correlated increase in the oxygen content. Both these methods have the same effect on the optoelectrical properties: The increased magnesium content leads to a systematic decrease in the free charge carrier concentration regime from 1019 cm−3 to 1015 cm−3, a decrease in Hall mobility from 54 cm2 V−1 s−1 to 9 cm2 V−1 s−1, and a spectral shift of the absorption edge from 1.3 eV to 1.7 eV. The amorphous phase of zinc magnesium oxynitride is maintained until MgO crystallites form at a magnesium content ≥3 at. %. The electrical properties of the zinc magnesium oxynitride thin films show excellent long-term stability for at least 12 months.