Effect of thermal oxidation on the optical, electrical, and chemical properties of zinc nitride films grown by reactive magnetron sputtering

We have studied the effect of post growth annealing in oxygen ambient on the optical, chemical and electronic properties of zinc nitride thin films. The films were prepared by reactive radio frequency magnetron sputtering of zinc target in the presence of argon and nitrogen gasses at a substrate temperature of 300 °C. Post growth annealing was performed at annealing temperatures of 300, 400, 500, 600, and 700 °C in the oxygen environment to transform the zinc nitride films into p-type zinc oxide. Atomic force microscopy of the films reveal that surface roughness and grain size of the films are directly proportional to the post-growth annealing temperature. X-ray photoelectron spectroscopy of the films revealed that as-grown film has the highest intensity of nitrogen in the film whereas little nitrogen remains in the films that were annealed at 500 °C and higher temperatures. Films annealed at higher temperatures have lower carrier concentration but higher Hall mobility compared to the as-grown film and the films annealed at lower temperature. Moreover, as-grown film and the films annealed at lower temperature have n-type conductivity whereas films annealed at temperatures above 500 °C exhibit p-type conductivity. Films annealed at lower temperature have bandgap values closer to the zinc oxynitride but bandgap of the films annealed at higher temperatures have values close to the bandgap of zinc oxide. This indicates that post growth annealing of zinc nitride films at 500 °C in oxygen ambient transforms it into p-type zinc oxide.