Influence of air exposure on the compositional nature of Zn3N2 thin films

Zinc nitride (Zn3N2) films were prepared by radio-frequency magnetron sputtering from a pure Zn target in a N2 ambient. Films were deposited on glass and Si(100) substrates at 298- and 473-K substrate temperatures (Ts). Ion beam analysis (IBA) techniques, spectroscopic ellipsometry (SE) and transmission spectroscopy were used to characterize the samples as a function of Ts and time. IBA studies showed that the Zn and N concentrations matched the stoichiometric values 3:2 of the cubic anti-bixbyte structure and revealed the partial transformation of Zn3N2 into zinc oxide (ZnO) due to the exposure to ambient air. IBA and SE techniques revealed films grown at higher Ts were less affected by the oxidation process. Transmission spectroscopy showed that the band gap energy blue shifted as Ts decreased. It was also found that the oxidation process produced a blue shift of the band gap energy. For the sake of comparison, ZnO/Zn3N2 heterostructures were synthesized using the same system and characterized in parallel to unintentionally oxidized nitride layers. SE studies of the heterostructure showed that the deposition of a ZnO layer helped to prevent nitride oxidation.