Effect of native oxidation and hydroxidation on earth-abundant ZnSnN₂ grown by reactive RF magnetron sputtering

II-IV-N₂ semiconductors such as ZnSnN₂ have emerged as promising earth-abundant materials, but their heterovalent bonding structure is more susceptible to oxidation and hydroxidation than conventional III-nitrides. In this study, we focus on native oxidation and hydroxidation of ZnSnN₂ thin films grown by RF magnetron sputtering and investigate the roles of atmospheric moisture and oxygen in material degradation. By exposing ZnSnN₂ to controlled environments with varying humidity, we observed significant oxidation and hydroxidation under humid conditions, as confirmed by energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis. In particular, the formation of the oxides (SnO₂) and hydroxides (Zn(OH)₂ and ZnSn(OH)₆) on the surface remained unaffected, indicating surface-limited oxidation. Angle-resolved XPS revealed a self-passivating oxide and hydroxide layer that prevents deep oxidation and hydroxidation. These findings demonstrate a self-limiting property of an oxide and hydroxide layer formed under humid conditions, providing valuable insight into the environmental stability of ZnSnN₂.