Stability and electronic properties of ‘4-8’-type ZnSnN2 thin films free of spontaneous polarization for optoelectronic applications

Abstract

Ternary nitride ZnSnN2 is a promising photovoltaic absorber material. In this work, we using first-principles calculations investigate the stability and electronic properties of ‘4–8’-type ZnSnN2 thin films. We find that below a certain thickness ‘4–8’-type thin films have lower total energy than polar films in the wurtzite-derived structures. For 4-layer ZnSnN2 thin film, the Pna21/Pmc21 → 4–8 transitions can spontaneously occur at finite temperatures. All ‘4–8’-type thin films studied are semiconducting and free of spontaneous polarization, the bandgap of which can be tuned by the thickness of films, ranging from 1.4 eV to 1.8 eV. Furthermore, these films show light electron effective masses, and octet-rule-preserving disorder has insignificant effects on the electronic properties. Our results provide new insights into the structure of ZnSnN2 in the thin film form and guidance for the experimental investigation.