Stability, and electronic and optical properties of ternary nitride phases of MgSnN2: A first-principles study

Abstract

We have studied the disordered rocksalt, orthorhombic, and disordered wurtzite phases of the ternary nitride semiconductor MgSnN2 by first-principles methods using density functional theory (DFT) and beyond. The results imply that MgSnN2 is mechanically and dynamically stable in all three phases. However, pCOHP analysis suggests that the disordered rocksalt structure has antibonding states below the Fermi level between −5 eV and −2 eV, as compared to the bonding states in the other two phases, indicative of its thermodynamic metastability. Computed lattice constant and electronic band-gap values of 4.56 Å and 2.69 eV for MgSnN2 in the disordered rocksalt structure compare well with experimentally reported values of 4.48 Å and 2.3 eV, respectively. Furthermore, band gaps were computed for MgSnN2-xOx (x = 0.5, 1.0, 1.5, 2.0) to elucidate the role of possible oxygen impurities. Band-gap bowing is suggested to occur upon alloying with oxygen. Of the three phases, the disordered rocksalt structure shows the lowest charge carrier effective masses. Moreover, the absorption coefficient and reflectivity of this phase make it promising for use as the absorber layer of tandem solar cells in the higher energy region of the visible portion of the solar spectrum. The other two phases, disordered wurtzite and orthorhombic, might be utilized as the window layer of solar cells owing to their larger band-gap values of 4.36 eV and 4.86 eV, respectively.