Elastic Constants of the II-IV Nitride Semiconductors MgSiN_2, MgGeN_2 and MgSnN_2

The single crystal elastic constants, polycrystalline elastic moduli and related properties of orthorhombic MgSiN_2, MgGeN_2 and MgSnN_2 have been calculated using density functional theory and compared to the related wurtzite structured AlN, GaN and InN. Since there are no experimental studies of single crystal elastic properties of neither MgSiN_2, MgGeN_2 or MgSnN_2, we have established the accuracy of the calculations by comparison with experimental data for AlN, GaN and InN. The calculated polycrystalline elastic moduli of MgSiN_2 are found to be in good agreement with available experimental elastic moduli. It will be shown that MgSiN_2 and MgGeN_2 have a small xy-plane lattice mismatch with AlN and GaN, respectively, while at the same time being significantly softer than both AlN and GaN. This shows that MgSiN_2 and MgGeN_2 should be possible to be grown on AlN and GaN without significant lattice mismatch or strain.