Structure and lattice dynamics of the wide band gap semiconductors MgSiN_2 and MgGeN_2

摘要

We have determined the structural and lattice dynamical properties of the orthorhombic, wide band gap semiconductors MgSiN_2 and MgGeN_2 using density functional theory. In addition, we present the structural properties and Raman spectra of MgSiN_2 powder. The structural properties and lattice dynamics of the orthorhombic systems are compared to those of wurtzite AlN. We find clear differences in the lattice dynamics between MgSiN_2, MgGeN_2 and AlN, for example, we find that the highest phonon frequency in MgSiN_2 is about 100 cm~(-1) higher than the highest frequency in AlN, and that MgGeN_2 is much softer. We also provide the Born effective charge tensors and dielectric tensors of MgSiN_2, MgGeN_2 and AlN. Phonon related thermodynamic properties, such as the heat capacity and the entropy, have also been evaluated and are found to be in very good agreement with available experimental results.