Calculated phonon modes, infrared, and Raman spectra in ZnGeGa2N4

Abstract

Alloys between group III nitrides and the corresponding heterovalent II–IV-N2 compounds have recently been proposed as a further way of tuning the properties of nitride semiconductors. At 50% composition, a new ordered compound with composition ZnGeGa2N4 and space group Pmn21 was found, which has the lowest energy among wurtzite based structures. This structure obeys the local octet rule that every N is surrounded by two Ga, one Zn, and one Ge, ensuring local charge neutrality. Here, we investigate the vibrational properties of this new compound and provide predictions for its related infrared and Raman spectra, which may become useful for the characterization of this material. A group theoretical analysis, phonon frequencies and related Born effective charges, dielectric constants, infrared oscillator strengths, and Raman tensors are presented. Polarized infrared and Raman spectra for different scattering geometries are presented, as well as the phonon band structure and density of states.