# Structure and lattice dynamics of the wide band gap semiconductors MgSiN$_{2}$ and MgGeN$_{2}$

## TL;DR

This study uses density functional theory to analyze the structural and lattice dynamical properties of wide band gap semiconductors MgSiN₂ and MgGeN₂, comparing them to AlN and providing insights into their phonon spectra and thermodynamic properties.

## Contribution

The paper presents the first detailed theoretical analysis of the lattice dynamics and related properties of MgSiN₂ and MgGeN₂, including phonon spectra and dielectric tensors, with experimental validation.

## Key findings

- MgSiN₂ has a phonon frequency about 100 cm⁻¹ higher than AlN.
- MgGeN₂ exhibits much softer lattice dynamics compared to MgSiN₂ and AlN.
- Phonon-related thermodynamic properties match experimental data.

## Abstract

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 structural properties and Raman spectra of a MgSiN$_{2}$ powder. The structural properties and lattice dynamics of the orthorhombic systems are compared to 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 entropy, are in very good agreement with available experimental results.