Specific features investigation of the AE₂ZnN₂ (AE=Ca, Sr, Ba) compounds from indirect to direct band gap: DFT study

First principles calculations are performed to investigate the structural, electronic, optical and transport properties of the ternary semiconducting compounds AE₂ZnN₂ (AE=Ca, Sr, Ba) in the tetragonal crystal phase by using a modern and highly accurate full potential linearized augmented plane wave method. In the tetragonal ternary nitrides AE₂ZnN₂, Zn has a unusual linear coordination with nitrogen (N-Zn-N) along the c-axis. The band gap values for the AE₂ZnN₂ compounds are calculated with the modified Becke–Johnson (mBJ) approximation. The band gap calculation suggests that these materials are extremely attractive for excellent thermoelectric performance. Subsequently, semi-classic Boltzmann transport theory has been utilized to calculate the thermoelectric properties of the AE₂ZnN₂ (AE=Ca, Sr, Ba) compounds. The band gap of these compounds varies by replacing the cation AE and the band gap dependent optical parameters are predicted for experimental perspectives. In addition, the optical response suggests that the AE₂ZnN₂ materials are useful for optoelectronic devices. Furthermore, the figures of merit, thermo power, power factor, electrical and thermal conductivity are calculated for each compound.