Band Gap Engineering of Cu2-II-IV-VI4 Quaternary Semiconductors Using PBE-GGA, TB-mBJ and mBJ+U Potentials

Abstract

The structural and electronic properties of Cu 2 ZnGeX 4 (X = S, Se and Te) with a tetrahedral coordinated stannite structure have been investigated using first-principles calculations. The optimized lattice constants, anion displacement u, tetragonal distortion parameter η, band gap, density of states and bulk modulus values are reported. The modified Becke-Johnson exchange potential (TB-mBJ), is used to calculate the electronic properties of Cu based quaternary semiconductors Cu 2 ZnGeX 4 (X = S, Se and Te) and thus the results for the band gap and other electronic properties such as Total Density of States (TDOS) and Partial Density of States (PDOS) are analyzed in detail. Also the results obtained using TB-mBJ potential are compared with the standard local density and generalized gradient approximation (GGA). Even though the comparison of results shows that the results obtained by TB-mBJ are still underestimating the experimental results. This explains the inadequacy of mBJ potential for semiconductors with strongly delocalized d electrons. Thus in this paper an on-site Coulomb U is incorporated within mBJ potential (mBJ + U) which leads to a better description of the pd hybridization and therefore the band gap which is very much comparable with the experimental results.