Interband and exciton related optical properties of ZnGeN2 in comparison to GaN

In this work, the optical dielectric function of ZnGeN2 is calculated from the interband transitions using the energy bands calculated in the quasiparticle self-consistent (QS)GWˆ method with two different levels of approximation: the independent particle approximation (IPA) and the Bethe-Salpeter Equation (BSE) approach. While the IPA allows us to relate peaks in ε2(ω) to specific bands and k-points, it does not include electron-hole interaction effects. The second approximation includes electron-hole interaction or excitonic effects. The corresponding changes due to these excitonic effects in the shape of ε2(ω) are found to be similar to those in GaN. The screened Coulomb interaction Wˆ is here calculated including electron-hole interactions in the polarization function and gives a band structure already going beyond the random phase approximation. The convergence of the bound excitons with the density of the k-mesh included in the BSE is studied. The excitons are related to each of the three-fold split valence bands and the splittings of the latter are also studied as a function of strain. 

This work was supported by the U.S. Department of Energy Basic Energy Sciences (DOE-BES) under grant No. DE-SC0008933.