Quasiparticle self-consistent GW electronic band structure of Cd-IV-N2 compounds

Abstract

Quasiparticle self-consistent GW calculations of the electronic band structures of Cd-IV-N2 with group-IV elements, Si, Ge, and Sn, are reported. The lattice parameters in the Pna21 crystal structure are obtained both in the local density approximation and generalized gradient approximation (GGA) and provide respectively an underestimate and overestimate of the lattice constants for these until now not synthesized materials. The Wyckoff positions are obtained by structural minimization. At the GGA lattice constant, which is expected to be the most reliable, CdSiN2 is found to have an indirect gap (U-Γ) of 2.72 eV, which is 0.55 eV lower than the direct gap at Γ of 3.27 eV. In CdGeN2, the indirect gap of 2.01 eV is only 0.1 eV smaller than the direct gap of 2.11 eV, and in CdSnN2 the gap is direct and equals 0.64 eV close to that of InN, as expected. The direct/indirect nature of CdGeN2 is found to be sensitive to shear strain. The conduction band effective masses decrease from CdSiN2 to CdGeN2 to CdSnSn2. The energies of formation indicate these materials to be stable with the possible exception of CdSnN2.