Tight binding modeling of CdSe/ZnS and CdZnS/CdS II-VI heterostructures for solar cells: Role of d-orbitals

We present a semiempirical tight binding model with sp3d5 basis set to investigate the alloy composition and strain effects on the electronic band structure of group II-VI heterostructures for solar cells. The model Hamiltonian includes nearest neighbor interactions and spin-orbit splitting of p-states. Bond lengths and atomic energies of cation and anion forming compound semiconductors are taken as nonlinear function of composition. Using this scheme, we investigated the composition and strain effects on electronic band structure in Cd1-xZnxS/CdS and CdSe/ZnS heterostructures. We found that the sp3d5 TB model accurately reproduces the band gaps and both the valence band and conduction band dispersion curves at Γ, X and L high symmetry points at the edge of Brillouin zone. A good agreement is found between model predictions and experiment for nonlinear variation of band gaps at Γ, X and L symmetry points