Tight-binding calculations of ZnSe/Si wurtzite superlattices: Electronic structure and optical properties

Abstract

Our study is devoted to the theoretical investigation of the electronic and optical properties of (ZnSe)n/(Si2)m (0001) wurtzite (WZ) superlattices (SLs) with the range n=m=1–18, giving special attention to the role of interface states at the Zn–Si and Se–Si polar interfaces. The calculations are performed by means of a semiempirical tight-binding model with an sp3s∗ basis. The procedure involves the construction of a tight-binding Hamiltonian model of WZ SLs from the WZ bulk in the (0001) direction with different n and m layers. For (ZnSe)16/(Si2)16 SL, we found that the energy band gap is close to 1.665 eV, with the conduction-band minimum located at the Γ point. The states at the conduction- and valence-band edges are confined two dimensionally in the Si layers. For a valence-band discontinuity ΔEv=1.09 eV given by Harrison theory, the band gap between the confined band edges states increases (2.37 eV at the Γ point for n=m=2) by decreasing the superlattice period. It is shown that the heterointerface bond relaxation strongly affects interface band in the band gap. In the (ZnSe)10/(Si2)10 SL, the relaxed Si bonds at the heterointerface induce a vacant interface band and a filled interface band in the band gap. The band structures of (ZnSe)n/(Si2)m (0001) (WZ) (SLs) with different layer thickness are used to determine the electron and hole effective masses. Furthermore, the calculated absorption spectra of the superlattices are found to be quite different from those of bulk ZnSe and Si but fairly close to their average. The electronic structure of the superlattice turns out to be quite sensitive to the combination of the well and barrier layer thickness. This sensitivy suggests the possibility of designing suitable band structures for device application.