Electronic structure and optical properties of (ZnS${)}_{\mathit{n}}$/(${\mathrm{Si}}_2$${)}_{\mathit{m}}$ superlattices

An approach has been suggested to integrate the superior properties of the ZnS semiconductor with the mature technology of Si. In a semiempirical tight-binding scheme, the detailed calculations of electronic structure and optical properties of the (ZnS${)}_{\mathit{n}}$/(${\mathrm{Si}}_2$ ${)}_{\mathit{m}}$ (110) superlattices are performed with a wide range of n,m≤20. A strong quantum confinement effect is found that causes the states at the conduction- and the valence-band edges confined in two dimensions in the Si wells. For a valence-band discontinuity Δ${\mathit{E}}_{\mathit{v}}$=1.9 eV given by Harrison theory, the band gap between the confined band-edge states increases (2.37 eV at the X̃ point for n=m=2) by decreasing the superlattice period. An empty interface band is identified in the upper region of the gap, which extends over a quite different region of k space. The influence of valence-band discontinuity has been checked for all possible energy ranges. It is found that the dispersion and relative position of the interface band depend on valence-band discontinuity, but it does not disappear from the gap. Furthermore, the absorption spectra of the superlattices are calculated, which are found to be quite different from those of bulk ZnS and Si, but fairly close to their average.