Alloy effects on the band offsets ofZnSxSe1−x-ZnSe heterostructures

The band offsets of ${\mathrm{ZnS}}_{\mathit{x}}$ ${\mathrm{Se}}_{1\mathrm{-}\mathit{x}}$-ZnSe heterostructures are calculated within a self-consistent ${\mathit{sp}}^3$ ${\mathit{s}}^{\mathrm{*}}$ tight-binding model including spin-orbit coupling considering several sulfur concentrations x and in the two extreme strain states that can be imposed on the structure (strained to a ZnSe or to a ${\mathrm{ZnS}}_{\mathit{x}}$ ${\mathrm{Se}}_{1\mathrm{-}\mathit{x}}$ lattice parameter). The commutativity of the valence- and conduction-band offsets is examined. The conduction-band offset Δ${\mathit{E}}_{\mathit{c}}$ is found to be weak for x≃1 and whatever the strain state imposed. The variation of Δ${\mathit{E}}_{\mathit{c}}$ with respect to the sulfur concentration x is mainly driven by the bowing effect of the band gap. We show that the vanishing value of the conduction-band offset can be obtained through a diminution of the band-gap bowing effect which may be achieved in ${\mathrm{ZnS}}_{\mathit{x}}$ ${\mathrm{Se}}_{1\mathrm{-}\mathit{x}}$-${\mathrm{ZnS}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Se}}_{\mathit{x}}$ superlattices, leading to the possibility for these structures to be effective-mass superlattices.