Prediction of direct band gaps in monolayer (001) and (111) GaAs/GaP superlattices

The bulk GaAs0.5P0.5 alloy with lattice constant a(0.5) has an indirect band gap. First-principles self-consistent pseudopotential band structure calculations show that the monolayer (GaAs)1 (GaP)1 superlattice (SL) in either the (001) or the (111) layer orientation G is also indirect if constrained epitaxially on a substrate whose lattice constant is a(0.5). However, if grown coherently on a GaAs substrate we predict that both of these SLs will have a direct band gap. This is explained in terms of the deformation potentials of the underlying materials. Predicted band offsets are given for both (001) and (111) GaP/GaAs.