Large interfacial charge density in unstrained GaAs-AlAs(111) superlattices

We calculate the formation enthalpy of (GaAs${)}_{\mathrm{n}}$(AlAs${)}_{\mathrm{n}}$(111) superlattices for n=1 and 3 and compare with previous (001) and (110) calculations. The (111) interfacial double layer and valence-band offsets for n=3 are also compared with (001) and (110) calculations. A new feature of the (111) unstrained superlattice is large zeroth-order internal electric fields which set up large interfacial charge densities (∼±4.3×${10}^{\mathrm{-}2}$ C/${\mathrm{m}}^2$) whose fields very nearly exactly cancel the zeroth-order fields.