Structure and local dipole of Si interface layers in AlAs-GaAs heterostructures

lAs-Si-GaAs(001) and GaAs-Si-AlAs(001) heterostructures were synthesized by molecular-beam epitaxy. Transmission electron microscopy and in situ x-ray photoemission spectroscopy, together with x-ray interference measurements of model GaAs-Si-GaAs(001) structures and Si-GaAs(001) superlattices, indicate that pseudomorphic Si layers can be grown at the interface for layer thickness <=4-8 monolayers with no detectable dislocation or twin formation. While the band offsets for isovalent AlAs-GaAs heterostructures follow the commutativity rule, the presence of Si at the interface is found to give rise to deviations from the rule as large as ±0.4 eV. Such deviations are associated with a Si-induced local dipole that can be established with high reproducibility within the interface region.