AlAs-GaAs Heterojunction Engineering by Means of Group IV Elemental Interface Layers

Valence- and conduction-band discontinuities in AlAs-GaAs heterostructures can be continously tuned through fabrication of pseudomorphic elemental Ge or Si layers of controlled thickness at the interface. The local interface dipole associated with the group-IV interface layer can be added to or subtracted from the natural band offsets depending on the growth sequence. Comparison of high-resolution x-ray-photoemission studies of AlAs-Ge-GaAs and AlAs-Si-GaAs heterostructures prepared in situ by molecular-beam epitaxy as a function of the interface concentration of group-IV elements shows qualitative similarities and surprising quantitative differences. The observed dipole per group-IV atom is 3 times as large for Ge as for Si, but the total maximum dipole achievable at the interface is identical (0.4 eV), within experimental uncertainty, for the two group-IV elements.