TUNING ALAS-GAAS HETEROSTRUCTURE PROPERTIES BY MEANS OF MBE-GROWN SI INTERFACE LAYERS

AlAs-GaAs(001) and GaAs-AlAs(001) heterostructures with Si interface layers have been grown by molecular beam epitaxy in a new facility which allows in situ high-resolution X-ray photoemission spectroscopy analysis of electronic parameters. Reflection high-energy diffraction studies of Si growth on GaAs show under As flux an intermediate 2 X 1 pattern at low Si coverage, followed by a sharp 3 X 1 pattern throughout the 0.2-2.0 monolayer coverage range. Photoemission indicates that most of the deposited Si atoms remain at the AlAs-GaAs interface during the following stages of heterostructure fabrication. The presence of Si yields an additional dipole-induced band offset of up to 0.38 eV, which can be added to, or subtracted from the original heterojunction band discontinuity of 0.40 eV depending on the growth protocol. The direction and order of magnitude of the dipole are consistent with the predictions of a recently proposed model of group IV elemental layers at polar III-V semiconductor interfaces. The Si concentration dependence of the dipole, however, is in stark contrast with theoretical expectations.