We have used high-energy x-ray photoelectron diffraction to investigate the structure of the first monolayer of epitaxial Si on GaAs(001)-(2×4). Analysis reveals that Si indiffusion occurs, resulting in Si occupancies of ∼0.6, 0.3, and 0.1 in the first, second, and third layers, respectively. In addition, Si atoms are displaced from their respective bulk truncated coordinates by 0.5±0.1 Å along [110] in the first layer, and by 0.4±0.1 Å along [1¯10] in the second layer. These results provide an explanation for the unusual band-offset behavior at AlAs/Si/GaAs heterojunctions.

• Received 25 January 1993

DOI:https://doi.org/10.1103/PhysRevB.47.13023