STRUCTURE AND BAND BENDING AT SI GAAS(001)-(2X4) INTERFACES/

We have grown thin, epitaxial overlayers of undoped and As-doped Si on As-stabilized n- and p-type GaAs(001)-(2X4) in order to investigate t he influence such overlayers have on band bending in the surface deple tion region. We have carried out structural, chemical, and electronic investigations of the resulting interfaces by means of x-ray photoemis sion spectroscopy, low-energy electron diffraction, and x-ray photoele ctron diffraction. Strained, epitaxial overlayers of Si could be grown for thicknesses of up to 10+/-1 angstrom at a growth temperature of 4 00-degrees-C. The perpendicular lattice constant of the overlayer is e stimated to be 5.32+/-0. 10 angstrom in this coverage regime. An inter face reaction between Si and Ga is observed for all coverages. Growth of undoped Si overlayers essentially conserves the band bending that e xists on the free surface (approximately 0.6 eV on n-type GaAs and app roximately 0.5 eV on p-type GaAs). However, the growth of heavily As-d oped Si flattens the bands to approximately 0.3 eV on n-type GaAs, but increases the band bending on p-type GaAs to approximately 0.8 eV. Th e influences that undoped and n + -doped Si overlayers have on the sur face band bending are readily explained by a simple model in which it is recognized that (1) epitaxial Si does not unpin the Fermi level in the sense that interface states are eliminated, and (2) a decrease (in crease) in the net electric field in the depletion region of n-type (p -type) GaAs is brought about by charge transfer from the n+--doped Si epilayer to the near-surface region of the GaAs substrate.