Empty states investigation of epitaxial Sn/Si( 100) systems

The Sn on the Si(100) system constitutes an epitaxial interface of Group-IV elements. Its phase diagram presents several surface reconstructions, whose structure depends on the Sn adlayer coverage and the annealing temperature. The interfaces of Sn grown at room temperature on Si(100)(2 X 1) and the superstructures obtained after annealing have been studied by means of inverse photoemission (IPES), and Auger and LEED spectroscopy, to characterize the electronic empty states of the different overlayer phases and relate them with other electronic properties. Sn/Si(100) systems, both at room temperature deposition and after thermal treatment, present the onset of a metallic overlayer for tin coverages above 1 ML. For the interfaces grown at room temperature the IPES spectra with Sn thicknesses below 1 ML show a peak at about 1.0 eV above the Fermi level. At the E(F) level no emission is present. The IPES spectra of Sn/Si(100) after annealing clearly show that the empty states evolution can be related to the kind of reconstruction observed by LEED. These results indicate the formation of interfaces with peculiar properties. In particular in the Sn/Si(100)c(8 X 4) system the phase is semiconducting and the gap is reduced; a new prominent state appears at 1.1 eV above E(F). The role played at the interface by the Sn-Sn dimers, related to the dimensionality, is discussed.