Initial stages of interface formation between group III, IV, and V elements and silicon and germanium surfaces

Abstract

The initial stages of interface formation between various group III, IV, and V adsorbates and the Si and Ge surfaces have been examined with high resolution angle-integrated and angle-resolved photoemission spectroscopy using synchrotron radiation. The Si 2p and Ge 3d surface-shifted core level components are seen to be converted into components which are indistinguishable from the bulk component through submonolayer adsorption for the following systems: In/Si(001), Sb/Si(001), Sb/Si(111), Sn/Si(001), and Sb/Ge(001). For In/Ge(001), a chemically shifted Ge 3d core level interface component, distinguishable from the bulk component, is observed. The average number of Si and Ge surface dimer atoms which are modified in the presence of an adsorbate atom, which is referred to as the adsorbate-to-substrate bonding coordination number (BCN), is obtained for various In, Sb, and Sn coverages on Si(001) and Ge(001). The relative homogeneity of the adsorbate site bonding is evaluated by examining the line shapes of the Sn, In and Sb 4d core level spectra. Structural models, consistent with the data, are presented. The Fermi-level positions relative to the gaps and the Schottky-barrier heights are obtained for the various systems. Photoemission of the Sb-saturated Si(001), Si(111), and Si(110) surfaces revealed that the Fermi-level position crosses the conduction-band minimum (CBM) of Si for Sb coverages approaching a one-monolayer saturation limit. Momentum-resolved photoemission of the Sb-saturated Si(001) and Si(110) surfaces showed the existence of an occupied initial state located near the CBM. The photoemission intensity of the state has been examined as a function of photon energy with constant initial-state difference spectroscopy which showed various resonances occurring due to transitions to different final states from the CBM. The metallic character of the surface is shown to be due to degenerate doping in the near-surface region. The Sb saturation of Si(111) and Si(001) was found to allow the measurement of the bulk band-dispersion relations along the high symmetry $\Gamma$-$\Lambda$-L and $\Gamma$-$\Lambda$-X directions over a wide photon energy range (37-153 eV). The surface electronic topography of Sb/Si(001) is probed with scanning tunneling microscopy which shows changes in the spatial distribution of the occupied and unoccupied states derived from the Si-dimer dangling bonds upon Sb adsorption.