Surface electronic structure of Si(001)2×2-In studied by angle-resolved photoelectron spectroscopy

Angle-resolved photoelectron spectroscopy (ARPES) using synchrotron radiation was employed to study the electronic structure of a well-ordered single-domain Si(001)2×{}2-In surface. The existence of five surface state bands, denoted as S₁, S₂, S₂^', S₃, and S₃^' is revealed within the bulk band gap between 0.6 and 2.2 eV in binding energy (EB). The dispersions of these surface states are determined for most of the symmetry axes in the 2×{}2 surface Brillouin zone (SBZ), which turn out to be essentially identical to those observed for Si(001) 2×{}2-Al recently [Surf. Sci. Lett. 321, L177 (1994)]. Symmetries of the surface states with respect to two mirror axes of the SBZ are determined by the polarization dependence of ARPES intensities. A comparison to a theoretical calculation makes it possible to determine that the smallest EB state S₁ is due to the In dimer bond and S₂, S₂^', S₃, and S₃^' are due to bonds between In dimers and topmost Si atoms, and that the In dimers are parallel to the substrate Si dimers. Besides these five surface state bands, two other spectral features are observed within the bulk band gap, which can be related to similar features observed for a clean Si(001) surface.