Electronic structure of Si(111)-B(√3 × √3 )<i>R</i>30° studied by Si 2<i>p</i>and B 1<i>s</i>core-level photoelectron spectroscopy

Abstract

An investigation of the Si(111)-B(\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} system has been performed using high-resolution photoelectron spectroscopy of the Si 2p core level and polarization-dependent studies of the B 1s absorption edge. Least-squares analysis of the Si 2p core-level line shape reveals that it comprises a bulk component and a surface component shifted by 0.40\ifmmode\pm\else\textpm\fi{}0.02 eV to higher binding energy. The exceptionally large surface-to-bulk ratio that is observed in this system suggests that the range of influence of the B atoms extends to more than 1 monolayer of Si atoms. The magnitude of the surface-to-bulk ratio is consistent with a model in which B occupies a subsurface site below a Si adatom. The B 1s edge contains a feature which is excited by the component of the electric field vector perpendicular to the surface. We argue that this arises from an electronic transition from the B 1s level into an empty surface orbital, orientated perpendicularly to the surface. We also study the change of the electronic structure as the surface is covered with Si, thereby producing a buried \ensuremath{\delta}-doping layer.