Unoccupied bulk and surface bands in the Gamma KX- Gamma KX plane of GaAs as observed by inverse photoemission spectroscopy.

Abstract

An extensive set of isochromat inverse photoemission data has been collected from the (110) face of a cleaved GaAs crystal for angles of electron incidence up to 63\ifmmode^\circ\else\textdegree\fi{} from the normal. In these data, transitions are observed across the full width of the \ensuremath{\Gamma}KX-\ensuremath{\Gamma}KX plane of the GaAs Brillouin zone, and the bands involved in these transitions are assigned with the guidance of an ab initio linear muffin-tin orbital (LMTO) calculation. A symmetry method for absolute K-space determination is outlined, and this is used to locate several of these transitions. Along the \ensuremath{\Gamma}KX symmetry line, an unoccupied state on the LMTO band eight saddle is found at 6.3 eV above the valence-band maximum (VBM) and another transition is observed at 8.6 eV, near the LMTO band 9 minimum. The band 5 maximum along the \ensuremath{\Gamma}\ensuremath{\Delta}X symmetry line is estimated to be 3.2 eV above VBM. An intense resonance is observed for angles of electron incidence near 10\ifmmode^\circ\else\textdegree\fi{}, where the energy of surface-state transitions approaches that of bulk transitions. The surface state is found to disperse to a minimum energy of 2.0 eV, and to have a bandwidth of at least 0.7 eV. \textcopyright{} 1996 The American Physical Society.