Conduction-band dispersion, critical points, and unoccupied surface states on GaAs(110): A high-resolution angle-resolved inverse photoemission study

We report the first angle-resolved, high-resolution inverse photoemission study of the cleaved (110) surface of GaAs. The dispersion of the lowest conduction bands along the Γ-K-X main symmetry direction has been measured using inverse photoemission spectroscopy with tunable electron energy for initial energies between 10 and 30 eV. The photon spectra can be explained by direct optical interband transitions if bulk umklapp processes are taken into account. The ${\Gamma }_{15}$ critical point is found at 4.8 eV above the valence-band maximum. The maximum of the ${\Gamma }_1$ $X_1$ band is seen at 3.5 eV and the saddle of the ${\Sigma }_1$ band from ${\Gamma }_{15}$ to $X_5$ has been measured at 6.2 eV. In the center of the surface Brillouin zone at Γ¯ a surface resonance is located at 2.1 eV above the valence-band maximum in the conduction band. The surface state shows noticeable downward dispersion with $k_{?}$ of -0.4 eV in the direction toward X¯ and little dispersion of -0.1 eV toward X¯’.