Investigation of Intrinsic Unoccupied Surface States at GaAs(110) by Isochromat Spectroscopy

Bremsstrahlung isochromat spectroscopy has been employed to measure the density of unoccupied electronic states on GaAs(110). The experiment was carried out at a quantum energy of 70 eV, resulting in a maximum of surface sensitivity. The theoretically predicted empty surface states ${B_1}^{\prime }$, ${S_1}^{\prime }$, ${B_2}^{\prime }$ and ${S_2}^{\prime }$, are identified. Their energetic positions as well as relative strengths are in excellent agreement with calculations based on the bond-relaxation model. A binding energy of 1.0 eV for the Ga $3d$ surface exciton is obtained.