CORE TO SURFACE EXCITATIONS ON GaAs(110).

The authors have carried out ab initio calculations of surface core excitations on finite cluster models of the GaAs(110) surface. For the Ga core excitation the authors find a localized excited state involving excitation into the empty Ga-4p orbital and bound with respect to the conduction band minimum (CBM) by 0. 7 ev. This is in reasonable agreement with experiment (binding energy APP GRTH 0. 8 ev). This transition, which is not analogous to bulk core excitations, is termed a core surfaston to emphasize the character of the state. It is found that the As core surfaston is above the CBM by 1. 0 ev and hence should be difficult to observe.