OVERLAYER-INDUCED VALENCE STATES, AND EVIDENCE FOR CHARGE-TRANSFER IN NA/GAP(110) AND NA/GAAS(110) - A COMPARATIVE PHOTOEMISSION-STUDY

Core and valence level photoemission experiments for Na overlayers on GaP(110) and GaAs(110) reveal new peaks which are interpreted in terms of Na-Ga charge transfer, as predicted by total energy calculations. New peaks in the region above the valence band are identified with the previously empty Ga surface state which is filled by the charge transfer process. The role of this gap emission in the pinning of the Fermi level at submonolayer to metallic coverages is discussed for both semiconductors.