DEVELOPMENT OF ALKALI-INDUCED ELECTRONIC STATES AT GAAS(001) SURFACESAND THEIR ELECTRON-TRANSFER INTERACTION WITH HELIUM METASTABLE ATOMS

Modifications in the surface local electronic structure by the adsorpt ion of alkali metals and its charge-transfer interaction with excited- state helium atoms have been investigated by metastable deexcitation s pectroscopy (MDS) at Cs-adsorbed GaAs(0 0 1)(4 x 2) surfaces. Energy d istributions of electrons ejected by Auger-type decay processes of hol es on the incident He atoms were measured as a function of Cs coverag e. At a clean GaAs(0 0 1) surface, He atoms were deexcited via resona nce ionization followed by Auger neutralization (AN), from which the t oplayer density of states was extracted. With the adsorption of Cs (th eta < 0.25), a new peak relating to the Ga dangling bonds filled by ch arge transfer from adsorbed Cs appeared by an Auger deexcitation (AD) process. At around theta similar to 0.5, we observed a development of Cs 6s-induced states at E-F. We discuss a local nature in the charge-t ransfer interaction of the alkali-induced states with the He atoms at semiconductor surfaces. (C) 1998 Elsevier Science B.V. All rights res erved.