Development of alkali-induced electronic states at GaAs(0 0 1) surfaces and their electron-transfer interaction with helium metastable atoms

Modifications in the surface local electronic structure by the adsorption of alkali metals and its charge-transfer interaction with excited-state helium atoms have been investigated by metastable deexcitation spectroscopy (MDS) at Cs-adsorbed GaAs(0 0 1)(4×2) surfaces. Energy distributions of electrons ejected by Auger-type decay processes of holes on the incident He* atoms were measured as a function of Cs coverage. At a clean GaAs(0 0 1) surface, He* atoms were deexcited via resonance ionization followed by Auger neutralization (AN), from which the toplayer density of states was extracted. With the adsorption of Cs (θ<0.25), a new peak relating to the Ga dangling bonds filled by charge transfer from adsorbed Cs appeared by an Auger deexcitation (AD) process. At around θ∼0.5, we observed a development of Cs 6s-induced states at EF. We discuss a local nature in the charge-transfer interaction of the alkali-induced states with the He* atoms at semiconductor surfaces.