We show by synchrotron radiation core level photoemission spectroscopy
that minute amounts of Cs induce at room temperature a giant jump of
the Fermi level into the conduction band when deposited on well-cleave
d InAs(110) surfaces. This stage corresponds to a single Cs adsorption
site. When more Cs is added a new adsorption site appears while corre
latively the band bending gradually decreases. The complete interface
formation (electronic structure, chemistry) is followed up to saturati
on at one monolayer and analyzed in terms of the present models of Sch
ottky barrier formation.