Structural and electronic transformations at the Cs/GaAs(1 0 0) interface

Combined study of the structure and electronic properties of the Cs/GaAs(1 0 0) interface is performed by means of low-energy electron diffraction, electron energy loss spectra (EELS), X-ray photoelectron spectroscopy and photoreflectance (PR) techniques. Under Cs adsorption on As-rich (2×4)/c(2×8) surface at room temperature, the order-to-disorder transition was observed at small coverages θ∼0.1 ML, while on Ga-rich surface cesium adsorbs in an ordered way, so that sharp (4×1) structure is observed up to θ∼0.5 ML. At Cs coverages θ∼0.5 ML, a phase transition takes place at which the isolated Cs adatoms condense into closely packed two-dimensional metallic islands with local plasmon excitations detected by EELS. At the same coverages, by means of PR spectroscopy, we observed the decrease of surface photovoltage and acceleration of photoelectron kinetics due to the increase of lateral conductance and, therefore, of the surface recombination velocity.