CS ADSORPTION ON N-TYPE AND P-TYPE GAAS(001)(2X4) SURFACES

A study of room temperature Cs adsorption on both n- and p-type GaAs(001)(2 x 4) surfaces is presented. We find that initially the work function decreases linearly with Cs exposure saturating 3 eV below the clean surface value. Unlike GaAs(110) which forms an ordered overlayer, Cs deposition on (001) is amorphous. Adsorption steadily degrades the initial c(2 x 8) LEED pattern, and no additional superstructure is observed. Preliminary STM images obtained at low coverage indicate that at room temperature the Cs does not adsorb at any particular atomic site. Cs atoms adsorb both on top of the arsenic dimers and above the Ga in the missing dimer row. Tunneling spectroscopic measurements obtained at a range of coverages show that the surface remains semiconducting up to saturation coverage.