Surface photovoltage in heavily doped $p^+$-GaAs with adsorbed cesium and oxygen overlayers

A new method for measuring the surface photovoltage based on the dependence of photoemission quantum yield on the band bending has been developed. Using this technique, the evolution of photovoltage in heavily doped $p^+$-GaAs (6$\cdot$10$^{18}$ cm$^{-3}$) under cesium and oxygen adsorption is studied. Reversible changes in photovoltage, which differ qualitatively from those observed earlier on lightly doped $p$-GaAs, are presented. The observed behavior is explained by the variations in surface recombination velocity during the formation and decay of two-dimensional cesium clusters.