PHOTOINDUCED FORMATION OF DIMERS AT A LIQUID (001)GAAS INTERFACE/

Using reflectance anisotropy spectroscopy (RAS), we show that surface dimers, which so far have only been observed on surfaces in an ultrahi gh-vacuum environment, can exist at semiconductor/liquid interfaces. W e consider here As and Ga dimers at the interface between GaAs and sod ium sulfide solutions. These dimers appear as the result of photochemi cal reactions and are identified by their RA signatures. Their observa tion requires (i) dark treatment of the surface in the solution (1 h) in order to form an overlayer which isolates the surface from the solu tion, (ii) subsequent above band-gap light excitation which induces ph otoassisted breaking of respectively As-related and Ga-related chemica l bonds at the interface between the semiconductor and the protective layer. Analysis of the growth under light excitation of the dimer sign al gives evidence that gallium dimers are created at the expense of ar senic dimers by breaking of chemical bonds between gallium and overlyi ng arsenic atoms.