Photoinduced formation of dimers at a liquid/(001)GaAs interface.

Abstract

Using reflectance anisotropy spectroscopy (RAS), we show that surface dimers, which so far have only been observed on surfaces in an ultrahigh-vacuum environment, can exist at semiconductor/liquid interfaces. We consider here As and Ga dimers at the interface between GaAs and sodium sulfide solutions. These dimers appear as the result of photochemical reactions and are identified by their RA signatures. Their observation requires (i) dark treatment of the surface in the solution (1 h) in order to form an overlayer which isolates the surface from the solution, (ii) subsequent above band-gap light excitation which induces photoassisted breaking of respectively As-related and Ga-related chemical bonds at the interface between the semiconductor and the protective layer. Analysis of the growth under light excitation of the dimer signal gives evidence that gallium dimers are created at the expense of arsenic dimers by breaking of chemical bonds between gallium and overlying arsenic atoms.