GaAs(111) A and B surfaces in hydrazine sulfide solutions: Extreme polarity dependence of surface adsorption processes

Chemical bonds formed by hydrazine-sulfide treatment of GaAs(111) were studied by synchrotron photoemission spectroscopy. At the B surface, the top arsenic atoms are replaced by nitrogen atoms, while GaAs(111)A is covered by sulfur, also bonded to underlying gallium, despite the sulfide molar concentration being 10(3) times smaller than that of the hydrazine. This extreme dependence on surface polarity is explained by competitive adsorption processes of HS(-) and OH(-) anions and of hydrazine molecules, on Ga-adsorption sites, which have distinct configurations on the A and B surfaces.