The electronic nature of the Cl adatom at GaAs(110) surfaces due to Cl-2 dissociative adsorption and CCl4 photodecomposition

Clean, well defined GaAs(110) surfaces at room temperature, were exposed to carbon tetrachloride vapor. Only when illuminated during the exposure (wit h 400 mW/cm(2) of 532 nm light) could adsorbed species be observed with sca nning tunneling microscopy (STM) on flat terraces. The features in the STM Images were compared to those due to exposure to Cl-2 gas in the dark, and the CCl4 decomposition products were shown to be identical to chlorine adat oms which are bound to surface Ga atoms (A-type). Since the CI adatoms appe ar dark at low positive sample bias, and bright at high bias. and from the absence of localized contrast in atomically-resolved surface photovoltage i mages, we deduce that the Cl adatom interacts with the Ga-induced C-3 surfa ce resonance, that it (or the Cl-Ga complex) is not charged, and it does no t give rise to any surface state in the GaAs band gap that could pin the Fe rmi level. (C) 2001 Published by Elsevier Science B.V.