Ultraviolet photon-induced interaction of Cl2 with GaAs(110): Dissociation by means of charge transfer

Abstract

We have studied the UV photon-induced interaction of molecular chlorine with a well-defined GaAs(110) surface under ultrahigh vacuum (UHV) conditions. Without illumination, chlorine was found to adsorb both molecularly and dissociatively at 85 K. Illumination of a molecular chlorine-covered surface at 85 K with 193, 248, and 351 nm radiation led to the desorption of Cl atoms and to the formation of AsCl3. We suggest that the surface reaction, that is responsible for the AsCl3 formation, is initiated by molecular chlorine dissociation. While direct absorption by an individual Cl2 molecule may be the cause for the chlorine dissociation at 351 nm, we propose an intermolecular charge-transfer absorption within the condensed Cl2 overlayer for the cases of 248 and 193 nm. Support for this mechanism comes from the dependence of time-of-flight distributions and AsCl3 coverages on the molecular chlorine surface coverage, on the laser wavelengths, and on the use of different substrates.