Theory of adsorption of Cl-2 molecules on GaAs(001) surfaces

The energetics of the dissociative adsorption of Cl-2 molecules on reconstructed GaAs(001) surfaces is theoretically investigated, employing the first-principles pseudopotential density-functional approach within the generalized gradient approximation. The Cl-2 molecule is found to dissociate with no potential barrier over the Ga dimer on the Ga-rich GaAs(001)-(4 x 2) surface and the Ga dimer is also simultaneously broken upon the Cl-2 dissociative adsorption, resulting in formation of GaCl with two backbonds to the As layer below, On the As-rich (2 x 4) surface, the dissociation of the Cl-2 molecule over the As dimer is an activated process and does not break the As dimer, whereas the Cl-2 dissociation over the As dimer vacancy is a barrierless and exothermic reaction, The geometry and stability of the chlorinated GaAs(001) surface are also discussed. The obtained results are consistent with recent experiments such as temperature-programmed desorption measurements.