C and Si impurity atoms on a GaAs(001) surface

AB initio pseudopotential calculations of C and Si impurity atoms on on As- terminated GaAs(001) surface have been performed. First, the C atom is roun d to stay near a midpoint between the As atoms on the surface and the Si at om a cation site. Secondly, we find that the C atom is more strongly bound to the GaAs surface than the Si atom. Geometrically as well as energeticall y, the C atom is more difficult to remove from the GaAs surface. The presen t results agree with an experimental fact that in contrast with the case of Si, eliminating the C impurity through the surface requires thermal etchin g at such a high temperature of 750 degreesC.