Quasiparticle calculations for point defects on semiconductor surfaces

We discuss the implementation of quasiparticle calculations for point defects on semiconductor surfaces and, as a specific example, present an ab initio study of the electronic structure of the As vacancy in the +1 charge state on the GaAs(110) surface. The structural properties are calculated with the plane-wave pseudopotential method, and the quasiparticle energies are obtained from Hedin's GW approximation. Our calculations show that the 1a" vacancy state in the band gap is shifted from 0.06 to 0.65 eV above the valence-band maximum after the self-energy correction to the Kohn-Sham eigenvalues. The GW result is in close agreement with a recent surface photovoltage imaging measurement.