ELECTRONIC AND STRUCTURAL-PROPERTIES OF THE AS VACANCY ON THE (110)SURFACE OF GAAS

The isolated As vacancy on the GaAs (110) surface is investigated usin g ab initio pseudopotentials. The relaxed atomic structure reveals an inward relaxation of the neighboring surface Ga atoms regardless of th e vacancy charge state. The stable charge state is determined to be (1) in p-type material from the formation energies. Three vacancy state s, two located within the band gap, are identified. The character of t he vacancy wavefunctions is described in detail and discussed in conne ction with the charge-state dependent relaxation. Despite the inward r elaxation of surface Ga neighbors, the theoretical scanning tunneling microscopy topography shows enhanced tunneling into these sites, which is in agreement with existing experiments. The origin of this apparen t contradiction is attributed to the nature of the wavefunction for on e of the unoccupied vacancy states. (C) 1998 Elsevier Science B.V. All rights reserved.