RELAXATION AND BOND BREAKING AT DEFECT SITES ON GAP (110) SURFACES BY PHONON-ASSISTED MULTIHOLE LOCALIZATION

Motivated by recent experimental observation of defect-initiated emission of Ga atoms induced by valence-electron excitation by intense laser pulses, showing superlinear dependence on fluence, we have investigated the consequence of phonon-assisted multihole localization at defect sites on the GaP (110) surface. We perform calculations of the effects on cascade excitation of the Ga adatom and show that the second excitation of the relaxed Ga adatom after ionization or excitation leads to bond breaking. We perform calculations also on the effect of excitation of the Ga antisite defect, a double acceptor, located in the second topmost layer, and find that catastrophic lattice relaxation is induced after excitation. These results are interpreted in terms of bond weakening as a result of multihole localization on the atom on the surface. The results demonstrate that the lack of symmetry for surface atoms leads to a variety of processes which may play a role in the bond weakening of surface atoms and hence particle emission.