LOCALIZED EXCITONS AND BREAKING OF CHEMICAL-BONDS AT III-V (110)SURFACES

Electron-hole excitations in the surface bands of GaAs(110) are analyz ed using constrained density-functional theory calculations. The resul ts reveal formation of autolocalized Frenkel-type excitons which merge in microscopic ''droplets'' due to attraction initiated by exciton-in duced unrelaxation of the surface. A substantial weakening of the bond ing of the topmost Ga atom is found in such an ''exciton droplet.'' Th is finding suggests a microscopic mechanism of laser-induced emission of the neutral Ga atoms from GaAs and GaP (110) surfaces.