Adatom-adatom and adatom-surface interactions: Islands and chains of Cl on GaAs(110)

Calculations are presented that quantify the adatom-surface and adatom-adatom interactions for Cl adsorption on GaAs(110). Expanding on a previous study of uniform Cl adatom islands, the present work investigates the surface relaxation energy in response to uniform Cl coverage. Compared to the bare (110) surface relaxation, a Cl adatom adsorbed near the surface Ga atom (the A site) causes relaxation back toward the zincblende atomic positions, which lowers the cell energy by about 1 eV, while a Cl adatom adsorbed on top of a surface As (the B site) has very little effect on the surface geometry. Additionally, the stability of linear chains of adatoms, similar to chains seen experimentally, and their effect on the surface GaAs geometry is investigated. We find an attractive Cl-Cl pair interaction, which is approximately 1.25 eV per Cl(A)-Cl(B) pair in the linear chain geometry.