Molecular dynamics simulations of GaAs sputtering under low-energy argon ion bombardment

Abstract

Results from molecular dynamics (MD) simulations of low-energy (50–200eV) Ar+ ion bombardment on (110) GaAs surfaces are reported. A new analytical bond-order potential, originally developed for molecular beam epitaxy studies, is used and tested in the context of etching to investigate the nature and effects of physical sputtering on GaAs compounds. It is found that a thermal desorption model, which accounts for long time scale phenomena between MD simulated impacts, is necessary to achieve steady state sputtering. An initial rapid etch of both atomic species is observed up to 4×1016ions∕cm2 fluence with preferential sputtering of Ga atoms. At high fluences, simulations show the formation of an As-rich layer on the top surface, a subsurface enrichment of Ga, and a return to stoichiometry deeper in the solid. More than 97% of sputtered or desorbed species appear to be Ga or As atoms; sputtering of GaAs molecules is negligible. All these observations are in agreement with published experimental results. Finally, a significant fraction of the atoms leave the surface with more than 10% of the incident ion energy, which could alter passivation layers on sidewalls during etching.