The chemical structure and site location of sulfur atoms on n-GaAs (100) surface treated by bombardment of S+ ions over their energy range from 10 to 100 eV have been studied by X-ray photoelectron spectroscopy and low energy electron diffraction. The formation of Ga-S and As-S species on the S+ ion bombarded n-GaAs surface is observed. An apparent donor doping effect is observed for the n-GaAs by the 100 eV S+ ion bombardment. It is found that the S+ ions with higher energy are more effective in the formation of Ga-S species, which assists the n-GaAs (100) surface in reconstruction into an ordered (1 x 1) structure upon subsequent annealing. The treatment is further extended to repair Ar+ ion damaged n-GaAs (100) surface. It is found that after a n-GaAs (100) sample is damaged by 150 eV Ar+ ion bombardment, and followed by 50 eV S+ ion treatment and subsequent annealing process,finally an (1 x 1) ordering GaAs (100) surface with low surface states is obtained. (C) 2008 Elsevier B. V. All rights reserved.