Calculations based on Density Functional Theory are carried out to study interstitial generation close to the Si(100) surface with further consideration of effects related to the presence of substitutional Ge atoms on the surface. Defect structures, vacancy and Si interstitial, and associated energies are calculated We observe that germanium atoms tend to increase the stability of created defects, promote the generation of interstitials through drastic structural changes and blocks the climb of Si interstitials towards the surface (C) 2009 Elsevier B V All rights reserved