Dimer vacancies and dimer-vacancy complexes on the Si(100) surface

Ab initio total-energy calculations are performed using a conjugate-gradients minimization technique to calculate the properties of various dimer vacancies and dimer-vacancy complexes on the Si(100) surface. A dimer vacancy is found to be a much more probable intrinsic defect for this surface than the recently proposed dimer interstitial. Two mechanisms are identified that contribute to the low formation energy and stability of dimer vacancies on the surface: (i) the need to eliminate dangling bonds in the second layer and (ii) the need for atoms to readjust in order to relax the strain. The results of the calculations provide a good quantitative explanation of the major features of scanning-tunnel-microscopy images obtained from the Si(100) surface. These include the abundance of dimer vacancies, the tendency of dimer vacancies to cluster, and the details of the nonthermal population distribution of distinctive vacancy complexes.