Reconstruction of group-IV semiconductor surfaces : origin, energetics and consequences

This work presents extensive first-principles studies of the energetics and the reconstructions of the clean low-index (111), (110), (100) and high-index (113) surfaces of the three group- IV semiconductors diamond, silicon, and germanium. The calculations have been performed within density-functional-theory (DFT) using the local-density-approximation (LDA) and the repeated-slab approximation. Different reconstructions including the largest ones observed experimentally such as Si(111)7?7 and Si(110)16?2 have been investigated. The atomic geometries have been optimized in order to find the minimum of the total energy. For these atomic structures the electronic band structures have also been calculated. For the most interesting surface reconstructions scanning-tunneling-microscopy (STM) images have been simulated in order to make a comparison with experimentally observed surface images. Presented results highlight the physical origins of the reconstruction behavior in dependence on surface orientation and size of the group-IV atoms. Clear evidence for an opposite reconstruction behavior of diamond and Si or Ge surfaces is shown. Adatoms, interstitials, and symmetry-breaking distortions are unlikely for diamond as a consequence of the short interatomic distances and strong bonds. However, such elements of the surface reconstruction occur on Si and Ge surfaces. The complicated interplay of bonding, resulting atomic geometry, and accompanying electronic structure has been derived and used to discuss driving forces for the surface reconstruction. A rather complete data base of absolute surface energies of group-IV semiconductors is presented. For all the elements, there is a strong tendency to reduce substantially surface energies by taking into account surface reconstructions. The absolute surface energies have been used to discuss the equilibrium shapes of diamond, silicon and germanium.