We present an extensive first-principles study of the pressure dependence of the formation enthalpies of all the know vacancy and self-interstitial configurations in silicon, in each charge state from −2 through +2. The neutral vacancy is found to have a formation volume that varies markedly with pressure, leading to a remarkably large negative value (−0.68 atomic volumes) for the zero-pressure formation volume of a Frenkel pair (V + I). The interaction of volume and charge was examined, leading to pressure-Fermi level stability diagrams of the defects. Finally, we quantify the anisotropic nature of the lattice relaxation around the neutral defects.

Low-temperature crystal growth techniques can deposit silicon films with impurity concentration orders of magnitude above their bulk solubility limits. First-principles calculations were performed of the energies (relative to the bulk) of single substitutional carbon, germanium, boron, and arsenic atoms at several positions within a thin (100) slab of silicon reconstructed as c(4×2). The energies of these impurities were found to be at least 0.2eV lower than in the bulk, corresponding to surface enrichments of 1000 or greater at a temperature of 500°C. General trends can be explained using the concepts of hybridization energy and lone pairs. The large surface reconstruction strain gives rise to this complex potential energy surface, and favors long-ranged order among impurities near the surface. As a result, we expect a complex dependence of trapped impurity concentrations on growth rate and temperature, with a high sensitivity to these parameters when the exchange rate of the impurity with neigboring sites is comparable to the monolayer deposition rate.