First Principles Analysis of Ultra-Thin Silicon Films with Dimer Structures

Abstract

ABSTRACTThe impact of dimer formations at the surfaces of the internal atoms of silicon (Si) thin film was evaluated by examining silicon-on-insulator (SOI) and plate models. In the SOI models, a dimer formation was modeled at one side of the Si thin film. The plate models had two dimers at each surface, which had been considered as a Si bulk model in previous studies. First principles calculation showed that the deviations of Si atoms from the first to fourth layers of the SOI models did not differ remarkably from those of the plate models. The internal atoms deeper than the fifth layer showed near-zero deviation in some of the SOI models and had evident non-zero deviation in the other SOI models. All the SOI and plate models showed lower Si atom self-energy than in the Si bulk. The layer-to-layer distance of internal atoms in the films became longer than that of atoms in Si bulk. These results indicated that (i) Si films with dimer surfaces are relaxed by deviations in the whole film, and (ii) even the thick plate model with 32 layers dose not reveal the nature of Si bulk.