Specific features of band structure in large-sized Si2-xCx (1.04 ≤ x < 1.10) nanocrystallites

The band structure of large-sized (20-35 nm) nanocrystallites (NCs) of Si2-xCx (1.04 < x < 1.10) has been investigated using different band energy approaches and a modified Car-Parinello molecular dynamics structure optimization of the NC interfaces. The excess of carbon favours the appearance of a thin prevailingly carbon-contained layer (with thickness of about 1 nm) covering the crystallites. As a consequence we observe a substantial structural reconstruction of near-the-interface SiC crystalline layers. Optical absorption spectra of the investigated sheets were performed. The numerical modelling shows that these NCs can be considered as SiC reconstructed crystalline films with a thickness of about 2 nm covering the SiC crystallites. The observed data are considered within different one-electron band structure methods. It was shown that the carbon sheet plays a key role in the modified band structure. The independent manifestation of the important role played by the reconstructed confined layers is due to the experimentally discovered excitonic-like resonances. Low-temperature absorption measurements confirm the existence of sharp-like absorption resonances originating from the reconstructed layers.