Energy Landscapes and Tunable Electronic Properties of Polar and Non-Polar SiC Nanofilms

The energy landscapes and electronic properties of non-polar and polar nanofilms of silicon carbide are studied using periodic hybrid density functional calculations. Relative energies and electronic properties are reported as a function of film thickness for a set of structures derived from those of wurtzite, zinc blende and graphite. The energy landscape of the films is complex with pronounced nano-polymorphism. Across polar films different mechanisms in different cases remove or reduce the dipole moment, including charge transfer and phase transitions to the graphitic-like structures which are stable for the thinnest films. Graphitic structures are lowest in energy for the thinnest films. For ten layers non-polar films - zinc blende (110) and wurtzite (101bar0 ) - with tetrahedrally-coordinated Si and C in Si3C3 rings in chair conformations - are lowest in energy, followed, ∼0.1 eV per formula unit higher in energy, by a body-centred tetragonal structure containing Si3C3 rings in boat conformations. In the planar graphene structure the energy of the anti-site defect CSi-SiC (∼0.3 eV)) is more than an order of magnitude lower than in the bulk, suggesting a much higher degree of disorder in such films. One staggered graphitic-like structure with ABC stacking, a local minimum in the energy landscape, is of particular interest, since it lies in a regime of uncompensated polarity and possesses a direct band gap that decreases linearly with film thickness., from ∼2 eV (3 layers) to zero (6 layers).