First-principles study of the effects of polytype and size on energy gaps in SiC nanoclusters

We have studied the band-gap variation and stability energy in silicon carbide (SiC) nanoclusters of different polytypes using density functional theory (DFT) based on a gradient-corrected approximation. We have obtained a series of spherical SiC nanoclusters with dimensions up to 2 nm from bulk 2H, 3C, and 4H polytype crystals. All clusters with diameters smaller than 1 nm exhibit similar energy-gap-size variations, while energy gaps for clusters larger than 1 nm show a distinct size dependence with different polytypes and approach their bulk gaps with an increase in cluster size. In contrast to their bulk behavior, the binding energy difference between polytypes of clusters within the diameter range 0.5 nm-2 nm is found to be negligible, suggesting that the problems associated with the synthesis of polytypes of SiC in bulk may disappear for small clusters. The convergence of the energy gap and binding energy with different polytypes at small size clusters and the transition between the clusters to bulk behavior in SiC systems could be exploited for making future nano-optoelectronics devices.