Effect of Al and B Substitution on the Electronic Structure and Thermoelectric Properties of Silicon Carbide Nanoparticles

Partial substitution of Al for Si and B for C has enabled us to synthesize, using spark plasma techniques, doped nanoensembles of SiC that have Seebeck coefficients of 330 microV/K at 900 K. In attempting to attain an understanding of the Seebeck coefficient, we have extended earlier density functional calculations on stacked graphene sheets to 3C SiC nanoclusters with substitutions of Al in Si sites and B in C sites. The calculations show that both types of doping lead to hole states resulting in pronounced decreases in the HOMO-LUMO gap. As a consequence, some of the Al hole states are located near the Fermi level analogous to the situation encountered in stacked graphene sheets. Each of the large number of discrete electronic states introduced into SiC due to doping are associated with a particular Al and B configuration. The implications of these studies are discussed.