First-principles evaluations of dielectric constants for ultra-thin semiconducting films

We have explored dielectric properties of ultra-thin 2H(wurtzite)-SiC(0 0 0 1) and 3C(zinc-blende)-SiC(1 1 1) films using the density functional first-principles calculations. When the thickness of the film increases, the optical dielectric constants evaluated at the center of the films approach values near to their experimental bulk dielectric constants at a thickness of only five bi-layers: 7.3 and 6.9 for 2H- and 3C-SiC, respectively. Furthermore, we have revealed that the optical dielectric constant for the SiC film is reduced distinctly at the first few bi-layers at the ( 1 1 1 ¯ ) or ( 0 0 0 1 ¯ ) surface, but not for (1 1 1) or (0 0 0 1). Such a polarity dependence is due to the difference in work function between the surfaces.