Second-harmonic generation and linear electro-optical coefficients of SiC polytypes and nanotubes

The second-order nonlinear optical susceptibility [chi((2))(abc)] and linear electro-optical coefficient (r(abc)) of a large number of single-walled zigzag, armchair, and chiral silicon carbide (SiC) nanotubes (SiC NTs), as well as bulk SiC polytypes (2H-, 4H-, 6H-, and 3C-SiC) and single graphitic SiC sheet have been calculated from the first principles. The calculations are based on the density-functional theory in the local-density approximation where the highly accurate full-potential projector augmented-wave method was used. Both the zigzag and chiral SiC NTs are found to exhibit large second-order nonlinear optical behaviors with the chi((2))(abc) and r(abc) coefficients being up to ten times larger than that of bulk SiC polytypes and also being up to thirteen times larger than the counterparts of the corresponding BN NTs, indicating that SiC NTs are promising materials for nonlinear optical and optoelectric applications. The features in the spectra of chi((2))(abc)(-2 omega,omega,omega) of the SiC NTs are discussed in terms of the single- and two-photon resonances and also related to the features in the linear dielectric function epsilon(omega).