ASNOM mapping of SiC epilayer doping profile and of surface phonon polariton waveguiding

Apertureless scanning near-field optical microscopy mapping of a slightly doped 4H-SiC epitaxial layer grown on a heavily doped 4H-SiC substrate was performed in a cleaved edge geometry. Surface phonon polariton waves excited by an external coherent light were observed on a sample surface that contains such an epilayer-defined strip near its edge. The light frequency was tuned close to the lattice resonance. Due to a low doping level in an epilayer, its electromagnetic response is determined mainly by the SiC lattice resonance. The rest of the sample surface corresponds to a substrate whose electromagnetic response is determined mainly by the free carriers so that phonon polariton phenomena get suppressed. Such an epilayer-defined strip (vanishing at 895 cm(-1) frequency) becomes more pronounced at 920 cm(-1) and, finally, the excited state gets completely confined within such a strip (938 cm(-1)) due to the differences in the electromagnetic properties of doped and undoped SiC.