Diameter-dependent modulation and polarization anisotropy in Raman scattering from individual nanowires

Polarized light scattering experiments from individual apolar (Si) and polar (SiC) semiconductor nanowires of uniform diameter reveal a large polarization anisotropy. The origin of this anisotropy is traced to the dielectric constant mismatch between a nanowire and its surroundings (air). For polar nanowires, a quantitative account of the anisotropy is obtained only after considering crystal structure effects, that is, the anisotropy of the Raman tensor. In the case of Si nanowires, where a broader size distribution could be probed in the experiments, the experimental polarization anisotropy exhibits strong oscillations as a function of nanowire diameter. These oscillations are interpreted as "shape resonances" and found in good agreement with theoretical calculations. Experiments on individual 3C-SiC nanowires further illustrate fundamental and practical implications of these polarization phenomena.