Optical phonons in polar semiconductor nanowires

We show that the long-range dipolar interactions in a crystalline cubic polar semiconducting nanowire give rise to an important splitting of the Raman-active transverse optic (TO) and longitudinal optic (LO) phonons at the center of the Brillouin zone. The dipole sums that determine the two LO and two TO phonon frequencies in the nanowire are sensitive to the aspect ratio (L/D), where L and D are the length and diameter, respectively. In the limit L/D -->infinity, we predict the phonon frequencies for several important polar semiconducting nanowires. Our calculated results are also compared with Raman scattering data obtained on crystalline GaP and GaAs semiconducting wires.