Probing crystallographic orientation of a single GaN nanotube using polarized Raman imaging

We report the study of crystallographic orientation of a highly anisotropic square-shaped single wurtzite GaN nanotube (NT) probed by polarized Raman imaging. The polarization-dependent Raman intensities are collected in two mutually orthogonal directions with respect to the NT long axis. Variation in intensities of symmetry allowed A₁(LO) mode of GaN with two different polarization directions reveals the possible crystalline orientations in the NT. The polarized Raman spectral imaging illustrates the fact of inhomogeneous crystalline orientations along the edges of the NT facets owing to its finite wall thickness. The deviation of polarization selection rule for GaN is attributed to the geometrical anisotropy of the NT. Electron microscopic structural data confirms the spectral imaging analyses.