Polarized photoluminescence from single GaN nanorods: effects of optical confinement.

By measuring linearly polarized photoluminescence (PL) from single, isolated gallium nitride (GaN) nanorods with the rod diameters in the subwavelength regime (30-90 nm), we present clear evidence for size dependence of polarization anisotropy. The maximum polarization ratio at room temperature (approximately 0.9 with emission and excitation light polarized parallel to the long axis of nanorod) occurs at the rod diameter of approximately 40 nm. The experimental data are compared with the recent theoretical model proposed for thick semiconductor nanowires. It is concluded that the optical confinement effects in this size regime play an important role in the observed giant polarization anisotropy. Furthermore, we have performed a temperature-dependent study of polarized PL to show the importance of internal emission anisotropy at low temperatures.