Polarization- and temperature-dependent photoluminescence (PL) measurements were performed on individual GaN nanowires. These were grown by catalyst-free molecular beam epitaxy on Si(111) substrates, ultrasonically removed, and subsequently dispersed on sapphire substrates. The wires were typically 5–10μm in length, c-axis oriented, and 30–100nm in diameter. Single wires produced sufficient emission intensity to enable high signal-to-noise PL data. Polarized PL spectra differed for the σ and π polarization cases, illustrating the polarization anisotropy of the exciton emission associated with high-quality wurtzite GaN. This anisotropy in PL emission persisted even up to room temperature (4–296K). Additionally, the nanowire PL varied with excitation intensity and with (325nm) pump exposure time.
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Schlager et al. (2006) studied this question.