Vibrational and optical properties of GaN nanowires synthesized by Ni-assisted catalyticgrowth

Abstract

GaN nanowires synthesized by Ni-assisted catalytic vapour–liquid–solid growth at differenttemperatures were studied by scanning electron microscopy (SEM), transmission electronmicroscopy (TEM), micro-Raman spectroscopy, and photoluminescence spectroscopy. Thenanowires exhibit low defect density. The growth direction of the nanowires is []. For nanowires grown at 800 °C, Raman scattering is consistent with the presence of point defects and subsequently yellowluminescence dominating their photoluminescence properties. A low free carrier concentration of lessthan 1017 cm−3 is present in the nanowires. In contrast, for nanowires grown at900 °C,strong phonon–plasmon coupling was evidenced, suggesting a free carrier concentration in excess of themid-1018 cm−3 region. Photoluminescence spectra show strong near-band-edge luminescence andnegligible yellow luminescence. A Ni-related luminescence peak was observed at3.436 eV at 80 K. Raman and photoluminescence results obtained from individualnanowires demonstrate that the nanowire crystalline quality improves not only withincreasing growth temperature, but also along the nanowire growth direction.