Optical properties of GaN and GaN/AlN nanowires: the effect of doping and structural defects

International audienceWe report on the optical properties of different classes of nitride-based nanowire systems grown by plasma assisted molecular beam epitaxy (PA-MBE) on Si(111) substrates at temperature T=780°C. Micro-photoluminescence (micro-PL) spectroscopy has been performed on homogeneous GaN nanowires with different doping type and distribution, as well as on nanowires containing AlN/GaN heterostructures. The Micro-PL spectrum of the individual nanowire has been correlated to the transmission electron microscopy (TEM) image of the same nano-object, in order to investigate the influence of structural defects on the radiative emission lines. Doping is found to enhance the sub-bandgap radiative paths such as the donoracceptor pair (DAP) related lines found at energies below E=3.26 eV. Other sub-bandgap emission lines, particularly those centred around 3.41-3.42 eV, are related to surface states and are the dominant emission in systems of coalesced nanowires. Finally, the presence of extended line defects has been correlated to a strong reduction of the PL radiative efficiency