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

Abstract

AbstractWe 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 donor‐acceptor 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 (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)