Photoluminescence of GaN Nanowires of Different Crystallographic Orientations

Abstract

We utilized time-integrated and time-resolved photoluminescence of a-axis and c-axis gallium nitride nanowires to elucidate the origin of the blue-shifted ultraviolet photoluminescence in a-axis GaN nanowires relative to c-axis GaN nanowires. We attribute this blue-shifted ultraviolet photoluminescence to emission from surface trap states as opposed to previously proposed causes such as strain effects or built-in polarization. These results demonstrate the importance of accounting for surface effects when considering ultraviolet optoelectronic devices based on GaN nanowires.

Optical properties of functionalized GaN nanowires

“…The presence of high-energy tails in GaN NWs has been proposed to be associated with the native surface-oxide induced states. 23 The elimination of the highenergy tail together with the narrowing of the D o X emission clearly indicates a quality improvement of the GaN NWs, and hence supports our previous claim of the effective surface-passivation role of MPTMS. Conversely, the origin of the $3.43 eV (I d ) emission is not conclusive, since the emissions at 3.41-3.43 eV can be associated with extended defects, which are most likely stacking faults.…”

Direct comparison of catalyst-free and catalyst-induced GaN nanowires

“…In both approaches, M-planes constitute the NW sidewalls. The same facet orientation has been reported before for catalyst-free GaN NWs [17] but it was not clear, a priori, that catalyst-induced NWs should grow in the same shape [22][23][24]. Although the crystal structure of the different types of NWs is the same, their polarity could still be different.…”

Anisotropic optical response of GaN and AlN nanowires

“…[14] Besides, the refinement of the growth techniques leads the reduction of the NW size until quantum confinement effects emerge. [15,17,16] In this context, theory and numerical simulations play a crucial role in the explanation of NWs properties and a better understanding of the observed phenomena. Theoretical studies are also required to contribute in the interpretation of the experiments or to investigate the trends in the optical properties, helping in the design of a more efficient fabrication of devices.…”