Franck Guell, Université de Barcelona

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Franck Guell, Université de Barcelona sera présent du 21 au 24 juin au laboratoire, invité par Europhotonics.
Il fera un exposé le 22 Juin, 11h, Salle Pierre Cotton, sur les "ZnO nanowires for photonics applications".

Titre : ZnO nanowires for photonic applications

Résumé : The quest for novel semiconductor materials with improved optoelectronic performance has
triggered intense research activities to exploit the great diversity of effects offered by low
dimensional systems. In this work, we investigate the influence of the ZnO nanowires (NWs)
growth parameters on their optical properties. ZnO NWs have been grown by the vapor-transport
method using Au as catalyst over quartz and SiO2/Si substrates with lengths and diameters ranging
from 0.2 to 2 μm and 40 to 200 nm, respectively. Room-temperature absorption spectra show a
well-defined exciton peak in the ultraviolet. Photoluminescence measurements show two emission
bands at room-temperature, the exciton emission peak in the ultraviolet, and a very broad emission
band in the visible range from 420 to 800 nm, which exhibits three distinct peak-like contributions
in the Green, Yellow and Red at around 520, 590 and 720 nm (2.38, 2.10 and 1.72 eV), respectively.
The intensities of these emission bands in the visible change as a function of the ZnO NW growth
parameters, which correspond to different defect-related recombination processes, and were clearly
correlated with the quantity and type of defects present in the material. We show that the intensity
of the broad emission band in the visible increases relative to that of the exciton emission as the
ZnO NWs diameter decreases. This result is of great relevance regarding future devices based on
these nanostructures since a detailed understanding of the origin of the shell states (surface states) is
mandatory for a precise device design. The highly spatially localized nature of the shell states is a
fundamental aspect to control in applications where charge transfer processes play a key role, e.g.,
detectors such as gas sensors.