White Light Emission from Porous Silicon/ZnO Nanocones under UV Excitation

MARIN, OSCAR; GRINBLAT, GUSTAVO; GENNARO, ANA MARÍA; TIRADO, MONICA; KOROPECKI, ROBERTO; COMEDI, DAVID

Paris

Simposio; 22th International Symposium on Metastable, Amorphous and Nanostructured Materials: ISMANAM 2015; 2015

INP Grenoble, FRANCE

In general, to obtain ZnO nanowires by vapor transport (VT) technique, the use of metallic nanocatalysts on the substrate is often necessary. In order to circumvent this need, several research groups have tried different substrates, finding promising results for porous silicon (PS). The deposition of nano-ZnO on PS not only eliminates the necessity of using metallic nanocatalysts, but is also an attractive way of integrating the ZnO with the silicon-based optoelectronics nanotechnology. In this work, ZnO nanocones were grown on bare PS by VT method at different temperatures and O2 flow rates. The samples were studied through scanning electron microscopy (SEM), photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies. The ZnO/PS samples were found to emit white light under UV excitation. The PL spectra, shown in the Figure, include essentially five components, which are centered at 674, 600, 540, 498 and 374 nm. The peaks at 498 and 600 nm were related to oxygen vacancies in ZnO, that at 540 nm to Zn vacancies, and the one at 674 nm to the PS substrate. The relatively low excitonic emission intensity at 374 nm and the observed rough ZnO nanocone walls suggest the presence of nonradiative recombination channels associated with surface trap states. In consistency with this, the g = 1.96 resonance, typically attributed to free electrons in the conduction band, was absent from the EPR spectra, revealing strong carrier depletion caused by the charge traps. In summary, the conditions for ZnO cone-like nanowire growth on PS without the need of metallic nanocatalysts are presented. The distinct components of the PL and EPR spectra are identified and their origin elucidated [1].[1] Oscar Marin, Gustavo Grinblat, Ana María Gennaro, Mónica Tirado, Roberto R. Koropecki, David Comedi, Superlatt. Micros. 79, (2015), 29-37.