White Ligth Emission from Porous Silicon/ZnO Nanocones Under UV Excitation

O. MARÍN; G. GRINBLAT; A. M. GENNARO; M. TIRADO; R. R. KOROPECKI; D. COMEDI

Simposio; International Symposium on Metastable, Amorphous and Nanostructured Materials; 2015

ZnO nanocones were grown on porous silicon (PS) by vapor transport (VT) at different temperatures and O2 flow rates without metal nanocatalysts. The samples were studied using scanning electron microscopy (SEM), photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies. In particular, to obtain ZnO NWs using the VT technique the use of Au nanoclusters, which act as nucleation centers on the growth substrates, is often necessary. In order to avoid the use of gold, several research groups have tried various types of substrates, finding promising results with PS. In addition to the possibility of avoiding the use of Au nanoclusters, the deposition of ZnO on PS is an attractive way of integrating the ZnO with the silicon-based electronics technology.The ZnO/PS samples are found to emit white light under UV excitation. The PL spectra were found to include five main components centered at 1.84, 2.06, 2.30, 2.48 and 3.31 eV. The components at 2.48 and 2.06 eV were related to oxygen vacancies in ZnO, that at 2.3 eV to Zn vacancies and the one at 1.84 eV to the PS substrate. The relatively low excitonic emission at 3.31 eV and the observed rough ZnO nanocone surfaces suggest the presence of nonradiative recombination channels associated with surface trap states, which are known to cause strong carrier depletion in ZnO nanostructures. The absence from the EPR spectra of the g = 1.96 resonance, which is often attributed to free electrons in the conduction band, supports the strong carrier depletion hypothesis. Finally, an EPR line at g = 2.006, attributed to a Zn divacancy interacting with a hole in ZnO, is observed.In summary, the conditions for ZnO cone-like NW growth on PS without the need of metallic nanocatalysts are found.The distinct components of the PL and orresponding EPR spectra are identified and their origin elucidated [1].[1] Oscar Marin, Gustavo Grinblat, Ana María Gennaro, Mónica Tirado, Roberto R. Koropecki, and David Comedi, Superlatt. Micros. 79, (2015), 29-37.