Nanocomposites and nanomaterials
Electrical and luminescence properties of Freestanding Porous SiC
I.V. Gavrilchenko1, Y.S. Milovanov1, V.A. Skryshevsky1, S.V. Alekseev2
Taras Shevchenko National University of Kyiv, 01601 Volodymyrska str. 64, Kyiv, Ukraine.
E-mail: ir@univ.kiev.ua

Semiconductor based sensors such as those made from Sn02 or porous Si, are well known. Recent developments in silicon carbide material growth technology make it possible to construct sensors using porous SiC (PSiC). Previously, it was obtained that PSiC shows good sensing properties toward Н2O, NH3, H2 [1,2].The operational principle of chemical sensors on PSiC is based on the change of PSiC electrical conductivity at the adsorption/desorption of molecules on its developed surface.
Freestanding PSiC was produced by electrochemical etching of 3C-SiC polycrystalline wafers with resistivity ρ=1.5 mΩcm. The sample was etched in a HF:H2O = 1:3 solution at current density 50 mAcm-2 for 360 min. After the end of anodizing process the PSiC formed film was separated from the base by additional etching in HF:EtOH (1:1) solution at current density 3 Acm-2 for 15 min. The free standing porous layer was washed with de-ionized water and dried in ambient air.
The morphology, photoluminescence spectra and impedance spectroscopy of freestanding PSiC were analyzed. The impedance spectra were measured at room temperature using Z-2000 impedance meter.
It was found from SEM images that PSiC has homogenous nanostructured surface morphology, the thickness of the porous layer is about 120 μm, the average pore diameter is about 10 nm.Samples show a visible photoluminescence with a several maximum at 1.98, 2.48, 3,31 eV . The full width at half maximum (FWHM) of the spectrum is about 0,306 eV, 1,051 eV, 0,368 eV, respectively.
To analyze the influence of ethanol desorption on the charge transfer of PSiC the impedance spectroscopy was applied. It was found that the results can be interpreted using two RCPE equivalent circuits connected in series.  After exposure to ethanol solution the value of Rv decreases (Rvair/Rveth=2.1), and Rb increases (Rbair/Rbeth=0.45).

1. Yu. Zakharko at al. Influence of the interfacial chemical environment on the luminescence of 3C-SiC nanoparticles // J. Appl. Phys.-2010.-107.-P. 013503.
2. E.J. Connolly, B. Timmer, H.T.M. Pham, at al., A porous SiC ammonia sensor // Sensors and Actuators B.-2005.-109.-P.45-46.