Influence of fluorine doping on the microstructure, optical and electrical properties of SnO2 nanoparticles

Tin dioxide (SnO2) is one of the most promising functional semiconductor materials; it has stimulated considerable research interest for its wide applications such as optoelectronic devices and solar cells technology. Undoped and fluorine doped tin oxide aerogel nanoparticles have been successfully synthesized by sol-gel route and dryed under supercritical conditions of ethanol. The effect of fluorine concentration on SnO2 nanoparticles properties was systematically investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, UV-Vis-IR spectroscopy and impedance spectroscopy. Characterization data showed that both pure SnO2 and FTO aerogels have a polycrystalline tetragonal rutile structure with a highly (110) plane preferred orientation. The grain sizes in the range of 11-25 nm were obtained depending on the elaboration conditions. Raman spectra show the fundamental peaks at 477, 632, and 782 cm(-1), corresponding to the E-g, A(1g), and B-2g vibration modes, respectively, in good agreement with those for the rutile bulk SnO2. The optical band gap value of tin oxide decreases from 3.88 to 3.44 eV with the increase of fluorine content. Impedance spectroscopy results indicate that the electrical properties are strongly dependent on temperature and doping rate. These results show the strong correlation between the structural, morphological, optical and electrical properties of the samples depending on doping content which was well reflected on the quality of the nanoparticles.