Study of charge transport in Fe-doped SnO2 nanoparticles prepared by hydrothermal method

In order to follow the electrical comportment of the tin oxide (SnO2) with iron (Fe) addition, Fe doped SnO2 nanoparticles with various iron contents (0, 5%, 10%, 15% and 20 at%) were prepared via hydrothermal method. The effect of introducing iron in the structural, optical and electrical properties of SnO2 has been studied. The X-ray diffraction (XRD) patterns show that the peaks are indexed to the cassiterite structure without any trace of an extra phase even for relatively high Fe doping (20%). The impedance spectra were analyzed in terms of equivalent circuits involving resistors and constant phase elements (CPE). From the impedance measurements, the ac conductivity σac(ω)σac(ω) was calculated and studied. The electrical resistivity shows an increase with iron ratio. A conversion from n- to p- conductivity type with iron incorporation was interpreted. In SnO2 nanostructures, the surface activity and the grain size seem to be a major factors that must to be taking into account when looking for the modification of the material conductivity through doping. In fact, and contrary to what has been expected, the activation energy was found to increase with iron concentration. This rise was attributed to the expansion of the grain boundaries role in conductivity process and confirms the highly sensitive character of Fe-doped SnO2 surface. This fact was confirmed by the calculation of the Schottky barrier. The optical diffuse-reflectance measurement was carried out and a large reduction of the band gap was observed with iron ratio showing that a band gap decrease do not necessarily signify an amelioration of SnO2 conductivity.