Conductivity Mechanisms in Sb-Doped SnO2 Nanoparticle Assemblies: DC and Terahertz Regime

Assemblies of undoped and antimony-doped tin oxide nanoparticles synthesized via a nonaqueous sol–gel procedure, pressed into pellets, and annealed under various conditions were investigated using time-domain terahertz spectroscopy, scanning electron microscopy, atomic force microscopy, and dc conductivity measurements. Combination of these methods made it possible to resolve the conductivity limitations imposed by intrinsic properties of the material and by the morphology of the samples. Percolation of the nanoparticles was confirmed in all samples. The undoped samples exhibit a weak hopping conductivity, whereas bandlike conduction of charges partially confined in the nanoparticles dominates in the doped samples. The conductivity of nanoparticles and their connectivity can be greatly controlled during the sample preparation, namely by the calcination temperature and by the order of technological steps. A substantial increase of the conductivity inside nanoparticles and of the charge transport between them is achieved upon calcination at 500 °C.