Analysis of the effects of substrate temperature, concentration of tin chloride and nature of dopants on the structural and electrical properties of sprayed SnO2 films
Abstract
The correlations between structural and electrical properties of sprayed SnO2 films have been investigated as a function of substrate temperature (380–560 °C), concentration of tin precursor (0.02–0.8 M SnCl4) and the nature of the doping agent (chlorine, fluorine, antimony). High-resolution transmission electron microscopy has shown that chlorine or fluorine incorporation promotes the same type of defects, which are <0 1 1> twins. These latter behave as neutral defects, the density of which limits the carrier mobility of degenerated fluorine- or chlorine-doped films to around 20 cm2 V−1 s−1. The situation is totally different with antimony. Below the solubility limit in the SnO2 lattice (3%–4% Sb/Sn), Sn4+ are substituted by Sb5+, creating two conduction electrons per site and acting as point-charged defects which lower carrier mobility. Above this limit, the Sb3+ and Sb5+ forms coexist and are associated with an extremely large concentration of structural defects, especially twins induced by the Sb3+ species. These ions enter two-dimensional arrangements on both sides of the twins, making them planar charged defects.