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

The correlations between structural and electrical properties of spray ed SnO2 films have been investigated as a function of substrate temper ature (380-560 degrees C), concentration of tin precursor (0.02-0.8 M SnCl4) and the nature of the doping agent (chlorine, fluorine, antimon y). High-resolution transmission ef ectron microscopy has shown that c hlorine or fluorine incorporation promotes the same type of defects, w hich are [0 1 1] twins. These latter behave as neutral defects, the de nsity of which limits the carrier mobility of degenerated fluorine- or chlorine-doped films to around 20 cm(2) V-1 s(-2). The situation is t otally different with antimony. Below the solubility limit in the SnO2 lattice (3%-4% Sb/Sn), Sn4+ are substituted by Sb5+, creating two con duction electrons per site and acting as point-charged defects which l ower carrier mobility. Above this limit, the Sb3+ and Sb5+ forms coexi st and are associated with an extremely large concentration of structu ral 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.