Structural and electrical studies on sol–gel derived spun TiO2 thin films

Titanium dioxide thin films were prepared by spin coating of sol precursor onto microscopic glass slides, silicon and indium tin oxide (ITO) coated glass substrates. Spin speed was varied between 1000 and 6000 rpm. From the morphological analysis, it is found that thin films spun with speed *w # < 4000 rpm assume higher ordered structure than those spun at a speed higher than 4000 rpm. Conduction at low voltages is believed to be variable range hopping at temperatures T < 220 K while the ionization of donors situated at Ea = 0.46 eV below the conduction band edge becomes dominant at temperatures higher than 220 K. At high field charge transport is due to trap-controlled space charge limited mechanism. Traps with a density Nt #~ 1 x 1022 m-3 are thought to be situated at energy level Et = 0.3 eV below the conduction band and are associated with film nonstoichiometry and interface states.