Thermal-frequency dependence study of the sub-band localized states effect in Sb-doped SnO2 based sol-gel thin films

Abstract

Films of transparent conducting antimony-doped tin oxide have been deposited by sol-gel based Dip-coating technique. The morphological analysis revealed that the deposited films are homogenous, smooth and the roughness depends on the Sb-doping. The Raman scattering showed that the vibrational modes are sensitive to oxygen deficiency, structural disorder and were red-shifted compared to the rutile SnO2 single crystal. The FTIR study depicted the presence of SnO (610cm−1) and SnOSn (740cm−1) bonds in the films. Optical measurements revealed high transparency (~85%) over the visible region. The optical band gap varies from 3.87 to 3.79eV with increasing the width of tail states and corresponds to direct allowed transition in the bulk. The AC-conductivity (σac) exhibits a semiconductor temperature-dependence behavior and varies from extrinsic to intrinsic conduction. The thermal energy promotes the polarization involving electrons localized at randomly oriented oxygen vacancies of the inhomogeneous dielectric structure grain/grain boundary and induces high dielectric constant. σac was found to follow the power law: σac=A. f0.49 at high frequencies and the experimental results showed that the correlated barrier hopping mechanism is appropriate for the charge transfer between localized states.