Synthesis and Characterization of Al-Doped SnO2 Thin Films

4Aluminum-doped tin oxide thin films are synthesized by a sol-gel spin coating method. The synthesized samples are thin, uniform, and adherent to the substrate support. The XRD studies show that the phase of thin films is pure tetragonal SnO₂. For pure SnO₂, the lattice parameters are a = 4.7284 A and c = 3.2673 A. Not much change is observed in lattice parameters with Al-doping concentration. The average crystallite size is 6.6 nm and decreases with the increase in Al-doping concentration. SEM studies show that growth of the film takes place with porous structure embedded with nanogranules, increasing the open surface area of the film. Optical study revealed that band gap of SnO₂ is 3.96 eV with direct band-to-band transitions and increases with Al-doping concentration. Gas-sensing characteristics showed that SnO₂ films are sensitive as well as fast responding to CO gas at 275°C. The sensor response increases with Al-doping concentration up to 1 wt% and decreases afterwards. A high sensitivity for CO gas indicates that the SnO₂ films are selective for this gas. The rise time and recovery time are 27 and 80 s, respectively. The mechanism of gas sensing is explained adequately.