Effect of Al doping on structural, optical and electrical properties of SnO2 thin films synthesized by pulsed laser deposition

Aluminium-doped (Al=0-5 wt.%) SnO2 thin films with low-electrical resistivity and high optical transparency have been successfully synthesized by pulsed laser deposition technique at 500 degrees C. Structural, optical and electrical properties of the as-deposited and post-annealed thin films were investigated. X-ray diffraction patterns suggest that the films transform from crystalline to amorphous state with increasing aluminium content. The root mean square (R-q) surface roughness parameter, determined by atomic force microscopy decreases upon annealing of the as-deposited film. While resistivity of the film is the lowest (9.49x10(-4)omega-cm) at a critical doping level of 1 wt.% Al, optical transparency is the highest (nearly 90%) in the as-deposited condition. Temperature dependence of the electrical resistivity suggests that the Mott's variable range hopping process is the dominant carrier transport mechanism in the lower temperature range (40-135K) for all the films whereas, thermally activated band conduction mechanism seems to account for conduction in the higher temperature region (200-300K).