Effect of Al doping on the carrier transport characteristics of TiO2 thin films anchored on glass substrates

Abstract

Aluminium-doped TiO2 thin films are grown by sol–gel spin-coating method, and the impact of Al doping on structural, optical, and electrical properties is investigated. Morphology of the films exhibited decrease in the grain size with the increase in incorporation of Al dopants. EDS affirmed the presence of Al atoms in the doped films. A built-in tensile stress is observed with increasing dopant concentration in the films due to the deviation of the (101) plane from its ideal position. Raman spectra confirmed the anatase phase of TiO2 and effects of Al doping on it. A blue shift in the energy gap and an increase in the average transmittance of the Al doped samples are accounted. Ellipsometry revealed the decrease in refractive index and thickness of the film upon Al doping. The obtained non-linear refractive index values of the films showed a decreasing trend with increasing doping concentration due to the deteriorated polarizability in doped films. The predominance of grain-boundary scattering in the doped films is confirmed by the decreasing trend in the values of mobility and the mean-free path of the carriers. The mobility of the carriers is reduced by one order in doped films due to the dominant grain-boundary scattering mechanism.