Band gap tuning of p-type al-doped tio2 thin films for gas sensing applications

Transparent conducting titanium dioxide (TiO2) thin films were synthesized by a spray pyrolysis technique. In this work, the effect of Al doping on the structural, morphological, topographical, optical, and electronic properties of TiO2 thin film samples was studied in detail. The deposited film shows 66 nm to 82 nm nanostructured crystallite size. The cell parameters are found in good agreement with the experimental and theoretical calculations. The pore diameters are found to be between 6 nm and 9 nm as revealed by the field emission scanning electron microscopy images. The energy dispersive X-ray analysis, spectra show that all the samples are in stoichiometric conditions. Atomic force microscope images show that the surface roughness varies from 34.72 nm to 89.83 nm. The bandgap tuning has been observed both experimentally and theoretically. The study of optical properties shows that the absorption limit of the Al-doped TiO2 sample is shifted towards the lower energy region compared with the un-doped sample. The electrical band structure energy (3.11 to 3.64 eV) values are much closer to those of the optical band structure energy (3.18 to 3.01 eV for indirect and 3.70 to 3.49 eV for direct). The charge density map ensures that the covalent bond is present in the as-deposited sample. A combined analysis of the structural, morphological, topographical, optical, and electronic properties of the compound suggests that Ti1-x AlxO2 is a potential candidate for gas sensing and photovoltaic device.