The main role of thermal annealing in controlling the structural and optical properties of ITO thin film layer

In this study, indium tin oxide (ITO) films (~350 nm) were prepared using the electron beam gun technology. Influence of thermal treatment of the films at a variety of temperatures on the structure and electrical and optical properties of the ITO films was studied. The XRD patterns were used to determine the structural parameters (lattice strain and crystallite size). The XRD results showed that the ITO films possess a cubic poly-crystalline structure and the characterized peak of diffraction intensity of the (222) plane increases dramatically in the post-annealing, which suggests a major improvement in the crystallization performance of the film being deposited. The electrical properties of the ITO films with different thicknesses were measured by the standard four-point probe method. It can be seen that the measured electrical properties refer to a decrease in the sheet resistance Rs (Ω/sq) with the increase in the annealing temperature. This means that the ITO films with lower electrical properties will be more appropriate for high-efficiency Cd/Te solar cells. In the higher absorption spectral regions of the transmittance and reflectance, the absorption coefficient was determined and the optical energy gap was calculated. The optical bandgaps of the studied ITO films have values increasing with the increase in the annealing temperature, showing a maximum value at 250 °C (3.72eV). The increase in the bandgap can be explained basing on the B-M effect. Finally, the (n and k) of the ITO films exhibited lowest values at 350 °C while the transmittance was highest, which emphasize that the ITO films are good transparent layers.