Investigation on structural, optical and electrical properties of Nd doped titania films and application of optical model

The effect of dopant concentration and temperature on the structural, optical and electrical properties of TiO₂ (Titania) thin films deposited through sol-gel spin coating was investigated. The X-Ray Diffractometer was used for phase analysis, UV–Vis spectrometer and Ellipsometer techniques were used for the optical measurements and Hall effect was used for the electrical characterization. Annealing temperature and dopant concentration were chosen as the parameters in the present study. The optical band gap marginally increased from 3.40 eV to 3.43 eV with increase in dopant concentration for the films annealed at 350 ֯C. The increasing trend was also observed for the films annealed at 450 °C with the optical band gap in the range 3.34 eV–3.39 eV. Using ellipsometric measurement, thickness and optical constants were obtained and we compared the refractive index values with those obtained from PARAV software. For Nd doped films, a single oscillator model was tested by using the refractive index values from ellipsometric measurement. The carrier density and plasma frequency were calculated using the Wemple Di Domenico (W-D) model. The electrical properties indicate decreased resistivity from 10³ Ωcm to 10¹ Ωcm and increased carrier density from 10¹⁵ cm^-3 to 10¹⁷ cm^-3 with increase in annealing temperature. Similarly, with increase in dopant concentration at a given annealing temperature, we have observed a decreased resistivity compared to the prestine samples. However, the carrier density increased marginally with increase in dopant concentration.