Interplay between the heat treatment and structural and optical properties of Nb2O5 thin films

Thin films of Nb2O5 were synthesized by RF sputtering. The effect of annealing, at different temperatures (100, 150, 200, 250, 300, 350, and 400 degrees C), on the structural and optical properties was studied. The crystallinity and structural characteristics of the Nb2O5 thin films were examined employing the X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD and SEM analyses showed an amorphous nature for the as-deposited and annealed samples from 100 to 350 degrees C and crystalline structure for the annealed sample at 400 degrees C. The high values of the transmittance and low reflection make these films used as a window layer in solar cell systems. Upon increasing annealing temperature, the energy band gap E-g increased from 4.039 to 4.175 eV. E-g high values again make these films suitable to be used as a window layer in solar cell system. Urbach tail, E-U, decreased with increasing annealing temperature. The refractive index showed the normal dispersion. The dispersion energies were found to have the same behavior with respect to annealing temperature, besides, the single oscillator energy E-o had a lower value compared to the dispersion energy E-d. The plasma frequency omega(p) was found to increase with annealing temperature. The first and third optical moments had peak values depending on the incident photon energy.