Structural and optical properties of flash evaporated Bi<inf>2</inf>Te<inf>2</inf>Se thin films

Thin films of Bi2Te2Se of different thicknesses were deposited on to clean glass plates by the flash evaporation technique in a vacuum of 2×10-5 torr. The annealed films were used for the transmittance and reflectance measurements in the range 400 nm-2400 nm. There was a reflectance minimum observed in the reflectance spectra around 1000 nm which is due to the influence of the glass plate. The optical constant, real and imaginary parts of the dielectric constant and the optical band gap were evaluated from the measured transmittance and reflectance values. The high frequency dielectric constant ε0 was evaluated from the plot of (n2-1)-1 and λ-2 according to the simple classical dispersion relation for a single oscillator. Thickness dependance of the band gap of the films is attributed to the strain caused in the films due to the defects.