Optical properties of (Se80Te20)100-xZnx (2 ≤ x ≤ 6) amorphous thin films

The (Se80Te20)(100-x)Zn-x (2 <= x <= 6) thin film compositions have been prepared by melt quenching technique followed by electron-beam physical vapour deposition. X-ray diffraction pattern and SEM micrographs ascertain the amorphous nature of prepared thin films. The transmission spectra from UV/VIS/NIR double beam spectrophotometer (500 <= lambda (nm) <= 2600) is used for optical characterization of thin films. The absorption coefficient and energetic parameter (A) for various compositions indicate that the absorption mechanism in Se-Te-Zn glassy system occur via allowed indirect transitions. The optical band gap for thin films lies at the edge of near infrared region in A-band (lambda similar to 900 nm).The average heat of atomization has no essential influence on the optical band gap energy values. The refractive index (n) for thin films exhibit normal dispersion in the wavelength range 800 nm <= lambda <= 1100 nm (IR-A), and is nearly constant at longer wavelength lambda >= 1400 nm (IR-B). The dispersion of refractive index below the band gap energy region is studied using the Wemple-DiDomenico (WDD) single oscillator model. It is found that, to a good approximation the single-oscillator energy scales with the optical band gap (E-o approximate to 1.4E(g)(opt)). The deduced value of parameter beta = 0.24 +/- 0.01 corresponds to ionic character of bonds in the Se-Te-Zn system. The dielectric parameters (epsilon', epsilon '',epsilon(infinity), epsilon(L)), optical conductivity (sigma(1), sigma(2)), ratio of carrier concentration to the effective mass (N/m*) have also been deduced for thin films. The calculated values of plasma frequency omega p and N-opt are in good agreement with carrier concentration of semiconductors. The energy loss occurred in the interior of the Se-Te-Zn thin films is found to be due to the interband electronic transitions.