Effect of antimony addition on the optical behaviour of germanium selenide thin films

This paper reports the influence of antimony (Sb) addition on the optical properties (optical energy gap and refractive index) of thin solid films of the chalcogenide glassy Ge0.17Se0.83-x Sb-x(x = 0, 0.03, 0.09, 0.12, 0.15) system. This has been done by analysing the transmittance (T) and reflectance (R) spectra in the spectral region 400-2000 nm. It was found that the optical energy gap decreases with increasing Sb content from 1.92 to 1.63 eV with an uncertainty of +/- 0.01 eV. The results were interpreted in terms of bond energies and on the basis of the concept of electronegativity. The refractive index has been found to increase with increasing Sb content. The increase in the refractive index has been explained on the basis of polarizability. Dispersion of refractive index has been analysed using the Wemple-DiDomenico single oscillator model. The static refractive index increased from 2.45 to 2.91 for the studied compositions. An estimate of the energy gap has also been taken theoretically and it has been found that both the optical energy gap (measured from T and R spectra) and the theoretical energy gap follow similar trends.