Optical spectroscopy and dispersion parameters of Ge₁₅Se₆₀X₂₅ (X = As or Sn) amorphous thin films

Physics Department, Faculty of Education, Ain Shams University, Cairo, Egypt

^a e-mail: Hebaelghrip@hotmail.com

Received: 22 February 2013
Revised: 19 May 2013
Accepted: 21 May 2013
Published online: 5 July 2013

Abstract

In the present work the optical properties of Ge₁₅Se₆₀X₂₅ (X = As or Sn) films have been studied. Optical reflectance and transmittance of films were obtained at normal incident in the wavelength range (500–2500 nm). The transmittance measurements were used to calculate the refractive index n and the absorption index k depending on Swanepole’s method. The analysis of the optical absorption data revealed that the optical band gap E_g^opt was allowed indirect transitions. The optical constants such as complex dielectric constant, dispersion parameters (E₀ and E_d), ε_∞, VELF, SELF and dissipation factor tan δ were determined. It was found that E_g^opt and the oscillator energy E₀ decreased with As addition than Sn addition. Whereas, the Urbach tail energy E_e, the dispersion energy E_d, the real and imaginary dielectric constants ε₁ and ε₁, the high frequency dielectric constant ε_∞ and the dissipation factor tan δ increased with As addition than Sn addition.