Eur. Phys. J. B (2018) 91: 245
https://doi.org/10.1140/epjb/e2018-90273-7

Regular Article

Determination of allowed transitions types and the optical parameters of Se–Ge–Ag chalcogenide films

Semiconductor Laboratory, Physics Department, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt

^a e-mail: amshakra@yahoo.com

Received: 22 April 2018
Received in final form: 25 June 2018
Published online: 10 October 2018

Abstract

Amorphous Se_0.68Ge_0.24Ag_0.08 films were prepared by the known thermal evaporation method. X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analysis were used to identify the structure of the prepared samples. Transmittance T(λ) was measured at room temperature in the wave length range (400–2500 nm) for the investigated films of different thicknesses in range (221.2–815.2 nm). Swanepoel’s method was used to calculate the index of refraction n and absorption k. The allowed transitions in the studied composition are indirect. Values of optical band gap E_g^opt were determined using two different methods. The obtained values of E_g^opt are equal 1.90 and 1.91 eV, also the value of Urbach energy E_e equal 0.50 ± 0.01 eV. Dispersion of refractive index n is analyzed using a single-oscillator model. The optical high frequency dielectric constant ε_∞ and the optical dispersion parameters (E_o and E_d) were calculated by analyzing the obtained values of n. The obtained values of E_o, E_d and the average value of ε_∞ are found to be 5.36 eV, 18.86 eV and 4.60, respectively. The ratio N∕m^* for the investigated composition is 3.87 × 10⁵⁵ m⁻³. The dependence of real ε₁ and imaginary ε₂ parts of dielectric constant, relaxation time τ and the optical conductivity σ_opt on photon energy hν was also studied for Se_0.68Ge_0.24Ag_0.08 films. The obtained results showed that ε₁, ε₂, τ and σ_opt increased with photon energy.