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

Amorphous Se0.68Ge0.24Ag0.08 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 Egopt were determined using two different methods. The obtained values of Egopt are equal 1.90 and 1.91 eV, also the value of Urbach energy Ee 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 (Eo and Ed) were calculated by analyzing the obtained values of n. The obtained values of Eo, Ed 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 σopt on photon energy hν was also studied for Se0.68Ge0.24Ag0.08 films. The obtained results showed that ε1, ε2, τ and σopt increased with photon energy.