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

Abstract

Amorphous Se0:68Ge0:24Ag0:08 lms were prepared by the known thermal evaporation method. X-ray di raction (XRD) and energy dispersive X-ray (EDX) analysis were used to identify the structure of the prepared samples. Transmittance T( ) was measured at room temperature in the wave length range (400{2500 nm) for the investigated lms of di erent 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 Eopt g were determined using two di erent methods. The obtained values of Eopt g 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 "1 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 "1 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 "1 and imaginary "2 parts of dielectric constant, relaxation time and the optical conductivity opt on photon energy h was also studied for Se0:68Ge0:24Ag0:08 lms. The obtained results showed that "1, "2, and opt increased with photon energy.