Physical characterization of Ge–Zn–Se thin films

Different \({(\mathrm{GeZn})}_{100-\mathrm{x}}{\mathrm{Se}}_{\mathrm{x}}\) films have been thermally evaporated. The film absorbance (A) has been measured in the 0.3–0.9 μm spectral range. The non-crystalline state of \({(\mathrm{GeZn})}_{100-\mathrm{x}}{\mathrm{Se}}_{\mathrm{x}}\) films was confirmed by X-ray diffractograms. A small deviation between the selected compositions and those experimentally investigated was confirmed by energy-dispersive X-ray analysis. The ultrasonic longitudinal (\({v}_{L}\)) and shear (\({v}_{T}\)) velocities of \({(\mathrm{GeZn})}_{100-\mathrm{x}}{\mathrm{Se}}_{\mathrm{x}}\) glasses were measured using the pulse-echo technique. The composition dependence of the optical band gap (E_g) is well discussed in terms of the Mott and Davies Model (MDM). The linear correlation between the changes in the optical band gap (ΔE_g) and in the band tail parameter (\(\Delta \sqrt{B}\)) confirmed the disorder’s decrease, which explains the observed increase in the E_g values. The latter was increased from 1.75 to 2.32 eV with increasing Se content, i.e., these films can be used as optical absorbers in the wavelength range of 0.530–0.710 μm. On the other hand, Duffy’s relationship was used for the theoretical estimation of optical gap (\({E}_{g}^{th}\)) values. There is a good match between the \({E}_{g}^{th}\) values and those experimentally investigated. With the help of the Herve and Vandamme relationship, the value of the refractive index (nth) of the studied films was investigated. The nth values are found to decrease with increasing Se content, which is because of decreasing glass density (\(\rho\)). The values of the ultrasonic velocities are increased with increasing Se content, which explains the observed increase in the elastic moduli, Poisson’s ratio \((\mathcal{o}),\) and Debye temperature (\({\theta }_{D}\)). The obtained results are well explained in terms of composition effects on the distribution of the chemical bonds, the total mean bond energy < E > , the mean bond energy (E_s), the number of constraints (N_s) and the cohesive energy (CE).