Compositional dependence of the optical constants of amorphous Ge_xAs₂₀Se_80−xthin films

Abstract

This paper reports the effect of replacement of selenium by germanium on the optical constants of chalcogenide GexAs20Se80−x (where x = 0, 5, 10, 15 and 20 at.%) thin films. Films of GexAs20Se80−x glasses were prepared by thermal evaporation of the bulk samples. The transmission spectra, T(λ), of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. A straightforward analysis proposed by Swanepoel, based on the use of the maxima and minima of the interference fringes, has been applied to derive the real and imaginary parts of the complex index of refraction and also the film thickness. Increasing germanium content is found to affect the refractive index and the extinction coefficient of the GexAs20Se80−x films. Optical absorption measurements show that the fundamental absorption edge is a function of composition. With increasing germanium content the refractive index decreases while the optical band gap increases.

On the study of the optical constants for different compositions of Sn x (GeSe)100−x thin films in terms of the electronic polarizability, electronegativity and bulk modulus

“…On the other side, a clear shift to the long-wavelength side of the extinction coefficient was observed with increasing Sn content as shown in the inset Fig. 4 The strong, medium and transport ranges of the measured T and R spectra, the two envelopes R M (k) and R m (k) for Ge 1 Se 2 thin film and the measured substrate transmittance T s (k) and reflectance R s (k) spectra The calculated values of absorption coefficient for the prepared films are of the order of *10 5 cm -1 which is consistent with that previously published [36]. Furthermore, the absorption coefficient of (Ge 1 Se 2 ) 1-x Sn x films obeyed the rule of indirect transition which is described by the following expression [35][36][37][38].…”

“…Cauchy's dispersion relationship in the form of n = a ? bk -2 (where a is the intercept and b is the slope of the linear relation between n and k -2 ) successfully extrapolates the wavelength dependence of the refractive index over the whole measurement range [36][37][38]. Figure 5 and its inset investigate both the n and k values as a function of the incident photon energy for different compositions of (Ge 1 Se 2 ) 1-xSn x films.…”

“…Based on the values of R M and R m in the transparent range of spectra, the film thicknesses, refractive index and the extinction coefficient have been calculated with high accuracy [34,35]. It should be emphasized that the accuracy of the final thickness is better than 1 % with similar accuracies in the n values [36,37]. Cauchy's dispersion relationship in the form of n = a ?…”

Characterization of quaternary chalcogenide As-Ge-Te-Si thin films

“…One observes that E g , as well as H s /N co increase with increasing Si content, which suggests that one of the main factors determining E g is the average single bond in the alloy [25]. The values of the absorption coefficient α for the studied films were calculated from transmittance T and reflectance R using the equation: [26,27] for the allowed non-direct transition, the photon energy dependence of the absorption coefficient can be described by:…”

Optical Characterization of (TMA)<sub>2</sub>ZnCl<sub>4</sub> Single Crystals in the Normal Phase

“…χ c -hν relationship is depicted in Figure 6, then the value of electric susceptibility χ c calculated near the energy gap at 5.9 eV is listed in Table 1. Lattice dielectric constant ε L and contribution of charge carriers (N) can be calculated by the fitting of the linear part of the relation [18];…”