Optical constants of quaternary Ge–As–Te–In amorphous thin films evaluated from their reflectance spectra

Abstract

Thin films of amorphous Ge 9 As 20 Te 71Àx In x with different compositions (x ¼ 0, 3, 6 and 9 at. %) were obtained by deposition onto glass substrates by thermal evaporation. The reflection spectra, R(), of the films were obtained in the spectral region from 400 to 2500 nm. A straightforward analysis proposed by Ruiz-Perez et al., 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, the thickness and the thickness variation of the studied films. Increasing In content is found to affect the refractive index and the extinction coefficient of the films. Optical absorption measurements were used to obtain the fundamental absorption edge as a function of composition. With increasing In content, the refractive index decreases, whereas the optical band gap, E g , increases.The relationship between E g and the chemical composition of the Ge 9 As 20 Te 71Àx In x system is discussed in terms of the cohesive energy, the average heat of atomization, H s , and the average coordination number, N r .

Optical band gap and refractive index dispersion parameters of In–Se–Te amorphous films

“…These results indicate that, the cohesive energies of these glasses show an increase with increasing the In content. According to the chemical bond approach we can say that the highest Se-Se band gap 1.95 eV [34] are replaced by the lowest band gap such as Se-Te and In-Se [35] bonds that can be interpreted the decrease of the E g with increasing the In content.…”

Optical Characteristics of Thermally Evaporated Thin a-(Cu2ZnGe)50−xSe50+x Films

“…Optical properties and parameters have been investigated and discussed after measuring the reflectance, R(λ), and transmittance, T(λ), spectra (400-2500 nm) of the films. The envelope methods (Swanepoel and Minkov), 16,34 use the transmittance and reflectance measured spectra, respectively, to get the refractive index and film thickness.…”

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

“…where b is a two-valued constant with either an ionic or a covalent value (b i = 0.26 ± 0.03 eV and b c = 0.37 ± 0.04 eV, respectively) [44,45]. The deduced values of E d using Eq.…”

“…It is shown that the single-oscillator energy E 0 decreases, while both of the dispersion energy E d and n(0) increased with increasing tin content. The oscillator energy is an average energy gap, and to a good approximation scales with the optical band gap, E g * 0.5 E 0 [43,44]. It is worth mentioning that the dispersion energy (E d ) is related to other physical parameters such as the effective coordination number of the cation nearest neighbor to the anion (N c ), the formal chemical valency of the anion (Z a ) and the effective number of valence electrons per anion (N e ) through the following relation:…”