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

Abstract

Thin films of amorphous Ge₉As₂₀Te_{71− x} In _x with different compositions (x = 0, 3, 6 and 9 at. %) were obtained by deposition onto glass substrates by thermal evaporation. The reflection spectra, R(λ), 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 Ge₉As₂₀Te_{71− x} 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 .

Keywords:

• optical constant
• amorphous thin film
• band gap
• absorption edge

Acknowledgements

The author would like to thank Al-Azhar University for financial support. Also the author would like to thank Dr. A. Dahshan, Faculty of Science, Suez Canal University, Port Said, Egypt, for his help and advice throughout this work.