"

Cookies ussage consent

Our site saves small pieces of text information (cookies) on your device in order to deliver better content and for statistical purposes. You can disable the usage of cookies by changing the settings of your browser. By browsing our site without changing the browser settings you grant us permission to store that information on your device.

I agree, do not show this message again.

Structure, linear and non-linear optical properties of thin AsxSe1-x films

K. PETKOV1, R. TODOROV1, J. TASSEVA1, D. TSANKOV2

Affiliation

  1. Central Laboratory of Photoprocesses “Acad. J. Malinowski”, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 109, 1113 Sofia, Bulgaria
  2. Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev St., bl 9, 1113 Sofia, Bulgaria

Abstract

Amorphous AsxSe100-x thin films with different compositions (28 ≤ x ≤ 60) were deposited onto Si wafers and optical glass substrates BK-7 by thermal evaporation. The changes in the optical properties and structure of thin films as a function of the composition, film thickness and conditions of thermal evaporation and exposure to light were studied. Optical constants (refractive index, n, and absorption coefficient, α) and thickness, d, as well as the optical band gap, Eg, were determined using a method similar to Swanepoel’s envelope method and two triple - TRfRm and TRbRm methods (for very thin films). Applying the Wemple and Di Domenico model, the dispersion energy, Ed, single-oscillator energy, E0, and effective coordination number per cation, Nc, for the studied films were estimated. It was shown that the calculated values of n, k and Eg do not depend on the evaporation rate (0.2–25 nm/s), film thickness (50-1000nm) and other conditions of evaporation. The maximum value of n was found to be in thin As40Se60 films. After exposure to light, an increase in n and decrease in thin film’s thickness and optical band gap was observed. We have found that E0 and Nc increase with increasing the Secontent. Non-linear parameters obtained by different formulae for prediction of non-linear absorption and refractive index were compared. A correlation between the non-linear refractive index and linear optical properties of As-Se thin films was demonstrated. The results of photo-induced changes in the infrared spectra of thermally deposited As-Se were interpreted in terms of the changes in the film structure due to the photopolymerization of As4Se4 molecular units and selenium chains into an As2Se3 glassy network. The great changes in n after exposure to light of As-rich films suggest an opportunity for applying the films examined as inorganic photoresists, in multi-layered structures and for producing Bragg gratings..

Keywords

Thin films, Chalcogenide glasses, Optical properties, Nonlinear refractive index, IR spectroscopy.

Submitted at: July 5, 2009
Accepted at: Dec. 10, 2009

Citation

K. PETKOV, R. TODOROV, J. TASSEVA, D. TSANKOV, Structure, linear and non-linear optical properties of thin AsxSe1-x films, Journal of Optoelectronics and Advanced Materials Vol. 11, Iss. 12, pp. 2093-2101 (2009)