Optical properties of indium sulphide thin films deposited by thermal evaporation

Abstract

Indium sulphide (In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) thin films were deposited by vacuum thermal evaporation a base pressure of 1.5times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> mbar. The structural and optical properties of these films are studied by X-ray diffraction, X-ray reflectometry and optical transmission in the UV-Visible-Near infrared region. X-ray diffraction analysis showed that the as-deposited In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films are amorphous. The measured optical transmission enabled the determination of the thicknesses and optical constants of the films in a wavelength range 200 to 2500 nm. The optical transmittance of as-deposited films varied on average between 80 and 90% in the visible spectral range. The analysis of the optical absorption of these thin films showed that they have a direct band gap which varies between 1.65 eV and 2.13 eV depending on the film thickness. Fourier transform infrared spectroscopy analysis was also carried out and the results will be presented and discussed.