Optical Parameters of Both As 2 S 3 and As 2 Se 3 Thin Films from Ultraviolet to the Near-Infrared via Variable-Angle Sp
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URFACES, INTERFACES, AND THIN FILMS
Optical Parameters of Both As2S3 and As2Se3 Thin Films from Ultraviolet to the Near-Infrared via Variable-Angle Spectroscopic Ellipsometer F. Abdel-Wahaba, I. M. Ashraf b,a, and F. B. M. Ahmeda,* a Department
b
of Physics, Faculty of Science, Aswan University, Aswan, Egypt Advanced Functional Materials and Optoelectronics Laboratory (AFMOL), Department of Physics, College of Science, King Khalid University, Abha, 61413 Saudi Arabia *e-mail: [email protected] Received May 25, 2020; revised June 22, 2020; accepted July 1, 2020
Abstract—In the UV-visible-near infrared regions from 245 to 1000 nm, variable-angle spectroscopic ellipsometer (VASE) was used to investigate optical functions of As2S3 and As2Se3 thin films. In the entire measured spectral range, data were analyzed by assembly from several dispersion models. These assemblies comprise individual Tauc–Lorentz supplemented by several Lorentz (TL-group) or single Cody–Lorentz with several Lorentz (CL-group) models. For As2S3 and As2Se3 thin films, the optical parameters were quantified. The model parameters, such as the Lorentz amplitude, resonance frequency, oscillator width, extinction coefficients, refractive indices, and Urbach and optical band energy of both films were obtained. The band gap energy Eg was experimentally determined using the obtained data of CL-group from (αhν)1/2 vs. hν plots. It is found that the band gap energies of As2Se3 and As2S3 were 1.796 and 2.349 eV, respectively. The Eg values for the films were theoretically investigated by the bond statistics of the random covalent network model (CRNM) with the aid of Manca’s relation. Plausible agreement between the experimental and calculated Eg values for both samples was obtained. Keywords: chalcogenide thin films, variable-angle spectroscopic ellipsometer, Tauc–Lorentz model, Cody– Lorentz model DOI: 10.1134/S1063782620110020
1. INTRODUCTION Glasses that based on sulfur (S), selenium (Se), and tellurium (Te) combined are known as chalcogenide glasses [1]. To increase both robustness and glass stability, chalcogenide can contain elements from IV, V, and VII groups. These glasses have been studied extensively because of their unique properties and a wide range of applications in infrared and integrated optics, optical imaging, optical recording microelectronics, and optical communications [2]. They are applicable as radiation-sensitive materials with enhanced optical properties and high optical resolution and also promising for nanotechnology and photosensitive photorecording. Depending on their formation, a wide transmission range (1–20 μm) can be obtained, making chalcogenide glasses suitable for detecting environmental changes in the infrared region [3]. Furthermore, amorphous chalcogenides demonstrate high non-linear refractive indices that are approximately two orders of magnitude larger than that of the silica glass, making chalcogenide glasses attractive for second-harmonic generation [3, 4].
Optical properties of chalcogenide films such a
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