Calculation of the Optical Constants of Amorphous Semiconducting As40s60, As40s35se25 and As40se60 Thin Films from Transmittance and Reflectance Measurements
Titel:
Calculation of the Optical Constants of Amorphous Semiconducting As40s60, As40s35se25 and As40se60 Thin Films from Transmittance and Reflectance Measurements
Auteur:
E.R. Shaaban
Verschenen in:
Journal of applied sciences
Paginering:
Jaargang 6 (2006) nr. 2 pagina's 340-346
Jaar:
2006
Inhoud:
Compositional dependencies of the optical properties of as-deposited amorphous As40S60, As40S35Se25 and As40Se60 prepared by thermal evaporation, have been studied. The direct analysis proposed by Swanepoel has been successfully employed and it has allowed us to determine the average thickness<img src="../xml/jas/2006/images/image1-2k6-340-346.gif" width="13" height="17">and the refractive index, n, of the films, with accuracies approximately 1%. The refractive index, n and film average thickness<img src="../xml/jas/2006/images/image1-2k6-340-346.gif" width="13" height="17"> has been determined from the upper and lower envelopes of the transmission spectra measured at normal incidence, in the spectral range from 400 to 2500 nm. The absorption coefficient α, therefore extinction coefficient k, have been determined from both the transmission spectra and reflection spectra at the strong absorption region. The values of refractive index increase towards As40Se60 over the entire spectral range studied increase is related to the increased polarizability of the larger Se atoms atomic radius, 115 pm), in comparison with S atoms (atomic radius, 100 pm). The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model and the optical absorption edge is described using the non-direct transition model proposed by Tauc. Likewise, the optical energy gap is derived from Tauc`s extrapolation. The optical band gap in three different composition thin films of As40S60, As40S35Se25 and As40Se60 chalcogenide glass are 2.37, 2.06 and 1.81 eV, respectively. The decrease has been obtained in both single-oscillator energy Eo and optical <img src="../xml/jas/2006/images/image2-2k6-340-346.gif" width="23" height="21">gap were interpreted in terms of the bond-strengths of the chemical bonds present in the glass compositions under study.
Uitgever:
Asian Network for Scientific Information, Pakistan (provided by DOAJ)
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