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Issue Eur. Phys. J. Appl. Phys.
Volume 17, Number 3, March 2002
Page(s) 179 - 186
Section Characterization of Materials
DOI 10.1051/epjap:2002010



Eur. Phys. J. AP 17, 179-186 (2002)
DOI: 10.1051/epjap:2002010

Annealing and thickness effect on the optical absorption of Ge $_\mathsf{20}$Te $_\mathsf{80}$ and Cu $_\mathsf{6}$Ge $_\mathsf{14}$Te $_\mathsf{80}$ films

H. El-Zahed1, M. Dongol2 and M. Radwan3

1  University Girls College for Arts, Science and Education, Ain Shams University, Cairo, Egypt
2  Physics Department, Faculty of Science, South Valley University, Qena, Egypt
3  Math. & Phys. Dept., Faculty of Engineering, Cairo University, Fayoum branch, Egypt

amer2000@omantel.net.om

(Received: 7 April 2001 / Received in final form: 26 September 2001 / Accepted: 23 October 2001)

Abstract
Thin films of Ge 20Te 80 and Cu 6Ge 14Te 80 of different thicknesses are deposited on glass substrate by thermal evaporation under vacuum. The effect of incorporation of copper in Ge 20Te 80 film is studied by measuring the optical absorption. The mechanism of optical absorption follows the rule of direct transition. The films are annealed at different elevated temperatures from 370 to 520 K. The measurements were carried on as-deposited and annealed specimens. The optical energy gap ( $E_{\rm g}$) was found to decrease with increasing the annealing temperatures in the case of Ge 20Te 80 films. But in the case of Cu 6Ge 14Te 80 films, $E_{\rm g}$ first increases with annealing temperature up to 410 K, then decreases sharply after further increasing the annealing temperature above the glass transition temperature. The decreases of $E_{\rm g}$ and the increase of the width of localized states $E_{\rm e}$ could be attributed to the amorphous - crystalline transformation. The values of optical energy gap $E_{\rm g}$ are also found to increase with thickness of both two-type films. The effect of films thickness on optical energy gap ( $E_{\rm g}$) of the films is interpreted in terms of the density of state model of Mott and Davis. The refractive index n, extinction coefficient k and dielectric constant $\varepsilon_{\rm i}$ and $\varepsilon_{\rm r}$ are also calculated for all samples.

PACS
78.20.Ci - Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity).
78.66.Jg - Amorphous semiconductors; glasses.


© EDP Sciences 2002


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