Abstract
Amorphous (GeSe2)100−x –Bi x (x=0, 0.4, 2 and 4) films were prepared by the pulsed laser deposition technique. The optical transmission spectra, absorption spectra and Raman spectra of the films were measured. The short-wavelength absorption edges in the strong absorption region of the films were described using the ‘non-direct-transition’ model proposed by Tauc and the optical band gaps (\(E_{\mathrm{g}}^{\mathrm{opt}})\) were determined. The Urbach energy (E u) was derived in the exponential part of the absorption edge. Both \(E_{\mathrm{g}}^{\mathrm{opt}}\) and Tauc slopes (B 1/2) decreased with increasing Bi content, while E u had the opposite trend. The refractive indices of the films were calculated from the transmission spectra by using the Swanepoel method. Analysis of Raman spectra and absorption spectra shows that Bi addition decreases the mean bond energy and increases E u in the amorphous films, which caused the decrease of \(E_{\mathrm{g}}^{\mathrm{opt}}\). The changes of the refractive indices are also discussed.
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