Structure and optical properties of amorphous Ge–Se films prepared by pulsed laser deposition

Amorphous GeSex (x = 2, 4, 6) films were prepared by pulsed laser deposition technique. The optical band gaps (Egopt) and refractive indices of the films were derived from the absorption spectra and optical transmission spectra, respectively. The short-wave absorption edges of the films were well consistent with the ‘non-direct transition’ model proposed by Tauc. The dispersion of the refractive index was analyzed in terms of the single-oscillator Wemple–Di Domenico model. The structural units of the films were characterized using Raman spectroscopy. In addition to the basic structural units of edge-sharing GeSe4/2 tetrahedra, there are SeSe homopolar bonds in Se-rich GeSe4 and GeSe6 films. And GeGe bonds exist in stoichiometric GeSe2 film. The results also show that the refractive index of the films changes with the Se content. Egopt decreases with the reduction of Se content in the GeSex films. The changes of Egopt were discussed in relation to the structures of the films confirmed by the Raman spectra analysis.