The optical behaviour of modified GeSe:Fex‐films (0 ≦ × ≦ 0.1) prepard by co‐sputtering is investigated using transmissionmeasurements and a new algorithm for the determination of the optical constants. An increase of the rfractive index and a nonlinear shift of the absorption edge to lower energies due to the increase of the Fe concentcation are observed. The results can be interpreted by a decrease of the bond strength, an increase of the densityof valence electrons, and an increase of the density of states neaar th mobility edges. For the interpreation of the shift of the absorption edge a density of states model (DOS mode) is proposed. In accordance with results of eletrical investigations it is supposed that the increase of the density of states near the mobilityy dege influences the electrical conductivity by modification, too.

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