Influence of composition on the electrical and optical properties of Ge20BixSe80-x films

The optical gap and electrical resistivity of a series of Ge20BixSe80-x glasses (x = 0, 5, 9 10, 15, 20, 25) was measured. In order to determine the optical gap, E-g, the absorption spectra of films with different Bi content, (denoted by x), were analyzed. The optical band gap showed a sharp decrease from 2.1 to 1.65 eV as the Bi content increased to 10 at.%. A slight change was observed for Bi > 10 at.%. The electrical activation energy of the films was determined by investigating the temperature dependence of resistivity. A large decrease in the electrical activation energy from 0.97 to 0.09 eV was observed as the Bi content was increased up to 10 at.%. The optical and electrical data suggest that the addition of Bi produces localized states near the conduction band edge so the electrical transport is due to the hopping of electrons after being excited into localized states at the conduction band edge. (C) 2000 Elsevier Science S.A. All rights reserved.