Optical constants and electrical conductivity of Ge20Se60Sb20 thin films

Optical absorption and electrical resistivity of amorphous Ge(2)0Se(6)0Sb(2)0 films are investigated as a function of the thermal annealing. The dependence of the optical absorption coefficient on the photon energy is ascribed by the relation (alpha h nu) = B(h nu-E-o)(2). Increasing the annealing temperature from 423 K to 553 K, decreases the optical gap of the film from 1.25 eV to 0.78 eV. The effect of annealing temperature on high frequency dielectric constant (epsilon(infinity)) and carrier concentration (N) was also studied. As a result of annealing the film at 533 K, the electrical resistivity and activation energy for conduction decreased from 5.7 x 10(7) to 2.9 x 10(2) Ohm . cm and from 0.94 to 0.34 eV, respectively. The crystalline structures resulting from heat treatment at different elevated temperatures have been studied by X-ray Diffraction (XRD). The optical and electrical changes were attributed to the amorphous-crystalline transformations in the chalcogenide films. (C) 2000 Kluwer Academic Publishers.