Identification of a new function model for the AC-impedance of thermally evaporated undoped selenium films using the Eigen-coordinates method

The experimental AC-impedance data of undoped amorphous and polycrystalline selenium films were taken at T = 300K in the frequency range 100 Hz-10 kHz in the dark and under band-gap illumination. The data were analyzed using the Eigen-coordinates method in conjunction with a 'separation' procedure w ithout prior use of equivalent circuits. A unified circuit model with gener alized impedances was recognized to parameterize well the observed AC-imped ance behavior. The features of this electrical model were linked to the fra ctality of the heterogeneous structural regions in these selenium specimens via one or two recap elements, each represented by a complex impedance of fractional power-law frequency behavior. These recap elements reflect the e lectric properties of scale-invariant circuits of self-affine normal (ideal ) resistor-capacitor (RC) cells of the Cauer/Forster type. (C) 2001 Elsevie r Science B.V. All rights reserved.