Anisotropy of the picosecond photocurrent in stretchedtrans-polyacetylene for above- and below-gap excitation

Abstract

The temperature dependence of the picosecond photocurrent with below-gap excitation (1.06 μm) was measured for a highly oriented form of trans-polyacetylene. The one-dimensional (1D) picosecond photocurrent was found to be independent of temperature, while the 3D picosecond photocurrent was found to be temperature dependent with an activation energy of 63 meV. In addition, the anisotropy of the photoresponse of trans-polyacetylene for both above- (0.53-μm) and below-gap (1.06-μm) excitation was studied. The anisotropy ratio for below-gap excitation was independent of intensity, while the anisotropy ratio of the photoresponse for above-gap excitation decreased as the intensity increased. It was found that the picosecond photoconductive response was greatest with below-gap excitation. These results demonstrate the photoproduction of nonlinear charged carriers (solitons and polarons) at energies that are below the principal interband absorption edge and are explained qualitatively using the bimolecular recombination model.