High field conduction in poly(p-phenylene vinylene)

We have shown that in polyacetylene, for electric fields above 10⁶ V/cm polarons are dissociated because the electron or hole can move much faster than the lattice distortion. Similar results should hold for poly(p-phenylene vinylene), PPV. To determine whether the free carriers thus created can be heated by the field sufficiently to allow impact ionization, we investigated free-carrier scattering in PPV. The important scatterers are longitudinal acoustic modes, molecular vibrations, and librational torsional modes. The coupling constants and important frequencies are known approximately for the first two of these processes in PPV. Using these values, some reasonable values for librons, and the calculated band structure of PPV, we conclude that at least some of the carriers could be heated to 2 eV at a field of ∼10⁶ V/cm, and that they could acquire energy required for impact ionization at not much higher fields.