Temperature dependence of transient radiation-induced conductivity in polymers

The temperature dependence of the transient radiation induced conductivity of a large group of polymers (about 20 in number) is studied. The test samples are irradiated in vacuum in the temperature range 25 to 180 0C by single pulses (0.3 ms long) of 65 keV electrons. The observed activation energies for the delayed component of the current transients vary from 0.06 to 0.8 eV, the larger values being typical for polar polymers. Results for the free charge carriers are interpreted in terms of the thermal dissociation of the bound electron-hole pairs in the presence of the applied electric field considering the dispersive electron transport. The high activation energies characteristic for the geminate electrons are considered to arise from the fact that shallow electron traps are separated from the bottom of the conduction band by an energy gap. The possibility of electron tunnelling is also discussed. The presence of certain chemical units in a polymer is surmised to influence considerably its radiation induced conductivity. (author)