Photoelctric Effects in Insulating Polymers and Their Relation to Conduction Processes

There are four distinct spectral regions in which photoelectric effects occur in synthetic high polymers. In the infrared, there is transient motion of charge which is reversible, and the most likely reason is thermal expansion, coupled with some redistribution of space charge in the sample. In the near ultraviolet, there is injection of electrons and/or holes, with marked dependence upon the electrode material and strong time variations. The threshold energies are ~4 eV and we show a very schematic band structure which accounts for such energies. The origin of the time dependence is not clear. In the vacuum ultraviolet, interband excitation and photoemission experiments give estimates of band gap (Eg ≃ 9 eV) and work function (ϕ I ≃4 eV) which agree with other measurements, and are consistent with the near ultraviolet work. In the gamma (and hard beta) region there are immediate (prompt) and delayed effects, which appear to correspond to the motion of free carriers with high mobility ( μ ≥ 10-2/V sec ) and of carriers with a lower, thermally activated mobility ( μ ~ 10-4 cm2/ V sec ) respectively. The latter values have also been found by other methods. Much lower mobilities ( μ ~ 10-11 cm2/V sec) have been found by other means. The remarkable feature is that the schubweg (μτ) is of order 10-10 cm2/V-1 in all cases. In analysing these data, we criticize the conventional method of shallow trapping and interband recombination.