Ionic and electronic transport in conducting polymer systems
Wang, Yongjun, 1975-
The electrical properties of conducting polymer-based devices are investigated in order to better understand charge transport through conducting polymers and charge transfer at conducting polymer interfaces with metals and inorganic semiconductors. Experiments on two specific systems are reported: (1) an anionically functionalized conducting polymer between metal electrodes and (2) nanostructured doped conducting polymer-semiconductor interfaces. Temperature dependent impedance measurements are reported on an anionically functionalized polyacetylene sandwiched between two gold electrodes (Au|P A |Au). These measurements provide key quantities regarding the ionic carriers in this system, such as the characteristic frequency for electrode polarization, ionic DC conductivity, activation energy, effective ion concentration, and hopping frequency. Impedance measurements are also reported on samples where excess electronic carriers had been introduced with a DC bias and at temperatures sufficiently low so as to freeze out the ionic carriers. In addition to providing information about the dielectric relaxation of electronic carriers such as the characteristic frequency for electrode polarization and activation energy, these low-temperature impedance measurements also support the ionic dielectric relaxation assignments. Temperature-dependent potential step experiments, in combination with the dielectric measurements probing ionic carriers, demonstrate the direct connection between the redistribution of ions and an enhancement in carrier injection in the Au|P A |Au system. Further potential step experiments followed by relaxation through either a short- or open-circuit configuration demonstrate that the electric field distribution is closely related to the amount of injected electronic carriers. The electric field distribution changes from being mostly determined by ionic carriers to being jointly determined by both ionic and injected electronic carriers when the density of injected electronic carriers is higher than that of the effective ionic carriers. To investigate charge depletion and transport at length scales less than the depletion width of a semiconductor interface, nanoscale metal-InP contacts with low barrier height were embedded within conducting polymer-InP contacts with high barrier height. Electrical measurements on these hybrid interfaces indicate that charge transport across the nanoscale metal contacts is affected by the neighboring high barrier region when the size of the metal contacts is less than the depletion width of the conducting polymer-InP background.