Alternating Current Electrical Characterization of Plasma Polymerized Pyrrole Thin Films

Abstract

The alternating current (ac) electrical characterization of plasma polymerized pyrrole (PPPy) thin films have been discussed in this article. A parallel plate capacitively coupled glow discharge reactor was used to deposit PPPy thin films. To study the ac electrical conduction in the thin film, the variation of ac conductivity and dielectric constant of different thicknesses were investigated as the function of frequency and temperature. The observed frequency dependence of the ac conductivity is attributed to relaxations caused by the motion of electrons, which could be involved to hopping or tunneling between equilibrium sites. It is also concluded that, the ac conduction mechanism in PPPy thin films shows the correlated barrier hopping (CBH) model. The strong dependence of conductivity on frequency and the low activation energies of the carriers are also an indication of a hopping conduction mechanism at low temperatures. At high temperatures it may be due to the movements of thermally excited carriers from energy levels within the band gap. In conductivity vs temperature study a weak dependence of σac on temperature is observed which interprets the ac conduction mechanism as the hopping between localized states at the Fermi level. The observed frequency dependence of the dielectric constant in this study is attributed to the interfacial or space charge polarization and to the orientational polarization of molecular chains. On the other hand, the strong temperature dependence of dielectric constant at higher temperature and lower frequencies is attributed to the thermally activated electron hopping mechanism.