Electrical sensing properties of polypyrrole

Thin films of polypyrrole doped with dodecylbenzene sulfonic acid were studied using complex impedance spectroscopy, current density measurements as a function of voltage (J-V) and capacitance-voltage (C-V) measurements. The J-V characteristics of these junctions are asymmetrical and nonlinear, and there is no tendency to saturate for the reverse current. In both forward bias and reverse bias, these junctions exhibit a significant, fast and reversible response to methane gas, which was explained by changes in the Schottky barrier height and in the carrier concentration of the polypyrrole sample due to methane exposure. The junction parameters, such as the ideality and rectification factors, are strongly influenced by the gas. From the C-V characteristics, the built-in voltage and the charge concentration are found to be also influenced by the gas. Complex impedance spectroscopy showed a single semicircular arc, which can be represented by a very simple equivalent circuit that is characteristic of a metal-semiconductor contact. The parameters extracted from these measurements are in agreement with the proposed mechanism.