Electrical and chemical sensing properties of doped polypyrrole/gold Schottky barrier diodes

Electrochemically polymerized polypyrrole (PPy), using tetraethylammonium t oluenesulfonate (TOS), nickel phthalocyanine toluenesulfonate (NiPcTS), or copper phthalocyanine toluenesulfonate (CuPcTS) as dopants, forms a conduct ing organic polymer. The electrical properties of a gold contact to these d oped PPy-layers (Au/PPy) were evaluated by current-voltage characteristics and capacitance-voltage measurements. The I-V characteristics of these junc tions are asymmetrical and nonlinear. The junction parameters, as the ideal ity and the rectification factor, are strongly influenced by the dopant of the conducting polymer. In both forward bias and reverse bias, these juncti ons exhibit a significant, fast and reversible response to NOx gas, which w as explained by changes in the Schottky barrier height and in the carrier c oncentration of the PPy layer due to NOx exposure. A simultaneous compensat ory effect of NOx gas of the barrier region and of the neutral bulk of the Au/PPy-CuPcTS junction with a PPy layer thickness of 1.8 mu m was observed and confirmed by C-V characteristics. (C) 1999 Elsevier Science S.A. All ri ghts reserved.