Ltt. Tuyen et al., ELECTRICAL-PROPERTIES OF DOPED POLYPYRROLE SILICON HETEROJUNCTION DIODES AND THEIR RESPONSE TO NOX GAS/, Thin solid films, 292(1-2), 1997, pp. 293-298
The fabrication of a heterojunction between p-doped polypyrrole and p-
doped silicon and its possible use in the detecting of nitrogen oxide
gas (NOx) is described. Pyrrole was photoelectrochemically polymerized
onto a silicon surface from an aqueous solution in the presence of so
dium p-toluenesulfonate or p-toluenesulfonic acid. The silicon surface
was chemically treated in different ways. Current-voltage characteris
tics with regard to the viability of the development as sensor for NOx
at room temperature were measured. At low forward bias voltages, the
forward currents show standard diode behaviors with diode quality fact
ors close to unity. The saturation current densities are of the order
of 10(-8) A cm(-2). In the high forward bias voltage region, the heter
ojunction diodes exhibit a significant, fast and reversible response t
o NOx gas, described by a NOx-induced voltage shift, which corresponds
to a NOx-induced decrease in the resistance of the polymer layer. Fur
thermore, it was found that the electrical properties of these heteroj
unction diodes depend strongly on both the supporting electrolyte used
for doping and the chemical treatment of the silicon surface.