The electrical conductivity, thermoelectric power, and metal−insulator−semiconductor diode properties of polyaniline prepared in ionic liquid (PANI) have been investigated. The electrical conductivity of the polyaniline increases exponentially with increasing temperature. The electrical conductivity value at 28 °C is 0.21 S/cm. The Seebeck coefficient of the PANI decreases with increasing temperature. The electrical conductivity and thermoelectric power results suggest that the PANI is a p-type semiconductor polymer. The Al/PANI Schottky diode was fabricated and is a metal−insulator−semiconductor type device. The ideality factor n and barrier height φb values of the diode at 298 K were found to be 2.78 and 0.85 eV, respectively. The barrier inhomogeneities are a very important explanation of the higher values of the ideality factor. The Gaussian distribution function was suggested for describing barrier height inhomogeneities. The standard deviation of the barrier height distribution σo indicates the presence of the interface inhomogeneities. The φB value obtained from C−V measurement is higher than that of the φB value obtained I−V measurements.

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The electrical, optical, and metal-semiconductor contact properties of the polyaniline prepared by emulsion polymerization have been investigated to obtain an organic semiconductor material. The obtained results suggest that the polyaniline (PANI) studied is an organic semiconductor material with optical band gap (E(g) = 2.21 eV) and room electrical conductivity (sigma(25) = 3.12 x 10(-2) S/cm) values. A Schottky diode with configuration Ag/PANI/n-Si was fabricated. The ideality factor and barrier height of Ag/PANI/n-Si diode at room temperature were found to be 4.59 and 0.38 eV, respectively. The obtained diode parameters change with temperature. The Richardson constant A* value for the Ag/PANI/n-Si diode was found to be 3.81 x 10(-4) A/cm(2).K. The Ag/PANI/n-Si diode is a metal-insulator-semiconductor-type device. The standard deviation, which is a measure of the barrier homogeneity, was found to be 0.14, indicating the presence of interface inhomogeneities. It can be concluded that the polyaniline prepared by emulsion polymerization is an organic semiconductor and Ag/PANI/n-Si configuration shows a Schottky contact.

The electrical conductivity, thermoelectric power (TEP), and optical properties of organo-soluble polyaniline doped with HCl have been investigated. The electrical conductivity and TEP of the sample increase with increasing temperature. The electrical conductivity and TEP results of the polymer suggest that it is a p-type semiconductor. The fundamental absorption edge in the polymer is formed by the direct allowed transitions, and the optical band gap value was found to be 2.79 eV. The absorption spectra for an acidic solution of the polymer indicate two new absorption bands, which are due to polaron formation. The polaron bands are responsible for the conductivity of the polymer. The TEP results indicate that the conductivity mechanism of the polymer is controlled by the large polaron hopping model.

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