Carrier transport properties of aluminum oxide/polypyrrole films doped with naphthalene-1,5-disulfonic acid

The electrical structure of the Al/Al2O3/PPy-NDSA/Au has been investigated by means of current–voltage (I–V) and capacitance–voltage (C–V) measurements, in a temperature range of 90–350 K. The forward C–V measurements have been carried out in the range of frequency of 1 kHz to 20 MHz. The effects of series resistance, interfacial layer and interface states on I–V and C–V characteristics are investigated. At high current densities in the forward direction, the series resistance effect has been observed for voltages greater than 0.7 V. The analysis of I–V characteristics based on the thermionic emission mechanism has been explained by the assumption of a Gaussian distribution of barrier heights, due to barrier height inhomogeneities that prevail at the interface. It has been observed that the forward C–V plot exhibits a peak, whose position shifts towards lower voltages and that decreases with increasing frequency. The non-linearity of 1/C2 versus V plot at high frequency was explained with the assumption that only some of the interface states follow the applied ac signal. Surface analysis by X-ray photoelectron spectroscopy (XPS) was performed in order to evaluate the chemical states of the constituents of the Al/Al2O3/PPy-NDSA/Au sample.