Measurements and modelling of the barrier heights and ideality factors in the metal/conducting polymer composite Schottky device

Abstract

Metal/polymer Schottky contacts have been fabricated using electrochemically prepared free standing thin films of conducting polyaniline/polycarbonate composite as well as conducting polyaniline pellets with various metals such as Al, In, Pb and Sn. The current–voltage characteristics have been studied from room temperature down to 100 K. The data have been analyzed and interpreted on the basis of the thermionic emission mechanism. The barrier height varies from 0.6 to 0.7 V for pellet and from 0.7 to 0.8 V for composite films. There is little dependence of metal on the work function. The ideality factor is dependent on the amount of polyaniline incorporation in polycarbonate, as indicated by the shift in the carbonyl peak in the Fourier transform infrared spectrum. The abnormal decrease in barrier height and increase of ideality factor with decrease in temperature have been interpreted assuming a Gaussian distribution of barrier heights at the interface. This takes account of the nonuniformity and inhomogeneities at the interface. As in the case of inorganic semiconductor diodes, the analysis indicates an apparent decrease in zero bias height and nonlinearity in activation plots. The bias dependence of barrier height and standard deviation causing an increase in ideality factor at low temperature has also been explored.