Fabrication and electrical characterization of polyaniline/silicon carbide heterojunctions

We report on the fabrication of silicon carbide/polyaniline heterojunctions produced by spin coating of polyaniline films onto n-type 6H-SiC and 4H-SiC substrates. Atomic force microscopy was used to estimate the surface roughness, and their electrical characteristics were investigated by means of current, capacitance and conductance measurements as a function of frequency and voltages. Reproducible characteristics and rectification ratios as high as 2 x 10(6) at +/- 2V for the 6H-SiC based heterojunctions were obtained. The devices were modelled as Schottky diodes with series resistance and an oxide interfacial oxide layer to account for interface traps. By analysing the forward bias I-V characteristics, we found that the interface trap density for 4H-SiC/PANI heterojunctions is approximately one order of magnitude higher than for 6H-SiC/PANI heterojunctions, which is consistent with previous studies on SiC/SiO2 interface traps. The average value of interface trap densities for 6H-SiC devices was 8.4 x 10(11) eV(-1) cm(-2) and for 4H-SiC it was 2.7 x 10(13) eV(-1) cm(-2). These values are in the range of previous reports on Schottky diodes with polymer layers.