Impedance spectroscopy study of an organic semiconductor: Alizarin

The electrical properties of alizarin, a pi-conjugated organic semiconductor, were investigated by the complex impedance spectroscopy technique. A transition from semiconducting to conducting state has been observed and the transition temperature shifts to higher side with the increment in frequency. The dielectric relaxation was found to be of non-Debye type (polydispersive). Evidences of temperature-dependent electrical relaxation phenomena as well as negative temperature coefficient of resistance (NTCR) character of the sample have also been observed. The AC conductivity obeys the power law and the dispersion in conductivity was observed in the lower frequency region. Also, the frequency-dependent AC conductivity at different temperatures indicated that the conduction process is thermally activated process. The activation energy, density of states at Fermi level and number of pi-electrons per molecule has been estimated from AC conductivity temperature data and was found, respectively, to be 0.78eV, 1.2 x 10(19) cm(-3) eV(-1) and 25. Modulus analysis has indicated the possibility of hopping mechanism for electrical transport processes in the system with non-exponential-type conductivity relaxation. (c) 2006 Elsevier B.V. All rights reserved.