Electrical conduction processes in semiconducting organic films has been a subject of great debate for a number of decades. There is a general agreement that the energy band models are inappropriate, for describing the electronic conduction in such materials. Several analytical transport models including the Gaussian disorder¹, multiple trapping and release², and variable range hopping³, have been proposed to describe the charge transport mechanism in organic semiconductors. Despite the differences in the analytical approaches, there is a general agreement that the charge carrier transport is governed by thermally assisted tunnelling or hopping between localised states. More needs to be done to unify the principle of electronic conduction in such materials, with the classical treatment of carrier flow in terms of carrier drift, diffusion and their relationships to Fermi and quasi-Fermi levels, and the slopes of these energies, which classically predict the flow of current in semiconductors and semiconductor devices. In this work, we present an analytical model, describing the conduction processes in disordered and polycrystalline organic Schottky diode, by employing the so-called Universal Mobility Law^4-6, on the exponential distribution of the intrinsic and extrinsic density of states. The Schottky barrier is possibly the only electrical method, which allows the study of both intrinsic and extrinsic regions, since the applied voltage moves the dopant energy level to the top of the barrier. From the analysis of the measured current of the organic disordered and polycrystalline Schottky barriers, key parameters such as the effective temperature associated with the distribution of the intrinsic and extrinsic states, and subsequently the Meyer-Neldel energy are extracted, and compared to those obtained from temperature analysis. Moreover, from the Arrhenius plots of the forward currents, the activation energies of the disordered and polycrystalline organic semiconductors are determined. The development of such models is essential in generating accurate simulation of the properties of the organic semiconductor devices, which subsequently predicts the circuit performance for mixed signal applications.

References

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[5] M. Raja et. al., IET Circ. Dev. Syst. 6(2), 122 (2012).

[6] M. Raja et. al., J. Appl. Phys. 112, 084503 (2012).