We investigate rubrene single-crystal field-effect transistors, whose stability and reproducibility are sufficient to measure systematically the shift in threshold voltage as a function of channel length and source-drain voltage. The shift is due to space-charge transferred from the contacts, and can be modeled quantitatively without free fitting parameters, using Poisson's equation, and by assuming that the density of states in rubrene is that of a conventional inorganic semiconductor. Our results demonstrate the consistency, at the quantitative level, of a variety of recent experiments on rubrene crystals, and show how the use of FET measurements can enable the determination of microscopic parameters (e.g., the effective mass of charge carriers).
@article{arxiv.0905.1067,
title = {Threshold voltage and space charge in organic transistors},
author = {I. Gutiérrez Lezama and A. F. Morpurgo},
journal= {arXiv preprint arXiv:0905.1067},
year = {2009}
}