2003/12/07 by B. H. Hamadani, D. Natelson
Physics and Astronomy · #cond-mat.mes-hall
paper · pdf · doi:10.1063/1.1635979
published as J. Appl. Phys. 95, 1227 (2004). · 22 pages, 7 figures, accepted to J. Appl. Phys
arxiv created 2003/12/07 · arxiv updated 2009/12/01
We measure hole transport in poly(3-hexylthiophene) field effect transistors with channel lengths from 3 μm down to 200 nm, from room temperature down to 10 K. Near room temperature effective mobilities inferred from linear regime transconductance are strongly dependent on temperature, gate voltage, and source-drain voltage. As T is reduced below 200 K and at high source-drain bias, we find transport becomes highly nonlinear and is very strongly modulated by the gate. We consider whether this nonlinear transport is contact limited or a bulk process by examining the length dependence of linear conduction to extract contact and channel contributions to the source-drain resistance. The results indicate that these devices are bulk-limited at room temperature, and remain so as the temperature is lowered. The nonlinear conduction is consistent with a model of Poole-Frenkel-like hopping mechanism in the space-charge limited current regime. Further analysis within this model reveals consistency with a strongly energy dependent density of (localized) valence band states, and a crossover from thermally activated to nonthermal hopping below 30 K.