Temperature dependence of the Hall effect is measured for both single-crystal and thin-film field-effect transistors of pentacene. At room temperature, the inverse Hall coefficient $1/R_H$ exceeds field-induced charge density $Q$ by a factor of 2 at each gate-electric field for all the samples, regardless of their charge-carrier mobility and detailed subthreshold properties. Violating the band-transport model that $1/R_H$ equals to $Q$, the excess $1/R_H$ does not measure the charge amount anymore so that the result possibly indicates insufficient electromagnetic coupling due to somewhat reduced charge coherence. At lower temperatures, the deviation of $1/R_H$ from $Q$ gradually diminishes to approach the band-transport behavior. Interestingly, the degree of the deviation has been universal for the measured five samples, including both polycrystal and single-crystal pentacene films. The result suggests that significant molecular fluctuation near room temperature can affect the fundamental electronic state.

• Received 28 April 2011

DOI:https://doi.org/10.1103/PhysRevB.85.035313