Evidence of water-related discrete trap state formation in pentacene single-crystal field-effect transistors

Abstract

We report on the generation of a discrete trap state during negative gate bias stress in pentacene single-crystal “flip-crystal” field-effect transistors with a $\mathrm{Si}{\mathrm{O}}_2$ gate dielectric. Trap densities of up to $2\bullet {10}^{12}{\mathrm{cm}}^{-2}$ were created in the experiments. Trap formation and trap relaxation are distinctly different above and below $\sim 280\mathrm{K}$ . In devices in which a self-assembled monolayer on top of the $\mathrm{Si}{\mathrm{O}}_2$ provides a hydrophobic insulator surface we do not observe trap formation. These results indicate the microscopic cause of the trap state to be related to molecular layers of water adsorbed on the $\mathrm{Si}{\mathrm{O}}_2$ surface.