Oxygen-Related Doping Effects in Single Crystalline Rubrene Field-Effect-Transistors

We report the first measurements of oxygen-related doping effects in rubrene single crystals. We can successfully introduce oxygen-related bandgap states into crystalline rubrene by annealing in oxygen at 380K. The induced bandgap states are stable in vacuum at room temperature. We also find that vacuum annealing at 380K removes the induced dopant states. The oxygen-related states cause threshold voltages to decrease significantly while the field-effect mobilities are not affected by the localized gap states.