Microscopic mechanisms behind the high mobility in rubrene single-crystal transistors as revealed by field-induced electron spin resonance

The microscopic mechanisms behind the very high mobility in rubrene single-crystal transistors achieved by interface treatments with self-assembled monolayers (SAMs) have been clarified by using field-induced electron spin resonance (FI-ESR). Clearly observed FI-ESR signals exhibit extremely narrow linewidths owing to the very high carrier mobility. The precise angular dependence of FI-ESR g values shows that crystallinity in the semiconductor channel is unchanged by the SAM treatments. The trapping time of charge carriers at the interface directly evaluated from the ESR linewidth greatly decreases from {~}700 to {~}60 ps concomitant with the remarkable improvement in mobility because of the SAM treatments.