Hall Effect in the Accumulation Layers on the Surface of Organic Semiconductors

We have observed the Hall effect in the field-induced accumulation layer on the surface of single-crystal samples of a small-molecule organic semiconductor rubrene. The Hall mobility ${\mu }_{\mathrm{H}}$ increases with decreasing temperature in both the intrinsic (high-temperature) and trap-dominated (low-temperature) conduction regimes. In the intrinsic regime, the density of mobile field-induced charge carriers extracted from the Hall measurements, $n_{\mathrm{H}}$, coincides with the density $n$ calculated using the gate-channel capacitance and becomes smaller than $n$ in the trap-dominated regime. The Hall data are consistent with the diffusive bandlike motion of field-induced charge carriers between trapping events.