Influence of interface modifications on carrier mobilities in rubrene single crystal ambipolar field-effect transistors

Carrier mobilities in ambipolar field-effect transistors (FETs) are studied using a rubrene single crystal assembled with Au/Ca electrodes and $SiO2$ gate insulators modified by polymethylmethacrylate (PMMA), parylene-C, and hexamethyldisilazane (HMDS). The experimental results are interpreted in terms of the two interfacial efficiency parameters, the injection, and the transport efficiencies. The efficiency of electron carrier injection can be evaluated using Au–Au and Au–Ca electrodes. The efficiency of electron carrier transport was compared among the device with PMMA, parylene-C, and HMDS modification layer. The shallow trap density at the semiconductor-gate dielectric interface is shown not to be the most important factor for controlling FET mobilities. Instead, the surface polarization associated with the surface molecular structure is proposed to be another possible parameter. Furthermore, the shift of light emitting with applied gate voltage was observed in a device with PMMA modified insulator and Au–Ca asymmetric metals.