In-crystal carriers in organic single crystal transistors

The intrinsic semiconductor character of organic semiconductors, consisting of one molecular species, causes peculiar features different from those of doped inorganic semiconductors, when they are built in field-effect transistors (FETs). The effect can be most drastic with purified organic single crystal devices because of their minimized impurity (defect) concentrations of $\sim $ 10$^{14}$ cm$^{-3}$, resulting in relatively long length scale (more than 1 $\mu $m) of band bending and carrier distribution in the direction of the crystalline thickness. In this presentation, we report effects of the in-crystal carriers in two FET structures of clean rubrene single-crystals with the thickness comparable to the length scale of the distribution. With a double-gate device incorporating two transistor structures on the both sides of the crystal, we found that each transistor cross-talks with each other, inducing high-mobility (higher than 30 cm$^{2}$/Vs) carriers inside the crystal. The similar cross-talking events are observed also for a device with an acceptor layer of F$_{4}$-TCNQ on one side of the rubrene crystal.