New growth method of rubrene single crystal for organic field-effect transistor

A rubrene single crystal, for the active material of an organic field-effect transistor (OFET), was directly grown from a rubrene powder in the single growing zone of a furnace, which is different from a conventional organic vapor transport method for the crystal growth. The growth time of the needle-shaped rubrene single crystals was ∼30 min without any purification process. Structural properties and the geometrical shape of the rubrene single crystals were characterized through a single crystal X-ray diffractometer and a scanning electron microscope. The rubrene single crystal OFETs were fabricated through both the bottom and top contact methods. The Si₃N₄ and polymer were used for a gate insulator in the bottom and top contact OFETs, respectively. From the current-voltage characteristics of the OFETs, a typical p-type transistor nature was observed. The mobility of the top contact OFETs was measured to be ∼1.12 cm²/V s, which was approximately seven times higher than that of the bottom contact OFETs, because of the direct contact of the rubrene single crystals with both Au electrode and polymer gate insulator.