The authors report the fabrication and characterization of tetracene single-crystal field-effect transistors (FETs) utilizing an air or vacuum gap as the gate dielectric. The linear mobility of the device can be as high as 1.6 cm2/V s in air, with a subthreshold slope lower than 0.5 V nF/decade cm2. By changing the orientation of the same crystal on the air-gap substrate, surface charge transport along different crystallographic directions was measured. There is pronounced anisotropy in the mobility; temperature dependent measurements show the mobility is activated (in contrast to air-gap FETs based on rubrene) and that the activation energy is independent of transport direction. Gate electrode displacement current was also recorded for these devices, allowing accurate determination of the gate induced surface charge and the fraction of trapped charge.
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The authors thank Etienne Menard, Bryan Olmsted, and Yan Liang for helpful discussion. This work was partially supported by the NSF Materials Research Science and Engineering Center Program (DMR-0212302). Support also came from the US Department of Energy, Office of Basic Energy Sciences.