Field-effect transistors on tetracene single crystals

Abstract

We report on the fabrication and electrical characterization of field-effect transistors at the surface of tetracene single crystals. We find that the mobility of these transistors reaches the room-temperature value of 0.4 cm 2 /V s. The nonmonotonous temperature dependence of the mobility, its weak gate voltage dependence, as well as the sharpness of the subthreshold slope, confirm the high quality of single-crystal devices. This is due to the fabrication process that does not substantially affect the crystal quality. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1629144͔Common strategies for the fabrication of organic fieldeffect transistors ͑FETs͒ are based on thin-film technology. 1,2This choice is motivated by the existing deposition techniques for organic thin films that facilitate device fabrication. At the same time, thin films usually contain a considerable amount of structural imperfections, which affect negatively the transistor performance. 3For small organic molecules, crystalline films can be used to reduce the amount of structural defects. It has been found, however, that also the performance of transistors based on these films are affected by structural imperfections, even when only one crystalline grain is present between the source and drain.4 This is due to disorder present in the first few molecular layers, in contact with the substrate, which constitute the device active region.5 For this reason, improving the quality of organic thin-film transistors ͑TFTs͒ requires highly ordered molecular films, in which the order extends up to the interface with the substrate.An alternative route to the production of high-quality organic FETs is to fabricate devices on the surface of a freestanding single crystal of organic molecules. If a fabrication process that preserves the quality of the crystals 6,7 can be developed, the resulting single-crystal FETs should perform better than their TFT counterpart. Whereas considerable amount of work is currently aiming at improving the quality of organic TFTs, 2,4,5,8,9 the investigation of single-crystal organic FETs has received only limited attention. [10][11][12][13][14] In this letter, we discuss the fabrication and electrical characterization of field-effect transistors at the surface of tetracene single crystals. The fabrication process is based on adhesion of pregrown, free-standing crystals to a thermally oxidized Si wafer on which source and drain electrodes are deposited in advance. As we will show, this process preserves the quality of the starting crystals. From the electrical evaluation of a large number of devices we find that the mobility of the charge carriers ͑holes͒ in our single-crystal FETs is reproducibly high, reaching 0.4 cm 2 /V s in the best device. In addition, the observed temperature and gate voltage dependence of the mobility as well as the subthreshold slope indicate that the performance of single-crystal devices compares well to the best existing organic thin film transistors. 3The FET fabrication involves two main steps: th...

Large surface relaxation in the organic semiconductor tetracene

“…11 We should, however, mention that this estimate is at most the semi-quantitative one. There are many other models that are used to determine the mobilities of organic crystals, but discussing the quality of each of the theoretical models is beyond the scope of this study.…”

“…Therefore, the surface of single crystals is of importance. Structural information pertaining to the crystal surface is useful to better understand bulk properties, as the mobility, the standard measure of the performance of an organic semiconductor, is evaluated by fabricating OFETs [9][10][11] , which is actually the surface mobility 4 . Also, the transport properties in polycrystalline samples are largely affected by scattering at the grain boundaries, which certainly is related to the detail of the interfaces; the knowledge of the surfaces is in fact important as a first step.…”

Photoinduced Charge Transfer across the Interface between Organic Molecular Crystals and Polymers

“…To study the charge transfer between an organic semiconductor and a polymer, we have used the field-effect structures based on organic molecular crystals (OMC) [8,9,10,11]. High quality of the OMC surface facilitates fabrication of reproducible and well-characterized interfaces 3 between OMC and a polymer parylene used as the gate dielectric in these devices.…”

Intrinsic Charge Transport on the Surface of Organic Semiconductors

“…Fabrication of the single-crystal organic field-effect transistors (OFETs) (see, e.g., [6,7,8]) provides an opportunity to study the charge transport on the organic surface with significantly reduced disorder. It also offers a possibility to explore the regime of high charge densities, many orders of magnitude greater than in the TOF experiments, which may lead to observation of new electronic phases.…”