Organic semiconductors/insulators

We have used the bottom contact structure with the gate at the bottom and source-drain contact at the top. The fabrication of the structure is explained in detail in Sect. 3.2 after a short discussion of the organic semiconductor, insulators, and self-assembled monolayers (SAMs) for surface treatment in that order. 

So it seems to be the task to identify an appropriate and easily applicable modification of a suited organic semiconductor/insulator combination together with the right choice of the source/drain metals in order to convert an ambipolar OFET to either a p-type or n-type OFET and/or even to an organic CMOS device. 

To understand the reason for the initial absence of electron transport in pentacene based OFETs let us consider the results of impedance measurements on MIS-diodes based on a Ca/pentacene/Si02/p -Si layer stack analog to the typically used OFET device structure [46, 62]. In Fig. 9 a differential capacitance measurement is shown where Cdiei is the capacitance of the Si02 dielectric, while Cm stands for the total device capacitance of the organic semiconductor/insulator bilayer. 

The highly conductive class of soHds based on TTF—TCNQ have less than complete charge transfer (- 0.6 electrons/unit for TTF—TCNQ) and display metallic behavior above a certain temperature. However, these soHds undergo a metal-to-insulator transition and behave as organic semiconductors at lower temperatures. The change from a metallic to semiconducting state in these chain-like one-dimensional (ID) systems is a result of a Peieds instabihty. Although for tme one-dimensional systems this transition should take place at 0 Kelvin, interchain interactions lead to effective non-ID behavior and inhibit the onset of the transition (6). 

Ultrathin metallic, semiconductor, insulator, or organic overlayers can be deposited on SERS-active metal surfaces. 

Figure 29. For the latter case, it is considered that the semiconducting re-electron systems are separated by insulating hydrocarbon spacers, resulting in alternate thin layers of organic semiconductor and insulator in these monolayer assemblies. The direct current - voltage (I - V) characteristics were mea- sured for the multilayers H2Pc(R)8 and Cu-Pc(R)8 in directions perpendicular and parallel to the film plane. In both cases, the linear I - V relationships of Ohm s law were observed at low electric field and obtained DC conductivities are summarized in Table 3. The normal conductivity (ajJ were ca. 10 13 S cm-1, while the lateral ones p//) were 3.4 x 10-7 and 9.9 x 10 7 S cm 1 for films of the metal-free and copper Pc derivatives, respectively. The former (ojJ tended to decrease slightly with increase of Figure 29. Schematical illustration of the substituent alkyl chain length,...

Table 6.1. Values of fi. h for selected organic semiconductors and insulators as active components ofOFETs...

III), were prepared by Kim et al. (4) and used in gate electrode, a gate insulating layer, an organic semiconductor layer, and in source/drain electrodes applications. 

Semiconductors are materials that are characterized by resistivities intermediate between those of metals and of insulators. The study of organic semiconductors has grown from research on conductivity mechanisms and structure—property relationships in solids to include applications-based research on working semiconductor junction devices. Oiganic materials are now used in transistors, photochromic devices, and commercially viable light-emitting diodes, and the utility of oiganic semiconductors continues to increase. 

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