P-channel materials

Typical DHa6T OTFT I-V characteristics are reported in figure 3. The curves are relevant to OTFT of different channel length, namely 1 and 0.2 mm. The square root of I vs. Vg curves are reported as inset of the figures as well (figures 3a and 3b insets). The devices were tested as p-channel materials and the field effect mobilities in saturation regimes were extracted using the well-know equation [10] ... 

Soluble derivatives of fused aromatic systems are not limited to p-channel materials however, they are far fewer in number. A soluble derivative of NTCDA has recently been developed that can be cast from a,a,a-trifluorotoluene (Figure 5.3.lid) [66]. Devices prepared from this derivative showed electron mobilities of 0.01 cmWs [67]. This is currently the only nonfullerene solution-cast n-channel material. 

HOMO of DBTTF and the LUMO of TCNQ, respectively (Fig. 4b). Source and drain electrodes are several organic metals of the TTF TCNQ type having different chemical potentials predicted using Fig. 4c which is the same as Fig. 2a. For the electrodes whose chemical potentials are set within the conduction band of the channel material, FET exhibited n-type behavior (A in Fig. 4d). When the chemical potentials of organic metals are allocated within or near the valence band of the channel, p-type behaviors were observed (E, F in Fig. 4d). When the chemical potentials of the electrodes are within the gap of the channel, FET exhibited ambipolar-type behavior (B-D in Fig. 4d). Since the channel material is the alternating CT solid, the drain current is not excellent and a Mott type insulator of DA type or almost neutral CT solid having segregated stacks is much preferable in this context. 

Figure 5.25 shows the FET characteristics of a device in p-channel mode with MDMO-PPV as the channel material. Figures 5.25a and b show the situation for MDMO-PPV spin-cast from a toluene solution. The hole current... 

The usual TFT structure is shown in Fig. 10.7 and comprises the a-Si H channel, a gate dielectric, and source, drain, and gate contacts. N-channel accumulation mode operation using an undoped a-Si H channel is the only structure widely used. Depletion mode devices are prevented by the high defect density of doped material, which makes it difficult to deplete the channel. The much lower mobility of holes compared to electrons gives p channel devices a lower current by about a factor 100, which is undesirable. 

The area on the surface of the p-type material between the drain and the source is called the channel (see the dark shaded area in Figure 21 F-2a). Note that the channel is separated from the gate connection by an insulating layer of Si02- When an electrical potential is applied between the gate and the source. 

It is remarkable, however, that despite a roughness which is larger than the film thickness in some of our films (see below), all of them show n-channel as well as p-channel transport. Obviously, there still exists a percolation path for conduction in both materials independent of phase separation and order formation. We also note that the bulk morphology does not necessarily provide precise information for organic ficld-cffcct transistors since in these devices the active channel is restricted to the first few molecular layers at the interface to the gate dielectric [48-50]. 

Besides semiconducting SWCNTs, properly doped diamonds can also be nsed as the channel material for fabricating FETs for biosensing as demonstrated by Song et al. [75]. DNA probes are immobilized directly on the aminated snr-face of a p-type polycrystalline diamond film which serves as the conduction channel between the source and drain electrodes. Since a diamond surface is chemically stable and presents a wide potential window, it permits direct contact of biomolecules with the channel surface, eliminating the needs of a polymer coating (in CNT FETs) or dielectric encapsulation (in Si-FETs). As a result, diamond FET is potentially a much more sensitive and faster biosensor, which can operate in solution. Hybridization with complementary and 3-mer mismatched DNA targets in 10 pM can be discriminated in cyclically repeated hybridization and denatnre experiments. 

If 6 x 1016 cm 3 boron atoms are implanted in the gate region of the p-channel MOSFET fabricated on <111> oriented n-type material with Nj) 1015 cm 3, the compensated results yields ... 

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