Field-effect transistor hole mobilities

A polyacetylene field-effect transistor has been described622 but the response time is slow, apparently because the carrier mobility is low. An FET has been made from polythiophene but source-drain currents were less than 20 nA for drain voltages up to 50 V. The hole mobility was very low, calculated to be 2 x 10 5 cm2 V-1 s 1 623). 

Pentacene routinely yields field-effect transistor (FET) devices with reliable hole mobility of 1 cm2 V-1 s 1 [6], with mobility > 3 cm2 V-1 s-1 reported for thin-film devices on polymer gate dielectrics [9]. For transistors fabricated on single crystals of pentacene, the measured mobility approaches 60 cm2 V-1 s 1 [10]. 

Table 4.2. Highest hole mobilities from analyses of p-type organic field-effect transistors [23]...

Because of these fundamental difficulties in applying the time-of-flight method for arbitrary molecular materials, today most mobilities known for molecular materials have in fact been extracted from the electrical characteristics of organic field effect transistors. There are several methods to extract the electron and hole mobilities from the electrical device characteristics of an OFET. For a more thorough description of the different procedures, the reader is referred to the paper by Scheinert and Paasch [13]. 

Podzorov, V. et ah. Single-crystal organic field effect transistors with the hole mobility 8 cmW s,Appl. Phys. Lett., 83, 3504, 2003. 

FIGURE 2.3.9 Hole mobility as a function of charge carrier concentration in diode and field-effect transistors for P3HT and a PPV derivative. (From Tanase, C. et al., Phys. Rev. Lett., 91, 216601, 2003. Reprinted with permission. Copyright 2003, American Physical Society.)... 

Organic field effect transistor (OFET) devices have been fabricated from pBTTT polymer solutions and hole mobility values of up to 0.8cm /V s were reported in a nitrogen atmosphere. These values approach that of high performing evaporated small molecule devices and are comparable to amorphous silicon. In bottom gate, bottom-contact devices, in which the active semiconductor layer is the exposed top surface, the effect of different ambient conditions has been evaluated. Exposure to unpurified, ambient air in which the humidity is -50%, results in an initial increase in the off-current of the device. In filtered, low humidity air, transistor devices remain very stable over time. 

An ambipolar charge transport was observed in transistors based on HD-PPTV. In contrast, only a hole transport mechanism was observed in HD-PPPV. Field-effect transistors that were fabricated from HD-PPTV showed hole and electron mobilities of 0.2 and 0.03 cm V s Integration of the ambipolar HD-PPTV transistors into complementary inverters showed sharp switching characteristics with voltage gains up to 27. 

The field effect transistor method has also been applied for the determination of hole mobilities. For Spiro-TAD 56 in a top-contact structure field effect transistor (Fig. 29a), we measured an apparent mobility of 8 x 10 cm /Vs by evaluating the transfer characteristic in the saturation regime [112]. 

PTCDI-Ci3H27 and (b) device structure of bipolar field-effect transistor consisting of a coevaporated thin film of 5T and PTCDI-Ci3H27. (c) Electron (filled circles) and hole (filled squares) field-effect mobilities for different bulk-... 

The first demonstration of a polymer blend transistor with appreciable ambipolar mobUities was accomplished by Meijer et al. by blending poly(2-methoxy-5-(3,7-dimethyloctoxy)- p-phenylene vinylene) (OCiCio-PPV) and PCBM (Figure 16.12a) [13]. Here, the hole and electron mobilities reached 7 x 10 cm (V s ) and 3 x 10 cm (V s ), respectively. A representation of the interpenetrating network and cross-section of the field-effect transistor is presented in Figure 16.12a. For both materials the charge injection comes from... 

Zen et al. synthesized a pentathiophene-based swivel cruciform (76, Figure 16.33), which allows rotation between the cruciform arms [143]. Homogeneous microcrystalline films were processed from solution, and field effect transistors based on this dimer afforded hole mobilities up to 0.012 cm V s . Recently, Cravino et al. demonstrated that high hole mobilities can be obtained with an amorphous oligomer that contains a triarylamine (TAA) core with hexyl-terminated terthiophene arms (77) [144], Hole mobilities up to 0.01 cm V s were measured for vapor-deposited Aims. Furthermore, Saragi et al. compared the field effect mobility of a TAA oligomer series and their spiro-linked analogues [145], All compounds... 

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