Field-effect mobility table

That the main effect of the enhanced conductivity by higher structural order is the enhanced mobility is corroborated by measurements of field effect mobilities (Table 10) [100, 132, 333, 334, 342-346], although field effect mobilities are lower if compared to intrinsic mobilities due to parasitic series resistances in short channel devices [347][348] and channel length shortening [348, 349]. Today thin films can be prepared in which the mobility of a-6T films nearly meets that of single crystals and... 

Another significant feature found recently is that the effect of the chain length on the field-effect mobility is much less pronounced than indicated in earlier reports [68, 74]. The increase from 4T to 6T corresponds to about a factor of ten, while that from 6T to 8T is only two (the low mobility measured for the dihexyl-substituted 8T must be ascribed to the difficulty in synthesizing and purifying this compound 75 J). Representative data arc gathered in Table 14-1. Also note that the effect of alkyl end substitution is reduced by a factor of two to three (as compared to up to 1000 in earlier reports 68 ). 

Table 14-1. Typical field-effect mobility (in cm2 V 1 s ) of unsubsliluled and dialkyl-subsliluled oli-gothiophenes.

Table 8.2 Field effect hole mobilities //, threshold voltages Fj, and channel lengths L of the samples A to F (see Table 1). The values were determined according to method A. denotes the thermal activation energy of the field effect mobility determined from the slopes of the plots in Figure 8.8.

Table 3.1.1 contains field-effect mobilities and on/off ratios. 

Field effect mobilities were also determined by these two groups (Table 13.6) [68,246-250], From this it can be deduced that the mobility is also enhanced by higher structural order due to alkyl-substitution but also by the chain-length. 

Table 13.9. Field effect mobility of a6T-based FETs influence of gate insulator. Reproduced from [288] with kind permission of Elsevier publishers...

Table 7.3. Field-effect mobility and threshold voltage of 6PTTP6 FET before and after exposure to DMMP vapor...

The field-effect mobility values are listed in Table I, together with the one recently reported by S. Hotta et al. on the very similar ct,a) dimethyl sexithiophene using a Si02 insulating layer.23 The agreement of field-effect mobilities, determined independently for alkyl substituted sexithiophene, brings a clear confirmation of the considerable... 

Table 2.1 Summary of previous work on effect of side-chain length on field effect mobility for regioregular poly(3-alkylthlophene)s...

Oligomers based on 4,4-difluorocyclopentadithiophene repeat units exhibit n-type semiconducting behavior [109]. The maximum field effect mobility (0.018 cm V s ) was obtained for a quaterthiophene compound furnished with perfluorohexyl end groups (entry 35, Table 3.1). 

A regioregular homopolymer of 3-nonylthieno[3,2-Z>]thiophene was also prepared (Table 17.1, 10) however the molecular weight was low and no evidence of thermal transitions was observed by DSC [51]. Charge transport characteristics were not reported. The homopolymer of 3,6-dimethoxythieno[3,2-f>]thiophene [53] and copolymers of 3,4-dialkoxythieno[2,3-f>]thiophene [54] have recently been reported as a possible alternative to the conducting polymer ethylenedioxythiophene (PEDOT). Co-polymers of thieno[3,2-Z>]thiophene [55-57] and thieno[2,3-f>]thiophene [58] with 9,9-dialkyl fluorene have also been reported for both transistor and OLED applications. In the case of the thieno[3,2-b]thiophene copolymer, the polymer exhibited thermotropic liquid crystalline behavior with a nematic phase at high temperature [59]. p-Type field effect mobilities in transistor devices were on the order of 1 x 10 cm V s . Although the value is on the low side of acceptable performance, a comparison to the well-studied... 

Table 5.2-26 Field-effect mobilities of semiconductors. References to original papers are given in [2.47]...

The very low field effect mobilities reported in Table 5.2-26, show that the Fermi level is pinned in the gap because of the large concentration of surface states. Pinning positions of the Fermi level with respect to the top of the valence band at the surface are given in Table 5.2-27 for various semiconductors. 

Table 2. Field-effect mobilities for samples deposited at different substrate...

Table 4. Summary of field-effect mobilities (cmWs) for different substituted...

Conductivities of unsubstituted molecules are summarized in Table 11, field effect mobilities can be taken from Table 10. In older papers a strong dependence of the mobility on the chain-length was found [342, 343, 354, 355] although a nearly independent mobUity is expected. From newer data [100, 333, 334, 356] this independence can really be determined. Therefore the older data are masked by structural disorder and/or impurities. The decrease in mobility observed for a-8T and polythiophene may also stem from an increase of conjugation defects. The lack of field effect in a-3T can be explained because this chain is regarded to be too short to bear a radical cation but extrapolation of data obtained in a-3T/polycar-bonate mixtures with different a-3T concentrations to the pure oligomer yield /i = 3.3 X IQ- cm V- s [357]. 

Table 1. Dependence of the field-effect mobility of oligothiophenes as a function of chain length and alkyl substitution at end position.

Table 2. Recent data on the field effect mobility of unsubstituted and alkyl substituted oligothiophenes.

Two methods have been shown useful in lowering the off-current while keeping the field-effect mobility almost unchanged [84]. In the first method, the films were treated with ammonia by bubbling N2 through ammonium hydroxide aqueous solution (see Table 2 entries 7 and 14). It was also found that thermal treatments such as heating the samples under N2 at 100°C for 5 min can lower off-currents (see Table 2 entry 11). However, heating to 150 "C lowers the mobility dramatically. 

Table 2. Field-effect mobilities and on/off ratios of regioregular PHT transistors preapred from different conditions. Condition 1, cast, vacuum pumped for 24 hours Condition 2, spin-coated Condition 3, treated with NH3 for 10 h Condition 4, heated to 100°C under N2 for 5 min Condition 5, heated to 150°C under N. for 35 min [84], Reprinted with permission from Ref 84. Copyright 1996. American Institute of Physics.

Fig. 2 The evolution of the hole field-effect mobility of various organic semiconductors in time. The data of Table 1 are grouped into families of molecules with similar main chain. Additionally, hole field-effect mobilities of rubrene and pentacene in single crystals are depicted. For comparison, the electron mobilities of a-Si H and poly-Si are shown...

A pentacene OFET where a Si02 gate dielectric has been implemented, shows typically decent p-channel behavior with field-effect mobilities exceeding 0.1cm V [60] while a lack of any electron conduction is usually observed. This disparity in the n- and p-type behavior is also mirrored in Fig. 8 where exem-plarily the evalution of the electron and hole field-effect mobilities of pentacene over the last 15 years is depicted. Respective data are listed in Table 2. While from the year 1992 up to now the hole field-effect mobility in pentacene steadily increased from 0.002 to 5cm V s the first signature of electron transport in field-effect transistors was not found before 2003 [35]. Nowadays, comparable field-effect mobilities for electrons and holes are obtained in transistors comprising polycrystalline pentacene [60, 61]. 

Fig. 8 The evolution of the electron and hole field-effect mobility of pentacene in time. For comparison, the electron mobility of a-Si H is shown. The data are listed in Table 2...

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