Contact effects and extraction of intrinsic parameters in poly(3-alkylthiophene) thin film field-effect transistors

Abstract

We report on contact effects in polymeric thin film transistors based on poly(3-octylthiophene) and poly(3-hexadecylthiophene) with gold contact electrodes and in the bottom contact configuration. A method to extract the intrinsic channel mobility from the measured extrinsic mobility over a broad range of gate voltage is presented. This method uses the I-V characteristics of the transistor in its reverse mode operation. The results show that the intrinsic mobility in the channel is gate voltage dependent and increases almost linearly with voltages at biases above the threshold voltage. By applying a model based on the theory of space-charge-limited conduction, the dependence of the threshold voltage on the contacts and the shifts observed in this parameter with different polymer film thicknesses are explained. We also apply this model to explain the effects of light in reducing the contact effects and changing the device parameters from extrinsic in the dark to intrinsic under illumination.

Experimental and numerical analysis of channel-length-dependent electrical properties in bottom-gate, bottom-contact organic thin-film transistors with Schottky contact

“…For understanding the operation mechanism and evaluating properly the potential of semiconductor materials toward the performance improvement of the OTFTs, the reliable characterization methods for the parasitic resistance and real channel resistance have been demanded, and actually various extraction procedures of physical parameters on carrier transport in the OTFTs have been proposed [5][6][7][8][9]. Transfer (or transmission) line method (TLM) is the most widespread technique utilized by many research groups to separately estimate the parasitic resistance and the channel resistance [10][11][12][13][14][15][16], where data plots of the total resistance given by the ratio of the drain voltage and the drain current over the channel length have to reveal linear relationships for each gate voltage.…”

Compact Modeling of Organic Thin-Film Transistors with Solution Processed Octadecyl Substituted Tetrabenzotriazaporphyrin as an Active Layer

“…In previous works [20], [25], [26] It is observed experimentally that output characteristics measured in OTFTs with contact effects show linear or quadratic behaviors at low drain voltages [18], [25]. Therefore, the I D − V S relation can be approximated by the respective relations:…”

“…Nevertheless, significant efforts have been spent in recent years to include the charge transport in organic semiconductor, which is clearly different from the transport in crystalline semiconductors, and is usually modeled with a gate-voltage dependent mobility [11], [12], [13], [14], [15]. They can also include detrimental effects produced by the contact region of the organic transistors [16], [17], [18], [19]. These models are also associated with methods to extract their respective parameters from the output characteristics of a transistor.…”

Contactless charge carrier mobility measurement in organic field-effect transistors

“…Then the contacts do not absorb or inject any charges and do not play a role in the AC measurement. With this condition fulfilled, this method differs fundamentally from conventional impedance measurements in which the source and drain do need to absorb and inject charge [31][32][33][34][35]. …”

“…The HOMO and LUMO levels of PDPPTPT were earlier determined with cyclic voltammetry to be À5. 35 and À3.53 eV, respectively [29]. Based on these numbers, a hole injection barrier may be expected when using solvent cleaned gold and not when using plasma cleaned gold.…”