Quantitative analysis of density-dependent transport in tetramethyltetraselenafulvalene single-crystal transistors: Intrinsic properties and trapping

We perform a combined experimental and theoretical study of tetramethyltetraselenafulvalene (TMTSF) single-crystal field-effect transistors, whose electrical characteristics exhibit clear signatures of the intrinsic transport properties of the material. We present a simple, well-defined model based on physical parameters and we successfully reproduce quantitatively the device properties as a function of temperature and carrier density. The analysis allows its internal consistency to be checked, and enables the reliable extraction of the density and characteristic energy of shallow and deep traps in the material. Our findings provide indications as to the origin of shallow traps in TMTSF transistors.

Figure 1

(Color online) (a) Chemical structure of TMTSF molecule. (b) Schematic cross section of our PDMS-based TMTSF transistors. (c) Optical microscope image of a TMTSF PDMS FET (the separation between source and drain is $300\mu \text{m}$).

Figure 2

Panel (a) shows the source-drain current, measured at room temperature, as a function of gate voltage, for two values of source-drain voltage ($V_{SD}=1$ and 3 V). Panel (b) shows the source-drain current as a function of source-bias voltage, for different values of $V_G$ (from $-1$ to $-19\text{V}$, in $-2\text{V}$ steps). These measurements were taken on device S1 whose mobility and threshold voltage data are shown in Fig. 4.

Figure 3

(Color online) Transfer characteristics $\left(I_{SD}\text{−}{V}_G\right)$ measured on a high-quality TMTSF single-crystal FET, at different values of temperature. The inset shows the gate-voltage dependent mobility extracted from these measurements. These measurements were taken on device S1 whose mobility and threshold voltage data are shown in Fig. 4.

Figure 4

(Color online) In panels (a) and (b), the symbols represent the temperature dependent mobility (a) and threshold voltage (b) measured on three different devices. The solid lines represents the result of our model, using the parameters listed in Table ; the red and black lines are obtained using a constant and a Gaussian density of shallow traps, respectively.

Figure 5

(Color online) In panels (a) and (b), the symbols show the mobility extracted from FET measurements as a function of carrier density at different temperatures, on devices 1 and 3. The solid lines are calculated using the parameter values extracted from the fits shown in Fig. 4 (no other parameters need to be introduced). For device 2, a similar agreement between data and model is obtained.