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Reversible memory effects and acceptor states in pentacene-based organic thin-film transistors
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Image of FIG. 1.
FIG. 1.

Transfer curves with (mostly in the linear regime), swept in both directions, of a typical device with and , under four conditions. Strongest hysteresis was observed in air under illumination, while only minimal hysteresis in the dark dry box. In the on state, on-to-off swept curves always well resemble straight lines, suggesting bias-insensitive mobility. Moreover, this mobility is not affected by testing condition. Inset: The structure of OTFTs under study.

Image of FIG. 2.
FIG. 2.

Time domain measurement data of a device taken in ambient air and under ambient room illumination for various . For all measurements, .

Image of FIG. 3.
FIG. 3.

Time domain measurement data and fitting functions. (a) Device under test in ambient air and under ambient room illumination. Two measurements ( for both) with and are presented. The large difference in between the two is due to multiple time domain measurements performed prior to the measurement as well as between the two, which significantly shifted first in the positive and then in the negative direction. (b) Device under test in the dry box in the dark, , . (c) In air in the dark, , . (d) In the dry box with illumination, , . Panels (b), (c), and (d) are on the same scale while (a) is different. The value of is chosen for each measurement to ensure that the device operates in a region where is linear. The data in (b) fit well to a stretched exponential representing the bias stress effect, indicating the absence of the concerned acceptor states. Amplitudes of the decay processes in (c) and (d) are significantly lower than in (a). All these tested OTFTs exhibit linear regime extracted field effect mobilities of .

Image of FIG. 4.
FIG. 4.

Intermediate results of fitting the data of Fig. 3(a) to illustrate the fitting procedure. (a) Values of , the total drain current decay, on the log-log scale, along with the stretched exponential fit to the contribution from the bias stress effect, , showing that the fitting is good for , validating the choice of fitting to the stretched exponential for (shaded area). The deviation at is due to the exponential decays. (b) Values of , the contribution of the excess hole population decay to the current decay, along with the first order exponential decay fit, . For , the first order exponential decay fits well, while the deviation at is due to faster decay processes to be further fitted. The fitting was done for (shaded region).

Image of FIG. 5.
FIG. 5.

Drain current decay behavior of a typical pentacene OTFT solely due to the stress bias effect. Measured data (symbol) are shown as , where and are parameters in Eq. (3). The fit to Eq. (3) is also shown (line). Plotting vs on the log-log scale reveals excellent fit in detail and shows that the power-law approximation is not good for .

Image of FIG. 6.
FIG. 6.

Decay time constant “spectrum” of , the contribution of exponential decays to the total drain current decay, in the data of Fig. 3(a), as calculated by a chi-square fit with fixed . The result serves as a consistency check for the graphic and modified Prony methods. The shoulder at indicates two merged peaks.


Generic image for table
Table I.

List of fitting parameter values in time domain measurement data analysis along with derived quantities.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Reversible memory effects and acceptor states in pentacene-based organic thin-film transistors