Recent experiments have demonstrated ambipolar channel conduction and light emission in conjugated polymer field-effect transistors (FETs). The devices have sourcedrain contacts fabricated using metals with different work functions. Negative charge carriers are injected from a low work-function metal contact and positive charge carriers from a high work-function contact. In the ambipolar mode of operation, the gate potential lies between the potentials of the electron and hole injecting contacts, so that electrons dominate the channel conductance near the electron injecting contact and holes dominate channel conductance near the hole injecting contact. The injected charge carriers propagate along the FET channel and recombine in regions where both types of carriers are present. The location and intensity of maximum recombination and light emission is controlled by the voltages applied to the transistor terminals. In this paper a device model for ambipolar organic field-effect transistors based on the gradual channel approximation is presented. The model includes the effect of charge carrier trapping through density dependent mobilities. The resulting nonlinear differential equation for the channel potential is solved numerically. The results of the device model are in good agreement with the published experimental data.
Bibliographical noteFunding Information:
We thank A. J. Heeger for useful suggestions and discussions. The work at Los Alamos National Laboratory was supported by DOE Office of Basic Energy Sciences Work Proposal No. 08SCPE973.
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