Prof Laura Herz FRS

Abstract:

We have used differential terahertz spectroscopy to monitor performance degradation in state-of-the-art polymer field effect transistors (pFETs) based on poly[(9,9-dioetylfluorene-2,7-diyl)-co-(bithiophene)] (F8T2). After extended periods of operation holes are trapped in the polymer, increasing the device's threshold voltage. We monitor the trapped charge density using THz spectroscopy, and investigate the device's recovery as trapped holes are thermally removed. Illuminating the devices for a period with above-bandgap photons leads to a change in the terahertz transmission through the device, which is short lived after switching the light off.

Abstract:

Research on polymer-based transistors is leading to the development of flexible, printable circuitry, which will be extremely cost effective to manufacture. However, the longterm performance of state-of-the-art polymer field effect transistors (pFETs) is limited by device degradation. We show that terahertz spectroscopy is an ideal tool to probe polymer device performance. Specifically we have monitored charge carrier trapping at the polymer-insulator boundary of a pFET. From these results we show that device degradation is primarily caused by a trapping of holes in the channel of the pFET, rather than by a change in hole mobility.