Gate-enhanced exciton-phonon coupling in photocurrent of (6,5) single-walled carbon nanotube based visible sensing field effect transistor

A visible sensing field effect transistor (FET) with a channel length of 100 nm for individual (6,5) single-walled carbon nanotubes (SWCNTs) is fabricated via a selective sorting method using 9,9-dioctyfluorenyl-2,7-diyl–bipyridine (PFO–BPy) polymer. The FET of the (6,5) SWCNTs shows p-type behavior with hundreds of on-off ratios and on-state conductivity of 50 ± 4.0 (Ω m)⁻¹. In addition, the photocurrent of the FET of the (6,5) SWCNTs in the visible range increases (maximum 200 times at 620 nm) with higher gate voltage. E₂₂ transition and PFO-BPy transition are observed in the FET of the (6,5) SWCNTs without application of a gate voltage. Interestingly, exciton-phonon coupled E₂₂ transition due to gate-doping (p-type), which has been reported in photoluminescence and absorption studies, is expected to occur in the photocurrent of the FET at negatively higher gate voltage (≤−4 V). In addition, the exciton-phonon coupled E₂₂ transition is prominently observable when carrier concentration by gate doping becomes approximately two-hundred sixty times (260 ± 43) larger than carrier concentration without application of a gate voltage. This demonstration would be useful for the development of SWCNT-based visible sensors with gate control in the SWCNT devices.