Photoluminescence of single-walled carbon nanotubes in field-effect transistors

We have studied the photoluminescence (PL) of individual single-walled carbon nanotubes (SWNTs) placed in field-effect transistor structures. The SWNTs were suspended in the air so that strong PL was obtained. When an external bias voltage was applied to the device, no spectral changes could be detected, but the intensity drastically increased or decreased. This behaviour is explained by the injection/extraction of carriers from/to the electrodes by the electric field. In the case of p-type FETs in the air, PL intensity increased due to hole injection by applying a small negative gate bias. After the device was heated in vacuum, the maximum PL intensity was obtained at zero gate bias. This can be explained by the change in the interface between the SWNT and contact electrodes. The drain field dependence of the PL intensity shows a monotonic decrease, which is explained by a competition between the recombination lifetime and transit time of photo-excited carriers in the SWNT. Using analytical steady-state rate equations on carrier density in the SWNT, the relation between the recombination lifetime and carrier transit time has been evaluated. The carrier saturation velocity has also been estimated.