Interpretation of Coulomb oscillations in carbon-nanotube-based field-effect transistors

Bias-voltage and temperature-dependent Coulomb oscillations are demonstrated in long-channel (∼1500 nm) single-walled carbon-nanotube-based field-effect transistors. The oscillation peaks disappear gradually with increasing temperatures up to 70 K. Diamond-shaped channel current suppression regions are observed at 15 K when the current is plotted with contour lines in the gate voltage versus source-drain voltage plane. Interestingly, these characteristics are only found in one kind of carbon-nanotube-based field-effect transistors, in which a long single-walled carbon-nanotube bundle bridges the source/drain electrodes, while several short single-walled carbon-nanotube bundles are attached to the source/drain contacts. The long-tube channel may act as an electrometer to detect single-charge charging signals in the short single-walled carbon nanotubes. On one hand, charges trapped in the short tubes could be quantized due to the Coulomb blockade. On the other hand, the electrostatic potential at the long-tube/electrodes contacts could be influenced by the quantum charges stored in the short single-walled carbon nanotubes so that the channel current is modulated.