Effective energy gap of the double-walled carbon nanotubes with field effect transistors ambipolar characteristics

We have investigated the transport property of the double-walled carbon nanotubes (DWCNT)-field effect transistor (FET) devices with HfO2 insulating layers at room temperature and 4.2 K. These devices show the ambipolar FET characteristics after deposition of HfO2 insulating layer. The off-regions of ambipolar behavior have clear dependence on their DWCNT diameter. The conversion factor of gate voltages and bias voltages is estimated from low temperature Coulomb Diamond measurement. Using same device structure and dimensions to all devices, these off-regions of threshold voltage are converted to effective energy gap. These energy gaps are in good agreement with theoretical predictions.