n-Type Doping for Single-Walled Carbon Nanotubes by Oxygen Ion Implantation with 25 eV Ultralow-Energy Ion Beam

Oxygen ions with the ultralow-energy of 25 eV are implanted in single walled carbon nanotube (SWNT) field-effect transistors (FETs), which convert the SWNT from p-type to n-type. The dose amount ranged from 1.8×1011 to 8.2×1012 ions/cm2. In the drain current–gate voltage characteristic, the hole current begins to decrease while the electron current begins to increase as the dose of the oxygen ions implanted in SWNT-FETs increases. Moreover, the threshold voltage of the hole transport shifted to the negative direction of the gate voltage. These changes in the electrical properties of SWNT-FET after the oxygen-ion implantation correspond to the n-type conversion and to the shift in Fermi level from the valence band edge to the conduction band edge. The implanted oxygen ions may substitute the carbon atoms in the SWNT and act as donor impurities.