Doping of Carbon Nanotubes Using Low Energy Ion Implantation

Carbon nanotubes (CNTs) were implanted with thermally decomposed oxygen (O-2(+)) and nitrogen (N-2(+)) ions at an acceleration voltage of 20 V. With a low dose of oxygen ions, the CNT-FET exhibited p-type behaviors with substantial changes in threshold voltage and in the slope of the source-drain current (I-sd). However, at high dosages, the device exhibited metallic behaviors. After nitrogen doping, we did not observe the effects of electron doping. Instead, nitrogen doping significantly increased I-sd with no gating effect. Our theoretical results showed that the metallic behavior of nitrogen-doped CNTs arose from the impurity conduction band, which results from the overlapping wave function of the nitrogen impurity.