Electrically Excited, Localized Infrared Emission from Single Carbon Nanotubes

Carbon nanotube field-effect transistors (CNTFETs) produce band gap derived infrared emission under both <i>ambipolar</i> and unipolar transport conditions. We demonstrate here that heterogeneities/defects in the local environment of a CNTFET perturb the local potentials and, as a result, the characteristic bias dependent motion of the ambipolar light emission. Such defects can also introduce localized infrared emission due to impact excitation by carriers accelerated by a voltage drop at the defect. The correlation of the change in the motion of the <i>ambipolar </i>light emission and of the <i>stationary </i>electroluminescence with the electrical characteristics of the CNTFETs shows that <i>stationary </i>electroluminescence can identify “environmental defects” in carbon nanotubes and help evaluate their influence on electrical transport and device operation. A number of different defects are studied involving local dielectric environment changes (partially polymer-covered nanotubes), nanotube−nanotube contacts in looped nanotubes, and nanotube segments close to the electronic contacts. Random defects due to local charging are also observed.