It is possible to observe electroluminescence from single-walled carbon nanotubes by injecting electrons and holes using electrical contacts. Since photoluminescence becomes weak when nanotubes are on the substrate, we have fabricated light emitting diode utilizing individual air-suspended carbon nanotubes.

In this device, the top silicon layer of a silicon-on-insulator substrate is used for split gates. By applying opposite polarity voltages to the two gates, a p-n junction is formed due to accumulation of electrons and holes. Application of a bias voltage across source and drain electrodes will result in light emission.

The top-left figure shows electroluminescence (EL) and photoluminescence (PL) spectra from a suspended nanotube. As the emission wavelengths are the same, we assign the emission to exciton recombination.

The top-right figure shows gate voltage dependence of electroluminescence intensity. The horizontal axis is the voltage V_G1 applied to Gate 1, while the vertical axis is the voltage V_G2 applied to Gate 2. Electroluminescence is observed in the region where V_G1 is positive and V_G2 is negative, where a forward-biased p-n junction should be formed.

To learn more about this work, please refer to:
N. Higashide, M. Yoshida, T. Uda, A. Ishii, Y. K. Kato Cold exciton electroluminescence from air-suspended carbon nanotube split-gate devices Appl. Phys. Lett. 110, 191101 (2017).