Electroluminescence Spectral Shape in Carbon Nanotube Field Effect Transistors under High Bias Conditions

In carbon nanotube field effect transistors, electroluminescence excited by intra-nanotube impact excitation at high source-drain bias reveals strongly broadened electronic transitions (FWHM $\sim$150 to $\sim$300 meV for the lowest energy peak observed) in the E$_{11}$ to E$_{22}$ energy range. Through the bias and polarization dependence of the spectra, we investigate the production mechanism of these states and consider possible causes for their bias-dependent broad lineshapes, including exciton-exciton annihilation, and high electron and phonon temperatures.