Optoelectronics with Carbon Nanotubes

Figure III-11. Comparison between the experimental width (black squares) of the EL
spectra in Figure III-4 and the broadening calculated from Equation III.3. Similar slopes
indicate that the field ionization effect can account for the change in width.
Having accounted for the double peak, acoustic phonons and broadening due to field
ionization, there is still about 60 ± 10 meV of broadening that needs to be explained. This value
does not vary as a function of power; power-dependent broadening was already accounted for by
the field effect. One possible effect is electron heating. If we follow the linear power-
dependence demonstrated by Steiner et al., we arrive at extremely high electron temperatures, in
thousands of Kelvin at high power. However, as it has been discussed already, it is likely that
the phonon population saturates as the field increases over the impact excitation threshold.
Scattering with surface polar optical phonons of the substrate has also been shown to be
important as an energy dissipating mechanism 112, 126 . As a more realistic estimate, we can use
the temperature of 1200 K in a suspended metallic nanotube as the upper limit of the optical
phonon temperature, since this was observed in the NDC regime in Ref. 87. Steiner et al. also
found zone boundary K phonons up to 1500 K, and G phonons close to 1000 K on the substrate
112 . We do not observe NDC in our data (see the linear I-V in Figure III-6), so we assume that
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