Optoelectronics with Carbon Nanotubes

The polarization dependence of light absorption and emission has been observed
experimentally in CNTs. Lefebvre et al. has conducted spectral studies of PL and PLE for
different polarizations 119, 134 and EL emission intensity as a function of polarization has also
been measured experimentally 73, 87 . The results from the PL/PLE studies agree with the
theoretical prediction that light in parallel polarization couples strongly with the E11 and E22
transitions, while the E12 resonance is observed in transverse polarization, although it is much
weaker than the E11 and E22 parallel resonances 119, 134 . A photocurrent study has also shown the
maximum excitation when the light is polarized along the direction of the nanotube 27, 135, 136 .
However, there has never been a spectral study of polarization dependence in EL, which we now
discuss.
Figure III-14. EL intensity as a function of the angle between the tube direction and a
linear polarizer. The ratio of maximum (0 degrees) and minimum (90 degrees) is 3.4
which is extracted from the fit. The large error is mostly due to the instability of the
device.
Figure III-14 shows the polarization of emitted light intensity from a CNTFET. Because
the channel length is much smaller than the spatial resolution of the equipment, the light appears
as a point source and the polarizer transmits the component of the emitted light that aligns with
the filter direction. The cosine squared fit gives a maximum (at 0 degrees) to minimum (at 90
degrees) ratio of about 3.4, which is similar to the observation of polarization in EL first reported
by Misewich et al. in 2003 73 . In terms of the degree of polarization (DOP), this translates to
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