07.08.2013 Views

Optoelectronics with Carbon Nanotubes

Optoelectronics with Carbon Nanotubes

Optoelectronics with Carbon Nanotubes

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

3. Conclusions<br />

We have examined the intensity and spectral shapes of EL from single-tube CNTFETs.<br />

From transport measurements, it is seen that their electrical transfer depends on the control of<br />

Schottky barriers at metal contacts. In agreement <strong>with</strong> an impact-excitation process of exciton<br />

generation, a threshold behavior is observed at the EL onset. The very broad lineshape of the E11<br />

transition is attributed to tube non-homogeneity, phonon scattering, electronic heating, and the<br />

effect of external electric field in the longitudinal direction. There is evidence that phonon<br />

temperatures (and <strong>with</strong> it, possibly electron temperatures) saturate at very high input power,<br />

possibly because of the energy dissipation by the EL mechanism.<br />

We have observed E11 and E22 peaks, defect-mediated E11 peak, and the E11 - optical<br />

phonon side band complex. In polarized measurements, a clear suppression of E11 and E22 peaks<br />

is observed in the perpendicular direction. Conversely, we were able to observe the E12<br />

transition for the first time in EL by investigating perpendicularly polarized component of the<br />

emission.<br />

Our data point to possible future explorations that include phonon and electron<br />

temperature measurements, a more detailed investigation of the broadening mechanisms, and a<br />

realization of better signal-to-noise ratio for superior spectroscopic data. While polarized EL<br />

from CNT may have interesting applications in future nano-scale optoelectronics, there are many<br />

issues, especially in carrier and phonon dynamics and their interactions, that still need to be<br />

better understood.<br />

66

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!