Optoelectronics with Carbon Nanotubes

of Schottky barriers. This estimation is consistent with the field strength of 30 to 60 V/μm for
the onset of emission has been suggested for 1D CNTs by energetic considerations and optical
phonon scattering length 71 .
Once the emission threshold field is exceeded, it is reasonable to assume that the
emission efficiency increases as the accelerating field is increased. In fact, as observed in
Figure III-7 showing the integrated EL intensity as a function of current, a reasonable fit to the
nonlinear behavior is obtained by using a polynomial function of the form y = a + bx 2 . While the
functional form of this fit cannot be discussed without knowing details such as the electronic
temperature (i.e. Fermi distribution of the charge carriers) and the potential profile at the
contacts, it still indicates that the emission is indeed more efficient at a higher VDS, as the
accelerating field is increased.
Figure III-7. EL intensity as a function of current. The best fit (solid line) is a
polynomial fit with the exponent of 1.98 and no linear component.
iii. Electroluminescence Spectra
To understand the characteristics of electrically-induced emission in greater detail, we
now move onto an analysis of the spectral shape. In particular, various peaks and their widths in
emission spectra give clues to different mechanisms that influence the emission process. First,
we examine the spectral width as a function of input power in order to elucidate the role of
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