Optoelectronics with Carbon Nanotubes

In the reverse direction (i.e., negative VDS in this case; the left half of each panel in
Figure V-4), split gate voltage has the opposite effect, namely suppression of electronic transport
resulting from the increase between the top gates. This is precisely what is expected from a
diode that is reverse-biased (unless it is in the avalanche regime). At 0V/0V, it works more like
a regular resistor, although the effect of Schottky barriers is evident at small VDS from the
nonlinearity of IDS-VDS near zero. As the voltage between the split gates is increased in
magnitude, the device becomes more resistive. Again this effect is more pronounced in the
longer-channel diode with a better on-off ratio. In summary, by increasing the potential drop
between the split gates, we obtain a gradual improvement of the rectifying behavior in the CNT
film diode.
(a) (b)
Figure V-4 (a, b) Electrical output characteristics measured for the same devices as in
Figure V-3 (a, b), respectively. In the forward bias direction (marked “Forward”:
positive VDS), the electrical output increases as a function of the difference between
the two split gate voltages from 0V/0V (black) to -10V/10V (magenta).(potential
drop), while the output is generally suppressed in the reverse direction (marked
“Reverse”) as a function of greater split-gate voltage. After Ref. 152.
We should emphasize here that we use the terms “forward bias” and “reverse bias” as
they are used in conventional p-n diodes. Indeed, we applied drain-source and split-gate voltages
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