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We have made electrical measurements on a system using carbon nanotubes as the dopant material. A semiconjugated, organic polymer was mixed with carbon nanotubes to form a wholly organic composite. Composite formation from low to high nanotube concentration increases the conductivity dramatically by ten orders of magnitude, indicative of percolative behavior. Effective mobilities were calculated from the space-charge regions of the current-voltage characteristics for the 0--8 % mass fractions. After an initial rise these were seen to fall from 1--8 % doping levels as predicted by theory. From the values for conductivity and mobility, an effective carrier density was calculated. This was seen to decrease between 0% and 1%, before rising steadily.
Coleman et al. (Tue,) studied this question.