Displacement current detection of photoconduction in carbon nanotubes

Using a capacitive photocurrent measurement technique, we demonstrate the ability of both semiconducting and metallic single wall nanotubes to function as photodetectors over a wide spectral range. We observe clear peaks in the photo induced displacement current of a nanotube-plated capacitor that correspond directly to the semiconducting and metallic transitions in the nanotube absorbance spectrum. The signal increases substantially as the carrier drift velocity is raised with applied bias. A large increase in the photocurrent observed below temperatures of 100 K suggests that the nanotube hot carrier relaxation rate decreases substantially at low temperatures.