PHOTOCONDUCTIVITY OF CARBON AEROGELS

Photoconductivity was measured on a series of carbon aerogels to investigate their electronic properties. Carbon aerogels are a special class of low-density microcellular foams, consisting of interconnected carbon particles (approximately 120 angstrom diameter) and narrow graphitic ribbons (approximately 25 angstrom width) intertwined within each particle. Both the dark- and photoconductivities show drastic changes in the temperature range 5-300 K, which are similar to those in a-Si and chalcogenide photoconductors. At high temperatures, the photoconductivity is dominated by the carrier recombination within each particle. The photoconductivity at low temperatures is dominated by the same carrier transport mechanism as that for the dark conductivity, which is based on hopping and tunneling transport. The activation energy values for transport and recombination identify the electronic structure of the particles among samples of different bulk density. The long decay time of the photoconductivity suggests a relaxation mechanism associated with the dangling bonds.