PHOTOCONDUCTIVITY AND ELECTRONIC TRANSPORT IN TETRAHEDRAL AMORPHOUS-CARBON AND HYDROGENATED TETRAHEDRAL AMORPHOUS-CARBON

The photoconductivity of tetrahedral amorphous carbon (ta-C) and hydro genated tetrahedral amorphous carbon (ta-C:H) has been studied as a fu nction of temperature, photon energy, and light intensity in order to understand the transport and recombination processes. ta-C and ta-C: H are found to be low mobility solids with mu tau products of order 10( -11)-10(-12) cm(2)/V at room temperature because of their relatively h igh defect densities. Deep defects tend to be the dominant recombinati on centers, but at high and moderate temperatures only a fraction of t hese centers or even tail states can act as recombination centers beca use the carrier demarcation levels do not always span the gap. For exc itation by high energy UV photons, a peak in the photoconductivity is found at 200 K, similar to the thermal quenching effect found in a-Si: H, and attributed to competitive recombination between two classes of centers with very different capture cross sections. (C) 1998 American Institute of Physics. [S0021-8979(98)05422-X].