Photoconductivity of diamond-like carbon

We have studied the photoconductivity in pure tetrahedral amorphous carbon (ta-C) and hydrogenated tetrahedral amorphous carbon (ta-C:H). Good photoconductive properties are demonstrated for ta-C:H, showing that the hydrogenated form of ta-C is of a higher electronic quality. Transport and recombination parameters are derived. Ta-C:H are low mobility solids with a jrr product of the order of 10-12 cm2 V"-and a recombination time Tr of about 10-7 s. At low energy excitation, the photoconductivity shows a sublinear dependence on the light intensity over a wide temperature range. The relationship between the photoconductivity and the density of spin defect centers is discussed. UV light is used to excite carriers into the extended states. Competitive recombination centers may be involved at high excitation energy.