The steady-state photoconductivity of tetrahedral amorphous carbon (ta-C) and hydrogenated ta-C (ta-C:H) has been studied as a function of temperature, light intensity, and photon energy, in order to understand the recombination process in diamond-like carbon. It is found that the levels demarking the recombination states can span only part of the gap, so that the recombination centres can vary from every defect, to some defects, to some tail states, according to conditions.
Ilie, A., Robertson, J., Conway, N., Kleinsorge, B., & Milne, WI. (1999). Photoconductivity and recombination in diamond-like carbon. Carbon, 37(5), 829 - 833. https://doi.org/10.1016/S0008-6223(98)00279-6