Photoconductivity and photoluminescence processes in amorphous carbon

The photoconductivities of various sp3 bonded amorphous carbons were studied to understand their recombination and photoluminescence processes. At temperatures >200 K, the photoconductivity of each type of carbon does not vary inversely with the paramagnetic defect density, indicating that paramagnetic defects are not the only recombination centres. This effect occurs because carrier demarcation levels lie in the band tails, so both defects and tail states act as recombination centres. The temperature regime <200 K is due to energy loss hopping. The localisation radius is not constant, so the capture radius cannot be treated as constant when describing luminescence efficiency in hydrogenated amorphous carbon (a-C:H) of different band gaps.