The luminescence of amorphous hydrogenated material was described as a modification of the band-tail luminescence in hydrogenated amorphous Si. The tail states of the present material were formed from clusters of sp2 sites, and luminescence occurred via recombination within each cluster. The paramagnetic defects were confirmed to be the non-radiative recombination centers. The weaker temperature dependence of the luminescence efficiency of amorphous hydrogenated C, as compared with amorphous hydrogenated Si, was attributed to its wider tails. These inhibited carrier hopping. The luminescence efficiency was also quenched by narrow optical gaps, because carriers could tunnel to defects more easily in the sp2-rich narrow-gap amorphous hydrogenated C. However, defect quenching was less strong because of the smaller Bohr radius of localized states in amorphous hydrogenated C.

J.Robertson: Physical Review B, 1996, 53[24], 16302-5