Optically excited paramagnetic centers in hydrogenated amorphous germanium

Optically excited paramagnetic centers in amorphous hydrogenated germanium (a-Ge:H) are reported. The light induced electron spin resonance (LESR) spectra are comprised of two components, which are ascribed to electrons and holes in the conduction- and valence-band-tail states, respectively. There is no evidence of spin pairing, charge defect creation or LESR of Ge dangling bonds. Over about three orders of magnitude in light intensity the decay curves are dispersive with a dispersive parameter of ∼0.5. The spectra are best fit assuming bimolecular recombination. The LESR spin density depends only weakly on the photo-generation rate.