%'e report cw and time-resolved optically detected magnetic resonance data on samples of a-Si:H prepared by reactive sputtering, glow-discharge, and chemical vapor deposition. Two distinct luminescence processes are inferred near 1.3 -1.4 and 0.9 eV. An enhancing signal at g =2.0065 is observed on the 0.9-eV photoluminescence (PL) band and is linked to distant-pair radiative recombination between a dangling bond and a hole localized in a valence-band tail state. The high-energy PL band shows a quenching resonance at g =2.005, which can be associated with shunt processes involving dangling bonds. Enhancing signals are also observed on this high-energy band: In lowdefect-density sputtered samples, a 200-6-wide line at g=2.01 is associated with short radiative lifetimes (-ms) and narrows for longer lifetimes ( -s). In all other samples studied, a narrower line (19 G) at g =2.0078 is linked to short lifetimes and broadens for longer lifetimes. Both signals are consistent with a model in which the high-energy PL band arises from radiative recombination of carriers localized in band tail states, and are successfully explained by exchange interaction.
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