Recombination ina-Si:H: Auger effects and nongeminate recombination

Excitation-intensity effects in the luminescence of plasma-deposited $a$-Si:H are described. At low temperatures (50 K) the quantum efficiency increases with excitation intensity, particularly in samples of low spin density. This result is attributed to the onset of bimolecular, nongeminate, radiative recombination. Analysis of the rate equations shows that the primary nonradiative process in $a$-Si:H involves capture of free carriers at singly occupied dangling-bond defects. Estimates of the recombination rates are obtained.