Role of dangling-bond defects in early recombination in hydrogenated amorphous silicon

Relaxation of photoexcited carriers is studied in $a$-Si: H with the use of photoinduced ir absorption. The role of the dangling-bond defect in recombination is investigated with samples of defect density from ${10}^{15}$ to > ${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$. We find that during the first microsecond the dangling bond does not cause rapid recombination, but rather actually slows recombination by acting indirectly through its influence on the density and shape of the exponential distribution of states near the band edge.