Subnanosecond Total-Light Decay and Spectra ina-Si: H

With use of an ultrafast Ge photodiode and a high-power picosecond laser system, the fastest radiative processes in plasma-deposited $a$-Si: H have been resolved. Spectrally integrated measurements on a 250-ps time scale provide a simple picture that for the first time isolates single rates in the recombination dynamics, permitting quantitative physical modeling. Spectral shifts are observed on time scales faster than the radiative decay, providing clear evidence of slow relaxation processes.