Exciting hot carrier to a high energy state by impact excitation in low density nanocrystalline Si films

The carrier recombination processes in low density nanocrystalline (nc-) Si films have been studied by steady and time-resolved photoluminescence (PL) spectra, and the hot carriers have been excited to a high energy state by impact excitation. A yellow-green PL band locating at 580 nm appears when the studied film is excited by two optical beams. The yellow-green PL band results from band-to-band transition in Si nanocrystals with double-bonded oxygen atoms, which is caused by impact excitation among the carriers in the nc-Si film. The decay time of the yellow-green PL band is 230 ns, which is much longer than the hot carrier cooling. The results indicate that the lost energy in the solar cell may be collected from the new recombination center in the further structural design.