Pathways of carrier recombination in Si/SiO2 nanocrystal superlattices

We investigated picosecond carrier recombination in Si/SiO2 nanocrystal superlattices by ultrafast transient transmission, time-resolved photoluminescence, and Raman spectroscopy. The recombination is of multicarrier origin and it depends strongly on the nanoscale structure of the samples (e.g., crystallinity, percolation, and size distribution). Several recombination pathways were found, including Auger recombination, trapped-carrier Auger recombination, exciton–exciton recombination, and subsequent trapping in band tail states of amorphous silicon phase. The sample microscopic structure is determined using a single parameter, the stoichiometric parameter x, during the plasma-enhanced chemical-vapor deposition process. The percolated samples are hot candidates for all-silicon tandem photovoltaic solar cells in the future.