Nonradiative recombination in strongly interacting silicon nanocrystals embedded in amorphous silicon-oxide films

The optically induced free-carrier absorption coefficient (alpha(FC)) of densely packed (2 X 10(18) cm(-3)) Si nanocrystals (NCs) embedded in a glass matrix was accurately measured in the near-infrared using two complementary pump-probe techniques. When compared to established carrier dynamical models, the dependence of alpha(FC) on optical pump intensity reveals enhanced nonradiative recombination at high pump intensity (> 10 KW/cm(2)), which can be explained by the interaction of excited carriers located in spatially separated NCs. The rate of recombination due to the interaction between a pair of excited NCs is determined to increase inversely with the sixth power of their separation distance (tau(-1) similar to gamma R(-6); gamma approximate to 2.6 x 10(-31) cm(6) s(-1)) and is indicative of near-field dipole-dipole energy transfer. These results explain the source of an apparent inconsistency in power-law behavior found in previous carrier dynamics studies on similar materials which did not account for this interaction.