PHOTOLUMINESCENCE DECAY DYNAMICS OF ION-IRRADIATED POROUS SILICON - EVIDENCE FOR THE ABSENCE OF CARRIER MIGRATION

We have measured the photoluminescence (PS) decay properties of porous silicon samples subjected to ion irradiation up to a dose of 10(15) c m(-2) at 30 kV. It is found that while the PL intensity decreases down to 1/100 of the initial value due to induced nonradiative recombinati on centers, its decay constant is unchanged. This observation is incon sistent with the hypothesis that photoexcited carriers migrate among t he Si nanocrystallites in PS. The results are compared with those of P S samples subjected to thermal annealing instead of ion irradiation, w here the PL quenching in this case is accompanied by a large reduction in the decay constant. Infrared absorption spectra of ion-irradiated samples show essentially no chemical bonding change. In contrast, thos e of the annealed samples show loss of hydrogen bonding and increase o f surface oxidation. (C) 1998 American Institute of Physics. [S0003-69 51(98)00142-9].