Model for efficient visible emission from Si nanocrystals ion beam synthesized in SiO2

The photoluminescence (PL) emission of Si nanocrystals ion beam synthesized in SiO2 is studied in this work as a function of annealing time and initia l Si atomic excess (super-saturation), The optical properties of this syste m have been correlated with the characteristics of the nanocrystal populati on. The Si nanocrystals show a wide and very intense PL red/infrared emissi on. This emission peaks at about 1.7 eV for the low super-saturation range between 1% and 10% and shifts to the infrared for higher super-saturation ( 20% and 30%). Remarkably, there is a linear increase of PL intensity versus super-saturation in the low range. Moreover, the annealing kinetic studies show a typical behavior of PL intensity with annealing time, with a fast t ransitory increase that bends over to reach asymptotic saturation. The PL i ntensity saturation is satisfactorily explained by the Ostwald ripening sta ge of the nanocrystal population while the transient stage is a consequence of both nanocrystal growth and nanocrystal surface passivation mechanisms acting together. Indeed, electron spin resonance measurements demonstrate t hat the concentration of Pb centers (Si dangling bonds) at the Si-SiO2 inte rface correlates inversely with PL intensity during most of the transient s tage. (C) 2001 Elsevier Science B.V. All rights reserved.