Si nanocrystals (diameter 2-5 nm) were formed by 35 keV Si+ implantation at a fluence of 6 x 10(16) Si/cm(2) into a 100 nm thick thermally grown SiO2 film on Si (100), followed by thermal annealing at 1100 degrees C for 10 min. The nanocrystals show a broad photoluminescence spectrum, peaking at 880 nm, attributed to the recombination of quantum confined excitons. Rutherford backscattering spectrometry and transmission electron microscopy show that annealing these samples in flowing O-2 at 1000 degrees C for times up to 30 min results in oxidation of the Si nanocrystals, first close to the SiO2 film surface and later at greater depths. Upon oxidation for 30 min the photoluminescence peak wavelength blueshifts by more than 200 nm. This blueshift is attributed to a quantum size effect in which a reduction of the average nanocrystal size leads to emission at shorter wavelengths. The room temperature luminescence lifetime measured at 700 nm increases from 12 mu s for the unoxidized film to 43 mu s for the film that was oxidized for 29 min. (C) 1998 American Institute of Physics. References: 10
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