TUNING THE EMISSION WAVELENGTH OF SI NANOCRYSTALS IN SIO2 BY OXIDATION

Si nanocrystals (diameter 2-5 nm) were formed by 35 keV Si+ implantati on at a fluence of 6 x 10(16) Si/cm(2) into a 100 nm thick thermally g rown SiO2 film on Si (100), followed by thermal annealing at 1100 degr ees C for 10 min. The nanocrystals show a broad photoluminescence spec trum, peaking at 880 nm, attributed to the recombination of quantum co nfined excitons. Rutherford backscattering spectrometry and transmissi on 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 gr eater depths. Upon oxidation for 30 min the photoluminescence peak wav elength blueshifts by more than 200 nm. This blueshift is attributed t o a quantum size effect in which a reduction of the average nanocrysta l size leads to emission at shorter wavelengths. The room temperature luminescence lifetime measured at 700 nm increases from 12 mu s for th e unoxidized film to 43 mu s for the film that was oxidized for 29 min . (C) 1998 American Institute of Physics.