Optical properties of silicon nanocrystals formed by ion implantation

摘要

Photoluminescence from silicon nanocrystals fabricated by ion implantation has been investigated using size selective otpical excitation techniques. A comparison of the results rom size selectrive excitation measurements for a fixed ion dose to data rom measurements at a fixed photon energy for several different ion doses has been made to separate size effects from secondary effects associated with variations in the ion dose. The data show a much greater dependence on ion dose than on excitation photon energy. Both the photoluminescence spectra and the decay of the photoluminescence are virtually unchanged for samples of a vien dose as the excitation photon energy is varied from 3.50 eV to 1.91 eV. Photoluminescence spectra for a fixed excitation photon energy, on the other hand, show a redshift of approx 0.2 Ev as the ion dose is changed from 1 x 10~(21) ions/cm~3to 1 x10~(22)ions/cm~3. Photoluminescence decay times extracted from time resolved measurements as a function of implanted ion density also show much larger variations than those observed as a result of tuning the excitaton photon energy, ranging from approx 250 mu s for the lowest dose sample to approx 600 mu s for the highest dose sample. These measurements given greater weight to theories which exclude recombination o f excitions within the nanocrystals as the source of the bright visible photolouminescence observed previouslh in silicon nanocrystals.