Silicon nanocrystal synthesis by implantation of natural Si isotopes

Implantations of pure image, image, and image into image can provide significant insight into the formation of silicon nanocrystals (Si-nc) and their light emission properties. Si-nc produced with different fractions of the heavier Si isotopes have been characterized by Raman and photoluminescence spectroscopy. Weak Stokes shifts of the Si-nc phonon peaks indicate that both the implanted Si and the native Si from the image substrate contribute to Si-nc nucleation. The Raman measurements also indicate that the Si isotopic composition of the Si-nc is similar to the Si isotopic fraction of the implanted image. The Si-nc photoluminescence (PL) spectra are shifted towards the blue with increasing Si isotope mass, an indication that the increase of the Si-nc effective mass enhances the excitonic bandgap. Measurements from samples implanted with heavy isotopes at high Si excess concentrations indicate that the Si-nc isotope fraction evolves with annealing time such that the heaviest Si isotope are more concentrated in the vicinity of the image interface, which can modify the energy states involved in the radiative transitions associated with Si-nc.