Silicon nanocrystal synthesis by implantation of natural Si isotopes

Implantations of pure Si+28, Si+29, and Si+30 into SiO2 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 SiO2 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 SiO2. 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 Si-nc/SiO2 interface, which can modify the energy states involved in the radiative transitions associated with Si-nc.