Silicon nanocrystal synthesis by implantation of natural Si isotopes

Abstract

Implantations of pure Si + 28 , Si + 29 , and Si + 30 into SiO 2 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 SiO 2 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 SiO 2 . 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 / SiO 2 interface, which can modify the energy states involved in the radiative transitions associated with Si-nc.