Silicon nanocluster aggregation in SiO2:Si layers

Energy-filtered transmission electron microscopy (EFTEM) in combination with electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) have been used to investigate Si+-implanted amorphous silicon dioxide layers and the formation of Si nanoclusters. Therefore, amorphous, thermally grown SiO2 layers on Si substrate were implanted by Siþ ions with an energy of 150 keV and a dose of 5x1016 ions/cm2 leading to an atomic dopant fraction of about 4 at%. Afterwards a post-implantation thermal annealing has been performed at temperatures Ta=700–1300 °C, for 60 min in vacuum. This thermal annealing leads to Si cluster formation and a change of the SiOx matrix from about x=1.923 to 1.929 connected with additional visible luminescence bands in the green-yellow region. CL spectra in the near infrared (NIR) region indicate such Si aggregation by appearance of an additional band in extension of the common NBOHC band at 1.9 eV towards the NIR region. This band shifts with increasing annealing temperatures of the implanted sample to lower energies, probably, due to cluster growth and quantum confinement effects.