Characterization of Si+ ion-implanted SiO2 films and silica glasses

We report here electron spin resonance (ESR), Raman scattering, photoluminescence (PL), and absorption studies of Si+ ions implanted into silica glasses and thermally grown SiO2 films on Si wafers. The aim is to understand the defect formation and luminescence mechanism as the films were annealed at several temperatures. In as-grown Si-implanted films, paramagnetic defects in the form of Si-E' and nonbridging oxygen hole centers (NBOHC) were detected by ESR. A luminescence band, centered at 650 nm, was observed in these samples. The E' and NBOHC defects were annealed out in samples annealed above 500 degrees C, but Si dangling bonds in the form of P-b centers were observed. In films annealed above 800 degrees C, Si nanocrystals of varying size between and 5 nm were formed. as detected by transmission electron microscopy. A red PL band (>700 nm) and a Si-phonon band at 510 cm(-1) gradually evolved as a function of anneal temperature. The observation of the Si-phonon mode with a 15 cm(-1) shift in the peak position from the bulk affirms the presence of Si clusters in the annealed ion-implanted SiO2 films and silica glasses. We attribute this red PL band to excitonic recombination in Si nanocrystals. The peak position of this PL band was found to shift with excitation wavelength. The shift of the PL spectra as a function of excitation energy was interpreted as the emission from Si particles of certain sizes that are excited by the incident energy. An energy band gap distribution due to a size distribution was used to model the PL spectra at each excitation energy. (C) 1998 American Institute of Physics. [S0021-8979(98)07121-7].