Visible Photoluminescence From Si Ion-Implanted and Thermally Annealed SiO 2 Films
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ABSTRACT We have experimentally studied the photoluminescence (PL) properties of Si clusters in SiO 2 glassy matrices. Si clusters in the SiO 2 matrices were fabricated by Si' ion implantation into SiO 2 glasses and then thermally annealed in forming gas. Broad PL peaks are observed in the visible spectral region at room temperature. Resonantly excited PL spectra indicate that the strong coupling of excitons and stretching vibrations of the Si-O bonds causes the broad luminescent spectra. It is concluded that the interaction between electronic and vibrational excitations controls the luminescent emission and the observed dynamics.
INTRODUCTION The goal of achieving efficient visible luminescence from Si nanocrystals has stimulated considerable research in understanding the optical properties of group IV semiconductor nanocrystals [1]. A size reduction to a few nanometers is required for the observation of visible light emission from Si nanocrystals when the band structure is modified from that of bulk Si, which has an indirect gap of 1.1 eV. The large surface-to-volume ratios of Si nanocrystals are expected to enhance surface effects to the extent that the PL peak wavelength [2], the PL intensity [3] and the fine structures in the PL spectrum at low temperatures [4] will be modified by the surface chemistry of the Si nanocrystals, particularly with regard to the amounts of oxygen and hydrogen on the surfaces. Although there are many extensive studies concerning the origin of visible light emission, the mechanism of visible luminescence in Si nanocrystals and porous Si is still not clear. In order to investigate the luminescence from Si nanostructures, we need to fabricate Si nanostructures with near identical and stable surfaces [5,6]. Silicon nanocrystals and clusters embedded in a Si0 2 matrix offer some advantages because Si0 2 is a wellcharacterized material known to passivate Si surfaces where the Si/Si0 2 system is fully compatible with Si technology. Si nanocrystals in the Si0 2 system have been produced by ion implantation and thermal annealing techniques [7-10]. Ion implantation can be used to create supersaturated Si solid solutions while the thermal annealing provides energy which drives the system to a two phase (Si/Si0 2) state. In this paper we discuss the PL properties of Si+-implanted and annealed Si0 2 films on bulk Si and commercially available fused silica 99 Mat. Res. Soc. Symp. Proc. Vol. 452 01997 Materials Research Society
substrates. The excitation energy dependence of the PL spectra is presented and the data are interpreted in terms of strong coupling of excitonic and vibrational excitations.
EXPERIMENT The substrates used in this work were thermally grown- 1 A m Si0 2 thin films on bulk silicon substrate and commercially available fused silica glass of 1 mm thickness. All the samples used in these experiments were prepared by implanting at room temperature a dose of 2x1017 cm 2, 200 or 400 keV 21Si+ ions followed by lamp annealing in forming gas (10% H2 + 90 % N 2) or N 2 gas for 3-180
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