Blue, Yellow-Green and Red Simultaneous Emission from SiO 2 Matrices Co-Implanted with Si and C
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STRACT Dual Si+C implantations at high doses (3x1017 cm-2 ) were performed in thermal Si0 2 layers. The C implantation energy was fixed at 60 keV while the Si ones were performed at different energies (150 keV and 60 keV) with the aim of synthetizing carbon rich luminescent centers. Annealings up to 1100 'C were performed in an inert N2 atmosphere either for short times in a rapid thermal processing furnace and up to two hours in a conventional furnace. Evidence of the formation of silicon and carbon-rich clusters was provided by XPS, SIMS, Raman and TEM experiments. Photoluminescence experiments under blue and ultraviolet excitations showed intense emission bands peaking at 1.5-1.7 eV (red), 2.20 eV (yellowgreen) and 2.75 eV (blue). The relative intensity and spectral shape of the emission bands was found to depend strongly upon implantation and annealing conditions and offered the possibility of tuning the desired dominant emission wavelength. The possible formation of SiC clusters and even SiC crystallites at the SiO 2/Si interface could explain the origin of the highly intense blue emission band found for these samples. INTRODUCTION
Among several other techniques for synthetizing composite materials for optoelectronics, ion implantation emerged as a suitable choice mainly due to its ability to control the profile of the implanted ions and thus to determine the location and density of the precipitates, usually obtained after the thermal treatments. In recent years, the synthesis of nanocrystalline elemental and compound semiconductors embedded in Si0 2 matrices has attracted much attention because of a fundamental interest in low-dimensional properties but mostly because of novel applications as photonic switching devices and visible light emitters, since the efficient visible luminescence reported from porous silicon and from Si and Ge nanocrystals in SiO 2 [1-4]. In this framework, the formation of carbon containing nanoprecipitates in Si0 2 is interesting because a shift of the emission towards higher energies -related to the higher bandgap of diamond and SiC- is expected, as was previously reported for SiC nanoparticles in Si [5-6]. For C implantation in SiO 2, several authors have reported the loss of C during annealing by exodifusion and/or precipitation of SiC in the Si/SiQ interface for Si0 2 buried layers [7]. The approach we have followed to minimize C diffusion in Si0 2 in order to favour clustering has been to create a great number of Si-Si bonds in excess by performing a high dose Si÷ implant at different energies [8]. Thus, we report in this work the analysis of photoluminescent (PL) structures formed by sequential implantation of silicon and carbon in SiO2 237
Mat. Res. Soc. Symp. Proc. Vol. 486 01998 Materials Research Society
films. The observation of strong visible luminescence in the red, yellow-green and blue regions has been correlated with processing parameters and in the light of the structural characterization performed from SIMS, Raman, TEM and XPS measurements. The results have been c
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