Comparative Study of Implanted and Sputtered Systems of Si Nanograins Embedded In SiO 2
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ABSTRACT Si nanograins embedded in silicon oxide matrix have been obtained by thermal annealing at 1100°C during one hour, either after implantation of Si' into thermal SiO 2 layers or after magnetron cosputtering of both Si and Si0 2. The spectral distribution of the photoluminescence (PL) in both systems is similar and peaks in the red visible region (1.451.60 eV). The results obtained indicate that for high PL efficiency, the films have to be annealed at temperatures high enough to achieve phase separation. This was observed from the gradual shift of the infrared bands of the silica matrix toward those of thermal Si0 2, together with the appearance of the crystalline silicon Raman vibrational mode in the spectra. The similar behavior of samples obtained by ion implantation and by sputtering suggests a more complex origin of the PL than quantum confinement. INTRODUCTION
Strong visible photoluminescence (PL) from Si nanostructures has stimulated many experimental and theoretical studies due to the possibility of development of those systems for optoelectronic devices. The PL visible spectra have been reported for porous Si [1] and for other silicon-based materials [2], obtained by different techniques such as ion implantation and sputtering [3,4]. As far as the luminescence mechanism is concerned, many authors suggested an origin lying in the quantum size effect caused by the confinement of carriers and the exciton recombination in the small-sized particle [3,5], while others explained their data by involving radiative interface states [6]. Thus, the mechanism of visible luminescence innanostructured Si is still a matter of debate [7]. In this paper we report a study on the optical and structural properties of Si-rich silicon oxide films, obtained by both ion implantation and magnetron sputtering, followed by thermal annealing at different temperatures and durations. The optical and structural characterizations have been performed by means of PL, infrared spectroscopy (IR) and Raman scattering measurements.
225 Mat. Res. Soc. Symp. Proc. Vol. 486 0 1998 Materials Research Society
EXPERIMENTAL Si-rich Si0 2 films were fabricated by RF magnetron cosputtering and ion implantation of Si+ into thermally grown Si0 2. Concerning sputtering, either 12 or 16 Si wafers (1 cm2) were uniformly located on the surface of the Si0 2 target (purity 99.9%, 10 cm in diameter). This corresponds to a surface ratio of 14.8% or 19.5 %, respectively. The chamber has been evacuated down to 1.0x10- 7 Torr before starting the deposition process. This latter was performed under an argon pressure of 1.0x10"2 Torr, a RF power density of 0.76 mW/cm 2 and a substrate temperature of 500*C. The film thickness was in the range 500-900 nim. Two kinds of substrates were used: Si wafers for IR absorption and fused quartz plates for Raman spectroscopy. Implanted samples were elaborated using as substrates 800 nun SiQ 2 layers thermally grown on Si wafers. The Si+ implantation was performed at an energy of 150 keV and a dose of 3.0x1017 cmn2, which
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