The microstructural and optical analysis of SiO 2 layers emitting white luminescence is reported. These structures have been synthesized by sequential Si ϩ and C ϩ ion implantation and high-temperature annealing. Their white emission results from the presence of up to three bands in the photoluminescence ͑PL͒ spectra, covering the whole visible spectral range. The microstructural characterization reveals the presence of a complex multilayer structure: Si nanocrystals are only observed outside the main C-implanted peak region, with a lower density closer to the surface, being also smaller in size. This lack of uniformity in their density has been related to the inhibiting role of C in their growth dynamics. These nanocrystals are responsible for the band appearing in the red region of the PL spectrum. The analysis of the thermal evolution of the red PL band and its behavior after hydrogenation shows that carbon implantation also prevents the formation of well passivated Si/SiO 2 interfaces. On the other hand, the PL bands appearing at higher energies show the existence of two different characteristics as a function of the implanted dose. For excess atomic concentrations below or equal to 10%, the spectra show a PL band in the blue region. At higher doses, two bands dominate the green-blue spectral region. The evolution of these bands with the implanted dose and annealing time suggests that they are related to the formation of carbon-rich precipitates in the implanted region. Moreover, PL versus depth measurements provide a direct correlation of the green band with the carbon-implanted profile. These PL bands have been assigned to two distinct amorphous phases, with a composition close to elemental graphitic carbon or stoichiometric SiC.

Metal-oxide-semiconductor (MOS) capacitors with Si nanocrystals (Si-nc) obtained by ion implantation in SiO2 have been studied for nonvolatile memory applications. The use of a thermal oxide and the accurate tuning of the postimplantation processing conditions allow good integrity, reliability, and high retention times. We propose an additional thermal oxidation step after the formation of the Si-nc. This process has enabled growing a thin tunnel oxide at the Si/SiO2 interface completely free of Si-nc and Si excess, leading to a formidable increase of the retention time. In addition the additional oxidation makes it possible to control the size and density of Si-nc. Finally, we show its impact on the memory characteristics of the nanocrystal device (writing speed and programming window).

The injection and storage of charge in Si nanocrystals obtained by ion implantation and annealing have been studied for different tunnel oxide thicknesses. The energy of the ions was kept fixed at 15 keV, which is compatible with most ion implanters used in Si technology, and the distance between the Si nanocrystals and the substrate was controlled by using gate oxides with different thicknesses. The processing conditions were adjusted for precipitating all the Si excess and for having Si–SiO2 interfaces free of defects. Consequently, reliable structures were obtained working in the direct tunneling injection regime, which show unprecedented longer retention times. Furthermore, it is shown that by changing only the oxide thickness it is possible to engineer devices with a tradeoff between writing speed and retention time.

The analysis of the white photoluminescence (PL) from Si+ and C+ coimplanted SiO2 is reported as a function of the implanted dose. By both steady and time-resolved measurements, the presence of several components in the emission between 2 and 3.3 eV has been resolved. The decays of the PL transients are characterized by short lifetimes, below 2 ns. For the emission at 2.1–2.3 eV, photoluminescence decay transients have been measured, obtaining a fast relaxation component of about 50–70 ps, followed by a slower component of the order of 1 ns. These values contrast with the very slow behavior, characteristic for the light emission from Si nanocrystals, and make carbon-related emitting centers interesting for optoelectronic applications where fast switching behavior is important.

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