Light-emitting Si nanostructures formed by swift heavy ions in a-Si:H/SiO2 multilayer heterostructures

Light-emitting nanoclusters were formed in Si/SiO2 multilayer structures irradiated with 167 MeV Xe ions to the doses of 1011-3 × 1014 cm−2 and annealed in the forming-gas at 500 °C and in nitrogen at 800-1100 °C, 30 min. The thicknesses were ~4 nm or ~7-8 for the Si, and ~10 nm for the SiO2 layers. The structures were studied using photoluminescence (PL), Raman spectroscopy, and the cross-sectional high resolution transmission electron microscopy (HRTEM). As-irradiated samples showed the PL, correlating with the growth of the ion doses. HRTEM found the layers to be partly disintegrated. The thickness of the amorphous Si layer was crucial. For 4 nm thick Si layers the PL was peaking at ~490 nm, and quenched by the annealing. It was ascribed to the structural imperfections. For the thicker Si layers the PL was peaking at ~600 nm and was attributed to the Si-rich nanoclusters in silicon oxide. The annealing increases the PL intensity and shifts the band to ~790 nm, typical of Si nanocrystals. Its intensity was proportional to the dose. Raman spectra confirmed the nanocrystals formation. All the results obtained evidence the material melting in the tracks for 10−11-10−10 s providing thereby fast diffusivities of the atoms. The thicker Si layers provide more excess Si to create the nanoclusters via a molten state diffusion.