Spectroscopic investigation of quantum confinement effects in ion implanted silicon-on-sapphire films

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Crystalline Silicon-on-Sapphire (SOS) films were implanted with boron (B+) and phosphorous (P+) ions. Different samples, prepared by varying the ion dose in the range 10¹⁴ to 5 x 10¹⁵ and ion energy in the range 150-350 keV, were investigated by the Raman spectroscopy, photoluminescence (PL) spectroscopy and glancing angle x-ray diffraction (GAXRD). The Raman results from dose dependent B+ implanted samples show red-shifted and asymmetrically broadened Raman line-shape for B+ dose greater than 10¹⁴ ions cm⁻². The asymmetry and red shift in the Raman line-shape is explained in terms of quantum confinement of phonons in silicon nanostructures formed as a result of ion implantation. PL spectra shows size dependent visible luminescence at 1.9 eV at room temperature, which confirms the presence of silicon nanostructures. Raman studies on P+ implanted samples were also done as a function of ion energy. The Raman results show an amorphous top SOS surface for sample implanted with 150 keV P+ ions of dose 5 x 10¹⁵ ions cm⁻². The nanostructures are formed when the P+ energy is increased to 350 keV by keeping the ion dose fixed. The GAXRD results show consistency with the Raman results.