Crystallinities and light emitting properties of nanostructured SiGe alloy prepared by pulsed laser ablation in inert background gases

For studying the material properties of nanostructured group IV materials, we have developed a pulsed laser ablation method into inert background gases. SiGe alloy nanocrystallites have possibility of novel band structure engineering by controlling not only compositions but also particle sizes. An ArF excimer laser was focused onto the surface of the powder-sintered Si_xGe_1-x target. During the laser ablation, He gas was introduced into a vacuum chamber and was maintained at a constant pressure. Size distribution of the Si_xGe_1-x ultrafine particles decreases with decreasing composition x under fixed conditions of deposition such as background gas pressure. Raman scattering spectra of the deposited SiGe ultrafine particles show three peaks ascribed to mixed crystalline SiGe after annealing, and the linewidths of these peaks broaden due to the reduced size of the crystallites. The frequencies and intensities of the peaks depend on the composition x. Visible PL spectra have broad peaks from 2.25 eV to 2.10 eV, at room temperature. The peak positions show blue shifts with increasing x. Electroluminescent diodes with the Si_0.8Ge_0.2 nanocrystallite active region were fabricated, and emit visible light peaked at around 1.8 eV, at room temperature.