Photoluminescence and Raman scattering in three-dimensional Si/Si1-xGex nanostructures

We report detailed Raman and photoluminescence (PL) measurements in Si/Si1-xGex nanostructures grown by molecular-beam epitaxy under conditions of near Stranski-Krastanov (S-K) growth mode. In a series of samples with x controllably increased from 0.098 to 0.53, we observe that an increase in Raman signal related to Ge-Ge vibrations clearly correlates with (i) a redshift in the PL peak position, (ii) an increase in the activation energy of PL thermal quenching, and (iii) an increase in the PL quantum efficiency. The results indicate that in S-K Si/Si1-xGex nanostructures with x>0.5 Ge atoms form nanometer-sized clusters with a nearly pure Ge core and a SiGe shell. (C) 2004 American Institute of Physics.