Vibrational and light-emitting properties of Si/Si$_{1-x}$Sn$_x$ heterostructures

Multilayer heterostructures Si/Si$_{1-x}$Sn$_x$ grown by molecular beam epitaxy on Si (001) substrates have been studied by Raman and photoluminescence spectroscopy. Raman spectra exhibit peaks corresponding to the vibrations of Si-Sn and Sn-Sn bonds; the vibrations of Sn-Sn bonds imply the presence of tin nanocrystals in heterostructures. Two photoluminescence bands at 0.75 eV (1650 nm) and 0.65 eV (1900 nm) have been observed in heterostructures at low temperatures. The former band can be attributed to optical transitions in quantum wells in the type II heterostructure Si/Si$_{1-x}$Sn$_x$. The latter band can be associated with excitons localized in tin nanocrystals.