Vibrational properties of Si/Ge superlattices incorporating biatomic sheets of silicon and germanium

We find that the incorporation of a biatomic sheet of either Si or Ge into a Si/Ge short-period superlattice gives rise to a distinctive Raman spectrum in the wave-number range 370–410 cm-1. We prove that this signal is due to the interfaces of the superlattice and originates from phonon modes within the superlattice, which should not normally be observed in the scattering configuration employed. As symmetry arguments, supported by detailed three-dimensional modeling, preclude the effect from being seen in structures with monatomic or triatomic sheets, we propose that the Raman line shape can be used as a sensitive tool to detect the presence of biatomic sheets of Si in Si/Ge superlattices.