Micro-raman characterization of molecular-beam epitaxial ge heterolayers on Si substrates

Molecular-beam epitaxial germanium heterolayers on silicon are characterized by micro-Raman spectroscopy. The samples are angle-lapped to probe the near-interface region. A small positive shift in the germanium phonon frequency is observed near the interface compared with the surface of the 1 μm thick layer. This indicates that the misfit stress is not relaxed completely in the as-grown layers. The samples are annealed at 700°C, a temperature higher than the growth temperature, and then the germanium peak shifts toward lower frequency near the interface. This would be due to both thermal stress and formation of an interfacial alloy layer by the interdiffusion. After annealing at 850°C, the germanium peak shifts downward further because of the interdiffusion, and the peak due to the Si−Ge vibration is clearly observed near the interface.