Raman-Brillouin scattering from a thin Ge layer: Acoustic phonons for probing Ge/GeO₂ interfaces

We report on Raman–Brillouin scattering by acoustic phonons from a thin Ge layer. The high frequency acoustic phonons involved in this scattering are used to probe the native oxide present on top of the Ge layer. By comparing experiment and photoelastic modelling, a quantitative analysis is performed which shows that an interfacial layer is located in between the Ge and GeO₂ oxide layers. The native oxide is found to be composed of a 0.5 nm thick interfacial layer and a 1 nm thick GeO₂ layer on top of it. Sensitivity down to the sub-nm scale is evidenced.