Influence of GeSi interfacial layer on Ge–Ge optical phonon mode in SiO2 films embedded with Ge nanocrystals

The Ge–Ge optical phonon peak at 300 cm−1 acquired from amorphous SiO2 films embedded with Ge nanocrystals by Raman scattering is sensitive to the Si content. When the Si concentration is high, a thin GeSi interfacial layer forms around the Ge nanocrystals. A tensile stress is produced to partially offset the compressive stress imposed by the SiO2 matrix on the Ge nanocrystals, consequently downshifting the frequency of the optical phonon and increasing its linewidth. Theoretical calculation based on phonon confinement and compressive effects discloses that the interfacial layer plays a crucial role in the optical phonon behavior.