Structure and optical properties of Si and SiGe layers grown on SiO₂ by chemical vapor deposition

The properties of thin Si and SiGe layers grown on SiO₂ by chemical vapor deposition (CVD) were studied using transmission electron and atomic force microscopies, and Raman and photoluminescence (PL) spectroscopies. The layers with a composition of Si_0.5Ge_0.5 become composed of nanocrystals with an average size of about 100 nm at growth temperatures of 550 °C which is significantly lower than that for the pure Si layers. Moreover, the Si_0.5Ge_0.5 layers exhibit a broad PL peak centered at 0.8 eV, whereas the bandgap of unstrained Si_0.5Ge_0.5 is about 1 eV. This indicates that PL occurs through deep energy levels in the bandgap, which can be associated with crystal defects. The predominance of deep-level PL in radiative emission can be the result of a high concentration of defects that appear due to a low growth temperature. - Highlights: • The Si_0.5Ge_0.5 layers grown on SiO₂ become polycrystalline at 550 °C. • They exhibit a PL peak at 0.8 eV, whereas the Si_0.5Ge_0.5 bandgap is about 1 eV. • Such properties make the layers interesting for applications in photonics