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 Si0.5Ge0.5 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 Si0.5Ge0.5 layers exhibit a broad PL peak centered at 0.8 eV, whereas the bandgap of unstrained Si0.5Ge0.5 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.