Germanosilicate layers were grown on Si substrates by plasma enhanced chemical vapor deposition (PECVD) and annealed at different temperatures ranging from 700-1010 °C for durations of 5 to 60 min. Transmission electron microscopy (TEM) was used to investigate Ge nanocrystal formation in SiO 2:Ge films. High-resolution cross section TEM images, electron energy-loss spectroscopy and energy dispersive X-ray analysis (EDX) data indicate that Ge nanocrystals are present in the amorphous silicon dioxide films. These nanocrystals are formed in two spatially separated layers with average sizes of 15 and 50 nm, respectively. EDX analysis indicates that Ge also diffuses into the Si substrate.