Infrared luminescence of annealed germanosilicate layers

In the light of growing importance of semiconductor nanocrystals for photonics, we report on the growth and characterization of annealed germanosilicate layers used for Ge nanocrystal formation. The films are grown using plasma enhanced chemical vapor deposition (PECVD) and post-annealed in nitrogen at temperatures between 600 and 1200 °C for as long as 2 h. Transmission electron microscopy (TEM), Raman scattering and photoluminescence spectroscopy (PL) has been used to characterize the samples both structurally and optically. Formation of Ge precipitates in the germanosilicate layers have been observed using Raman spectroscopy for a variety of PECVD growth parameters, annealing temperatures and times. Ge–Ge mode at ∼300 cm−1 is clearly observed at temperatures as low as 700 °C for annealing durations for 45 min. Raman results indicate that upon annealing for extended periods of time at temperatures above 900 °C; nanocrystals of few tens of nanometers in diameter inside the oxide matrix and precipitation and interdiffusion of Ge, forming SiGe alloy at the silicon and oxide interface take place. Low temperature PL spectroscopy has been used to observe luminescence from these samples in the vicinity of 1550 nm, an important wavelength for telecommunications. Observed luminescence quenches at 140 K. The photoluminescence data displays three peaks closely interrelated at approximately 1490, 1530 and 1610 nm. PL spectra persist even after removing the oxide layer indicating that the origin of the infrared luminescent centers are not related to the Ge nanocrystals in the oxide layer. -- Highlights: • Nanostructures of Ge formed by precipitation of germanium in PECVD grown germanosilicate films were studied. • We have fabricated SiOx:Ge thin films using PECVD. • Annealing of SiOx:Ge films result in of formation of Ge nanocrystals and SiGe alloy the oxide Si interface. • Low temperature photoluminescence around 1500 nm has been indentified as Ge islands formed at silicon and oxide interface