Influence of the crystallization process on the luminescence of multilayers of SiGe nanocrystals embedded in SiO2

Multilayers of SiGe nanocrystals embedded in an oxide matrix have been fabricated by low-pressure chemical vapor deposition of SiGe and SiO2 onto Si wafers (in a single run at 390 °C and 50 mTorr, using GeH4, Si2H6 and O2) followed by a rapid thermal annealing treatment to crystallize the SiGe nanoparticles. The main emission band is located at 400 nm in both cathodoluminescence and photoluminescence experiments at 80 K and also at room temperature. The annealing conditions (temperatures ranging from 700 to 1000 °C and for times of 30 and 60 s) have been investigated in samples with different diameter of the nanoparticles (from ≈3 to ≥5 nm) and oxide interlayer thickness (15 and 35 nm) in order to establish a correlation between the crystallization of the nanoparticles, the degradation of their composition by Ge diffusion and the intensity of the luminescence emission band. Structures with small nanoparticles (3–4.5 nm) separated by thick oxide barriers (≈35 nm) annealed at 900 °C for 60 s yield the maximum intensity of the luminescence. An additional treatment at 450 °C in forming gas for dangling-bond passivation increases the intensity of the luminescence band by 25–30%.