Raman and photoluminescence characterization of Ge nanocrystals in co-sputtered Ge+SiO2 system

Raman and photoluminescence (PL) results of Ge nanocrystals prepared from co-sputtered Ge+SiO2 samples under rapid-thermal annealling (RTA) with different annealing conditions are presented. The Raman results showed a transition from amorphous to nanocrystalline Ge when the samples were annealed at a temperature higher than 700 °C for longer than 300 s. The Raman spectrum of sample annealed at 1000 °C is very similar to that of the as-deposited amorphous sample. However, when the annealing duration is reduced to less than 50 s, clear Raman signals can be seen for samples annealed at 1000 °C. Transmission electron micrographs showed that uniform Ge nanocrystals were obtained for samples annealed at 800 °C for 300 s or 1000 °C for 50 s, and nanocrystals with multiple twinned structure (of diameter ∼200 Å) were observed near the Si–SiO2 interface (1000 °C for 300 s). PL results showed that maximum intensity of the 1.9 and 3.0 eV peaks was obtained from samples annealed at 800 °C for 20 s or transiently to 1000 °C at 30 °C/s. These results suggest that a critical thermal budget is required for the formation of uniform nanocrystals and for maximum PL emission.