Influence of reductant and germanium concentration on the growth and stress development of germanium nanocrystals in silicon oxide matrix

Germanium (Ge) nanocrystals have been synthesized by annealing co-sputtered SiO2-Ge samples in N-2 or forming gas (90% N-2 + 10% H-2) at temperatures ranging from 700 to 1000 degrees C. We concluded that the annealing ambient, temperature and Ge concentration have a significant influence on the formation and evolution of the nanocrystals. We showed that a careful selective etching of the annealed samples in hydrofluoric acid solution enabled the embedded Ge nanocrystals to be liberated from the SiO2 matrix. From the Raman results of the as-grown and the liberated nanocrystals, we established that the nanocrystals generally experienced compressive stress in the oxide matrix and the evolution of these stress states was intimately linked to the distribution, density, size and quality of the Ge nanocrystals.