Study of Stress Evolution of Germanium Nanocrystals Embedded in Silicon Oxide Matrix

Germanium (Ge) nanocrystals had been synthesized by annealing co-sputtered SiO2-Ge in N2 and/or forming gas (90% N2 + 10% H2) at temperatures ranging from 700 to 1000°C from 15 to 60 min. It was concluded that the annealing ambient, temperature and time have a significant influence on the formation and evolution of the nanocrystals. We also showed that a careful selective etching of the annealed samples in hydrofluoric solution enabled the embedded Ge nanocrystals to be liberated from the Si oxide 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 link to the distribution, density, size and quality of the Ge nanocrystals.