Influence of Thermal Treatments on the Chemistry and Self-Assembly of Ge Nanoparticles on SiO_2 Surfaces

摘要

GeH_4 is thermally cracked over a hot filament depositing 0.7-15 ML Ge onto 2-7 nm SiO_2/Si(100) at substrate temperatures of 300-970 K. Ge, GeH_x, GeO, and GeO_2 desorption is monitored through temperature programmed desorption in the temperature range 300-1000 K. Ge bonding changes are analyzed during annealing from 300-1000 K with X-ray photoelectron spectroscopy (XPS). Low temperature desorption features are attributed to GeO and GeH_4. No GeO_2 desorption is observed, but GeO_2 decomposition to Ge through high temperature pathways is seen above 700 K. Germanium oxidization results from Ge etching of the oxide substrate, which is demonstrated through XPS. Ge nanoparticle formation on SiO_2 is demonstrated using the agglomeration process. With these results, explanations for the difficulties of conventional chemical vapor deposition to produce Ge nanocrystals on SiO_2 surfaces are proposed.