Germanium diffusion during $HfO2$ growth on Ge by molecular beam epitaxy

The authors study the Ge diffusion during $HfO2$ growth by molecular beam epitaxy on differently in situ prepared germanium substrates and at different growth temperatures. While $HfO2$ layers grown directly on Ge do not show any germanium contamination, oxygen rich interfacial layers such as $GeOx$ or $GeOxNy$ partly dissolve into the $HfO2$ layer, giving rise to high Ge contamination (from 1% to 10%). The use of nitridated interfacial layers does not prevent Ge diffusion into the $HfO2$ during the growth process because of the high oxygen content present in the nitridated germanium layer.