Thermally driven atomic transport in HfO2 /GeO2/substrate structures on Ge 001 and Si 001 was investigated in N2 ambient as function of annealing temperature and time. As-deposited stacks showed no detectable intermixing and no instabilities were observed on Si. On Ge, loss of O and Ge was detected in all annealed samples, presumably due to evolution of GeO from the GeO2 /Ge interface. In addition, hafnium germanate is formed at 600 °C. Our data indicate that at 500 °C and above HfO2 /GeO2 stacks are stable only if isolated from the Ge substrate
