Evolution of the Al2O3/Ge(1Â 0Â 0) interface for reactively sputter-deposited films submitted to postdeposition anneals

► Al2O3 sputter deposited on Ge. ► Evidence of a GeO2 interlayer in as-deposited samples. ► Ar and forming gas annealings reduced the amount of oxidized Ge. ► Remaining transition layer consisted of aluminum germanates. ► Al2O3/Ge is more stable than Al2O3/Si in the absence of an oxidizing agent.