Whether Ge-Rich ZrO₂ and Ge-Rich HfO₂ Materials Have Similar Reaction on Annealing Treatment?

Abstract

The properties of Ge-HfO2 and Ge-ZrO2 films were studied versus Ge content and annealing temperature by means of Raman scattering, FTIR and X-ray diffraction methods. Ge-HfO2 films with [Ge]<5 at.% were polycrystalline, whereas higher Ge content stabilized amorphous structure that was stable for T<600°C. The T increase caused the formation of Ge clusters and tetragonal HfO2 phase. This latter appeared at T=600-670°C, while the Ge clusters crystallized at T=700-800°C. Unlike to Ge-rich HfO2 films, as-deposited Ge-ZrO2 films and those annealed at T≤600°C were amorphous. In these films, formation of Ge clusters and their crystallization occurred at T=640-700°C depending on Ge content, whereas ZrO2 phase crystalized at T=680-700°C that allowed to form Ge nanocrystals in amorphous matrix at T=640-680°C. For T>800°C, the films showed appearance of monoclinic HfO2 or ZrO2 phases that was explained by the Ge content decrease via volatile GeO formation. Obtained results supported theoretical prediction of the stability of tetragonal phases in these oxides via Ge doping. However, our results showed also some difference in the phase separation process of Ge-rich HfO2 and Ge-rich ZrO2 upon thermal treatment.