Optical and structural characterization of Ge clusters embedded in ZrO₂

The change of optical and structural properties of Ge nanoclusters in ZrO₂ matrix have been investigated by spectroscopic ellipsometry versus annealing temperatures. Radio-frequency top-down magnetron sputtering approach was used to produce the samples of different types, i.e. single-layers of pure Ge, pure ZrO₂ and Ge-rich-ZrO₂ as well as multi-layers stacked of 40 periods of 5-nm-Ge-rich-ZrO₂ layers alternated by 5-nm-ZrO₂ ones. Germanium nanoclusters in ZrO₂ host were formed by rapid-thermal annealing at 600-800°C during 30s in nitrogen atmosphere. Reference optical properties for pure ZrO₂ and pure Ge have been extracted using single-layer samples. As-deposited multi-layer structures can be perfectly modeled using the effective medium theory. However, annealed multi-layers demonstrated a significant diffusion of elements that was confirmed by medium energy ion scattering measurements. This fact prevents fitting of such annealed structure either by homogeneous or by periodic multi-layer models.