Nanocrystallized Ge-Rich SiGe-HfO₂ Highly Photosensitive in Short-Wave Infrared

Group IV nanocrystals (NCs), in particular from the Si-Ge system, are of high interest for Si photonics applications. Ge-rich SiGe NCs embedded in nanocrystallized HfO₂ were obtained by magnetron sputtering deposition followed by rapid thermal annealing at 600 °C for nanostructuring. The complex characterization of morphology and crystalline structure by X-ray diffraction, μ-Raman spectroscopy, and cross-section transmission electron microscopy evidenced the formation of Ge-rich SiGe NCs (3-7 nm diameter) in a matrix of nanocrystallized HfO₂. For avoiding the fast diffusion of Ge, the layer containing SiGe NCs was cladded by very thin top and bottom pure HfO₂ layers. Nanocrystallized HfO₂ with tetragonal/orthorhombic structure was revealed beside the monoclinic phase in both buffer HfO₂ and SiGe NCs-HfO₂ layers. In the top part, the film is mainly crystallized in the monoclinic phase. High efficiency of the photocurrent was obtained in a broad spectral range of curves of 600-2000 nm at low temperatures. The high-quality SiGe NC/HfO₂ matrix interface together with the strain induced in SiGe NCs by nanocrystallization of both HfO₂ matrix and SiGe nanoparticles explain the unexpectedly extended photoelectric sensitivity in short-wave infrared up to about 2000 nm that is more than the sensitivity limit for Ge, in spite of the increase of bandgap by well-known quantum confinement effect in SiGe NCs.