Abstract
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.
Highlights
There is considerable interest in nanostructured materials from the group IV Si–Ge system for photonics applications [1,2,3,4,5,6,7,8,9,10]
Another proposed route targeted the host matrix considering its role in the Ge quantum dots (QDs) growth kinetics and morphology (QDs density and separation distances) and in the light absorption of Ge QDs embedded in matrix, i.e., better Si3N4 instead of SiO2 [20]
Short wave infrared (SWIR) extended spectral photocurrent is ensured by stabilization of Ge-rich alloy SiGe NCs [25] against fast Ge diffusion [31] as we showed for Ge-rich SiGe NCs embedded in TiO2
Summary
There is considerable interest in nanostructured materials from the group IV Si–Ge system for photonics applications [1,2,3,4,5,6,7,8,9,10]. The most important inconvenience of this system is the low light absorption-emission efficiency of bulk Si–Ge with an indirect band gap that counts against the long-held goal of integrated group IV photonics This inconvenience can be solved by nanostructuring (quantum confinement) combined with strain [11,12,13] or by exploiting other crystalline structures different from Fd-3m diamond [14,15], such as metastable hexagonal phase [16]. Other solutions are to develop plasmonic structures [17], to fabricate structures with GeSi quantum dots (QDs) embedded in microresonators [18], or by employing hydrogenation technique for passivating detrimental defects [19], all these enabling the enhancement of GeSi and Ge QDs photoluminescence Another proposed route targeted the host matrix considering its role in the Ge QD growth kinetics and morphology (QDs density and separation distances) and in the light absorption of Ge QDs embedded in matrix, i.e., better Si3N4 instead of SiO2 [20]. The cap and buffer are very thin HfO2 layers hampering the fast diffusion of Ge from the active layer, without blocking the electrical contact to the substrate and top contacts
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