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Aqueous acidic ozone (O 3 )-containing solutions are increasingly used for silicon treatment in photovoltaic and semiconductor industries. We studied the behavior of aqueous hydrofluoric acid (HF)-containing solutions (i.e., HF−O 3 , HF−H 2 SO 4 −O 3 , and HF−HCl−O 3 mixtures) toward boron-doped solar-grade (100) silicon wafers. The solubility of O 3 and etching rates at 20 °C were investigated. The mixtures were analyzed for the potential oxidizing species by UV−vis and Raman spectroscopy. Concentrations of O 3 (aq) , O 3 (g) , and Cl 2 (aq) were determined by titrimetric volumetric analysis. F − , Cl − , and SO 4 2− ion contents were determined by ion chromatography. Model experiments were performed to investigate the oxidation of Hterminated silicon surfaces by H 2 O−O 2 , H 2 O−O 3 , H 2 O−H 2 SO 4 −O 3 , and H 2 O−HCl−O 3 mixtures. The oxidation was monitored by diffuse reflection infrared Fourier transformation (DRIFT) spectroscopy. The resulting surfaces were examined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). HF−H 2 O−O 3 mixtures show a polishing etching behavior, whereas HF−HCl−H 2 O−O 3 mixtures exhibit slight anisotropic etching. Formation of pyramidal-like morphologies on (100) silicon surfaces was observed. In all cases, cleaned and H-terminated silicon surfaces are obtained. The results were used to draw conclusions about the dissolution mechanism of silicon in the respective solutions. In HF−H 2 O−O 3 mixtures, silicon is dissolved by an O 3(aq) -diffusion-controlled tetravalent etching mechanism. Interestingly, in H 2 SO 4 -rich aqueous HF−H 2 SO 4 −O 3 solutions, only the native oxide is removed, whereas silicon is not attacked and dissolved. In HCl-containing solutions, Cl 2 or Cl 3− are responsible for silicon oxidation. HCl can be considered as a catalyst resulting in a divalent silicon dissolution mechanism similar to the etching in alkaline solutions.

Germanium nanocrystals embedded in high-k dielectric matrices are of main interest for infrared sensing application, as a role model for Ge-based nanoelectronics passivation or for nonvolatile memory devices. The capability of the size control of those nanocrystals via rapid thermal processing of superlattice structures is shown for the [Ge–TaZrOx/TaZrOx]n, [Ge–TaZrOx/SiO2/TaZrOx]6, and [TaZrOx/Ge–SiO2]n superlattice systems. All superlattices were deposited by radiofrequency magnetron sputtering. Transmission electron microscopy (TEM) imaging confirms the formation of spherically shaped nanocrystals. Raman scattering proved the crystallization of Ge above 700°C. The TaZrOx crystallizes above 770°C, associated with a phase separation of Ta2O5 and ZrO2 as confirmed by x-ray diffraction. For the composite layers having 3 nm and 6 nm thickness, the size of the Ge nanocrystals correlates with the deposited layer thickness. Thicker composite layers (above 9 nm) form two fractions of nanocrystals with different sizes. An additional SiO2 layer in the [Ge–TaZrOx/SiO2/TaZrOx]6 superlattice stacks facilitates the formation of larger and better separated Ge nanocrystals. The deposition of Ge-SiO2 composite layers separated by pure TaZrOx illustrates the barrier effect of TaZrOx against Ge diffusion. All three material systems allow the controlled formation of Ge nanocrystals in amorphous matrices at temperatures above 700 and below 770°C. Graphical abstract

Germanium nanocrystals (nc) offer promising properties for different applications in electronics and photonics, like non-volatile memories [1] or photodiodes for the visible or infrared wavelength region [2, 3]. For those applications, a spatially and size controlled synthesis is necessary to enable for example electrical isolation between the nanocrystals or the proper adjustment of the optical bandgap. Recent work has shown that the material systems Ge/TaZrOx, Ge/SiO2 and Ge/TaZrOx/SiO2 fulfil these requirements. To form size controlled nc, a Ge rich oxide layer like SiO2 or TaZrOx and pure oxide layer are deposited alternatingly via co-sputtering. Subsequent rapid thermal annealing forms the Ge nc by phase separation and crystallization. During the annealing process the pure TaZrOx interlayers act as a diffusion barrier for Ge, so these nc are confined to the thickness of the deposited mixed layer. The addition of a pure SiO2 interlayer leads to enlarged nc size by growth of the nc into the SiO2 layer. The use of an additional SiO2 layer has the further advantage of improved lateral nc separation in comparison to structures without the SiO2 interlayers. This leads to an improved electrical isolation of each nc. Still the bandgap of these nc can be adjusted easily by their size due to the quantum confinement effect. Another advantage of Ge is the full compatibility to Si based processes. However, both Si and Ge has an indirect band gap, so the efficiency of e.g. light emitting diodes is low. The fabrication of Sn containing Ge can lead to a direct bandgap [4]. In our work we show the formation of Sn doped Ge nc in TaZrOx and SiO2, to create nc of controlled size. Our focus is the crystallization process of the nc, to avoid formation of pure Sn crystals, but still achieve a complete separation of the Ge-Sn alloy from the oxides. Samples with different Sn concentrations are annealed in a range of 500 °C to 800 °C and checked by Raman scattering and TEM. Furthermore, the influence of the used oxide on the nc crystallization temperature is investigated. [1] Tiwari, S. Appl. Phys. Lett. 1996, 69, 1232 [2] Haas, S. J. Appl. Phys. 2013, 113, 44303 [3] Lehninger et al. Phys . Stat. Sol. (a), 2018, 155, 1701028 [4] Slav, A. et al. ACS Appl.NanoMater. 2019, 2, 3626−3635