Optically transparent, electrically conductive n-Si/n-GaAs direct wafer bonds are achieved by athorough optimization of surface conditioning using fast atom beams. Bonding at room temperature under high-vacuum conditions is systematically investigated after in situ surface deoxidization using either argon or helium fast atom beams. Using argon, high bond energies of up to 900 mJ/m2 areobtained and further enhanced to achieve bulk strength through rapid annealing at 290 C, thereby enabling the production of thermally stable and mechanically robust hybrid substrates. Moreover, the interface conductivity is significantly improved by an additional thermal annealing at 400 C. Although it is anticipated to induce higher quality interfaces, helium treatment yields, however, limited and unstable bonding. This difference is attributed to an important surface nano-texturing that occurs during fast atom beam processing, a phenomenon that is peculiar to helium and absent in argon treatment

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Ar polycrystals grown for VUV laser applications show an increase of the luminescence efficiency with grain size by a factor of two. Mean grain sizes between 0.05 and 0.7 mm due to different growing conditions are identified by X‐ray diffraction. The crystals have good optical quality and are highly transparent from 1000 nm down to 110 nm.

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