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The purpose of this work is to refine the microstructure of eutectic halides, candidates to polaritonic metamaterials, through the directional solidification of ternary compositions. NaCl-LiF- $$\hbox {CaF}_{2}$$ ternary composites have been solidified using Bridgman and micro-pulling-down techniques at pulling rates from 3 to 300 mm/h for the first time. The interparticle spacing is 12% smaller for this composition than for the binary fibrous NaCl-LiF eutectic. Conditions for solidification and growth in order to generate ternary aligned microstructures are discussed. The very small amount of melt remaining in the mixtures until $$580\,^{\circ }\hbox {C}$$ is probably the consequence of solid solubility of LiCl in NaCl and the formation of the reciprocal salt pairs, as in NaCl-LiF. However, it does not prevent the solidification of homogenous ternary microstructures. [ABSTRACT FROM AUTHOR]

Sn-doped β-GaO epitaxial layers have been grown on (100) β-GaO substrates by metal organic vapour-phase epitaxy. Triethylgallium (TEGa), molecular oxygen (O) and tetraethyltin (TESn) were used as Ga, O and Sn precursors, respectively. Layers grown at optimized temperature and chamber pressure, i.e. 850 °C and 5 mbar, had flat surfaces with a rms roughness of about 600 pm. Structural analysis by transmission electron microscopy revealed that the main defects in the layers were stacking faults and twin lamella. The incoherent boundaries of these defects are supposed to act as compensation and scattering centres, limiting the carrier mobility. Sn was homogeneously incorporated with a flat profile throughout the whole layer at concentration levels ranging from 2 × 10 to 3 × 10 cm proportionally to the used TESn flux. All layers were electrically conductive. However, an unambiguous Hall effect was measurable only for Sn concentrations higher than 1 × 10 cm, resulting in electron concentrations from 5 × 10 to 2 × 10 cm at room temperature. For increasing free carrier concentrations, the electron mobility showed the tendency to increase from 10 to 30 cm/Vs. The maximum mobility of 41 cm/Vs, measured in a sample with free carrier concentration of 1 × 10 cm, represents the highest value reported for β-GaO layers grown by MOVPE so far. [ABSTRACT FROM AUTHOR]