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Transparent semiconducting β-Ga 2 O 3 single crystals were grown by the Czochralski method from an iridium crucible under a dynamic protective atmosphere to control partial pressures of volatile species of Ga 2 O 3 . Thermodynamic calculations on different atmospheres containing CO 2 , Ar and O 2 reveal that CO 2 growth atmosphere combined with overpressure significantly decreases evaporation of volatile Ga 2 O 3 species without any harm to iridium crucible. It has been found that CO 2 , besides providing high oxygen concentration at high temperatures, is also acting as a minor reducing agent for Ga 2 O 3 . Different coloration of obtained crystals as well as optical and electrical properties are directly correlated with growth conditions (atmosphere, pressure and temperature gradients), but not with residual impurities. Typical electrical properties of the n-type β-Ga 2 O 3 crystals at room temperature are: ρ = 0.1 -0.3 Ωcm, μ n,Hall = 110 -150 cm 2 V -1 s -1 , n Hall = 2 -6×10 17 cm -3 and E Ionisation = 30 -40 meV. A decrease of transmission in the IR-region is directly correlated with the free carrier concentration and can be effectively modulated by the dynamic growth atmosphere. Electron paramagnetic resonance (EPR) spectra exhibit an isotropic shallow donor level and anisotropic defect level. According to differential thermal analysis (DTA) measurements, there is substantially no mass change of β-Ga 2 O 3 crystals below 1200 °C (i.e. no decomposition) under oxidizing or neutral atmosphere, while the mass gradually decreases with temperature above 1200 °C. High resolution transmission electron microscopy (HRTEM) images at atomic resolution show the presence of vacancies, which can be attributed to Ga or O sites, and interstitials, which can likely be attributed to Ga atoms.

We present a new approach for scaling-up the growth of β-Ga2O3 single crystals grown from the melt by the Czochralski method, which has also a direct application to other melt-growth techniques involving a noble metal crucible. Experimental and theoretical results point to melt thermodynamics as the crucial factor in increasing the volume of a growing crystal. In particular, the formation of metallic gallium in the liquid phase in large melt volumes causes problems with crystal growth and eutectic or intermetallic phase formation with the noble metal crucible. The larger crystals to be grown the higher oxygen concentration is required. The minimum oxygen concentration ranges from about 8 to 100 vol.% for 2 to 4 inch diameter cylindrical crystals, challenging the use of iridium crucibles in a combination with such high oxygen concentrations. A specific way of oxygen delivery to a growth furnace with the iridium crucible allows to minimize the formation of metallic gallium in the melt and thus obtaining large crystal volumes while decreasing the probability of the eutectic formation.

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The crystal chemistry of GdScO3 and, for the first time, of DyScO3, SmScO3 and NdScO3 has been investigated using single crystals. The structure of the Czochralski grown crystals was refined from single crystal X-ray diffraction data, their chemical compositions were analysed by inductively coupled plasma optical emission spectrometry (ICP OES). Orthorhombic distorted perovskite structure types with the space group Pnma could be confirmed in all cases. The B-site of the lanthanoid scandates shows with 2.090 to 2.116 Å typical bond lengths for octahedrally coordinated scandium. The distortion of the B-site is rather small. The A-site is occupied by the lanthanoid (Ln) and the Ln—O bond distances vary from 2.233 to 3.722 Å. This indicates its high distortion and makes an assignment of the coordination number difficult. However, an 8-fold coordination for the A-site has to be assumed. The Ln-scandates show a continuous structural evolution with the size of the lanthanoid. A discontinuity within the intermediate members of the Ln-scandates — which had previously been described — was not observed. The ICP OES investigation of these samples results in non-stoichiometric chemical compositions: the chemical analyses show always a depletion in the lanthanoid. Site occupancy refinements based on single crystal diffraction data support the idea of the Ln-depletion on the A-site (inducing O-defects on the O2-position). Several substitution mechanisms are discussed, but the authors favour that vacancies on the A-site coupled with oxygen vacancies cause the Ln-deficiencies. The crystallochemical formula of the investigated Ln-scandates may be written as: (∀0.056Dy0.944)ScO2.916,(∀0.048Gd0.952)ScO2.928, (∀0.045Sm0.955)ScO2.933 and (∀0.033Nd0.967)ScO2.951.

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