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We have systematically studied the growth, by the Czochralski method, and basic physical properties of a 2 cm and 2 in. diameter bulk β-(AlxGa1−x)2O3 single crystal with [Al] = 0–35 mol. % in the melt in 5 mol. % steps. The segregation coefficient of Al in the Ga2O3 melt of 1.1–1.2 results in a higher Al content in the crystals than in the melt. The crystals were also co-doped with Si or Mg. [Al] = 30 mol. % in the melt (33–36 mol. % in the crystals) seems to be a limit for obtaining bulk single crystals of high structural quality suitable for homoepitaxy. The crystals were either semiconducting (no intentional co-dopants with [Al] = 0–30 mol. % and Si-doped with [Al] = 15–20 mol. %), degenerately semiconducting (Si-doped with [Al] ≤ 15 mol. %), or semi-insulating ([Al] ≥ 25 mol. % and/or Mg-doped). The full width at half maximum of the rocking curve was 30–50 arcsec. The crystals showed a linear but anisotropic decrease in all lattice constants and a linear increase in the optical bandgap (5.6 eV for [Al] = 30 mol. %). The room temperature electron mobility at similar free electron concentrations gradually decreases with [Al], presumably due to enhanced scattering at phonons as the result of a larger lattice distortion. In Si co-doped crystals, the scattering is enhanced by ionized impurities. Measured electron mobilities and bandgaps enabled to estimate the Baliga figure of merit for electronic devices. [ABSTRACT FROM AUTHOR]

Laser‐flash measurements of the thermal conductivity λ(hkl)$\lambda _{(hkl)}$ of Czochralski‐grown β‐Ga2O3 single crystals are reported perpendicular to four independent crystallographic lattice planes (hkl)=(2¯01)$(hkl)=(\bar{2}01)$, (010), (001), and (100) between room temperature and 1200 K. λ is represented by a symmetric tensor of rank 2 and has four independent components. Tensor components λ11=λ(100)=12.13$\lambda _{11}=\lambda _{(100)}=12.13$ W m−1 K−1 and λ22=λ(010)=24.26$\lambda _{22}=\lambda _{(010)}=24.26$ W m−1 K−1 (values for 300 K) can be directly measured. λ33=14.09$\lambda _{33}=14.09$ W m−1 K−1 and λ13=−0.992$\lambda _{13}=-0.992$ W m−1 K−1, instead, are obtained by combining λ(001)=13.53$\lambda _{(001)}=13.53$ W m−1 K and λ(2¯01)=14.33$\lambda _{(\bar{2}01)}=14.33$ W m−1 K. The crystallographic b⃗$\vec{b}$‐axis is the direction with the highest thermal conductivity, λ22. The thermal conductivity assumes its lowest value (11.73 W m−1 K−1) in a direction close to the crystallographic a⃗$\vec{a}$‐axis. However, this direction does not coincide with a⃗$\vec{a}$, and changes with temperature. [ABSTRACT FROM AUTHOR]

Iron(II) oxide, wüstite, is the iron oxide with the lowest oxygen content. Under ambient conditions it is metastable for two reasons: (1) it undergoes eutectoid decomposition to Fe and Fe3O4 below ≈570° C, and (2) depending on temperature, it is thermodynamically stable only for very low oxygen partial pressures, down to below 10−20 bar. Hence, for the growth of single crystals from the melt, the growth atmosphere must contain reducing components to keep the oxygen partial pressure on the required low level. With Ar/CO2/CO mixtures this aim can be reached. It is shown experimentally and by thermodynamic calculation, that the grown crystals contain carbon inclusions. Theoretically it is shown that wüstite crystals without carbon inclusions could be grown in humid N2/H2 mixtures. First experiments are presented in this article, but a further adjustment of experimental parameters is required. [ABSTRACT FROM AUTHOR]

Two inch diameter, highly conducting (Si-doped) bulk β-Ga2O3 single crystals with the cylinder length up to one inch were grown by the Czochralski method. The obtained crystals revealed high structural quality characterized by narrow x-ray rocking curves (FWHM ≤ 25 arc sec) and high surface smoothness (RMS < 200 pm) of the epi-ready wafers. The free electron concentration and Hall mobility at room temperature were in the range of 1.6–9 × 1018 cm−3 and 118 – 52 cm2 V−1 s−1, respectively, which are not affected by a heat treatment at temperatures up to 1000 °C in an oxidizing atmosphere. Temperature-dependent electrical properties of the crystals revealed a degenerated semiconducting state. Both high structural quality and electrical properties make the crystals well suited as substrates for homoepitaxy and electronic device fabrication in the vertical configuration. [ABSTRACT FROM AUTHOR]

Large bulk LaInO3 single crystals are grown from the melt contained within iridium crucibles by the vertical gradient freeze (VGF) method. The obtained crystals are undoped or intentionally doped with Ba or Ce, and enabled wafer fabrication of size 10 × 10 mm2. High melting point of LaInO3 (≈1880 °C) and thermal instability at high temperatures require specific conditions for bulk crystal growth. The crystals do not undergo any phase transition up to 1300 °C, above which a noticeable thermal decomposition takes place. The good structural quality of the crystals makes them suitable for epitaxy. The onset of strong optical absorption shows orientation‐dependent behavior due to the orthorhombic symmetry of the LaInO3 crystals. Assuming direct transitions, optical bandgaps of 4.35 and 4.39 eV are obtained for polarizations along the [010] and the [100], [001] crystallographic directions, respectively. There is an additional weak absorption in the range between 2.8 and 4 eV due to oxygen vacancies. Density‐functional‐theory calculations support the interpretation of the optical absorption data. Cathodoluminescence spectra show a broad, structured emission band peaking at ≈2.2 eV. All bulk crystals are electrically insulating. The relative static dielectric constant is determined at a value of 24.6 along the [001] direction. [ABSTRACT FROM AUTHOR]

Truly bulk ZnGa2O4 single crystals were obtained directly from the melt. High melting point of 1900 ± 20 °C and highly incongruent evaporation of the Zn- and Ga-containing species impose restrictions on growth conditions. The obtained crystals are characterized by a stoichiometric or near-stoichiometric composition with a normal spinel structure at room temperature and by a narrow full width at half maximum of the rocking curve of the 400 peak of (100)-oriented samples of 23 arcsec. ZnGa2O4 is a single crystalline spinel phase with the Ga/Zn atomic ratio up to about 2.17. Melt-grown ZnGa2O4 single crystals are thermally stable up to 1100 and 700 °C when subjected to annealing for 10 h in oxidizing and reducing atmospheres, respectively. The obtained ZnGa2O4 single crystals were either electrical insulators or n-type semiconductors/degenerate semiconductors depending on growth conditions and starting material composition. The as-grown semiconducting crystals had the resistivity, free electron concentration, and maximum Hall mobility of 0.002–0.1 Ωcm, 3 × 1018–9 × 1019 cm−3, and 107 cm2 V−1 s−1, respectively. The semiconducting crystals could be switched into the electrically insulating state by annealing in the presence of oxygen at temperatures ≥700 °C for at least several hours. The optical absorption edge is steep and originates at 275 nm, followed by full transparency in the visible and near infrared spectral regions. The optical bandgap gathered from the absorption coefficient is direct with a value of about 4.6 eV, close to that of β-Ga2O3. Additionally, with a lattice constant of a = 8.3336 Å, ZnGa2O4 may serve as a good lattice-matched substrate for magnetic Fe-based spinel films. [ABSTRACT FROM AUTHOR]

Bulk MgGa2O4 single crystals with inverse spinel structure were grown from the melt by different methods. The degree of inversion could be changed by suitable annealing, which was confirmed by differential scanning calorimetry analysis and corresponding changes of the specific heat capacity. MgGa2O4 is thermally much more stable at high temperatures than β-Ga2O3 despite of a higher melting point of about 1930 °C and could be grown under a neutral atmosphere. Melt-grown MgGa2O4 crystals were found to be either electrical insulators or n-type semiconductors depending on the presence of oxygen in the growth atmosphere and the growth method applied. Growing the crystals in the presence of oxygen resulted in electrically insulating crystals. For as-grown and intentionally undoped semiconducting crystals, the free electron concentration was in the range of 1017-1018 cm−3, but the electron mobility was relatively low, just a few cm2V−1s−1. The free electron concentration remained at a level of 1018 cm−3 after annealing in a hydrogen-containing atmosphere at 600-900 °C for 10 h. On the other hand, annealing in an oxygen-containing atmosphere above 600 °C for 10-40 h turns the crystals from the semiconducting to the insulating state. The optical bandgap at room temperature amounts to about 4.9 eV. It decreases with temperature at a rate of 1.35 meV/K. Cathodoluminescence spectra of as-grown crystals show a dominant band at 362 nm. The melt-grown crystals have sufficient size and structural quality to be used as substrates for epitaxy. [ABSTRACT FROM AUTHOR]

The TiO2 rich part of the (1 - x)SrO + xTiO2 phase diagram (0.5 ⩽ x ⩽ 1.0) was redetermined and the eutectic point between SrTiO3 and TiO2 was found at xeut = 0.7700 ± 0.0001; Teut = 1449 ± 3 °C. From TiO2 rich melt solutions, x = 0.75, centimeter-sized single crystals could be grown. The best crystals with an etch pit density of <2 × 104 cm-2 were obtained for growth directions (110) and (100). AFM investigation of the interface reveals layer-by-layer growth. [ABSTRACT FROM AUTHOR]

SnO2 is a semiconductor with a wide optical bandgap (3.5 eV), which makes it an attractive transparent semiconducting oxide (TSO) for electronic and opto-electronic applications. At elevated temperatures it is, however, much more unstable than other TSOs (such as ZnO, Ga2O3, or In2O3). This leads to a rapid decomposition even under very high oxygen pressures. Our experiments showed that stoichiometric SnO2 does not melt up to 2100 °C, in contradiction to earlier published data. Bulk SnO2 single crystals, that could provide substrates for epitaxial growth, have not been reported so far. Hereby we report on truly bulk SnO2 single crystals of 1 inch diameter grown by physical vapor transport (PVT). The most volatile species during SnO2 decomposition is, in addition to oxygen, SnO, which is stable in the gas phase at high temperature and reacts again with oxygen at lower temperatures to form SnO2. We identified a relatively narrow temperature window, temperature gradients and a ratio of SnO/O2 for providing the best conditions for SnO2 single crystal growth. X-ray powder diffraction (XRD) proved the single SnO2 phase. Moreover, by selecting a suitable SnO/O2 ratio it was possible to obtain either n-type conductivity with electron concentrations up to 2 × 1018 cm−3 and electron mobilities up to 200 cm2 V−1 s−1, or insulating behavior. The crystals exhibited an optical absorption edge located at 330-355 nm, depending on the crystal orientation, and a good transparency over visible and near infrared (NIR) spectra. [ABSTRACT FROM AUTHOR]

Lithium niobate tantalate (LiNb 1− x Ta x O 3 , LNT) solid solutions offer exciting new possibilities for applications ranging from optics, piezotronics, and electronics beyond the capabilities of the widely used singular compounds of lithium niobate (LiNbO 3 , LN) or lithium tantalate (LiTaO 3 , LT). Crystal growth of homogeneous LNT single crystals by the Czochralski method is still challenging. One key aspect of homogeneous growth is the accurate knowledge of thermal conductivity through the crystal boule during the growth, which is central to control the crystal growth. Therefore, the temperature dependent thermal conductivity of pure LN, LT, and LNT solid solutions, as well as of selected doped LN and LT crystals (Mg, Zn) was investigated across the temperature range from 300 to 1300 K. The results that span across the whole composition range can directly be applied for optimizing growth conditions of both LNT solid solutions as well as doped and undoped LN and LT crystals. [ABSTRACT FROM AUTHOR]

The ternary phase diagram of copper–iron–aluminium delafossite is established with FactSage calculations to improve the conditions for solution growth and the electrical conductivity of the transparent p‐type semiconductor copper–aluminium delafossite by addition of iron oxide. Initial growth experiments with the optical float zone method show that the growth of single crystals with commercially relevant dimensions is not expected in the near future. [ABSTRACT FROM AUTHOR]

Highlights • Growth of Al 1−x Sc x N bulk single crystals. • Substrate for AlGaN based UVB optoelectronic devices. • Sublimation by physical vapor transport (PVT). • Aluminum scandium nitride alloy growth. Abstract We describe the preparation of wurtzite Al 1−x Sc x N bulk single crystals by physical vapor transport by introducing scandium to the aluminum nitride (AlN) source material. The Al 1−x Sc x N single crystals obtained exhibit a maximum scandium atomic concentration of about x = 0.55% in axial c-direction while being uniform within the c-plane. The high structural quality as determined by high resolution x-ray diffraction is comparable to that of AlN bulk crystals. However, the incorporated scandium concentration is about 15 times lower than expected from thermodynamic considerations. This behavior is ascribed to a pronounced scandium segregation or agglomeration in the gas phase and parasitic deposition/loss of ScN during growth. [ABSTRACT FROM AUTHOR]

The pseudobinary system LaLuO 3 –LaScO 3 was explored in hopes of discovering new perovskite-type substrates with pseudocubic lattice parameters above 4 Å. A complete solid solution of the type (LaLuO 3 ) 1− x (LaScO 3 ) x forms between the end members LaLuO 3 and LaScO 3 , enabling large single crystals of (LaLuO 3 ) 1− x (LaScO 3 ) x to be grown from the melt. A single crystal with x ≈0.34 was demonstrated. Considering the maximum thermal load of the iridium crucibles appropriate for Czochralski growth of this solid solution, the theoretically maximum achievable x -value is ~0.67. Based on the phase diagram determined, it is anticipated that single crystals with pseudocubic lattice constants between 4.09 and 4.18 Å can be grown in this system by the Czochralski method. [ABSTRACT FROM AUTHOR]

Measurements of thermal diffusivity ? (using laser flash analysis) for temperatures from 100 °C to 1200 °C and of the inversion parameter x (using X-ray analysis) for the single crystal spinel MgGa2O4 have been performed. X-ray analysis showed a small change in x for samples annealed at 800 °C (x = 0.838) and 1200 °C (x = 0.834). Thermal diffusivity revealed a significant rise of ? for temperatures higher than 950 °C, deviating from the typical 1/T drop of ?. An additional systematic rise of ? with time is observed for temperatures between 950 °C and 1100 °C. A connection between cation disordering processes typical for spinels at elevated temperatures and the observed deviation of ? is proposed: Data indicate that cations changing their occupancy site at equilibration processes contribute significantly to ? and therefore represent a new type of heat transport. [ABSTRACT FROM AUTHOR]

The growth of bulkx β-Ga 2 O 3 single crystals by the Czochralski method is reported and discussed in terms of crucial growth conditions and correlated with basic electrical and optical properties of the obtained crystals. β-Ga 2 O 3 crystals have a tendency to a spiral formation due to free carrier absorption in the near infrared (NIR) wavelength range, which hampers radiative heat transfer through the growing crystal. Moderate or low free electron concentrations (<5×10 17 cm −3 ) lead to cylindrical crystals with a high crystallized fraction ( g ≥0.5). The use of a CO 2 -containing growth atmosphere provides oxygen partial pressures between 0.8 and 4.4×10 −2 bar that is sufficient to obtain cylindrical and semiconducting crystals. Doping with Sn increases the free electron concentration in the crystals to high values (~10 19 cm −3 ) that lead to an immediate spiral formation, while doping with Mg (>6 wt ppm) provides insulating crystals with reduced probability of the spiral formation. The estimated Mg equilibrium segregation coefficient across the liquid–solid interface is 0.10–0.12. Annealing of undoped crystals in an oxidizing atmosphere at temperatures ≥1200 °C for 20 h decreases the bulk free electron concentration by about one order of magnitude, while the crystal surface becomes insulating. However, Mg:β-Ga 2 O 3 crystals are insensitive to annealing in both oxygen- and hydrogen-containing atmospheres. The transmittance spectra showed a steep absorption edge at 260 nm and virtually full transparency in the visible and NIR wavelength range for low and moderate free electron concentrations. We also demonstrated the possibility of growing 2 in. diameter β-Ga 2 O 3 single crystals by the Czochralski method. The good crystal quality is evidenced by rocking curve FWHM values of below 50". We noted that most dislocations propagate parallel to (100) plane. Further, we also provide thermal properties of the crystals as a function of temperature. [ABSTRACT FROM AUTHOR]

In the course of development of transparent semiconducting oxides (TSOs) we compare the growth and basic physical properties bulk single crystals of ultra-wide bandgap (UWBG) TSOs, namely β-Ga 2 O 3 and Ga-based spinels MgGa 2 O 4 , ZnGa 2 O 4 , and Zn 1-x Mg x Ga 2 O 4. High melting points of the materials of about 1800 -1930 °C and their thermal instability, including incongruent decomposition of Ga-based spinels, require additional tools to obtain large crystal volume of high structural quality that can be used for electronic and optoelectronic devices. Bulk β-Ga 2 O 3 single crystals were grown by the Czochralski method with a diameter up to 2 inch, while the Ga-based spinel single crystals either by the Czochralski, Kyropoulos-like, or vertical gradient freeze / Bridgman methods with a volume of several to over a dozen cm3. The UWBG TSOs discussed here have optical bandgaps of about 4.6 - 5 eV and great transparency in the UV / visible spectrum. The materials can be obtained as electrical insulators, n -type semiconductors, or n -type degenerate semiconductors. The free electron concentration (n e) of bulk β-Ga 2 O 3 crystals can be tuned within three orders of magnitude 1016 - 1019 cm−3 with a maximum Hall electron mobility (μ) of 160 cm2V−1s−1, that gradually decreases with n e. In the case of the bulk Ga-based spinel crystals with no intentional doping, the maximum of n e and μ increase with decreasing the Mg content in the compound and reach values of about 1020 cm−3 and about 100 cm2V−1s−1 (at n e > 1019 cm−3), respectively, for pure ZnGa 2 O 4. [ABSTRACT FROM AUTHOR]

β-Ga 2 O 3 is an emerging ultra-wide bandgap (4.9 eV) oxide semiconductor that additionally scintillates under gamma excitation. A unique combination of transparency in the UV/visible spectrum, semiconducting, and scintillation properties makes that compound interesting for fundamental studies of underlying physics and design of novel devices, in particular compact detectors for gamma radiation. Undoped, and singly (Ce, Si, Al), doubly (Ce + Si, Ce + Al), and triply (Ce + Al + Si) doped bulk β-Ga 2 O 3 single crystals were grown by the Czochralski method under very similar conditions and systematically studied in terms of electrical and optical properties that were correlated with scintillation light yield under gamma excitation. A wide spectrum of doping enabled to control the free electron concentration in semiconducting β-Ga 2 O 3 crystals within almost three orders of magnitude (7 × 1015–6 × 1018 cm−3) with the Hall mobility approaching 150 cm2 V−1s−1. The maximum of light yield under gamma excitation was recorded for undoped and Ce-doped β-Ga 2 O 3 single crystals having the free electron concentration of mid 1016 cm−3. The light yield significantly decreases for both electrically insulating and highly conducting (Si-doped) crystals. None of the dopants (Ce, Si, Al) introduces any absorption bands in the spectral region of light emission (340–410 nm) under gamma excitation. The dopants in quest do not affect the structure of neither cathodoluminescence (CL) nor radioluminescence (RL) emissions, but modify their absolute intensity. A double-band structure of RL spectra corresponds to UV and blue emissions observed in CL spectra that are assigned to self-trapped excitons. Image 1 • Doped semiconducting β-Ga 2 O 3 was grown and studied for gamma radiation detection. • The crystals are fully transparent to scintillation emissions at 340–410 nm. • Maximum of light yield was found at free electron concentration of mid 1016 cm−3. • Luminescence spectra point to self-trapped excitons in scintillation mechanism. [ABSTRACT FROM AUTHOR]

• CuFeO 2 crystals up to 50 mm in length and up to 10 mm in diameter were grown by OFZ. • Crystals will be used for MBE growth of other functional delafossites. • The melting of CuFeO 2 is not simply incongruent, the gas phase is also involved. CuFeO 2 single crystals up to 50 mm in length and up to 10 mm in diameter were grown by the optical floating-zone method. Stoichiometric polycrystalline rods with a diameter of 6–12 mm were used as feed materials to produce crystals of sufficient size to be used as substrates for the growth of thin films of delafossites. For stable growth along the c -axis, low growth rates of 0.4 mm/h are necessary. Due to the incongruent melting behavior of CuFeO 2 , a stable melt zone requires adjustment of the lamp power during growth. The melting of CuFeO 2 is not simply incongruent because the thermodynamic equilibrium includes more than two solid phases and the melt; the gas phase is also involved. The crystals were characterized by X-ray diffraction and X-ray fluorescence measurements. [ABSTRACT FROM AUTHOR]

• Bulk β-Ga 2 O 3 single crystals are grown the Czochralski method. • The crystals are doped with a number of mono-, di-, tri-, and tetravalent ions. • Incorporation of the dopants into bulk crystals is investigated. • Impact of dopants on growth stability and physical properties of crystals is studied. The present report relates to a systematic study of dopant incorporation into bulk β-Ga 2 O 3 single crystals grown by the Czochralski method, and their impact on growth stability, crystal appearance (growth habit), electrical properties, and transmittance of the obtained crystals. At very similar growth conditions, the dopant incorporation is driven mainly by ionic radii difference between dopant and Ga3+ ion and by thermal stability of the dopant during crystal growth. Good growth stability was achieved with Li1+, Mg2+, Co2+, Ni2+, Ce3+, Al3+, and Ge4+ doping, as that resulted in lowering or entirely compensating the free electron concentration (n e), and, in some cases, presence of additional oxygen through a dopant oxide/carbonate decomposition that is added to the starting material. Undoped crystals had the n e of 2.5 × 1016–2 × 1018 cm−3 with the Hall mobility of 80–152 cm2 V−1 s−1. The n e within that range was also achieved by doping the melt with Li1+, Cu1+, Cr3+, Ce3+, and Ge4+. The two former (Li, Cu) and the latter (Ge) dopants entirely evaporate during or even before growth due to very high partial pressures, but at the same time they leave in the melt extra oxygen that affect to some extent (depending on its initial concentration) the n e. Therefore, we provide a new tool to control the free electron concentration at low levels (n e = 1016–1017 cm−3) by doping a Ga 2 O 3 starting material with thermally unstable oxides or carbonates (such as GeO 2 or Li 2 CO 3) that undergo thermal decomposition at high temperatures with entirely evaporated cations and released in the melt an extra oxygen (dopant acting as an additional oxygen source). Si4+ and Sn4+ increase the n e to 2.5 × 1018–1019 cm−3, consistent with previous studies. At such high n e , the Hall mobility drops to values of 50–84 cm2 V−1 s−1. Divalent ions (Mg2+, Co2+, Ni2+) and trivalent Al3+ made the crystals electrically insulating. We also empirically showed that the underlying conductivity of undoped β-Ga 2 O 3 crystals is caused by residual solid impurities, mainly by Si4+ and hydrogen, the latter could be easily removed by annealing. The transmittance near the absorption edge is not affected by the dopants at studied concentrations, except Cr3+, Co2+, and Ni2+ that introduce an extra absorption in the UV and blue spectral regions, and Al3+ that slightly shifts the absorption edge towards shorter wavelengths. [ABSTRACT FROM AUTHOR]