Bulk single crystals and physical properties of β-(AlxGa1−x)2O3 (x = 0–0.35) grown by the Czochralski method

• Published in: Journal of applied physics 2023-01, Vol.133 (3)
• Main Authors: Galazka, Zbigniew, Fiedler, Andreas, Popp, Andreas, Ganschow, Steffen, Kwasniewski, Albert, Seyidov, Palvan, Pietsch, Mike, Dittmar, Andrea, Anooz, Saud Bin, Irmscher, Klaus, Suendermann, Manuela, Klimm, Detlef, Chou, Ta-Shun, Rehm, Jana, Schroeder, Thomas, Bickermann, Matthias
• Format: Article
• Language: English
• Subjects: Aluminum; Crystal lattices; Czochralski method; Diameters; Doped crystals; Electron mobility; Electronic devices; Energy gap; Figure of merit; Free electrons; Gallium oxides; Lattice parameters; Magnesium; Physical properties; Room temperature; Scattering; Silicon; Single crystals
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/5.0131285

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.