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Solid-Solution Limits and Thorough Characterization of Bulk β-(AlxGa1-x)2O Single Crystals Grown by the Czochralski Method

Z. Galazka1, A. Fiedler1, A. Popp1, P. Seyidov1, S. Bin Anooz1, R. Blukis1, J. Rehm1, K. Tetzner2, M. Pietsch1, A. Dittmar1, S. Ganschow1, A. Akhtar1, T. Remmele1, M. Albrecht1, T. Schulz1, T.-S. Chou1, A. Kwasniewski1, M. Suendermann1, T. Schroeder1,3, and M. Bickermann1,4

Published in:

Adv.Mater.Interfaces, vol. 12, no. 2: Special Issue: Progresses and Frontiers in Ultrawide Bandgap Semiconductors, pp. 2400122, doi:10.1002/admi.202400122 (2025).

Abstract:

With comprehensive crystal growth experiments of β-(AlxGa1-x)2O3 by the Czochralski method this work concludes a maximum [Al] = 40 mol% (35 mol% in the melt) that can be incorporated into β-Ga2O3 crystal lattice while keeping single crystalline and monoclinic phase, resulting in the formula of β-(Al0.4Ga0.6)2O3. Transmission Electron Microscopy (TEM) analysis reveals random distribution of Al across both octahedral and tetrahedral sites. This work has shown, that incorporation of only [Ga] ≥ 5 mol% into α-Al2O3 crystals leads to a phase separation of (α + θ)-Al2O3. With electrical measurements this work proves an increase of the electrical resistivity of β-(AlxGa1-x)2O3:Mg as compared to β-Ga2O3:Mg. The static dielectric constant and refractive index both decrease with [Al]. Raman spectra shows a continuous shift and broadening of the peaks, with the low energy optical phonons Ag(3) having a large contribution to a decrease in the electron mobility. Further, Ir incorporation into the crystals decreases with [Al], wherein Ir4+ Raman peak disappears already at [Al] ≥ 15 mol%. Finally, thermal conductivity measurements on β-(AlxGa1-x)2O3 crystals show a drastic decrease of its values with [Al], to about 1/3 of the β-Ga2O3 value at [Al] = 30 mol%.

1 Leibniz-Institut für Kristallzüchtung, Max-Born-Str. 2, 12489 Berlin, Germany
2 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany
3 Humboldt-Universität zu Berlin, Institut für Physik, Newtonstr. 15, 12489 Berlin, Germany
4 Technische Universität Berlin, Institut für Chemie, Straße des 17. Juni 115, 10623 Berlin, Germany

Keywords:

bulk β-(AlxGa1-x)2O3 single crystal, Czochralski method, doping, physical properties, wafers

©2024 The Author(s). Advanced Materials Interfaces published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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