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

With comprehensive crystal growth experiments of β‐(Al x Ga 1‐x ) 2 O 3 by the Czochralski method this work concludes a maximum [Al] = 40 mol% (35 mol% in the melt) that can be incorporated into β‐Ga 2 O 3 crystal lattice while keeping single crystalline and monoclinic phase, resulting in the formula of β‐(Al 0.4 Ga 0.6 ) 2 O 3 . 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‐Al 2 O 3 crystals leads to a phase separation of (α + θ)‐Al 2 O 3 . With electrical measurements this work proves an increase of the electrical resistivity of β‐(Al x Ga 1‐x ) 2 O 3 :Mg as compared to β‐Ga 2 O 3 :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 A g (3) having a large contribution to a decrease in the electron mobility. Further, Ir incorporation into the crystals decreases with [Al], wherein Ir 4+ Raman peak disappears already at [Al] ≥ 15 mol%. Finally, thermal conductivity measurements on β‐(Al x Ga 1‐x ) 2 O 3 crystals show a drastic decrease of its values with [Al], to about 1/3 of the β‐Ga 2 O 3 value at [Al] = 30 mol%.