Growth Phenomena and Bandgap Shift in Melt-Grown β-(In_xGa_1−x)₂O₃ Alloys

β-Ga₂O₃ is an emerging ultra-wide bandgap semiconductor with great promise for power electronics and optoelectronics. Alloys in the In₂O₃-Ga₂O₃ system are interesting for optoelectronic applications, particularly where bandgap tuning is desirable. Herein, β-(In_xGa_1–x)₂O₃ alloys with target compositions x = 0.025 or 0.10 are grown from the melt using the Czochralski and vertical gradient freeze techniques. Growth with 10 mol% In yields only small, needle-like crystals, while 2.5 mol% In allows growth of centimeter-sized single crystals. A substantial degree of indium segregation is unveiled by spatial measurements of lattice parameters and the bandgap. The bandgap decreases by a maximum of 0.28 eV in the case of the highest In content crystals. Z-contrast transmission electron microscopy confirms a solely octahedral coordination of In in the β-Ga₂O₃ lattice. With indium concentrations higher than 2.5 mol%, samples contain micron-scale voids that impart a dark coloration. All measured crystals are electrically conductive, with carrier concentrations varying 10¹⁶–10¹⁷cm⁻³ depending upon the location of the sample in the growth. Lastly, a unique luminescence with unknown origin centered around 2.0 eV is revealed by photoluminescence spectroscopy.