Combinatorial Synthesis and Characterization of Lattice‐Matched Ga ₂ O ₃ –Cr ₂ O ₃ and Ga ₂ O ₃ –V ₂ O ₃ Sesquioxide Alloys for Ultrawide‐Bandgap Semiconductor Applications

Gallium sesquioxide is a wide‐bandgap semiconductor of high interest for power electronics and deep UV‐sensing applications. The α‐phase ( E _g = 5.6 eV) can be synthesized with excellent crystal quality on isostructural Al ₂ O ₃ substrates, removing the need for expensive homoepitaxial growth that is required for the thermodynamically stable β‐phase ( E _g = 4.9 eV). Here, continuous composition spread material libraries of (Ga _{1‐ x} V _x ) ₂ O ₃ and (Ga _{1‐ x} Cr _x ) ₂ O ₃ with 0.05 < x < 0.45 are synthesized by pulsed laser deposition, and characterized structurally and optically with the aim of decreasing the optical absorption edge of α‐Ga ₂ O ₃ to expand the range of potential optoelectronic applications. The (Cr _x Ga _{1‐ x} ) ₂ O ₃ material library remained stable in the rhombohedral α‐phase throughout the investigated compositional range, exhibiting high crystal quality with minimal changes to the unit cell parameters. A systematic shift in optical absorption edge from 5.5 to 3.9 eV is observed, as determined by spectrophotometry. The (Ga _{1‐ x} V _x ) ₂ O ₃ material library exhibits a systematic shift from 5.2 to 2.9 eV with increasing x _V , but a region of decreased crystal quality is observed for 0.11 ≤ x _V ≤ 0.20. Additionally, a secondary V ₂ O ₅ phase is observed for x _V > 0.23. Overall, bandgap engineering of α‐(Ga _{1‐ x} V _x ) ₂ O ₃ and α‐(Ga _{1‐ x} Cr _x ) ₂ O ₃ is demonstrated, and chromium substitution is identified as especially promising due to high crystallinity and systematic change of optical absorption edge.