Toward Ultrawide Bandgap Engineering: Physical Properties of an α‐(Ti _<i>x</i> Ga _{1− <i>x</i>} ) ₂ O ₃ Material Library

Due to its high bandgap of 5.3–5.6 eV and high predicted breakdown field of 10 MV cm −1 , much attention is drawn to the ultrawide bandgap semiconductor α‐Ga 2 O 3 for applications in high‐power and solar blind optoelectronic devices. In contrast to the thermodynamically most stable β‐phase of Ga 2 O 3 , various transition metal sesquioxides with rhombohedral crystal structure and similar lattice constants to α‐Ga 2 O 3 are available for bandgap engineering toward lower bandgap energies. Therefore the material system α‐(Ti x Ga 1− x ) 2 O 3 in principle offers the possibility to tune the materials bandgap for wavelength selective optoelectronics over an extremely wide range from 5.6 eV (α‐Ga 2 O 3 ) down to 0.14 eV (α‐Ti 2 O 3 ). In this work, high‐throughput combinatorial synthesis by pulsed laser deposition is employed to realize a spatially addressable material library covering almost the entire composition range within the ternary (Ti x Ga 1− x ) y O z solid solution. Phase‐pure growth of (Ti x Ga 1− x ) 2 O 3 up to x = 0.25 is reported, exceeding previously found miscibility limits by a factor of 5. The physical properties of the material system are investigated in relation to x and bandgap engineering within the rhombohedral α‐(Ti x Ga 1− x ) 2 O 3 material system is demonstrated over an up to now unprecedented large spectral range from 4.4 to 5.3 eV.