Toward Ultrawide Bandgap Engineering: Physical Properties of an α-(TixGa1-x)2O3 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 alpha-Ga2O3 for applications in high-power and solar blind optoelectronic devices. In contrast to the thermodynamically most stable beta-phase of Ga2O3, various transition metal sesquioxides with rhombohedral crystal structure and similar lattice constants to alpha-Ga2O3 are available for bandgap engineering toward lower bandgap energies. Therefore the material system alpha-(TixGa1-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 (alpha-Ga2O3) down to 0.14 eV (alpha-Ti2O3). 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 (TixGa1-x)(y)O-z solid solution. Phase-pure growth of (TixGa1-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 alpha-(TixGa1-x)(2)O-3 material system is demonstrated over an up to now unprecedented large spectral range from 4.4 to 5.3 eV.