Ordinary dielectric function of corundumlike alpha-Ga2O3 from 40 meV to 20 eV

The linear optical response of metastable alpha-Ga2O3 is investigated by spectroscopic ellipsometry. We determine the ordinary dielectric function from lattice vibrations up to the vacuum ultraviolet spectral range at room temperature for a sample with a (0001) surface. Three out of four E-u infrared-active phonon modes are unambiguously determined, and their frequencies are in good agreement with density functional theory calculations. The dispersion of the refractive index in the visible and ultraviolet part of the spectrum is determined. High-energy interband transitions are characterized up to 20 eV. By comparison with the optical response of alpha-Al2O3 and with theoretical results, a tentative assignment of interband transitions is proposed.We acknowledge the expert beamtime support at the Metrology Light Source (MLS) in Berlin by the Physikalisch Technische Bundesanstalt (PTB) and financial support by the Deutsche Forschungsgemeinschaft (DFG) in the framework of Major Research Instrumentation Program No. INST272/230-1 and by the Ministerium fur Innovation, Wissenschaft und Forschung des Landes Nordrhein-Westfalen, the Senatsverwaltung fur Wirtschaft, Technologie und Forschung des Landes Berlin, and the Bundesministerium fur Bildung und Forschung. The part of the German groups of this work was performed within the framework of GraFOx, a Leibniz-Science Campus. This work was also supported by the Spanish MINECO/FEDER under Contract No. MAT2015-71305-R.Peer reviewe