Optical properties of corundum-structured In₂O₃

The optical properties of a single-phase corundum-structured In2O3 epilayer grown by a mist chemical vapor deposition method have been studied. Raman scattering measurements on a c face and on a lateral face reveal all of the seven Raman-active modes of the corundum structure, with good adherence to the Raman selection rules. Three out of the four infrared-active modes are observed in the spectroscopic ellipsometry measurements. The phonon frequencies obtained from Raman and ellipsometry measurements are in excellent agreement with density functional perturbation theory calculations. No trace of bixbyite phase was detected in the spectra. In the UV region, the imaginary part of the dielectric function shows two distinct onsets of strong absorption associated with direct band-to-band transitions at 3.38 and 3.86 eV.