Temperature-dependent exciton resonance energies and their correlation with IR-active optical phonon modes in β-Ga2O3 single crystals

Temperature-dependent exciton resonance energies E-exciton in beta-Ga2O3 single crystals are studied by using polarized reflectance measurement. The E-exciton values exhibit large energy changes in the range of 179-268 meV from 5 to 300 K. The IR-active A(u) and B-u optical phonon modes are selectively observed in the IR spectroscopic ellipsometry spectra by reflecting the polarization selection rules. The longitudinal optical (LO) phonon energies can be divided into three ranges: (h) over bar omega(LO) = 35-48, 70-73, and 88-99 meV. The broadening parameters, which are obtained from the reflectance measurements, correspond to the lower two ranges of (h) over bar omega(LO) at low temperature and 75 meV above 150 K. The large E-exciton changes with temperature in beta-Ga2O3 are found to be originated from the exciton-LO-phonon interaction. (C) 2016 AIP Publishing LLC.