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

Temperature-dependent exciton resonance energies Eexciton in β-Ga2O3 single crystals are studied by using polarized reflectance measurement. The Eexciton values exhibit large energy changes in the range of 179–268 meV from 5 to 300 K. The IR-active Au and Bu 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: ℏωLO = 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 ℏωLO at low temperature and 75 meV above 150 K. The large Eexciton changes with temperature in β-Ga2O3 are found to be originated from the exciton-LO-phonon interaction.