Temperature dependence of dielectric functions in Yb2O3 and Lu2O3 epitaxial thin films on sapphire (0001)

The fundamental band-gaps of Yb2O3 and Lu2O3 films on sapphire (0001) substrates grown by pulsed laser deposition have been measured by optical transmission and reflectance spectroscopies as a function of temperature. The temperature dependence of the band-gap was analyzed by a model based on phonon dispersion effects and could be explained in terms of phonon-related parameters such as the optical phonon temperature. The phonon dispersion in Yb2O3 was found to fall into material trend based on the data for a large variety of element and binary semiconductors.