Excitonic nature of the anisotropic optical response of α-Ga 2 O 3 studied by temperature-dependent ellipsometry

The anisotropic Dielectric Functions (DFs) of α-Ga 2 O 3 were studied in the spectral range from 1.5 to 8.4 eV and their temperature-dependency has been analyzed from 4.5 to 6.5 eV between 80 and 293 K. Temperature-dependent spectroscopic ellipsometry was employed from the near-infrared to ultraviolet spectral range, complemented by room temperature vacuum ultraviolet ellipsometry, to determine the ordinary and extraordinary DF of c-plane and m-plane α-Ga 2 O 3 , as well as of m-plane α-(Al 0.02 Ga 0.98 ) 2 O 3 . Analysis of the DF provides clarity over excitonic contributions and temperature-dependent fundamental direct band transitions.