Optical properties of CuFeO$_{2}$ and CuFe$_{1-x}$Ga$_{x}$O$_{2} \quad_{\, }$highly epitaxial thin films

Delafossite thin films of 20 and 200 nm CuFeO$_{2}$ and 52 nm CuFe$_{1-x}$Ga$_{x}$O$_{2\, }$were grown by Pulsed Laser Deposition (PLD) on Al$_{2}$O$_{3}$ (0001) substrates. High epitaxial quality of the films was verified by the techniques of X-Ray Diffraction and Raman spectroscopy.. Optical transmission and reflection spectroscopies were performed on the films under vacuum and in CO$_{2}$ controlled atmosphere, respectively. Tauc plots based on transmission data yielded direct optical band gap at 2.4 eV, 2.8eV and 3.1eV and indirect band gap at 0.9 eV and 1.3 eV for CuFe$_{1-x}$Ga$_{x}$O$_{2}$ (x$=$0.25) and the direct band gap at 1.9eV, 3.1eV and the indirect band gap at 1.1eV for the CuFeO$_{2\, }$films.