Effect of in content on optical properties of Ge-In-Se thin films

Amorphous Ge-In-Se thin films were prepared by a magnetron co-sputtering technique. The morphology, structure and optical properties of the thin films were analyzed by X-ray diffraction, visible/near-infrared transmission spectroscopy and Raman spectroscopy, respectively. The results show that the Ge-In-Se thin films have the amorphous characteristics. It was indicated that the high frequency vibration mode of Ge-Se bond in [GeSe₄] tetrahedral was the main one in the Ge-In-Se thin films, and the vibration intensity decreased with increasing In content. When In content was 13.87% in mole, the [GeSe₄] tetrahedral disappears and [InSe₄] tetrahedral became the dominate structure. According to the analysis by the Swanepoel method and the classic Tauc equation, it was found that the red shift appeared at a short-wavelength absorption edge, the refractive index increased and the optical band gap decreased with the increase of In content.