Multiple singularities of optical properties in GexTe100-x films

Abstract We deposited germanium telluride films and investigated their optical properties. We found multiple singularities in compositional dependent cut-off absorption edge, optical band gap, and refractive index. We further measured Raman spectra of the films and decomposed the spectra into different structural units, and found that, for the structural origins in the changes of optical properties, homopolar Te-Te bonds in anti-symmetric stretching of Te3 pyramid and heteropolar Ge-Te bonds in corner sharing structure are dominated in Te-rich GexTe100-x (x ≤ 33) films, while Ge-Ge bonds in v3(F2) mode and GeGe4 tetrahedron are dominated in Ge-rich GexTe100-x (x ≥ 33) films.