Germanium- aluminium (a-Ge/Al) bilayer thin films with two different Al thickness were deposited onto glass substrates by thermal evaporation technique. The structural and optical properties were investigated and the effect of Al layer thickness on film properties was discussed. X-ray diffraction (XRD) confirmed the amorphous nature of the films under study. The small values of the roughness (7.04 nm, 7.2 nm) obtained from atomic force microscopy (AFM) measurements show relatively smooth surfaces. The optical properties of aGe-Al bilayer thin films were determined from the analysis of measured spectroscopy ellipsometry over the wavelength range 300-1000 nm at room temperature. The refractive index, extinction coefficient and thickness were obtained by the analysis of the ellipsometric spectra through Cauchy, and the Tauc-Lorenz models have been calculated. The optical energy gap was estimated from the absorption coefficient values which were estimated from the absorption coefficient values using Tauc's procedure. Our results show that the optical band gap decreases with increasing Al layer thickness.
