Study of thermally-induced effects on Si–Ge amorphous layers using optical measurements

Thin films of elemental Si and Ge were grown one after another onto glass substrate using electron beam evaporation method. Optical measurements were used to probe the thermally-induced effects on Si–Ge layers upon annealing at 100 °C. Thermal treatment of the films was carried out under vacuum, to avoid oxidation of the films, at a temperature of 100 °C. X-ray diffraction, XRD, showed that the as-deposited layers are amorphous. The change of some optical parameters such as transmission and optical energy gap, as a result of the heat treatment, was explored. The optical energy gap as well as the optical transmission of the dual layer sample was found to increase with annealing time. The obtained results show the possibility of tailoring the layer structure to meet certain technological applications in terms of optical transmission and optical energy gap. Scanning Electron Microscope, SEM, was used to study the morphology of the as-deposited and annealed films. As-deposited films showed no crystalline features. However, the annealed films show some partial crystallization that increases with annealing time. The observed structural changes result in an increase of the optical energy gap with annealing.