  We report the synthesis of polycrystalline (poly)-SiGe alloy thin films
through solid state reaction of Si/Ge multilayer thin films on Si and glass
substrates at low temperature of 500 {\deg}C. The pristine thin film was
deposited using electron beam evaporation with optimized in-situ substrate
heating. Our results show the co-existence of amorphous Si (a-Si) phase along
with the poly-SiGe phase in the pristine thin film. The a-Si phase was found to
subsume into the SiGe phase upon post deposition annealing in the temperature
range from 600 to 800 {\deg}C. Additionally, dual energy band gaps could be
observed in the optical properties of the annealed poly-SiGe thin films. The
stoichiometric evolution of the pristine thin film and its subsequent effect on
the band gap upon annealing are discussed on the basis of diffusion
characteristics of Si in poly-SiGe.
