The effect of annealing on structural and optical properties of α-Fe2O3/CdS/α-Fe2O3 multilayer heterostructures

•Thin film multilayer heterostructures of CdS/α-Fe2O3 were fabricated through physical vapor deposition (PVD) techniques.•The effects of various annealing temperatures on multilayer heterostructures were examined.•Surface modification and crystallization of CdS/α-Fe2O3 composite films were observed during annealing.•A red shift in absorption bandedge of CdS/α-Fe2O3 composite films was noticed due to CdS together with annealing. Multilayered thin film heterostructures of α-Fe2O3/CdS/α-Fe2O3 were prepared through physical vapor deposition. Each α-Fe2O3 layer was deposited by e-beam evaporation of iron in an oxygen atmosphere. The CdS layer was deposited by thermal evaporation in a vacuum. The effect of post annealing of multilayered thin films in air in the temperature range 250°C to 450°C was investigated. Structural characterization indicated the growth of the α-Fe2O3 phase with a polycrystalline structure without any CdS crystalline phase. As-deposited multilayer heterostructures were amorphous and transformed into polycrystalline upon annealing. The surface modification of the films during annealing was revealed by scanning electron microscopy. Spectrophotometric measurements were used to determine the optical properties, including the transmittance, absorbance, and band gap. All the films had both direct as well as indirect band gaps.