Effect of heat treatment on the optical properties of In2Se3thin films

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Abstract
Transmission measurements in the spectral range of 400-900 nm in conjunction with the Kramers-Kronig relation were used in calculating the optical constants (the refractive index n and the absorption index k) of In2Se3 thin films deposited at room temperature on a glass substrate. The refractive index n has anomalous behaviour in the region of the fundamental absorption edge. The allowed optical transitions were found to be indirect transitions with an optical gap of 1.37 eV for the samples under test. On annealing, the gap increases with temperature as well as with time periods of annealing in the case of In2Se3 thin films in the amorphous state. The increase in the value of Egopt with heat treatment is interpreted in terms of the density of states model proposed by Mott and Davis (1971). Analysis of the refractive indices has yielded optical dielectric constants as a function of temperature. X-ray analysis showed that the prepared sample in its bulk form had alpha phase, the prepared films at room temperature had amorphous structure. When the temperature is raised to 523 K, In2Se3 films have beta -phase polycrystalline structure.