Structural and optical properties of Ag ₂SeTe nano thin films prepared by thermal evaporation

Semiconducting Ag ₂SeTe thin films were prepared with different thicknesses onto glass substrates at room temperature using thermal evaporation technique. The structural properties were determined as a function of thickness by XRD exhibiting no preferential orientation along any plane, however the films are found to have peaks corresponding to mixed phase. The XRD studies were used to calculate the crystallite size and microstrain of the Ag ₂SeTe films. The calculated microstructure parameters reveal that the crystallite size increases and micro strain decreases with increasing film thickness. The refractive index, dielectric constants and thereby the optical bandgap of the films were calculated from transmittance spectral data recorded in the range 400-1200 nm by UV-VIS-Spectrometer. The direct optical bandgap of the Ag ₂SeTe thin films deposited on glass substrates with different thicknesses 50-230 nm were found to be in the range 1.48-1.59 eV. The carrier density value is estimated to be around 9.8 × 10 ²¹ cm ^-1 for the film thickness of 150 nm. The compositions estimated from the optical band gap studies reveal a value of 0.75 for Tellurium concentration. These structural and optical parameters are found to be very sensitive to the thin film thickness.