Thickness dependence of structural and optical properties of cadmium iodide thin films

• Different thicknesses of CdI2 films were prepared.
• Both crystallite size and microstrain of the films has been determined.
• The room temperature reflectance and transmittance data are analyzed.
• The refractive index and energy gap are determined.

Structural and optical properties as a function of film thickness have been studied for the thermally evaporated cadmium iodide (CdI2) films. According to XRD structure, the thickness of investigated films extends from 272 to 696 nm, showing hexagonal structure and good c-axis alignment normal to glass substrate plane. Both of crystallite size and lattice strain have been determined in terms of Voight method of the main peak. The optical constants, refractive index (n), and extinction coefficient (k) have been determined using envelope method. The optical absorption data indicates an allowed direct inter – band transition near the absorption edge with an optical energy gap that decreases continuously from 3.572 to 3.767 eV. Both of optical constants and energy gap show thickness dependence that can be explained in terms of structure parameters, crystallite size, and lattice strain.