Determination of dispersive optical constants of nanocrystalline CdSe (nc-CdSe) thin films

The nanocrystalline thin films of CdSe are prepared by thermal evaporation technique at room temperature. These thin films are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). The transmission spectra are recorded in the transmission range 400–3300 nm for nc-CdSe thin films. Transmittance measurements are used to calculate the refractive index (n) and absorption coefficient (α  ) using Swanepoel's method. The optical band gap (Egopt) has been determined from the absorption coefficient values using Tauc's procedure. The optical constants such as extinction coefficient (k), real (ɛ1) and imaginary (ɛ2) dielectric constants, dielectric loss (tan δ), optical conductivity (σopt), Urbach energy (Eu) and steepness parameter (σ) are also calculated for nc-CdSe thin films. The normal dispersion of refractive index is described using Wemple–DiDomenico single-oscillator model. Refractive index dispersion is further analysed to calculate lattice dielectric constant (ɛL).

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► nc-CdSe thin films are prepared by thermal vacuum evaporation technique.
► TEM analysis shows NCs are spherical in shape.
► XRD reveals the hexagonal (wurtzite) crystal structure of nc-CdSe thin films.
► The direct optical bandgap of nc-CdSe is 2.25 eV in contrast to bulk (1.7 eV).
► Dispersion of refractive index is discussed in terms of Wemple–DiDomenico single oscillator model.