Influence of nanocrystalline size on optical band gap in CdSe thin films prepared by DC sputtering

•CdSe thin films have been deposited on glass substrate by using DC-plasma sputtering.•The crystallite size of CdSe thin films increased with thin films thickness increase.•XRD data shows the crystallite size and crystalline nature increased with thickness increase.•The energy band gaps were found to be in the range of 2.2 eV to 1.94 eV.•The optical band gap increased when the crystallite size of the CdSe thin films decreased.

Cadmium selenide CdSe thin films have been deposited on glass substrate by using plasma sputtering at room temperature with different times of sputtering. The CdSe thin films are characterized using XRD. The crystallite size of the film is calculated from XRD data, which is found as 12.65 nm as-deposited. It is also found that crystallite size of CdSe thin films increased with thin films thickness. The optical properties concerning the absorption spectra were studied for the prepared thin films. The energy band gaps were found to be in the range of 2.21 eV to 1.8 eV. On varying the film thickness in the range of 350 nm to 600 nm, it was found that the optical band gap increased due to the nanocrystalline size of the CdSe thin films decreased.