Tuning of band gap and photoluminescence properties of Zn doped Cu2S thin films by CBD method

Undoped Cu2S and Zn-doped Cu2S thin films were deposited successfully on glass substrate using chemical bath deposition method. The amorphous nature and hexagonal structure of the deposited films were confirmed by X-ray diffraction. Scanning electron microscope showed a densely packed flower like morphology of Cu2S film, which is broadened and blurred by Zn-doping. Energy dispersive X-ray spectra confirmed their normal stoichiometry and chemical purity of the films. The low absorption between 500 and 750 nm of the UV-Vis absorption spectra indicated the good transparency of the film in the visible region. The observed higher optical transmittance of Zn-doped Cu2S film is due to the greater crystallite size as a result of lower photon scattering by the crystallite boundaries. The blue shift of energy gap from 2.7 eV (undoped Cu2S) to 3.4 eV (Zn-doped Cu2S) was attributed to the generation of additional charge carriers by Zn-doping. The broad visible violet band centered at 396 nm is due to the band to band transition and a weak green band centered at 507 nm is due to radiative recombination between the conduction band and the wide spread copper-vacancy-related acceptor levels around the valence band edge.