Influence of Zinc Ion Concentration on the Structural, Surface Morphology and Optical Properties of Zinc Selenide Thin Films

ZnSe thin films were deposited on nonconducting glass substrates using different Zn${}^{2+}$ ion concentrations. The films were deposited at 80${}^{\circ }$C for 2.0h via photo-assisted chemical bath technique and annealed for 2.0h at 250${}^{\circ }$C. X-ray diffraction revealed a hexagonal structure with preferred orientation along the (002) plane and the average crystallite size decreased from 10.5nm to 6.8nm with increased Zn${}^{2+}$ ions. Raman spectra were used to confirm ZnSe phonon modes whose intensity increased with Zn${}^{2+}$ ion concentrations although with fluctuation. Optical analysis showed higher absorbance and low transmittance in the visible region than near infrared making the thin films good materials for selective absorber surfaces. The band gap increased from 2.52eV to 2.78eV as the Zn${}^{2+}$ ion concentration varied from 0.05% to 0.25%. The presence of the desired elements was confirmed by the EDS. Photoluminescence studies revealed three emission peaks which were all ascribed to defect state levels in ZnSe and all the samples emitted in reddish color according to CIE color chromaticity analysis. The selective absorption, wide band gap and broad emission properties suggest that the material is promising for optoelectronic applications.