Laser processing and characterization of ZnS-Cu thin films

ZnS films were deposited using an original chemical method under atmospheric pressure on to a glass and ceramics substrates. The ZnS films were doped with Cu, Cl by a thermal diffusion method from a ZnS-Cu, Cl powder. Laser processing realized by a pulse nitrogen laser (337 nm) with a pulse time 5 ns. The power density varied from 10 to 32 MW/cm2. The morphology of films was investigated by atomic force microscopy (AFM). It was found that the luminescent properties and the surface morphology of the ZnS-Cu film undergo a change starting with the power density of 20 MW/cm2. The analysis of results shows that optimum dose is 23 MW/cm2. There is a laser ablation of the layer surface ZnS film during laser processing at the power densities greater than 20 MW/cm2. Basic roughness of the surface film was 55 nm.The laser processing resulted in the smoothing of surface. The roughness decreases to 27 nm. The emission and the excitation spectra measured before the laser processing and later are different. The excitation spectra consist of two bands at 337 and 375 nm. The laser processing changes the ratio of the bands intensities. The emission band maximum is 525 nm. The maximum shifts to 521 nm after the laser irradiation. The emission band shape changes too. It becomes asymmetric because of increase short-wave wing. An analysis of the available data is accomplished taking into account two alternative possibilities: an inhomogeneous distribution of the emission centers along the direction of the growth of the film and the laser processing of ZnS-Cu film.