Influence of Annealing Temperature Modulation on the Structural and Optical Properties of ZnSe Thin Films

The research work is devoted to study the influence of annealing temperature on the structural and optical properties of ZnSe thin films. The samples are prepared by a thermal evaporation technique and part of the as-deposited films are annealed. X-ray diffraction patterns and Raman spectra analysis reveal that the ZnSe thin films have cubic zinc-blende crystal structure and the crystallinity increases as the annealing temperature increases. For the linear optical parameters, the absorption edge moves to shorter wavelengths with the increase of annealing temperature. Based on Swanepoel's method, the refractive index, film thickness, absorption coefficient and optical band gap are determined. The values of band gap are found to increase from 2.63 to 2.68 eV as the annealing temperature increases. By performing an open aperture Z-scan technique with femtosecond pulses under 800 nm wavelength, all ZnSe samples show two-photon absorption responses. It is found that the modulation depth and the two-photon absorption coefficient decrease with increasing annealing temperature. Moreover, all samples exhibit better optical limiting responses at higher incident power intensities. These novel properties render this a promising material for traditional optoelectronic devices and optical limiters.