The role of crystallographic orientation in thickness assisted modulation of optical properties of ZnSe thin-film

Zinc-selenide thin-films with thickness ranging from 200 to 2000nm were deposited on glass substrate by thermal vapor deposition technique. The two-dimensional pole Figure mappings for the thin-films with different thicknesses reveal the evolution of orientation distribution of crystallites with respect to (Ill) and (311) crystallographic planes. The thickness dependent effective optical band gap was estimated from transmittance spectra. The Swanepoel envelop method could be applied for the two samples having thicknesses of 395 and 1018 nm. A conspicuous thickness dependent bandgap was reported to vary from 2.57 to 2.627eV. The optical parameters: refractive index, nonlinear refractive index, 3
^rd
order nonlinear susceptibility, optical electronegativity, plasma frequency etc. exhibited some degree of thickness dependence, which could be associated with a crystallographic transition of the thin-film from random to the preferred orientation.