Composition, annealing and thickness dependence of structural and optical studies on Zn1−xMnxS nanocrystalline semiconductor thin films

Nanocrystalline diluted magnetic semiconductors Zn1−xMnxS films (0 ≤ x ≤ 0.2) were deposited on glass substrate by electron beam evaporation technique. The thickness of the films was varied in the range 300–830 nm. The films were annealed at different temperatures. The structural investigation was carried out by using X-ray diffraction measurements and energy dispersive X-ray analysis. All the films exhibit hexagonal type structure. The optical properties were preformed by spectrophotometry measurements. The optical transition was found to be direct transition with energy gap decreases from 3.936 eV for x = 0 to 3.416 eV for x = 0.2. It was also found that the range of optical band gap lie between 3.670 eV and 3.550 eV as the film thickness increases from 300 nm to 830 nm for x = 0.1. The decrease in the optical band gap with increasing the annealing temperature was observed. The refractive index of the nanocrystalline samples has been obtained and found to increase with the increase of the Mn content. Also, the increase in the refractive index was detected as both the thickness and annealing temperature increases. The results show that the annealing temperature and film thickness modifies the optical constants of Zn1−xMnxS thin films. The dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single oscillator model. The oscillator parameters; the single oscillator energy Eo, the dispersion energy Ed, the static refractive index n0, average interband oscillator wavelength λ0, and the average oscillator strength So and optical conductivity were estimated.