Abstract
This study reveals that electron beam irradiation (5-15 kGy) induced changes in the microstructure and the optoelectronic properties of nanostructured diluted magnetic semiconductor Sn0.96Co0.04O2 thin film deposited by the spray pyrolysis method. XRD investigation shows that a single tetragonal phase remains almost constant during the whole irradiation process. The lattice parameter (a) increases as the irradiated doses increase followed by a reduction in the lattice parameter c, which may be assigned to the increase in the lattice vibrations influenced by the energetic electron beam irradiation. Microstructural analysis using the Rietveld method implied the roughly monotonous reduction in the average crystallite size by the irradiation, which might be owing to the creation of irradiation-induced point defects and/or defect clusters and could affect greatly the bond lengths that appear in the changes of the strain values. AFM results show that the electron beam irradiation causes variation in the grain size and surface roughness of the film. FTIR indicated that the concentration of defects increased as the irradiation doses increased. The optical investigation of the films using spectroscopic ellipsometry (SE) showed remarkable increases in the optical parameters such as refractive index and extinction coefficient with increasing electron beam radiation doses. The observed increase in the refractive index with electron beam irradiation is directly connected to the increase in oxygen content produced in the films, which increases the polarizability of the films by radiation. Moreover, the increase in electron beam irradiation reveals strong effects on the dispersive parameters that were discussed in terms of the Wemple-DiDomenico single oscillator model. Finally, it was found that the optical band gap decreases with the increase in the electron beam irradiation doses, which is discussed based on the bases of breaking of SnO2 bond into Sn and oxygen under the effect of electron beam irradiation and the oxygen migration resulting in the formation of delocalized defect states created close the valence band. The extended non-localization in the valence band rises as the concentration of oxygen vacancies increases, resulting in a narrowing of the band gap Sn0.96Co0.04O2 nanocrystalline films. These results confirm that the electron beam irradiation effects make changes to the optoelectronic properties of Co-doped SnO2 film, indicating that this material is a candidate for radiation sensors.