Strain gradients in polycrystalline CdS thin films

The strain gradient through an 800-nm thick CdS thin film, deposited on an ITO substrate by chemical bath deposition (CBD) has been analyzed by using grazing incidence X-ray diffraction (GIXD). The main X-ray diffraction peak found in the CdS film was separated in the cubic-(111) and hexagonal-(002) reflections by a multi-Gaussian fit. We measured the d-spacings of the h-(002) and c-(111) phases mixed in the CdS film as a function of the penetration depth of the incidence X-ray beam. Afterwards, we calculated their respective strain. Both the c-(111) and h-(002) strain tend gradually to reach a top value from the surface to the depth of the films. These strain magnitudes were correlated with the misfit parameter between the CdS [c-(111) and h-(002)] phases and the ITO substrate. From the experimental results we concluded that strain is therefore induced by the mismatch and by other effects, as grain size of the CdS film, and ITO substrate roughness.