Effect of swift heavy ion irradiation on spray deposited CdX (X = S, Te) thin films

Cadmium sulfide and cadmium telluride thin films are irradiated with high energy heavy ion beam to study the irradiation induced effects in these films. The polycrystalline thin film samples deposited by spray pyrolysis are irradiated with 60 MeV Oxygen ions using tandem Pelletron accelerator. The X-ray diffraction patterns exhibit a reduction in peak intensities in both CdS and CdTe films. The grain size decrease with fluence is observed for both CdS and CdTe films, with more decrease for CdTe films. The AFM results support this observation. The films show opposite trend in the variation of electrical resistivity with irradiation fluence. A decrease in resistivity is observed for CdS films due to an increase of carrier concentration arising by the creation of sulfur vacancies during the irradiation. The creation of sulfur vacancies is confirmed by XPS studies. The stoichiometric changes seen from XPS studies support this observation. An enhancement of grain boundary scattering due to the reduction of grain size leads to the increase of electrical resistivity for CdTe films.