DIFFUSION AND INTERACTION OF GROUP-I IMPURITIES WITH VACANCIES IN CDSTHIN-FILMS

The influence of Group I impurities (lithium: sodium, copper and silve r) on the electrical, photoelectrical and luminescence properties of C dS films, prepared by the chemical spray pyrolysis method, are investi gated. It is shown that, the appearance of a photoconductivity band wi th maximum at lambda = 550 nm and green emission band at lambda = 510- 540 nm in CdS are connected with one and the same centre-negatively ch arged cadmium vacancies. The increase of the intensities of these band s under diffusion doping by lithium and sodium ions and their decrease after the introduction of copper and silver ions, are due to donor-ac ceptor interaction of diffused Group I impurities with charged cadmium vacancies. The absence of a photoconductivity maximum at lambda = 550 nm and green emission in CdS, doped by sodium impurity during the dep osition process (by addition of NaCl to the solution) is attributed to the precipitation of sodium impurity (as well as copper impurity) in the intergrain spaces of CdS films.