The CdSe polycrystalline layer was analyzed by means of ESCA, SIMS, photoconductivity and Hall effect methods, and surface and bulk phenomena were researched. The activation of photoconductivity during the thermal treatment in air with and without CdCl2 was investigated. It was found that the oxide formation decreased, if the chlorine was in the ambient, which caused the achievement of a higher compensation level. The prevalence of Cd or Se vacancies in the formation determined the conductivity and photosensitivity of the polycrystalline layer. Thermal quenching, persistent conductivity and the percolation regime at low temperatures were analyzed as well.