AbstractThe growth modes of CdS thin films on glass in a chemical bath were analysed using scanning electron microscopy and optical microscopy. The results of these studies show that the film growth occurs by ion‐by‐ion condensation and by colloidal particles of CdS adhering to the substrate. Both mechanisms are operative from the initial stages of film growth. The predominance of one or other of these two growth modes depends on the abundance of Cd and S ions present in the solution, which is determined by the amount of complexing and sulphurising agents and ammonia used for the controlled release of Cd and S ions into the solution. The growth mode influences the optical properties of the fi