Dimorphism and perturbed growth kinetics of cadmium sulfide thin films in a chemical working solution

Abstract

Thin films of numerous compound semiconductors, which crystallize in a (cubic) sphalerite structure, often display an alternative allotropic form as (hexagonal) wurtzite. The relative proportion of each depends in a characteristic manner on the growth conditions chosen. We applied an external magnetic flux during the growth of cadmium sulfide thin films from a chemical working solution, where the CdS molecules or small clusters are formed by a controlled reaction in an aqueous solution. The incorporation mechanism of such neutral particles into the polycrystalline CdS thin film is supposed to happen in a transition layer via a dissociation into charged constituents close to the growing interface. We found a clear effect of the external magnetic field on the film morphology, when the Lorentz force was acting parallel to the surface plane of the layer. Band-gap energy data from optical absorption measurements suggest dimorphism of the grown films, where the field application turns the commonly cubic crystal modification (Eg = 2.38 eV) into a hexagonal polytype with a 200 meV larger energy gap. PACS Nos.: 81.05Dz, 81.15Lm, 81.15Aa, 81.70Fy, 82.65My, 82.80Ch, 82.80Ej