Characterization of thin film cadmium sulfide grown using a modified chemical bath deposition process

Cadmium sulfide polycrystalline films with potential for application as a solar cell window layer have been grown by a modified chemical bath deposition process, using ethylenediamine as a complexing agent and employing direct heating of the substrate. Films have been characterized using atomic force microscopy, scanning electron microscopy, grazing incidence X-ray diffraction, photoluminescence, photoconductivity, and optical absorption. Both as-grown films and films processed by annealing using cadmium chloride (CdCl₂) exhibit promising properties for this use. As-grown films are crystalline, possess low surface roughness (4.4 nm RMS), small grain size (18 nm), large direct bandgap (2.54 eV) and are highly textured with some degree of hexagonal phase present. On annealing with CdCl₂ there is an increase in surface roughness (24.5 nm RMS), modest grain growth (23 nm), a decrease in bandgap (2.44 eV) and diffraction data are consistent with increasing hexagonal character. There is also evidence of better crystalline quality and a large reduction in electron trapping states upon CdCl₂ annealing.