Comparative Study of CdS Films Annealed in Neutral, Oxidizing and Reducing Atmospheres

Chemical bath deposited CdS:Cl thin films on glass substrates were annealed in H2, N2 and air at 250 oC and 400 oC, and then characterized by XRD, Van der Paw, Raman, photoluminescence and transmittance - reflectance spectroscopy.Different properties of CdS film are found depending on the neutral, reducing or oxidizing annealing gas. Strong activity of chlorine as a flux and dopant agent is observed in the air- annealed CdS films. This is expressed by the strongestphotoluminescence intensity of the 2.24 eV peak. Oxygen containing phases CdSO3 and CdO are shown by XRD patterns for air- and N2- annealed CdS films at 400 oC. Longest N2 annealing generated pure CdS layers, similarly with the H2- annealed ones. Also, the H2 annealing shows a shift of the main (111) CdS peak toward the pure cubic modification proportionally with the annealing time, while N2 and air annealing fixed the peak at intermediate cubic-hexagonal position. This could be explained by incorporation of oxygen in CdS lattice for N2 and air annealing, supported by the presence of oxide phases in CdS XRDpatterns. H2 annealing removes the incorporated oxygen from the lattice and oxide phases from the grain boundaries, leaving pure CdS films. Behavior of CdS structural properties unambiguously demonstrates the incorporation of hydroxide group and oxygen into the CdS crystallite lattice and explains the changes of structural, optical and electrical properties of CdS films in the annealing process.