Synthesis, microstructure study and optical characterization of chemical bath deposited nanocrystalline CdSe thin films

We report on the preparation of high-quality nanocrystalline CdSe thin films, which have been deposited successfully by the chemical bath deposition method using triethanolamine as a complexing agent. The effect of various process parameters, such as deposition time and temperature, concentration of species, speed of magnetic stirring, reflux time in condenser for the preparation of selenium precursor, pH of bath etc. on the growth and quality of the films are studied experimentally. Structural morphology is observed by scanning electron microscope (SEM). Band gap measurements for the prepared films have been done with the help of optical transmission spectra using UV-VIS-NIR spectrophotometer (190-1100 angstrom). The action spectra showed displacement in the absorption edge towards lower wavelength side after formation of nano phase material at room temperature. The energy gap increased from 1.74 eV (bulk-CdSe) to 2.65 eV (nano-CdSe) for 0.4M concentration in 24 hour deposition. This substantial improvement of the properties of the prepared films was accomplished by a modification of the chemical bath deposition procedure. The values of some important parameters of the studied films (extinction coefficient, refractive index, dielectric constant and optical conductivity) are determined from transmission spectra. The size of the nano particles is calculated using Effective Mass Approximation method.