Structural, optical, and morphological properties of chemically deposited CdSe thin films by ammonia-free precursor solution

Abstract

We present a simple route for developing high-quality CdSe thin films at low temperature by means of the chemical bath deposition technique using an ammonia-free formulation. The effect of the concentration of the precursor solutions was evaluated through four formulations. The crystalline, optical, and morphological properties of the CdSe thin films were analyzed for the four deposition conditions. As-deposited CdSe films exhibited hexagonal phase and strong crystalline orientation along the [002] direction as observed by XRD analysis. The diffraction peak corresponding to the (002) crystalline planes shifts to higher two theta values in the patterns of the films deposited with increasing precursors concentration, showing the shrinkage of the crystalline lattice of up to 1.58%, as a product of the tensile stresses through the substrate-film interface. UV-Vis-NIR analysis revealed highly reflective films and good optical quality. The refractive index showed a maximum of 2.20–2.26 around 640 nm, while the extinction coefficient was zero at wavelengths lower than the absorption edge. The SEM and AFM analysis revealed the homogeneous and compact CdSe films surface with low average roughness. The energy band gap of the CdSe thin films varied in the range from 1.78 to 1.9 eV and the variation has been associated with the stresses induced in the film-substrate interface during the film growth. We found an opposite trend between the lattice constant (c) and the energy band gap of the CdSe thin films, which enable the adjustment of their optical properties through the concentration of the precursor solutions during the deposition process.