A facile approach to achieve grain growth in CdS thin films by MgCl ₂ activation: thermal annealing evolution

The present work explores the grain growth mechanism and optimization of physical properties of CdS films by environment-friendly MgCl2 activation. The CdS films are thermally evaporated and treated with saturated solution of MgCl2 compound, followed by thermal annealing at 100°C, 200°C, and 300°C temperatures. A structural study reveals the polycrystalline nature of CdS films having diffraction peaks corresponding to cubic and hexagonal phases with preferential orientation along (220)C plane. The estimated crystallite size of CdS films is found in the 13–45 nm range with MgCl2 activation, and an indication of phase conversion from (220)C to (002)H orientation is observed at 300°C. Transverse current–voltage characteristics validate Ohmic behavior where electrical conductivity is fluctuated with MgCl2 activation. The Tauc's plots yielded optical energy band-gap for prepared CdS films in 1.82–2.35 eV range, and the extinction coefficient and transmittance of CdS films fluctuated with activation temperature. A broad PL emission peak appears in spectral range of ∼660–710 nm, corresponding to photon energy range of ∼1.74–1.87 eV. The PL intensity of the broad emission is boosted with activation up to 200 °C. Surface topographical micrographs indicate hill- and valley-like structures, and surface roughness is observed in 2.18–29.41 nm range with MgCl2 activation temperature.