Influence of annealing temperature on the structural, optical and electrical properties of amorphous Zinc Sulfide thin films

Abstract

Zinc sulfide films have been deposited on glass substrates at room temperature by the chemical bath deposition technique. The growth mechanism is studied using X-ray diffraction, scanning electron microscopy, optical absorption spectra and electrical measurements. The as-deposited film was given thermal annealing treatment in air atmosphere at various temperatures (100, 200, 300 400 and 500 °C) for 1 h. The annealed film was also characterized by structural, optical and electrical studies. The structural analyses revealed that the as-deposited film was amorphous, but after being annealed at 500 °C, it changed to polycrystalline. The optical band gap is direct with a value of 4.01 eV, but this value decreased to 3.74 eV with annealing temperature, except for the 500 °C anneal where it only decreased to 3.82 eV. The refractive index (n), extinction coefficient (k), and real (ε1) and imaginary (ε2) parts of the dielectric constant are evaluated. Raman peaks appearing at ∼478 cm-1, ∼546 cm-1, ∼778 cm-1 and ∼1082 cm-1 for the annealed film (500 °C) were attributed to [TOl+LA Σ, 2TOΓ, 2LO, 3LO phonons of ZnS. The electrical conductivities of both as-deposited and annealed films have been calculated to be of the order of ∼10-10 (Ω cm) -1.