Effects of annealing on structural, electrical and optical properties of AgGa(Se_0.5S_0.5)₂ thin films deposited by using sintered stoichometric powder

The structural, electrical and optical properties of AgGa(Se _0.5S_0.5)₂ thin films deposited by using the thermal evaporation method have been investigated as a function of annealing in the temperature range of 450-600°C. X-ray diffraction (XRD) analysis showed that the structural transformation from amorphous to polycrystalline structure started, at 450°C with mixed binary phases of Ga₂Se₃, Ga₂S₃, ternary phase of AgGaS2 and single phase of S. The compositional analysis with the energy dispersive X-ray analysis (EDXA.) revealed that the as- grown film has different elemental composition with the percentage values of Ag, Ga, Se and S being 5.58, 27.76, 1.3.84 and 52.82 % than the evaporation source powder, and the detailed information about the stoichometry and the segregation mechanisms of the constituent elements in the structure have been obtained. The optical band gap values as a function of annealing temperature were calculated as 2.68, 2.85, 2.82, 2.83, and 2.81 eV for as-grown, annealed at 450, 500, 550, and 600°C samples, respectively. It was determined that these changes in the band gap are related with the structural changes with annealing. The temperature dependent conductivity measurements were carried out in the temperature range of 250-430 K for all samples. The room temperature resistivity value of as-grown film was found to be 0.7×10⁸ (Ω-cm) and reduced to 0.9×10⁷ (Ω-cm) following to the annealing. From the variation of electrical conductivity as a function of the ambient temperature, the activation energies at specific temperature intervals for each sample were evaluated.