Influence of growth temperature and silver to sulfur molar ratios on optical, electrical and thermoelectrical properties of nanostructured Ag₂S thin films

Abstract

Silver sulfide (Ag₂S) thin films have been deposited onto glass substrates using spray pyrolysis technique. The substrate temperature (260–310 °C) and also Ag to S molar ratio (0.33 and 0.43) dependent structural, morphological, optical, electrical and thermoelectrical properties of samples have been studied. The X-ray diffraction studies showed that the samples have single acanthite (α-Ag₂S) phase with monoclinic structure and preferred orientation change from $(\bar{1}12)$ to $(\bar{1}03)$ plan with increasing sulfur content. SEM and AFM analyses revealed a compact surface morphology with slightly rough surface. Optical measurements showed a relatively high absorption coefficient (∼5 × 10⁴–6 × 10⁵ cm⁻¹) in the visible range, with an effective optical band gap of ∼2.01–2.23 eV. The electrical studies showed that all these samples have an n-type conductivity and the free electron density increases with increasing the substrate temperature, in agreement with the reflectance spectra of the layers. The thermoelectric measurements revealed that the maximum Seebeck coefficient of −198 μV/K (at T = 400 K) was obtained for Ag₂S (Ag:S = 0.33 at.%) film at substrate temperature of 310 °C.