We examined the structural and electrical properties of silver sulfide films as a function of the sulfurization time of 70-nm -thick Ag films. Variations in the sulfurization time caused variations in the AgS atomic percentage ratio of the silver sulfide films, and as-grown films with various compositions, such as S-rich (AgS=1.59), stoichiometric (AgS=2), and Ag-rich (AgS=2.16) films were formed. Amongst the various as-grown films, Ag ions existed in the most polarizable environment in the Ag-rich films. All the films existed in the acanthite α -phase, and the sulfurization conditions did not cause any drastic change in the preferred orientation of this phase. The resistivity of these films strongly depended on the AgS ratio. While the resistivity of stoichiometric or S-rich films was about 107 - 108 Ω cm, excess Ag of the Ag-rich film caused a decrease in the resistivity by four orders of magnitude. The AgS ratio also played a significant role in our observation of the change in resistance within the films from high- to low-resistance state and vice versa with the reversal of the bias polarity of the film. Distinct switching of the resistance was observed only for the Ag-rich film. We also examined the effects of post-deposition annealing (PDA) of various films at 190 °C. PDA caused the formation of Ag-rich films (AgS=2.12-2.17) in all cases, and Ag ions existed in a more polarizable environment in all the films as compared with stoichiometric film. All the annealed films contained mixed acanthite α -phase and argentite Β -phase. Furthermore, all the films had low resistivities of about 0.01-0.02 Ω cm, which indicated that the coexisting metallic argentite Β -phase of the films significantly improved the conductivity of the films as compared to the as-grown film with similar AgS ratio. Clear switching behavior of the resistance could be observed within all the annealed films, thereby indicating that excess Ag in the silver sulfide films is a requirement for observation of such a phenomenon.
ASJC Scopus subject areas
- Physics and Astronomy(all)