Effect of sulfurization conditions and post-deposition annealing treatment on structural and electrical properties of silver sulfide films

Abstract

We examined the structural and electrical properties of silver sulfide films as a function of the sulfurization time of $70\text{-}\mathrm{nm}$ -thick Ag films. Variations in the sulfurization time caused variations in the $\mathrm{Ag}∕\mathrm{S}$ atomic percentage ratio of the silver sulfide films, and as-grown films with various compositions, such as S-rich $(\mathrm{Ag}∕\mathrm{S}=1.59)$ , stoichiometric $(\mathrm{Ag}∕\mathrm{S}=2)$ , and Ag-rich $(\mathrm{Ag}∕\mathrm{S}=2.16)$ 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 $\alpha$ -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 $\mathrm{Ag}∕\mathrm{S}$ ratio. While the resistivity of stoichiometric or S-rich films was about ${10}^7–{10}^8\Omega \mathrm{cm}$ , excess Ag of the Ag-rich film caused a decrease in the resistivity by four orders of magnitude. The $\mathrm{Ag}∕\mathrm{S}$ 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 $190°\mathrm{C}$ . PDA caused the formation of Ag-rich films $(\mathrm{Ag}∕\mathrm{S}=2.12–2.17)$ 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 $\alpha$ -phase and argentite $\beta$ -phase. Furthermore, all the films had low resistivities of about $0.01–0.02\Omega \mathrm{cm}$ , which indicated that the coexisting metallic argentite $\beta$ -phase of the films significantly improved the conductivity of the films as compared to the as-grown film with similar $\mathrm{Ag}∕\mathrm{S}$ 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.