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

摘要

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 Ag/S atomic percentage ratio of the silver sulfide films, and as-grown films with various compositions, such as S-rich (Ag/S = 1.59), stoichiometric (Ag/S = 2), and Ag-rich (Ag/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 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 Ag/S ratio. While the resistivity of stoichiometric or S-rich films was about 10~7-10~8 Ω cm, excess Ag of the Ag-rich film caused a decrease in the resistivity by four orders of magnitude. The Ag/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℃. PDA caused the formation of Ag-rich films (Ag/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 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 Ag/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.