Sn tuned microstructure and phase-change characteristics of GeTe nanowires

Sn-doped GeTe (SGT) nanowires (NWs) were investigated systematically for use in phase-change memory (PCM) applications. Composition and microstructure characterizations indicate that SGT with ∼3.0% Sn (SGT_3.0) NWs preserves the GeTe rhombohedral (R) structure, whereas SGT with a Sn content of ∼25.0% (SGT_25.0) NWs exhibits a cubic (C) structure. R–C structural conversion of SGT NWs is revealed with increasing Sn content. According to ab initio calculations, optimizing doping leads to a decrease in density of states near the Fermi level and reduces electrical conductivity, and thereby, SGT_3.0 is more applicable for PCM than SGT_25.0, which is attributed to Sn-induced structural change that brings about a diversity in the electrical properties. Experimentally, SGT_3.0 NWs have two significant threshold switchings and ideal high/low resistance ratio (∼105). Compared with undoped GeTe, SGT_3.0 NWs experience an increase in crystalline resistance, in agreement with our theoretical calculations, perfectly satisfying the requirement of low programming currents for PCM.