Polymorphism of GeSbTe Superlattice Nanowires

Abstract

Scaling-down of phase change materials to a nanowire (NW) geometry is critical to a fast switching speed of nonvolatile memory devices. Herein, we report novel composition-phase-tuned GeSbTe NWs, synthesized by a chemical vapor transport method, which guarantees promising. applications in the field of nanoscale electric devices. As the Sb content increased, they showed a distinctive rhombohedral-cubic-rhombohedral phase evolution. Remarkable superlattice structures were identified for the Ge8Sb2Te11, Ge3Sb2Te6, Ge3Sb8Te6, and Ge2Sb7Te4 NWs. The coexisting cubic-rhombohedral phase Ge3Sb2Te6 NWs exhibited an exclusively uniform superlattice structure consisting of 2.2 nm period slabs. The rhombohedral phase Ge3Sb8Te6 and Ge2Sb7Te4 NWs adopted an innovative structure; 3Sb(2) layers intercalated the Ge3Sb2Te6 and Ge2Sb1Te4 domains, respectively, producing 3.4 and 2.7 nm period slabs. The current-voltage measurement of the individual NW revealed that the vacancy layers of Ge8Sb2Te11 and Ge3Sb2Te6 decreased the electrical conductivity.