Phase Stability and Anisotropic Sublimation of Cubic Ge-Sb-Te Alloy Observed by In Situ Transmission Electron Microscopy

Phase stability and anisotropic sublimation dynamics of the cubic Ge-Sb-Te alloy have been investigated by in situ transmission electron microscopy (TEM). The starting point of the phase-transition study is an epitaxially aligned Ge1Sb2Te4 grain on a Si(111) substrate. Upon in situ heating, the cubic phase remains stable up to the sublimation point without a transition to the thermodynamically stable trigonal crystal structure which is attributed to Si diffusion into the Ge1Sb2Te4 grain. The sublimation process is made visible with atomic resolution. The anisotropic process leads to the formation of stable {111} facets via kink nucleation on stable steps and subsequent sublimation from those kink sites as predicated by the terrace step-kink model. Kink nucleation sites are identified and are in accordance with the broken-bond model approach.