Vacancy or not: An insight on the intrinsic vacancies in rocksalt-structured GeSbTe alloys from ab initio calculations

Rocksalt-structured GeSbTe (GST) phase-change materials contain significant amounts of intrinsic vacancies at one sublattice. On the basis of ab initio total energy calculations, we have shown that the so-called intrinsic vacancies result from geometrical voids that originate from packing spaces for lone pairs of electrons tightly bound to specific Te layers where a weak bonding exists. The existence of such geometrical voids is concomitant with a narrow band gap. The present results will shed new insights on the intrinsic vacancies in rocksalt-structured GST.