Structure of the Ge–Sb–Te phase-change materials studied by theory and experiment

We have studied the structure of GeSb2Te4, GeSb4Te7, and Ge3Sb2Te6 compounds using theoretical and experimental means. Based on ab initio calculations, we propose the stacking sequence in the [111] direction of GeSb2Te4, GeSb4Te7, and Ge3Sb2Te6 phases to be Te–Ge–Te–Sb–Te–v–Te–Sb–, Te–Ge–Te–Sb–Te–v–Te–Sb–Te–Sb–Te–v–Te–Sb–, and Te–Ge–Te–Ge–Te–Sb–Te–v–Te–Sb–Te–Ge–, respectively, where v is an ordered vacancy layer. This structural model agrees with the X-ray diffraction data of sputter-deposited Ge2Sb2Te5, GeSb2Te4, GeSb4Te7, and Ge3Sb2Te6 thin films.