Phase-Change Mechanism and Role of Each Element in Ag-In-Sb-Te: Chemical Bond Modulation

Reversible crystallization from the amorphous phase is one of the most promising bases on which to store data for universal electronic memory. However, crystallization mechanism at atomic scale and role of element in Ag-In-Sb-Te are still unsolved, whose memory properties are outstanding. To elucidate them, we studied the bonding topologies through spectroscopic techniques and density functional simulations. It is shown by in-situ X-ray photoelectron spectroscopy that element In dramatically changes its bonding topology on crystallization from Sb-bonds to Te-bonds, which are characterized as that of InSb and AgInTe2, respectively by density functional simulations. Further, the degree of atomic ordering is identified to highly dependent on local environment of In by spectroscopic ellipsometry. The overall results suggest that crystallization of Ag-In-Sb-Te is triggered by the local environment transition of In from InSb-like to AgInTe2-like site. Thereby, Ag provides structural flexibility for local environment transition of In, In disrupts crystallization, and Te assists the other elements to play their respective roles. The present work accounts for unsolved memory properties of Ag-In-Sb-Te and opens the gate to develop enhanced materials for the memory.