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Oxygen is widely used to tune the performance of chalcogenide phase-changematerials in the usage of phase-Change random access memory (PCRAM) which isconsidered as the most promising next-generation non-volatile memory. However,the microscopic role of oxygen in the write-erase process, i.e., the reversiblephase transition between crystalline and amorphous state of phase-changematerials is not clear yet. Using oxygen doped GeTe as an example, this workunravels the role of oxygen at the atomic scale by means of ab initio totalenergy calculations and ab initio molecular dynamics simulations. Our mainfinding is that after the amorphization and the subsequent re-crystallizationprocess simulated by ab initio molecular dynamics, oxygen will drag one Ge atomout of its lattice site and both atoms stay in the interstitial region near theTe vacancy that was originally occupied by the oxygen, forming a"dumbbell-like" defect (O-VTe-Ge), which is in sharp contrast to the results ofab initio total energy calculations at 0 K showing that the oxygen prefers tosubstitute Te in crystalline GeTe. This specific defect configuration is foundto be responsible for the slower crystallization speed and hence the improveddata retention of oxygen doped GeTe as reported in recent experimental work.Moreover, we find that the oxygen will increase the effective mass of thecarrier and thus increases the resistivity of GeTe. Our results unravel themicroscopic mechanism of the oxygen-doping optimization of phase-changematerial GeTe, and the present reported mechanism can be applied to otheroxygen doped ternary chalcogenide phase-change materials.

Insight into the Role of Oxygen in Phase-Change Material GeTe