Electronic Structure of Transition-Metal Based Cu₂GeTe₃ Phase Change Material: Revealing the Key Role of Cu d Electrons

The electronic structure of the as-deposited amorphous and crystalline phases of transition-metal based Cu₂GeTe₃ phase-change memory material has been systematically investigated using hard-X-ray photoemission spectroscopy and density-functional theory simulations. We shed light on the role of Cu d electrons and reveal that participation of d electrons in bonding plays an important role during the phase-change process. A large electrical contrast as well as fast switching is preserved even in the tetrahedrally bonded crystal structure, which does not exhibit resonant bonding. On the basis of the obtained results, we propose that transition-metal based phase change memory materials, a class of materials that have been previously overlooked, will be candidates not only for nonvolatile memory applications, but also for emerging applications.