Defect models and electrical storage mechanism in GeSbTe phase change materials

The nature of defects in the crystalline and amorphous GeTe structures are calculated in order to understand the electrical conduction properties of GeSbTe phase change materials, as used for data storage. The principle defect in the rhombohedral GeTe phase, representing crystalline GeSbTe, is the Ge vacancy. This pins the Fermi level to the valence band edge, making degenerate p-type conduction. The defects in the amorphous phase are typically the Te interstitial or bulk Te sites, and these pin the Fermi level in the middle of the band gap, giving the amorphous phase a higher electrical resistivity.