Atomic structure and electronic properties of the SixSb100−xphase-change memory material

Abstract

The electronic and structural properties of Si${}_{x}$Sb${}_{100\ensuremath{-}x}$ ($x$\ensuremath{\sim}16) materials are investigated using first-principles molecular dynamics simulations. Crystalline-liquid-amorphous phase transitions are examined and remarkable changes in the local structure around the Si atoms are found. The average Si coordination number 6 (3 long $+$ 3 short Si-Sb bonds) of the crystalline phase changes to 4 (3 long Si-Sb $+$ 1 short Si-Si bonds) by preserving three Si-Sb bonds in both the liquid and the amorphous phases. In the amorphous phase \ensuremath{\sim}90% of the Si atoms are fourfold coordinated compared to 40% in the liquid. The electronic density of states is metal-like in both the crystalline and the liquid phases, but it exhibits a pseudogap at the Fermi level in the amorphous phase, reflecting the strong abundance of fourfold coordinated Si in the amorphous phase.