Effects of excess Sb on crystallization of δ-phase SbTe binary thin films

The phase-change temperature and crystal structures of the δ-phase SbTe alloy for Sb contents of 64 at%, 72 at%, and 76 at% have been investigated. The δ-phase SbTe alloy has a rhombohedral crystal structure, and crystallization occurs in an extremely narrow temperature range of 140-145°C compared with Sb ₄₀Te ₆₀). We have determined the relationship between the Sb content and the crystalline structure using X-ray diffraction and selected area electron diffraction. When the Sb content increases, the number of Sb layers stacked with Sb ₂Te ₃ in the unit cell increases, which results in the lowering of the activation energy for crystallization and a lower ovonic threshold voltage.