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The influence of nitrogen dopant on the structure of the phase-change material Sb has been investigated by ab initio molecular dynamics simulations. The doped N exist as SbN complex in amorphous phase and would not enter into the rhombohedra phase of crystalline Sb. During crystallization of the amorphous phase, no N2 molecule is formed and part of the N–Sb bonds are broken to release Sb atoms which contribute to growth of crystal nuclei by forming more Sb–Sb bonds. Remaining N–Sb bonds would segregate at the grain boundaries and retard growth of crystal nuclei.

Superlattice-like Ge50Te50/Ge8Sb92 (SLL GT/GS) thin film was systematically investigated for multi-level storage and ultra-fast switching phase-change memory application. In situ resistance measurement indicates that SLL GT/GS thin film exhibits two distinct resistance steps with elevated temperature. The thermal stability of the amorphous state and intermediate state were evaluated with the Kissinger and Arrhenius plots. The phase-structure evolution revealed that the amorphous SLL GT/GS thin film crystallized into rhombohedral Sb phase first, then the rhombohedral GeTe phase. The microstructure, layered structure, and interface stability of SLL GT/GS thin film was confirmed by using transmission electron microscopy. The transition speed of crystallization and amorphization was measured by the picosecond laser pump-probe system. The volume variation during the crystallization was obtained from x-ray reflectivity. Phase-change memory (PCM) cells based on SLL GT/GS thin film were fabricated to verify the multi-level switching under an electrical pulse as short as 30 ns. These results illustrate that the SLL GT/GS thin film has great potentiality in high-density and high-speed PCM applications.

Multilayer SnSb4/ZnSb (SS/ZS) thin films have been investigated for phase change applications. The composition [SS (4 nm)/ZS (10 nm)]4 exhibits a high crystallization temperature (T c ~ 230 °C), high data retention temperature for 10 years (T 10-yr ~ 152 °C), small density change, and low thermal conductivity. A cell based on [SS (4 nm)/ZS (10 nm)]4 achieves fast SET/RESET switching speed (~10 ns) and low reset power consumption (the energy for RESET operation = 9.6 × 10−13 J).

Effects of oxygen incorporation on the crystallization characteristics and crystal structure of Ge8Sb92 films were systematically investigated. The amorphous-to-crystalline transition was studied by in situ resistance measurement. The thermal stability, electrical resistance and band gap of Ge8Sb92 material increase significantly by the addition of oxygen. X-ray diffraction, transmission electron microscopy and x-ray photoelectron spectroscopy illustrate that a small amount of oxygen dopant can inhibit the grain growth and limit the grain size because of the formation of Ge and Sb oxide. Atomic force microscopy and x-ray reflectivity results indicate that the film surface becomes smoother and the film thickness change becomes smaller after oxygen doping. Phase change memory cells based on oxygen-doped Ge8Sb92 film were fabricated to evaluate the electrical properties as well. All the results demonstrate that suitable incorporation of oxygen is an effective way to enhance the comprehensive performance of Ge8Sb92 thin films for phase change memory application.