Characteristics of phase transition and separation in a In-Ge-Sb-Te system

In-doped GeSbTe films were deposited by ion beam sputtering deposition (IBSD) using Ge ₂ Sb ₂ Te ₅ (GST) and In ₃ Sb ₁ Te ₂ (IST) as targets. The phase change characteristics of the resulting films were then investigated by electrical measurements, including static testing, in situ 4-point R _s measurements, X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy. The threshold voltage of the films increased, with increasing levels of IST. This phenomenon is consistent with the increased crystallization temperature in X-ray data and in situ 4-point R _s data. In addition, in In ₂₈ Ge ₁₂ Sb ₂₆ Te ₃₄ , multiple V _th values with a stepwise change are observed. The minimum time for the crystallization of InGeSbTe films was shorter than that for GST. X-ray data and Raman data for the crystalline structure show that phase separation to In ₂ Te ₃ occurred in all of the InGeSbTe samples after annealing at 350°C. Moreover, in the case of InGeSbTe films with high concentrations of In (28 at.%), Sb phase separation was also observed. The observed phases indicate that the origin of the phase separation of InGeSbTe films is from the enthalpy change of formation and differences in Ge-Te, In-Te, Sb-Te, In-Sb and In-In bond energies.