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

► InGeSbTe films were fabricated via co-deposition stoichiometric GST and IST targets. ► As the amount of IST was increased in InGeSbTe, the value for Vth and the phase transition temperature were increased. ► The phase separation in InGeSbTe is caused by differences in the enthalpy change for formation and different atomic concentrations. In-doped GeSbTe films were deposited by ion beam sputtering deposition (IBSD) using Ge2Sb2Te5 (GST) and In3Sb1Te2 (IST) as targets. The phase change characteristics of the resulting films were then investigated by electrical measurements, including static testing, in situ 4-point Rs 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 Rs data. In addition, in In28Ge12Sb26Te34, multiple Vth 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 In2Te3 occurred in all of the InGeSbTe samples after annealing at 350°C. Moreover, in the case of InGeSbTe films with high concentrations of In (28at.%), 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.