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The crystallization times of Ge–Te phase change materials with variable Ge concentrations (29.5–72.4 at. %) were studied. A very strong dependence of the crystallization time on the composition for as-deposited, amorphous films was confirmed, with a minimum for the stoichiometric composition GeTe. The dependence is weaker for melt-quenched, amorphous material and crystallization times are between one to almost four orders of magnitude shorter than for as-deposited materials. This is promising for applications because recrystallization from the melt-quenched phase is the relevant process for optical and solid state memory, and fast crystallization and weak dependence on compositional variations are desirable.

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Key experimental information on intermediate-range atomic structures in amorphous Ge2Sb2Te5 phase change materialThis study investigates the detailed phase transition behavior of Ge 2 Sb 2 Te 5 ͑GST͒ thin films in the thickness range between 4-30 nm using a static laser tester. It was found that the crystallization time has a minimum for both as-deposited ͑around 12 nm͒ and melt-quenched ͑around 10 nm͒ amorphous materials. Capping the GST with a thin SiO 2 layer changes this behavior and leads to a monotonic increase in crystallization time with film thickness for as-deposited amorphous samples but a decrease in time for melt-quenched, amorphous samples. The shortest crystallization time of about 7 ns was observed for the melt-quenched, amorphous 6 nm thick film. It was also found that the recrystallization time of melt-quenched, amorphous GST was shorter when the melt-quenched area was surrounded by GST in the hexagonal phase compared to GST in the rocksalt phase. The shorter recrystallization times for thinner, capped GST films indicate a promising scaling behavior of these materials for rewritable optical storage and phase change memory.