GeSbTe

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GeSbTe, or Germanium-Antimony-Tellurium, also known as GST or 225, is a phase change material from the group of chalcogenide glasses, used in rewritable optical discs and phase-change memory applications. It is a ternary compound of germanium, antimony, and tellurium, with composition GeTe-Sb₂Te₃. Its recrystallization time is down to 20 nanoseconds, allowing writing bitrates of up to 35 Mbit/s, and direct overwrite capability up to 10⁵ cycles. It is suitable for land-groove recording formats. It is often used in rewritable DVDs. The new phase-change memories are likely using N-doped GeSbTe semiconductor. The melting point of the alloy is about 600 °C and the crystallization temperature is about 400 °C.

During writing, the material is first erased, initialized into its crystalline state, with long, lower-intensity laser irradiation. The material heats up to its crystallization temperature, but not up to its melting point, and crystallizes. Then the information is written on the crystalline phase, by heating spots of it with short (<10 ns), high-intensity laser pulses; the material locally melts and is quickly cooled, remaining in the amorphous phase. As the amorphous phase has lower reflectivity than the crystalline phase, the bitstream can be recorded as "dark" amorphous spots on the crystalline background.[1]. Recently a novel liquid organogermanium precursor, isobutylgermane, was used in conjunction with the metalorganics of antimony and tellurium to grow GeSbTe and other chalcogenide films of very high purity by metalorganic vapor phase epitaxy (MOVPE).

Other similar material is eg. AgInSbTe. It offers higher linear density, but has lower overwrite cycles by 1-2 orders of magnitude. It is used in groove-only recording formats, often in rewritable CDs.