Phase Transformation and Switching Behavior of Magnetron Plasma Sputtered Ge2Sb2Se4Te

Despite their importance in applications such as nonvolatile memory, integrated photonics, and compact optics, the crystalline-to-amorphous transition in chalcogenide phase-change materials (PCMs) is not understood. Herein, this transition in a technologically relevant infrared (IR) transparent chalcogenide material, Ge2Sb2Se4Te1 (GSST), is examined. Thin films of GSST using fully depleted silicon on insulator (FDSOI) microheaters are discussed and the phase transitions by polarized and unpolarized Raman spectroscopy is studied. It is confirmed that the crystalline-to-amorphous transition is driven by conversion of Ge-6Se octahedra to Ge-4Se tetrahedra with the extra Se being incorporated into an Se-Se network. This is similar to the mechanism reported in earlier work for Ge2Sb2Te5 (GST). Recrystallization requires disrupting the Se-Se network and the crystallization activation energy is consistent with the Se-Se bond energy. Across 1000 crystallization-amorphization cycles, GSST exhibits no qualitative change in the Raman spectrum, suggesting limited film oxidation or chemical decomposition. After several hundred cycles, recrystallization is less complete, likely due to dewetting of GSST during the high-temperature amorphization step leading to compromise of the capping layer and loss of GSST. The utility of GSST as a photonic material through fabrication and testing of a GSST-coated, integrated silicon photonic Mach-Zender interferometer, is discussed.

Automated summary

This study investigates the crystalline-to-amorphous transition in the chalcogenide phase-change material GSST, confirming that the transition is driven by the conversion of Ge-6Se octahedra to Ge-4Se tetrahedra with additional Se being incorporated into the Se-Se network. The study also shows that GSST exhibits no qualitative change in the Raman spectrum across 1000 crystallization-amorphization cycles. However, recrystallization becomes less complete after several hundred cycles, likely due to dewetting of GSST during high-temperature amorphization.