High pressure Raman spectroscopy of phase change materials

We used high-pressure Raman spectroscopy to study the evolution of vibrational frequencies of the phase change materials (PCMs) Ge$_{2}$Sb$_{2}$Te$_{5}$, GeSb$_{2}$Te$_{4}$, and SnSb$_{2}$Te$_{4}$. We found that the critical pressure for triggering amorphization in the PCMs decreases with increasing vacancy concentration, demonstrating that the presence of vacancies, rather than differences in the atomic covalent radii, is crucial for pressure-induced amorphization in PCMs. Compared to the \textit{as-deposited} amorphous phase, the \textit{pressure-induced} amorphous phase has a similar vibrational spectrum, but requires much lower laser power to transform into the crystalline phase, suggesting different kinetics of crystallization, which may have implications for applications of PCMs in non-volatile data storage.