Abstract

Rapid and reversible switching between amorphous and crystalline phases of phase-change material promises to revolutionize the field of information processing with a wide range of applications including electronic, optoelectronics, and photonic memory devices. However, achieving faster crystallization is a key challenge. Here, we demonstrate femtosecond-driven transient inspection of ultrafast crystallization of as-deposited amorphous ${\mathrm{Ge}}_1{\mathrm{Sb}}_2{\mathrm{Te}}_4$ and ${\mathrm{Ge}}_1{\mathrm{Sb}}_4{\mathrm{Te}}_7$ thin films induced by a series of 120 fs laser pulses. The snapshots of phase transitions are correlated with the time-resolved measurements of change in the absorption of the samples. The crystallization is attributed to the reiterative excitation of an intermediate state with subcritical nuclei at a strikingly low fluence of $3.19\mathrm{mJ}/{\mathrm{cm}}^2$ for ${\mathrm{Ge}}_1{\mathrm{Sb}}_2{\mathrm{Te}}_4$ and $1.59\mathrm{mJ}/{\mathrm{cm}}^2$ for ${\mathrm{Ge}}_1{\mathrm{Sb}}_4{\mathrm{Te}}_7$. Furthermore, 100% volumetric crystallization of ${\mathrm{Ge}}_1{\mathrm{Sb}}_4{\mathrm{Te}}_7$ was achieved with the fluence of $4.78\mathrm{mJ}/{\mathrm{cm}}^2$, and also reamorphization is seen for a continuous stimulation at the same repetition rate and fluence. A systematic confirmation of structural transformations of all samples is validated by Raman spectroscopic measurements on the spots produced by the various excitation fluences.

© 2018 Optical Society of America

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