Cylindrical laser beams for a-Ge2Sb2Te5 thin film modification

Chalcogenide phase-change materials are promising for optical technologies, since they allow rapid (tens of nanoseconds) reversible switching between the amorphous and crystalline phase states characterized by significantly different electrical and optical parameters. In this work we experimentally studied the local optical transition of as-deposited amorphous Ge ₂Sb ₂Te ₅ thin films into the crystalline state under the action of structured continuous-wave laser beams. For cylindrical laser beams with an annular intensity profile obtained through the phase singularity or through the axially symmetric polarization distribution, significantly more efficient crystallization was observed in comparison with the commonly used fundamental Hermite–Gaussian HG ₀₀ mode. The numerical simulation showed that the annular intensity distribution results in a more uniform temperature profile inside the irradiated region, which is necessary for more uniform crystallization. To analyze the degree of crystallinity we used Raman spectroscopy and optical microscopy, enhanced with digital brightness filtering for characterization of the reflectance within the modified region.