Laser-induced modification of the surface of Ge$_{2}$Sb$_{2}$Te$_{5}$ thin films: phase changes and periodic-structure formation

Submicron periodic lattices are formed at the surface of phase-change-memory film materials based on the complex chalcogenide Ge$_{2}$Sb$_{2}$Te$_{5}$ when exposed to nanosecond laser pulses. The geometric characteristics and structural properties of laser-induced lattices are studied by optical and atomic-force microscopies and Raman spectroscopy. It is shown that, at appropriately chosen parameters of exposure to laser radiation, it is possible to implement periodic modulation of the refractive index in the structures formed. Modulation is due to the postexposure solidification of grating ridges and valleys in different phase states, whose dielectric constants widely differ from each other. In the vicinity of the maxima of the wavy structure, the amorphous state is mainly formed, whereas in the region of minima, the Ge$_{2}$Sb$_{2}$Te$_{5}$ structure corresponds mainly to the crystalline phase.