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LASER-MATTER INTERACTION
Anisotropic structuring of Ge2Sb2Te. thin films by femtosecond laser pulses
A.V. Kolchin1, S. V. Zabotnov1, D. V. Shuleiko1, L. A. Golovan1, M. N. Martyshov1, A. I. Efimova1, V. B. Glukhenkaya2, P. I. Lazarenko2, T. S. Kunkel3'4, S. A. Kozyukhin4, E. V. Kuzmin5, P. K. Kashkarov1
1-Lomonosov Moscow State University, Faculty of Physics, Moscow, Russia 2-National Research University of Electronic Technology, Zelenograd, Russia 3-Moscow Institute of Physics and Technology, Dolgoprudniy, Russia 4-Kurnakov Institute of General and Inorganic Chemistry of RAS, Moscow, Russia 5- Lebedev Physical Institute of RAS, Moscow, Russia avkolchin@physics.msu.ru
Phase-change material Ge2Sb2Te5 (GST225) is widely used for development of memory and nanophotonical devices [1]. In turn, femtosecond laser irradiation allows to fabricate structures which possesses optical [2] and electrophysical properties [3]. Thus, such technology may be used for improvement of GST225-based applications.
Amorphous GST225 thin films with the thickness 200±20 nm on the dielectric substrates (SiO2/c-Si) were formed by magnetron sputtering. The area with the sizes 3x3 mm2 was irradiated by femtosecond laser system Avesta (wavelength 1250 nm, pulse duration 135 fs, repetition rate 10 Hz, energy fluence 0.2 J/cm2, pulse number 240) at the scanning mode. Surface morphology was investigated by optical (OM; Olympus BX41) and scanning electron microscopies (SEM; Carl Zeiss Supra 40). Experimental and theoretical studies of ultrafast phase transition were provided by Raman (Horiba Jobin Yvon HR800; excitation wavelength 488 nm) and energy-dispersive X-ray (EDX; Tuscan Vega 3) spectroscopies, as well two-temperature model (TTM) calculations [4], consequently. In turn, optical and electrophysical properties were studied by IR-Fourie-spectroscopy (Bruker IFS-66/v) and picoampermeter Keitheley 6487 with ARS DE-204SE nitrogen cryostat.
OM- and SEM-images show formation of so-called laser-induced periodic surface structures (LIPSS). Such ripples exhibit the period 1050-1150 nm. As well, the surface gratings are directed orthogonally to the laser polarization. These structural properties can indicate surface plasmon-polariton excitation [3]. In turn, Raman spectra demonstrate transition to face-centered cubic (fcc) crystalline phase [1]. TTM calculations confirm such suggestion. Furthermore, EDX spectroscopy data exhibit that femtosecond laser structuring doesn't influence on GST225 stoichiometry.
Anisotropy of the optical reflectance was observed in the range (800-2000 nm). Such behavior can be explained as alternating of amorphous and crystalline stripes [2]. In turn, conductivity alongside the scanlines is higher on 1-5 order than same value in orthogonal direction. The heterogeneous crystallization most likely emerge electrophysical anisotropy [3].
The observed results can improve memory and nanophotonical devices which is based on GST225.
This work was supported by Russian Foundation for Basic Research (grants №20-32-90111).
[1] B. Gerislioglu et al., Mater. Today Phys., vol. 12, pp. 100178, (2020).
[2] R. Drevinskas et al., Appl. Phys. Lett., vol. 106, pp. 171106, (2015).
[3] D. Shuleiko et al., Nanomaterials, vol. 11., pp. 42, (2021).
[4] N.A. Inogamov et al., High Temperature, vol. 58., pp. 632-646, (2020).
