CC BY
11LM-I-17
Femtosecond Laser Induced Surface Crystalline-Amorphous Alternating Structure on a GST225 Thin Film for Optical
Applications
S. Kozyukhin1, T. Kunkel2, M. Smayev3, Yu. Vorobyov4, P. Lazarenko5
1 — Kurnakov Institute of General and Inorganic Chemistry of RAS, 31, Leninsky pr., Moscow, 119991, Russia 2 - Moscow Institute of Physics and Technology, 9 Institutskiy Per., Dolgoprudny, 141701, Russia 3 - P.N. Lebedev Physical Institute of RAS, 53, Leninsky Pr., Moscow, 119333, Russia 4 - Ryazan State Radio Engineering University, Gagarin st. 59/1, Ryazan, 390005, Russia;
5 - National Research University of Electronic Technology, Shokin sq. 1, Zelenograd, 124498, Russia
sergkoz@igic. ras. ru
The fast switching time of Ge2Sb2Te5 thin films between amorphous and crystalline states initiated by laser beam as well as significant change of their optical properties open wide perspectives for the application of these materials to fully optical devices, in particular, to reconfigurable metasurfaces. In this work, the formation of two-phase laser-induced periodic surface structures (LIPSS) on the surface of the initially amorphous Ge2Sb2Te5 thin films under the illumination by fs-laser pulses has been studied [1,2]. The LIPSS appearance can be explained by the formation of surface plasmon-polariton and its subsequent interference with the incident beam resulting in spatial modulation of temperature on the film surface. The effect of parameters such as wavelength (from 515 nm to 1030 um), frequency (1 kGz to 1 MGz), number of laser pulses (from 1 to 220), direction of the light field vector of the laser beam, thickness of Ge2Sb2Te5 thin film (from 30 nm to 130 nm) and type of substrate material (dielectric and conductor) on LIPSS parameters was investigated. We have determined LIPSS parameters by several methods (optical microscopy, SEM, TEM, AFM, c-AFM) which correlate with each other. As the results indicate, the valleys consist of the crystalline phase, while the ridges remain amorphous, and their period depends on the wavelength of induced laser irradiation. The height difference between the valley and the ridge is several nanometers only, namely 2-3 nm, according to the AFM data in the case of X=1030 nm. This value is more than the roughness of the as-deposited amorphous film, but significantly less than the height of the ripples observed in the similar film after the femtosecond laser irradiation with X = 515 nm, where the 20 nm height ripples were observed. The formation of ripples has a trigger nature and begins with a certain threshold fluence at a constant number of laser pulses. It is shown that an increase in the pulse number leads to an exponential decrease in the threshold fluence, which is explained by the presence of positive feedback in the studied system. Additionally, we covered large areas with coherent LIPPS. The large area patterns created by scanning technique appear very regular, the effect of individual laser spots cannot be recognized and the ripples are all in phase with each other. This work was supported by RFBR (20-03-00379).
[1] S. Kozyukhin, P. Lazarenko, Yu. Vorobyov et al. Laser-induced modification and formation of periodic surface structures (ripples) of amorphous GST225 phase change materials. Optics and Laser Technology, 113, 87-94 (2019).
[2] S. Kozyukhin, M. Smayev, V. Sigaev et al. Specific features of formation of laser-induced periodic surface structures on GST225
amorphous thin films under illumination by femtosecond laser pulses. Phys. Status Solidi B, 1900617 (2020).
