Laser-induced modification and formation of periodic surface structures (ripples) of amorphous GST225 phase change materials

Specific Features of Formation of Laser‐Induced Periodic Surface Structures on Ge2Sb2Te5 Amorphous Thin Films under Illumination by Femtosecond Laser Pulses

“…The spatial concentration of laser radiation in a thinner surface layer (15 nm in ref. [14] and 85 nm in current study due to different laser wavelengths) leads to the formation of ripples with a strongly pronounced relief—the heights of the ripples are 20 and 2 nm, respectively. We suppose that the amplitudes of the initial surface inhomogeneities were approximately the same in both cases because we used the same thin films, and they are not very important for the formation of ripples, [ 20 ] but the laser wavelength plays the most significant role.…”

“…Note that 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 λ = 515 nm, where the 20 nm height ripples were observed. [ 14 ]…”

“…In addition, light–GST material interaction is accompanied by the appearance of a series of effects, such as laser crystallization, [ 7 ] recrystallization, [ 8 ] reamorphization, [ 9,10 ] whole or partial material ablation, and formation of laser‐induced periodic surface structures (LIPSS or ripples). [ 11–16 ] In the last case, the possibility to make phase transitions of GST with comparative ease leads to the formation of LIPSS with combined phase states – amorphous and crystalline ones. [ 11,13–16 ] It should be noted that the ripples attract the attention currently because many researchers see them as an alternative to lithography process, for example.…”

“…[ 11–16 ] In the last case, the possibility to make phase transitions of GST with comparative ease leads to the formation of LIPSS with combined phase states – amorphous and crystalline ones. [ 11,13–16 ] It should be noted that the ripples attract the attention currently because many researchers see them as an alternative to lithography process, for example. [ 17–19 ] On the one hand, accordingly, the nature of this phenomenon must be well understood to reproducibly obtain LIPSS on a large surface; on the other hand, achieving control over nanostructure formation remains difficult because of high sensitivity of this process to the type of material and laser irradiation parameters that hinder reproducibility and uniformity of periodic patterns.…”

“…We have previously observed the formation of high‐ and low‐spatial frequency LIPSS on the surface of amorphous Ge 2 Sb 2 Te 5 (GST225) thin films at a wavelength λ of 515 nm (2.4 eV) that corresponds to absorption coefficient α = 5.8 × 10 5 cm −1 and light penetration depth of about 15 nm at a film thickness of about 120 nm. [ 14 ] In the present study, we used the laser with λ = 1030 nm (1.2 eV), and this wavelength corresponds to α = 1.2 × 10 5 cm −1 and light penetration depth of about 83 nm at the same film thickness. In both cases the photon energy at the wavelength of irradiation was larger than the bandgap: hυ > E g .…”