Ion-irradiation-induced selective bond rearrangements in amorphous GeTe thin films

Abstract

The change in the local order of amorphous sputter deposited GeTe thin films irradiated with Ge + ion and its influence on the subsequent thermal induced crystallization has been investigated by means of micro-Raman spectroscopy and in situ time-resolved reflectivity. A reduction in the Ge-rich tetrahedral species and an enhancement of the crystallization kinetics occurred in the irradiated amorphous samples. The rearrangement of the amorphous network is suggested to be related to thermal spikes effects rather than to the defects produced by the ions in the collision cascade.

Nucleation and grain growth in as deposited and ion implanted GeTe thin films

“…Therefore, in comparison with as deposited sample and according to simulations, we believe that a reduction of the homopolar Te-Te bonds, forbidden in the crystalline structure, occurs during ion implantation. Moreover, the Raman spectra collected in the amorphous region of partially crystallized GeTe film exhibited a reduction of the 125 cm − 1 peak intensity similar to that observed in the irradiated samples [8]. This evidence further confirms that ion implantation establishes a favorable environment for crystallization.…”

“…amorphous GeTe specimens by Raman spectroscopy. As recently shown [5] Raman spectrum supports the vibrational response of the GeTe amorphous system in terms of defective octahedral sites, although previous studies assigned its peaks to several tetrahedral vibrational modes [8].…”

“…In particular for Ge 2 Sb 2 Te 5 and GeTe, recent experiments [7,8] and atomistic simulations [9] have been focused on the different crystallization behavior between as deposited (as dep. ), melt quenched (m.q.)…”

n-type chalcogenides by ion implantation

“…Tetrahedral species of the type GeTe 4 À n Ge n (n ¼ 0, 1, 2, 3, 4) are the main building blocks of amorphous GeTe 16 . The Raman spectrum of unimplanted GeTe was typical of that for sputtered amorphous GeTe films 17 , with a deconvolution into Gaussians revealing six bands at 107, 122, 139, 153, 222 and 269 cm À 1 (A-F, respectively). Band A has been attributed 16,17 to corner-sharing GeTe 4 and GeTe 3 Ge tetrahedra; the relative intensity of this band increased by B200% in the Bi-implanted film.…”

Functional Properties of Phase Change Materials from Atomistic Simulations

“…These phonons localized on tetrahedra show up as a distinctive feature in the Raman spectrum of a-GeTe as demonstrated from calculations of the Raman spectrum from DFT phonons and polarizabilities based on the semi-empirical bond polarizability model [39]. The agreement between the theoretical [39] and experimental spectra [55][56][57] is good and allowed assigning the main peaks to vibrations of defective octahedra and some tiny features above 170 cm −1 to vibrations of tetrahedra. Similar calculations have been performed for amorphous and crystalline Ge 2 Sb 2 Te 5 [42].…”