Impact of Oxidation on Ge₂Sb₂Te₅and GeTe Phase-Change Properties

Abstract

Effects of Ge 2 Sb 2 Te 5 and GeTe oxidation on their phase-change properties were studied by optical measurements and Parallel Angle Resolved X-ray Photoelectron Spectroscopy (PARXPS). The influence of oxygen on the active material was depicted in order to explain variations of the phase-change properties. The surface analysis evidenced a two-steps oxidation involving the formation of germanium and antimony oxides then tellurium oxide. A smooth surface sputtering allowed physically distinguishing the different oxides on GeTe sample overlayer and gave information about oxidation mechanisms. A significant drift of crystallization temperatures and activation energies were observed after 12 months air exposure time that points out the influence of the phase-change materials oxidation on their active properties.

A zero density change phase change memory material: GeTe-O structural characteristics upon crystallisation

“…1(a,b). The T xt and T xt of the pure GeTe film is 194 ± 1 °C and 195 ±1 °C, respectively, as shown by the dash lines in the figures, which agrees well with values reported elsewhere2528. Oxygen doping substantially increases the T x of GeTe.…”

“…The crystallisation activation energy of GeTe was found to be 2.26 eV inside the film and 2.31 eV at the film’s surface, which are in the range of values reported in literature (i.e. 2.0 to 2.72 eV)242528. We suspect the reason for the higher activation energy is due to stress in the films.…”

“…Moreover, there are limited reports of environmental oxidation of GeTe films2829. Therefore, the aims of the present work are: (1) to investigate the effect of oxidation on the fundamental crystallisation properties of GeTe and (2) to explore an hypothesised increase in the stability of GeTe-O materials, which could extend the use of PCMs to extreme environments.…”

Ab initio study of the high‐temperature phase transition in crystalline GeO2

“…Besides these obvious direct applications, there are also some indirect cases where germanium dioxide is either a beneficial or an unwanted compound. A solid mixture of m GeO 2 × n TeO 2 has been proposed as the final oxidation product of GeTe surfaces, and may well be relevant for other phase‐change data‐storage devices which must be protected from oxidation . Germanium nanowires with an amorphous GeO 2 layer on the outside have been experimentally characterized by Zhang et al, and in fact, oxide species were found to promote growth of silicon and germanium nanostructures .…”

“…A solid mixture of m GeO 2 3 n TeO 2 has been proposed as the final oxidation product of GeTe surfaces, [8] and may well be relevant for other phasechange data-storage devices which must be protected from oxidation. [9] Germanium nanowires with an amorphous GeO 2 layer on the outside have been experimentally characterized by Zhang et al, [10] and in fact, oxide species were found to promote growth of silicon and germanium nanostructures. [11] Chemical reactions at the surface of germanium nanowires, including oxidation mechanisms, were discussed in detail by Hanrath and Korgel.…”