Short‐ and intermediate‐range order in amorphous GeTe

Abstract

We have investigated amorphous GeTe by anomalous X‐ray scattering coupled with reverse Monte Carlo modeling. Experiments were conducted at the two K‐absorption edges in order to determine differential structure factors for both elements. The results indicate that simple models like the 8−N bonding rule cannot accurately rationalize the atomic structure. Te atoms are found to be over‐coordinated with a mean coordination number of about 2.5. Moreover, evidence is given for a high level of intermediate‐range order based on Ge, which has not been reported previously. This order has a pronounced effect on the ring statistics observed in the amorphous network, and thereby on the phase‐change speed of GeTe.

Towards accurate models for amorphous GeTe: Crucial effect of dispersive van der Waals corrections on the structural properties involved in the phase-change mechanism

“…[34]. These were found to reproduce very accurately the measured pair-correlation functions and structure factors for somewhat different compositions [29,[48][49][50]. Molecular dynamics (MD) simulations of Car-Parrinello type (CPMD code) were performed on a 200atom system in a cubic box with periodic boundary conditions and a density equal to experimental ones (0.0337Å…”

“…Three amorphous models were obtained by quenching previously equilibrated liquids obtained at 820 K following a TABLE I. Elaboration and investigation characteristics of GeTe amorphous films studied by different research groups [29,[48][49][50]. The information marked with an asterisk (*) corresponds to deposition of Ge-Sb-Te amorphous films performed by the group of Yamada and Matsunaga [51].…”

“…Several research groups [29,[48][49][50] have been studying the structure of GeTe amorphous films in the last ten years. The films were elaborated by either radio frequency or dc magnetron sputtering from a stoichiometric GeTe target.…”

Local order in binary Ge-Te glasses – An experimental study

“…Some early studies suggested the so called 3-3 model (both Ge and Te are threefold coordinated) but later the 4-2 model became prevailing. However, some recent works raised doubts about the validity of the 8-N rule [9][10][11]. The precise determination of the coordination numbers of Ge and Te in amorphous Ge-Te alloys is a rather difficult task.…”

Generating large starting configurations for molecular Reverse Monte Carlo modelling of an unique non-linear optical amorphous solid

“…Additionally, different scattering laws of the same substance are often employed. Such functions may be available from neutron scattering using isotopic substitution techniques [11][12][13] or from anomalous x-ray scattering [12,14,15]. Another strong constraint exists if known significant structural correlations exist between certain atoms in the sample as is the case in disordered materials made up of molecular units.…”