Amorphous structures of Ge/Sb/Te alloys: Density functional simulations

Abstract

Since their first development in the 1960s, phase change (PC) memory materials have become essential components of optical memories (DVD‐RW, Blu‐ray Disc, …) used in countless households worldwide. They are now poised to play a decisive role in future non‐volatile computer memories. PC memory materials are restricted to those with an extremely rapid and reversible transition between the amorphous and crystalline phases of an appropriate recording medium, and their development and optimization has been hindered by the inherent difficulties in determining amorphous structures. Alloys of germanium, antimony, and tellurium (“GST” alloys) are among the most widely used in the above contexts, and there has been much speculation concerning their amorphous structures. Theoreticians were slow to appreciate the rich array of problems awaiting their attention, but the past few years have seen a dramatic change in this situation. Density functional (DF) calculations, which are generally free of adjustable parameters, have now been reported on numerous systems. We review here the information that has resulted about the amorphous structures of GST‐alloys.

Tuning electronic properties of graphene heterostructures by amorphous-to-crystalline phase transitions

“…The parametrization of Perdew, Burke, and Ernzerhof (PBE) [36] for the exchange-correlation energy has provided reliable descriptions of structural properties in many Ge/Sb/Te materials [37], and is used here. The description of the weak dispersion forces between graphene and the layers has been improved by using the DFT-D3 van der Waals corrections of Grimme et al [38].…”

Functional Properties of Phase Change Materials from Atomistic Simulations

“…This misfit might be ascribed to deficiencies in the mostly used Perdew-Becke-Ernzerhof (PBE) [46] generalized gradient approximation (GGA) to the exchange-correlation functional. Actually, slightly shorter bonds are found in [47] by using the meta-GGA functional by Tao et al [48]. It has also been suggested that the discrepancies with experiments might originate from an underestimation of 2 where the sum runs over the couples of atoms bonded to a central atom j and forming a bonding angle θ i jk .…”

pyMolDyn: Identification, structure, and properties of cavities in condensed matter and molecules

“…1(a), we now construct spheres centered on each atom with radii specified for each atom type (element). In earlier work on alloys of Ge/Sb/Te [AJ07], [AJ12] and Ag/In/Sb/Te [Metal11], the radius was chosen to be the same (2.8 Å) for all elements [r C in Fig. 1(a)].…”

“…In phase change materials, for example, they play an essential role in the rapid and reversible transformation between amorphous and crystalline regions of chalcogenide semiconductors [AJ07], [AJ08], [AJ12]. In soft matter, such as polymers, cavities can lead to structural failure and are often crucial for diffusion of small molecules.…”

“…• "Surface-based" cavities [AJ07], where the boundaries are determined by Dirichlet-Voronoi constructions from each point on the domain surface to neighboring atoms, have been used in numerous studies of phase change materials [AJ12], [CBP10], [KAJ14].…”