Bonding Nature and Optical Properties of As₂Te₃ Phase‐Change Material

Abstract

Chalcogenide phase‐change materials (PCMs) are a promising candidate for advanced memory and computing technologies. PCM‐based random access memories have entered the global memory market as storage‐class memory. In these products, the element arsenic plays an essential role in the selector layers, but how arsenic stabilizes the thermal stability of the chalcogenide glass remains elusive. Herein, thorough ab initio simulations are carried out to understand the chemical bonding, electronic structure, and optical properties of an important arsenic alloy As2Te3 in both crystalline and amorphous forms. In comparison with the homologue alloy Sb2Te3, the importance of homopolar bonds in stabilizing the amorphous phase of As2Te3 is revealed. Also, a strategy for the design of As x Sb2−x Te3 alloys with optimal material properties for nonvolatile photonic phase‐change applications is proposed.

Phase‐Change and Ovonic Materials (Third Edition)

“…Moreover, the large reflectivity contrast between amorphous and crystalline As 2 Te 3 phases is in good agreement with what could be expected from the “Metavalent Bonding” (MVB) map (for details see Ref. [6]). The optical difference between rhombohedral and monoclinic As 2 Te 3 would be explained here by the reduction in coordination number and the reinforced Peierls distortion, which weakens the MVB in the monoclinic phase.…”

“…These transport coefficients are of paramount importance for electro‐thermal modeling of PCM devices. Using also calculations, Sun et al [ 6 ] investigated the structural and optical properties of As 2 Te 3 in both crystalline and amorphous phases using ab initio simulations. Homopolar bonds and five‐fold primitive rings present in the amorphous with respect to its crystalline counterparts enhances the glassy phase stability against rapid crystallization.…”

Revisiting the Nature of Chemical Bonding in Chalcogenides to Explain and Design their Properties

“…Besides, the metavalently bonded materials already mentioned, As 2 Te 3 has been also been proposed to employ this unconventional bonding mechanism. [132] Interestingly, metavalent bonded solids are also particularly prone to disorder and anharmonic effects. This is presumably closely related to the weak bonds which characterize these materials.…”

Metavalent Bonding in Layered Phase‐Change Memory Materials

“…Trigonal Sb 2 Te 3 , GeSb 2 Te 4 and Ge 2 Sb 2 Te 5 were all modeled in their hexagonal unit cell or supercell. The amorphous Sb 2 Te 3 was generated using VASP following a standard melt-quench protocol, [99] and the rocksalt Sb 2 Te 3 was built in a 3×3×3 supercell, where the distribution of vacancies was generated using a random number generator. Both sets of models contained 180 atoms.…”