The Origin of Optical Contrast in Sb2Te3‐Based Phase‐Change Materials. Issue 1 (25th September 2019)

• Record Type: Journal Article
• Authors: Martinez, Jose C.; Lu, Li; Ning, Jing; Dong, Weiling; Cao, Tun; Simpson, Robert E.
• Is Part Of: Physica status solidi. Volume 257:Issue 1(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2019-09-25
• Subjects: chalcogenides -- crystal fields -- dielectric function -- optical contrast -- phase-change materials -- Sb2Te3 -- spin–orbit interaction; Solid state physics -- Periodicals; Solids -- Periodicals; Atomic structure -- Periodicals; 530.41
• DOI: 10.1002/pssb.201900289
• Languages: English
• ISSNs: 0370-1972

Abstract

Abstract : The optical contrast between the crystalline and amorphous forms of phase‐change materials (PCMs) is so marked as to make it ideal for data storage. Various explanations have been given, including smearing of bands, changes in the local structural order and bonding, and resonant bonding. A consensus has not been reached. Herein, the dielectric function of crystalline and amorphous Sb2 Te3, a topological insulator and prototype PCM, is studied using density functional theory and ellipsometry measurements; an expression for interplay between the crystalline electric field and the spin–orbit interaction on the valence band orbitals is derived. It is found that the crystalline electric field and spin–orbit interaction are responsible for this difference and the unusually large refractive index in the crystalline phase. Upon amorphization, a second‐order electronic phase transition is induced by the spin–orbit interaction's effect on the p z orbitals. This mechanism explains how a substantial optical gap can open in systems that have a small electronic band gap. Abstract : The optical contrast in phase‐change materials (PCMs), while rendering them useful for data storage, remains controversial. The dielectric function of Sb2 Te3, a prototype PCM, is studied using density functional theory, ellipsometry, and a theory of its crystalline field and spin–orbit interaction. The latter explains the crystalline refractive index. Upon amorphization, a phase transition on the p z orbitals yields the contrast.