In‐Plane Twinning Defects in Hexagonal GeSb₂Te₄

Abstract

Ge–Sb–Te (GST) alloys are an important family of phase‐change materials employed in non‐volatile memories and neuromorphic devices. Conventional memory cells based on GST rely on the switching between an amorphous state and a metastable, disordered rocksalt‐like phase. Recently, however, it has been proposed that a special type of defect in layer‐structured GST—the so called “swapped bilayer” defect—is responsible for a novel phase‐change mechanism observed in GST‐based superlattices. Thus, disorder appears to play an important role in both types of switching mechanisms. Here, the observation of a new in‐plane twinning defect in hexagonal GeSb2Te4 by direct atomic‐scale imaging experiments is reported, which serves as the key ingredient to account for the abundance of inverted stacking faults in hexagonal GST and superlattices. Ab initio simulations reveal a low energy cost for these extended defects, and indicate that such defects can affect the electrical properties by inducing electron localization. This work provides additional insight into the nature and effects of structural disorder in GST phase‐change materials.

Spin Glass Behavior in Amorphous Cr2Ge2Te6 Phase‐Change Alloy

“…Artificial intelligence and big data analytics require continued advances in data storage and processing. Emerging electronic materials, such as phase-change materials (PCM), [1][2][3][4][5][6][7][8][9][10] resistive-switching oxides, [11] spintronic materials, [12] as well as two-dimensional (2D) materials, [13] are being heavily investigated for the development of non-volatile memory and neuro-inspired computing, which hold promises to substantially improve the computing and power efficiencies of electronic devices. [14] Recently, the 2D van der Waals (vdW) crystal Cr 2 Ge 2 Te 6 ("CrGT" in the following) has attracted much attention, since it exhibits both long-range ferromagnetic (FM) ordering with a negligible coercivity below the Curie temperature (≈66 K) and semiconducting characteristics.…”

Metavalent Bonding in Layered Phase‐Change Memory Materials

“…Similar stacking disorder was also observed in layer-structured GeSb 2 Te 4 , Ge 2 Sb 2 Te 5 and GeTe/Sb 2 Te 3 superlattices. [63][64][65][66][67][68][69] The compositional order between normal and inverse atomic blocks remains the same, [66] and the enlarged interatomic spacing is consistently observed at the inverse stacking boundaries. [67] This stacking fault is a consequence of vacancy-ordering mediated structural transformation from the rocksalt phase, [40,70] which is absent in the high-quality epitaxial grown thin film of t-Sb 2 Te 3 (Figure S3, Supporting Information).…”