Revealing the intrinsic nature of the mid-gap defects in amorphous Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub>.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 31296874.
- Also identified by DOI 10.1038/s41467-019-10980-w and PMC identifier 6624207.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Understanding the relation between the time-dependent resistance drift in the amorphous state of phase-change materials and the localised states in the band gap of the glass is crucial for the development of memory devices with increased storage density. Here a machine-learned interatomic potential is utilised to generate an ensemble of glass models of the prototypical phase-change alloy, Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub>, to obtain reliable statistics. Hybrid density-functional theory is used to identify and characterise the geometric and electronic structures of the mid-gap states. 5-coordinated Ge atoms are the local defective bonding environments mainly responsible for these electronic states. The structural motif for the localisation of the mid-gap states is a crystalline-like atomic environment within the amorphous network. An extra electron is trapped spontaneously by these mid-gap states, creating deep traps in the band gap. The results provide significant insights that can help to rationalise the design of multi-level-storage memory devices.