Mapping the band structure of GeSbTe phase change alloys around the Fermi level

Kellner, Jens; Bihlmayer, Gustav; Liebmann, Marcus; Otto, Sebastian; Pauly, Christian; Boschker, Jos E.; Bragaglia, Valeria; Cecchi, Stefano; Wang, Rui Ning; Deringer, Volker L.; Philipp, Küppers,; Bhaskar, P. Uday; Golias, E.; Sánchez-Barriga, J.; Dronskowski, Richard; Fauster, Thomas; Rader, O.; Calarco, Raffaella; Morgenstern, Markus

doi:10.1038/s42005-018-0005-8

Cited by 21 publications

(33 citation statements)

References 67 publications

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“…This doping is typically related to excess vacancies [36][37][38]. The epitaxial films also exhibit a significantly improved mobility μ with respect to polycrystalline films prepared by magnetron sputtering, i.e., an increase of μ by more than an order of magnitude [24,26,39]. Since μ of the polycrystalline films barely depends on grain size [11,39], this corroborates the improved order in the epitaxial films.…”

Section: Introductionmentioning

confidence: 73%

“…Comparing the density of states (DOS) with and without SOC, we find only a small reduction of the band gap due to the level splittings by SOC. Notably, no topological surface states were found in the gap, in contrast to more ordered configurations of GST-225 [26,35,70].…”

Section: Density Functional Theorymentioning

confidence: 90%

“…DFT calculations without spin-orbit coupling (SOC) are performed using the PBE-GGA parametrization [60] and the VASP implementation [61][62][63] of the projector augmented plane wave method [64] as described in more detail elsewhere [26]. Ge 4s 4p, Sb 5s 5p, and Te 5s 5p states were expanded into plane waves up to an energy cutoff of 250 eV, and k space was sampled using a -centered 1 × 1 × 3 grid (the point only) for bulk (surface) cells, respectively.…”

Section: Density Functional Theorymentioning

confidence: 99%

“…This provides the first STM study on single crystalline phase-change materials. High surface quality without contaminations is achieved either by transferring the samples by an ultrahigh vacuum (UHV) shuttle to the STM [26] or via cleaning them by a dip in deionized water prior to the insertion into the STM chamber [27].…”

Section: Introductionmentioning

confidence: 99%

“…This more ordered phase deviates from the rocksalt structure and has recently been dubbed the metastable vacancy-ordered phase [28]. Moreover, it is known that the epitaxial films are strongly p-type doped [35] with an unintentionally varying charge carrier density p = (0.1-3) × 10 26 m −3 [24,26]. This doping is typically related to excess vacancies [36][37][38].…”

Section: Introductionmentioning

confidence: 99%

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Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

et al. 2017

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Scanning tunneling microscopy (STM) and spectroscopy (STS) in combination with density functional theory (DFT) calculations are employed to study the surface and subsurface properties of the metastable phase of the phase-change material Ge 2 Sb 2 Te 5 as grown by molecular beam epitaxy. The (111) surface is covered by an intact Te layer, which nevertheless permits the detection of the more disordered subsurface layer made of Ge and Sb atoms. Centrally, we find that the subsurface layer is significantly more ordered than expected for metastable Ge 2 Sb 2 Te 5 . First, we show that vacancies are nearly absent within the subsurface layer. Secondly, the potential fluctuation, tracked by the spatial variation of the valence band onset, is significantly less than expected for a random distribution of atoms and vacancies in the subsurface layer. The strength of the fluctuation is compatible with the potential distribution of charged acceptors without being influenced by other types of defects. Thirdly, DFT calculations predict a partially tetrahedral Ge bonding within a disordered subsurface layer, exhibiting a clear fingerprint in the local density of states as a peak close to the conduction band onset. This peak is absent in the STS data implying the absence of tetrahedral Ge, which is likely due to the missing vacancies required for structural relaxation around the shorter tetrahedral Ge bonds. Finally, isolated defect configurations with a low density of 10 −4 nm −2 are identified by comparison of STM and DFT data, which corroborates the significantly improved order in the epitaxial films driven by the buildup of vacancy layers.

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Section: Introductionmentioning

confidence: 73%

Section: Density Functional Theorymentioning

confidence: 90%

Section: Density Functional Theorymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

et al. 2017

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All‐Optical Switching of Structural Color with a Fabry–Pérot Cavity

Abdelraouf,

Wang,

Goh Ken

et al. 2023

Advanced Photonics Research

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Fine tuning the optical responses of thin‐film devices is highly attractive for emerging applications, such as optical memories, solar cells, nanophotonics, and photodetectors. Even though thin‐film technology is well established, dynamically switching the optical responses of thin films after fabrication remains challenging because of passive materials and device structures. This work demonstrates an approach for all‐optical switching of structural colors excited by a Fabry–Pérot (FP) cavity inside a metal–dielectric–metal (MDM) thin‐film stack. A low‐loss phase‐change material (PCM), that is, antimony trisulfide (Sb2S3), which is embedded in the stack, enables efficient FP cavity resonance in the visible spectrum. 1) Color reflectivity of >60%; 2) multistructural colors using a single MDM cavity; 3) a wide dynamic range of colors of up to ≈220 nm; and 4) a gamut coverage of more than 80% of standard RGB (sRGB) are achieved. The all‐optical switching is realized via the crystallization and reamorphization of Sb2S3 using continuous‐wave and pulsed lasers, respectively. The findings provide a framework for the cost‐effective realization of dynamically responsive thin‐film‐based nanophotonic devices.

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Thick Does the Trick: Genesis of Ferroelectricity in 2D GeTe‐Rich (GeTe)_m(Sb₂Te₃)_n Lamellae

Cecchi,

Momand,

Dragoni

et al. 2023

Advanced Science

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The possibility to engineer (GeTe)m(Sb2Te3)n phase‐change materials to co‐host ferroelectricity is extremely attractive. The combination of these functionalities holds great technological impact, potentially enabling the design of novel multifunctional devices. Here an experimental and theoretical study of epitaxial (GeTe)m(Sb2Te3)n with GeTe‐rich composition is presented. These layered films feature a tunable distribution of (GeTe)m(Sb2Te3)1 blocks of different sizes. Breakthrough evidence of ferroelectric displacement in thick (GeTe)m(Sb2Te3)1 lamellae is provided. The density functional theory calculations suggest the formation of a tilted (GeTe)m slab sandwiched in GeTe‐rich blocks. That is, the net ferroelectric polarization is confined almost in‐plane, representing an unprecedented case between 2D and bulk ferroelectric materials. The ferroelectric behavior is confirmed by piezoresponse force microscopy and electroresistive measurements. The resilience of the quasi van der Waals character of the films, regardless of their composition, is also demonstrated. Hence, the material developed hereby gathers in a unique 2D platform the phase‐change and ferroelectric switching properties, paving the way for the conception of innovative device architectures.

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Mapping the band structure of GeSbTe phase change alloys around the Fermi level

Cited by 21 publications

References 67 publications

Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

All‐Optical Switching of Structural Color with a Fabry–Pérot Cavity

Thick Does the Trick: Genesis of Ferroelectricity in 2D GeTe‐Rich (GeTe)_m(Sb₂Te₃)_n Lamellae

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Mapping the band structure of GeSbTe phase change alloys around the Fermi level

Cited by 21 publications

References 67 publications

Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

All‐Optical Switching of Structural Color with a Fabry–Pérot Cavity

Thick Does the Trick: Genesis of Ferroelectricity in 2D GeTe‐Rich (GeTe)m(Sb2Te3)n Lamellae

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Thick Does the Trick: Genesis of Ferroelectricity in 2D GeTe‐Rich (GeTe)_m(Sb₂Te₃)_n Lamellae