Unexpectedly large energy variations from dopant interactions in ferroelectric HfO2 from high-throughput ab initio calculations

Falkowski, Max; Kuenneth, Christopher; Materlik, Robin; Kersch, Alfred

doi:10.1038/s41524-018-0133-4

Cited by 20 publications

(21 citation statements)

References 60 publications

(86 reference statements)

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“…The results, represented by open green symbols in Figure a, show that the PE‐t state becomes dominant as the amount of Si grows. (A similar stabilization of PE‐t has already been reported in the study by Falkowski et al) Even more interestingly, our results also show that the FE‐o polymorph becomes more stable than the PE‐m state for Si concentrations of 12.5–25%.…”

supporting

confidence: 91%

“…In our simulations with representative tetravalent dopants, it quickly became clear that (some) doping atoms have a (very strong) preference to adopt specific spatial arrangements. An important conclusion follows: it is not appropriate to assume—as implicitly done in the all cited DFT works except the study by Falkowski et al and, to some extent, the study by Künneth et al—that the dopants locate randomly in the

{HfO}_{2}

lattice. We thus focus on this issue and address the following questions: What is the preferred spatial configuration of substitutional cation dopants in

{HfO}_{2}

?…”

mentioning

confidence: 99%

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Effect of Dopant Ordering on the Stability of Ferroelectric Hafnia

Dutta

Aramberri

Schenk

et al. 2020

Physica Rapid Research Ltrs

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Films of all-important compound hafnia (HfO2) can be prepared in an orthorhombic ferroelectric (FE) state that is ideal for applications, e.g. in memories or negative-capacitance field-effect transistors. The origin of this FE state remains a mystery, though, as none of the proposed mechanisms for its stabilization -from surface and size effects to formation kinetics -is fully convincing. Interestingly, it is known that doping HfO2 with various cations favors the occurrence of the FE polymorph; however, existing first-principles works suggest that doping by itself is not sufficient to stabilize the polar phase over the usual non-polar monoclinic ground state. Here we use first-principles methods to reexamine this question. We consider two representative isovalent substitutional dopants, Si and Zr, and study their preferred arrangement within the HfO2 lattice. Our results reveal that small atoms like Si can adopt very stable configurations (forming layers within specific crystallographic planes) in the FE orthorhombic phase of HfO2, but comparatively less so in the non-polar monoclinic one. Further, we find that, at low concentrations, such a dopant ordering yields a FE ground state, the usual paraelectric phase becoming a higher-energy metastable polymorph. We discuss the implications of our findings, which constitute a definite step forward towards understanding ferroelectricity in HfO2.

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supporting

confidence: 91%

{HfO}_{2}

lattice. We thus focus on this issue and address the following questions: What is the preferred spatial configuration of substitutional cation dopants in

{HfO}_{2}

?…”

mentioning

confidence: 99%

Effect of Dopant Ordering on the Stability of Ferroelectric Hafnia

Dutta

Aramberri

Schenk

et al. 2020

Physica Rapid Research Ltrs

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“…They found the most significant stabilization of the ferroelectric phase for oxygen rich processing conditions like in atomic layer deposition (ALD) and a competition between ferroelectric and tetragonal phase for oxygen poor processing. A high‐throughput study by Falkowski et al confirmed the results with a much higher number of relaxed structures. While a reproduction of the remarkable P r of 40 µC cm –2 has never been reported in subsequent publications, a recent work by Schroeder et al achieved P r between 25 and 30 µC cm –2 for a wide dopant concentration range …”

Section: Introductionmentioning

confidence: 74%

“…A high-throughput study by Falkowski et al [9] confirmed the results with a much higher number of relaxed structures. They found the most significant stabilization of the ferroelectric phase for oxygen rich processing conditions like in atomic layer deposition (ALD) and a competition between ferroelectric and tetragonal phase for oxygen poor processing.…”

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confidence: 70%

On the Origin of the Large Remanent Polarization in La:HfO₂

Schenk

Fancher

Park

et al. 2019

Adv Elect Materials

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104

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extraordinary result. [2][3][4][5][6][7] A physical explanation for these results has remained elusive. The dopant size has been speculated to be a key parameter and larger dopants seem in general favorable compared to dopants with a smaller ionic radius than Hf. [2,8] This trend has been confirmed theoretically by Batra et al., [5] who additionally conclude that trivalent dopants in general are a good choice to favor the polar phase in HfO 2 . Large trivalent dopants, as the lanthanoid series are therefore especially suitable to promote ferroelectricity. In comparison to Gd, as another lanthanoid, La lowers the total energy difference to the monoclinic ground state the most. Also, they derived general trends that a larger ionic radius and a lower electronegativity of a dopant are favorable for the FE phase. Batra et al. [5] did not firmly conclude that La is the most favorable dopant to promote ferroelectricty in hafnia because a clear identification of the relaxed structures was not always possible and assumptions required concerning the distribution of oxygen vacancies and dopants in the high-throughput computational approach. They rather focused on the aforementioned general chemical trends of dopant attributes that promote the FE Pca2 1 phase. Further clarification of this trend could be provided by Materlik et al., [6] who compared La with Al and Y (also trivalent, but different in atomic radius) andThe outstanding remanent polarization of 40 µC cm -2 reported for a 10 nm thin La:HfO 2 film in 2013 has attracted much attention. However, up to now, no explanation for this large remanent polarization has been presented. Density functional theory and X-ray diffraction are used to shine light onto three major aspects that impact the macroscopically observed remanent polarization: phase fraction, spontaneous polarization, and crystallographic texture. Density functional theory calculations show that the spontaneous polarization (P s ) of La:HfO 2 is indeed a bit larger than for other HfO 2 -or ZrO 2 -based compounds; however, the P s is not large enough to explain the observed differences in remanent polarization. While neither phase fractions nor spontaneous polarization nor strain are significantly different from those in other HfO 2 films, a prominent 020/002 texture distinguishes La doped from other HfO 2 -based ferroelectric films. Angulardependent diffraction data provide a pathway to calculate the theoretically expected remanent polarization, which is in agreement with the experimental observations. Finally, an interplay of the in-plane strain and texture is proposed to impact the formation of the ferroelectric phase during annealing. Further aspects of the special role of La as a dopant are collected and discussed to motivate future research.

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“…Zhou 26 on the other hand investigated several electronically compensated defect structures, consistent with the previously shown simulation results. 21,24 Falkowski 58 has investigated the effect of the spatial distribution of La and Si dopants including and not including vacancies. He found a stronger local variation of energy than expected with the implication that spatial arrangements of dopants have an effect on phase stability, distinguishing ALD from CSD processes.…”

Section: Doped Hfomentioning

confidence: 99%