Interface-engineered electron and hole tunneling

Rui Guo^{1

2}, Lingling Tao³, Ming Li³, Zhongran Liu⁴, Weinan Lin¹, Guowei Zhou^{1

5}, Xiaoxin Chen⁴, Liang Liu¹, Xiaobing Yan², He Tian⁶, Evgeny Y Tsymbal⁷, Jingsheng Chen⁸

Affiliations

¹ Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore, Singapore.
² College of Electron and Information Engineering, Hebei University, Baoding 071002, China.
³ Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE 68588-0299, USA.
⁴ Center of Electron Microscope, State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China.
⁵ Key Laboratory of Magnetic Molecules and Magnetic Information Materials of Ministry of Education, School of Chemistry and Materials Science, Shanxi Normal University, Linfen 041004, China.
⁶ Center of Electron Microscope, State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China. msecj@nus.edu.sg tsymbal@unl.edu hetian@zju.edu.cn.
⁷ Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE 68588-0299, USA. msecj@nus.edu.sg tsymbal@unl.edu hetian@zju.edu.cn.
⁸ Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore, Singapore. msecj@nus.edu.sg tsymbal@unl.edu hetian@zju.edu.cn.

PMID: 33762343
PMCID: PMC7990336
DOI: 10.1126/sciadv.abf1033

Interface-engineered electron and hole tunneling

Rui Guo et al. Sci Adv. 2021.

. 2021 Mar 24;7(13):eabf1033.

doi: 10.1126/sciadv.abf1033. Print 2021 Mar.

Authors

Rui Guo^{1

2}, Lingling Tao³, Ming Li³, Zhongran Liu⁴, Weinan Lin¹, Guowei Zhou^{1

5}, Xiaoxin Chen⁴, Liang Liu¹, Xiaobing Yan², He Tian⁶, Evgeny Y Tsymbal⁷, Jingsheng Chen⁸

Affiliations

¹ Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore, Singapore.
² College of Electron and Information Engineering, Hebei University, Baoding 071002, China.
³ Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE 68588-0299, USA.
⁴ Center of Electron Microscope, State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China.
⁵ Key Laboratory of Magnetic Molecules and Magnetic Information Materials of Ministry of Education, School of Chemistry and Materials Science, Shanxi Normal University, Linfen 041004, China.
⁶ Center of Electron Microscope, State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China. msecj@nus.edu.sg tsymbal@unl.edu hetian@zju.edu.cn.
⁷ Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE 68588-0299, USA. msecj@nus.edu.sg tsymbal@unl.edu hetian@zju.edu.cn.
⁸ Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore, Singapore. msecj@nus.edu.sg tsymbal@unl.edu hetian@zju.edu.cn.

PMID: 33762343
PMCID: PMC7990336
DOI: 10.1126/sciadv.abf1033

Abstract

Although the phenomenon of tunneling has been known since the advent of quantum mechanics, it continues to enrich our understanding of many fields of science. Commonly, this effect is described in terms of electrons traversing the potential barrier that exceeds their kinetic energy due to the wave nature of electrons. This picture of electron tunneling fails, however, for tunnel junctions, where the Fermi energy lies sufficiently close to the insulator valence band, in which case, hole tunneling dominates. We demonstrate the deterministic control of electron and hole tunneling in interface-engineered Pt/BaTiO₃/La_0.7Sr_0.3MnO₃ ferroelectric tunnel junctions by reversal of tunneling electroresistance. Our electrical measurements, electron microscopy and spectroscopy characterization, and theoretical modeling unambiguously point out to electron or hole tunneling regimes depending on interface termination. The interface control of the tunneling regime offers designed functionalities of electronic devices.

Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).

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Figures

**Fig. 1. Crossover between electron and hole tunneling and its role in an FTJ.**
(A) Decay constant κ (red line) versus energy E. Electron and hole tunneling regimes are distinguished by the Fermi energy (dashed lines) in the bandgap of the insulator. (B to E) Schematic of the TER effect. For electron tunneling, resistance is low (B) when polarization (shown by arrow) is pointing from metal 2 with a shorter screening length to metal 1 with a longer screening length, and resistance is high (C) for reversed polarization. For hole tunneling, the effect is opposite: Resistance is high (D) for polarization pointing from metal 1 to metal 2, and resistance is low (E) for reversed polarization. FE stands for ferroelectric.

**Fig. 2. RHEED and scanning probe microscopy characterization of A- and B-type FTJs.**
(A and B) Schematic of A-type (A) and B-type (B) FTJs. The atomic plane sequences across the BTO/LSMO interfaces are indicated. In the notation, LaSrO stands for La_0.7Sr_0.3O. (C) RHEED intensity oscillations of the specular reflected beam during the growth of 1 u.c. of SRO layer on the TiO₂-terminated STO substrate to obtain the SrO termination and the subsequent growth of the 15-u.c. LSMO and then 5-u.c. BTO thin films on top of it. a.u., arbitrary units. (D) RHEED intensity oscillations of the specular reflected beam during the growth of the 15-u.c. LSMO thin film on the TiO₂-terminated STO substrate and the following growth of the 5-u.c. BTO thin film. The insets show the RHEED patterns before and after each thin-film layer growth. (E and F) Atomic force microscopy topography (left) and out-of-plane PFM phase images (right) of the BTO thin films in A-type (E) and B-type (F) BTO/LSMO/STO heterostructures measured directly on the BTO films after the film deposition. The yellow and purple contrasts in the PFM phase images represent the upward and downward polarization direction, respectively. (G and H) Typical local PFM amplitude (circles) and phase (squares) hysteresis loops of BTO thin films for A-type (G) and B-type (H) Pt/BTO/LSMO FTJs measured on top Pt electrodes.

**Fig. 3. Transport properties of Pt/BTO (5 u.c.)/LSMO (15 u.c.) FTJs with different interface terminations.**
(A and B) Typical I-V curves within a small voltage range for A-type (A) and B-type (B) FTJs. The I-V curves are measured after poling the BTO layer upward (downward) using a voltage bias pulse of −6 V (+6 V) and duration of 1 ms. (C and D) Typical I-V switching curves for A-type (C) and B-type (D) FTJs. Absolute values of the current are used to plot the data in the logarithmic scale. (E and F) Representative R-V hysteresis loops for A-type (E) and B-type (F) FTJs.

**Fig. 4. STEM results for BTO/LSMO/STO heterostructures with different interface terminations.**
(A and B) High-angle annular dark-field (HAADF) images and EDX elemental maps of A-type (A) and B-type (B) heterostructures. The insets show the off-center displacement of Ti ions in the BTO layer. (C and D) Layer-resolved EELS spectra of Ti-L_2,3 and Mn-L_2,3 edges for A-type (C) and B-type (D) heterostructures. Arrows indicate the scan direction. Dashed lines mark the Ti-L₃ and Mn-L₃ peak positions.

**Fig. 5. Calculated electronic structure of LSMO/BTO superlattice and evanescent states in BTO.**
(A and B) Local density of states (DOS) across the BTO layer for (A) TiO₂/La0_.7Sr_0.3O (A-type) and (B) BaO/MnO₂ (B-type) terminations. Positive and negative DOS correspond to up- and down-spin contributions. Dashed lines indicate the Fermi energy. Ferroelectric polarization of BTO is assumed to be pointing down. Right panels in (A) and (B) show the LSMO/BTO supercells used in the calculations. (C) Calculated decay constant κ at the $\bar{Γ}$ point (k_∥ = 0) as a function of energy. Evanescent bands of Δ₁ and Δ₅ symmetry are indicated. (D) Calculated transmission across the 5-u.c.-thick BTO layer.

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References

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Interface-engineered electron and hole tunneling

Affiliations

Interface-engineered electron and hole tunneling

Authors

Affiliations

Abstract

Figures

References

LinkOut - more resources

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Research Materials