Charge carrier injection and transport engineering in two-dimensional transition metal dichalcogenides

Retamal, José Ramón Durán; Periyanagounder, Dharmaraj; Ke, Jr‐Jian; Tsai, Meng‐Lin; He, Jr‐Hau

doi:10.1039/c8sc02609b

Cited by 82 publications

(122 citation statements)

References 215 publications

(248 reference statements)

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“…This result was expected because when a bulk material is downsized to atomically thin dimensions, a strong correlation between the surface states (or traps) and charge carriers would significantly impair the mobility of free charges. [ 15 ] It has also been reported that the band gap of atomically thin ZnO increases up to 4.0 eV, becoming more insulating. [ 16 ]…”

Section: Figurementioning

confidence: 99%

Memristive Behavior Enabled by Amorphous–Crystalline 2D Oxide Heterostructure

et al. 2020

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broad selection of electrical properties. In particular, ZnO thin films have attracted great interest due to their facile preparation approaches, excellent compatibility for device integration, and controllable electronic and optoelectronic behavior. [9] Their memristive behavior is primarily associated with the non-equilibrium distribution of oxygen vacancies in response to an external electrical field. This switching mechanism allows robust cycling endurance, but it is always associated with low switching speed. [10] In contrast, 2D nanomaterials offer a quantum-confined medium which can have exceptional transport properties and substantially improved memristive behavior compared to conventional bulk materials. For example, single atomic layer 2D transition metal dichalcogenide memristors exhibited high-frequency switching with an extremely low power consumption, [6,11] and memristors based on ultrathin singlecrystalline SiGe layer demonstrated significantly improved reproducibility and low energy consumption. [3] Developing memory devices with low operating voltages and low energy consumption go in the direction of a connection between instrinsically neuromorphic devices and living neurons. [12] Nevertheless, due to the unavailability of 2D oxides nanomaterials and the high entropy of introducing vacancies in 2D confined geometry, stable 2D oxide-based memristors have yet to be demonstrated. [9] Recently, ionic layer epitaxy (ILE) was developed as a versatile solution-based approach for growing large-area oxide nanosheets on a liquid surface. [13] Atomically thin single-crystalline ZnO nanosheets were synthesized with sizes over 10 µm, enabling the study of the memristor properties based on 2D metal oxides. In this work, we show extraordinary memristive behavior enabled by interfacing atomically thin single crystalline ZnO nanosheets with a few-nm thick amorphous Al 2 O 3 layer. The conduction mechanism was attributed to the classic oxygen vacancy conductive channels in the lateral transistor module. In this configuration, the ZnO nanosheet provides a 2D host of oxygen vacancies, while the amorphous Al 2 O 3 facilitates the generation and stabilization of the oxygen vacancies. The 2D heterointerface brought a new promise for flexible nonvolatile and ultralow power memory devices.Atomically thin single-crystalline ZnO nanosheets were synthesized by ILE, [13,14] in which amphiphilic molecules (oleyl sulfate) self-assembled into a monolayer at the water-air The emergence of memristive behavior in amorphous-crystalline 2D oxide heterostructures, which are synthesized by atomic layer deposition (ALD) of a few-nanometer amorphous Al 2 O 3 layers onto atomically thin single-crystallineZnO nanosheets, is demonstrated. The conduction mechanism is identified based on classic oxygen vacancy conductive channels. ZnO nanosheets provide a 2D host for oxygen vacancies, while the amorphous Al 2 O 3 facilitates the generation and stabilization of the oxygen vacancies. The conduction mechanism in the high-resistance state follo...

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Section: Figurementioning

confidence: 99%

Memristive Behavior Enabled by Amorphous–Crystalline 2D Oxide Heterostructure

et al. 2020

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“…In this sense, as shown in the present work, it is important to design the conducting layer carefully such that it is energetically well-matched to enable a feasible carrier transport from the photoelectrodes. Regardless of the recent monumental findings allowing high STC% using a multi-junction device 15,20 , the interface energy barrier design, has not been well identified and optimized for redox cell applications, whereas it has been well-studied in PEC water splitting community 31,40 . Specifically, this puts emphasis that choosing an appropriate conductivity type of the electrode surface upon combination with high work function conductors, such as Pt and C, is of great importance for minimizing the reaction overpotential.…”

Section: Photoelectrochemical Behaviour and Efficiency Loss Analysismentioning

confidence: 99%

Design principles for efficient photoelectrodes in solar rechargeable redox flow cell applications

et al. 2020

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Recent advances in photoelectrochemical redox flow cells, such as solar redox flow batteries, have received much attention as an alternative integrated technology for simultaneous conversion and storage of solar energy. Theoretically, it has been reported that even singlephoton devices can demonstrate unbiased photo-charging with high solar-to-chemical conversion efficiency; however, the poor redox kinetics of photoelectrodes reported thus far severely limit the photo-charging performance. Here, we report a band alignment design and propose surface coverage control to reduce the charge extraction barrier and create a facile carrier pathway from both n-and p-type photoelectrodes to the electrolyte with the respective redox reaction. Based on these observations, we develop a single-photon photocharging device with a solar-to-chemical conversion efficiency over 9.4% for a redox flow cell system. Along with these findings, we provide design principles for simultaneous optimisation, which may lead to enhanced conversion efficiency in the further development of solarrechargeable redox flow cells.

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“…Electronic and spin transport [82][83][84][85] in TMDCs is becoming an important topic. It has been shown that the carrier mobility increases with the number of TMDC layers 69,84 , due to reduced Coulomb scattering in thicker samples 86 , while phonon scattering limits the room temperature mobility 85 .…”

Section: Introductionmentioning

confidence: 99%

Giant proximity exchange and valley splitting in transition metal dichalcogenide/ hBN /(Co, Ni) heterostructures

2020

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We investigate the proximity-induced exchange coupling in transition-metal dichalcogenides (TMDCs), originating from spin injector geometries composed of hexagonal boron-nitride (hBN) and ferromagnetic (FM) cobalt (Co) or nickel (Ni), from first-principles. We employ a minimal tightbinding Hamiltonian that captures the low energy bands of the TMDCs around K and K' valleys, to extract orbital, spin-orbit, and exchange parameters. The TMDC/hBN/FM heterostructure calculations show that due to the hBN buffer layer, the band structure of the TMDC is preserved, with an additional proximity-induced exchange splitting in the bands. We extract proximity exchange parameters in the 1-10 meV range, depending on the FM. The combination of proximity-induced exchange and intrinsic spin-orbit coupling (SOC) of the TMDCs, leads to a valley polarization, translating into magnetic exchange fields of tens of Tesla. The extracted parameters are useful for subsequent exciton calculations of TMDCs in the presence of a hBN/FM spin injector. Our calculated absorption spectra show a large splitting of the first exciton peak; in the case of MoS2/hBN/Co we find a value of about 8 meV, corresponding to about 50 Tesla external magnetic field in bare TMDCs. The reason lies in the band structure, where a hybridization with Co d orbitals causes a giant valence band exchange splitting of more than 10 meV. Structures with Ni do not show any d level hybridization features, but still sizeable proximity exchange and exciton peak splittings of around 2 meV are present in the TMDCs.

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Charge carrier injection and transport engineering in two-dimensional transition metal dichalcogenides

Abstract: This review intertwines current engineering strategies tailoring the carrier injection and carrier transport of two-dimensional transition metal dichalcogenides toward efficient electronic devices.

Cited by 82 publications

References 215 publications

Memristive Behavior Enabled by Amorphous–Crystalline 2D Oxide Heterostructure

Memristive Behavior Enabled by Amorphous–Crystalline 2D Oxide Heterostructure

Design principles for efficient photoelectrodes in solar rechargeable redox flow cell applications

Giant proximity exchange and valley splitting in transition metal dichalcogenide/ hBN /(Co, Ni) heterostructures

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