Jiuxiang Dai

Journal of Applied Physics, Volume 133, Issue 8, February 2023.
The model of lateral β-Ga2O3 metal–oxide–semiconductor field-effect transistor (MOSFET) was established using Sentaurus Technology Computer Aided Design software. The gate-to-drain distance of the device was 13.7 μm, and the breakdown voltage was 1135 V. The single event effect simulation model caused by heavy ion irradiation was introduced, and the effects of heavy ions’ incident position, angle, drain bias voltage, and linear energy transfer on the single event effect were studied. It is found that x = 7.7 μm is the sensitive location of the single event effect at the gate corner near the drain side and the peak value of the transient current is 177 mA/mm. The effect of the terminal structure of the field plate on the transient effect of the single event effect of β-Ga2O3 MOSFET is studied. It is also found that the sensitive position of the single event effect of the conventional structure, gate-field plate structure, and gate–source composite field plate structure is around x = 7.7 μm when VDS = 10 V. The peak transient currents obtained are 177, 161, and 148 mA/mm. The single event effect pulse current of the three structures increases with an increase in the drain bias voltage, while the peak pulse current of the conventional structure is larger than that of the gate-field plate structure and the gate–source composite structure. The research shows that the terminal structure of the field plate is reliable means to reduce the single particle effect.

Journal of Applied Physics, Volume 133, Issue 8, February 2023.
Recent theoretical and experimental discoveries of two-dimensional (2D) ferromagnetic (FM) materials have sparked intense interest for their potential applications in spintronics. 2D FM materials with high spin polarization are extremely desirable for future low-dimensional spintronics. Half-metallicity plays a key role in the development of such devices. Here, we reported a new 2D nanomagnet VClI[math] using the first-principles based density functional theory calculations. VClI[math] shows an exciting half-metallic character with a wide half-metallic gap of 0.4 eV. The ground state favors ferromagnetic coupling with a Curie temperature [math] of 21 K. The half-metallicity with a FM ground state is further achieved by the application of an external strain and by the combined effects of the strain and the electric field. A phase transition from a half-metallic [math] semiconductor [math] metal was further observed under different stimuli with an antiferromagnetic ground state. At [math] V/nm and in the presence of [math] strain, the calculated [math] is estimated at 35 K, which shows a 67% increment than the [math] observed in the unstrained condition. The fascinating and unique properties suggest that VClI[math] is a promising two-dimensional ferromagnetic half-metal, which can be useful for applications in future memory devices to enrich the 2D magnetic materials library.

The motion of ferroelectric liquid dropletson a ferroelectric solid substrate is controlled by a light beam of moderate intensity. Upon entering the ferroelectric phase, droplets are either attracted toward the center of the beam or repelled, depending on which side of the ferroelectric substrate is exposed to light. Moving the beam results in walking the ferroelectric droplet over long distances on the substrate.

Abstract

The motion of ferroelectric liquid sessile droplets deposited on a ferroelectric lithium niobate substrate can be controlled by a light beam of moderate intensity irradiating the substrate at a distance of several droplet diameters from the droplet itself. The ferroelectric liquid is a nematic liquid crystal, in which almost complete polar ordering of the molecular dipoles generates an internal macroscopic polarization locally collinear to the mean molecular long axis. Upon entering the ferroelectric phase, droplets are either attracted toward the center of the beam or repelled, depending on the side of the lithium niobate exposed to light irradiation. Moreover, moving the beam results in walking the ferroelectric droplet over long distances on the substrate. This behavior is understood as due to the coupling between the polarization of the ferroelectric droplet and the polarization photoinduced in the irradiated region of the lithium niobate substrate. Indeed, the effect is not observed in the conventional nematic phase, suggesting the crucial role of the ferroelectric liquid crystal polarization.

Asymmetrical contact measurements (ACMs) are demonstrated to explore scaling effects in Ni–MoS₂ contacts. ACMs compare electron injection at different contact lengths on the same MoS₂ channel to eliminate channel-to-channel variations. Importantly, source contacts yield more degradation in transistor current when scaled than drain contacts. ACMs provide a framework for generating new understanding of 2D-metal interfaces.

Abstract

2D semiconducting materials have immense potential for future electronics due to their atomically thin nature, which enables better scalability. While the channel scalability of 2D materials has been extensively studied, the current understanding of contact scaling in 2D devices is inconsistent and oversimplified. Here physically scaled contacts and asymmetrical contact measurements (ACMs) are combined to investigate the contact scaling behavior in 2D field-effect transistors. The ACMs directly compare electron injection at different contact lengths while using the exact same MoS₂ channel, eliminating channel-to-channel variations. The results show that scaled source contacts can limit the drain current, whereas scaled drain contacts do not. Compared to devices with long contact lengths, devices with short contact lengths (scaled contacts) exhibit larger variations, 15% lower drain currents at high drain–source voltages, and a higher chance of early saturation and negative differential resistance. Quantum transport simulations reveal that the transfer length of Ni–MoS₂ contacts can be as short as 5 nm. Furthermore, it is clearly identified that the actual transfer length depends on the quality of the metal-2D interface. The ACMs demonstrated here will enable further understanding of contact scaling behavior at various interfaces.

Recently, sharp exciton resonances in antiferromagnet NiPS₃ have been reported to correlate with magnetic order. It is found that the polarization of maximal exciton emission in NiPS₃ rotate locally, revealing three possible spin chain directions. This discovery establishes a new understanding of the antiferromagnetic order hidden in previous neutron scattering and optical experiments.

Abstract

A long-standing pursuit in materials science is to identify suitable magnetic semiconductors for integrated information storage, processing, and transfer. Van der Waals magnets have brought forth new material candidates for this purpose. Recently, sharp exciton resonances in antiferromagnet NiPS₃ have been reported to correlate with magnetic order, that is, the exciton photoluminescence intensity diminishes above the Néel temperature. Here, it is found that the polarization of maximal exciton emission rotates locally, revealing three possible spin chain directions. This discovery establishes a new understanding of the antiferromagnet order hidden in previous neutron scattering and optical experiments. Furthermore, defect-bound states are suggested as an alternative exciton formation mechanism that has yet to be explored in NiPS₃. The supporting evidence includes chemical analysis, excitation power, and thickness dependent photoluminescence and first-principles calculations. This mechanism for exciton formation is also consistent with the presence of strong phonon side bands. This study shows that anisotropic exciton photoluminescence can be used to read out local spin chain directions in antiferromagnets and realize multi-functional devices via spin-photon transduction.

A new self-assembly method can increase the information storage density in ferroelectric memories. A scroll-like 3D memory is fabricated by self-rolling-up freestanding single-crystalline ferroic oxide membranes. The information storage density can be enhanced at least one order of magnitude (experimentally 45.7 times) and 100–450 times (theoretically) than planar thin films.

Abstract

Ferroelectric memory is one of the most attractive emerging nonvolatile memory. Conventional methods to increase storage density in ferroelectrics include reducing the storage bit size or fabricating 3D stacks. However, the former will face a physical limit finally, and the integration of single-crystalline ferroelectric oxide following the latter still remains a great challenge. Here, a new method is introduced to construct a scroll-like 3D memory structure by self-rolling-up single-crystalline ferroelectric oxides. PbZr_0.3Ti_0.7O₃ single-crystalline thin film is chosen as a prototype and epitaxially grown on another oxide stressor layer with a few lattice-mismatch. Releasing such “Pb(Zr, Ti)O₃/stressor” bilayered structure from the substrate induces self-rolling-up due to the internal stress from the lattice-mismatch. High-density information can be written in the form of switched ferroelectric domains on those flat “Pb(Zr, Ti)O₃/stressor” membranes via piezoelectric force microscopy. In self-rolling-up membranes, information density can be experimentally enhanced up to 45 times. Theoretically, the freestanding “Pb(Zr, Ti)O₃/stressor” membranes have a strongly driven force to self-rolling-up, and the area ratio can enhance 100–450 times, corresponding to an ultra-high density information storage of 10² Tbit In⁻². This study provides a new and general method to develop compact, high-density, and 3D memories from oxide materials.

Nature Reviews Materials, Published online: 28 February 2023; doi:10.1038/s41578-023-00550-4

An article in Nature presents a conceptually new scanning probe microscope, called a quantum twisting microscope, which enables both momentum-resolved measurements and in situ tuning of the twist angle between 2D materials stacked on top of each other.

Applied Physics Letters, Volume 122, Issue 8, February 2023.
Thin-film lithium niobate (TFLN) photonic integrated circuits (PICs) have emerged as a promising integrated photonics platform for the optical communication, microwave photonics, and sensing applications. In recent years, rapid progress has been made on the development of low-loss TFLN waveguides, high-speed modulators, and various passive components. However, the integration of laser sources on the TFLN photonics platform is still one of the main hurdles in the path toward fully integrated TFLN PICs. Here, we present the heterogeneous integration of InP-based semiconductor lasers on a TFLN PIC. The III–V epitaxial layer stack is adhesively bonded to a TFLN waveguide circuit. In the laser device, the light is coupled from the III–V gain section to the TFLN waveguide via a multi-section spot size converter. A waveguide-coupled output power above 1 mW is achieved for the device operating at room temperature. This heterogeneous integration approach can also be used to realize on-chip photodetectors based on the same epitaxial layer stack and the same process flow, thereby enabling large-volume, low-cost manufacturing of fully integrated III–V-on-lithium niobate systems for next-generation high-capacity communication applications.

Applied Physics Letters, Volume 122, Issue 8, February 2023.
Antiferromagnetic transition metal oxides are an established and widely studied materials system in the context of spin-based electronics, commonly used as passive elements in exchange bias-based memory devices. Currently, major interest has resurged due to the recent observation of long-distance spin transport, current-induced switching, and THz emission. As a result, insulating transition metal oxides are now considered to be attractive candidates for active elements in future spintronic devices. Here, we discuss some of the most promising materials systems and highlight recent advances in reading and writing antiferromagnetic ordering. This article aims to provide an overview of the current research and potential future directions in the field of antiferromagnetic insulatronics.

Ab initio quantum transport simulation reveals that giant asymmetry between the n- and p-type devices in bulk InAs field-effect transistors (FETs) is significantly reduced in the sub-2-nm-diameter gate-all-around InAs nanowire FETs. The reason lies in the band inversion and quantum confinement effect.

Abstract

Complementary metal-oxide-semiconductor (CMOS) field-effect transistors (FETs) are the key component of a chip. Bulk indium arsenide (InAs) owns nearly 30 times higher electron mobility µ _e than silicon but suffers from a much lower hole mobility µ _h (µ _e/µ _h = 80), thus unsuited to CMOS application with a single material. Through the accurate ab initio quantum-transport simulations, the performance gap between the NMOS and PMOS is significantly narrowed is predicted and even vanished in the sub-2-nm-diameter gate-all-around (GAA) InAs nanowires (NW) FETs because the inversion of the light and heavy hole bands occurs when the diameter is shorter than 3 nm. It is further proposed several feasible strategies for further improving the performance symmetry in the GAA InAs NWFETs. Short-channel effects are effectively depressed in the symmetric n- and p-type GAA InAs NWFETs till the gate length is scaled down to 2 nm according to the standards of the International Technology Roadmap for Semiconductors. Therefore, the ultrasmall GAA InAs NWFETs possess tremendous prospects in CMOS integrated circuits.

The categories of different sites and elementary compositions of honeycomb-layered-oxides are discussed. Recent progress on honeycomb-layered-oxides as well as Na₃Ni₂SbO₆ and Na₃Ni₂BiO₆ as two representative materials is introduced, and the crystal and electronic structure, electrochemical performance, and modification strategies are summarized. This review would inspire more interest in high output voltage, long lifespan sodium-ion batteries.

Abstract

Sodium-ion batteries (SIBs) are becoming promising candidates for energy storage devices due to the low cost, abundant reserves, and excellent electrochemical performance. As the most important unit, layered cathodes attract much attention, where honeycomb-layered-oxides (HLOs) manifest outstanding structural stability, high redox potential, and long-life electrochemistry. Here, recent progress on HLOs as well as Na₃Ni₂SbO₆ and Na₃Ni₂BiO₆ as two representative materials are introduced, and the crystal and electronic structure, electrochemical performance, and modification strategies are summarized. The advanced high nickel HLOs are highlighted toward development of state-of-the-art sodium-ion batteries. This review would deepen the understanding of superstructure in layered oxides, as well as structure–property relationship, and inspire more interest in high output voltage, long lifespan sodium-ion batteries.

Journal of Applied Physics, Volume 133, Issue 7, February 2023.
Oxygen vacancy is crucial to the optical properties in In[math]O[math], however, the single oxygen vacancy model fails to explain the observed multi-peak emission in the experiment. Herein, we have theoretically investigated the diversity of oxygen vacancy distribution, revealing the relationship between the defect configurations and the optical properties. Combining the first-principles calculations and bayesian regularized artificial neural networks, we demonstrate that the structural stability can be remarkably enhanced by multi-oxygen vacancy aggregation, which will evolve with the defect concentration and temperature. Notably, our results indicate that the single oxygen vacancy will induce the emission peaks centered at 1.35 eV, while multi-peak emission near 2.35 eV will be attributed to the distribution of aggregated double oxygen vacancies. Our findings provide a comprehensive understanding of multi-peak emission observed in In[math]O[math], and the rules of the vacancy distribution may be extended for other metal oxides to modulate the optical properties in practice.

Nature Photonics, Published online: 27 February 2023; doi:10.1038/s41566-023-01167-3

Single-crystal perovskite LEDs exhibit reduced ion migration and Auger recombination and increased device lifetime. Perovskite single-crystals-based LEDs exhibit a maximum brightness of 86,000 cd m−2, a peak EQE of 11.2% and T50 lifetime of 12,500 h at an initial luminance of 100 cd m−2.

Nature Communications, Published online: 23 February 2023; doi:10.1038/s41467-023-36715-6

Laminated van der Waals (vdW) metallic electrodes can improve the contact of 2D electronic devices, but their scalability is usually limited by the transfer process. Here, the authors report a strategy to deposit vdW contacts onto various 2D and 3D semiconductors at the wafer scale.

Nature Communications, Published online: 21 February 2023; doi:10.1038/s41467-023-36619-5

2D nonlayered materials exhibit interesting properties for catalysis, nanoelectronics and spintronics applications, but their growth is still challenging. Here, the authors report a theoretical model and an experimental strategy to synthesize various 2D nonlayered transition metal oxides with room-temperature magnetic properties.

2-nm-thick indium oxide nanosheets with high electron mobility have been synthesized utilizing a liquid metal printing technique and thermal annealing in air. Transmission electron microscopy with in situ annealing reveals that the improvement in device performances is due to nanostructural changes during annealing process. This work highlights a facile and ambient air compatible method for fabricating high-quality semiconductors, which find application in emerging electronics and optoelectronics.

Abstract

Thin film transistors (TFTs) are key components for the fabrication of electronic and optoelectronic devices, resulting in a push for the wider exploration of semiconducting materials and cost-effective synthesis processes. In this report, a simple approach is proposed to achieve 2-nm-thick indium oxide nanosheets from liquid metal surfaces by employing a squeeze printing technique and thermal annealing at 250 °C in air. The resulting materials exhibit a high degree of transparency (>99 %) and an excellent electron mobility of ≈96 cm² V⁻¹ s⁻¹, surpassing that of pristine printed 2D In₂O₃ and many other reported 2D semiconductors. UV-detectors based on annealed 2D In₂O₃ also benefit from this process step, with the photoresponsivity reaching 5.2 × 10⁴ and 9.4 × 10³ A W⁻¹ at the wavelengths of 285 and 365 nm, respectively. These values are an order of magnitude higher than for as-synthesized 2D In₂O₃. Utilizing transmission electron microscopy with in situ annealing, it is demonstrated that the improvement in device performances is due to nanostructural changes within the oxide layers during annealing process. This work highlights a facile and ambient air compatible method for fabricating high-quality semiconducting oxides, which will find application in emerging transparent electronics and optoelectronics.

A dry patterning approach together with the electrode transfer method for 2D solution-processed organic single-crystal field-effect transistors via bottom-up fabrication is demonstrated. High-performance flexible monolayer OFETs and high-speed organic rectifiers are fabricated based on these strategies.

Abstract

Organic field-effect transistors (OFETs) based on 2D monolayer organic semiconductors (OSC) have demonstrated promising potentials for various applications, such as light emitting diode (LED) display drivers, logic circuits, and wearable electrocardiography (ECG) sensors. To date, the fabrications of this class of highly crystallized 2D organic semiconductors (OSC) are dominated by solution shearing. As these organic active layers are only a few molecular layers thick, their compatibilities with conventional thermal evaporated top electrodes or sophisticated photolithography patterning are very limited, which also restricts their device density. Here, an electrode transfer stamp and a semiconductor patterning stamp are developed to fabricate OFETs with channel lengths down to 3 µm over a large area without using any chemicals or causing any damage to the active layer. 2D 2,9-didecyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C₁₀-DNTT) monolayer OFETs developed by this new approach shows decent performance properties with a low threshold voltage (V _TH) less than 0.5 V, intrinsic mobility higher than 10 cm² V⁻¹ s⁻¹ and a subthreshold swing (SS) less than 100 mV dec⁻¹. The proposed patterning approach is completely comparable with ultraflexible parylene substrate less than 2 µm thick. By further reducing the channel length down to 2 µm and using the monolayer OFET in an AC/DC rectifying circuit, the measured cutoff frequency is up to 17.3 MHz with an input voltage of 4 V. The newly proposed electrode transfer and patterning stamps have addressed the long-lasting compatibility problem of depositing electrodes onto 2D organic monolayer and the semiconductor patterning. It opens a new path to reduce the fabrication cost and simplify the manufacturing process of high-density OFETs for more advanced electronic or biomedical applications.