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Atomic chalcogen vacancy is the most commonly observed defect category in two dimensional (2D) transition‐metal dichalcogenides, which can be detrimental to the intrinsic properties and device performance. Here a low‐defect density, high‐uniform, wafer‐scale single crystal epitaxial technology by in situ oxygen‐incorporated "growth‐repair" strategy is reported. For the first time, the oxygen‐repairing efficiency on MoS2 monolayers at atomic scale is quantitatively evaluated. The sulfur defect density is greatly reduced from (2.71 ± 0.65) × 1013 down to (4.28 ± 0.27) × 1012 cm−2, which is one order of magnitude lower than reported as‐grown MoS2. Such prominent defect deduction is owing to the kinetically more favorable configuration of oxygen substitution and an increase in sulfur vacancy formation energy around oxygen‐incorporated sites by the first‐principle calculations. Furthermore, the sulfur vacancies induced donor defect states is largely eliminated confirmed by quenched defect‐related emission. The devices exhibit improved carrier mobility by more than three times up to 65.2 cm2 V−1 s−1 and lower Schottky barrier height reduced by half (less than 20 meV), originating from the suppressed Fermi‐level pinning effect from disorder‐induced gap state. The work provides an effective route toward engineering the intrinsic defect density and electronic states through modulating synthesis kinetics of 2D materials. [ABSTRACT FROM AUTHOR]

Whispering gallery mode (WGM) laser with single‐mode is important for optoelectronic applications because of the higher stability during the light signal transmission. But till now, for InGaN‐based WGM laser, most reports of lasing behavior are multimode lasing. To achieve single‐mode WGM laser, an InGaN‐based micro‐ring laser is proposed and demonstrated with lateral nanoporous distributed Bragg reflector (DBR), where the high‐order lasing modes are strongly suppressed. The side mode suppression ratio (SMSR) is more than 9 times larger than that of the micro‐disk laser with the same radius. Combined with FDTD simulation, the results show that the enhancements are originated from the suppression of the high‐order resonant mode because of the inner boundary of micro‐ring. This work provides a new solution to achieve stable single‐mode WGM laser for future photonic integration. [ABSTRACT FROM AUTHOR]

Spin orbit torque (SOT) devices with the advantages of high speed, low power consumption, and high stability have wide application prospects in the field of spintronics. The SOT‐based crossbar array device is an important extension of SOT devices, but it is not reported so far. Here, the all electrical magnetization switching of Hall crossings based on SOT crossbar array devices is realized. Through analyzing the current distribution and micromagnetic simulations, it is found that this field‐free SOT switching in the array devices comes from the asymmetric current density gradient distribution at the Hall‐crossings due to the shunt effect of grid circuits. All electrical tristate magnetization switching and the write protection of spin crossbar array devices are demonstrated. This work will further promote the application of the efficient memory or edge computing based on spin crossbar array devices. [ABSTRACT FROM AUTHOR]

Spin–orbit torque (SOT) efficiencies are systematically investigated in [Pt (tPt)/Ru (1−tPt)]10/Pt (0.8 nm)/Co multilayer systems with perpendicular magnetic anisotropy and in‐plane magnetic anisotropy. A high SOT efficiency is achieved by the optimized Pt‐based multilayer structures. The maximum damping‐like efficiency ξDL of 0.31 is found in [Pt (tPt)/Ru (1−tPt)]10/Pt (0.8 nm)/Co multilayers with relatively low resistivity (58.8 μΩ cm), which is three times larger than that of pure Pt layer and is also significantly larger than the PtnRu1−n alloy with the same composition. Considering the interface transparency, intrinsic spin Hall ratio θSH of around 0.7, being close to the upper limit 0.8 for Pt‐based heavy metals, is obtained. The strongly enhanced ξDL is attributed to the high spin Hall conductivity contributed by the intrinsic spin Hall contribution and the enhanced resistivity due to enhanced interfacial scattering. This work provides a good balance of SOT efficiency and resistivity through the optimized Pt‐based multilayer structure, which is expected to be applicable in beyond Pt‐based systems and has great potential in building energy‐efficient SOT devices in the future. [ABSTRACT FROM AUTHOR]

Control of spins by spin–orbit torque brings novel strategies to design spintronic devices with potentially high impact in data storage and logic‐in‐memory computing architectures. Although various attempts have been proposed to avoid the participation of magnetic field during magnetization switching for realizing multifunctional spin logic devices, simpler and more feasible approaches are still strongly desired. Here, field‐free current‐induced magnetization switching is achieved through magnetic domain wall (DW) motion in a dual‐channels device, where the chiral Néel DW is stabilized by the strong Dzyaloshinskii–Moriya interaction in Pt/Co/Ru asymmetric structure. By electrically programming the initial magnetization states of the device with two opposite switching modes, four Boolean logic gates of AND, NAND, OR, and NOR are demonstrated. This work demonstrates that ingenious geometry design can be important for developing the spin logic devices and in‐memory computing architectures. [ABSTRACT FROM AUTHOR]

Low‐dimensional semiconductors with in‐plane anisotropy and narrow bandgap have been extensively applied to polarized detection in the near‐infrared (NIR) region. However, the narrow bandgap can cause noise owing to the high dark current in photodetectors. This article reports quasi‐1D ZrGeTe4 nanoribbon‐based photodetectors with low dark current and broadband polarization detection. The photodetector was fabricated by evaporating 50‐nm‐thick Au electrodes on a ZrGeTe4 nanoribbon. Benefiting from the photovoltaic characteristics in the ZrGeTe4 nanoribbon and Au electrodes, these photodetectors can operate without bias voltage, with decreased dark current, and improved device performance. Furthermore, the quasi‐1D ZrGeTe4 nanoribbon‐based photodetectors demonstrate a polarization sensitivity in a broadband from visible (VIS) to the NIR region, such as a high photoresponsivity of 625.65 mA W−1, large external quantum efficiency of 145.9% at 532 nm, and photocurrent anisotropy ratio of 2.04 at 1064 nm. They exhibit a novel perpendicular optical reversal of 90° in polarization‐sensitive photodetection, angle‐resolved absorption spectra, and azimuth‐dependent reflectance difference microscopy (ADRDM) from VIS to the NIR region, as opposed to other nanoribbon‐based polarization‐sensitive photodetectors. This work paves the way for utilizing photovoltaic photodetectors based on low‐dimensional materials for broad‐spectrum polarized photodetection. [ABSTRACT FROM AUTHOR]

Spin‐orbit torque (SOT)‐based magnetization switching is a promising candidate for the innovation and developments of spintronic devices. However, the necessity of an in‐plane magnetic field to induce deterministic switching is an obstacle to feasibility in practical applications. Here, it is shown that the field‐free current‐induced magnetization switching in a perpendicular magnetized Pt1−xMox/Co/Ru heterostructure with x = 0, 0.04, 0.07, 0.12, and 0.17. Applying an in‐plane charge current through the Pt1−xMox layer, the device can achieve a high‐efficiency field‐free current‐induced magnetization switching with competing spin currents generated from a single Pt1−xMox alloy layer due to opposite spin Hall angles (θSHA) of Pt and Mo atoms and locally induced electric field. Remarkably, the large θSHA of about 0.35 is achieved in the optimal composition of Pt0.88Mo0.12 alloy, which is much higher than that of the pure Pt structure. The results pave the way to resolve the future problems of scalability and thermal stability for SOT‐driven magnetic tunnelling junctions. [ABSTRACT FROM AUTHOR]

Neuromorphic computing using multilevel nonvolatile memories as synapses offers opportunities for future energy‐ and area‐efficient artificial intelligence. Among these memories, artificial synapses based on current‐induced magnetization switching driven by spin–orbit torques (SOTs) have attracted great attention recently. Herein, the gradient descent algorithm, a primary learning algorithm, implemented on a 2 × 1 SOT synaptic array is reported. Successful pattern classifications are experimentally realized through the tuning of cycle‐to‐cycle variation, linearity range, and linearity deviation of the multilevel SOT synapse. Also, a larger m × n SOT synaptic array with m controlling transistors is proposed and it is found that the classification accuracies can be improved dramatically by decreasing the cycle‐to‐cycle variation. A way for the application of spin–orbit device arrays in neuromorphic computing is paved and the crucial importance of the cycle‐to‐cycle variation for a multilevel SOT synapse is suggested. [ABSTRACT FROM AUTHOR]

Creation and annihilation of skyrmions are two crucial issues for constructing skyrmion‐based memory and logic devices. To date, these operations were mainly achieved by means of external magnetic, electrical, and optical modulations. In this work, we demonstrated an effective strain‐induced skyrmion nucleation/annihilation phenomenon in [Pt/Co/Ta]n multilayers utilizing the shape memory effect of a TiNiNb substrate. A tunable tensile strain up to 1.0% can be realized in the films by thermally driving phase transition of the substrate, which significantly decreases the nucleation field of skyrmions by as many as 400 Oe and facilitates the field‐free manipulation of skyrmions with the strain. Such a strain effect can be attributed to the synergetic interplay of the planar magnetic moment twirling and decrement of interfacial Dzyaloshinskii–Moriya interaction. In addition, the strain tunability is found to be strongly related to the strain direction due to magnetoelastic interaction. These findings provide a novel strategy for developing strain‐assisted skyrmion‐based memory and logic devices. [ABSTRACT FROM AUTHOR]

Polarized photodetectors with wide spectral detection and ultra‐fast photoresponses based on anisotropic semiconductors have potential applications in military and civilian fields and have been widely studied in recent years. The dual advantages of low‐symmetry crystal structure and special electronic band‐structure make Sb2S3 the perfect choice for polarized photodetection. In this work, the optical, vibrational, and optoelectronic anisotropy of the high‐quality orthorhombic Sb2S3 nanowires are systematically investigated by experimental and theoretical studies. The metal‐semiconductor‐metal photodetectors based on a single Sb2S3 nanowire exhibit good polarization sensitivity in a broadband range from ultraviolet to near‐infrared (360 to 1550 nm) and the obtained maximum dichroic ratio is 2.54 at 638 nm. The polarization‐sensitive photocurrent mapping results show that the photocurrent is mainly derived from the Schottky junction at the interface between Au and Sb2S3. The effective separation of the photo‐generated carriers near the Schottky junction gives a photodetector response time of 470 µs. The direct polarimetric imaging demonstrates that the gray value of the image obtained by the imaging system is sensitive to the object's polarized direction. This natural sensitivity of the Sb2S3‐based photodetector to polarized objects makes it possible to image polarized objects directly as an image sensor. [ABSTRACT FROM AUTHOR]

Spin–orbit torque (SOT) induced perpendicular magnetization switching in Pt1‐xGdx/Co/Al2O3 heterostructure with x = 0, 0.02, 0.14, 0.30, and 0.33 is investigated. With in‐plane charge current flowing through the Pt1‐xGdx layer, field‐free current‐induced magnetization switching is observed for all nonzero x due to the existence of opposite spin Hall angles (θSHA) from Pt1‐xGdx alloys. Furthermore, the large θSHA of about 0.27 is obtained in the optimal Pt0.70Gd0.30 alloy films, which is about four times larger than that of the pure Pt. This work suggests a simple and scalable method for realizing field‐free SOT switching, and provides potential candidates of spin Hall materials that can be used to produce highly efficient SOTs. [ABSTRACT FROM AUTHOR]

Current‐driven switching of nonvolatile spintronic materials and devices based on spin–orbit torques offer fast data processing speed, low power consumption, and unlimited endurance for future information processing applications. Analogous to conventional complementary metal‐oxide‐semiconductors technology, it is important to develop complementary spin–orbit devices with differentiated magnetization switching senses as elementary building blocks for realizing sophisticated logic functionalities. Various attempts using external magnetic field or complicated stack/circuit designs have been proposed; however, plainer and more feasible approaches are still strongly desired. Here it is shown that a pair of two locally laser annealed perpendicular Pt/Co/Pt devices with opposite laser track configurations and thereby inverse field‐free lateral spin–orbit torques (LSOTs) induced switching senses can be adopted as such complementary spin–orbit building blocks. By electrically programming the initial magnetization states (spin down/up) of each sample, Boolean logic gates of AND, OR, NAND, and NOR as well as a spin–orbit half adder containing an exclusive‐OR gate are obtained. Moreover, various initialization‐free programmable stateful logic operations, including material implication gate, are also demonstrated by regarding the magnetization state as a logic input. The complementary LSOT building blocks provide a potentially applicable way toward future efficient spin logics and in‐memory computing architectures. [ABSTRACT FROM AUTHOR]

In the field of memory and spin‐logical devices, multiferroics have the potentials of low‐energy informational operation. A novel memory and logic device in a PbZr0.2Ti0.8O3/Co/Pt (PZT/Co/Pt) multiferroic heterostructure with perpendicular magnetic anisotropy (PMA) is proposed. The PMA of PZT/Co/Pt structure can be modulated via the PZT/Co interface by switching the polarization field in the PZT layer. Moreover, the anomalous Hall voltage (AHV) under downward polarization is about 63% higher than that under upward polarization at 50 K without magnetic field. Interestingly, this AHV modulation is reversible, fast, and nonvolatile. Furthermore, the multiferroic random access memory and logic device operations are demonstrated based on the ferroelectric‐modulated AHV, which can lower the operating current density. This nonvolatile manipulation via ferroelectric polarizations will offer a new pathway to improve spintronic and spin‐logical applications. [ABSTRACT FROM AUTHOR]

Atomically thin layers of van der Waals (vdW) crystals offer an ideal material platform to realize tunnel field‐effect transistors (TFETs) that exploit the tunneling of charge carriers across the forbidden gap of a vdW heterojunction. This type of device requires a precise energy band alignment of the different layers of the junction to optimize the tunnel current. Among 2D vdW materials, black phosphorus (BP) and indium selenide (InSe) have a Brillouin zone‐centered conduction and valence bands, and a type II band offset, both ideally suited for band‐to‐band tunneling. TFETs based on BP/InSe heterojunctions with diverse electrical transport characteristics are demonstrated: forward rectifying, Zener tunneling, and backward rectifying characteristics are realized in BP/InSe junctions with different thickness of the BP layer or by electrostatic gating of the junction. Electrostatic gating yields a large on/off current ratio of up to 108 and negative differential resistance at low applied voltages (V ≈ 0.2 V). These findings illustrate versatile functionalities of TFETs based on BP and InSe, offering opportunities for applications of these 2D materials beyond the device architectures reported in the current literature. [ABSTRACT FROM AUTHOR]

Manipulation of the antiferromagnetic moment in antiferromagnets (AFMs) is a crucial issue for developing AFM‐based spintronic devices. Lattice strain is an effective strategy to modulate the antiferromagnetic moment and is traditionally based on a direct crystalline tailoring of AFMs. A novel method for strain tuning the antiferromagnetic moment by controlling the exchange spring in the AFM, which is applicable to other conventional AFM materials, is reported. Specifically, a TiNi(Nb) shape memory alloy (SMA) is used as the substrate of Ta/NiFe/FeMn multilayers. By thermally driven inverse martensitic phase transformation in the SMA, a significant strain of 1.3% is transferred into the film, which toggles a noticeable magnetic moment rotation of NiFe by nearly 90° in the film plane, resulting in a consequent twirling of the Néel vector of FeMn due to interfacial exchange interaction. In turn, the antiferromagnetic moment of FeMn is tailorable by tuning the exchange spring. Simultaneously, the exchange bias field is tuned significantly with a maximal variation of 350% due to the twist of the antiferromagnetic moment, which facilitates strain‐assisted magnetization reversal for developing a logic memory device. These findings provide an alternative strategy to advance the development of an AFM‐based memorizer by temperature‐driven strain engineering. [ABSTRACT FROM AUTHOR]

The implementation of blue‐light photodiodes based on InGaN in emerging technologies, such as free‐space visible light communication (VLC), requires transformative approaches toward enhanced performance, miniaturization, and integration beyond current Si‐based technologies. This work reports on the design and realization of high‐performance InGaN‐based resonant cavity photodiodes with high‐reflectivity lateral porous GaN distributed Bragg reflectors. The well‐controlled porosification of GaN on the 2‐inch wafers enables design and fabrication of optical components, unlocking the potential of nitride semiconductors for several applications. These resonant‐cavity‐enhanced photodiodes, which have a 12 nm‐thick optically active region, exhibit a high responsivity (≈0.1 A W−1) to blue‐light even without any externally applied voltage. Furthermore, the device can operate as both an emitter and a detector of visible light at well‐defined wavelengths with spectral overlap between the electroluminescence emission and photocurrent responsivity, meeting the requirement of wavelength selectivity, thermal stability, and low‐power consumption for VLC, with potential for integration of different functionalities, that is, light emission and detection, on a single chip without additional light filters. [ABSTRACT FROM AUTHOR]

Abstract: Electrical current–induced deterministic magnetization switching in a magnetic multilayer structure without any external magnetic field is realized by utilizing interlayer exchange coupling. Two ferromagnetic Co layers, with in‐plane and out‐of‐plane anisotropy, respectively, are separated by a spacer Ta layer, which plays a dual role in inducing antiferromagnetic interlayer coupling, and contributing to the current‐induced effective magnetic field through the spin Hall effect. The current‐induced magnetization switching behavior can be tuned by premagnetizing the in‐plane Co layer. The antiferromagnetic exchange coupling field increases with decreasing thickness of the Ta layer, reaching 630 ± 5 Oe for a Ta thickness of 1.5 nm. A model is developed to separate the Joule heating and spin–orbit torques caused by the electrical current. The magnitude of the current‐induced perpendicular effective magnetic field from spin–orbit torque is 9.2 Oe/(107 A cm−2). The large spin Hall angle of Ta, opposite in sign to that of Pt, results in a low critical current density of 9 × 106 A cm−2. This approach is promising for the electrical switching of magnetic memory elements without any external magnetic field. [ABSTRACT FROM AUTHOR]

Abstract: Band engineering in layered metal dichalcogenides leads to a variety of physical phenomena and has obtained considerable attention recently. In this work, pressure‐induced metallization and superconductivity in pristine 1T‐SnSe2 is reported via electrical transport and synchrotron X‐ray diffraction experiments. Electrical transport results show that the metallization emerges above 15.2 GPa followed by appearance of superconducting transition at 18.6 GPa. The superconductivity is robust with a nearly constant Tc ≈ 6.1 K between 30.1 and 50.3 GPa. High‐pressure synchrotron X‐ray diffraction experiments indicate that the 1T‐SnSe2 phase maintains up to 46.0 GPa. Although the theoretical predicted structural transition and decomposition of SnSe2 into Sn3Se4 and Se are not detected, it is argued that the structural instability under high pressure might be crucial for the superconductivity. These findings demonstrate that 1T‐SnSe2 is a very rare system from which superconductivity can be driven via multiple ways. [ABSTRACT FROM AUTHOR]

Abstract: The Weyl semimetal WTe2 and MoTe2 show great potential in generating large spin currents since they possess topologically protected spin‐polarized states and can carry a very large current density. In addition, the intrinsic non‐centrosymmetry of WTe2 and MoTe2 endows with a unique property of crystal symmetry‐controlled spin–orbit torques. An important question to be answered for developing spintronic devices is how spins relax in WTe2 and MoTe2. Here, a room‐temperature spin relaxation time of 1.2 ns (0.4 ns) in WTe2 (MoTe2) thin film using the time‐resolved Kerr rotation (TRKR) is reported. Based on ab initio calculation, a mechanism of long‐lived spin polarization resulting from a large spin splitting around the bottom of the conduction band, low electron–hole recombination rate, and suppression of backscattering required by time‐reversal and lattice symmetry operation is identified. In addition, it is found that the spin polarization is firmly pinned along the strong internal out‐of‐plane magnetic field induced by large spin splitting. This work provides an insight into the physical origin of long‐lived spin polarization in Weyl semimetals, which could be useful to manipulate spins for a long time at room temperature. [ABSTRACT FROM AUTHOR]

In order to increase the response speed of the InSe‐based photodetector with high photoresponsivity, graphene is used as the transparent electrodes to modify the difference of the work function between the electrodes and the InSe. As expected, the response speed of InSe/graphene photodetectors is down to 120 μs, which is about 40 times faster than that of an InSe/metal device. It can also be tuned by the back‐gate voltage from 310 μs down to 100 μs. With the high response speed, the photoresponsivity can reach as high as 60 A W−1 simultaneously. Meanwhile the InSe/graphene photodetectors possess a broad spectral range at 400–1000 nm. The design of 2D crystal/graphene electrical contacts can be important for high‐performance optoelectronic devices. [ABSTRACT FROM AUTHOR]

Ferromagnets with binary states are limited for applications as artificial synapses for neuromorphic computing. Here, it is shown how synaptic plasticity of a perpendicular ferromagnetic layer (FM1) can be obtained when it is interlayer exchange‐coupled by another in‐plane ferromagnetic layer (FM2), where a magnetic field‐free current‐driven multistate magnetization switching of FM1 in the Pt/FM1/Ta/FM2 structure is induced by spin–orbit torque. Current pulses are used to set the perpendicular magnetization state, which acts as the synapse weight, and spintronic implementation of the excitatory/inhibitory postsynaptic potentials and spike timing‐dependent plasticity are demonstrated. This functionality is made possible by the action of the in‐plane interlayer exchange coupling field which leads to broadened, multistate magnetic reversal characteristics. Numerical simulations, combined with investigations of a reference sample with a single perpendicular magnetized Pt/FM1/Ta structure, reveal that the broadening is due to the in‐plane field component tuning the efficiency of the spin–orbit torque to drive domain walls across a landscape of varying pinning potentials. The conventionally binary FM1 inside the Pt/FM1/Ta/FM2 structure with an inherent in‐plane coupling field is therefore tuned into a multistate perpendicular ferromagnet and represents a synaptic emulator for neuromorphic computing, demonstrating a significant pathway toward a combination of spintronics and synaptic electronics. [ABSTRACT FROM AUTHOR]

Atomically thin 2D materials are promising candidates for miniaturized high‐performance optoelectronic devices. This study reports on multilayer MoTe2 photodetectors contacted with asymmetric electrodes based on n‐ and p‐type graphene layers. The asymmetry in the graphene contacts creates a large (Ebi  ∼ 100 kV cm−1) built‐in electric field across the short (l = 15 nm) MoTe2 channel, causing a high and broad (λ = 400–1400 nm) photoresponse even without any externally applied voltage. Spatially resolved photovoltage maps reveal an enhanced photoresponse and larger built‐in electric field in regions of the MoTe2 layer between the two graphene contacts. Furthermore, a fast (∼10 µs) photoresponse is achieved in both the photovoltaic and photoconductive operation modes of the junction. The findings can be extended to other 2D materials and offer prospects for the implementation of asymmetric graphene contacts in future low‐power optoelectronic applications. [ABSTRACT FROM AUTHOR]

Highlights from the article: Metal Chalcogenides: Versatile Crystal Structures and (Opto)electronic Applications of the 2D Metal Mono-, Di-, and Tri-Chalcogenide Nanosheets (Adv. Funct. In article number 1900040, Zhongming Wei and co-workers present elements that can be used to constitute 2D metal chalcogenides and three types of crystal structures belonging to monochalcogenides, dichalcogenides, and trichalcogenides, respectively. Integrated circuits, light emitting, chip models, and bulb models represent different device applications based on 2D metal chalcogenides.

Emerging 2D metal chalcogenides present excellent performance for electronic and optoelectronic applications. In contrast to graphene and other 2D materials, 2D metal chalcogenides possess intrinsic bandgaps, versatile band structures, and superior atmospheric stability. The many categories of 2D metal chalcogenides ensure that they can be applied to various practical scenarios. 2D metal monochalcogenides, dichalcogenides, and trichalcogenides are the three main categories of these materials. They have distinct crystal structures resulting in different characteristics. Some basic device characteristics, such as the charge carrier characteristics, scattering mechanisms, interfacial contacts, and band alignments of heterojunctions, are vital factors for practical device applications that ensure that the desired properties can be achieved. Various electronic, optoelectronic, and photonic applications based on 2D metal chalcogenides have been extensively investigated. 2D metal chalcogenides are considered as competitive candidates for future electronic and optoelectronic applications. [ABSTRACT FROM AUTHOR]