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Parallel wireless digital communication with ultralow power consumption is critical for emerging edge technologies such as 5G and Internet of Things. However, the physical separation between digital computing units and analogue transmission units in traditional wireless technology leads to high power consumption. Here we report a parallel in-memory wireless computing scheme. The approach combines in-memory computing with wireless communication using memristive crossbar arrays. We show that the system can be used for the radio transmission of a binary stream of 480 bits with a bit error rate of 0. The in-memory wireless computing uses two orders of magnitude less power than conventional technology (based on digital-to-analogue and analogue-to-digital converters). We also show that the approach can be applied to acoustic and optical wireless communications

Two-dimensional (2D) ferrovalley semiconductor (FVSC) with spontaneous valley polarization offers an exciting material platform for probing Berry phase physics. How FVSC can be incorporated in valleytronic device applications, however, remain an open question. Here we generalize the concept of metal/semiconductor (MS) contact into the realm of valleytronics. We propose a half-valley Ohmic contact based on FVSC/graphene heterostructure where the two valleys of FVSC separately forms Ohmic and Schottky contacts with those of graphene, thus allowing current to be valley-selectively injected through the `Ohmic' valley while being blocked in the `Schottky' valley. We develop a theory of contact-limited valley-contrasting current injection and demonstrate that such transport mechanism can produce gate-tunable valley-polarized injection current. Using RuCl$_2$/graphene heterostructure as an example, we illustrate a device concept of valleytronic barristor where high valley polarization efficiency and sizable current on/off ratio, can be achieved under experimentally feasible electrostatic gating conditions. These findings uncover contact-limited valley-contrasting current injection as an efficient mechanism for valley polarization manipulation, and reveals the potential of valleytronic MS contact as a functional building block of valleytronic device technology., Comment: 9 pages, 5 figures

Recent experimental synthesis of ambient-stable MoSi2N4 monolayer have garnered enormous research interests. The intercalation morphology of MoSi2N4 - composed of a transition metal nitride (Mo-N) inner sub-monolayer sandwiched by two silicon nitride (Si-N) outer sub-monolayers - have motivated the computational discovery of an expansive family of synthetic MA2Z4 monolayers with no bulk (3D) material counterpart (where M = transition metals or alkaline earth metals; A = Si, Ge; and N = N, P, As). MA2Z4 monolayers exhibit interesting electronic, magnetic, optical, spintronic, valleytronic and topological properties, making them a compelling material platform for next-generation device technologies. Furthermore, heterostructure engineering enormously expands the opportunities of MA2Z4. In this review, we summarize the recent rapid progress in the computational design of MA2Z4-based heterostructures based on first-principle density functional theory (DFT) simulations - a central \emph{work horse} widely used to understand the physics, chemistry and general design rules for specific targeted functions. We systematically classify the MA2Z4-based heterostructures based on their contact types, and review their physical properties, with a focus on their performances in electronics, optoelectronics and energy conversion applications. We review the performance and promises of MA2Z4-based heterostructures for device applications that include electrical contacts, transistors, spintronic devices, photodetectors, solar cells, and photocatalytic water splitting. This review unveils the vast device application potential of MA2Z4-based heterostructures, and paves a roadmap for the future experimental and theoretical development of MA2Z4-based functional heterostructures and devices., Comment: 32 pages, 15 figures

Realizing both ultra-low breakdown voltage and ultra-high gain has been one of the major challenges in the development of high-performance avalanche photodetector. Here, we report that an ultra-high avalanche gain of 3*10^5 can be realized in the graphite/InSe Schottky photodetector at a breakdown voltage down to 5.5 V. Remarkably, the threshold breakdown voltage can be further reduced down to 1.8 V by raising the operating temperature, approaching the theoretical limit of 1.5E_g/e with E_g the band gap of semiconductor. We develop a two-dimensional impact ionization model and uncover that observation of high gain at low breakdown voltage arises from reduced dimensionality of electron-phonon (e-ph) scattering in the layered InSe flake. Our findings open up a promising avenue for developing novel weak-light detectors with low energy consumption and high sensitivity.

Two-dimensional (2D) materials van der Waals heterostructures (vdWHs) provides a revolutionary route towards high-performance solar energy conversion devices beyond the conventional silicon-based pn junction solar cells. Despite tremendous research progress accomplished in recent years, the searches of vdWHs with exceptional excitonic solar cell conversion efficiency and optical properties remain an open theoretical and experimental quest. Here we show that the vdWH family composed of MoSi$_2$N$_4$ and WSi$_2$N$_4$ monolayers provides a compelling material platform for developing high-performance ultrathin excitonic solar cells and photonics devices. Using first-principle calculations, we construct and classify 51 types of MoSi$_2$N$_4$ and WSi$_2$N$_4$-based [(Mo,W)Si$_2$N$_4$] vdWHs composed of various metallic, semimetallic, semiconducting, insulating and topological 2D materials. Intriguingly, MoSi$_2$N$_4$/(InSe, WSe$_2$) are identified as Type-II vdWHs with exceptional excitonic solar cell power conversion efficiency reaching well over 20%, which are competitive to state-of-art silicon solar cells. The (Mo,W)Si$_2$N$_4$ vdWH family exhibits strong optical absorption in both the visible and ultraviolet regimes. Exceedingly large peak ultraviolet absorptions over 40%, approaching the maximum absorption limit of a free-standing 2D material, can be achieved in (Mo,W)Si$_2$N$_4$/$\alpha_2$-(Mo,W)Ge$_2$P$_4$ vdWHs. Our findings unravel the enormous potential of (Mo,W)Si$_2$N$_4$ vdWHs in designing ultimately compact excitonic solar cell device technology., Comment: 30 pages, 7 figures

Multiferroic van der Waals (vdW) heterostrucutres offers an exciting route towards novel nanoelectronics and spintronics device technology. Here we investigate the electronic and transport properties of multiferroic vdW heterostructure composed of ferromagnetic FeCl$_2$ monolayer and ferroelectric Sc$_2$CO$_2$ monolayer using first-principles density functional theory and quantum transport simulations. We show that FeCl$_2$/Sc$_2$CO$_2$ heterostructure can be reversibly switched from semiconducting to half-metallic behavior by electrically modulating the ferroelectric polarization states of Sc$_2$CO$_2$. Intriguingly, the half-metallic phase exhibits a Type-III broken gap band alignment, which can be beneficial for tunnelling field-effect transistor application. We perform a quantum transport simulation, based on a \emph{proof-of-concept} two-terminal nanodevice, to demonstrate all-electric-controlled valving effects uniquely enabled by the nonvolatile ferroelectric switching of the heterostructure. These findings unravels the potential of FeCl$_2$/Sc$_2$CO$_2$ vdW heterostructures as a building block for designing a next generation of ultimately compact information processing, data storage and spintronics devices., Comment: 9 pages, 5 figures, accepted for publication in Physical Review B (2022)

The growth of connected intelligent devices in the Internet of Things has created a pressing need for real-time processing and understanding of large volumes of analogue data. The difficulty in boosting the computing speed renders digital computing unable to meet the demand for processing analogue information that is intrinsically continuous in magnitude and time. By utilizing a continuous data representation in a nanoscale crossbar array, parallel computing can be implemented for the direct processing of analogue information in real time. Here, we propose a scalable massively parallel computing scheme by exploiting a continuous-time data representation and frequency multiplexing in a nanoscale crossbar array. This computing scheme enables the parallel reading of stored data and the one-shot operation of matrix-matrix multiplications in the crossbar array. Furthermore, we achieve the one-shot recognition of 16 letter images based on two physically interconnected crossbar arrays and demonstrate that the processing and modulation of analogue information can be simultaneously performed in a memristive crossbar array., Comment: 18 pages, 4 figures

Metal contacts to two-dimensional (2D) semiconductors are ubiquitous in modern electronic and optoelectronic devices. Such contacts are, however, often plagued by strong Fermi level pinning (FLP) effect which reduces the tunability of the Schottky barrier height (SBH) and degrades the performance of 2D-semiconductor-based devices. In this work, we show that monolayer MoSi$_2$N$_4$ and WSi$_2$N$_4$ - a recently synthesized 2D material class with exceptional mechanical and electronic properties - exhibit strongly suppressed FLP and wide-range tunable SBH when contacted by metals. An exceptionally large SBH slope parameter of S=0.7 is obtained, which outperform the vast majority of other 2D semiconductors. Such surprising behavior arises from the unique morphology of MoSi$_2$N$_4$ and WSi$_2$N$_4$. The outlying Si-N layer forms a native atomic layer that protects the semiconducting inner-core from the perturbance of metal contacts, thus suppressing the FLP. Our findings reveal the potential of MoSi$_2$N$_4$ and WSi$_2$N$_4$ monolayers as a novel 2D material platform for designing high-performance and energy-efficient 2D nanodevices., Comment: 28 pages, 5 figures

Early processing of visual information takes place in the human retina. Mimicking neurobiological structures and functionalities of the retina provide a promising pathway to achieving vision sensor with highly efficient image processing. Here, we demonstrate a prototype vision sensor that operates via the gate-tunable positive and negative photoresponses of the van der Waals (vdW) vertical heterostructures. The sensor emulates not only the neurobiological functionalities of bipolar cells and photoreceptors but also the unique synaptic connectivity between bipolar cells and photoreceptors. By tuning gate voltage for each pixel, we achieve reconfigurable vision sensor for simultaneously image sensing and processing. Furthermore, our prototype vision sensor itself can be trained to classify the input images, via updating the gate voltages applied individually to each pixel in the sensor. Our work indicates that vdW vertical heterostructures offer a promising platform for the development of neural network vision sensor., Comment: 20 pages, 4 figures

Semiconducting nanowires offer many opportunities for electronic and optoelectronic device applications due to their special geometries and unique physical properties. However, it has been challenging to synthesize semiconducting nanowires directly on SiO2/Si substrate due to lattice mismatch. Here, we developed a catalysis-free approach to achieve direct synthesis of long and straight InSe nanowires on SiO2/Si substrate through edge-homoepitaxial growth. We further achieved parallel InSe nanowires on SiO2/Si substrate through controlling growth conditions. We attributed the underlying growth mechanism to selenium self-driven vapor-liquid-solid process, which is distinct from conventional metal-catalytic vapor-liquid-solid method widely used for growing Si and III-V nanowires. Furthermore, we demonstrated that the as-grown InSe nanowire-based visible light photodetector simultaneously possesses an extraordinary photoresponsivity of 271 A/W, ultrahigh detectivity of 1.57*10^14 Jones and a fast response speed of microsecond scale. The excellent performance of the photodetector indicates that as-grown InSe nanowires are promising in future optoelectronic applications. More importantly, the proposed edge-homoepitaxial approach may open up a novel avenue for direct synthesis of semiconducting nanowire arrays on SiO2/Si substrate., Comment: 19 pages, 4 figures, published in Small

Discovery of two-dimensional materials with unique electronic, superior optoelectronic or intrinsic magnetic order have triggered worldwide interests among the fields of material science, condensed matter physics and device physics. Vertically stacking of two-dimensional materials with distinct electronic and optical as well as magnetic properties enables to create a large variety of van der Waals heterostructures. The diverse properties of the vertical heterostructures open up unprecedented opportunities for various kinds of device applications, e.g. vertical field effect transistors, ultrasensitive infrared photodetectors, spin-filtering devices and so on, which are inaccessible in the conventional material heterostructures. Here, we review the current status of vertical heterostructures device applications in vertical transistors, infrared photodetectors and spintronic memory/transistors. The relevant challenges for achieving high-performance devices are presented. We also provide outlook on future development of vertical heterostructure devices with integrated electronic and optoelectronic as well as spintronic functinalities., Comment: 49 pages, 18 figures, published in Advanced Materials

With many fantastic properties, memristive devices have been proposed as top candidate for next-generation memory and neuromorphic computing chips. Significant research progresses have been made in improving performance of individual memristive devices and in demonstrating functional applications based on small-scale memristive crossbar arrays. However, practical deployment of large-scale traditional metal oxides based memristive crossbar array has been challenging due to several issues, such as high-power consumption, poor device reliability, low integration density and so on. To solve these issues, new materials that possess superior properties are required. Two-dimensional (2D) layered materials exhibit many unique physical properties and show great promise in solving these challenges, further providing new opportunities to implement practical applications in neuromorphic computing. Here, recent research progress on 2D layered materials based memristive device applications is reviewed. We provide an overview of the progresses and challenges on how 2D layered materials are used to solve the issues of conventional memristive devices and to realize more complex functionalities in neuromorphic computing. Besides, we also provide an outlook on exploitation of unique properties of 2D layered materials and van der Waals heterostructures for developing new types of memristive devices and artificial neural mircrocircuits., Comment: 38 pages,10 figures published in Advanced Electronic Materials

Circular polarized photocurrent is observed near the electrodes on a few-layer ReS2sample at room temperature. For both electrodes, the spatial distribution of the circular polarized photocurrent shows a feature of two wings, with one positive and the other negative. We suggest that this phenomenon arises from the inverse spin Hall effect due to local electric field near the electrode. Bias voltage that modulates this field further controls the sign and magnitude of the inverse spin Hall effect photocurrent. Our research shows that electric field near electrodes has a significant impact on spin transmission operation, hence it could be taken into account for manufacturing spintronic devices in future., Comment: 14 pages,6 figures