Reconfigurable Logic‐in‐Memory and Multilingual Artificial Synapses Based on 2D Heterostructures

Nonvolatile logic devices have attracted intensive research attentions recently for energy efficiency computing, where data computing and storage can be realized in the same device structure. Various approaches have been adopted to build such devices; however, the functionality and versatility are still very limited. Here, 2D van der Waals heterostructures based on direct bandgap materials black phosphorus and rhenium disulfide for the nonvolatile ternary logic operations is demonstrated for the first time with the ultrathin oxide layer from the black phosphorus serving as the charge trapping as well as band‐to‐band tunneling layer. Furthermore, an artificial electronic synapse based on this heterostructure is demonstrated to mimic trilingual synaptic response by changing the input base voltage. Besides, artificial neural network simulation based on the electronic synaptic arrays using the handwritten digits data sets demonstrates a high recognition accuracy of 91.3%. This work provides a path toward realizing multifunctional nonvolatile logic‐in‐memory applications based on novel 2D heterostructures.     

Broadband polarized photodetector based on p-BP/n-ReS2 heterojunction

Two-dimensional(2D) atomic crystals,such as graphene,black phosphorus(BP) and transition metal dichalcogenides(TMDCs) are attractive for use in optoelectronic devices,due to their unique crystal structures and optical absorption properties.In this study,we fabricated BP/ReS2 van der Waals(vdWs) heterojunction devices.The devices realized broadband photoresponse from visible to near infrared(NIR)(400–1800 nm) with stable and repeatable photoswitch characteristics,and the photoresponsivity reached 1.8 mA/W at 1550 nm.In addition,the polarization sensitive detection in the visible to NIR spectrum(532–1750 nm) was demonstrated,and the photodetector showed a highly polarization sensitive photocurrent with an anisotropy ratio as high as 6.44 at 1064 nm.Our study shows that van der Waals heterojunction is an effective way to realize the broadband polarization sensitive photodetection,which is of great significance to the realization and application of multi-functional devices based on 2D vdWs heterostructures.     

Self‐Aligned and Scalable Growth of Monolayer WSe2–MoS2 Lateral Heterojunctions

2D layered heterostructures have attracted intensive interests due to their unique optical, transport, and interfacial properties. The laterally stitched heterojunction based on dissimilar 2D transition metal dichalcogenides forms an intrinsic p–n junction without the necessity of applying an external voltage. However, no scalable processes are reported to construct the devices with such lateral heterostructures. Here, a scalable strategy, two‐step and location‐selective chemical vapor deposition, is reported to synthesize self‐aligned WSe₂–MoS₂ monolayer lateral heterojunction arrays and demonstrates their light‐emitting devices. The proposed fabrication process enables the growth of high‐quality interfaces and the first successful observation of electroluminescence at the WSe₂–MoS₂ lateral heterojunction. The electroluminescence study has confirmed the type‐I alignment at the interface rather than commonly believed type‐II alignment. This self‐aligned growth process paves the way for constructing various 2D lateral heterostructures in a scalable manner, practically important for integrated 2D circuit applications.     

Progress and Insight of Van der Waals Heterostructures Containing Interlayer Transition for Near Infrared Photodetectors

Van der Waals (vdWs) heterostructures enable bandgap engineering of different 2D materials to realize the interlayer transition via type-II band alignment leading to broaden spectrum that is beyond the cut-off wavelength of individual 2D materials. Interlayer transition has a significant effect on the optoelectronic performance of vdWs heterostructure devices, and strong interlayer transition in 2D vdWs heterojunction is always demandable for sufficient charge transfer and rapid speed response. Herein, a state-of-the-art review is presented on recent progress on interlayer transition in vdWs heterostructures for near-infrared (NIR) photodetectors. First, the general synthesis techniques for vdWs heterostructures, band alignments in the vdWs heterostructures are provided. Then, the mechanism of interlayer transition in vdWs heterostructure and recent progress on interlayer transition in vdWs heterostructures for NIR photodetectors are summarized. Afterward, some worthy applications of NIR photodetectors are reviewed in related areas of this topic. At the last, an outlook, challenges, and future research directions of vdWs heterostructures for photodetectors at broaden response spectrum are presented.     

State-of-the-Art Progress in Diverse Black Phosphorus-Based Structures: Basic Properties,Synthesis, Stability,Photo- and Electrocatalysis-Driven Energy Conversion

Over the past few decades, the design and development of advanced catalysts for efficient energy conversion technologies have undergone extensive study. Black phosphorus (BP) is considered to be one of the most promising catalysts, exhibiting remarkable performance and drawing significant attention, because of its extraordinary physicochemical properties: a unique layered structure, anisotropic structure, tunable direct bandgap, and ultrahigh charge mobility. In this review, the fundamentals of bulk BP, single- and few-layer phosphorene, and BP quantum dots are briefly introduced, along with their crystal structure, optical and electrical properties, stability, and synthetic methods. Furthermore, recent progress toward diverse BP-based materials for photo- and electrocatalysis for renewable energy is summarized, specifically focusing on water splitting, CO₂ conversion, and nitrogen fixation. Finally, the challenges ahead for these BP-based catalysts are also emphasized, alongside and perspectives on their further development as part of the this fast-flourishing renewable energy field.     

Nonvolatile Floating‐Gate Memories Based on Stacked Black Phosphorus–Boron Nitride–MoS2 Heterostructures

Research on van der Waals heterostructures based on stacked 2D atomic crystals is intense due to their prominent properties and potential applications for flexible transparent electronics and optoelectronics. Here, nonvolatile memory devices based on floating‐gate field‐effect transistors that are stacked with 2D materials are reported, where few‐layer black phosphorus acts as channel layer, hexagonal boron nitride as tunnel barrier layer, and MoS₂ as charge trapping layer. Because of the ambipolar behavior of black phosphorus, electrons and holes can be stored in the MoS₂ charge trapping layer. The heterostructures exhibit remarkable erase/program ratio and endurance performance, and can be developed for high‐performance type‐switching memories and reconfigurable inverter logic circuits, indicating that it is promising for application in memory devices completely based on 2D atomic crystals.     

Progress,Challenges, and Opportunities for 2D Material Based Photodetectors

2D material based photodetectors have attracted many research projects due to their unique structures and excellent electronic and optoelectronic properties. These 2D materials, including semimetallic graphene, semiconducting black phosphorus, transition metal dichalcogenides, insulating hexagonal boron nitride, and their various heterostructures, show a wide distribution in bandgap values. To date, hundreds of photodetectors based on 2D materials have been reported. Here, a review of photodetectors based on 2D materials covering the detection spectrum from ultraviolet to infrared is presented. First, a brief insight into the detection mechanisms of 2D material photodetectors as well as introducing the figure‐of‐merits which are key factors for a reasonable comparison between different photodetectors is provided. Then, the recent progress on 2D material based photodetectors is reviewed. Particularly, the excellent performances such as broadband spectrum detection, ultrahigh photoresponsivity and sensitivity, fast response speed and high bandwidth, polarization‐sensitive detection are pointed out on the basis of the state‐of‐the‐art 2D photodetectors. Initial applications based on 2D material photodetectors are mentioned. Finally, an outlook is delivered, the challenges and future directions are discussed, and general advice for designing and realizing novel high‐performance photodetectors is given to provide a guideline for the future development of this fast‐developing field.     

Self‐Assembly of Atomically Thin Chiral Copper Heterostructures Templated by Black Phosphorus

The fabrication of 2D systems for electronic devices is not straightforward, with top‐down low‐yield methods often employed leading to irregular nanostructures and lower quality devices. Here, a simple and reproducible method to trigger self‐assembly of arrays of high aspect‐ratio chiral copper heterostructures templated by the structural anisotropy in black phosphorus (BP) nanosheets is presented. Using quantitative atomic resolution aberration‐corrected scanning transmission electron microscopy imaging, in situ heating transmission electron microscopy and electron energy‐loss spectroscopy arrays of heterostructures forming at speeds exceeding 100 nm s^?1 and displaying long‐range order over micrometers are observed. The controlled instigation of the self‐assembly of the Cu heterostructures embedded in BP is achieved using conventional electron beam lithography combined with site specific placement of Cu nanoparticles. Density functional theory calculations are used to investigate the atomic structure and suggest a metallic nature of the Cu heterostructures grown in BP. The findings of this new hybrid material with unique dimensionality, chirality, and metallic nature and its triggered self‐assembly open new and exciting opportunities for next generation, self‐assembling devices.     

2D Black Phosphorus–Based Biomedical Applications

Black phosphorus (BP) has increasingly attracted scientific attention since its first applications in biomedicine due to its unique properties and excellent biocompatibility. In particular, its layer‐dependent bandgap, moderate carrier mobility, large surface‐area‐to‐volume ratio, biodegradability, intrinsic photoacoustic properties, and biocompatibility make it an ideal candidate for use in photothermal therapy, photodynamic therapy, drug delivery, 3D printing, bioimaging, biosensing, and theranostics, which are reviewed here. In addition, the article discusses strategies to overcome challenges related to surface instability due to chemical degradation, a major obstacle for its application. This review not only provides a comprehensive summary on BP preparation and biomedical applications but also summarizes recent research and future possibilities.     

3D Chemical Cross‐Linking Structure of Black Phosphorus@CNTs Hybrid as a Promising Anode Material for Lithium Ion Batteries

The existence of rechargeable lithium ion batteries with high operating voltage, high energy density, and excellent cycling performance are drawing increasing attention due to their viability to be used as portable power and in electrical applications. However, there is a considerable problem that the conductivity of the active material becomes poor due to the volume expansion under the condition of repeated circulation, which reduces the performance of the device, thus hindering its practical application. As an emerging 2D material, black phosphorus (BP) has drawn significant attention in the field of Li‐ion battery energy storage due to its large theoretical capacity of 2596 mA h g^?1 and ability to absorb large amount of Li atoms. Here, a unique 3D conductive structure with the BP and carbon nanotubes (CNTs), displaying good stability and high conductivity for the fabrication of BP@CNTs hybrid‐based Li‐ion batteries is described. With strong trapping, good affinity, structure stable, and high adsorption for polyphosphorus, the developed BP@CNTs hybrid electrodes display high capacity, good electrical conductivity, and a stable cycle life. Additionally, the lithium ion batteries can illuminate the light emitting diode, proving that the materials have great potential for development of energy storage devices.     

Silicon-based semiconductor heterostructures: column IV bandgapengineering

The use of strained layer epitaxy to grow high-quality Ge_x Si_1-x/Si heterostructures and their application to a wide range of heterostructure devices are addressed. The author reviews the mechanisms of strained layer growth, the bandstructure of the resulting material, and its use in test devices, including superlattice avalanche photodiodes for fiber optic communication, intrasubband optical detectors and arrays operating in the 10-15 μm wavelength range, mobility enhanced modulation-doped transistors, heterojunction bipolar transistors with cutoff frequencies of 75 GHz, and negative resistance devices based on resonant tunneling and real-space carrier transfer     

Fluorinated Black Phosphorene Nanosheets with Robust Ambient Stability for Efficient and Stable Perovskite Solar Cells

Extraordinary electronic and photonic features (e.g., tunable direct bandgap, high ambipolar carrier mobility) render few-layer black phosphorus (BP) nanosheets/quantum dots an important optoelectronic material. However, most of the BP applied in metal halide perovskite solar cells (PSCs) are produced by sonication-assisted liquid exfoliation, which inevitably brings inferior electronic properties, thus leading to limited beneficial effects. Furthermore, this study uncovers that the intrinsic instability of BP nanosheets sandwiched between (CsFAMA)Pb(BrI)₃ perovskite and spiro-OMeTAD has a deleterious effect on the performance stabilization of PSCs. To address the above constraints, a feasible strategy herein is developed by introducing high-quality fluorinated BP (F-BP) nanosheets synthesized by one-step electrochemical delamination. In addition to P-Pb coordination, there is a strong hydrogen bond between F^? and MA⁺/FA⁺ as well as an ionic bond between F^? and Pb²⁺ for the perovskite/F-BP interface, thus leading to fewer interfacial traps than perovskite/BP, which is responsible for the highest power conversion efficiency (22.06%) of F-BP devices. More importantly, F-BP devices exhibit significantly improved humidity and shelf-life stabilities due to the excellent ambient stability of F-BP, resulting from the antioxidation and antihydration behavior of fluorine adatoms. Overall, the findings provide a promising strategy to simultaneously enhance the photovoltaic performance and long-term stability of BP-based PSCs.     

Thermal Transport in 2D Semiconductors—Considerations for Device Applications

The discovery of graphene has stimulated the search for and investigations into other 2D materials because of the rich physics and unusual properties exhibited by many of these layered materials. Transition metal dichalcogenides (TMDs), black phosphorus, and SnSe among many others, have emerged to show highly tunable physical and chemical properties that can be exploited in a whole host of promising applications. Alongside the novel electronic and optical properties of such 2D semiconductors, their thermal transport properties have also attracted substantial attention. Here, a comprehensive review of the unique thermal transport properties of various emerging 2D semiconductors is provided, including TMDs, black‐ and blue‐phosphorene among others, and the different mechanisms underlying their thermal conductivity characteristics. The focus is placed on the phonon‐related phenomena and issues encountered in various applications based on 2D semiconductor materials and their heterostructures, including thermoelectric power generation and electron–phonon coupling effect in photoelectric and thermal transistor devices. A thorough understanding of phonon transport physics in 2D semiconductor materials to inform thermal management of next‐generation nanoelectronic devices is comprehensively presented along with strategies for controlling heat energy transport and conversion.     

Environmentally Robust Black Phosphorus Nanosheets in Solution: Application for Self‐Powered Photodetector

Large‐size 2D black phosphorus (BP) nanosheets have been successfully synthesized by a facile liquid exfoliation method. The as‐prepared BP nanosheets are used to fabricate electrodes for a self‐powered photodetector and exhibit preferable photoresponse activity as well as environmental robustness. Photoelectrochemical (PEC) tests demonstrate that the current density of BP nanosheets can reach up to 265 nA cm^?2 under light irradiation, while the dark current densities fluctuate near 1 nA cm^?2 in 0.1 M KOH. UV–vis and Raman spectra are carried out and confirm the inherent optical and physical properties of BP nanosheets. In addition, the cycle stability measurement exhibits no detectable distinction after processing 50 and 100 cycles, while an excellent on/off behavior is still preserved even after one month. Furthermore, the PEC performance of BP nanosheets‐based photodetector is evaluated in various KOH concentrations, which demonstrates that the as‐prepared BP nanosheets may have a great potential application in self‐powered photodetector. It is anticipated that the present work can provide fundamental acknowledgement of the performance of a PEC‐type BP nanosheets‐based photodetector, offering extendable availabilities for 2D BP‐based heterostructures to construct high‐performance PEC devices.     

Highly Polarized and Fast Photoresponse of Black Phosphorus‐InSe Vertical p–n Heterojunctions

The van der Waals heterojunctions of 2D materials offer tremendous opportunities in designing and investigating multifunctional and high‐performance electronic and optoelectronic devices. In this study, a vertical p–n diode is constructed by vertically stacking p‐type few‐layer black phosphorus (BP) on n‐type few‐layer indium selenide (InSe). The photodetector based on the heterojunction displays a broadband and gate‐modulated photoresponse under illumination. More importantly, by taking advantage of the strong linear dichroism of BP, the device demonstrates a highly polarization‐sensitive photocurrent with an anisotropy ratio as high as 0.83. Additionally, the device can function in a zero‐bias photovoltaic mode, enabling a fast photoresponse and low dark current. The external quantum efficiency can reach ≈3%, which is impressive for BP‐based devices. The results pave the way for the implementation of p‐BP/n‐InSe heterostructure as a promising candidate for future multifunctional optoelectronics and, especially, polarization‐sensitive applications.     

Polarization-Resolved Broadband MoS2/Black Phosphorus/MoS2 Optoelectronic Memory with Ultralong Retention Time and Ultrahigh Switching Ratio

The rapidly emerging requirement for device miniaturization and structural flexibility make 2D semiconductors and their van der Waals (vdWs) heterostructures extremely attractive for nonvolatile optoelectronic memory (NOM) applications. Although several concepts for 2D NOM have been demonstrated, multi-heterojunction devices capable of further improving storage performance have received little attention. This work reports a concept for MoS₂/black phosphorus (BP)/MoS₂ multi-heterojunction NOM with artificial trap sites through the BP oxidation, in which the trapped holes at BP/PO_x interface intrigue a persistent photoconductivity that hardly recovers within the experimental time scales (exceeding 10⁴ s). As a result of the interfacial trap-controlled charge injection, the device exhibits excellent photoresponsive memory characteristics, including a record high detectivity of ≈1.2 × 10¹⁶ Jones, a large light-to-dark switching ratio of ≈1.5 × 10⁷_, an ultralow off-state current of ≈1.2 pA, and an outstanding multi-bit storage capacity (11 storage states, 546 nC state^–1). In addition, the middle BP layer in the multi-heterojunction enables broadband spectrum distinction (375–1064 nm), together with a high polarization ratio of 8.4. The obtained results represent the significant step toward the high-density integration of optoelectronic memories with 2D vdWs heterostructures.     

氮化物半导体电子器件的若干研究进展

近年来,氮化物半导体电子器件和材料研究有了重大的进展。在国家自然科学基金资助下,西安电子科技大学、北京大学和中科院微电子所完成了国家自然科学基金重点项目《GaN宽禁带微电子材料和器件重大基础问题研究》。致力于通过氮化物电子材料和器件的基础物理机理研究提高GaN电子材料的结晶质量和电学性能、发展新结构GaN异质结材料研究,获得高性能的GaN HEMT微波功率器件。本文主要介绍该项目在GaN微波功率HEMT和新型高k栅介质MOS-HEMT、InAlN/GaN材料的生长和物性缺陷分析以及HEMT器件研制、GaN异质结的量子输运和自旋性质研究以及GaN材料高场输运性质和耿氏器件等几个方面取得的研究进展。     

Progress in Group Ⅲ nitride semiconductor electronic devices

Recently there has been a rapid domestic development in groupⅢnitride semiconductor electronic materials and devices.This paper reviews the important progress in GaN-based wide bandgap microelectronic materials and devices in the Key Program of the National Natural Science Foundation of China,which focuses on the research of the fundamental physical mechanisms of group III nitride semiconductor electronic materials and devices with the aim to enhance the crystal quality and electric performance of GaN-based electronic materials, develop new GaN heterostructures,and eventually achieve high performance GaN microwave power devices.Some remarkable progresses achieved in the program will be introduced,including those in GaN high electron mobility transistors(HEMTs) and metal-oxide-semiconductor high electron mobility transistors(MOSHEMTs) with novel high-k gate insulators,and material growth,defect analysis and material properties of InAlN/GaN heterostructures and HEMT fabrication,and quantum transport and spintronic properties of GaN-based heterostructures,and highelectric -field electron transport properties of GaN material and GaN Gunn devices used in terahertz sources.     

Recent progress of the optoelectronic properties of 2D Ruddlesden-Popper perovskites

Two-dimensional(2 D) hybrid organic-inorganic perovskites have recently attracted attention due to their layered nature, naturally formed quantum well structure, large exciton binding energy and especially better long-term environmental stability compared with their three-dimensional(3 D) counterparts. In this report, we present a brief overview of the recent progress of the optoelectronic applications in 2 D perovskites. The layer number dependent physical properties of 2 D perovskites will first be introduced and then the different synthetic approaches to achieve 2 D perovskites with different morphologies will be discussed. The optical, optoelectronic properties and self-trapped states in 2 D perovskites will be described, which are indispensable for designing the new device structures with novel functionalities and improving the device performance. Subsequently, a brief summary of the advantages and the current research status of the 2 D perovskite-based heterostructures will be illustrated.Finally, a perspective of 2 D perovskite materials is given toward their material synthesis and novel device applications.     

Recent Developments in Stability and Passivation Techniques of Phosphorene toward Next‐Generation Device Applications

Phosphorene as a rising star is a monolayer or few‐layer form of black phosphorus (BP), which is used as a 2D material, in addition to graphene. This monoelemental 2D material has gained considerable attention in the fields of electronics, optoelectronics, and biomedicine due to its extraordinary physical properties. However, as both theoretical and experimental works show, the intrinsic instability of phosphorene under ambient conditions is a major challenge in practical applications. Various theoretical and experimental researches regarding the mechanism of the degradation and passivation strategies are proposed and reported to overcome the problem of the ambient instability of phosphorene. These strategies have enabled researchers to conduct fundamental studies on phosphorene's extraordinary properties. Here, not only an extensive summary of these passivation strategies but also an overview of the fabrication methods, challenges, and suitable applications of phosphorene are provided.