Comparative coherence between layered and traditional semiconductors: unique opportunities for heterogeneous integration

As Moore’s law deteriorates,the research and development of new materials system are crucial for transitioning into the post Moore era.Traditional semiconductor materials,such as silicon,have served as the cornerstone of modern technologies for over half a century.This has been due to extensive research and engineering on new techniques to continuously enrich silicon-based materials system and,subsequently,to develop better performed silicon-based devices.Meanwhile,in the emerging post Moore era,layered semiconductor materials,such as transition metal dichalcogenides(TMDs),have garnered considerable research interest due to their unique electronic and optoelectronic properties,which hold great promise for powering the new era of next generation electronics.As a result,techniques for engineering the properties of layered semiconductors have expanded the possibilities of layered semiconductor-based devices.However,there remain significant limitations in the synthesis and engineering of layered semiconductors,impeding the utilization of layered semiconductor-based devices for mass applications.As a practical alternative,heterogeneous integration between layered and traditional semiconductors provides valuable opportunities to combine the distinctive properties of layered semiconductors with well-developed traditional semiconductors materials system.Here,we provide an overview of the comparative coherence between layered and traditional semiconductors,starting with TMDs as the representation of layered semiconductors.We highlight the meaningful opportunities presented by the heterogeneous integration of layered semiconductors with traditional semiconductors,representing an optimal strategy poised to propel the emerging semiconductor research community and chip industry towards unprecedented advancements in the coming decades.

Near-zero Poisson's ratio and suppressed mechanical anisotropy in strained black phosphorene/SnSe van der Waals heterostructure:a first-principles study

Black phosphorene(BP)and its analogs have attracted intensive attention due to their unique puckered structures,anisotropic characteristics,and negative Poisson’s ratio.The van der Waals(vdW)heterostructures assembly by stacking different materials show novel physical properties,however,the parent materials do not possess.In this work,the first-principles calculations are performed to study the mechanical properties of the vdW heterostructure.Interestingly,a near-zero Poisson’s ratio ν_(zx)is found in BP/SnSe heterostructure.In addition,compared with the parent materials BP and SnSe with strong in-plane anisotropic mechanical properties,the BP/SnSe heterostructure shows strongly suppressed anisotropy.The results show that the vdW heterostructure has quite different mechanical properties compared with the parent materials,and provides new opportunities for the mechanical applications of the heterostructures.

PbI_(2)/Pb_(5)S_(2)I_(6)van der Waals Heterojunction Photodetector

Investigations of two-dimensional(2D)/one-dimensional(1D)van der Waals(vdW)heterojunctions have attracted significant attention due to their excellent properties such as the smooth heterointerface,the highly gate-tunable bandgap,and the ultrafast carrier transport.However,the complicated method of manufacturing vdW heterojunction represents a major problem that severely limits their practical applications.Herein,we develop one-step hydrothermal method and use it to synthesize 2D PbI_(2)/1D Pb_(5)S_(2)I_(6)vdW heterojunction.The PbI_(2)/Pb_(5)S_(2)I_(6)vdW heterojunction photodetector(PD)displays lower dark current(<20 pA),higher responsivity(up to 134 mA·W-1),self-powered and wider response spectrum in comparison with that of pristine PbI_(2)PD and Pb_(5)S_(2)I_(6)PD.This one-step hydrothermal method provides a new idea for preparing other mixed-dimensional heterojunction.

Electronic structure and phase transition engineering in NbS2: Crucial role of van der Waals interactions

Based on first-principles simulations,we revisit the crystal structures,electronic structures,and structural stability of the layered transition metal dichalcogenides(TMDCs)NbS2,and shed more light on the crucial roles of the van der Waals(vdW)interactions.Theoretically calculated results imply that the vdW corrections are important to reproduce the layered crystal structure,which is significant to correctly describe the electronic structure of NbS2.More interestingly,under hydrostatic pressure or tensile strain in ab plane,an isostructural phase transition from two-dimensional layered structure to three-dimensional bulk in the I4/mmm phase has been uncovered.The abnormal structural transition is closely related to the electronic structure instability and interlayer bonding effects.The interlayer Nb-S distances collapse and the interlayer vdW interactions disappear,concomitant with new covalent bond emerging and increasing coordination number.Present work highlights the significance of the vdW interactions,and provides new insights on the unconventional structural transitions in NbS2,which will attract wide audience working in the hectic field of TMDCs.

Van der Waals integration inch-scale 2D MoSe_(2) layers on Si for highly-sensitive broadband photodetection and imaging

As one of the most promising materials for two-dimensional transition metal chalcogenides(2D TMDs),molybdenum diselenide(MoSe_(2))has great potential in photodetectors due to its excellent properties like tunable bandgap,high carrier mobility,and excellent air stability.Although 2D MoSe_(2)-based photodetectors have been reported to exhibit admired performance,the large-area 2D MoSe_(2)layers are difficult to be achieved via conventional synthesis methods,which severely impedes its future applications.Here,we present the controllable growth of large-area 2D MoSe_(2)layers over 3.5-inch with excellent homogeneity by a simple post-selenization route.Further,a high-quality n-MoSe_(2)/p-Si van der Waals(vdW)heterojunction device is in-situ fabricated by directly growing 2D n-MoSe_(2)layers on the patterned p-Si substrate,which shows a self-driven broadband photoresponse ranging from ultraviolet to mid-wave infrared with an impressive responsivity of 720.5 mA·W^(−1),a high specific detectivity of 10^(13) Jones,and a fast response time to follow nanosecond pulsed optical signal.In addition,thanks to the inch-level 2D MoSe_(2)layers,a 4×4 integrated heterojunction device array is achieved,which has demonstrated good uniformity and satisfying imaging capability.The large-area 2D MoSe_(2)layer and its heterojunction device array have great promise for high-performance photodetection and imaging applications in integrated optoelectronic systems.

A study of highly activated hydrogen evolution reaction performance in acidic media by 2D heterostructure of N and S doped graphene on MoO_(x)

Herein,a layer of molybdenum oxide(MoO_(x)),a transition metal oxide(TMO),which has outstanding catalytic properties in combination with a carbonbased thin film,is modified to improve the hydrogen production performance and protect the MoO_(x)in acidic media.A thin film of graphene is transferred onto the MoO_(x)layer,after which the graphene structure is doped with N and S atoms at room temperature using a plasma doping method to modify the electronic structure and intrinsic properties of the material.The oxygen functional groups in graphene increase the interfacial interactions and electrical contacts between graphene and MoO_(x).The appearance of surface defects such as oxygen vacancies can result in vacancies in MoO_(x).This improves the electrical conductivity and electrochemically accessible surface area.Increasing the number of defects in graphene by adding dopants can significantly affect the chemical reaction at the interfaces and improve the electrochemical performance.These defects in graphene play a crucial role in the adsorption of H^(+)ions on the graphene surface and their transport to the MoO_(x)layer underneath.This enables MoO_(x)to participate in the reaction with the doped graphene.N^(‐)and S^(‐)doped graphene(NSGr)on MoO_(x)is active in acidic media and performs well in terms of hydrogen production.The initial overpotential value of 359 mV for the current density of−10 mA/cm^(2)is lowered to 228 mV after activation.

On-chip integrated GeSe_(2)/Si vdW heterojunction for ultravioletenhanced broadband photodetection,imaging,and secure optical communication

Broadband photodetection,spanning from ultraviolet(UV)to infrared(IR),is pivotal in diverse technological domains including astronomy,remote sensing,environmental monitoring,and medical diagnostics.However,current commercially available broadband photodetectors,predominately based on conventional narrow-bandgap semiconductors,exhibit limited sensitivity in the UV region.This limitation,stemming from the significant energy disparity between the semiconductor bandgap and UV photon,narrows their application scope.Herein,we report an innovative approach involving the in-situ van der Waals(vdW)integration of two-dimensional(2D)GeSe_(2)layers onto a Si substrate.This process yields a high-quality GeSe_(2)/Si vdW heterojunction device,which features a broad response range covering from UV to near-IR(NIR)with a greatly-enhanced sensitivity in the UV region.The device possesses high responsivities of 325 and 533.4 mA/W,large detectivities of 1.24×10^(13)and 2.57×10^(13)Jones,and fast response speeds of 20.6/82.1 and 17.7/81.0μs under 360 and 980 nm,respectively.Notably,the broadband image sensing and secure invisible optical communication capabilities of the GeSe_(2)/Si heterojunction device are demonstrated.Our work provides a viable approach for UV-enhanced broadband photodetection technology,opening up new possibilities and applications across various scientific and technological domains.

Van der Waals integration of artificial heterostructures and highorder superlattices

The recent blossom in 2D atomic crystals(2DACs)has ignited intense interest in a new type of bond-free van der Waals heterostructures(vdWHs),in which distinct material components are physically brought together within a vdW distance and held together by weak vdW interactions.Without direct chemical bonding between the constituent materials,the vdWHs negate the lattice matching requirements in typical epitaxially bonded heterostructures.Here we briefly summarize the key advances in the construction and fundamental investigation of versatile vdWHs from diverse 2DACs and beyond,and highlight a unique class of vdW superlattices(vdWSLs)consisting of alternating 2D atomic layers and/or self-assembled molecular layers,with tailored structural symmetry,electronic band modulation,interlayer coupling,and chirality.Lastly,we conclude with a brief outlook on the opportunities in exploring such artificial materials to unlock previously inaccessible physical limits and enable new device concepts beyond the reach of the existing materials.

Ultimate dielectric scaling of 2D transistors via van der Waals metal integration

The two-dimensional transition metal dichalcogenides(TMDs)have attracted intense interest as an atomically thin semiconductor channel for the continued transistor scaling.However,with a dangling bond free surface,it has been a key challenge to reliably integrate high-quality gate dielectrics on TMDs.In particular,the atomic layer deposition of dielectrics on TMDs typically features highly non-uniform nucleation and produces a highly rough or porous dielectric film with rich pinholes that are prone to further damage during the gate integration process.Herein we report a van der Waals(vdW)integration route towards highly reliable gate metal integration on porous dielectrics.The physical lamination process employed by the vdW integration avoids the direct deposition of metal electrodes into porous dielectrics to ensure reliable gate integration and produce low gate leakage devices.The electrical measurements demonstrate the vdW integrated MoS_(2) top gate devices exhibit substantially reduced gate leakage current that is about 3-5 orders of magnitude smaller than that with deposited metal electrodes.Furthermore,we show the vdW integration process can be used to create high performance top-gated MoS_(2) transistors with ultrathin Al_(2)O_(3) dielectrics down to 1 nm,representing the ultimate dielectric scaling for TMDs transistors.This study demonstrates that vdW integration can enable highly reliable gate integration on relatively low quality dielectrics on TMDs,and opens an interesting pathway to high-performance top-gate transistors using dangling bond free two-dimensional(2D)semiconductors.

Light trapping enhanced broadband photodetection and imaging based on MoSe_(2)/pyramid Si vdW heterojunction

Two-dimensional(2D)layered materials have been considered promising candidates for next-generation optoelectronics.However,the performance of 2D photodetectors still has much room for improvement due to weak light absorption of planar 2D materials and lack of high-quality heterojunction preparation technology.Notably,2D materials integrating with mature bulk semiconductors are a promising pathway to overcome this limitation and promote the practical application on optoelectronics.In this work,we present the patterned assembly of MoSe_(2)/pyramid Si mixed-dimensional van der Waals(vdW)heterojunction arrays for broadband photodetection and imaging.Benefited from the light trapping effect induced enhanced optical absorption and high-quality vdW heterojunction,the photodetector demonstrates a wide spectral response range from 265 to 1550 nm,large responsivity up to 0.67 A·W^(-1),high specific detectivity of 1.84×10^(13)Jones,and ultrafast response time of 0.34/5.6μs at 0 V.Moreover,the photodetector array exhibits outstanding broadband image sensing capability.This study offers a novel development route for high-performance and broadband photodetector array by MoSe_(2)/pyramid Si mixed-dimensional heterojunction.

Simplified Coarse-Grained Dynamic Model for Real Gases

A simplified model is proposed for an easy understanding of the coarse-grained technique and for achieving a first approximation to the behavior of gases. A mole of a gas substance, within a cubic container, is represented by six particles symmetrically moving. The impacts of particles on container walls, the inter-particle collisions, as well as the volume of particles and the inter-particle attractive forces, obeying a Lennard-Jones curve, are taken into account. Thanks to the symmetry, the problem is reduced to the nonlinear dynamic analysis of a SDOF oscillator, which is numerically solved by a step-by-step time integration algorithm. Five applications of proposed model, on Carbon Dioxide, are presented: 1) Ideal gas in STP conditions. 2) Real gas in STP conditions. 3) Condensation for small molar volume. 4) Critical point. 5) Iso-kinetic energy curves and iso-therms in the critical point region. Results of the proposed model are compared with test data and results of the Van der Waals model for real gases.

管间相互作用对细胞膜包裹碳纳米管的影响

目的针对平行放置于细胞膜表面的两单壁碳纳米管系统,探究两碳管间相互作用对膜包裹碳管方式的影响,并给出能量最优的构象。方法建立考虑两根碳管间范德华相互作用的膜包裹碳管的力学模型,并引入反映细胞膜形态的参数以及描述碳管相对位置的参数。利用基于Helfrich自由能的连续介质力学建模,计算膜弯曲能量,并利用Lennard-Jones势描述碳管之间的相互作用。通过查表法计算系统不同位置的自由能,并给出细胞膜包裹碳管的典型结构。结果与未考虑管间相互作用的情况相比,系统自由能曲线出现了较大改变:在碳管间距约为0.3倍管半径时,能量曲线上出现深势阱;随着碳管间距增大,自由能恢复到没有管间相互作用能时的大小。结论引入碳管间相互作用能后,膜包裹碳管的方式发生变化,两碳管倾向于以触碰到一起的方式进行协同胞吞。研究结果为理解并设计基于纳米管的药物输运系统提供理论借鉴。

On the Regularity and Chaos of the Hydrogen Atom Subjected to External Fields

In this paper, the integrable classical case of the Hydrogen atom subjected to three static external fields is investigated. The structuring and evolution of the real phase space are explored. The bifurcation diagram is found and the bifurcations of solutions are discussed. The periodic solutions and their associated periods for singular common-level sets of the first integrals of motion are explicitly described. Numerical investigations are performed for the integrable case by means of Poincaré surfaces of section and comparing them with nearby living nonintegrable solutions, all generic bifurcations that change the structure of the phase space are illustrated;the problem can exhibit regularity-chaos transition over a range of control parameters of system.

High gain,broadband p-WSe_(2)/n-Ge van der Waals heterojunction phototransistor with a Schottky barrier collector

Mixed-dimensional van der Waals(vdW)heterostructures based on two-dimensional transition metal dichalcogenides and threedimensional semiconductors have led to a new era in next-generation optoelectronics due to the high-quality interfaces and energy band complementation,especially in broadband photodetectors which can be used for all-weather navigation,object identification,etc.However,the reported photodetectors conventionally operated in photodiode mode with low responsivity and a narrow response spectrum.In this study,we report a p-WSe_(2)/n-Ge vdW heterojunction phototransistor with a Schottky barrier collector on n-Ge for broadband photodetection.Large hole/electron injection ratio from p-WSe_(2)/n-Ge heterojunction under forward bias due to their large bandgap offset renders the high photocurrent gain,while the Ge Schottky barrier limits the dark current.The responsivities of the phototransistor at 1.0 V emitter-collector bias are 55,95,and 120 A·W−1 at 405,1,310,and 1,550 nm,respectively,which is superior to that of the corresponding p-WSe_(2)/n-Ge photodiodes.The phototransistor shows a high photocurrent gain of 80,a specific detectivity of 1011 Jones,as well as a fast response time of 290μs at 1,550 nm.The results suggest that the novel phototransistor being implemented with complementary metal-oxide-semiconductor processing is an ideal strategy for high-performance broadband photodetection.

Edge induced band bending in van der Waals heterojunctions:A first principle study

The dangling bond free nature of two-dimensional(2D)material surface/interface makes van der Waals(vdW)heterostructure attractive for novel electronic and optoelectronic applications.But in practice,edge is unavoidable and could cause band bending at 2D material edge analog to surface/interface band bending in conventional three-dimensional(3D)materials.Here,we report a first principle simulation on edge band bending of free standing MoS2/WS2 vdW heterojunction.Due to the imbalance charges at edge,S terminated edge causes upward band bending while Mo/W terminated induces downward bending in undoped case.The edge band bending is comparable to band gap and could obviously harm electronic and optoelectronic properties.We also investigate the edge band bending of electrostatic doped heterojunction.N doping raises the edge band whereas p doping causes a decline of edge band.Heavy n doping even reverses the downward edge band bending at Mo/W terminated edge.In contrast,heavy p doping doesn’t invert the upward bending to downward.Comparing with former experiments,the expected band gap narrowing introduced by interlayer potential gradient at edge is not observed in our free-standing structures and suggests substrate’s important role in this imbalance charge induced phenomenon.

Directly integrated mixed-dimensional van der Waals graphene/perovskite heterojunction for fast photodetection

Mixed-dimensional(2D/3D)van der Waals(vdW)heterostructures made with complementary materials hold a lot of promise in the field of optoelectronic devices.Beyond simple mechanical stacking,directly growing the single-crystal perovskite on 2D materials to construct a high-quality vdW heterojunction can better promote carrier transport.In this work,a monolithic integrated graphene/perovskite heterojunction device is fabricated by directly growing a single-crystal hybrid perovskite on monolayer graphene.Due to the strong inter-face coupling,the hybrid device achieves self-powering behavior and exhibits prominent photoresponse properties with a fast response speed of up to 2.05μs.Moreover,the responsivity and detectivity can be boosted to up to 10.41 A W1 and 4.65×10^(12)Jones under the actuation of3 V bias.This technique not only improves the device performance,but also provides an effective guideline for the development of next-generation directly integrated vdW optoelectronic devices.

New solitary wave and other exact solutions of the van der Waals normal form for granular materials

The investigation of exact solitary wave solutions to the nonlinear partial differential equation plays an important role to understand any physical phenomena in diverse applied fields.The current work is re-lated to the most prominent nonlinear model named as the van der Waals normal form that appeared naturally and also industrially for the granular materials.In oceanography,the sea ice,sand and snow are some examples of aforesaid matter among others.We employ two novel integration approaches named as the simplest equation method and the exp a function method to explore the above mentioned van der Waals model.As a backlash,many new solitary waves and other exact solutions are retrieved.The ob-tained results depict that the used approaches are simple and effective to deal with nonlinear models.Also,the numerical simulation of some solutions via two and three dimension graphical configurations are presented for certainty and exactness.

具有亚2-nm沟道长度的二维垂直p-n结二极管

尺寸极限微缩的p-n结二极管对互补金属氧化物半导体(CMOS)集成电路的发展至关重要.然而,由于界面缺陷和短沟道效应,实现5 nm以下沟道长度的p-n结二极管仍然面临着巨大的挑战.本文展示了1.9 nm沟道的WSe_(2)/WS_(2)垂直p-n结二极管,实现了~8×10^(3)的高开关比和~17的整流比.此外,沟道长度为4.7 nm的器件具有~10^(4)的高开关比和~10^(3)的整流比.其高性能源于无肖特基势垒的接触导致的理想带排列,以及无缺陷的全范德华(vdW)界面导致的低隧穿电流和小的费米钉扎效应.因此,我们实现了p-n二极管的本征性能.该策略也可以扩展到其他的p-n结,如WSe_(2)/MoSe_(2)和WSe_(2)/MoS_(2),这表明我们的策略具有普适性.该策略为电子器件尺寸微缩和集成电路的进一步发展提供了新的思路.

High-performance asymmetric electrodes photodiode based on Sb/WSe2 heterostructure

Two-dimensional (2D) van der Waals (vdWs) metal-semiconductor heterostructures with atomically sharp interface and matched work functions have recently attracted great attention due to their unique electronic and optoelectronic properties. Here we report the vapor phase epitaxial growth of large-scale vertical Sb/WSe2 metal-semiconductor vdWs heterostructures with uniform stacking orientation. Compared with the growth on S1O2/S1 substrate, the thick ness of Sb nan osheet on WSe2 can be reduced effectively to mono layer. We con struct Sb-WSe2-Au asymmetric electrodes photodiode based on the Sb/WSe2 heterostructures. Electrical transport measurements indicate that the photodiode show obvious rectifying effect. Optoelectronic characterizations show prominent photoresponse with a high photoresposivity of 364 mA/W, a fast response time of less than 8 ms, a large open-circuit voltage of 0.27 V and a maximum electrical power output of 0.11 nW. The direct growth of high-quality metal-semiconductor vdWs heterostructures may open up new realms in 2D functional electronics and optoelectronics.

Predicting 2D silicon allotropes on SnS2

A first principles study on the stability and structural and electronic properties of two-dimensional silicon allotropes on a semiconducfing layered metal-chalcogenide compound, namely SnS2, is performed. The interactions between the two- dimensional silicon layer, commonly known as silicene, and the layered SnS2 template are investigated by analyzing different configurations of silicene. The calculated thermodynamic phase diagram suggests that the most stable configuration of silicene on SnS2 belongs to a family of structures with Si atoms placed on three different planes; so-called dumbbell silicene. This particular dumbbell silicene structure preserves its atomic configuration on SnS2 even at a temperature of 500 K or as a ＂flake＂ layer （i.e., a silicene cluster terminated by H atoms）, thanks to the weak interactions between the silicene and the SnS2 layers. Remarkably, an electric field can be used to tune the band gap of the silicene layer on SnS2, eventually changing its electronic behavior from semiconducting to （semi）metallic. The stability of silicene on SnS2 is very promising for the integration of silicene onto semiconducting or insulating substrates. The tunable electronic behavior of the silicene/SnS2 van der Walls heterostructure is very important not only for its use in future nanoelectronic devices, but also as a successful approach to engineering the bang-gap of layered SnS2 paving the way for the use of this layered compound in energy harvesting applications.