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As the trajectory of transistor scaling defined by Moore's law encounters challenges, the paradigm of ever-evolving integrated circuit technology shifts to explore unconventional materials and architectures to sustain progress. Two-dimensional (2D) semiconductors, characterized by their atomic-scale thickness and exceptional electronic properties, have emerged as a beacon of promise in this quest for the continued advancement of field-effect transistor (FET) technology. The energy-efficient complementary circuit integration necessitates strategic engineering of both n-channel and p-channel 2D FETs to achieve symmetrical high performance. This intricate process mandates the realization of demanding device characteristics, including low contact resistance, precisely controlled doping schemes, high mobility, and seamless incorporation of high- κ dielectrics. Furthermore, the uniform growth of wafer-scale 2D film is imperative to mitigate defect density, minimize device-to-device variation, and establish pristine interfaces within the integrated circuits. This review examines the latest breakthroughs with a focus on the preparation of 2D channel materials and device engineering in advanced FET structures. It also extensively summarizes critical aspects such as the scalability and compatibility of 2D FET devices with existing manufacturing technologies, elucidating the synergistic relationships crucial for realizing efficient and high-performance 2D FETs. These findings extend to potential integrated circuit applications in diverse functionalities. [ABSTRACT FROM AUTHOR]

Transition-metal dichalcogenides are among most studied two-dimensional semiconductors for applications in electronics, optoelectronics, spintronics, and memory devices. One of the simple commercially friendly methods to fabricate thin crystalline films is solid-state crystallization from the amorphous phase. In this work, using differential scanning calorimetry (DSC) measurements, we demonstrate that MoTe2 nanolayers deposited on different substrates (Ta, Al, W, Mo) manifest distinctly different crystallization behavior. We argue that these differences are associated with different chemical affinity of the film constituents towards the substrate material and propose a scheme of this complex crystallization process.

Objectives. The optical properties of two-dimensional semiconductor materials, specifically monolayered transition metal dichalcogenides, present new horizons in the field of nano- and optoelectronics. However, their practical application is hindered by the issue of low light absorption. When working with such thin structures, it is essential to consider numerous complex factors, such as resonance and plasmonic effects which can influence absorption efficiency. The aim of this study is the optimization of light absorption in a two-dimensional semiconductor in the Kretschmann configuration for future use in optoelectronic devices, considering the aforementioned phenomena. Methods. A numerical modeling method was applied using the finite element method for solving Maxwell’s equations. A parametric analysis was conducted focusing on three parameters: angle of light incidence, metallic layer thickness, and semiconductor layer thickness.Results. Parameters were identified at which the maximum area of absorption peak was observed, including the metallic layer thickness and angle of light incidence. Based on the resulting graphs, optimal parameters were determined, in order to achieve the highest absorption percentages in the two-dimensional semiconductor film.Conclusions. Based on numerical studies, it can be asserted that the optimal parameters for maximum absorption in the monolayer film are: Ag thickness

Abstract Spatial manipulation of excitonic quasiparticles, such as neutral excitons, charged excitons, and interlayer excitons, in two-dimensional semiconductors offers unique capabilities for a broad range of optoelectronic applications, encompassing photovoltaics, exciton-integrated circuits, and quantum light-emitting systems. Nonetheless, their practical implementation is significantly restricted by the absence of electrical controllability for neutral excitons, short lifetime of charged excitons, and low exciton funneling efficiency at room temperature, which remain a challenge in exciton transport. In this comprehensive review, we present the latest advancements in controlling exciton currents by harnessing the advanced techniques and the unique properties of various excitonic quasiparticles. We primarily focus on four distinct control parameters inducing the exciton current: electric fields, strain gradients, surface plasmon polaritons, and photonic cavities. For each approach, the underlying principles are introduced in conjunction with its progression through recent studies, gradually expanding their accessibility, efficiency, and functionality. Finally, we outline the prevailing challenges to fully harness the potential of excitonic quasiparticles and implement practical exciton-based optoelectronic devices.

Metal–semiconductor contacts are crucial components in semiconductor devices. Ultrathin two‐dimensional transition‐metal dichalcogenide semiconductors can sustain transistor scaling for next‐generation integrated circuits. However, their performance is often degraded by conventional metal deposition, which results in a high barrier due to chemical disorder and Fermi‐level pinning (FLP). Although, transferring electrodes can address these issues, they are limited in achieving universal transfer of full‐class metals due to strong adhesion between pre‐deposited metals and substrates. Here, we propose a nanobelt‐assisted transfer strategy that can avoid the adhesion limitation and enables the universal transfer of over 20 different types of electrodes. Our contacts obey the Schottky–Mott rule and exhibit a FLP of S = 0.99. Both the electron and hole contacts show record‐low Schottky barriers of 4.2 and 11.2 meV, respectively. As a demonstration, we construct a doping‐free WSe2 inverter with these high‐performance contacts, which exhibits a static power consumption of only 58 pW. This strategy provides a universal method of electrode preparation for building high‐performance post‐Moore electronic devices. [ABSTRACT FROM AUTHOR]

Spatial manipulation of excitonic quasiparticles, such as neutral excitons, charged excitons, and interlayer excitons, in two-dimensional semiconductors offers unique capabilities for a broad range of optoelectronic applications, encompassing photovoltaics, exciton-integrated circuits, and quantum light-emitting systems. Nonetheless, their practical implementation is significantly restricted by the absence of electrical controllability for neutral excitons, short lifetime of charged excitons, and low exciton funneling efficiency at room temperature, which remain a challenge in exciton transport. In this comprehensive review, we present the latest advancements in controlling exciton currents by harnessing the advanced techniques and the unique properties of various excitonic quasiparticles. We primarily focus on four distinct control parameters inducing the exciton current: electric fields, strain gradients, surface plasmon polaritons, and photonic cavities. For each approach, the underlying principles are introduced in conjunction with its progression through recent studies, gradually expanding their accessibility, efficiency, and functionality. Finally, we outline the prevailing challenges to fully harness the potential of excitonic quasiparticles and implement practical exciton-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

The mechanical properties, electronic structure, electric transport and optoelectronic properties of a recently predicted wide bandgap semiconductor β-HfNCl monolayer are systematically studied by means of first-principles calculations. β-HfNCl monolayer is isotropic in mechanical properties, whose calculated Young’s modulus, shear modulus, and layer modulus of β-HfNCl monolayer are 128.9–129.2, 44.28, and 119.46 N m−1, respectively. An appropriate tensile strain (i.e., beyond 3 %) can induce a transition from indirect bandgap to direct bandgap. In addition, we construct several conceptual nanodevice structures based on β-HfNCl monolayer, such as pn-junction diodes, pin-junction field-effect transistors (FETs) and phototransistors. The electronic transport results reveal that the pn-junction diodes have obvious rectification effect and strong electric anisotropy. Their rectification ratios and electric anisotropy ratio (η) can reach up to 106 and 3.69, respectively. The FETs have an obvious field-effect behavior with a slightly lower rectification ratio (105). Moreover, we investigate the photoelectric response of the phototransistors of β-HfNCl monolayer under the illumination of light. They have a strong response to the light whose energy is larger than the violet light, indicating that the β-HfNCl monolayer can be a platform to detect the ultraviolet light. These findings provide crucial insights into the potential applications of β-HfNCl monolayer in electronic and optoelectronic devices.

Abstract Metal–semiconductor contacts are crucial components in semiconductor devices. Ultrathin two‐dimensional transition‐metal dichalcogenide semiconductors can sustain transistor scaling for next‐generation integrated circuits. However, their performance is often degraded by conventional metal deposition, which results in a high barrier due to chemical disorder and Fermi‐level pinning (FLP). Although, transferring electrodes can address these issues, they are limited in achieving universal transfer of full‐class metals due to strong adhesion between pre‐deposited metals and substrates. Here, we propose a nanobelt‐assisted transfer strategy that can avoid the adhesion limitation and enables the universal transfer of over 20 different types of electrodes. Our contacts obey the Schottky–Mott rule and exhibit a FLP of S = 0.99. Both the electron and hole contacts show record‐low Schottky barriers of 4.2 and 11.2 meV, respectively. As a demonstration, we construct a doping‐free WSe2 inverter with these high‐performance contacts, which exhibits a static power consumption of only 58 pW. This strategy provides a universal method of electrode preparation for building high‐performance post‐Moore electronic devices.

Two-dimensional (2-D) semiconductors are emerging as strong contenders for the future of Angstrom technology nodes. Their potential lies in enhanced device scaling and energy-efficient switching compared to traditional bulk semiconductors like Si, Ge, and III-V compounds. These materials offer significant advantages, particularly in ultra-thin devices with atomic scale thicknesses. Their unique structures enable the creation of one-dimensional nanoribbons and vertical and lateral heterostructures. This versatility in design, coupled with their distinctive properties, paves the way for efficient energy switching in electronic devices. Moreover, 2-D semiconductors offer opportunities for integrating metallic nanoribbons, carbon nanotubes (CNT), and graphene with their 2-D channel materials. This integration helps overcome lithography limitations for gate patterning, allowing the realization of ultra-short gate dimensions. Considering these factors, the potential of 2-D semiconductors in electronics is vast. This concise review focuses on the latest advancements and engineering strategies in 2-D logic devices. [ABSTRACT FROM AUTHOR]

Two-dimensional (2-D) semiconductors are emerging as strong contenders for the future of Angstrom technology nodes. Their potential lies in enhanced device scaling and energy-efficient switching compared to traditional bulk semiconductors like Si, Ge, and III-V compounds. These materials offer significant advantages, particularly in ultra-thin devices with atomic scale thicknesses. Their unique structures enable the creation of one-dimensional nanoribbons and vertical and lateral heterostructures. This versatility in design, coupled with their distinctive properties, paves the way for efficient energy switching in electronic devices. Moreover, 2-D semiconductors offer opportunities for integrating metallic nanoribbons, carbon nanotubes (CNT), and graphene with their 2-D channel materials. This integration helps overcome lithography limitations for gate patterning, allowing the realization of ultra-short gate dimensions. Considering these factors, the potential of 2-D semiconductors in electronics is vast. This concise review focuses on the latest advancements and engineering strategies in 2-D logic devices.

Two-dimensional (2D) van der Waals (vdW) AIIIBVI semiconductor materials, such as InSe and GaSe, are of considerable interest due to their potential use in various microelectronics applications. The range of properties of materials of this class can be extended further through the use of quasi-binary alloys of the InSe(Te)-GaSe(Te) type. In this work, we study the effect of compositional and structural disorder in 2D In(Ga)Se(Te) on the band structure and electronic properties using first principles modeling. The results for In(Ga)Se demonstrate a noticeable decrease in the band gap for structures with a random distribution of indium and gallium cations, while for In(Ga)Te with a random cation distribution, metallization occurs. Changes in the compositional arrangement of chalcogens (there can be either the same or different atoms on each side of the vdW gap) lead to pronounced changes in the band gap, but no significant changes in topology are observed. In addition, a significant effect of the distance between the layers on the band gap under compression along the c axis was found for both alloys under study. An important point of our study is that van der Waals gap engineering is a very powerful tool to control the properties of 2D materials and its alloys. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) has emerged as a promising technology for the development of the next generation of low-power semiconductor electronics. The wafer-scaled growth of two-dimensional (2D) crystalline nanostructures is a fundamental step toward the development of advanced nanofabrication technologies. Ga2O3 is an ultra-wide bandgap metal oxide semiconductor for application in electronic devices. The polymorphous Ga2O3 with its unique electronic characteristics and doping capabilities is a functional option for heterointerface engineering at metal-semiconductor 2D heterojunctions for application in nanofabrication technology. Plasma-enhanced atomic layer deposition (PE-ALD) enabled the deposition of ultra-thin nanostructures at low-growth temperatures. The present study used the PE-ALD process for the deposition of atomically thin crystalline ß-Ga2O3 films for heterointerface engineering at 2D metal-semiconductor heterojunctions. Via the control of plasma gas composition and ALD temperature, the wafer-scaled deposition of ~5.0 nm thick crystalline ß-Ga2O3 at Au/Ga2O3-TiO2 heterointerfaces was achieved. Material characterization techniques showed the effects of plasma composition and ALD temperature on the properties and structure of Ga2O3 films. The following study on the electronic characteristics of Au/Ga2O3-TiO2 2D heterojunctions confirmed the tunability of this metal/semiconductor polarized junction, which works as functional electron channel layer developed based on tunable p-n junctions at 2D metal/semiconductor interfaces. [ABSTRACT FROM AUTHOR]

Abstract Vertical three-dimensional (3D) integration is a highly attractive strategy to integrate a large number of transistor devices per unit area. This approach has emerged to accommodate the higher demand of data processing capability and to circumvent the scaling limitation. A huge number of research efforts have been attempted to demonstrate vertically stacked electronics in the last two decades. In this review, we revisit materials and devices for the vertically integrated electronics with an emphasis on the emerging semiconductor materials that can be processable by bottom-up fabrication methods, which are suitable for future flexible and wearable electronics. The vertically stacked integrated circuits are reviewed based on the semiconductor materials: organic semiconductors, carbon nanotubes, metal oxide semiconductors, and atomically thin two-dimensional materials including transition metal dichalcogenides. The features, device performance, and fabrication methods for 3D integration of the transistor based on each semiconductor are discussed. Moreover, we highlight recent advances that can be important milestones in the vertically integrated electronics including advanced integrated circuits, sensors, and display systems. There are remaining challenges to overcome; however, we believe that the vertical 3D integration based on emerging semiconductor materials and devices can be a promising strategy for future electronics.

Two-dimensional (2D) semiconductors have garnered significant interest due to their atomically thin structure that greatly enhances 'More Moore' dimensional scaling and facilitates the advancement of 'More than Moore' technologies. While 2D transistors hold the promise of unprecedented breakthroughs in atomic-limit device performance, their actual performance has frequently fallen short of expectations. This discrepancy primarily arises from the complex nature of the few critical interfaces (e.g., metal/semiconductor, dielectric/semiconductor) that constitute 2D transistors, and therefore achieving high-quality heterogeneous interfaces is a major challenge for 2D transistor performance and system integration. In this review, we summarize these interfaces and classify them into four types: 1) metal/semiconductor contact interfaces, 2) dielectric/2D channel interfaces, 3) surface and substrate interfaces, and 4) interfaces in wafer-scale integration. From the perspective of forming high-quality interfaces through compatible integration techniques, we analyze in detail the current challenges, development trends and future prospects of these interfaces and highlight their importance in driving the development and future manufacturing integration of 2D transistors. We also present insights into leveraging advanced interface modulation techniques to push the performance boundaries of 2D transistors. This review aims to direct attention to the pivotal role of 2D transistor interfaces, steering scientific research towards enabling the transition of 2D semiconductors from the 'lab to fab' and realizing their full potential. [ABSTRACT FROM AUTHOR]

Objectives. Two-dimensional transition metal dichalcogenides (TMDs) are utilized for various optical applications due to the presence in these materials of a direct band gap corresponding to the visible and near-infrared spectral regions. However, a limited set of existing TMDs makes the region of the used spectral range discrete. The most effective way to solve this problem is to use two-dimensional TMD films based on multicomponent alloys, including three or more different chemical elements (while TMDs consist of two). By varying their morphological composition, one can control the value of the band gap and thus their optical absorption spectrum. However, since the band gap in such structures is highly nonlinear as far as their chemical composition is concerned, it can be challenging to select the required concentration in order to achieve uniform absorption. In this regard, the purpose of this work is to theoretically determine the dependence of the band gap of four-component two-dimensional MoxW1–xS2ySe2(1–y) alloys on their morphological composition.Methods. The calculations were performed within the framework of the density functional theory using the Quantum Espresso software package. Flakes of two-dimensional TMDs alloys were prepared from bulk TMDs crystals by mechanical exfoliation on a Si/SiO2 substrate. An experimental study of the photoluminescence characteristics was carried out using photoluminescence microscopy-spectroscopy. Results. In this work, the dependence of the band gap on the morphological composition of two-dimensional MoxW1–xS2ySe2(1–y) alloys was determined. Upon varying the composition of TMDs alloys, it was found that the band gap changes from 1.43 to 1.83 eV. The obtained theoretical results are in qualitative agreement with the experimental data.Conclusions. The minimum band gap is observed in alloys close to MoSe2, while alloys close to WS2 have the maximum band gap value.

Defect engineering of atomically thin semiconducting crystals is an attractive route to developing single‐photon sources and valleytronic devices. For these applications, defects with well‐defined optical characteristics need to be generated in a precisely controlled manner. However, defect‐induced optical features are often complicated by the presence of multiple defect species, hindering the identification of their structural origin. Here, we report systematic generation of optically active atomic defects in monolayer MoS2, WS2, MoSe2, and WSe2 via proton‐beam irradiation. Defect‐induced emissions are found to occur ≈100 to 200 meV below the neutral exciton peak, showing typical characteristics of localized excitons such as saturation at high‐excitation rates and long lifetime. Using scanning transmission electron microscopy, it is shown that freshly created chalcogen vacancies are responsible for the localized exciton emission. Density functional theory and ab initio GW plus Bethe‐Salpeter‐equation calculations reveal that the observed emission can be attributed to transitions involving defect levels of chalcogen vacancy and the valence band edge state. [ABSTRACT FROM AUTHOR]

Controlling charge transport at the interfaces of nanostructures is crucial for their successful use in optoelectronic and solar energy applications. Mixed-dimensional heterostructures based on single-walled carbon nanotubes (SWCNTs) and transition metal dichalcogenides (TMDCs) have demonstrated exceptionally long-lived charge-separated states. However, the factors that control the charge transport at these interfaces remain unclear. In this study, we directly image charge transport at the interfaces of single- and multilayered MoS 2 and (6,5) SWCNT heterostructures using transient absorption microscopy. We find that charge recombination becomes slower as the layer thickness of MoS 2 increases. This behavior can be explained by electron delocalization in multilayers and reduced orbital overlap with the SWCNTs, as suggested by nonadiabatic (NA) molecular dynamics (MD) simulations. Dipolar repulsion of interfacial excitons results in rapid density-dependent transport within the first 100 ps. Stronger repulsion and longer-range charge transport are observed in heterostructures with thicker MoS 2 layers, driven by electron delocalization and larger interfacial dipole moments. These findings are consistent with the results from NAMD simulations. Our results suggest that heterostructures with multilayer MoS 2 can facilitate long-lived charge separation and transport, which is promising for applications in photovoltaics and photocatalysis.

Bipolar junction transistors (BJTs) are crucial components in high-power electronic applications. However, while two-dimensional (2D) semiconductors with exceptional electrical properties have been extensively studied in field-effect transistors, their application in BJTs has received far less attention. In this study, we demonstrate high-gain MoS 2 BJTs based on metal-semiconductor Schottky contacts. The emitter-base junction uses the thermal ionization properties of a Schottky diode to emit electrons, while the collector-base junction leverages the Schottky barrier to collect electrons. This design enables thermal ionization of electrons into the base region, where they are subsequently accelerated and transferred to the collector region under the influence of the collector-base junction voltage. Our MoS 2 BJTs achieves a common-base current gain 0.99 and a remarkable common-emitter current gain of 1967, representing the highest performance reported for BJTs based on 2D semiconductors to date, which is comparable to traditional silicon-based BJTs.

The advent of memristors and resistive switching has transformed solid-state physics, enabling advanced applications such as neuromorphic computing. Inspired by these developments, we introduce the concept of Mem-emitters, devices that manipulate light-emission properties of semiconductors to achieve memory functionalities. Mem-emitters, influenced by past exposure to stimuli, offer a new approach to optoelectronic computing with potential for enhanced speed, efficiency, and integration. This study explores the unique properties of transition-metal dichalcogenide-based heterostructures as a promising platform for Mem-emitter functionalities because of their atomic-scale thickness, tunable electronic properties, and strong light-matter interaction. When distinguishing between population-driven and transition rate-driven Mem-emitters, we highlight their potential for various applications, including optoelectronic switches, variable light sources, and advanced communication systems. Understanding these mechanisms paves the way for innovative technologies in memory and computation, providing insights into the intrinsic dynamics of complex systems.

Highlights: The vertically integrated electronic devices based on emerging semiconductor materials including organic, metal oxide, and two-dimensional materials are revisited. Comprehensive aspects of the device architecture, performance, and fabrication method of the vertically stacked electronics according to each semiconductor material are discussed. Recent advances in vertically integrated electronic devices for emerging applications such as advanced integrated circuits, sensors, and display systems are highlighted. Vertical three-dimensional (3D) integration is a highly attractive strategy to integrate a large number of transistor devices per unit area. This approach has emerged to accommodate the higher demand of data processing capability and to circumvent the scaling limitation. A huge number of research efforts have been attempted to demonstrate vertically stacked electronics in the last two decades. In this review, we revisit materials and devices for the vertically integrated electronics with an emphasis on the emerging semiconductor materials that can be processable by bottom-up fabrication methods, which are suitable for future flexible and wearable electronics. The vertically stacked integrated circuits are reviewed based on the semiconductor materials: organic semiconductors, carbon nanotubes, metal oxide semiconductors, and atomically thin two-dimensional materials including transition metal dichalcogenides. The features, device performance, and fabrication methods for 3D integration of the transistor based on each semiconductor are discussed. Moreover, we highlight recent advances that can be important milestones in the vertically integrated electronics including advanced integrated circuits, sensors, and display systems. There are remaining challenges to overcome; however, we believe that the vertical 3D integration based on emerging semiconductor materials and devices can be a promising strategy for future electronics. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals (vdW) AIIIBVI semiconductor materials, such as InSe and GaSe, are of considerable interest due to their potential use in various microelectronics applications. The range of properties of materials of this class can be extended further through the use of quasi-binary alloys of the InSe(Te)-GaSe(Te) type. In this work, we study the effect of compositional and structural disorder in 2D In(Ga)Se(Te) on the band structure and electronic properties using first principles modeling. The results for In(Ga)Se demonstrate a noticeable decrease in the band gap for structures with a random distribution of indium and gallium cations, while for In(Ga)Te with a random cation distribution, metallization occurs. Changes in the compositional arrangement of chalcogens (there can be either the same or different atoms on each side of the vdW gap) lead to pronounced changes in the band gap, but no significant changes in topology are observed. In addition, a significant effect of the distance between the layers on the band gap under compression along the c axis was found for both alloys under study. An important point of our study is that van der Waals gap engineering is a very powerful tool to control the properties of 2D materials and its alloys.

Despite a decade of extensive research on two-dimensional transition metal dichalcogenides, there are still some gaps in our understanding of their remarkable properties, limiting their potential applications. One such gap relates to the properties of these alloys, which offer tunable band gaps and can serve as the basis for various optoelectronic and nonlinear optical devices. A comprehensive understanding of the ultrafast charge carrier excitation and relaxation dynamics as well as their characteristic relaxation time constants, is crucial for the further use of these materials in specific applications. In this work, we experimentally investigate the dynamics of ultrafast relaxation processes in monolayer MoS 2x Se 2(1-x) alloys on a Si/SiO 2 substrate using time-resolved spectroscopy. We determine the characteristic relaxation time constants for structures with different stoichiometric compositions and refine these constants by accounting for interference effects arising from the substrate. • Ultrafast relaxation dynamics in monolayer MoS 2x Se 2(1-x) alloys were investigated using time-resolved spectroscopy. • Relaxation times show a nonlinear dependence on the sulfur fraction (x) in MoS 2x Se 2(1-x) alloys. • The longest relaxation times are observed for pure MoS 2 , decreasing to a minimum for MoSe 2. • The Si/SiO 2 substrate's contribution to the determination of characteristic relaxation time constants is approximately 15 %. [ABSTRACT FROM AUTHOR]

Interaction of excitons with resident charge carriers in semiconductors gives rise to bound three-particle complexes, trions, whose optical response is conveniently described in the framework of many-body correlated Fermi polaron states. These states are formed as a result of correlation of photocreated trion with the Fermi sea hole and possess the angular momentum component of ±1 depending on the helicity of the photon. We study theoretically the energy spectrum fine structure of Fermi polarons in two-dimensional semiconductors based on transition metal dichalcogenides. We demonstrate both by the symmetry analysis and microscopic calculation that the Fermi polarons with nonzero in-plane wavevector k are split, similarly to the neutral exciton states, into the linearly polarized longitudinal and transverse, with respect to the k , states. The origin of this longitudinal-transverse splitting is the long-range electron-hole exchange interaction that can be also described as the interaction of Fermi polarons with their induced electromagnetic field. The effective Hamiltonian describing the Fermi polaron fine structure is derived, and its parameters are determined from the microscopic model. • Fermi polaron (Suris tetron) states are split by the electron-hole exchange interaction. • The Fermi polaron eigenstates in two-dimensional semiconductors are the longitudinal and transverse ones. • The mixing of inter- and intravalley Fermi polarons in tungsten based transition metal dichalcogenide monolayers is possible. [ABSTRACT FROM AUTHOR]

The elementary optical excitations of a two-dimensional electron or hole system have been identified as exciton-Fermi-polarons. Nevertheless, the connection between the bound state of an exciton and an electron, termed trion, and exciton–polarons is subject of ongoing debate. Here, we use an analogy to the Tavis–Cummings model of quantum optics to show that an exciton–polaron can be understood as a hybrid quasiparticle—a coherent superposition of a bare exciton in an unperturbed Fermi sea and a bright collective excitation of many trions. The analogy is valid to the extent that the Chevy Ansatz provides a good description of dynamical screening of excitons and provided the Fermi energy is much smaller than the trion binding energy. We anticipate our results to bring new insight that could help to explain the striking differences between absorption and emission spectra of two-dimensional semiconductors.

Interfacing CH 3 NH 3 PbI 3 (MAPbI 3 ) with 2D van der Waals materials in lateral photodetectors can suppress the dark current and driving voltage, while the interlayer charge separation also renders slower charge dynamics. In this work, we show that more than one order of magnitude faster photoresponse time can be achieved in MAPbI 3 /MoS 2 lateral photodetectors by locally separating the photocharge generation and recombination through a parallel channel of single-layer MAPbI 3 . Photocurrent ( I ph ) mapping reveals electron diffusion lengths of about 20 μm in single-layer MAPbI 3 and 4 μm in the MAPbI 3 /MoS 2 heterostructure. The illumination-power scaling of I ph and time-resolved photoluminescence studies point to the dominant roles of the heterostructure region in photogeneration and single-layer MAPbI 3 in charge recombination. Our results shed new light on the material design that can concurrently enhance photoresponsivity, reduce driving voltage, and sustain high operation speed, paving the path for developing high-performance lateral photodetectors based on hybrid perovskites.

Two-dimensional (2D) semiconductors, owing to their strong excitonic emission, are emerging as efficient gain media for constructing the ultimate nanolaser. The further integration of 2D semiconductors with plasmonic devices holds promise for realizing the thinnest laser. However, the implementation of 2D semiconductor plasmonic lasing is severely hindered by the limited cavity feedback and low gain resulting from insufficient plasmon-exciton interactions. Here, we report the realization of a room-temperature 2D semiconductor plasmonic laser by embedding an InSe nanoflake into a plasmonic Fabry-Perot (F-P) cavity. This plasmonic F-P cavity shows an exceptional ability to recycle the leaked dark surface plasmon, resulting in >2-fold enhancement of feedback compared to that of conventional metal-insulator-semiconductor nanolasers. Moreover, via combination of field enhancement and orientation matching, this cavity facilitates optimized plasmon-exciton coupling to ensure sufficient gain for sustaining room-temperature lasing. Our work may open up the possibilities for multifunctional photonic devices based on 2D materials.

Molybdenum disulfide (MoS2) has been actively explored as a direct bandgap semiconductor in the monolayer (ML) limit for various applications due to its prominent physical properties and stability. In order to broaden its application range further, diverse treatments have been developed to modulate the properties of ML-MoS2. The native point defects, such as S vacancies, are known to activate surface charge transfer doping in ML-MoS2. Unlike conventional semiconductors, ML-MoS2 shows distinct excitonic transitions that can be exploited for controlling its optical, optoelectronic, and electric characteristics via coupling with defect-driven doping. Here, the ambient photoluminescence (PL) of ML-MoS2 could be increased by ~1500% at the center of focused-laser irradiation (FLI). Expectedly, the PL intensity varied spatially along with exciton–trion transitions across the irradiation spot due to the Gaussian profile of laser intensity. Then, nano-Auger electron spectroscopy (n-AES) revealed that the spectral fraction of exciton PL increased by ~69.2% while that of trion PL decreased by ~49.9% with increasing S deficiency up to ~13.4 ± 3.5%. Cryogenic PL and field-effect transistor experiments were also performed to understand the defect-related phenomena comprehensively. This novel experimental combination of FLI with an n-AES probe provides a facile, effective, and cost-efficient approach for exploring defect effects in two-dimensional structures.

In 2D semiconductors, the Schottky barrier formed at the metal–semiconductor interface plays a crucial role in controlling electron and spin injection. To explore the spin injection mechanism under gate control, we study MoS 2 coupled to ferromagnetic metals. We introduce a spin drift diffusion model which is applicable to the Schottky contact. In this system, the current passing through the Schottky barrier can be larger for the minority spin than for the majority spin due to the tunnel effect. We observe a polarity switching in spin injection with gate voltage variation when the conduction band bottom of the minority spin ferromagnetic metal is closely aligned with the Fermi level. Our results also suggest the spin injection efficiency can be tuned by gate control for half-metals. • Research explores spin injection from ferromagnetic metal into 2D semiconductors. • Spin current polarization is examined by drift diffusion simulations. • Gate voltage can alter current switch polarity under specific conditions. • High spin injection efficiency can be realized with gate voltage for half-metals. [ABSTRACT FROM AUTHOR]

Novel 2D semiconductors play an increasingly important role in modern nanoelectronics and optoelectronics. Herein, a novel topology designer based on component fusion is introduced, featured by the submolecular component integration and properties inheritance. As expected, a new air‐stable 2D semiconductor PdPSe with a tailored puckered structure is successfully designed and synthesized via this method. Notably, the monolayer of PdPSe is constructed by two sublayers via PP bonds, different from 2D typical transition metal materials with sandwich‐structured monolayers. With the expected orthorhombic symmetry and intralayer puckering, PdPSe displays a strong Raman anisotropy. The field‐effect transistors and photodetectors based on few‐layer PdPSe demonstrate good electronic properties with high carrier mobility of ≈35 cm2 V−1 s−1 and a high on/off ratio of 106, as well as excellent optoelectronic performance, including high photoresponsivity, photogain, and detectivity with values up to 1.06 × 105 A W−1, 2.47 × 107%, and 4.84 × 1010 Jones, respectively. These results make PdPSe a promising air‐stable 2D semiconductor for various electronic and optoelectronic applications. This work suggests that the component‐fusion‐based topology designer is a novel approach to tailor 2D materials with expected structures and interesting properties. [ABSTRACT FROM AUTHOR]

Two-dimensional semiconductors (2DSCs) with appropriate band gaps and high mobilities are highly desired for future-generation electronic and optoelectronic applications. Here, using first-principles calculations, we report a novel class of 2DSCs, group-11-chalcogenide monolayers (M2X, M = Cu, Ag, Au; X = S, Se, Te), featuring with a broad range of energy band gaps and high carrier mobilities. Their energy band gaps extend from 0.49 to 3.76 eV at a hybrid density functional level, covering from ultraviolet-A, visible light to near-infrared region, which are crucial for broadband photoresponse. Significantly, the calculated room-temperature carrier mobilities of the M2X monolayers are as high as thousands of cm2·V−1·s−1. Particularly, the carrier mobilities of η-Au2Se and ε-Au2Te are up to 104 cm2·V−1·s−1, which is very attracitive for electronic devices. Benefitting from the broad range of energy band gaps and superior carrier mobilities, the group-11-chalcogenide M2X monolayers are promising candidates for future-generation nanoelectronics and optoelectronics. [ABSTRACT FROM AUTHOR]

Solar‐driven photocatalysis has been developing as a sustainable process and it holds appreciable promise to address the pollutants and risks posed by biohazards. The unique geometrical and electric features of 2D semiconductors have nurtured a variety of advanced photocatalytic bactericides where oxidative oxygen species are generated as the main disinfection reagents. Herein, the state‐of‐the‐art progress of solar‐driven photocatalytic disinfection based on 2D semiconductors with an emphasis on the generation and effects of various reactive oxygen species is summarized. Moreover, the immobility of the photocatalyst for practical applications is discussed. Finally, perspectives and challenges are presented to guide future research on photocatalytic disinfection. [ABSTRACT FROM AUTHOR]

Metal-oxide-semiconductor field effect transistors (MOSFET) based on two-dimensional (2D) semiconductors have attracted extensive attention owing to their excellent transport properties, atomically thin geometry, and tunable bandgaps. Besides improving the transistor performance of individual device, lots of efforts have been devoted to achieving 2D logic functions or integrated circuit towards practical application. In this review, we discussed the recent progresses of 2D-based logic circuit. We will first start with the different methods for realization of n-type metal-oxide-semiconductor (NMOS)-only (or p-type metal-oxide-semiconductor (PMOS)-only) logic circuit. Next, various device polarity control and complementary-metal-oxide-semiconductor (CMOS) approaches are summarized, including utilizing different 2D semiconductors with intrinsic complementary doping, charge transfer doping, contact engineering, and electrostatics doping. We will discuss the merits and drawbacks of each approach, and lastly conclude with a short perspective on the challenges and future developments of 2D logic circuit. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) are emerging as promising building blocks of high-performance photocatalysts for visible-light-driven water splitting because of their unique physical, chemical, electronic, and optical properties. This review focuses on the fundamentals of 2D TMDC-based mixed-dimensional heterostructures and their unique properties as visible-light-driven photocatalysts from the perspective of dimensionality and interface engineering. First, we discuss the approaches and advantages of surface modification and functionalization of 2D TMDCs for photocatalytic water splitting under visible-light illumination. We then classify the strategies for improving the photocatalytic activity of 2D TMDCs via combination with various low-dimensional nanomaterials to form mixed-dimensional heterostructures. Further, we highlight recent advances in the use of these mixed-dimensional heterostructures as high-efficiency visible-light-driven photocatalysts, particularly focusing on synthesis routes, modification approaches, and physiochemical mechanisms for improving their photoactivity. Finally, we provide our perspectives on future opportunities and challenges in promoting real-world photocatalytic applications of 2D TMDC-based heterostructures. [ABSTRACT FROM AUTHOR]

Metasurfaces allow light to be manipulated at the nanoscale. Integrating metasurfaces with transition metal dichalcogenide monolayers provides additional functionality to ultrathin optics, including tunable optical properties with enhanced light-matter interactions. In this work, we demonstrate the realization of a polaritonic metasurface utilizing the sizable light-matter coupling of excitons in monolayer WSe 2 and the collective lattice resonances of nanoplasmonic gold arrays. We developed a novel fabrication method to integrate gold nanodisk arrays in hexagonal boron nitride and thus simultaneously ensure spectrally narrow exciton transitions and their immediate proximity to the near-field of array surface lattice resonances. In the regime of strong light-matter coupling, the resulting van der Waals metasurface exhibits all key characteristics of lattice polaritons, with a directional and linearly polarized far-field emission profile dictated by the underlying nanoplasmonic lattice. Our work can be straightforwardly adapted to other lattice geometries, establishing structured van der Waals metasurfaces as means to engineer polaritonic lattices.

The study of exciton polarons has offered profound insights into the many-body interactions between bosonic excitations and their immersed Fermi sea within layered heterostructures. However, little is known about the properties of exciton polarons with interlayer interactions. Here, through magneto-optical reflectance contrast measurements, we experimentally investigate interlayer Fermi polarons for 2s excitons in WSe 2 /graphene heterostructures, where the excited exciton states (2s) in the WSe 2 layer are dressed by free charge carriers of the adjacent graphene layer in the Landau quantization regime. First, such a system enables an optical detection of integer and fractional quantum Hall states (e.g., ν = ±1/3, ±2/3) of monolayer graphene. Furthermore, we observe that the 2s state evolves into two distinct branches, denoted as attractive and repulsive polarons, when graphene is doped out of the incompressible quantum Hall gaps. Our work paves the way for the understanding of the excited composite quasiparticles and Bose-Fermi mixtures.

Organic semiconductors have been proven as emerging platforms for exploring strong light–matter interactions and quantum optics so as to develop coherent and quantum photonic devices. Though there has been abundant research on organic semiconductors, lasing action is rarely reported in individual 2D organic semiconductor waveguides or nanocavities. Herein, a strong optical waveguiding phenomenon is observed not only in the individual 2D organic semiconductor Znq2 nanosheet with micrometer size area, but also in the interconnecting or neighboring Znq2 nanosheets. The optical propagation loss coefficient of the interconnecting Znq2 sheets is ≈800 dB cm−1. More importantly, the phenomenon of optically pumped lasing in 2D Znq2 nanosheets is demonstrated, as evidenced by a sudden increase in emission intensity at a threshold pump pulse fluence of 49.9 W cm−2 at 480 nm. As verified by numerical FDTD simulations, the Znq2 nanosheet constitutes a microcavity that supports whisper gallery mode, providing suffcient feedback for laser oscillations. Herein, the coexistence of low‐loss waveguiding and excellent lasing in 2D organic semiconductor nanosheets are revealed, which open up a new pathway for photonics and quantum optics based on 2D organic semiconductors.

Abstract Searching for new stable free-standing atomically thin two-dimensional (2D) materials is of great interest in the fundamental and practical aspects of contemporary material sciences. Recently, the synthesis of layered SiAs single crystals has been realized, which indicates that their few layer structure can be mechanically exfoliated. Performing a first-principles density functional theory calculations, we proposed two dynamically and thermodynamically stable semiconducting SiAs and SiAs2 monolayers. Band structure calculation reveals that both of them exhibit indirect band gaps and an indirect to direct band even to metal transition are found by application of strain. Moreover, we find that SiAs and SiAs2 monolayers possess much higher carrier mobility than MoS2 and display anisotropic transportation like the black phosphorene, rendering them potential application in optoelectronics. Our works pave a new route at nanoscale for novel functionalities of optical devices.

The properties of bulk compounds required to be suitable for photovoltaic applications, such as excellent visible light absorption, favorable exciton formation, and charge separation are equally essential for two-dimensional (2D) materials. Here, we systematically study 2D group IV–V compounds such as SiAs2 and GeAs2 with regard to their structural, electronic and optical properties using density functional theory (DFT), hybrid functional and Bethe–Salpeter equation (BSE) approaches. We find that the exfoliation of single-layer SiAs2 and GeAs2 is highly feasible and in principle could be carried out experimentally by mechanical cleavage due to the dynamic stability of the compounds, which is inferred by analyzing their vibrational normal mode. SiAs2 and GeAs2 monolayers possess a bandgap of 1.91 and 1.64 eV, respectively, which is excellent for sunlight harvesting, while the exciton binding energy is found to be 0.25 and 0.14 eV, respectively. Furthermore, band-gap tuning is also possible by application of tensile strain. Our results highlight a new family of 2D materials with great potential for solar cell applications.

With the demand for high-performance and miniaturized semiconductor devices continuously rising, the development of innovative tunneling transistors via efficient stacking methods using two-dimensional (2D) building blocks has paramount importance in the electronic industry. Hence, 2D semiconductors with atomically thin geometries hold significant promise for advancements in electronics. In this study, we introduced tunneling memtransistors with a thin-film heterostructure composed of 2D semiconducting MoS 2 and WSe 2 . Devices with the dual function of tuning and memory operation were realized by the gate-regulated modulation of the barrier height at the heterojunction and manipulation of intrinsic defects within the exfoliated nanoflakes using solution processes. Further, our investigation revealed extensive edge defects and four distinct defect types, namely monoselenium vacancies, diselenium vacancies, tungsten vacancies, and tungsten adatoms, in the interior of electrochemically exfoliated WSe 2 nanoflakes. Additionally, we constructed complementary metal-oxide semiconductor-based logic-in-memory devices with a small static power in the range of picowatts using the developed tunneling memtransistors, demonstrating a promising approach for next-generation low-power nanoelectronics.

Impurity doping is a necessary technology for the application of semiconductor materials in microelectronic devices. The quantification of doping effects is crucial for controlling the transport properties of semiconductors. Here, taking two-dimensional (2D) hexagonal boron phosphide semiconductor as an example, we employ coherent potential approximation method to investigate the electronic properties of 2D semiconductor materials at low doping concentrations, which cannot be exploited with conventional density function theory. The results demonstrate that the positive or negative impurity potential in 2D semiconductors determines whether it is p-type or n-type doping, while the impurity potential strength decides whether it is shallow-level or deep-level doping. Impurity concentration has important impacts on not only the intensity but also the broadening of impurity peak in band gap. Importantly, we provide the operating temperature range of hexagonal boron phosphide as a semiconductor device under different impurity concentrations and impurity potentials. The methodology of this study can be applied to other 2D semiconductors, which is of great significance for quantitative research on the application of 2D semiconductors for electronic devices., (© 2024 IOP Publishing Ltd.)

Two-dimensional (2D) lateral heterojunction arrays, characterized by well-defined electronic interfaces, hold significant promise for advancing next-generation electronic devices. Despite this potential, the efficient synthesis of high-density lateral heterojunctions with tunable interfacial band alignment remains a challenging. Here, a novel strategy is reported for the fabrication of lateral heterojunction arrays between monolayer Si 2 Te 2 grown on Sb 2 Te 3 (ML-Si 2 Te 2 @Sb 2 Te 3 ) and one-quintuple-layer Sb 2 Te 3 grown on monolayer Si 2 Te 2 (1QL-Sb 2 Te 3 @ML-Si 2 Te 2 ) on a p-doped Sb 2 Te 3 substrate. The site-specific formation of numerous periodically arranged 2D ML-Si 2 Te 2 @Sb 2 Te 3 /1QL-Sb 2 Te 3 @ML-Si 2 Te 2 lateral heterojunctions is realized solely through three epitaxial growth steps of thick-Sb 2 Te 3 , ML-Si 2 Te 2 , and 1QL-Sb 2 Te 3 films, sequentially. More importantly, the precisely engineering of the interfacial band alignment is realized, by manipulating the substrate's p-doping effect with lateral spatial dependency, on each ML-Si 2 Te 2 @Sb 2 Te 3 /1QL-Sb 2 Te 3 @ML-Si 2 Te 2 junction. Atomically sharp interfaces of the junctions with continuous lattices are observed by scanning tunneling microscopy. Scanning tunneling spectroscopy measurements directly reveal the tailored type-II band bending at the interface. This reported strategy opens avenues for advancing lateral epitaxy technology, facilitating practical applications of 2D in-plane heterojunctions., (© 2024 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

Stacking monolayer semiconductors creates moiré patterns, leading to correlated and topological electronic phenomena, but measurements of the electronic structure underpinning these phenomena are scarce. Here, we investigate the properties of the conduction band in moiré heterobilayers of WS 2 /WSe 2 using submicrometer angle-resolved photoemission spectroscopy with electrostatic gating. We find that at all twist angles the conduction band edge is the K -point valley of the WS 2 , with a band gap of 1.58 ± 0.03 eV. From the resolved conduction band dispersion, we deduce an effective mass of 0.15 ± 0.02 m e . Additionally, we observe replicas of the conduction band displaced by reciprocal lattice vectors of the moiré superlattice. We argue that the replicas result from the moiré potential modifying the conduction band states rather than final-state diffraction. Interestingly, the replicas display an intensity pattern with reduced 3-fold symmetry, which we show implicates the pseudo vector potential associated with in-plane strain in moiré band formation.

We report experimental and theoretical studies of MoTe 2 -MoSe 2 heterobilayers with rigid moiré superlattices controlled by the twist angle. Using an effective continuum model that combines resonant interlayer electron tunneling with stacking-dependent moiré potentials, we identify the nature of moiré excitons and the dependence of their energies, oscillator strengths, and Landé g -factors on the twist angle. Within the same framework, we interpret distinct signatures of bound complexes among electrons and moiré excitons in nearly collinear heterostacks. Our work provides a fundamental understanding of hybrid moiré excitons and trions in MoTe 2 -MoSe 2 heterobilayers and establishes the material system as a prime candidate for optical studies of correlated phenomena in moiré lattices.

Parameters of terahertz (THz) emission in two-dimensional (2D) tungsten diselenide (WSe2) film grown by chemical vapor deposition from the gas phase have been studied for the first time. The main mechanism of THz radiation generation in this system is established. Dependence of the THz signal amplitude on azimuthal angle in a 2D WSe2 film has been studied. The distribution of the electric field of laser pumping in the WSe2/SiO2/Si structure has been calculated as dependent on the thickness of silicon dioxide layer. The choice of optimum structure geometry for effective generation of THz radiation by a WSe2 monolayer is theoretically substantiated. [ABSTRACT FROM AUTHOR]

• The β -HfNCl monolayer has isotropic mechanical properties. • The pn -junction diodes and pin -junction field-effect transistors of β -HfNCl monolayer have strong rectification effect and electrical anisotropy. • The pin -junction field-effect transistors of β -HfNCl monolayer show an obvious field-effect behavior. • The pin -junction phototransistors β -HfNCl monolayer have a strong response to ultraviolet light. The mechanical properties, electronic structure, electric transport and optoelectronic properties of a recently predicted wide bandgap semiconductor β -HfNCl monolayer are systematically studied by means of first-principles calculations. β -HfNCl monolayer is isotropic in mechanical properties, whose calculated Young's modulus, shear modulus, and layer modulus of β -HfNCl monolayer are 128.9–129.2, 44.28, and 119.46 N m−1, respectively. An appropriate tensile strain (i.e., beyond 3 %) can induce a transition from indirect bandgap to direct bandgap. In addition, we construct several conceptual nanodevice structures based on β -HfNCl monolayer, such as pn- junction diodes, pin- junction field-effect transistors (FETs) and phototransistors. The electronic transport results reveal that the pn- junction diodes have obvious rectification effect and strong electric anisotropy. Their rectification ratios and electric anisotropy ratio (η) can reach up to 106 and 3.69, respectively. The FETs have an obvious field-effect behavior with a slightly lower rectification ratio (1 0 5). Moreover, we investigate the photoelectric response of the phototransistors of β -HfNCl monolayer under the illumination of light. They have a strong response to the light whose energy is larger than the violet light, indicating that the β -HfNCl monolayer can be a platform to detect the ultraviolet light. These findings provide crucial insights into the potential applications of β -HfNCl monolayer in electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]