2D Bi2O2Te Semiconductor with Single-Crystal Native Oxide Layer

Following logic in the silicon semiconductor industry, the existence of native oxide and suitable fabrication technology is essential for 2D semiconductors in planar integronics, which are surface-sensitive to typical coating technologies. To date, very few types of integronics are found to possess this feature. Herein, the 2D Bi₂O₂Te developed recently is reported to possess large-area synthesis and controllable thermal oxidation behavior toward single-crystal native oxides. This shows that surface-adsorbed oxygen atoms are inclined to penetrate across [Bi₂O₂]_n²ⁿ⁺ layers and bond with the underlying [Te]_n²ⁿ⁻ at elevated temperatures, transforming directly into [TeO₄]_n²ⁿ⁻ with the basic architecture remaining stable. The oxide can be adjusted to form in an accurate layer-by-layer manner with a low-stress sharp interface. The native oxide Bi₂TeO₆ layer (bandgap of ≈2.9 eV) exhibits visible-light transparency and is compatible with wet-chemical selective etching technology. These advances demonstrate the potential of Bi₂O₂Te in planar-integrated functional nanoelectronics such as tunnel junction devices, field-effect transistors, and memristors.     

Nanoscale Selective Passivation of Electrodes Contacting a 2D Semiconductor

2D semiconducting materials have become the central component of various nanoelectronic devices and sensors. For sensors operating in liquid, it is crucial to efficiently block the electron transfer that occurs between the electrodes contacting the 2D material and the interfering redox species. This reduces current leakages and preserves a good signal‐to‐noise ratio. Here, a simple electrochemical method is presented for passivating the electrodes contacting a monolayer of MoS₂, a representative of transition metal dichalcogenide semiconductors. The method is based on blocking the electrode surface by a thin and compact layer of electronically nonconductive poly(phenylene oxide), PPO, formed by electrochemical polymerization of phenol. Since the phenol polymerization occurs in the potential window where MoS₂ is electrochemically inactive, the PPO deposition is area‐selective, limited to the electrode surface. The deposited PPO film is characterized by electrochemical, X‐ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy techniques. The applicability of this method is demonstrated by coating the electrodes of a MoS₂‐based field‐effect transistor coupled with a nanopore. The highly selective deposition, the simple approach, and the compatibility with MoS₂ makes this method a good strategy for efficient insulation of micro‐ and nanoelectrodes contacting 2D semiconductor‐based devices.     

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.     

Multiple Magnetic Phases in Van Der Waals Mn-Doped SnS2 Semiconductor

2D van der Waals magnetic semiconductors have emerged along with the possibilities of achieving an efficient gate tunability and a proximity effect with a high magnetic anisotropy compared with 3D counterparts. Little explored are multiple magnetic phases with a single crystallographic phase. Herein, the multiple magnetic phases in a Mn-doped SnS₂ single crystal with different doping concentrations using a one-step self-flux method are reported. Two ferromagnetic phases with a canted spin direction exist regardless of the Mn-doping concentration at up to 5 at%. Antiferromagnetism coexists with the ferromagnetic order and strengthens at high Mn-doping concentrations. A magnetoresistance measurement conducted on a 2 at% Mn-SnS₂ flake exhibits a positive-to-negative crossover with a value of as high as 50% and clear anisotropy, confirming the presence of ferromagnetic order in the material. By revealing multiple magnetic phases in Mn-doped SnS₂, the study broadens the scope of state-of-the-art research on layered magnetic semiconductors.     

A Quaternary van der Waals Ferromagnetic Semiconductor AgVP2Se6

The recent realization of 2D magnetism in van der Waals (vdWs) magnets holds promise for future information technology. However, the vdWs semiconducting ferromagnets, which remain rare, are especially important in developing 2D magnetic devices with new functionalities due to the possibility of simultaneous control of the carrier charge and spin. Metal thiophosphate (MTP), a multifunctional vdWs material system that combines the sought‐after properties of complex oxides, is a promising vdWs magnet system. Here, single crystals of a novel vdWs ferromagnetic semiconductor MTP AgVP₂Se₆ with a room‐temperature resistivity of 1 Ω m are successfully synthesized. Due to the nature of vdWs bonding along the c‐axis, the magnetic properties of the few‐layer AgVP₂Se₆ with different thicknesses are characterized on the exfoliated samples. The AgVP₂Se₆ flakes exhibit significant thickness‐dependent magnetic properties, and a rectangular hysteresis loop with a large coercive field of 750 Oe at 2 K and an undiminished Curie temperature of 19 K are observed in the 6.7 nm AgVP₂Se₆ flake. The discovered vdWs ferromagnet AgVP₂Se₆ with semiconducting behavior will provide alternative platforms for exploring 2D magnetism and potential applications in spintronic devices.     

Q2D半导体电子和空穴统计

用半导体统计方法导出准二维半导体自由载流子面密度的数学表达式 ,并给出面密度与体密度之间关系式。采用二维半导体自由载流子面密度表示式和范德堡 -霍尔实验测量在衬底 Ga As上 MBE生长的 Q2 D的样品 Ga Sb和 In As1-x Sbx ( x≈ 0 .2 2 )禁带宽度 Eg,获得满意结果。     

High-Throughput Screening Assisted Discovery of a Stable Layered Anti-Ferromagnetic Semiconductor: CdFeP2Se6

Recent advances in 2D magnetism have heightened interest in layered magnetic materials due to their potential for spintronics. In particular, layered semiconducting antiferromagnets exhibit intriguing low-dimensional semiconducting behavior with both charge and spin as carrier controls. However, synthesis of these compounds is challenging and remains rare. Here, first-principles based high-throughput search is conducted to screen potentially stable mixed metal phosphorous trichalcogenides (MM^′P₂X₆, where M and M^′ are transition metals and X is a chalcogenide) that have a wide range of tunable bandgaps and interesting magnetic properties. Among the potential candidates, a stable semiconducting layered magnetic material, CdFeP₂Se₆, that exhibits a short-range antiferromagnetic order at T_N = 21 K with an indirect bandgap of 2.23 eV is successfully synthesized . This work suggests that high-throughput screening assisted synthesis can be an effective method for layered magnetic materials discovery.     

Exciton Formation Dynamics and Band-Like Free Charge-Carrier Transport in 2D Metal Halide Perovskite Semiconductors

Metal halide perovskite (MHP) semiconductors have driven a revolution in optoelectronic technologies over the last decade, in particular for high-efficiency photovoltaic applications. Low-dimensional MHPs presenting electronic confinement have promising additional prospects in light emission and quantum technologies. However, the optimisation of such applications requires a comprehensive understanding of the nature of charge carriers and their transport mechanisms. This study employs a combination of ultrafast optical and terahertz spectroscopy to investigate phonon energies, charge-carrier mobilities, and exciton formation in 2D (PEA)₂PbI₄ and (BA)₂PbI₄ (where PEA is phenylethylammonium and BA is butylammonium). Temperature-dependent measurements of free charge-carrier mobilities reveal band transport in these strongly confined semiconductors, with surprisingly high in-plane mobilities. Enhanced charge-phonon coupling is shown to reduce charge-carrier mobilities in (BA)₂PbI₄ with respect to (PEA)₂PbI₄. Exciton and free charge-carrier dynamics are disentangled by simultaneous monitoring of transient absorption and THz photoconductivity. A sustained free charge-carrier population is observed, surpassing the Saha equation predictions even at low temperature. These findings provide new insights into the temperature-dependent interplay of exciton and free-carrier populations in 2D MHPs. Furthermore, such sustained free charge-carrier population and high mobilities demonstrate the potential of these semiconductors for applications such as solar cells, transistors, and electrically driven light sources.     

Discovery of Ultrasmall Polar Merons and Rich Topological Phase Transitions: Defects Make 2D Lead Chalcogenides Flexible Topological Materials

Atomic-scale polar topological configurations, such as skyrmions and merons, have garnered enormous interest due to their rich emergent physical phenomena and promising applications in next-generation electronics. Despite recent progress in the exploration of 2D ferroelectrics, isolated polar topological structures in 2D lattices have not yet been explored. Here, an original design principle is proposed to remove the point group limit for polar structures while achieving atomic-scale polar topological structures in non-ferroelectric monolayers caused by defects in 2D materials. The first-principles calculations show that an isolated polar meron with a diameter < 3.0 nm is generated in the deficient lead chalcogenide monolayer, and its formation is attributed to the synergic effects of vacancy-induced radial atomic displacements and symmetry reduction in 2D materials. The emergent polar meron can transform to rich topological configurations under external stimuli or by manipulation of the defect concentrations. Furthermore, this strategy of atomic-scale symmetry breaking via point defect engineering can be applied to a wide variety of 2D materials to induce polar topological structures. This work generalizes the polar topology from perovskite oxides to 2D materials, facilitating exciting opportunities to create high-density topological configurations that enable the exploration of meron/skyrmion-based functional nanodevices.     

基于二维半导体材料光电器件的研究进展

近年来,二维半导体材料因其独特的晶体结构和优良的电子、光电特性吸引了众多科研人员的关注。利用这些材料作为有源沟道,制备出了许多新颖的器件结构,性能较传统器件有很大的提升。在各种器件应用中,基于二维材料的光电探测器由于能够实现红外及太赫兹波段的光探测,得到了最为广泛的研究。综述了近年来二维材料在光电器件领域的应用,介绍了光电探测器的主要参数,从电极制备、异质结构筑、量子点和分子掺杂、表面等离激元耦合以及界面屏蔽5方面介绍了目前在二维材料中调控光电性能的方法,对已有方法进行了总结,并且对未来的发展进行了讨论。     

大功率半导体激光器二维阵列模块特性分析

根据固体激光器抽运的技术要求,设计了一种具有水冷装置的大功率半导体激光器二维阵列模块,并对半导体激光器热沉和致冷系统的热流进行了分析。在不同占空比下,对该模块进行了测试与分析。该模块的中心波长为810 nm,光谱半峰全宽(FWHM)为2.5 nm,工作电流为110 A(200μs,10%占空比),循环水温为15℃时输出峰值功率为280 W。结果表明,该封装结构在占空比小于5%时器件工作特性良好,在10%占空比下也可正常工作。利用该模块可以组合成多种几何结构、功率更高的半导体激光器组件。     

Ohmic Contact in 2D Semiconductors via the Formation of a Benzyl Viologen Interlayer

The fabrication of a polymeric Ohmic contact interlayer between a metal and a 2D material using solution‐processed benzyl viologen (BV) is reported here. Predoping of the polymer alters the contact surface to obtain electron‐doped materials with ultrahigh work functions that significantly enhance the current density across the contact and reduce the contact resistance and Schottky barrier height. The fabrication of solution‐processed polymeric contacts for the preparation of high mobility MoS₂, WSe₂, MoTe₂, and BP (black phosphorous) FETs with significantly lowered contact resistance is demonstrated. Ohmic contacts are achieved and produce 3‐, 700‐, 3000‐, and 17‐fold increases in electron mobilities, respectively, when the bottom gate voltage is 10 V compared to those respective materials alone. Ambipolar and p‐type 2D material based FETs could, therefore, be transformed into n‐type FETs. Most importantly, the devices exhibit excellent stability in both ambient and vacuum.     

Ferroelectric Control of Polarity of the Spin-polarized Current in Van Der Waals Multiferroic Heterostructures

Ferroelectric (FE) control of magnetism at nanoscale, for instance, FE control of the polarity of spin-polarized current is crucial for technological advances in magnetoelectric and spintronic applications. However, this fascinating functionality has not been reported in nanoscale systems yet. Herein, a new class of FE/A-type antiferromagnetic heterobilayer/FE van der Waals (vdW) multiferroic structures is found, in which the FE control of polarity of spin-polarized current is found possible. Take Sc₂CO₂/CrSiTe₃/CrGeTe₃/Sc₂CO₂ heterostructure as a successful example. First-principles calculations reveal that its polarity of half-metallicity can be switched by flipping the FE polarization orientation. Meanwhile, device transport simulation shows that its up/down spin current transmission ratio is as large as 0.1 × 10³ at $\overrightarrow{\mathrm{P}}\uparrow \uparrow$ Sc₂CO₂ configuration and is only 2.6 × 10⁻³ at $\overrightarrow{\mathrm{P}}\downarrow \downarrow$ Sc₂CO₂ configuration in the vdW multiferroic heterostructures. Essentially, it stems from the reversible FE switch of the internal electric field across the CrSiTe₃/CrGeTe₃ heterobilayer and the FE control of the interfacial effect between Sc₂CO₂ and Cr(Si/Ge)Te₃ layers. This work opens a direction for constructing low-energy-dissipation, non-volatile, and high-sensitive spintronic devices such as spin field-effect transistors.     

D2D技术在LTE-A系统中的应用

Device-to-Device（D2D）是一种在LTE-A系统中通过重用小区内宏蜂窝用户的资源来实现端到端通信的新型技术。本文从实际应用的角度出发,首先对D2D技术的原理和应用进行了分析,然后讨论D2D技术应用于LTE-A系统中的优缺点,接着通过仿真验证了D2D技术在LTE-A系统中的优势。最后阐述了D2D技术在LTE-A系统中应用可研究的方向及技术展望。     

Periodical Ripening for MOCVD Growth of Large 2D Transition Metal Dichalcogenide Domains

2D semiconductors, especially 2D transition metal dichalcogenides (TMDCs), have attracted ever-growing attention toward extending Moore's law beyond silicon. Metal–organic chemical vapor deposition (MOCVD) has been widely considered as a scalable technique to achieve wafer-scale TMDC films for applications. However, current MOCVD process usually suffers from small domain size with only hundreds of nanometers, in which dense grain boundary defects degrade the crystalline quality of the films. Here, a periodical varying-temperature ripening (PVTR) process is demonstrated to grow wafer-scale high crystalline TMDC films by MOCVD. It is found that the high-temperature ripening significantly reduces the nucleation density and therefore enables single-crystal domain size over 20 µm. In this process, no additives or etchants are involved, which facilitates low impurity concentration in the grown films. Atom-resolved electron microscopy imaging, variable temperature photoluminescence (PL) spectroscopy, and electrical transport results further confirm comparable crystalline quality to those observed in mechanically exfoliated TMDC films. The research provides a scalable route to produce high-quality 2D semiconducting films for applications in electronics and optoelectronics.     

Hollow Spherical Nanoshell Arrays of 2D Layered Semiconductor for High‐Performance Photodetector Device

Well‐defined hollow spherical nanoshell arrays of 2D transitional metal dichalcogenide (TMDC) nanomaterials for MoSe₂ and MoS₂ are grown via chemical vapor deposition technique for the first time. The hollow sphere arrays display the uniform dimensions of ≈450 nm with the shell thickness of ≈10 nm. The unique hollow sphere architecture with increased active surface area is forecasted to supply more efficient route to improve light‐harvesting efficiency through repeated light reflection and scattering inside the hollow structure without decay of response and recovery speed, because exceptional “SP–SP” junction barriers conducting mechanism can facilitate carriers tunneling and transport during the electron transfer procedure within the present particular structure. The MoSe₂ hollow sphere photodetector exhibits an outstanding responsivity (8.9 A W^?1), which is tenfold higher than that for MoSe₂ compact film (0.9 A W^?1), fast response and recovery speed, and good durability under illumination wavelength of 365 nm. Meanwhile, MoSe₂ hollow sphere arrays on flexible polyethylene terephthalate substrates reveal excellent bending stability. Therefore, this research indicates that unique hollow sphere architecture of 2D TMDC materials will be an anticipated avenue for efficient photodetector devices with far‐ranging capability.     

Nonvolatile Electrical Control and Heterointerface‐Induced Half‐Metallicity of 2D Ferromagnets

Electrical control of atom‐thick van der Waals (vdW) ferromagnets is a key toward future magnetoelectric nanodevices; however, state‐of‐the‐art control approaches are volatile. In this work, introducing ferroelectric switching as an aided layer is demonstrated to be an effective approach toward achieving nonvolatile electrical control of 2D ferromagnets. For example, when a ferromagnetic monolayer CrI₃ and ferroelectric MXene Sc₂CO₂ come together into multiferroic heterostructures, CrI₃ is controlled by polarized states P↑ and P↓ of Sc₂CO₂. P↑ Sc₂CO₂ does not change the semiconducting nature of CrI₃, but surprisingly P↓ Sc₂CO₂ makes CrI₃ half‐metallic. Nonvolatility of the electrical switching between two oppositely ferroelectric polarized states, therefore, indirectly enables nonvolatile electrical control of CrI₃ between ferromagnetic semiconductor and half‐metal. The heterointerface‐induced half‐metallicity in CrI₃ is intrinsic without resorting to any chemical functionalization or external physical modification, which is rather beneficial to the practical application. This work paves the way for nonvolatile electrical control of 2D vdW ferromagnets and applications of CrI₃ in half‐metal‐based nanospintronics.     

基于MAXWELL2D静磁场分析的特种电机教学

特种电机应用越来越广泛,已成为“电机学”教学的重要内容,其结构和磁场分布不同于传统同步电机,是“电机学”教学的难点之一。本文以永磁电机为例,探讨了MAXWELL2D建模实现电机旋转结构动画显示的方法,并利用MAXWELL2D对永磁电机进行静磁场有限元分析,直观呈现电机内磁场分布特点,便于学生理解和接受特种电机的结构和原理。本文方法对于其他特种电机的教学具有参考价值。     

Surface Regulation through Dipolar Molecule Boosting the Efficiency of Mixed 2D/3D Perovskite Solar Cell to 24%

Mixed 2D/3D perovskite solar cells (PSCs) show promising performances in efficiency and long-term stability. The functional groups terminated on a large organic molecule used to construct 2D capping layer play a key role in the chemical interaction mechanism and thus influence the device performance. In this study, 4-(trifluoromethyl) benzamidine hydrochloride (TFPhFACl) is adopted to construct 2D capping layer atop 3D perovskite. It is found that there are two mechanisms synergistically contributing to the increase of efficiency: 1) The TFPhFA⁺ cations form a dipole layer promoting the interfacial charge transport. 2) The suppressed nonradiative recombination of perovskite through the coordination of TFPhFA⁺ cations with Pb–I octahedron, as well as the recrystallization of 3D perovskite induced by Cl^- ions. As a result, the PSC delivers an efficiency of 24.0% with improved open-circuit voltage (V_OC) of 1.16 V, short-circuit current density (J_SC) of 25.42 mA cm^-2, and fill factor of 81.26%. The device shows no decrease in efficiency after 1500 h stored in the air indicating the good stability. The utilization of TFPhFACl not only provides a facile way to optimize the interfacial problems, but also gives a new perspective for rational design of large spacer molecule for constructing efficient 2D/3D PSCs.     

LTE与D2D异构网络的应用场景分析

文章首先介绍了LTE/D2D异构网络的发展背景。针对目前研究所涉及到的应用场景的多样性与差异性,我们对其进行了归纳分析。通过对LTE/D2D异构网络应用场景的分析,可以看出LTE/D2D异构网络具有极其广泛的前景,并且能有效节约信道资源、提高网络容量。