二维铁电半导体层级处理模块设计及低功耗高性能人工视觉系统应用

The growth of data and Internet of Things challenges traditional hardware,which encounters efficiency and power issues owing to separate functional units for sensors,memory,and computation.In this study,we designed an a-phase indium selenide(a-In_(2)Se_(3))transistor,which is a two-dimensional ferroelectric semiconductor as the channel material,to create artificial optic-neural and electro-neural synapses,enabling cutting-edge processing-in-sensor(PIS)and computing-in-memory(CIM)functionalities.As an optic-neural synapse for low-level sensory processing,the a-In_(2)Se_(3)transistor exhibits a high photoresponsivity(2855 A/W)and detectivity(2.91×10^(14)Jones),facilitating efficient feature extraction.For high-level processing tasks as an electro-neural synapse,it offers a fast program/erase speed of 40 ns/50μs and ultralow energy consumption of 0.37 aJ/spike.An AI vision system using a-In_(2)Se_(3)transistors has been demonstrated.It achieved an impressive recognition accuracy of 92.63%within 12 epochs owing to the synergistic combination of the PIS and CIM functionalities.This study demonstrates the potential of the a-In_(2)Se_(3)transistor in future vision hardware,enhancing processing,power efficiency,and AI applications.

Controlled growth of vertically stacked In_(2)Se_(3)/WSe_(2) heterostructures for ultrahigh responsivity photodetector

Transition metal dichalcogenides(TMDCs)are promising candidates for future optoelectronic devices accounting for their high carrier mobility and excellent quantum efficiency.However,the limited light absorption efficiency in atomically thin layers significantly hinders photocarrier generation,thereby impairing the optoelectronic performance and hindering practical applications.Herein,we successfully synthesized In_(2)Se_(3)/WSe_(2) heterostructures through a typical two-step chemical vapor deposition(CVD)method.The In_(2)Se_(3) nanosheet with strong light absorption capability,serving as the light absorption layer,was integrated with the monolayer WSe_(2),enhancing the photosensitivity of WSe_(2) significantly.Upon laser irradiation with a wavelength of 520 nm,the In_(2)Se_(3)/WSe_(2) heterostructure device shows an ultrahigh photoresponsivity with a value as high as 2333.5 A/W and a remarkable detectivity reaching up to 6.7×10^(12) Jones,which is the highest among almost the reported TMDCs-based heterostructures grown via CVD even some fabricated by mechanical exfoliation(ME).Combing the advantages of CVD method such as large scale,high yield,and clean interface,the In_(2)Se_(3)/WSe_(2) heterostructures would provide a novel path for future high-performance optoelectronic device.

超薄金属性MoO_(2)纳米片可控合成及其范德华接触应用研究

在二维半导体与金属材料间引入范德华接触构建器件被认为是解决二维材料电接触问题的有效途径之一.然而,迄今为止,研究主要集中在半导体材料合成与改性上,而对金属材料的制备和性能的研究较少.在这项工作中,我们报道了利用化学气相沉积法可控合成厚度从3.5到10^(6)nm的层状MoO_(2)金属二维纳米片.利用X射线衍射、扫描隧道显微镜和透射电子显微镜对制备的MoO_(2)纳米片进行了系统表征,结果表明,制备的MoO_(2)为单斜晶型、晶质质量高、稳定性好.电学表征表明,MoO_(2)具有优良的导电性能,其导电率超过10^(6)S m^(-1),可与石墨烯和某些金属相媲美.此外,我们还通过引入MoO_(2)薄片作为范德华接触材料,探索了其在MoS_(2)场效应晶体管中的接触应用.所获得的MoS_(2)场效应晶体管表现出低肖特基势垒(36 m e V)和高载流子迁移率(210 cm^(2)V^(-1)s^(-1),10 K).这项工作为金属二维材料的可控制备和应用提供了新思路,并有望促进二维材料电子器件的发展.

Epitaxial van der Waals contacts for low schottky barrier MoS_(2) field effect transistors

Small contact resistance and low Schottky barrier height(SBH)are the keys to energy-efficient electronics and optoelectronics.Two-dimensional(2D)semiconductors-based field effect transistors(FETs),holding great promise for next-generation information circuits,still suffer from poor contact quality at the metal–semiconductor junction interface,which severely hinders their further applications.Here,a novel contact strategy is proposed,where Bi_(2)Te_(3)nanosheets with high conductivity were in-situ epitaxially grown on MoS_(2)as van der Waals contacts,which can effectively avoid the damage to MoS_(2)caused during the device manufacturing process,leading to a high-performance MoS_(2)FET.Moreover,the small work function difference between Bi_(2)Te_(3)and MoS_(2)(Bi_(2)Te_(3):4.31 eV,MoS_(2):4.37 eV,measured by Kelvin probe force microscopy(KPFM)),enables small band bending and Ohmic contact at the junction interface.Electrical characterizations indicate that the MoS_(2)FET device with Bi_(2)Te_(3)contacts possesses a high current on/off ratio(5×107),large effective carrier mobility(90 cm^(2)/(V·s)),and low flat-band SBH(60 meV),which is favorable as compared with MoS_(2)FET with traditional Cr/Au electrodes contacts,and superior to the vast majority of the reported chemical vapor deposition(CVD)MoS_(2)-based FET device.The demonstration of epitaxial van der Waals Bi_(2)Te_(3)contacts will facilitate the application of 2D MoS_(2)nanosheet in next-generation low-power consumption electronics and optoelectronics.

Vapor growth of V‑doped MoS_(2)monolayers with enhanced B‑exciton emission and broad spectral response

Dynamically engineering the optical and electrical properties in two-dimensional(2D)materials is of great signifcance for designing the related functions and applications.The introduction of foreign-atoms has previously been proven to be a feasible way to tune the band structure and related properties of 3D materials;however,this approach still remains to be explored in 2D materials.Here,we systematically demonstrate the growth of vanadium-doped molybdenum disulfde(V-doped MoS_(2))monolayers via an alkali metal-assisted chemical vapor deposition method.Scanning transmission electron microscopy demonstrated that V atoms substituted the Mo atoms and became uniformly distributed in the MoS_(2)monolayers.This was also confrmed by Raman and X-ray photoelectron spectroscopy.Power-dependent photoluminescence spectra clearly revealed the enhanced B-exciton emission characteristics in the V-doped MoS_(2)monolayers(with low doping concentration).Most importantly,through temperature-dependent study,we observed efcient valley scattering of the B-exciton,greatly enhancing its emission intensity.Carrier transport experiments indicated that typical p-type conduction gradually arisen and was enhanced with increasing V composition in the V-doped MoS_(2),where a clear n-type behavior transited frst to ambipolar and then to lightly p-type charge carrier transport.In addition,visible to infrared wide-band photodetectors based on V-doped MoS_(2)monolayers(with low doping concentration)were demonstrated.The V-doped MoS_(2)monolayers with distinct B-exciton emission,enhanced p-type conduction and broad spectral response can provide new platforms for probing new physics and ofer novel materials for optoelectronic applications.

光驱动二维水平同质p-n结及其在光电互联电路中的应用

实现以光作为输入来控制器件行为的光驱动器件是现代光电互联电路研究的重点之一.本文基于二维材料体系,创新性地利用光栅极代替普通场效应晶体管中的栅极,利用光代替栅极电压作为输入,用以驱动器件从电阻状态转变为p-n二极管状态.在所制备的黑磷半光栅晶体管中,当无光照引入时,器件在电阻状态下工作,不具有整流;当引入光照后,由于半光栅极所产生的光生栅压效应,沟道层被定义于p-n二极管状态,表现出明显的整流行为和光伏特性.当撤掉光时,沟道层由二极管状态恢复至电阻状态,也进一步说明p-n结的形成依赖于光照的引入.也就是说,半光栅晶体管既可以利用光来形成p-n结,同时又可以把光转换为电,体现出"一体式"特点.该光控p-n结将会在新一代光电互联电路中找到一些新奇的应用.

Vapor growth of WSe2/WS2 heterostructures with stacking dependent optical properties

Two-dimensional(2D)vertically stacked heterostructures based on layered transition-metal dichalcogenides(MDCs)have remarkablepote ntial in future applications due to their rich in terlayer related properties,such as in terlayer excitons,tun able interlayer band alignments.However,the controlled growth of TMDC bilayer heterostructures with preferred stacking structure remains challenging.Here,we report atwo-step van der Waals epitaxial vapor growth of WSe2/WS2 vertically stacked bilayer heterostructures with controllable commensurate crystallographic alignments(so called AA and AB stacki ng),by controlling the deposition temperature.Moire patter ns were obtai ned in bothAA and AB stacked WSe2/WS2 heterostructures.The stacking configuration of the vertical heterostructures was verified by the secondharmonic generation signals.Photoluminescenee and Raman spectroscopy studies further confirm that the heterostructures with differentstacking configuration have obviously different optical properties,which is ascribed to the distinct in terlayer coupling and resonance excitation between the distinguishing AA and AB stacked heterostructures.The controlled growth of AA and AB stacked heterostructures could provide an importa nee platform not only for fun dame ntal researches but also for functional electronic and optoelectronic deviceapplications.

基于硫化镉-黑磷范德华异质结的超高响应光电二极管

近年来二维材料因其超薄的厚度及新颖的电、光及光电特性受到了广泛关注.此外,二维材料表面无悬挂键,这使得其可以直接通过范德华力相互结合形成范德华异质结,为构建具有优异性能的新型器件提供了新的机遇.本文采用范德华集成方法将n型硫化镉和p型黑磷垂直堆垛起来构筑了p-n结二极管.输运特性测试表明,该p-n结器件表现出高的整流比(8×103)和低的理想因子(1.5).同时,在光照下器件表现出超高的光响应度和比探测率,分别可达9.2×105A W-1和3.2×1013Jones,与目前所报道的二维异质结光电探测的最高水平相当.当器件工作于自驱动探测模式时,仍表现出极好的光探测性能,光响应度和响应速度分别可达0.27 A W-1和~10 ms.所制备的硫化镉/黑磷异质结器件将会在新一代纳米电子、光电子器件中扮演重要角色.

Interlayer exciton formation,relaxation,and transport in TMD van der Waals heterostructures

Van der Waals(vdW)heterostructures based on transition metal dichalcogenides(TMDs)generally possess a type-II band alignment that facilitates the formation of interlayer excitons between constituent monolayers.Manipulation of the interlayer excitons in TMD vdW heterostructures holds great promise for the development of excitonic integrated circuits that serve as the counterpart of electronic integrated circuits,which allows the photons and excitons to transform into each other and thus bridges optical communication and signal processing at the integrated circuit.As a consequence,numerous studies have been carried out to obtain deep insight into the physical properties of interlayer excitons,including revealing their ultrafast formation,long population recombination lifetimes,and intriguing spin-valley dynamics.These outstanding properties ensure interlayer excitons with good transport characteristics,and may pave the way for their potential applications in efficient excitonic devices based on TMD vdW heterostructures.At present,a systematic and comprehensive overview of interlayer exciton formation,relaxation,transport,and potential applications is still lacking.In this review,we give a comprehensive description and discussion of these frontier topics for interlayer excitons in TMD vdW heterostructures to provide valuable guidance for researchers in this field.

通过铟掺杂有效控制单层WS_(2)的发射和载流子极性

二维(2D)过渡金属硫族化合物(TMDs)的掺杂被认为是调控其光电特性的一种有效途径.但是TMDs材料在制备过程中会引入自身掺杂,使其可控掺杂仍具有较大的挑战.本文中我们通过含有钨(W)源和铟(In)源掺杂剂的化学气相沉积法(CVD)实现了不同铟掺杂浓度的单层WS2的可控制备.扫描透射电镜结果表明In原子成功取代了WS2晶体中的W原子.掺杂样品的发光特性受到了In掺杂浓度的明显调制,其发光强度随掺杂浓度呈现出先增强后衰减的趋势,最大增强倍数可达约35倍.这一现象主要归因于In掺杂后WS_(2)体系中激子与三激子的比例随掺杂浓度逐渐变化.基于In掺杂的WS_(2)场效应晶体管的电学特性表明,随着In掺杂浓度的增加,单层WS_(2)实现了从本征n型到双极性,最终到p型半导体的转变,表明掺杂样品的载流子极性也受到了掺杂浓度的有效调控.通过In掺杂可实现p型单层WS_(2)的成功制备,并且可对WS_(2)体系光学和电学特性进行双重调制,为实现2D材料光电特性的有效调控提供了一种潜在的可行方法.

Dual-channel type tunable field-effect transistors based on vertical bilayer WS2(1−x)Se2x/SnS2 heterostructures

Layered semiconductor heterostructures are essential elements in modern electronic and optoelectronic devices.Dynamically engineering the composition of these heterostructures may enable the flexible design of the properties of heterostructure-based electronics and optoelectronics as well as their optimization.Here,we report for the first time a two-step chemical vapor deposition approach for a series of WS2(1−x)Se2x/SnS2 vertical heterostructures with high-quality and large areas.The steady-state photoluminescence results exhibit an obvious composition-related quenching ratio,revealing a strong coherence between the band offset and the charge transfer efficiency at the junction interface.Based on the achieved heterostructures,dual-channel backgate field-effect transistors were successfully designed and exhibited typical composition-dependent transport behaviors,and pure n-type unipolar transistors to ambipolar transistors were realized in such systems.The direct vapor growth of these novel vertical WS2(1−x)Se2x/SnS2 heterostructures could offer an interesting system for probing new physical properties and provide a series of layered heterostructures for high-quality devices.

低亚阈值摆幅可重构场效应晶体管及高增益互补反相器

二维半导体材料由于具有超薄的厚度同时表现出优异的物理性能,被寄望突破传统半导体发展瓶颈,成为新一代集成电路的重要组成部分.目前基于二维材料的场效应晶体管分立器件被广泛研发,但受限于接触问题,大部分二维半导体晶体管所表现出的输运性能仍不理想.本文通过引入一个额外的接触栅极,对二维半导体接触区进行独立控制:通过对接触区静电掺杂浓度的调控,有效降低了器件的接触电阻,实现了器件在整个工作状态的欧姆接触,获得了近乎理想的输运性能;同时,作者还通过对接触区域载流子掺杂类型的有效控制实现了器件的可重构功能,利用控制栅电压的调控实现器件在n型FET和p型FET之间的灵活切换,并基于这一特性进一步构建了高增益互补反相器电路.本研究有望为新一代集成电路设计提供重要的原型器件,推动集成电路产业迅速发展.

Optical synaptic devices with ultra-low power consumption for neuromorphic computing

Brain-inspired neuromorphic computing,featured by parallel computing,is considered as one of the most energyefficient and time-saving architectures for massive data computing.However,photonic synapse,one of the key components,is still suffering high power consumption,potentially limiting its applications in artificial neural system.In this study,we present a BP/CdS heterostructure-based artificial photonic synapse with ultra-low power consumption.The device shows remarkable negative light response with maximum responsivity up to 4.1×10^(8)AW^(−1) at VD=0.5 V and light power intensity of 0.16μW cm^(−2)(1.78×10^(8)AW^(−1) on average),which further enables artificial synaptic applications with average power consumption as low as 4.78 fJ for each training process,representing the lowest among the reported results.Finally,a fully-connected optoelectronic neural network(FONN)is simulated with maximum image recognition accuracy up to 94.1%.This study provides new concept towards the designing of energy-efficient artificial photonic synapse and shows great potential in high-performance neuromorphic vision systems.

可激活抗癌光敏剂

光动力治疗(Photodynamic therapy,PDT)是利用光敏剂在光照下促使分子氧转为具有细胞毒性的活性氧,从而达到破坏靶细胞和靶组织效应的一种治疗手段。可激活光敏剂(Activatable photosensitizers,aPSs)是指事先屏蔽了光敏效应的光敏剂,只在特定因素下,如与肿瘤相关的特异性酶、酸性pH、核酸等的激活下,光敏剂转为激活状态,从而发挥诊断或者治疗的作用。可激活光敏剂由于具有更高的选择性而备受瞩目,成为医用光敏剂领域的研究前沿热点。本文将总结和分析近年来可激活抗癌光敏剂的研究现状和构效关系,以期为后续的相关研究提供参考。

Van der Waals epitaxial growth and optoelectronics of a vertical MoS_(2)/WSe_(2)p-n junction

Two-dimensional(2D)transition metal dichalcogenides(TMDs)have attracted extensive attention due to their unique electronic and optical properties.In particular,TMDs can be fexibly combined to form diverse vertical van der Waals(vdWs)heterostructures without the limitation of lattice matching,which creates vast opportunities for fundamental investigation of novel optoelectronic applications.Here,we report an atomically thin vertical p-n junction WSe_(2)/MoS_(2)produced by a chemical vapor deposition method.Transmission electron microscopy and steady-state photoluminescence experiments reveal its high quality and excellent optical properties.Back gate feld efect transistor(FET)constructed using this p-n junction exhibits bipolar behaviors and a mobility of 9 cm^(2)/(V·s).In addition,the photodetector based on MoS_(2)/WSe_(2)heterostructures displays outstanding optoelectronic properties(R=8 A/W,D^(*)=2.93×10^(11)Jones,on/of ratio of 10^(4)),which benefted from the built-in electric feld across the interface.The direct growth of TMDs p-n vertical heterostructures may ofer a novel platform for future optoelectronic applications.