A space monocrystalline silicon（c-Si） solar cell under low-energy（〈 1 MeV） electron irradiation was investigated using noncontact photocarrier radiometry（PCR）. Monte Carlo simulation（MCS） was employed to char...A space monocrystalline silicon（c-Si） solar cell under low-energy（〈 1 MeV） electron irradiation was investigated using noncontact photocarrier radiometry（PCR）. Monte Carlo simulation（MCS） was employed to characterize the effect of different energy electron irradiation on the c-Si solar cell. The carrier transport parameters（carrier lifetime, diffusion coefficient, and surface recombination velocities） were obtained by best fitting the experimental results with a theoretical one-dimensional two-layer PCR model. The results showed that the increase of the irradiation electron energy caused a large reduction of the carrier lifetime and diffusion length. Furthermore, the rear surface recombination velocity of the Si：p base of the solar cell at the irradiation electron energy of 1 Me V was dramatically enhanced due to 1 MeV electron passing through the whole cell. Short-circuit current（I sc） degradation evaluated by PCR was in good agreement with that obtained by electrical measurement.展开更多
An experimental study on the photocarrier radiometry signals of As^＋ ion implanted silicon wafers before and after rapid thermal annealing is performed. The dependences of photocarrier radiometry amplitude on ion imp...An experimental study on the photocarrier radiometry signals of As^＋ ion implanted silicon wafers before and after rapid thermal annealing is performed. The dependences of photocarrier radiometry amplitude on ion implantation dose （1×10^11-1×10^16/cm^2）, implantation energy （20-140 keV） and subsequent isochronical annealing temperature （500- 1100℃ are investigated. The results show that photocarrier radiometry signals are greatly enhanced for implanted samples annealed at high temperature, especially for those with a high implantation dose. The reduced surface recombination rate resulting from a high built-in electric field generated by annealing-activated impurities in the pn junction is believed to be responsible for the photocarrier radiometry signal enhancement. Photocarrier radiometry is contactless and can therefore be used as an effective in-line tool for the thermal annealing process monitoring of the ion-implanted wafers in semiconductor industries.展开更多
In the present paper,a new image processing method for photocarrierspeckle fringe is proposed.A simple and fast filter is designed for different kinds of specklefringe with certain direction to eliminate the speckle e...In the present paper,a new image processing method for photocarrierspeckle fringe is proposed.A simple and fast filter is designed for different kinds of specklefringe with certain direction to eliminate the speckle effect.Fringe multiplication is carriedout with personal computer.The procedure of photocarrier speckle image collecting,pro-cessing,calculating and verifying is described with a practical example.展开更多
This paper presents the principle of phase modulation of the optical wave,that is using a dense fringe family to modulate another fringe pattern,and its applicationin fringe multiplication.It is of universal significa...This paper presents the principle of phase modulation of the optical wave,that is using a dense fringe family to modulate another fringe pattern,and its applicationin fringe multiplication.It is of universal significance in optically experimental mechanics.展开更多
A combined frequency-swept and quasi-time-domain photocarrier radiometry （PCR） technique was developed to characterize thermally annealed silicon wafers with B＋, P＋, and As＋ ion implantation at doses ranging from...A combined frequency-swept and quasi-time-domain photocarrier radiometry （PCR） technique was developed to characterize thermally annealed silicon wafers with B＋, P＋, and As＋ ion implantation at doses ranging from 1 ×1011 cm-2 to 1 ×1016 cm-2. The implantation dose dependence of the PCR amplitude, the frequency dependencies of the PCR amplitude and phase, as well as the quasi-time-domain PCR waveforms were simultaneously employed to analyze all the ion-implanted silicon samples. The dependence of the effective lifetime on the implantation dose has been investigated and shown to be related to the trap density and the lifetime extracted from the transient PCR signals.展开更多
Graphene hosts intriguing photocarrier dynamics such as negative transient terahertz(THz) photoconductivity, high electron temperature, benefiting from the unique linear Dirac dispersion. In this work, the pressure ef...Graphene hosts intriguing photocarrier dynamics such as negative transient terahertz(THz) photoconductivity, high electron temperature, benefiting from the unique linear Dirac dispersion. In this work, the pressure effects of photocarrier dynamics of graphene have been investigated using in situ time-resolved THz spectroscopy in combination with diamond anvil cell exceeding 9 GPa. We find that the negative THz conductivity maintains in our studied pressure range both for monolayer and bilayer graphene. In particular, the amplitude of THz photoconductivity in monolayer graphene manifests an extraordinary dropping with pressure, compared with that from the counterparts such as bulk silicon and bilayer graphene.Concomitantly, the time constant is reduced with increasing pressure, highlighting the pressure-induced hot carrier cooling.The pressure dependence of photocarrier dynamics in monolayer graphene is likely related with the enhancement of the interfacial coupling between diamond surface and sample, allowing for the activity of new electron–phonon scattering. Our work is expected to provide an impetus for the studies of high-pressure THz spectroscopy of two-dimensional materials.展开更多
The measuring of the depth profile and electrical activity of implantation impurity in the top nanometer range of silicon encounters various difficulties and limitations, though it is known to be critical in fabricati...The measuring of the depth profile and electrical activity of implantation impurity in the top nanometer range of silicon encounters various difficulties and limitations, though it is known to be critical in fabrication of silicon complementary metal–oxide–semiconductor(CMOS) devices. In the present work, SRIM program and photocarrier radiometry(PCR)are employed to monitor the boron implantation in industrial-grade silicon in an ultra-low implantation energy range from 0.5 keV to 5 keV. The differential PCR technique, which is improved by greatly shortening the measurement time through the simplification of reference sample, is used to investigate the effects of implantation energy on the frequency behavior of the PCR signal for ultra-shallow junction. The transport parameters and thickness of shallow junction, extracted via multi-parameter fitting the dependence of differential PCR signal on modulation frequency to the corresponding theoretical model, well explain the energy dependence of PCR signal and further quantitatively characterize the recovery degree of structure damage induced by ion implantation and the electrical activation degree of impurities. The monitoring of nmlevel thickness and electronic properties exhibits high sensitivity and apparent monotonicity over the industrially relevant implantation energy range. The depth profiles of implantation boron in silicon with the typical electrical damage threshold(YED) of 5.3×10^(15)cm^(-3) are evaluated by the SRIM program, and the determined thickness values are consistent well with those extracted by the differential PCR. It is demonstrated that the SRIM and the PCR are both effective tools to characterize ultra-low energy ion implantation in silicon.展开更多
We report on the high-field magnetotransport of KTaO_(3)single crystals,which are a promising candidate for study in the extreme quantum limit.By photocarrier doping with 360 nm light,we observe a significant positive...We report on the high-field magnetotransport of KTaO_(3)single crystals,which are a promising candidate for study in the extreme quantum limit.By photocarrier doping with 360 nm light,we observe a significant positive,non-saturating,and linear magnetoresistance at low temperatures accompanied by a decreasing Hall coefficient.When cooling down to 10 K,the magnetoresistance value of KTaO_(3)(100)reaches~433%at a magnetic field of 12 T.Such behavior can be attributed to all the electrons occupying only the lowest Landau level in the extreme quantum limit.Light inhomogeneity may also contribute to large linear magnetoresistance.These results provide insights into novel magnetic devices based on complex materials and add a new family of materials with positive magnetoresistance.展开更多
Element doping can break the crystal symmetry and realize the topological phase transition in quantum materials,which enables the precise modulation of energy band structure and microscopic dynamical interaction.Herei...Element doping can break the crystal symmetry and realize the topological phase transition in quantum materials,which enables the precise modulation of energy band structure and microscopic dynamical interaction.Herein,we have studied the ultrafast photocarrier dynamics in Zn-doped 3D topological Dirac semimetal Cd_(3)As_(2)utilizing time-resolved optical pump-terahertz probe spectroscopy.Comparing to the pristine Cd_(3)As_(2),we found that the relaxation time of the lightly doped alloy is slightly shorter,while that of the heavily doped alloy exhibits a significant prolongation.Pump-fluence-and temperature-dependent transient terahertz spectroscopy indicated that in pristine and lightly doped samples within nontrivial semimetal phase,the photocarrier dynamics are dominated by the cooling of Dirac fermions.In heavily doped alloy,however,the observed longer relaxation process can be attributed to interband electron-hole recombination,which is a result of doping-induced transition into a trivial semiconductor phase.Our investigation highlights that Zn-doping is an effective and flexible scheme for engineering the electronic structure and transient carrier relaxation dynamics in Cd_(3)As_(2),and offers a control knob for functional switching between diverse optoelectronic devices within the realm of practical applications.展开更多
Owing to its anisotropic optical and electrical properties,rhenium diselenide(ReSe2)has garnered considerable attention recently as a candidate material for polarization-sensitive photodetectors.However,the direct and...Owing to its anisotropic optical and electrical properties,rhenium diselenide(ReSe2)has garnered considerable attention recently as a candidate material for polarization-sensitive photodetectors.However,the direct and controllable synthesis of large-sized ReSe2 with a uniform thickness is still a great challenge.Herein,we have refined the synthesis method to obtain uniform monolayer ReSe2 flakes with a size of up to^106μm on sapphire via an ambient-pressure chemical vapor deposition technique using Na promoter from sodium chloride.Interestingly,optical pump-probe spectroscopy revealed a fast switching from saturable absorption(SA)to absorption enhancement(AE)in subpicosecond time scale,followed by a slower decay induced by exciton recombination.Furthermore,both AE and SA signals exhibited clear angular dependence with a periodicity of 180°,which reflected the dichroism in nonlinear absorption dynamics.In addition,the photocarrier dynamics including free-carrier transport and subpicosecond relaxation due to exciton formation or surface trapping was probed using time resolved terahertz spectroscopy.We believe that our study serves as a reference for atomically controlled synthesis of large-sized ReSe2 and provides useful insights on its optoelectronic properties for novel device applications.展开更多
A comprehensive understanding of excited-state dynamics of semiconductor quantum dots or nanomaterials at the atomic or molecular level is of scientific importance.Pure inorganic(or non-covalently protected)seimicondu...A comprehensive understanding of excited-state dynamics of semiconductor quantum dots or nanomaterials at the atomic or molecular level is of scientific importance.Pure inorganic(or non-covalently protected)seimiconductor molecular nanoclusters with atomically precise structure are contributive to establish accurate correlation of excited-state dynamics with their composition/structure,however,the related studies are almost blank because of unresolved solvent dispersion issue.Herein,we designedly created the largest discrete chalcogenide seimiconductor molecular nanoclusters(denoted P2-CuMSnS,M=In or/and Ga)with great dispersibility,and revealed an interesting intracluster“core–shell”charge transfer relaxation dynamics.A systematic red shift in absorption spectra with the gradual substitution of In by Ga was experimentally and computationally investigated,and femtosecond transient absorption measurements further manifested there were three ultrafast processes in excited-state dynamics of P2 nanoclusters with the corresponding amplitudes directed by composition variation.Current results hold the great promise of the solution-processible applications of semiconductor-NC-based quantum dots and facilitate the development of atomically precise nano-chemistry.展开更多
Over the past decade, graphitic carbon nitride(g-C_(3)N_(4)) has emerged as a universal photocatalyst toward various sustainable carbo-neutral technologies. Despite solar applications discrepancy, g-C_(3)N_(4) is stil...Over the past decade, graphitic carbon nitride(g-C_(3)N_(4)) has emerged as a universal photocatalyst toward various sustainable carbo-neutral technologies. Despite solar applications discrepancy, g-C_(3)N_(4) is still confronted with a general fatal issue of insufficient supply of thermodynamically active photocarriers due to its inferior solar harvesting ability and sluggish charge transfer dynamics. Fortunately, this could be significantly alleviated by the “all-in-one” defect engineering strategy, which enables a simultaneous amelioration of both textural uniqueness and intrinsic electronic band structures. To this end, we have summarized an unprecedently comprehensive discussion on defect controls including the vacancy/non-metallic dopant creation with optimized electronic band structure and electronic density, metallic doping with ultraactive coordinated environment(M–N_(x), M–C_(2)N_(2), M–O bonding), functional group grafting with optimized band structure, and promoted crystallinity with extended conjugation π system with weakened interlayered van der Waals interaction. Among them, the defect states induced by various defect types such as N vacancy, P/S/halogen dopants, and cyano group in boosting solar harvesting and accelerating photocarrier transfer have also been emphasized. More importantly, the shallow defect traps identified by femtosecond transient absorption spectra(fs-TAS) have also been highlighted. It is believed that this review would pave the way for future readers with a unique insight into a more precise defective g-C_(3)N_(4) “customization”, motivating more profound thinking and flourishing research outputs on g-C_(3)N_(4)-based photocatalysis.展开更多
A dominant intrinsic luminescence band, which is due to the surface potential barriers of crystalline grains, and an edge doublet, which arises as an LO-phonon repetition of the e-h band, has been revealed in the low-...A dominant intrinsic luminescence band, which is due to the surface potential barriers of crystalline grains, and an edge doublet, which arises as an LO-phonon repetition of the e-h band, has been revealed in the low-temperature photoluminescence spectra of fine-grained obliquely deposited films. Doping film with In impurity leads to quenching of the doublet band, while further thermal treatment causes activation of the intrinsic band, the half-width and the blue shift of the red edge of which correlates with the maximum value of anomalously high photovoltage generated by the film.展开更多
The advancement of terahertz technology in recent years and its applications in various fields lead to an urgent need for functional terahertz components,among which a terahertz switch is one example of the most impor...The advancement of terahertz technology in recent years and its applications in various fields lead to an urgent need for functional terahertz components,among which a terahertz switch is one example of the most importance because it provides an effective interface between terahertz signals and information in another physical quantity.To date many types of terahertz switches have been investigated mainly in the form of metamaterials made from metallic structures and optically-active medium.However,these reported terahertz switches usually suffer from an inferior performance,e.g.,requiring a high pump laser power density due to a low quality factor of the metallic metamaterial resonances.In this paper,we report and numerically investigate a symmetry-broken silicon disk based terahertz resonator array which exhibits one resonance with ultrahigh quality factor for normal incidence of the terahertz radiations.This resonance,which can never be excited for regular circular Si disks,can help to realize a superior terahertz switch with which only an ultra-low optical pump power density is required to modify the free carrier concentration in Si and its refractive index in the terahertz band.Our findings demonstrate that to realize a high terahertz transmittance change from 0 to above 50%,the required optical pump power density is more than 3 orders of magnitude smaller than that required for a split-ring resonator(SRR)based terahertz switch reported in the literature.展开更多
CONSPECTUS:Electrochemical water purification and pollutant monitoring have garnered significant attention due to their unique technical advantages.The pursuit of safe,efficient,and economically viable catalysts remai...CONSPECTUS:Electrochemical water purification and pollutant monitoring have garnered significant attention due to their unique technical advantages.The pursuit of safe,efficient,and economically viable catalysts remains a critical priority.Titanium dioxide(TiO_(2)),a prototypical transition-metal oxide with substantial industrial importance,is widely recognized as a benchmark catalyst for photochemical reactions.However,its practical application is limited by restricted light absorption and rapid photocarrier recombination.Recently,TiO_(2) has emerged as a promising candidate in electrochemical catalysis,particularly in the fields of energy and environmental science.Its atomic and electronic structures can be precisely engineered through advanced techniques such as nanoscale morphology control,polar-facet engineering,vip-metal doping,and structural-defect modulation.This review examines recent advancements in TiO_(2)-based electrochemical applications,with a focus on water purification and pollutant monitoring.In this Account,we present our efforts to harness facet-and defect-engineered TiO_(2) as electrochemical catalysts for water purification,addressing critical challenges such as low conductivity and poor reactivity.Initially,we demonstrate that facetengineered TiO_(2),specifically designed to expose the high-energy{001}polar facet,facilitates the dissociation of both pollutant and water molecules.This significantly lowers energy barriers and enhances anodic reactions through both direct and indirect pathways,thereby markedly improving water purification efficiency.Furthermore,the dual photochemical and electrochemical functionalities of a single{001}-tailored TiO_(2) electrode enable synergistic UV-light-assisted electrochemical catalysis under low bias conditions,achieving superior energy efficiency and resistance to electrode fouling.Next,we explore the catalytic potential of defect-engineered TiO_(2)(TiO_(2−x)),highlighting the role of titanium(Ti^(3+))and oxygen vacancies(O_(v))in boosting electrochemical water purification.Surface and subsurface defects,characterized by localized atomic disorder and structural distortions,serve as active sites that drive beneficial structural transformations,enriched electronic distribution,enhanced spin−spin correlations,and polaron hopping mechanisms,all of which contribute to improved cathodic reduction.To stabilize these reactive sites under anodic polarization,we propose a practical visible-light-assisted electrochemical catalysis strategy.This approach leverages mild non-band-gap excitation pathways mediated by defect sub-bands,providing enhanced stability and catalytic efficiency.Finally,we identify the challenges associated with the application of self-engineered TiO_(2) in electrochemical water purification and outline directions for future research.Our studies deepen the fundamental understanding of structure−catalysis relationships and exemplify a self-tailoring strategy to advance oxide catalysis without reliance on noble or toxic-metal cocatalysts.By elucidating catalytic mechanisms and adopting innovative synthesis techniques,our insights provide a foundation for designing advanced electrocatalysts.Self-engineered TiO_(2) holds the potential to establish a new paradigm in electrochemical catalysis,opening pathways for transformative solutions in environmental remediation.展开更多
Neuromorphic vision hardware,embedded with multiple functions,has recently emerged as a potent platform for machine vision.To realize memory in sensor functions,reconfigurable and non-volatile manipulation of photocar...Neuromorphic vision hardware,embedded with multiple functions,has recently emerged as a potent platform for machine vision.To realize memory in sensor functions,reconfigurable and non-volatile manipulation of photocarriers is highly desirable.However,previous technologies bear mechanism challenges,such as the ambiguous optoelectronic memory mechanism and high potential barrier,resulting in a limited response speed and a high operating voltage.Here,for the first time,we propose a critical band-to-band tunnelling(BTBT)based device that combines sensing,integration and memory functions.The nearly infinitesimal barrier facilitates the tunnelling process,resulting in a broadband application range(94o nm).Furthermore,the observation of dual negative differential resistance(NDR)points confirms that the critical BTBT of photocarriers contributes to the sub-microsecond photomemory speed.Since the photomemory speed,with no motion blur,is important for motion detection,the critical BTBT memory is expected to enable moving target tracking and recognition,underscoring its superiority in intelligentperception.展开更多
Van der Waals(vdW)heterostructures based on two-dimensional transitionmetal dichalcogenides have provided unprecedented opportunities for photovoltaic detectors owing to their strong light-matter interaction and ultra...Van der Waals(vdW)heterostructures based on two-dimensional transitionmetal dichalcogenides have provided unprecedented opportunities for photovoltaic detectors owing to their strong light-matter interaction and ultrafast interfacial charge transfer.Despite continued advancement,insufficient control of photocarrier behaviors still limits the external quantum efficiency(EQE)and operation speed of such detectors.Here,we propose a synergistic strategy of contact-configuration design and thickness-modulation to construct high-performance vdW photodiodes based on the typical type II heterostructure(MoS2/WSe2).Through integrating three contact architectures into one device to exclude other factors,we solid the superiority of designed 1L-MoS2/WSe2/graphene heterostructures incorporating efficient photocarrier collection and gate modulation.Together with leveraging the layer-numberdependent properties of WSe2,we observe the critical thickness of WSe2(11 layers)for the highest EQE,which verifies the thickness-dependent competition between photocarrier generation,dissociation,and collection.Finally,we demonstrate the synergistic-engineered vdW heterostructure can trigger record-high EQE(61%)and manifest ultrafast photoresponse(4.1μs)at the atomically thin limit(8 nm).The proposed strategy enables architecture-design and thickness-engineering to unlock the potential to realize high-performance optoelectronic devices.展开更多
Spectroscopic ellipsometry (SE), photocarrier radiometry (PCR) and photoluminescence (PL) techniques were employed to measure the ultra-shallow junction (USJ) wafers. These USJ wafers were prepared by As+ ion implanta...Spectroscopic ellipsometry (SE), photocarrier radiometry (PCR) and photoluminescence (PL) techniques were employed to measure the ultra-shallow junction (USJ) wafers. These USJ wafers were prepared by As+ ion implantation at energies of 0.5-5 keV, at a dose of 1×1015 As+ /cm 2 and spike annealing. Experimentally the damaged layer of the as-implanted wafer and the recrystallization and activation of the post-annealed wafer were evaluated by SE in the spectral range from 0.27 to 20 m. The PCR amplitude decreased monotonically with the increasing implantation energy. The experimental results also showed that the PCR amplitudes of post-annealed USJ wafers were greatly enhanced, compared to the non-implanted and non-annealed substrate wafer. The PL measurements showed the enhanced PCR signals were attributed to the band-edge emissions of silicon. For explaining the PL enhancement, the electronic transport properties of USJ wafers were extracted via multi-wavelength PCR experiment and fitting. The fitted results showed the decreasing surface recombination velocity and the decreasing diffusion coefficient of the implanted layer contributed to the PCR signal enhancement with the decreasing implantation energy. SE, PCR and PL were proven to be non-destructive metrology tools for characterizing ultra-shallow junctions.展开更多
Two-photon fluorescence (TPF) ellipsoid formed by a focused femtosecond laser into luminescent media serves as a fundamental pixel for TPF spatiotemporal imaging. Visualizing spatiotemporal evolution of the TPF ellips...Two-photon fluorescence (TPF) ellipsoid formed by a focused femtosecond laser into luminescent media serves as a fundamental pixel for TPF spatiotemporal imaging. Visualizing spatiotemporal evolution of the TPF ellipsoid itself in a selected luminescent medium is important for correctly reconstructing and interpreting spatiotemporal information of imaged targets. Here, we report a new spatiotemporal sectioning technique with a luminescent CsPbBr_(3) nanosheet and visualize the spatiotemporal evolution of TPF ellipsoid along the axial direction. Time-resolved axial lengths of TPF ellipsoids turn out to broaden nonlinearly with a turning point at about 600 ps. By comparison experiments, observed phenomena are attributed to photocarrier trapping and TPF photon recycling processes within CsPbBr_(3) nanosheets. The spatiotemporal sectioning technique is expected to be widely applicable, which will ignite a plethora of investigations and applications utilizing TPF ellipsoid.展开更多
文摘A space monocrystalline silicon（c-Si） solar cell under low-energy（〈 1 MeV） electron irradiation was investigated using noncontact photocarrier radiometry（PCR）. Monte Carlo simulation（MCS） was employed to characterize the effect of different energy electron irradiation on the c-Si solar cell. The carrier transport parameters（carrier lifetime, diffusion coefficient, and surface recombination velocities） were obtained by best fitting the experimental results with a theoretical one-dimensional two-layer PCR model. The results showed that the increase of the irradiation electron energy caused a large reduction of the carrier lifetime and diffusion length. Furthermore, the rear surface recombination velocity of the Si：p base of the solar cell at the irradiation electron energy of 1 Me V was dramatically enhanced due to 1 MeV electron passing through the whole cell. Short-circuit current（I sc） degradation evaluated by PCR was in good agreement with that obtained by electrical measurement.
基金supported by the National Natural Science Foundation of China (Grant No.60676058)
文摘An experimental study on the photocarrier radiometry signals of As^＋ ion implanted silicon wafers before and after rapid thermal annealing is performed. The dependences of photocarrier radiometry amplitude on ion implantation dose （1×10^11-1×10^16/cm^2）, implantation energy （20-140 keV） and subsequent isochronical annealing temperature （500- 1100℃ are investigated. The results show that photocarrier radiometry signals are greatly enhanced for implanted samples annealed at high temperature, especially for those with a high implantation dose. The reduced surface recombination rate resulting from a high built-in electric field generated by annealing-activated impurities in the pn junction is believed to be responsible for the photocarrier radiometry signal enhancement. Photocarrier radiometry is contactless and can therefore be used as an effective in-line tool for the thermal annealing process monitoring of the ion-implanted wafers in semiconductor industries.
文摘In the present paper,a new image processing method for photocarrierspeckle fringe is proposed.A simple and fast filter is designed for different kinds of specklefringe with certain direction to eliminate the speckle effect.Fringe multiplication is carriedout with personal computer.The procedure of photocarrier speckle image collecting,pro-cessing,calculating and verifying is described with a practical example.
文摘This paper presents the principle of phase modulation of the optical wave,that is using a dense fringe family to modulate another fringe pattern,and its applicationin fringe multiplication.It is of universal significance in optically experimental mechanics.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60676058 and 61076090)
文摘A combined frequency-swept and quasi-time-domain photocarrier radiometry （PCR） technique was developed to characterize thermally annealed silicon wafers with B＋, P＋, and As＋ ion implantation at doses ranging from 1 ×1011 cm-2 to 1 ×1016 cm-2. The implantation dose dependence of the PCR amplitude, the frequency dependencies of the PCR amplitude and phase, as well as the quasi-time-domain PCR waveforms were simultaneously employed to analyze all the ion-implanted silicon samples. The dependence of the effective lifetime on the implantation dose has been investigated and shown to be related to the trap density and the lifetime extracted from the transient PCR signals.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12174398,12004387,51727806,51672279,11874361,and 12204484)the Innovation Program of Chinese Academy of Sciences(Grant No.CXJJ-19B08)+2 种基金the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2021446)the HFIPS Director’s Fund of Chinese Academy of Sciences(Grant Nos.2021YZGH03 and YZJJKX202202)China Postdoctoral Science Foundation(Grant No.2021M703255)。
文摘Graphene hosts intriguing photocarrier dynamics such as negative transient terahertz(THz) photoconductivity, high electron temperature, benefiting from the unique linear Dirac dispersion. In this work, the pressure effects of photocarrier dynamics of graphene have been investigated using in situ time-resolved THz spectroscopy in combination with diamond anvil cell exceeding 9 GPa. We find that the negative THz conductivity maintains in our studied pressure range both for monolayer and bilayer graphene. In particular, the amplitude of THz photoconductivity in monolayer graphene manifests an extraordinary dropping with pressure, compared with that from the counterparts such as bulk silicon and bilayer graphene.Concomitantly, the time constant is reduced with increasing pressure, highlighting the pressure-induced hot carrier cooling.The pressure dependence of photocarrier dynamics in monolayer graphene is likely related with the enhancement of the interfacial coupling between diamond surface and sample, allowing for the activity of new electron–phonon scattering. Our work is expected to provide an impetus for the studies of high-pressure THz spectroscopy of two-dimensional materials.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61771103, 61704023, and 61601092)。
文摘The measuring of the depth profile and electrical activity of implantation impurity in the top nanometer range of silicon encounters various difficulties and limitations, though it is known to be critical in fabrication of silicon complementary metal–oxide–semiconductor(CMOS) devices. In the present work, SRIM program and photocarrier radiometry(PCR)are employed to monitor the boron implantation in industrial-grade silicon in an ultra-low implantation energy range from 0.5 keV to 5 keV. The differential PCR technique, which is improved by greatly shortening the measurement time through the simplification of reference sample, is used to investigate the effects of implantation energy on the frequency behavior of the PCR signal for ultra-shallow junction. The transport parameters and thickness of shallow junction, extracted via multi-parameter fitting the dependence of differential PCR signal on modulation frequency to the corresponding theoretical model, well explain the energy dependence of PCR signal and further quantitatively characterize the recovery degree of structure damage induced by ion implantation and the electrical activation degree of impurities. The monitoring of nmlevel thickness and electronic properties exhibits high sensitivity and apparent monotonicity over the industrially relevant implantation energy range. The depth profiles of implantation boron in silicon with the typical electrical damage threshold(YED) of 5.3×10^(15)cm^(-3) are evaluated by the SRIM program, and the determined thickness values are consistent well with those extracted by the differential PCR. It is demonstrated that the SRIM and the PCR are both effective tools to characterize ultra-low energy ion implantation in silicon.
基金Project supported by the National Natural Science Foundation of China(Grant No.51572222)Key Research Project of the Natural Science Foundation of Shaanxi Province,China(Grant Nos.2021JZ-08 and 2020JM-088)+1 种基金the Natural Science Basic Research Plan in Shaanxi Province of China(Grant No.2021JM-041)the Fundamental Research Funds for the Central Universities(Grant Nos.3102017OQD074 and 310201911cx044)
文摘We report on the high-field magnetotransport of KTaO_(3)single crystals,which are a promising candidate for study in the extreme quantum limit.By photocarrier doping with 360 nm light,we observe a significant positive,non-saturating,and linear magnetoresistance at low temperatures accompanied by a decreasing Hall coefficient.When cooling down to 10 K,the magnetoresistance value of KTaO_(3)(100)reaches~433%at a magnetic field of 12 T.Such behavior can be attributed to all the electrons occupying only the lowest Landau level in the extreme quantum limit.Light inhomogeneity may also contribute to large linear magnetoresistance.These results provide insights into novel magnetic devices based on complex materials and add a new family of materials with positive magnetoresistance.
基金National Natural Science Foundation of China(12404396,92150101,52225207,52350001)China Postdoctoral Science Foundation(2024M751932)Postdoctoral Fellowship Program of CPSF(GZB20240418)。
文摘Element doping can break the crystal symmetry and realize the topological phase transition in quantum materials,which enables the precise modulation of energy band structure and microscopic dynamical interaction.Herein,we have studied the ultrafast photocarrier dynamics in Zn-doped 3D topological Dirac semimetal Cd_(3)As_(2)utilizing time-resolved optical pump-terahertz probe spectroscopy.Comparing to the pristine Cd_(3)As_(2),we found that the relaxation time of the lightly doped alloy is slightly shorter,while that of the heavily doped alloy exhibits a significant prolongation.Pump-fluence-and temperature-dependent transient terahertz spectroscopy indicated that in pristine and lightly doped samples within nontrivial semimetal phase,the photocarrier dynamics are dominated by the cooling of Dirac fermions.In heavily doped alloy,however,the observed longer relaxation process can be attributed to interband electron-hole recombination,which is a result of doping-induced transition into a trivial semiconductor phase.Our investigation highlights that Zn-doping is an effective and flexible scheme for engineering the electronic structure and transient carrier relaxation dynamics in Cd_(3)As_(2),and offers a control knob for functional switching between diverse optoelectronic devices within the realm of practical applications.
基金The work was supported by the National Key Research and Development Program of China(Nos.2018YFA0703700,2017YFA0304600,and 2017YFA0205700)the National Natural Science Foundation of China(Nos.51861135201,21473001,11774354,11674329,and 51727806)+4 种基金Beijing Natural Science Foundation(No.2192021)the Project funded by China Postdoctoral Science Foundation(No.2018M640023)Chinese Academy of Science(No.YZJJ201705)Open Research Fund Program of the State Key Laboratory of Low-dimensional Quantum Physics(No.KF201907)Start-up Funding of Peking University.
文摘Owing to its anisotropic optical and electrical properties,rhenium diselenide(ReSe2)has garnered considerable attention recently as a candidate material for polarization-sensitive photodetectors.However,the direct and controllable synthesis of large-sized ReSe2 with a uniform thickness is still a great challenge.Herein,we have refined the synthesis method to obtain uniform monolayer ReSe2 flakes with a size of up to^106μm on sapphire via an ambient-pressure chemical vapor deposition technique using Na promoter from sodium chloride.Interestingly,optical pump-probe spectroscopy revealed a fast switching from saturable absorption(SA)to absorption enhancement(AE)in subpicosecond time scale,followed by a slower decay induced by exciton recombination.Furthermore,both AE and SA signals exhibited clear angular dependence with a periodicity of 180°,which reflected the dichroism in nonlinear absorption dynamics.In addition,the photocarrier dynamics including free-carrier transport and subpicosecond relaxation due to exciton formation or surface trapping was probed using time resolved terahertz spectroscopy.We believe that our study serves as a reference for atomically controlled synthesis of large-sized ReSe2 and provides useful insights on its optoelectronic properties for novel device applications.
基金The authors acknowledge financial support from the National Natural Science Foundation of China(Nos.21671142,11804084 and 21875150)the Jiangsu Province Natural Science Fund for Distinguished Young Scholars(No.BK20160006)+2 种基金the 111 Project(No.D20015)the Project of Scientific and Technologic Infrastructure of Suzhou(No.SZS201905)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).The authors also thank Dr.D.C.Ma at Analytical and Testing Center,Sichuan University for technical help with the Material Studio calculations.
文摘A comprehensive understanding of excited-state dynamics of semiconductor quantum dots or nanomaterials at the atomic or molecular level is of scientific importance.Pure inorganic(or non-covalently protected)seimiconductor molecular nanoclusters with atomically precise structure are contributive to establish accurate correlation of excited-state dynamics with their composition/structure,however,the related studies are almost blank because of unresolved solvent dispersion issue.Herein,we designedly created the largest discrete chalcogenide seimiconductor molecular nanoclusters(denoted P2-CuMSnS,M=In or/and Ga)with great dispersibility,and revealed an interesting intracluster“core–shell”charge transfer relaxation dynamics.A systematic red shift in absorption spectra with the gradual substitution of In by Ga was experimentally and computationally investigated,and femtosecond transient absorption measurements further manifested there were three ultrafast processes in excited-state dynamics of P2 nanoclusters with the corresponding amplitudes directed by composition variation.Current results hold the great promise of the solution-processible applications of semiconductor-NC-based quantum dots and facilitate the development of atomically precise nano-chemistry.
基金the support of the Australia Research Council (ARC) through the Discovery Project (DP230101040)the Natural Science Foundation of Shandong Province (ZR2022QB139, No. ZR2020KF025)+3 种基金the Starting Research Fund (Grant No. 20210122) from the Ludong Universitythe Natural Science Foundation of China (12274190) from the Ludong Universitythe support of the Shandong Youth Innovation Team Introduction and Education Programthe Special Fund for Taishan Scholars Project (No. tsqn202211186) in Shandong Province。
文摘Over the past decade, graphitic carbon nitride(g-C_(3)N_(4)) has emerged as a universal photocatalyst toward various sustainable carbo-neutral technologies. Despite solar applications discrepancy, g-C_(3)N_(4) is still confronted with a general fatal issue of insufficient supply of thermodynamically active photocarriers due to its inferior solar harvesting ability and sluggish charge transfer dynamics. Fortunately, this could be significantly alleviated by the “all-in-one” defect engineering strategy, which enables a simultaneous amelioration of both textural uniqueness and intrinsic electronic band structures. To this end, we have summarized an unprecedently comprehensive discussion on defect controls including the vacancy/non-metallic dopant creation with optimized electronic band structure and electronic density, metallic doping with ultraactive coordinated environment(M–N_(x), M–C_(2)N_(2), M–O bonding), functional group grafting with optimized band structure, and promoted crystallinity with extended conjugation π system with weakened interlayered van der Waals interaction. Among them, the defect states induced by various defect types such as N vacancy, P/S/halogen dopants, and cyano group in boosting solar harvesting and accelerating photocarrier transfer have also been emphasized. More importantly, the shallow defect traps identified by femtosecond transient absorption spectra(fs-TAS) have also been highlighted. It is believed that this review would pave the way for future readers with a unique insight into a more precise defective g-C_(3)N_(4) “customization”, motivating more profound thinking and flourishing research outputs on g-C_(3)N_(4)-based photocatalysis.
文摘A dominant intrinsic luminescence band, which is due to the surface potential barriers of crystalline grains, and an edge doublet, which arises as an LO-phonon repetition of the e-h band, has been revealed in the low-temperature photoluminescence spectra of fine-grained obliquely deposited films. Doping film with In impurity leads to quenching of the doublet band, while further thermal treatment causes activation of the intrinsic band, the half-width and the blue shift of the red edge of which correlates with the maximum value of anomalously high photovoltage generated by the film.
基金the National Key R&D Program of China(Grant No.2017YFA0701005)the National Natural Science Foundation of China(Grant Nos.11974221,91750201,61927813,and 61775229)+1 种基金Z.Han also acknowledges the support from the Taishan Scholar Program of Shandong Province,China(Grant No.tsqn201909079)Zhejiang Provincial Natural Science Foundation of China(Grant No.LY15F050008).
文摘The advancement of terahertz technology in recent years and its applications in various fields lead to an urgent need for functional terahertz components,among which a terahertz switch is one example of the most importance because it provides an effective interface between terahertz signals and information in another physical quantity.To date many types of terahertz switches have been investigated mainly in the form of metamaterials made from metallic structures and optically-active medium.However,these reported terahertz switches usually suffer from an inferior performance,e.g.,requiring a high pump laser power density due to a low quality factor of the metallic metamaterial resonances.In this paper,we report and numerically investigate a symmetry-broken silicon disk based terahertz resonator array which exhibits one resonance with ultrahigh quality factor for normal incidence of the terahertz radiations.This resonance,which can never be excited for regular circular Si disks,can help to realize a superior terahertz switch with which only an ultra-low optical pump power density is required to modify the free carrier concentration in Si and its refractive index in the terahertz band.Our findings demonstrate that to realize a high terahertz transmittance change from 0 to above 50%,the required optical pump power density is more than 3 orders of magnitude smaller than that required for a split-ring resonator(SRR)based terahertz switch reported in the literature.
基金supported by the National Natural Science Foundation of China(22076036,52192684 and 52027815)the Anhui Provincial Natural Science Foundation(2308085J23 and 2408055US005).
文摘CONSPECTUS:Electrochemical water purification and pollutant monitoring have garnered significant attention due to their unique technical advantages.The pursuit of safe,efficient,and economically viable catalysts remains a critical priority.Titanium dioxide(TiO_(2)),a prototypical transition-metal oxide with substantial industrial importance,is widely recognized as a benchmark catalyst for photochemical reactions.However,its practical application is limited by restricted light absorption and rapid photocarrier recombination.Recently,TiO_(2) has emerged as a promising candidate in electrochemical catalysis,particularly in the fields of energy and environmental science.Its atomic and electronic structures can be precisely engineered through advanced techniques such as nanoscale morphology control,polar-facet engineering,vip-metal doping,and structural-defect modulation.This review examines recent advancements in TiO_(2)-based electrochemical applications,with a focus on water purification and pollutant monitoring.In this Account,we present our efforts to harness facet-and defect-engineered TiO_(2) as electrochemical catalysts for water purification,addressing critical challenges such as low conductivity and poor reactivity.Initially,we demonstrate that facetengineered TiO_(2),specifically designed to expose the high-energy{001}polar facet,facilitates the dissociation of both pollutant and water molecules.This significantly lowers energy barriers and enhances anodic reactions through both direct and indirect pathways,thereby markedly improving water purification efficiency.Furthermore,the dual photochemical and electrochemical functionalities of a single{001}-tailored TiO_(2) electrode enable synergistic UV-light-assisted electrochemical catalysis under low bias conditions,achieving superior energy efficiency and resistance to electrode fouling.Next,we explore the catalytic potential of defect-engineered TiO_(2)(TiO_(2−x)),highlighting the role of titanium(Ti^(3+))and oxygen vacancies(O_(v))in boosting electrochemical water purification.Surface and subsurface defects,characterized by localized atomic disorder and structural distortions,serve as active sites that drive beneficial structural transformations,enriched electronic distribution,enhanced spin−spin correlations,and polaron hopping mechanisms,all of which contribute to improved cathodic reduction.To stabilize these reactive sites under anodic polarization,we propose a practical visible-light-assisted electrochemical catalysis strategy.This approach leverages mild non-band-gap excitation pathways mediated by defect sub-bands,providing enhanced stability and catalytic efficiency.Finally,we identify the challenges associated with the application of self-engineered TiO_(2) in electrochemical water purification and outline directions for future research.Our studies deepen the fundamental understanding of structure−catalysis relationships and exemplify a self-tailoring strategy to advance oxide catalysis without reliance on noble or toxic-metal cocatalysts.By elucidating catalytic mechanisms and adopting innovative synthesis techniques,our insights provide a foundation for designing advanced electrocatalysts.Self-engineered TiO_(2) holds the potential to establish a new paradigm in electrochemical catalysis,opening pathways for transformative solutions in environmental remediation.
基金supported by the National Key Research and Development Programme of China(Grant No.2023YFB3611400)National Natural Science Foundation of China(Grant Nos.62327812,62361136587,62422410,62205360 and 62304229)+2 种基金Shanghai Rising-Star Programme(Grant No.24QA2711000)CAS Project for Young Scientists in Basic Research(Grant No.YSBR-113)CAS Pioneer Hundred Talents Program.
文摘Neuromorphic vision hardware,embedded with multiple functions,has recently emerged as a potent platform for machine vision.To realize memory in sensor functions,reconfigurable and non-volatile manipulation of photocarriers is highly desirable.However,previous technologies bear mechanism challenges,such as the ambiguous optoelectronic memory mechanism and high potential barrier,resulting in a limited response speed and a high operating voltage.Here,for the first time,we propose a critical band-to-band tunnelling(BTBT)based device that combines sensing,integration and memory functions.The nearly infinitesimal barrier facilitates the tunnelling process,resulting in a broadband application range(94o nm).Furthermore,the observation of dual negative differential resistance(NDR)points confirms that the critical BTBT of photocarriers contributes to the sub-microsecond photomemory speed.Since the photomemory speed,with no motion blur,is important for motion detection,the critical BTBT memory is expected to enable moving target tracking and recognition,underscoring its superiority in intelligentperception.
基金National Natural Science Foundation of China,Grant/Award Numbers:51672026,51972022,51991340,51991342,92163205the Fundamental Research Funds for the Central Universities,Grant/Award Number:FRF-TP-19-025A3+2 种基金the National Key Research and Development Program of China,Grant/Award Number:2018YFA0703503the Natural Science Foundation of Beijing Municipality,Grant/Award Number:Z180011the Overseas Expertise Introduction Projects for Discipline Innovation,Grant/Award Number:B14003。
文摘Van der Waals(vdW)heterostructures based on two-dimensional transitionmetal dichalcogenides have provided unprecedented opportunities for photovoltaic detectors owing to their strong light-matter interaction and ultrafast interfacial charge transfer.Despite continued advancement,insufficient control of photocarrier behaviors still limits the external quantum efficiency(EQE)and operation speed of such detectors.Here,we propose a synergistic strategy of contact-configuration design and thickness-modulation to construct high-performance vdW photodiodes based on the typical type II heterostructure(MoS2/WSe2).Through integrating three contact architectures into one device to exclude other factors,we solid the superiority of designed 1L-MoS2/WSe2/graphene heterostructures incorporating efficient photocarrier collection and gate modulation.Together with leveraging the layer-numberdependent properties of WSe2,we observe the critical thickness of WSe2(11 layers)for the highest EQE,which verifies the thickness-dependent competition between photocarrier generation,dissociation,and collection.Finally,we demonstrate the synergistic-engineered vdW heterostructure can trigger record-high EQE(61%)and manifest ultrafast photoresponse(4.1μs)at the atomically thin limit(8 nm).The proposed strategy enables architecture-design and thickness-engineering to unlock the potential to realize high-performance optoelectronic devices.
基金supported by the National Natural Science Foundation of China(Grant Nos. 61076090 and 60676058)
文摘Spectroscopic ellipsometry (SE), photocarrier radiometry (PCR) and photoluminescence (PL) techniques were employed to measure the ultra-shallow junction (USJ) wafers. These USJ wafers were prepared by As+ ion implantation at energies of 0.5-5 keV, at a dose of 1×1015 As+ /cm 2 and spike annealing. Experimentally the damaged layer of the as-implanted wafer and the recrystallization and activation of the post-annealed wafer were evaluated by SE in the spectral range from 0.27 to 20 m. The PCR amplitude decreased monotonically with the increasing implantation energy. The experimental results also showed that the PCR amplitudes of post-annealed USJ wafers were greatly enhanced, compared to the non-implanted and non-annealed substrate wafer. The PL measurements showed the enhanced PCR signals were attributed to the band-edge emissions of silicon. For explaining the PL enhancement, the electronic transport properties of USJ wafers were extracted via multi-wavelength PCR experiment and fitting. The fitted results showed the decreasing surface recombination velocity and the decreasing diffusion coefficient of the implanted layer contributed to the PCR signal enhancement with the decreasing implantation energy. SE, PCR and PL were proven to be non-destructive metrology tools for characterizing ultra-shallow junctions.
基金This work was supported by the National Natural Science Foundation of China(Nos.11734005,61704024,61821002,and 62075041)Natural Science Foundation of Jiangsu Province(No.BK20170696)+1 种基金the National Key Research and Development Program of China(Nos.2017YFA0700500 and 2018YFA0209101)Fundamental Research Funds for the Central Universities(No.2242021K10009).Q.N.C.gratefully acknowledges the support of Southeast University through Zhishan Young Scholar Fund.The authors thank Dr.Haibo Ding for insightful discussion.
文摘Two-photon fluorescence (TPF) ellipsoid formed by a focused femtosecond laser into luminescent media serves as a fundamental pixel for TPF spatiotemporal imaging. Visualizing spatiotemporal evolution of the TPF ellipsoid itself in a selected luminescent medium is important for correctly reconstructing and interpreting spatiotemporal information of imaged targets. Here, we report a new spatiotemporal sectioning technique with a luminescent CsPbBr_(3) nanosheet and visualize the spatiotemporal evolution of TPF ellipsoid along the axial direction. Time-resolved axial lengths of TPF ellipsoids turn out to broaden nonlinearly with a turning point at about 600 ps. By comparison experiments, observed phenomena are attributed to photocarrier trapping and TPF photon recycling processes within CsPbBr_(3) nanosheets. The spatiotemporal sectioning technique is expected to be widely applicable, which will ignite a plethora of investigations and applications utilizing TPF ellipsoid.
