The peculiar photoconduction in semi insulating GaAs photoconductive switch being triggered by 1064nm laser pulse is reported.The gap between two electrodes of the switch is 4mm.When it is triggered by laser pulse wi...The peculiar photoconduction in semi insulating GaAs photoconductive switch being triggered by 1064nm laser pulse is reported.The gap between two electrodes of the switch is 4mm.When it is triggered by laser pulse with energy of 0 8mJ and the pulse width of 5ns,and operated at biased electric field of 2 0 and 6 0kV/cm,both linear and nonlinear modes of the switch are observed respectively.Whereas the biased electric field adds to 9 5kV/cm,and the triggered laser is in range of 0 5～1 0mJ,the peculiar performed characteristic is observed:the switch gives a linear waveform firstly,and then after a delay time of about 20～250ns,it outputs a nonlinear waveform again.The physical mechanism of this specific phenomenon is associated with the anti site defects of semi insulating GaAs and two step single photon absorption.The delay time between linear waveform and nonlinear waveform is calculated,and the result matches the experiments.展开更多
Traditional Si-based photoconductive detectors face problems such as low response in the ultraviolet(UV)and infrared regions,high dark current,and low light absorption efficiency,which seriously limit their applicatio...Traditional Si-based photoconductive detectors face problems such as low response in the ultraviolet(UV)and infrared regions,high dark current,and low light absorption efficiency,which seriously limit their applications in the field of high-performance wide-spectrum detection.In this study,a self-powered broadband photodetector based on a Si/TiO_(2)heterojunction is proposed.The detector has a pyramidal structure.By constructing a pyramidal microstructure on the surface of silicon,the light capture and absorption efficiency is significantly improved,representing a breakthrough in response performance in the visible and near-infrared(NIR)bands.In order to further enhance the photoelectric response in the UV band,a TiO_(2)layer was coated on the surface of the silicon pyramid through a simple spin-coating method and annealing process.The introduction of TiO_(2)effectively broadened the spectral response range of the photoelectric detector and further improved the light absorption of the device.Meanwhile,due to the built-in electric field formed by the n-TiO_(2)/p-Si heterojunction,the dark current was effectively reduced,and the responsivity was improved.Experiments showed that the device exhibits high responsivity,high detectivity,and relatively low dark current in the range of 365-1305 nm.Under light at 780 nm,the device’s on-off ratio reached 2.7×10^(3);its specific detectivity,D^(*),was 3.9×10^(11)Jones;and its responsivity reached 0.174 A/W.In addition,this detector does not require the assistance of expensive equipment.Its preparation process is simple and inexpensive,and there is no need for an external power supply,which gives it broad application potential in wearable devices,environmental monitoring,communications,biosensing,and other fields.This study provides a brand-new strategy for the design of new wide-spectrum detectors.展开更多
In this work,we studied the persistent photoconductivity(PPC)spectra in single HgTe/CdHgTe quantum wells with different growth parameters and different types of dark conductivity.The studies were performed in a wide r...In this work,we studied the persistent photoconductivity(PPC)spectra in single HgTe/CdHgTe quantum wells with different growth parameters and different types of dark conductivity.The studies were performed in a wide radiation quantum energy range of 0.62–3.1 eV both at T=4.2 K and at T=77 K.Common features of the PPC spectra for all structures were revealed,and their relation to the presence of a CdTe cap layer in all structures and the appropriate cadmium fraction in the CdHgTe barrier layers was shown.One of the features was associated with the presence of a deep level in the CdTe layer.In addition,the oscillatory behavior of the PPC spectra in the region from 0.8–1.1 eV to 1.2–1.5 eV was observed.It is associated with the cascade emission of longitudinal optical phonons in CdHgTe barrier.展开更多
Bi_(2)YbO_(4)Cl with a fluorite layer structure belongs to the family of the bismuth rare-earth oxyhalides Bi_(2)REO_(4)X(X=Cl,B r,I).However,the synthesis and photoelectric properties of Bi_(2)YbO_(4)Cl have almost n...Bi_(2)YbO_(4)Cl with a fluorite layer structure belongs to the family of the bismuth rare-earth oxyhalides Bi_(2)REO_(4)X(X=Cl,B r,I).However,the synthesis and photoelectric properties of Bi_(2)YbO_(4)Cl have almost not been reported.In this work,Bi_(2)YbO_(4)Cl was synthesized using the solid-state method and the solvothermal method.Yb3+ions show a strong characteristic absorption peak at 980 nm,which was measured by ultraviolet-visible-near-infrared absorption spectra.The transient photoconductivity of Bi_(2)YbO_(4)Cl was obtained by time-resolved terahertz spectroscopy system under 400 and 800 nm laser excitations,respectively.The frequency-dependent transient photoconductivity analysis reveals the Drude-Smith behavior in Bi_(2)YbO_(4)Cl.Under photoexcitation,the hot charge carriers with a long relaxation lifetime and a carrier mobility of 48 cm^(2)/(V·s) are obtained.The synthesis of Bi_(2)YbO_(4)Cl is of great significance for the development of novel photocatalytic and photo harvesting materials with broad spectral response.展开更多
The utilization of processing capabilities within the detector holds significant promise in addressing energy consumption and latency challenges. Especially in the context of dynamic motion recognition tasks, where su...The utilization of processing capabilities within the detector holds significant promise in addressing energy consumption and latency challenges. Especially in the context of dynamic motion recognition tasks, where substantial data transfers are necessitated by the generation of extensive information and the need for frame-by-frame analysis. Herein, we present a novel approach for dynamic motion recognition, leveraging a spatial-temporal in-sensor computing system rooted in multiframe integration by employing photodetector. Our approach introduced a retinomorphic MoS_(2) photodetector device for motion detection and analysis. The device enables the generation of informative final states, nonlinearly embedding both past and present frames. Subsequent multiply-accumulate (MAC) calculations are efficiently performed as the classifier. When evaluating our devices for target detection and direction classification, we achieved an impressive recognition accuracy of 93.5%. By eliminating the need for frame-by-frame analysis, our system not only achieves high precision but also facilitates energy-efficient in-sensor computing.展开更多
Copolyfluorenes are of great interest due to their ability to form thin films with tunable optical and electrical properties.In this paper,copolymers of polyfluorene with electron withdrawing dicyanostilbene and dicya...Copolyfluorenes are of great interest due to their ability to form thin films with tunable optical and electrical properties.In this paper,copolymers of polyfluorene with electron withdrawing dicyanostilbene and dicyanophenanthrene moieties were synthesized;their thin films were characterized by electron spectroscopy,cyclic voltammetry,electrical,and photoelectrical measurements.The mobility of charge carriers in the copolymers was measured for the first time,with the acceptor components providing balanced electron and hole mobilities of the order of 10^(-6) cm^(2)·V^(-1)·s^(-1).Photodetectors based on the copolymer/PTCDI heterojunction exhibited the photoresponse band extended into the green region due to the absorption of PTCDI and an increased photocurrent in the UV-blue absorption band of the copolymer,which is related to the absorption of photoluminescent emission of the copolymers in PTCDI.The presented approach to improving the performance of a polymer-based photodetector is promising in organic optoelectronics.展开更多
Photoconductive semiconductor switch(PCSS)can be applied in pulsed high power systems and microwave techniques.However,reducing the damage and increasing the lifetime of silicon carbide(SiC)PCSS are still faced severe...Photoconductive semiconductor switch(PCSS)can be applied in pulsed high power systems and microwave techniques.However,reducing the damage and increasing the lifetime of silicon carbide(SiC)PCSS are still faced severe challenges.In this study,PCSSs with various structures were prepared on 4-inch diameter,500μm thick high-purity semi-insulating 4H-SiC substrates and their on-state resistance and damage mechanisms were investigated.It was found that the PCSS of an Au/TiW/Ni electrode system annealed at 950℃had a minimum on-state resistance of 6.0Ωat 1 kV bias voltage with a 532 nm and 170 mJ pulsed laser by backside illumination single trigger.The backside illumination single trigger could reduce on-state resistance and alleviate the damage of PCSS compared to the frontside trigger when the diameter of the laser spot was larger than the channel length of PCSS.For the 200 s trigger test by a 10 Hz laser,the black branch-like ablation on Au/TiW/Ni PCSS was mainly caused by thermal stress owing to hot carriers.Replacing metal Ni with boron gallium co-doped zinc oxide(BGZO)thin films annealed at 400℃,black branch-like ablation was alleviated while concentric arc damage was obvious at the anode.The major causes of concentric arc are both pulsed laser diffraction and thermal effect.展开更多
Covalent organic frameworks（COFs） as an emerging class of porous materials have achieved remarkable progress in recent years.Their high surface area,low mass densities,highly ordered periodic structures,and ease of ...Covalent organic frameworks（COFs） as an emerging class of porous materials have achieved remarkable progress in recent years.Their high surface area,low mass densities,highly ordered periodic structures,and ease of functionalization make COFs exhibit superior potential in gas storage and separation,optoelectronic device and catalysis.This mini review gives a brief introduction of COFs and highlights their applications in electronic and optical fields.展开更多
The experiment results of ultrawide band electromagnetic radiation with DC biased GaAs photoconductive semiconductor switch combining double ridge horn antenna triggered by high repeat frequency femto-second laser pul...The experiment results of ultrawide band electromagnetic radiation with DC biased GaAs photoconductive semiconductor switch combining double ridge horn antenna triggered by high repeat frequency femto-second laser pulse are reported.The GaAs switches are insulated by solid multi-layer transparent dielectrics and the distance of two electrodes is 3mm.The electrode material of the switch is ohmic contact through alloy technics with definite proportion of Au/Ge/Ni.This switch and double ridge horn antenna are integrated and the receive antenna is connected with the test instrument.From receiving antenna,ultra fast electrical pulse of 200ps rise time and 500ps pulse width is obtained,the repetition rate of the pulse is about 82MHz and the frequency spectrum is in the range of 4.7MHz～14GHz.The radiation characteristic of the ultrafast electrical pulse is analyzed.展开更多
Photocatalysis shows great promise in the field of solar energy conversion.One of the reasons for this is because it promotes the development of multi-field-coupled catalysis.In order to explore the principles of mult...Photocatalysis shows great promise in the field of solar energy conversion.One of the reasons for this is because it promotes the development of multi-field-coupled catalysis.In order to explore the principles of multi-field-coupled catalytic reactions,an in situ multi-field-coupled characterization technique is required.In this study,we obtained hydrogenated ST-01 TiO2 and observed enhanced catalytic activity by thermal coupled photocatalysis.In situ photoconductivity was employed to understand the activity enhancement.The effects of the reaction temperature,reaction atmosphere,and oxygen vacancy(Ov)on the photoconductivity of TiO2 were studied.After coupling thermal into photoconductivity measurement,highly active Ov-TiO2 displayed rapid decay of photoconductivity in a CO2 atmosphere and slow decay of photoconductivity in a N2 atmosphere.These phenomena revealed that photothermal coupling assisted the detrapping of electrons at the Ov surface and promoted electron transfer to CO2,which clearly explained the high photothermal catalytic activity of Ov-TiO2.This study demonstrated that photoconductivity is a useful tool to help understand photothermal catalytic phenomena.展开更多
A mode for the periodicity and weakening surge in semi-insulating GaAs photoconductive semiconductor switches is proposed based on the transferred-electron effect. It is shown that the periodicity and weakening surge ...A mode for the periodicity and weakening surge in semi-insulating GaAs photoconductive semiconductor switches is proposed based on the transferred-electron effect. It is shown that the periodicity and weakening surge is caused by the interaction between the self-excitation of the resonant circuit and transferred electron oscillation of the switch. The bias electric field （larger than Gunn threshold） across the switch is modulated by the AC elec-tric field,when the instantaneous bias electric field E is swinging below Gunn electric field threshold ET but grea-ter than the sustaining field Es （the minimum electric field required to support the domain） at the time of the do-main reaching the anode, and then the delayed-dipole domain mode of switch is obtained. It is the photon-activated carriers that satisfy the requirement of charge domain formation on carrier concentration and device length prod-uct of 10^12 cm^-2,and the semi-insulating GaAs photoconductive semiconductor switch is essentially a type of pho-ton-activated charge domain device.展开更多
A model for theoretical analysis of nonlinear (or high gain) mode of photoconductive semiconductor switches (PCSS's) is proposed.The switching transition of high gain PCSS's can be described with an optically...A model for theoretical analysis of nonlinear (or high gain) mode of photoconductive semiconductor switches (PCSS's) is proposed.The switching transition of high gain PCSS's can be described with an optically activated charge domain. The switching characteristics including rise time,delay and their relationship to electric field strength,optical trigger energies are discussed.The formation and radiation transit,accumulation of the charge domain are related with the triggering and sustaining phases of PCSS's,respectively.The results of the mathematical model on this mechanism agree with experimental results.展开更多
Experiments of a GaAs ultra\|fast Photo\|Conductive Semiconductor Switch (PCSS) are reported. Both the linear and nonlinear modes were observed when triggered by the μJ nano\|second laser. The peak current could...Experiments of a GaAs ultra\|fast Photo\|Conductive Semiconductor Switch (PCSS) are reported. Both the linear and nonlinear modes were observed when triggered by the μJ nano\|second laser. The peak current could be as high as 560A. The rise time of the current pulse responses is less than 200ps when triggered with 76MHz femto\|second laser.展开更多
The transient resistance,voltage,and power of a nonlinear GaAs photoconductive semiconductor switch （PCSS） are presented by the finite difference formula to deal with the experiment data, based on the conversation o...The transient resistance,voltage,and power of a nonlinear GaAs photoconductive semiconductor switch （PCSS） are presented by the finite difference formula to deal with the experiment data, based on the conversation of energy in the switch circuit. This method resolves the problem of directly measuring the transient characteristics of PCSS in nonlinear mode. The curve of transient voltage shows that the average electric field of PCSS in the lock-on period is always higher than the Gunn threshold,and increases monotonically. By comparing the transient power curves of the PCSS and the electrical source,it is demonstrated directly that the power shortage leads to the PCSS from the lock-on state into the selfturnoff state,so a controllable turnoff of the PCSS in lock-on by changing the distribution of the circuit power is predicted.展开更多
Light induced changes in a-Si∶H films are investigated by transient photoconductivity.The transient photoconductivity decay data can neither be fit well by common power-law for transient photocurrent in amorphous sem...Light induced changes in a-Si∶H films are investigated by transient photoconductivity.The transient photoconductivity decay data can neither be fit well by common power-law for transient photocurrent in amorphous semiconductors,nor by stretched exponential rule for transient decay from the steady state in photoconductivity.Instead,the data are fit fairly well with a sum of two exponential functions.The results show that the long time decay is governed by deep traps rather than band tail states,and two different traps locating separately at 0.52 and 0.59eV below E _c are responsible for the two exponential functions.They are designated as negatively charged dangling bond D - centers.The light-induced changes in photoconductivity are attributed mainly to the decrease in electron lifetime caused by the increase of recombination centers after light soaking.展开更多
Gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS's) with a 1.55mm gap spacing trigged by 1553nm femtosecond fiber laser pulse is presented.The switches are biased with 3.33～10.3kV/cm and irrad...Gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS's) with a 1.55mm gap spacing trigged by 1553nm femtosecond fiber laser pulse is presented.The switches are biased with 3.33～10.3kV/cm and irradiated by femtosecond fiber laser operated at a wavelength of 1553nm with pulse width of 200fs and pulse energy of 0.2nJ.The experiments show that,even if the semi-insulating GaAs photoconductive switch operates under the electrical field of 10.3kV/cm,it will be still linear response,and a clear corresponding output electric pulse with the peak voltage of 0.8mV is captured.From the weak photoconductivity on laser intensity,photoabsorption mediated by EL2 deep level defects is suggested,as the primary process for the photoconductivity.展开更多
We report on the transition of photovoltaic and photoconductive operation modes of the amorphous Ga_2O_3-based solar-blind photodetectors in metal–semiconductor–metal(MSM) configurations. The conversion from Ohmic t...We report on the transition of photovoltaic and photoconductive operation modes of the amorphous Ga_2O_3-based solar-blind photodetectors in metal–semiconductor–metal(MSM) configurations. The conversion from Ohmic to Schottky contacts at Ti/Ga_2O_3 interface is realized by tuning the conductivity of amorphous Ga_2O_3 films with delicate control of oxygen flux in the sputtering process. The abundant donor-like oxygen vacancies distributed near the Ti/Ga_2O_3 interface fascinate the tunneling process across the barrier and result in the formation of Ohmic contacts. As a consequence, the serious sub-gap absorption and persistent photoconductivity(PPC) effect degrades the performance of the photoconductive detectors. In contrast, the photovoltaic device with a Schottky contact exhibits an ultra-low dark current less than 1 pA,a high detectivity of 9.82×10^(12) cm·Hz^(1/2)·W^(-1), a fast response time of 243.9 μs, and a high ultraviolet C(UVC)-toultraviolet A(UVA) rejection ratio of 103. The promoting performance is attributed primarily to the reduction of the subgap states and the resultant suppression of PPC effect. With simple architecture, low fabrication cost, and easy fusion with modern high-speed integrated circuitry, these results provide a cost-effective way to realize high performance solar-blind photodetectors towards versatile practical applications.展开更多
Synchronization for multiple-pulse at nanosecond range shows a great value on the power multiplication and synchronous electric fieldsapplications. Nanosecond or sub-ns jitter synchronization is essential for the impr...Synchronization for multiple-pulse at nanosecond range shows a great value on the power multiplication and synchronous electric fieldsapplications. Nanosecond or sub-ns jitter synchronization is essential for the improved working efficiency of the large amounts of pulse modulesand accurate requirements for the power coherent combining applications. This paper presents a trigger generator based on a laser diodetriggered GaAs photoconductive semiconductor switch (PCSS) with low jitter and compact size characteristics. It avoids the high currentsthat are harmful to high-gain mode PCSSs. In the trigger circuit, a 200 pF capacitor is charged by a microsecond-scale 18 kV pulse and thendischarged via the high-gain mode GaAs PCSS to trigger the high-power trigatron switch. When triggered by the ~10 ns pulse generated by thePCSS, the DC-charged trigatron can operate in the 20e35 kV range with 10 ns rise time and 1 ns delay-time jitter.展开更多
In recent years,low-dimensional materials have received extensive attention in the field of electronics and optoelectronics.Among them,photoelectric devices based on photoconductive effect in low-dimensional materials...In recent years,low-dimensional materials have received extensive attention in the field of electronics and optoelectronics.Among them,photoelectric devices based on photoconductive effect in low-dimensional materials have a broad development space.In contrast to positive photoconductivity,negative photoconductivity(NPC)refers to a phenomenon that the conductivity decreases under illumination.It has novel application prospects in the field of optoelectronics,memory,and gas detection,etc.In this paper,we review reports about the NPC effect in low-dimensional materials and systematically summarize the mechanisms to form the NPC effect in existing low-dimensional materials.展开更多
Metal-organic frameworks(MOFs)are a class of hybrid materials with many promising applications.In recent years,lots of investigations have been oriented toward applications of MOFs in electronic and photoelectronic de...Metal-organic frameworks(MOFs)are a class of hybrid materials with many promising applications.In recent years,lots of investigations have been oriented toward applications of MOFs in electronic and photoelectronic devices.While many high-quality reviews have focused on synthesis and mechanisms of electrically conductive MOFs,few of them focus on their photophysical properties.Herein,we provide an in-depth review on photoconductive and photoluminescent properties of conductive MOFs together with their corresponding applications in solar cells,luminescent sensing,light emitting,and so forth.For integration of MOFs with practical devices,recent advances in fabrication of photoactive MOF thin films are also summarized.展开更多
文摘The peculiar photoconduction in semi insulating GaAs photoconductive switch being triggered by 1064nm laser pulse is reported.The gap between two electrodes of the switch is 4mm.When it is triggered by laser pulse with energy of 0 8mJ and the pulse width of 5ns,and operated at biased electric field of 2 0 and 6 0kV/cm,both linear and nonlinear modes of the switch are observed respectively.Whereas the biased electric field adds to 9 5kV/cm,and the triggered laser is in range of 0 5～1 0mJ,the peculiar performed characteristic is observed:the switch gives a linear waveform firstly,and then after a delay time of about 20～250ns,it outputs a nonlinear waveform again.The physical mechanism of this specific phenomenon is associated with the anti site defects of semi insulating GaAs and two step single photon absorption.The delay time between linear waveform and nonlinear waveform is calculated,and the result matches the experiments.
基金supported by the National Natural Science Foundation of China(Grant Nos.51902255 and 51803168)the Natural Science Foundation of Shaanxi Province(Grant No.2023-JC-YB-015)+1 种基金the Shaanxi Province Key Research and Development Projects(Grant No.2022GY-356)the Shaanxi Universities’Youth Innovation Team(Grant No.23JP174).
文摘Traditional Si-based photoconductive detectors face problems such as low response in the ultraviolet(UV)and infrared regions,high dark current,and low light absorption efficiency,which seriously limit their applications in the field of high-performance wide-spectrum detection.In this study,a self-powered broadband photodetector based on a Si/TiO_(2)heterojunction is proposed.The detector has a pyramidal structure.By constructing a pyramidal microstructure on the surface of silicon,the light capture and absorption efficiency is significantly improved,representing a breakthrough in response performance in the visible and near-infrared(NIR)bands.In order to further enhance the photoelectric response in the UV band,a TiO_(2)layer was coated on the surface of the silicon pyramid through a simple spin-coating method and annealing process.The introduction of TiO_(2)effectively broadened the spectral response range of the photoelectric detector and further improved the light absorption of the device.Meanwhile,due to the built-in electric field formed by the n-TiO_(2)/p-Si heterojunction,the dark current was effectively reduced,and the responsivity was improved.Experiments showed that the device exhibits high responsivity,high detectivity,and relatively low dark current in the range of 365-1305 nm.Under light at 780 nm,the device’s on-off ratio reached 2.7×10^(3);its specific detectivity,D^(*),was 3.9×10^(11)Jones;and its responsivity reached 0.174 A/W.In addition,this detector does not require the assistance of expensive equipment.Its preparation process is simple and inexpensive,and there is no need for an external power supply,which gives it broad application potential in wearable devices,environmental monitoring,communications,biosensing,and other fields.This study provides a brand-new strategy for the design of new wide-spectrum detectors.
基金supported by the Russian Science Foundation (Grant No. 22-12-00298)supported by the Center of Excellence "Center of Photonics" funded by the Ministry of Science and Higher Education of the Russian Federation, Contract #075-15-2022-316the Theoretical Physics and Mathematics Advancement Foundation "BASIS" scholarship for the support.
文摘In this work,we studied the persistent photoconductivity(PPC)spectra in single HgTe/CdHgTe quantum wells with different growth parameters and different types of dark conductivity.The studies were performed in a wide radiation quantum energy range of 0.62–3.1 eV both at T=4.2 K and at T=77 K.Common features of the PPC spectra for all structures were revealed,and their relation to the presence of a CdTe cap layer in all structures and the appropriate cadmium fraction in the CdHgTe barrier layers was shown.One of the features was associated with the presence of a deep level in the CdTe layer.In addition,the oscillatory behavior of the PPC spectra in the region from 0.8–1.1 eV to 1.2–1.5 eV was observed.It is associated with the cascade emission of longitudinal optical phonons in CdHgTe barrier.
基金Project supported by the National Natural Science Foundation of China (61988102)the Key-Area Research and Development Program of Guangdong Province(2019B090917007)the Science and Technology Planning Project of Guangdong Province (2019B090909011)。
文摘Bi_(2)YbO_(4)Cl with a fluorite layer structure belongs to the family of the bismuth rare-earth oxyhalides Bi_(2)REO_(4)X(X=Cl,B r,I).However,the synthesis and photoelectric properties of Bi_(2)YbO_(4)Cl have almost not been reported.In this work,Bi_(2)YbO_(4)Cl was synthesized using the solid-state method and the solvothermal method.Yb3+ions show a strong characteristic absorption peak at 980 nm,which was measured by ultraviolet-visible-near-infrared absorption spectra.The transient photoconductivity of Bi_(2)YbO_(4)Cl was obtained by time-resolved terahertz spectroscopy system under 400 and 800 nm laser excitations,respectively.The frequency-dependent transient photoconductivity analysis reveals the Drude-Smith behavior in Bi_(2)YbO_(4)Cl.Under photoexcitation,the hot charge carriers with a long relaxation lifetime and a carrier mobility of 48 cm^(2)/(V·s) are obtained.The synthesis of Bi_(2)YbO_(4)Cl is of great significance for the development of novel photocatalytic and photo harvesting materials with broad spectral response.
基金supported by the National Natural Science Foundation of China (52322210, 52172144, 22375069, 21825103, and U21A2069)National Key R&D Program of China (2021YFA1200501)+2 种基金Shenzhen Science and Technology Program (JCYJ20220818102215033, JCYJ20200109105422876)the Innovation Project of Optics Valley Laboratory (OVL2023PY007)Science and Technology Commission of Shanghai Municipality (21YF1454700)。
文摘The utilization of processing capabilities within the detector holds significant promise in addressing energy consumption and latency challenges. Especially in the context of dynamic motion recognition tasks, where substantial data transfers are necessitated by the generation of extensive information and the need for frame-by-frame analysis. Herein, we present a novel approach for dynamic motion recognition, leveraging a spatial-temporal in-sensor computing system rooted in multiframe integration by employing photodetector. Our approach introduced a retinomorphic MoS_(2) photodetector device for motion detection and analysis. The device enables the generation of informative final states, nonlinearly embedding both past and present frames. Subsequent multiply-accumulate (MAC) calculations are efficiently performed as the classifier. When evaluating our devices for target detection and direction classification, we achieved an impressive recognition accuracy of 93.5%. By eliminating the need for frame-by-frame analysis, our system not only achieves high precision but also facilitates energy-efficient in-sensor computing.
基金supported by the Russian Science Foundation(No.23-43-00060)financially supported by the Ministry of Science and Higher Education of the Russian Federation within the framework of the state assignment for scientific activity(No.122011300052-1).
文摘Copolyfluorenes are of great interest due to their ability to form thin films with tunable optical and electrical properties.In this paper,copolymers of polyfluorene with electron withdrawing dicyanostilbene and dicyanophenanthrene moieties were synthesized;their thin films were characterized by electron spectroscopy,cyclic voltammetry,electrical,and photoelectrical measurements.The mobility of charge carriers in the copolymers was measured for the first time,with the acceptor components providing balanced electron and hole mobilities of the order of 10^(-6) cm^(2)·V^(-1)·s^(-1).Photodetectors based on the copolymer/PTCDI heterojunction exhibited the photoresponse band extended into the green region due to the absorption of PTCDI and an increased photocurrent in the UV-blue absorption band of the copolymer,which is related to the absorption of photoluminescent emission of the copolymers in PTCDI.The presented approach to improving the performance of a polymer-based photodetector is promising in organic optoelectronics.
基金National Key R&D Program of China(2021YFA0716304)Shanghai Science and Technology Programs(22511100300,23DZ2201500)。
文摘Photoconductive semiconductor switch(PCSS)can be applied in pulsed high power systems and microwave techniques.However,reducing the damage and increasing the lifetime of silicon carbide(SiC)PCSS are still faced severe challenges.In this study,PCSSs with various structures were prepared on 4-inch diameter,500μm thick high-purity semi-insulating 4H-SiC substrates and their on-state resistance and damage mechanisms were investigated.It was found that the PCSS of an Au/TiW/Ni electrode system annealed at 950℃had a minimum on-state resistance of 6.0Ωat 1 kV bias voltage with a 532 nm and 170 mJ pulsed laser by backside illumination single trigger.The backside illumination single trigger could reduce on-state resistance and alleviate the damage of PCSS compared to the frontside trigger when the diameter of the laser spot was larger than the channel length of PCSS.For the 200 s trigger test by a 10 Hz laser,the black branch-like ablation on Au/TiW/Ni PCSS was mainly caused by thermal stress owing to hot carriers.Replacing metal Ni with boron gallium co-doped zinc oxide(BGZO)thin films annealed at 400℃,black branch-like ablation was alleviated while concentric arc damage was obvious at the anode.The major causes of concentric arc are both pulsed laser diffraction and thermal effect.
基金the 973 Program(No.2013CB834704)the National Natural Science Foundation of China(Nos.21471018,21201018,21404010)1000 Plan (Youth) for financial support
文摘Covalent organic frameworks（COFs） as an emerging class of porous materials have achieved remarkable progress in recent years.Their high surface area,low mass densities,highly ordered periodic structures,and ease of functionalization make COFs exhibit superior potential in gas storage and separation,optoelectronic device and catalysis.This mini review gives a brief introduction of COFs and highlights their applications in electronic and optical fields.
文摘The experiment results of ultrawide band electromagnetic radiation with DC biased GaAs photoconductive semiconductor switch combining double ridge horn antenna triggered by high repeat frequency femto-second laser pulse are reported.The GaAs switches are insulated by solid multi-layer transparent dielectrics and the distance of two electrodes is 3mm.The electrode material of the switch is ohmic contact through alloy technics with definite proportion of Au/Ge/Ni.This switch and double ridge horn antenna are integrated and the receive antenna is connected with the test instrument.From receiving antenna,ultra fast electrical pulse of 200ps rise time and 500ps pulse width is obtained,the repetition rate of the pulse is about 82MHz and the frequency spectrum is in the range of 4.7MHz～14GHz.The radiation characteristic of the ultrafast electrical pulse is analyzed.
基金supported by the Natural Science Foundation of China(51072032,51372036,51102001)the Key Project of Chinese Ministry of Education(113020A)+1 种基金the 111 project(B13013)Jilin Province Science and Technology Development Plan(20180101175JC,20160520170JH)~~
文摘Photocatalysis shows great promise in the field of solar energy conversion.One of the reasons for this is because it promotes the development of multi-field-coupled catalysis.In order to explore the principles of multi-field-coupled catalytic reactions,an in situ multi-field-coupled characterization technique is required.In this study,we obtained hydrogenated ST-01 TiO2 and observed enhanced catalytic activity by thermal coupled photocatalysis.In situ photoconductivity was employed to understand the activity enhancement.The effects of the reaction temperature,reaction atmosphere,and oxygen vacancy(Ov)on the photoconductivity of TiO2 were studied.After coupling thermal into photoconductivity measurement,highly active Ov-TiO2 displayed rapid decay of photoconductivity in a CO2 atmosphere and slow decay of photoconductivity in a N2 atmosphere.These phenomena revealed that photothermal coupling assisted the detrapping of electrons at the Ov surface and promoted electron transfer to CO2,which clearly explained the high photothermal catalytic activity of Ov-TiO2.This study demonstrated that photoconductivity is a useful tool to help understand photothermal catalytic phenomena.
文摘A mode for the periodicity and weakening surge in semi-insulating GaAs photoconductive semiconductor switches is proposed based on the transferred-electron effect. It is shown that the periodicity and weakening surge is caused by the interaction between the self-excitation of the resonant circuit and transferred electron oscillation of the switch. The bias electric field （larger than Gunn threshold） across the switch is modulated by the AC elec-tric field,when the instantaneous bias electric field E is swinging below Gunn electric field threshold ET but grea-ter than the sustaining field Es （the minimum electric field required to support the domain） at the time of the do-main reaching the anode, and then the delayed-dipole domain mode of switch is obtained. It is the photon-activated carriers that satisfy the requirement of charge domain formation on carrier concentration and device length prod-uct of 10^12 cm^-2,and the semi-insulating GaAs photoconductive semiconductor switch is essentially a type of pho-ton-activated charge domain device.
文摘A model for theoretical analysis of nonlinear (or high gain) mode of photoconductive semiconductor switches (PCSS's) is proposed.The switching transition of high gain PCSS's can be described with an optically activated charge domain. The switching characteristics including rise time,delay and their relationship to electric field strength,optical trigger energies are discussed.The formation and radiation transit,accumulation of the charge domain are related with the triggering and sustaining phases of PCSS's,respectively.The results of the mathematical model on this mechanism agree with experimental results.
文摘Experiments of a GaAs ultra\|fast Photo\|Conductive Semiconductor Switch (PCSS) are reported. Both the linear and nonlinear modes were observed when triggered by the μJ nano\|second laser. The peak current could be as high as 560A. The rise time of the current pulse responses is less than 200ps when triggered with 76MHz femto\|second laser.
文摘The transient resistance,voltage,and power of a nonlinear GaAs photoconductive semiconductor switch （PCSS） are presented by the finite difference formula to deal with the experiment data, based on the conversation of energy in the switch circuit. This method resolves the problem of directly measuring the transient characteristics of PCSS in nonlinear mode. The curve of transient voltage shows that the average electric field of PCSS in the lock-on period is always higher than the Gunn threshold,and increases monotonically. By comparing the transient power curves of the PCSS and the electrical source,it is demonstrated directly that the power shortage leads to the PCSS from the lock-on state into the selfturnoff state,so a controllable turnoff of the PCSS in lock-on by changing the distribution of the circuit power is predicted.
文摘Light induced changes in a-Si∶H films are investigated by transient photoconductivity.The transient photoconductivity decay data can neither be fit well by common power-law for transient photocurrent in amorphous semiconductors,nor by stretched exponential rule for transient decay from the steady state in photoconductivity.Instead,the data are fit fairly well with a sum of two exponential functions.The results show that the long time decay is governed by deep traps rather than band tail states,and two different traps locating separately at 0.52 and 0.59eV below E _c are responsible for the two exponential functions.They are designated as negatively charged dangling bond D - centers.The light-induced changes in photoconductivity are attributed mainly to the decrease in electron lifetime caused by the increase of recombination centers after light soaking.
文摘Gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS's) with a 1.55mm gap spacing trigged by 1553nm femtosecond fiber laser pulse is presented.The switches are biased with 3.33～10.3kV/cm and irradiated by femtosecond fiber laser operated at a wavelength of 1553nm with pulse width of 200fs and pulse energy of 0.2nJ.The experiments show that,even if the semi-insulating GaAs photoconductive switch operates under the electrical field of 10.3kV/cm,it will be still linear response,and a clear corresponding output electric pulse with the peak voltage of 0.8mV is captured.From the weak photoconductivity on laser intensity,photoabsorption mediated by EL2 deep level defects is suggested,as the primary process for the photoconductivity.
基金Project supported by the National Key Research and Development Project,China(Grant No.2017YFB0403003)the National Natural Science Foundation of China(Grant Nos.61774081,61322403,and 91850112)+3 种基金the State Key Research and Development Project of Jiangsu Province,China(Grant No.BE2018115)Shenzhen Fundamental Research Project,China(Grant Nos.201773239 and 201888588)the Project of the State Key Laboratory of Wide-Bandgap Semiconductor Power Electric Devices,China(Grant No.2017KF001)the Fundamental Research Funds for the Central Universities,China(Grant Nos.021014380093 and 021014380085)
文摘We report on the transition of photovoltaic and photoconductive operation modes of the amorphous Ga_2O_3-based solar-blind photodetectors in metal–semiconductor–metal(MSM) configurations. The conversion from Ohmic to Schottky contacts at Ti/Ga_2O_3 interface is realized by tuning the conductivity of amorphous Ga_2O_3 films with delicate control of oxygen flux in the sputtering process. The abundant donor-like oxygen vacancies distributed near the Ti/Ga_2O_3 interface fascinate the tunneling process across the barrier and result in the formation of Ohmic contacts. As a consequence, the serious sub-gap absorption and persistent photoconductivity(PPC) effect degrades the performance of the photoconductive detectors. In contrast, the photovoltaic device with a Schottky contact exhibits an ultra-low dark current less than 1 pA,a high detectivity of 9.82×10^(12) cm·Hz^(1/2)·W^(-1), a fast response time of 243.9 μs, and a high ultraviolet C(UVC)-toultraviolet A(UVA) rejection ratio of 103. The promoting performance is attributed primarily to the reduction of the subgap states and the resultant suppression of PPC effect. With simple architecture, low fabrication cost, and easy fusion with modern high-speed integrated circuitry, these results provide a cost-effective way to realize high performance solar-blind photodetectors towards versatile practical applications.
基金This work was supported by the National Science Foundation of China under grant No.51477177.
文摘Synchronization for multiple-pulse at nanosecond range shows a great value on the power multiplication and synchronous electric fieldsapplications. Nanosecond or sub-ns jitter synchronization is essential for the improved working efficiency of the large amounts of pulse modulesand accurate requirements for the power coherent combining applications. This paper presents a trigger generator based on a laser diodetriggered GaAs photoconductive semiconductor switch (PCSS) with low jitter and compact size characteristics. It avoids the high currentsthat are harmful to high-gain mode PCSSs. In the trigger circuit, a 200 pF capacitor is charged by a microsecond-scale 18 kV pulse and thendischarged via the high-gain mode GaAs PCSS to trigger the high-power trigatron switch. When triggered by the ~10 ns pulse generated by thePCSS, the DC-charged trigatron can operate in the 20e35 kV range with 10 ns rise time and 1 ns delay-time jitter.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61574011 and 51761145025)the Key Program of the National Natural Science Foundation of China(Grant No.No.61731019)the Natural Science Foundation of Beijing,China(Grant Nos.4182015 and 4182014)。
文摘In recent years,low-dimensional materials have received extensive attention in the field of electronics and optoelectronics.Among them,photoelectric devices based on photoconductive effect in low-dimensional materials have a broad development space.In contrast to positive photoconductivity,negative photoconductivity(NPC)refers to a phenomenon that the conductivity decreases under illumination.It has novel application prospects in the field of optoelectronics,memory,and gas detection,etc.In this paper,we review reports about the NPC effect in low-dimensional materials and systematically summarize the mechanisms to form the NPC effect in existing low-dimensional materials.
基金supported by the National Natural Science Foundation of China(Grant No.51603052)the FRF for the Central Universities(18lgjc66)。
文摘Metal-organic frameworks(MOFs)are a class of hybrid materials with many promising applications.In recent years,lots of investigations have been oriented toward applications of MOFs in electronic and photoelectronic devices.While many high-quality reviews have focused on synthesis and mechanisms of electrically conductive MOFs,few of them focus on their photophysical properties.Herein,we provide an in-depth review on photoconductive and photoluminescent properties of conductive MOFs together with their corresponding applications in solar cells,luminescent sensing,light emitting,and so forth.For integration of MOFs with practical devices,recent advances in fabrication of photoactive MOF thin films are also summarized.
