Investigation of helicity-dependent photocurrent of surface states in(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplate

Helicity-dependent photocurrent(HDPC)of the surface states in a high-quality topological insulator(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplate grown by chemical vapor deposition(CVD)is investigated.By investigating the angle-dependent HDPC,it is found that the HDPC is mainly contributed by the circular photogalvanic effect(CPGE)current when the incident plane is perpendicular to the connection of the two contacts,whereas the circular photon drag effect(CPDE)dominates the HDPC when the incident plane is parallel to the connection of the two contacts.In addition,the CPGE of the(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplate is regulated by temperature,light power,excitation wavelength,the source–drain and ionic liquid top-gate voltages,and the regulation mechanisms are discussed.It is demonstrated that(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplates may provide a good platform for novel opto-spintronics devices.

Oneε-Ga_(2)O_(3)-based solar-blind Schottky photodetector emphasizing high photocurrent gain and photocurrent-intensity linearity

Theε-Ga_(2)O_(3) thin film was grown on sapphire substrate by using metalorganic chemical vapor deposition(MOCVD)method,and then was used to fabricate a deep-ultraviolet(DUV)photodetector(PD).Theε-Ga_(2)O_(3) thin film shown good crystal quality and decent surface morphology.Irradiated by a 254-nm DUV light,the photodetector displayed good optoelectronic performance and high wavelength selectivity,such as photoresponsivity(R)of 175.69 A/W,detectivity(D*)of 2.46×10^(15) Jones,external quantum efficiency(EQE)of 8.6×10^(4)%and good photocurrent-intensity linearity,suggesting decent DUV photosensing performance.At 5 V and under illumination with light intensity of 800μW/cm2,the photocurrent gain is as high as 859 owing to the recycling gain mechanism and delayed carrier recombination;and the photocurrent gain decreases as the incident light intensity increases because of the recombination of photogenerated carriers by the large photon flux.

A spatiotemporal evolution model of a short-circuit arc to a secondary arc based on the improved charge simulation method

The initial shape of the secondary arc considerably influences its subsequent shape.To establish the model for the arcing time of the secondary arc and modify the single-phase reclosing sequence,theoretical and experimental analysis of the evolution process of the short-circuit arc to the secondary arc is critical.In this study,an improved charge simulation method was used to develop the internal-space electric-field model of the short-circuit arc.The intensity of the electric field was used as an independent variable to describe the initial shape of the secondary arc.A secondary arc evolution model was developed based on this model.Moreover,the accuracy of the model was evaluated by comparison with physical experimental results.When the secondary arc current increased,the arcing time and dispersion increased.There is an overall trend of increasing arc length with increasing arcing time.Nevertheless,there is a reduction in arc length during arc ignition due to short circuits between the arc columns.Furthermore,the arcing time decreased in the range of 0°-90°as the angle between the wind direction and the x-axis increased.This work investigated the method by which short-circuit arcs evolve into secondary arcs.The results can be used to develop the secondary arc evolution model and to provide both a technical and theoretical basis for secondary arc suppression.

Optimization of short-circuit transition parameters of Q235B steel GMAW based on orthogonal gray relational analysis

In gas metal arc welding(GMAW)process,the short-circuit transition was the most typical transition observed in molten metal droplets.This paper used orthogonal tests to explore the coupling effect law of welding process parameters on the quality of weld forming under short-circuit transition,the design of 3 factors and 3 levels of a total of 9 groups of orthogonal tests,welding current,welding voltage,welding speed as input parameters:effective area ratio,humps,actual linear power density,aspect ratio,Vickers hardness as output paramet-ers(response targets).Using range analysis and trend charts,we can visually depict the relationship between input parameters and a single output parameter,ultimately determining the optimal process parameters that impact the single output index.Then combined with gray the-ory to transform the three response targets into a single gray relational grade(GRG)for analysis,the optimal combination of the weld mor-phology parameters as follows:welding current 100 A,welding voltage 25 V,welding speed 30 cm/min.Finally,validation experiments were conducted,and the results showed that the error between the gray relational grade and the predicted value was 2.74%.It was observed that the effective area ratio of the response target significantly improved,validating the reliability of the orthogonal gray relational method.

Partitioning Calculation Method of Short-Circuit Current for High Proportion DG Access to Distribution Network

Aiming at the problemthat the traditional short-circuit current calculationmethod is not applicable to Distributed Generation(DG)accessing the distribution network,the paper proposes a short-circuit current partitioning calculation method considering the degree of voltage drop at the grid-connected point of DG.Firstly,the output characteristics of DG in the process of low voltage ride through are analyzed,and the equivalent output model of DG in the fault state is obtained.Secondly,by studying the network voltage distribution law after fault in distribution networks under different DG penetration rates,the degree of voltage drop at the grid-connected point of DG is used as a partition index to partition the distribution network.Then,iterative computation is performed within each partition,and data are transferred between partitions through split nodes to realize the fast partition calculation of short-circuit current for high proportion DG access to distribution network,which solves the problems of long iteration time and large calculation error of traditional short-circuit current.Finally,a 62-node real distribution network model containing a high proportion of DG access is constructed onMATLAB/Simulink,and the simulation verifies the effectiveness of the short-circuit current partitioning calculation method proposed in the paper,and its calculation speed is improved by 48.35%compared with the global iteration method.

Sub-bandgap photocurrent response and carrier transport properties of undoped semi-insulating LEG GaAs as a composite

Undoped (ND) semi-insulating (SI) liquid encapsulated Czochralski (LEC) GaAscrystals were investigated by photocurrent and temperature-dependent Hall measurements. It isindicated that strong nonuniformities in the distributions of impurities and defects can occur forthe NDSILEC GaAs crystal grown under a condition with strong constitutional supercooling. In suchcase, the deep level that dominates Fermi level is spacial location dependent, and the GaAs crystalbecomes a composite consisting of a large number of elementary domains with differentconductivities. The sub-bandgap photocurrent response and the carrier transport properties for thiskind of composite are quite different from those for homogeneous NDSILEC GaAs.

Helicity‐dependent THz emission induced by ultrafast spin photocurrent in nodal‐line semimetal candidate Mg3Bi2

Helicity-dependent ultrafast spin current generated by circularly polarized photons in topological materials holds the crux to many technological improvements,such as quantum communications,on-chip communication processing and storage.Here,we present the manipulation of helicity-dependent terahertz emission generated in a nodal line semimetal candidate Mg3Bi2 by using photon polarization states.The terahertz emission is mainly ascribed to the helicity-dependent photocurrent that is originated from circular photogalvanic effects,and the helicity-independent photocurrent that is attributed to linear photogalvanic effect.Our work will inspire more explorations into novel nodal line semimetals and open up new opportunities for developing ultrafast optoelectronics in the topological system.

Simple Method to Fabricate Au Nanoparticle-Decorated TiO2 Nanotube Arrays for Enhanced Visible Light Photocurrent

Au nanoparticle-decorated TiO2 nanotube arrays are prepared by a simple method, which is a thermal annealing thin gold film deposited on anodie oxidized TiO2 nanotube arrays. These electron microscope images present that Au nanoparticles are well dispersed within the wall and on the surface of the XiO2 nanotubes. Meanwhile, the morphologies of Au nanoparticles can be controlled by changing the thickness of the deposited gold film. Associ- ated with the excitation of localized surface plasmon resonances, the prepared Au nanoparticle-decorated TiO2 nanotube arrays could work as visible light responsive photocatalysts to produce a greatly enhanced photocurrent density. By varying the initial gold film thickness, such Au nanoparticle-decorated TiO2 nanotube arrays could be optimized to obtain the highest photocurrent generation efficiency in the visible and UV light regions.

Photocurrent improvement of an ultra-thin silicon solar cell using the localized surface plasmonic effect of clustering nanoparticles

The cluster-shaped plasmonic nanostructures are used to manage the incident light inside an ultra-thin silicon solar cell.Here we simulate spherical,conical,pyramidal,and cylindrical nanoparticles in a form of a cluster at the rear side of a thin silicon cell,using the finite difference time domain(FDTD)method.By calculating the optical absorption and hence the photocurrent,it is shown that the clustering of nanoparticles significantly improves them.The photocurrent enhancement is the result of the plasmonic effects of clustering the nanoparticles.For comparison,first a cell with a single nanoparticle at the rear side is evaluated.Then four smaller nanoparticles are put around it to make a cluster.The photocurrents of 20.478 mA/cm2,23.186 mA/cm2,21.427 mA/cm2,and 21.243 mA/cm2 are obtained for the cells using clustering conical,spherical,pyramidal,cylindrical NPs at the backside,respectively.These values are 13.987 mA/cm2,16.901 mA/cm2,16.507 mA/cm2,17.926 mA/cm2 for the cell with one conical,spherical,pyramidal,cylindrical NPs at the backside,respectively.Therefore,clustering can significantly improve the photocurrents.Finally,the distribution of the electric field and the generation rate for the proposed structures are calculated.

Studying the charge carrier properties in CuInS_2 films via femtosecond transient absorption and nanosecond transient photocurrents

The carrier behavior in CuInS_2 thin films at femtosecond and microsecond time scales is discussed in detail. Transient absorption data suggests that the photo-generated carriers relax rapidly accompanied by a change in energy. The photogenerated charge carriers are extracted by a bias electric field E in the nanosecond transient photocurrent system. An applied E improves the efficiency of photon conversion to charge carriers and enhances the velocity of the extracted charge carriers. In addition, there exists a threshold of illumination intensity in the extraction process of charge carriers in the CuInS_2 thin film, above which carrier recombination occurs. The corresponding loss further increases with illumination intensity and the recombination rate is almost independent of E. Our results provide useful insights into the characteristics of carriers in the CuInS_2 thin film and are important for the operation of optoelectronic devices realized with these films.

PHOTOCONDUCTIVE PROPERTIES OF PVK:Alq_3 BLEND FILMS STUDIED BY STEADY-STATE AND TIME-RESOLVED TRANSIENT PHOTOCURRENT SPECTRA

The carrier transport properties of the blends of the hole transport material poly(N-vinylcarbazole) (PVK) and the electron transport material tris (8-hydroxyquinolinolato) aluminumⅢ(Alq_3) are investigated at room temperature using steady-state and time-resolved transient photocurrent measurements as a function of doping concentration of Alq_3.Due to lower LUMO and higher HOMO energy level of Alq_3 than those of PVK,Alq_3 molecules may act as carrier trap states in PVK films at low concentration.However,at...

Deep Levels in Undoped Semi-insulating Liquid Encapsulated Czochralski GaAs Detected by Photocurrent Measurement

Deep levels in undoped semi insulating (SI) liquid encapsulated czochralski (LEC) GaAs were investigated through measuring extrinsic photocurrent spectra at 300 K. Two broad photoresponse bands M 1 and M 2 were observed in the range of 0.40 ～ 0.70 eV and the range from about 0.80 eV to the bandgap energy, respectively. It was shown that M 2 band is related to the photoionization of the deep defect EL2. M 1 band, which is reported for the first time, reveals several characteristic structures including five peaks at 0.46, 0.49, 0.56, 0.65 and 0.69 eV, respectively. The relative magnitudes of these peaks vary from sample to sample and are related to the thermal histories of the samples. These peaks are likely due to different deep levels.

Exploring photocurrent output from donor/acceptor bulk-heterojunctions by monitoring exciton quenching

In this work, a series of polymer bulk-heterojunctions is fabricated based on the combinations of different donors （Ds） （P3HT and PCPDTBT） and acceptors （As） （PCBM, ICBA, and F8BT）. Exciton quenching efficiencies of the D-A pairs are obtained in order to quantify charge-transfer between the donor and the acceptor via a modified approach developed in conjunction with experimental results of optical absorption and photoluminescence spectra. It is discovered that the exciton quenching efficiency in the combination of PCPDTBT：PCBM and P3HT：PCBM reaches 70% and over, but in PCPDTBT：ICBA it is about 12%. A relatively high ALUMOdonor_acceptor results in a relatively high exciton quenching efficiency, which is responsible for better charge separation. The results agreed well with the photocurrent effect of the heterojunction layers. The work offers a convenient way to predict a potentially promising photovoltaic material with a selected D-A pair.

Solvent and electric field dependence of the photocurrent generation in donor：acceptor blend system

This paper reports that the blend films of poly （2-methoxy-5-（2＇-ethyl-hexyloxy）-p-phenylene vinylene） （MEH-PPV） and N,N＇-bis（1-ethylpropyl）-3,4： 9,10-perylene bis （tetracarboxyl diimide） （EP-PDI） with the weight ratio of 1：2.5 have been prepared by spin-coating from chloroform （CF） and chlorobenzene （CB） solutions respectively. The absorption spectra and the morphology of the blend films show that large crystal-like EP-PDI aggregates are formed in film prepared from CB solution, which corresponds to a new absorption shoulder near 590 nm, while there is no shoulder around 590 nm in the UV-Vis absorption spectra of the blend film from CF solution. The electric-field dependence spectra of the photocurrent generation quantum yield of the film from CB solution shows that at weak electric field the EP-PDI aggregates act as more efficient sensitizers, but at strong electric field the quantum yields become almost invariable over the entire spectral range no matter what the state of EP-PDI, monomer or aggregate. At strong electric field, the photocurrent generation yields of both films from CF and CB solution saturate and their yield spectra become spectrally similar, mentioning that at strong electric field the photoexcitons dissociate efficiently and the free charges are collected by the electrodes almost completely.

(Bi-4I16)4- Iodobismuthate Tetramer Directed by Viologen-like Template:Enhanced Absorption Behavior, Optical Gap and Photocurrent Response Property Induced by I···I Interactions

Based on the template of protonated BPDO(B PDO = 4,4’-bipyridine N,N’-dioxide), a new iodobismuthate hybrid with formula of(H2 DPDO)2(Bi4 I16)(1) was synthesized under solvothermal conditions. The Bi4 I164- tetramer is built from four edge-sharing BiI6 octahedra. I···I interactions stabilize the structure and contribute to the structural extending from 0-D cluster to 1-D chain. The broader absorption band and lower energy gap of 1.76 eV are led by strong I···I interactions, so the small and rigid template can result in strong halogen···halogen interaction, which will be beneficial for its charge transfer. The photocurrent response property of this complex was discussed, and its mechanism has also been proposed.

Enhancement of Photocurrent Generation of a Novel Stilbazolium Dye Dimer in LB Monolayer Films

A novel dye dimer, bis-{[1-(N-hexadecyl-4-pyridinium)-2-(4-N, N-dimethylamino- phenyl)] ethenyl}methane diiodide (C16BP) was synthesized, and the photoelectrochemistry of the dye Langmuir-Blodgett monolayer modified ITO electrode was investigated. For comparison, the photoelectrochemistry of the monomer (E)-N-hexadecyl-4-[2-(4-N, N-dimethylaminophenyl) ethenyl] pyridinium iodide (C16P) was also measured. The results show that the photocurrent generation property of the dimer is enhanced. The photocurrent generation quantum yield is 0.38% for C16BP, while that for C16P is 0.23%.

Iodoplumbate(Ⅱ)-based Hybrid Templated by 1,4-Diazabicyclo[2.2.2]octane Derivative：Structure,Photocurrent Response Behavior and Photocatalytic Activity for the Degradation of Organic Dye

A new iodoplumbate/organic hybrid,[（Et_2DABCO）_2（Pb_3I_（11））（H3 O）]n（1,Et_2DABCO = N,N？-diethyl-1,4-diazabicyclo[2.2.2] octane） has been synthesized using solution method.According to X-ray diffraction structural analysis,the unique（Pb_3I_（11））_n^（5n-） chain in 1 is constructed from face-and edge-sharing PbI_6 octahedra,which is templated by（Et_2DABCO）^（2＋） dication possessing both rigidity and flexibility.C-H...I hydrogen bonds contribute to the structure extending from 1D chains to a 3D network.Its energy band gap of 2.64 eV indicates its broad-gap semiconductor nature.It exhibits both photocurrent response property and photocatalytic activity for the degradation of rhodamine B.

Ethoxycarbonylmethyl Viologen Induced Metal Halide-based Hybrids:Structures,Photoluminescence and Photocurrent Response Behavior

Two new ethoxycarbonylmethyl viologen induced metal halide-based hybrids,(Ae V)(BiI)(DMF)(1)and(Ae V)(CoCl)(2)(AeV=N,N?-bis(ethoxycarbonylmethyl)-4,4?-bipyridinium)have been synthesized and structurally determined by X-ray diffraction method.Under the direction of a new template AeV,the(BiI)tetramer constructed from four edge-sharing BiIoctahedra(for 1)and(CoCl)mono-nuclear(for 2)were obtained.Furthermore,C–H···O and C–H···X(X=I,Cl)hydrogen bonds contribute to the extension of structures from 0-D to 1-D chains.Their energy band gaps of 2.18 and 2.41 eV indicate their semiconductor properties,and the photoluminescence was detected on 1.Interestingly,2 exhibits good photocurrent response behavior.Electronic structure analysis was executed to correlate the structure/property.

2D Modeling of Solar Cell Radial Junction: Study of Carriers Charge Density and Photocurrent Density in Static Mode under Monochromatic Illumination

A theoretical study of a polysilicon solar cell with a radial junction in static regime under monochromatic illumination is presented in this paper. The junction radial solar cell geometry is illustrated and described. The carriers’ diffusion equation is established and solved under quasi-neutral base assumption with boundaries conditions and Bessel equations. New analytical expressions of electrons and holes density and photocurrent are found. The wavelength and structural parameters (base radius, emitter thickness) influences on charge carriers density and photocurrent are shown and examined.