Positive Photocurrent Research Articles

Optoelectronic Reconfigurable Logic Gates Based on Two-Dimensional Vertical Field-Effect Transistors.

Optoelectronic reconfigurable logic gates are promising candidates to meet the multifunctional and energy-efficient requirements of integrated circuits. However, complex device architectures need more power and hinder multifunctional device applications. Here, we design vertical field-effect transistors (VFET) based on the two-dimensional (2D) graphene/MoS2/WSe2/graphene van der Waals heterojunction forming ohmic and Schottky contact. The modulation of the Schottky barrier via gate bias enables the device to switch between positive and negative photocurrents, which can effectively achieve optoelectronic reconfigurable logic gates (XNOR, NOR, NAND, AND, OR, and Inhibit) in a single device. Particularly, the transistor number is reduced by 75% for ("XNOR", "NOR", "NAND") and 83% for ("AND", "OR") gates compared to traditional logic circuits. This work provides a promising route for using a single device to realize optoelectronic reconfigurable logic gates, which can advance the development of high-speed, high-throughput, and intricate data processing in future optical computing applications.

Enhanced photoresponse in Au-decorated MoSe2 photoanodes for dual-wavelength photoelectrochemical applications

By utilizing photovoltage competition between two photoelectrodes, we have successfully fabricated a photoelectrochemical (PEC) device that features switchable photocurrent polarity for wavelength-selective photodetection. Composed of distinct semiconductor materials, this device exhibits a negative photocurrent density of −1.98 μA/cm2 under 365 nm illumination and a positive photocurrent density of 0.46 μA/cm2 under 650 nm illumination, without requiring an external power source. The observed bidirectional photocurrent is attributed to the photovoltage competition mechanism between the photoelectrodes. Notably, the photocurrent and responsivity under 650 nm illumination are significantly enhanced following the deposition of Au nanoparticles on the MoSe2 photoelectrode. In a three-electrode system without ZnO electrodes, the photoresponse is increased by three orders of magnitude after Au nanoparticle modification. Similarly, in a two-electrode system with ZnO electrodes, the photoresponse is enhanced by more than fifty times following Au modification. This enhancement promotes more efficient redox reactions within the device, thereby offering a novel strategy for wavelength-selective photodetection. This innovation has substantial application potential in the field of photoelectrochemistry.

Self-Powered FTO/CdSe/Bi2Se3 Photodetector with Bipolar Photoresponse Characteristics.

Self-powered photodetectors with bipolar photoresponse characteristics are expected to play a critical role in the field of secure optical communication, artificial neuromorphic systems, and intelligent color sensors. In this work, asymmetric heterojunction devices exhibiting wavelength-dependent bipolar photoresponse with a structure of Glass/FTO/CdSe/Bi2Se3/Au were fabricated. Under a short wavelength light irradiation, the top CdSe absorber generates a high carrier concentration; the excited carriers are quickly separated by the built-in electric field induced by the FTO/CdSe diode, resulting in a negative photocurrent. For light with wavelengths beyond the CdSe absorption edge, it is absorbed by the bottom Bi2Se3 absorber, and a positive photocurrent can be observed. Therefore, based on the bandgap difference between the top CdSe absorber and the bottom Bi2Se3 absorber, combined with the photogenerated carriers separated by asymmetric back-to-back diode, a wavelength-dependent bipolar response is realized. In this work, by employing this structure, the responsivities of -33.3 and 0.3 mA/W were achieved under the illumination of 405 and 830 nm, respectively. This work provides important indications in the preparation and performance optimization for wavelength-dependent bipolar photodetectors.

Wavelength-modulated polarity switch self-powered Bi2Se3/GaN heterostructure photodetector

Van der Waals and wide-bandgap materials-based heterostructures have garnered substantial attention in developing self-powered broadband photodetectors owing to their exceptional photovoltaic capabilities. These materials also hold great potential for breakthroughs in optoelectronics. However, limitations to low selectivity constrain the potential of heterostructures-based broadband detectors. Here, we design wavelength-selective polarity switching in a heterostructure photodetector consisting of bismuth selenide (Bi2Se3) and gallium nitride (GaN). The analysis revealed a positive photocurrent under ultraviolet-C illumination to visible wavelength, whereas a negative photocurrent under infrared wavelengths at zero applied bias. The exposure to distinct optical wavelengths leads to an inversion in the electric field polarity across the junction, resulting in polarity switching. The fabricated Bi2Se3/GaN self-powered ultra-broadband photonic device demonstrates a peak photoresponsivity of 584 mAW−1 (−297 mAW−1) at 355 nm (1405 nm) wavelength illumination and can detect weak signals up to 650 femto-watt. Our strategy revealed alternative avenues for developing polarity-switchable, self-powered ultra-broadband photodetectors, offering a first step towards creating wavelength-adaptable sensors for future applications.

Self-powered SnSx/TiO2 photodetectors (PDs) with dual-band binary response and the applications in imaging and light-encrypted logic gates

In this work, we report the design and fabrication of self-powered binary response PDs based on II-type heterostructures consisting of SnSx nanoflakes (NFs) and rutile TiO2 nanorod arrays (NRs). The TiO2 NRs effectively block light with wavelengths below 400 nm from reaching SnSx. Under 385 nm light, the photoelectrons in TiO2 recombine with holes in SnSx at the interface due to the energy band bending, resulting in a positive photocurrent. Under 410 nm light, the photoelectrons in SnSx and the photogenerated holes in TiO2 accumulate at the interface, overcoming the interfacial potential barriers induced by the higher Fermi levels of SnSx and inducing a negative photocurrent. Based on the bipolar response, the dual-band imaging capability without external filters and the light-encrypted OR, AND, and NOT logic gates using a single device are demonstrated. This work provides a blueprint for the development of multifunctional self-powered PDs that can simplify system architecture, reduce the energy consumption, and improve accuracy for applications, such as visual systems, light-controlled logic circuits, and encrypted optical communications.

Self-Powered Programmable van der Waals Photodetectors with Nonvolatile Semifloating Gate.

Tunable photovoltaic photodetectors are of significant relevance in the fields of programmable and neuromorphic optoelectronics. However, their widespread adoption is hindered by intricate architectural design and energy consumption challenges. This study employs a nonvolatile MoTe2/hexagonal boron nitride/graphene semifloating photodetector to address these issues. Programed with pulsed gate voltage, the MoTe2 channel can be reconfigured from an n+-n to a p-n homojunction and the photocurrent transition changes from negative to positive values. Scanning photocurrent mapping reveals that the negative and positive photocurrents are attributed to Schottky junction and p-n homojunction, respectively. In the p-n configuration, the device demonstrates self-driven, linear, rapid response (∼3 ms), and broadband sensitivity (from 405 to 1500 nm) for photodetection, with typical performances of responsivity at ∼0.5 A/W and detectivity ∼1.6 × 1012 Jones under 635 nm illumination. These outstanding photodetection capabilities emphasize the potential of the semifloating photodetector as a pioneering approach for advancing logical and nonvolatile optoelectronics.

Gate‐controlled Multispectral Response in Graphene‐Based Heterostructure Photodetector

AbstractMultispectral photodetectors are crucial for detecting light across a wide wavelength range, serving applications requiring precise wavelength specificity and spectral imaging capabilities. However, the development of these photodetectors is hindered by several challenges, including material compatibility issues, low responsivity, the complexity of signal processing, and precise bandgap engineering. A strategy is proposed using a MoS2‐graphene photodetector to address these issues. Gate‐tunable spectral responses are achieved in a graphene photodetector by utilizing carrier transfer from MoS2 and interfacial gating effects from a SiO2/p‐doped Si substrate. Precise gate bias manipulation enables selective photocurrent capture in the range of 500–680 nm, identical to the absorption of MoS2. Furthermore, by applying a highly negative gate bias, photocurrent signals below the MoS2 bandgap, i.e., in the 680–800 nm region, are detected, significantly provoking broadband photodetection. The results highlight the versatility of gate‐tunable multispectral response, leading to an exceptional responsivity of up to 1.4 × 105 mA W−1. Moreover, through the precise modulation of gate bias and incident wavelength, it seamlessly switches between negative and positive photocurrents. This study provides important insight into carrier photogeneration in sensitized graphene‐based multifunctional optoelectronic devices, establishing a versatile platform for detecting a broad range of photocurrents with a single detector.

Abnormal Photocurrent in Semiconductor p‐n Heterojunctions: Toward Multifunctional Photoelectrochemical‐Type Photonic Devices and Beyond

AbstractSemiconductor p‐n heterojunctions are important building blocks for modern electronic and photonic devices. Further combining semiconductor p‐n heterojunctions with light and electrolyte environment, interesting photoelectrochemical (PEC) phenomena can occur, which enriches the design principles of multifunctional devices. In fact, recent years have witnessed the emergence of PEC‐type photonic devices. For PEC‐type photonic devices, a key to realize multifunctionality is to control the photocurrent polarity of the photoelectrode. In this study, an abnormal photocurrent is reported from p‐InGaN/n‐GaN nanowire heterojunctions under a blue light illumination: although n‐GaN is transparent to the blue light (and thus optical absorption mainly occurs in p‐InGaN) and p‐InGaN in principle can only give negative PEC photocurrent, the detailed experiments show that positive PEC photocurrent can be generated from the p‐InGaN segment due to the existence of the built‐in electric field at the p‐n junction. This study shows a new route to control the photocurrent polarity in a semiconductor p‐n heterojunction photoelectrode. This unveiled role of the built‐in electric field is expected to impact the design of emerging PEC‐type photonic devices, as well as other novel photonic and electronic devices based on semiconductor nanowire p‐n heterojunctions.

Self-Powered Wavelength-Dependent Dual-Polarity Response Photodetector Based on CdS@PEDOT:PSS@Au Sandwich-Structured Core-Shell Nanorod Arrays.

Self-powered operation and multifunctionality have significantly oriented the development of photodetectors (PDs), which could be realized through nanoarchitecture construction and energy band structure design. Herein, a self-powered wavelength-dependent dual-polarity response PD based on (CdS@PEDOT:PSS@Au) sandwich-structured core-shell nanorod arrays (NRAs) is proposed. The synthesis approach of this three-layer heterostructure consists of a hydrothermal reaction, spin coating, and thermal evaporation. The n-CdS/p-PEDOT:PSS junction and the PEDOT:PSS/Au Schottky junction at the interfaces provide two photocurrent driving forces in opposite directions, and their contribution to the net photocurrent is controlled by the incident light wavelength due to the different light absorption ranges of the CdS core and the PEDOT:PSS shell. As a result, the polarity of the photocurrent switches from negative to positive as the wavelength increases. In addition, the response speed of negative photocurrents (∼10 ms) is faster than that of positive photocurrents (∼100 ms), which is consistent with the underlying mechanism of the dual-polarity response. Furthermore, color discrimination and imaging capabilities are demonstrated by deploying the PDs as sensing pixels and recognizing green and red patterns. The sandwich-structured core-shell NRA heterojunction system introduces a novel idea for dual-polarity response PDs.

High‐Performance Silver‐Doped Porous CuBi2O4 Photocathode Integrated with NiO Hole‐Selective Layer for Improved Photoelectrochemical Water Splitting

AbstractCuBi2O4(CBO) has received considerable attention owing to its ideal optical bandgap and positive photocurrent onset potential. However, CBO photocathodes exhibit poor charge carrier separation and transfer across the conducting substrate interface. Herein, a systematic incorporation of Ag+‐cations into nanosized porous CBO network (ACBO) using a simple pulsed‐electrodeposition method. In ACBO photocathode, the Ag+‐ions replace the Bi3+‐ions, thereby building an increased hole concentration, which further signifies the photogenerated electron‐hole separation. Additionally, introducing a low‐cost NiO hole‐selective layer between ACBO and the conducting substrate enables a back‐interface‐aided hole‐extraction and electron blocking, resulting in an improved charge transfer across the back interface. Compared with an unmodified CBO, the NiO/ACBO photocathode exhibits a three‐fold enhanced photocurrent performance. This enhances the photocurrent originating from the incorporation of a substantial amount of Ag+‐ions into the CBO structure, leading to an increased acceptor density as well as the formation of an appropriate hole‐selective layer across the back‐contact. The absorption percentage, time‐resolved photoluminescence, and photoelectrochemical impedance spectroscopy measurements unveil the potential light harvesting, charge separation, and transfer characteristics of the NACBO photoelectrode, respectively. Through this systematic study, an efficient and simple strategy is determined for developing ternary metal oxide‐based photocathode/photoanode systems for sustainable energy applications.

Tunable negative photoconductivity in encapsulated ambipolar tellurene for functional optoelectronic device applications

Two-dimensional tellurium (2D Te) is a promising material for functional optoelectronic applications due to its narrow band gap and high carrier mobility. However, its light−matter interactions typically induce positive photoconductivity (PPC), leading to low photoresponsivity in 2D Te-based photodetectors due to their high dark current and the indirect 2D Te band gap. Here, we report novel tunable negative photoconductivity (NPC) in an Al2O3-encapsulated ambipolar 2D Te device, with excellent photoresponsivity of up to 6.9 × 104 A W−1, outperforming most previously reported 2D single-element chalcogen-based photodetectors. The NPC is attributed to the lower carrier mobility due to phonon scattering induced by the enhanced photothermal effect in the encapsulated Te layer. The threshold voltage can be tuned in the encapsulated 2D Te transistor under high-energy laser irradiation, demonstrating a new strategy for controlled 2D Te doping. Well-controlled gate-tunable negative and positive persistent photocurrents are achieved in the encapsulated 2D Te transistor, thus emulating biological synapse activity. An encapsulated 2D Te device with a flexible substrate also exhibits stable NPC after 1000 bending cycles, highlighting its potential use in wearable optoelectronic devices. The construction of ambipolar 2D Te phototransistors may pave the way for the development of novel functional optoelectronic devices.

Light-Induced Bipolar Photoresponse with Amplified Photocurrents in an Electrolyte-Assisted Bipolar p-n Junction.

The p-n junction with bipolar characteristics sets the fundamental unit to build electronics while its unique rectification behavior constrains the degree of carrier tunability for expanded functionalities. Herein, a bipolar-junction photoelectrode employed with a gallium nitride (GaN) p-n homojunction nanowire array that operates in electrolyte is reported, demonstrating bipolar photoresponse controlled by different wavelengths of light. Significantly, with rational decoration of a ruthenium oxides (RuOx ) layer on nanowires guided by theoretical modeling, the resulting RuOx /p-n GaN photoelectrode exhibits unambiguously boosted bipolar photoresponse by an enhancement of 775% and 3000% for positive and negative photocurrents, respectively, compared to the pristine nanowires. The loading of the RuOx layer on nanowire surface optimizes surface band bending, which facilitates charge transfer across the GaN/electrolyte interface, meanwhile promoting the efficiency of redox reaction for both hydrogen evolution reaction and oxygen evolution reaction which corresponds to the negative and positive photocurrents, respectively. Finally, a dual-channel optical communication system incorporated with such photoelectrode is constructed with using only one photoelectrode to decode dual-band signals with encrypted property. The proposed bipolar device architecture presents a viable route to manipulate the carrier dynamics for the development of a plethora of multifunctional optoelectronic devices for future sensing, communication, and imaging systems.

Feasibility and equivalence analysis of transient dose rate effect simulation by pulsed laser in level-shifting transceiver and TCAD simulation on its ESD circuits

Compared to linear accelerators, pulsed lasers have the characteristics of high efficiency, low cost, stable pulse output, and low environment interference for researching the transient dose rate effect (TDRE) on semiconductor devices. In this paper, pulsed laser radiation experiments are performed on a level-shifting transceiver. The experimental results are consistent with the results of the transient γ-ray radiation experiment, demonstrating the feasibility of using the pulsed laser in TDRE research on the level-shifting transceiver. This paper obtains theoretical and experimental conversion factors (CFs) through theoretical analysis and equivalency of the peak photocurrents, which are measured in pulsed laser and transient γ-ray radiation experiments. The CF results from the two approaches are within 7% of each other. In pulsed laser radiation experiments, an uncommon phenomenon is found. At the I/O (Input/Output) ports of the level-shifting transceiver, a trend of a positive photocurrent followed by a negative pulse is observed. A hypothesis is proposed that this photocurrent is produced by the turn-on and turn-off of the parasitic PNP (Positive-Negative-Positive) transistors in electrostatic discharge circuits at the level-shifting transceiver I/O ports. In addition, this hypothesis is verified by TCAD (Technology Computer Aided Design) simulations.

High-performance infrared photodetector based on single-wall carbon nanotube films

Bolometric photodetectors based on single-wall carbon nanotubes (SWCNTs) have shown advantages of an ultrawide absorption spectrum, high charge carrier mobility, good processability, and high mechanical flexibility. However, their detection performance needs to be improved to meet the requirements of real applications. A flexible infrared photodetector was fabricated based on high quality SWCNT films. The device showed an ultrahigh detectivity up to 1.35 × 108 Jones under a bias voltage of 0.2 V, and a short response time of 70 ms in air. In addition, we found that the photocurrent response of the detector was closely related to the structure of the SWCNT network. A negative photocurrent was measured using photodetectors constructed from highly-crystalline SWCNTs owing to dominant phonon scattering transfer, while a positive photocurrent was detected from those fabricated using defect-rich SWCNTs due to dominant electron hopping transfer. Our results shed light on the construction of high-performance SWCNT film-based infrared photodetectors.

Effect of oxygen vacancies on photoelectrochemical properties of amphoteric semiconductor Bi4Ti3O12 photoelectrode

Bi4Ti3O12 (BTO) photoelectrodes were fabricated by a sol-gel spin coating method and oxygen vacancy (OV) concentrations in BTO were regulated through a following heat-treatment in different atmospheres. Based on the results of XRD, XPS and HRTEM, OVs have been introduced in BTO after Ar processing. An interesting p/n type amphoteric photo-response characteristic was discovered in BTO as demonstrated by the LSV, CV plots and open-circuit photovoltage measurement. The typical amphoteric photo-response characteristic of BTO should be related to its special Fermi level structure and accordingly minor band bending in the interface between BTO and the electrolyte. The positive photocurrent density of Ar-BTO is 0.75 μA/cm2 at 0.5 V vs. Ag/AgCl, which is 4.4 times over that of BTO, and its photocurrent onset potential showed an obvious negative shift (∼0.1 V) in relative to BTO. The charge carrier densities of Ar-BTO was over 60% higher than that of BTO. The enhanced photoelectrochemical properties of Ar-BTO was ascribed to its abundant OVs which effectively inhibited recombination, boosted carrier injection efficiency and activated electrode surface as demonstrated by the EIS and PL characterizations. These findings provide new perspective for fabricating new type bismuth-based photoelectrodes and optimizing its photoelectrochemical performance.

High Performance Graphene-C60 -Bismuth Telluride-C60 -Graphene Nanometer Thin Film Phototransistor with Adjustable Positive and Negative Responses.

Graphene is a promising candidate for the next-generation infrared array image sensors at room temperature due to its high mobility, tunable energy band, wide band absorption, and compatibility with complementary metal oxide semiconductor process. However, it is difficult to simultaneously obtain ultrafast response time and ultrahigh responsivity, which limits the further improvement of graphene photoconductive devices. Here, a novel graphene/C60 /bismuth telluride/C60 /graphene vertical heterojunction phototransistor is proposed. The response spectral range covers 400-1800nm; the responsivity peak is 106 A W-1 ; and the peak detection rate and peak response speed reach 1014 Jones and 250 µs, respectively. In addition, the regulation of positive and negative photocurrents at a gate voltage is characterized and the ionization process in impurities of the designed phototransistor at a low temperature is analyzed. Tunable bidirectional response provides a new degree of freedom for phototransistors' signal resolution. The analysis of the dynamic change process of impurity energy level is conducted to improve the device's performance. From the perspective of manufacturing process, the ultrathin phototransistor (20-30nm) is compatible with functional metasurface to realize wavelength or polarization selection, making it possible to achieve large-scale production of integrated spectrometer or polarization imaging sensor by nanoimprinting process.

A tandem photoelectrochemical cell based on Cu2-xTe nanocrystals for solar energy conversion to hydrogen

In this work we present the design, assembly and characterization of a tandem photoelectrochemical (PEC) cell based on two different crystallographic phases of sub-stoichiometric copper telluride nanocrystals (NCs). The first one, a pseudo-cubic phase, pc-Cu 2-x Te, is characterized by positive photocurrents, while the second one, a hexagonal phase, h-Cu 2-x Te, favors negative ones. Taking advantage of the different optoelectronic properties of the two Cu 2-x Te structures, we prepared a PEC cell composed of a hybrid pc-Cu 2-x Te/TiO 2 photoanode, with TiO 2 acting as a light absorber and electron selective layer, and a h-Cu 2-x Te/CuI photocathode, with CuI behaving as a photo-absorber and hole selective layer. The tandem PEC cell shows a photocurrent density of ∼0.5 mA/cm 2 when measured in a 2-electrode configuration without any co-catalyst. Finally, to test the PEC cell performance for the hydrogen evolution reaction (HER), a thin film of Pt was deposited on top of the photocathode and ∼7 μmol of hydrogen were obtained at 0.6 V in a 1-h experiment, reaching a photocurrent of 1 mA/cm 2 with no losses. • Investigating the optoelectronic properties of different Cu2-XTe crystallographic phases and using them as photoelectrodes for the first time. • Combining Cu2-XTe with TiO2 and CuI to build fully working hybrid photoelectrodes. • Building a functional Tandem PEC cell for hydrogen evolution reaction (HER).

In2S3 Growth Templated by Aluminogermanate Double‐Walled Imogolite Nanotubes Toward Efficient Visible Light Photocatalysts

Different strategies combining semiconductors and nanomaterials have been explored to enhance the performance of visible light photocatalysts. This work reports the hydrothermal growth of In2S3 on the aluminogermanate double‐walled imogolite nanotubes and the photocatalytic properties of the resulting composites. The reaction conditions are optimized to ensure the linear growth of In2S3, while preserving the tubular structure of imogolite nanotubes. The imogolite–In2S3 composites show enhanced photocatalytic degradation of methyl orange compared to the control In2S3, exhibiting a fourfold increase in the photocatalytic dye degradation rate constant. Interestingly, these composites present a negative photocurrent response, indicating the generation of mobile holes, whereas both In2S3 and imogolite by themselves exhibit typical positive photocurrent behavior. The improvement in the photocatalytic dye degradation and the negative photocurrent response is attributed to the interface formation between In2S3 and imogolite in these composites and the p‐type character of the latter. Templating the colloidal synthesis of semiconducting nanoparticles in confined spaces could bring a step change in the design of catalytic and photocatalytic materials.

Wavelength and Polarization Sensitive Synaptic Phototransistor Based on Organic n-type Semiconductor/Supramolecular J-Aggregate Heterostructure.

Human retina- and brain-inspired optoelectronic synapses, which integrate light detection and signal memory functions for data processing, have significant interest because of their potential applications for artificial vision technology. In nature, many animals such as mantis shrimp use polarized light information as well as scalar information including wavelength and intensity; however, a spectropolarimetric organic optoelectronic synapse has been seldom investigated. Herein, we report an organic synaptic phototransistor, consisting of a charge trapping liquid-crystalline perylene bisimide J-aggregate and a charge transporting crystalline dichlorinated naphthalene diimide, that can detect both wavelength and polarization information. The device shows persistent positive and negative photocurrents under low and high voltage conditions, respectively. Furthermore, the aligned organic heterostructure in the thin-film enables linearly polarized light to be absorbed with a dichroic ratio of 1.4 and 3.7 under transverse polarized blue and red light illumination, respectively. These features allow polarized light sensitive postsynaptic functions in the device. Consequently, a simple polarization imaging sensor array is successfully demonstrated using photonic synapses, which suggests that a supramolecular material is an important candidate for the development of spectropolarimetric neuromorphic vision systems.

A hybrid graphene-PbS quantum dots photodetector with positive and negative photocurrents

Different graphene photodetectors may have different light response mechanisms, and in general, most graphene photodetectors tend to generate only positive or negative photocurrents. Here, we demonstrate a photodetector based on graphene grown by Chemical Vapor Deposition (CVD) and PbS quantum dots (QDs) with both positive and negative photocurrents. Under the irradiation of a 635 nm laser, the device generated positive photocurrents of 9 μA at a low laser power density (0.17 μW), the responsivity of which was up to 39.58 A/W due to the high gain mechanism. However, at high laser power density (9.59 μW), the device exhibits completely opposite characteristics due to thermal scattering. The negative photocurrents of 20 μA were generated and the responsivity of the device was 10.29 A/W. The device exhibits the coexistence of two response mechanisms. It is necessary to explore the mechanism of positive and negative photocurrent in graphene, which is helpful to investigate the regulation of graphene carriers, and can also provide a possible research direction for graphene-based memristor devices.