Ultrahigh, Ultrafast, and Self-Powered Visible-Near-Infrared Optical Position-Sensitive Detector Based on a CVD-Prepared Vertically Standing Few-Layer MoS2/Si Heterojunction

Ultrafast Multifunctional Photodetector Based on the NiAl2O4/4H-SiC Heterojunction

Solar-blind photodetectors based on wide bandgap semiconductors have recently attracted a lot of interest. Nickel-containing spinel phase oxides, such as NiAl2O4, are stable p-type semiconductors. This paper describes a multifunctional solar-blind photodetector based on a NiAl2O4/4H-SiC heterojunction that utilizes photovoltaic effects. The position sensitivity reaches a value of 1589.7 mV/mm under 405 nm laser illumination, while the relaxation times of vertical photovoltaic (VPV) effect and lateral photovoltaic (LPV) effect under 266 nm laser illumination are only 0.32 and 0.42 μs, respectively. This junction was used to create a space optical communication system with sunlight having little effect on its optoelectronic properties. The ultrafast photovoltaic relaxation time makes NiAl2O4/4H-SiC a promising candidate for self-powered high-performance solar-blind detectors.

Deciphering the bridge oxygen vacancy-induced cascading charge effect for electrochemical ammonia synthesis

Oxygen vacancy engineering has recently been gaining much interest as the charging effect it induces in a material can be used for varied applications. Usually, semiconductor materials act poorly in electrocatalysis, particularly in the nitrogen reduction reaction (NRR), owing to their inherent charge deficit and huge band gap. Vacancy introduction can be a viable material engineering route to make use of these materials for the NRR. However, a detailed investigation of the vacancy-type and its role for the structural reorientation and charge redistribution of a material is lagging in the field of NRRs. This work thus focuses on the synthesis of oxygen vacancy-engineered SnO2 with a gradual structural transformation from in-plane (iov) to bridge-type oxygen vacancy (bov) density. Consequently, the electron occupancy of the sp3d hybrid orbital changes, leading to an upshifted valence band maxima towards the Fermi level. This has a profound effect on the nature of N2 adsorption and the extent of NN bond polarization. Sn atoms adjacent to the bov are found to have a fair density of dangling charges that accomplish the NRR process at a comparatively low overpotential and determine the binding strength of the intermediates on the active site. The obscured yet stable reaction intermediates are thereby identified with in situ ATR-IR studies. A restricted hydrogen evolution reaction Faradaic on the Sn-site (favored over O-atoms) results in a Faradaic efficiency of 48.5%, which is better than that reported in all the literature reports on SnO2 for the NRR. This study thus unveils sufficient insights into the role of oxygen vacancies in a crystal as well as electronic structural alteration of SnO2 and the effect of active sites on the rate kinetics of the NRR.

Insight into the intrinsic activity of various transition metal sulfides for efficient hydrogen evolution reaction

The electrocatalytic hydrogen evolution reaction (HER) is an efficient approach to convert sustainable energy sources into clean energy carriers, H2. Although various transition metal sulfides (TMSs) have been reported as promising alternatives to precious metal-based catalysts, the top catalyst among TMSs remains unclear as there is a dearth of high-quality studies that provide a 'fair' comparison of the performance of these TMSs synthesized and tested under the same conditions. In this work, layered transition metal sulfides (MS2: MoS2, WS2, VS2) and non-layered transition metal sulfides (MxSy: FeS2, CoSx, NiS) were obtained by a straightforward hydrothermal method, and thus a comprehensive platform was established for the comparison of the intrinsic activity of these materials in the HER. Experimental results demonstrate that layered MS2 exhibits better performance than non-layered MxSy in acidic electrolytes, while CoSx and NiS can catalyze hydrogen evolution more effectively under alkaline conditions due to structural reconfiguration. MoS2 shows the best HER performance in both acidic and alkaline electrolytes, particularly in 1 M KOH solution. This work provides guidance for the optimal design of transition metal electrocatalysts, and structural engineering strategies can be used to further enhance their catalytic activity.

Polarization-Resolved Position-Sensitive Self-Powered Binary Photodetection in Multilayer Janus CrSBr

Recent progress in polarization-resolved photodetection based on low-symmetry 2D materials has formed the basis of cutting-edge optoelectronic devices, including quantum optical communication, 3D image processing, and sensing applications. Here, we report an optical polarization-resolving photodetector (PD) fabricated from multilayer semiconducting CrSBr single crystals with high structural anisotropy. We have demonstrated self-powered photodetection due to the formation of Schottky junctions at the Au-CrSBr interfaces, which also caused the photocurrent to display a position-sensitive and binary nature. The self-biased CrSBr PD showed a photoresponsivity of ∼0.26 mA/W with a detectivity of 3.4 × 108 Jones at 514 nm excitation of fluency (0.42 mW/cm2) under ambient conditions. The optical polarization-induced photoresponse exhibits a large dichroic ratio of 3.4, while the polarization is set along the a- and the b-axes of single-crystalline CrSBr. The PD also showed excellent stability, retaining >95% of the initial photoresponsivity in ambient conditions for more than five months without encapsulation. Thus, we demonstrate CrSBr as a fascinating material for ultralow-powered optical polarization-resolving optoelectronic devices for cutting-edge technology.

Photogating induced high sensitivity and speed from heterostructure of few-layer MoS2 and reduced graphene oxide-based photodetector

Over the past few years, two-dimensional transition metal dichalcogenides (2D-TMDC) have attracted huge attention due to their high mobility, high absorbance, and high performance in generating excitons (electron and hole pairs). Especially, 2D molybdenum disulfide (MoS2) has been extensively used in optoelectronic and photovoltaic applications. Due to the low photo-to-dark current ratio (Iphoto/dark) and low speed, pristine MoS2-based devices are unsuitable for these applications. So, they need some improvements, i.e., by adding layers or decorating with materials of complementary majority charges. In this work, we decorated pristine MoS2 with reduced graphene oxide (rGO) and got improved dark current, Iphoto/dark, and response time. When we compared the performance of pristine MoS2 based device and rGO decorated MoS2 based device, the rGO/MoS2-based device showed an improved performance of responsivity of 3.36 A W-1, along with an Iphoto/dark of about 154. The heterojunction device exhibited a detectivity of 4.75 × 1012 Jones, along with a very low response time of 0.184 ms. The stability is also outstanding having the same device performance even after six months.

High-Performance Self-Powered Photodetector Based on the Lateral Photovoltaic Effect of All-Inorganic Perovskite CsPbBr3 Heterojunctions

CsPbBr₃, an inorganic halide perovskite, has attracted great interest in recent years due to its excellent photoelectric properties. In this paper, we report a high-performance position-sensitive detector and laser communication sensor based on a CsPbBr₃/4H-SiC heterojunction that effectively exploits the lateral photovoltaic (LPV) effect. The X-ray diffraction, X-ray photoelectron spectra, and photoluminescence data indicate that a high-quality CsPbBr₃ film has been successfully obtained using pulsed laser deposition. The thickness of the CsPbBr₃ film is shown to play a key role in the open-circuit voltage and linear LPV. A large position sensitivity (up to 827 mV/mm) of the LPV with a fast relaxation time is observed. Moreover, the shortest relaxation time of only 0.34 μs for 532 nm laser irradiation among counterparts is achieved in the detector under consideration. Furthermore, the position sensitivity and relaxation time of the LPV in the CsPbBr₃/4H-SiC heterojunction show a weak dependence on the laser wavelength from 266 to 532 nm. The robust characteristics of fast relaxation time and high position sensitivity of the LPV make the CsPbBr₃ junction a promising candidate for both laser communication sensors and self-powered high-performance position-sensitive detectors.

A Time-Division Position-Sensitive Detector Image System for High-Speed Multitarget Trajectory Tracking

High-speed trajectory tracking with real-time processing capability is particularly important in the fields of pilotless automobiles, guidance systems, robotics, and filmmaking. The conventional optical approach to high-speed trajectory tracking involves charge coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) image sensors, which suffer from trade-offs between resolution and framerates, complexity of the system, and enormous data-analysis processes. Here, a high-speed trajectory tracking system is designed by using a time-division position-sensitive detector (TD-PSD) based on a graphene-silicon Schottky heterojunction. Benefiting from the high-speed optoelectronic response and sub-micrometer positional accuracy of the TD-PSD, multitarget real-time trajectory tracking is realized, with a maximum image output framerate of up to 62 000 frames per second. Moreover, multichannel trajectory tracking and image-distortion correction functionalities are realized by TD-PSD systems through frequency-related image preprocessing, which significantly improves the capacity of real-time information processing and image quality in complicated light environments.

Multifunctional high-performance position sensitive detector based on a Sb2Se3-nanorod/CdS core-shell heterojunction

Sb₂Se₃ exhibits fascinating optical and electrical properties owing to its unique one-dimensional crystal structure. In this study, a Sb₂Se₃-nanorod/CdS core-shell heterostructure was successfully constructed, and the lateral photovoltaic effect (LPE), as well as the lateral photocurrent and photoresistance effects, were first studied. The measurements indicate that this heterojunction exhibits excellent lateral photoelectric performance in a broad range of 405-1064 nm with the best position sensitivities (PSs) of 525.9 mV/mm, 79.1 µA/mm, and 25.6 kΩ/mm for the lateral photovoltage, photocurrent, and photoresistance, respectively, while the nonlinearity is maintained below 7%, demonstrating its great potential in a novel high-performance multifunctional position sensitive detector (PSD). Moreover, this PSD could work well at different frequencies with good stability and repeatability, and the rise and fall times were deduced to be 48 and 180 µs, respectively. Besides, large linear working distances are achieved in this heterojunction PSD, and the PS can still reach 75.5 mV/mm even at an ultra-large working distance of 9 mm. These outstanding performances can be attributed to the high-quality Sb₂Se₃ nanorod arrays and the fast charge-carrier separation and transport properties of this core-shell heterojunction. This study provides important ideas for developing high-performance, broadband, large working distances, and ultrafast multifunctional PSDs based on the new core-shell heterostructure.

Polarization Sensitive Photodetectors Based on Two-Dimensional WSe2

In this work we show the possibility of imparting polarization-sensitive properties to two-dimensional films of graphene-like semiconductors, using WSe2 as an example, by the application of ordered silver triangular nanoprisms. In addition, such nanoprisms made it possible to increase the optical sensitivity of optical detectors created on two-dimensional films by a factor of five due to surface plasmon resonance. The peculiarities of the surface plasmon resonance were shown by theoretical modeling, and the optimal conditions of its occurrence were determined. This article demonstrates an effective approach to creating spectrally selective, polarization-sensitive detectors based on two-dimensional graphene-like semiconductors.

Generation of a Charge Carrier Gradient in a 3C-SiC/Si Heterojunction with Asymmetric Configuration

It is critical to investigate the charge carrier gradient generation in semiconductor junctions with an asymmetric configuration, which can open a new platform for developing lateral photovoltaic and self-powered devices. This paper reports the generation of a charge carrier gradient in a 3C-SiC/Si heterojunction with an asymmetric electrode configuration. 3C-SiC/Si heterojunction devices with different electrode widths were illuminated by laser beams (wavelengths of 405, 521, and 637 nm) and a halogen bulb. The charge carrier distribution along the heterojunction was investigated by measuring the lateral photovoltage generated when the laser spot scans across the 3C-SiC surface between the two electrodes. The highest lateral photovoltage generated is 130.58 mV, measured in the device with an electrode width ratio of 5 and under 637 nm wavelength and 1000 μW illumination. Interestingly, the lateral photovoltage was generated even under uniform illumination at zero bias, which is unusual for the lateral photovoltage, as it can only be generated when unevenly distributed photogenerated charge carriers exist. In addition, the working mechanism and uncovered behavior of the lateral photovoltaic effect are explained based on the generation and separation of electron-hole pairs under light illumination and charge carrier diffusion theory. The finding further elaborates the underlying physics of the lateral photovoltaic effect in nano-heterojunctions and explores its potential in developing optoelectronic sensors.

High-performance broadband position-sensitive detector based on lateral photovoltaic effect of PbSe heterostructure

PbSe has attracted considerable attention due to its promising applications in optoelectronics and energy harvesting. In this work, we explore the lateral photovoltaic effect (LPE) of PbSe films with a simple PbSe/Si heterostructure under nonuniform light illumination and zero-bias conditions. The LPE response is strongly dependent on the thickness of the PbSe film, but always shows a linear dependence on the laser spot position in an ultra-large working size of 5 mm and exhibits a wide photoresponse ranging from visible to near-infrared. The maximum position sensitivity can reach up to 190 mV/mm for the 15-nm-thick PbSe device at 1064 nm and nonlinearity is less than 4%, demonstrating its new potential application in novel position sensitive detectors (PSDs). Besides, the device also shows an ultrafast response speed, with the rise and fall time of ∼40 µs and ∼105 µs, respectively, and excellent reproducibility. These results bring great inspirations for developing high-performance broadband and self-powered PSDs based on the PbSe/Si heterostructure.

Broadband photodetector based on ReS2/graphene/WSe2heterostructure

Two-dimensional van der Waals heterostructures can combine properties of individual materials to enable high-performance photodetection. Here, a novel ReS₂/graphene/WSe₂heterostructure, prepared by dry transfer, demonstrates air-stable, high-performance, polarization-sensitive, and broadband photodetection. Dark current can be strongly suppressed by the built-in electric field of the heterostructure. The specific detectivities are up to 10¹⁰Jones and 10⁹Jones under zero and reverse bias, respectively. Response time is on the order of a millisecond. The polarization-sensitive photodetection has been observed in the heterostructure due to the low lattice symmetry of ReS₂. Broadband photoresponse from visible to infrared range has been demonstrated. A high photoresponsivity of 1.02 A W^-1is achieved for illumination at the wavelength of 785 nm. This work provides a viable approach toward future high-performance, air-stable, and polarization-sensitive broadband photodetectors.

Multielement 2D layered material photodetectors

The pronounced quantum confinement effects, outstanding mechanical strength, strong light-matter interactions and reasonably high electric transport properties under atomically thin limit have conjointly established 2D layered materials (2DLMs) as compelling building blocks towards the next generation optoelectronic devices. By virtue of the diverse compositions and crystal structures which bring about abundant physical properties, multielement 2DLMs (ME2DLMs) have become a bran-new research focus of tremendous scientific enthusiasm. Herein, for the first time, this review provides a comprehensive overview on the latest evolution of ME2DLM photodetectors. The crystal structures, synthesis, and physical properties of various experimentally realized ME2DLMs as well as the development in metal-semiconductor-metal photodetectors are comprehensively summarized by dividing them into narrow-bandgap ME2DLMs (including Bi₂O₂X (X = S, Se, Te), EuMTe₃(M = Bi, Sb), Nb₂XTe₄(X = Si, Ge), Ta₂NiX₅(X = S, Se), M₂PdX₆(M = Ta, Nb; X = S, Se), PbSnS₂), moderate-bandgap ME2DLMs (including CuIn₇Se₁₁, CuTaS₃, GaGeTe, TlMX₂(M = Ga, In; X = S, Se)), wide-bandgap ME2DLMs (including BiOX (X = F, Cl, Br, I), MPX₃(M = Fe, Ni, Mn, Cd, Zn; X = S, Se), ABP₂X₆(A = Cu, Ag; B = In, Bi; X = S, Se), Ga₂In₄S₉), as well as topological ME2DLMs (MIrTe₄(M = Ta, Nb)). In the last section, the ongoing challenges standing in the way of further development are underscored and the potential strategies settling them are proposed, which is aimed at navigating the future advancement of this fascinating domain.

Contact Engineering of Vertically Grown ReS2 with Schottky Barrier Modulation

Forming metal contact with low contact resistance is essential for the development of electronics based on layered van der Waals materials. ReS₂ is a semiconducting transition metal dichalcogenide (TMD) with an MX₂ structure similar to that of MoS₂. While most TMDs grow parallel to the substrate when synthesized using chemical vapor deposition (CVD), ReS₂ tends to orient itself vertically during growth. Such a feature drastically increases the surface area and exposes chemically active edges, making ReS₂ an attractive layered material for energy and sensor applications. However, the contact resistances of vertically grown materials are known to be relatively high, compared to those of common 2H-phase TMDs, such as MoS₂. Most reported methods for lowering the contact resistance have been focused on exfoliated 2H-phase materials with only a few devices tested, and few works on distorted T-phase materials exist. Moreover, nearly all reported studies have been conducted on only a few devices with mechanically exfoliated fl Most reported methods for lowering the contact resistance have been ₂ contacts was modulated by conformally coating a thin tunneling interlayer between the metal and the dendritic ReS₂ film. Over a hundred devices were tested, and contact resistances were extracted for large-scale statistical analysis. Importantly, we compared various known materials and techniques for lowering contact resistance and found an optimized method. Finally, the reductions in barrier height were directly correlated with exponential reductions in contact resistance and increases in drive-current by almost 2 orders of magnitude.

Photothermoelectric SnTe Photodetector with Broad Spectral Response and High On/Off Ratio

A broadband photodetector with high performance is highly desirable for the optoelectric and sensing application. Herein, we report a "photo-thermo-electric" (PTE) detector based on an ultrathin SnTe film. The (001)-oriented SnTe films with the wafer size scale are epitaxially grown on the surface of sodium chloride crystals by a scalable sputtering method. Due to the giant PTE effect under laser spot excitation on the asymmetric position between two terminals, a built-in electrical field is produced to drive bulk carriers for a self-powered photodetector, leading to a broad spectral response in the wavelength range from 404 nm to 10.6 μm far beyond the limitation of the energy band gap. Significantly, the photodetector displays a high on/off photoswitching ratio of over 10⁵ with a suppressed dark current, which is 4-5 orders of magnitude higher than that of other reported SnTe-based detectors. Under zero external bias, the device yields the highest detectivity of ∼1.3 × 10¹⁰ cm Hz^1/2 W^-1 with a corresponding responsivity of ∼3.9 mA W^-1 and short rising/falling times of ∼78/84 ms. Furthermore, the photodetector transferred onto the flexible template exhibits excellent mechanical flexibility over 300 bending cycles. These findings offer feasible strategies toward designing and developing low-power-consumption wearable optoelectronics with competitive performance.

Device Architecture for Visible and Near-Infrared Photodetectors Based on Two-Dimensional SnSe2 and MoS2: A Review

While band gap and absorption coefficients are intrinsic properties of a material and determine its spectral range, response time is mainly controlled by the architecture of the device and electron/hole mobility. Further, 2D-layered materials such as transition metal dichalogenides (TMDCs) possess inherent and intriguing properties such as a layer-dependent band gap and are envisaged as alternative materials to replace conventional silicon (Si) and indium gallium arsenide (InGaAs) infrared photodetectors. The most researched 2D material is graphene with a response time between 50 and 100 ps and a responsivity of <10 mA/W across all wavelengths. Conventional Si photodiodes have a response time of about 50 ps with maximum responsivity of about 500 mA/W at 880 nm. Although the responsivity of TMDCs can reach beyond 10⁴ A/W, response times fall short by 3–6 orders of magnitude compared to graphene, commercial Si, and InGaAs photodiodes. Slow response times limit their application in devices requiring high frequency. Here, we highlight some of the recent developments made with visible and near-infrared photodetectors based on two dimensional SnSe₂ and MoS₂ materials and their performance with the main emphasis on the role played by the mobility of the constituency semiconductors to response/recovery times associated with the hetero-structures.

Effects of Mo vapor concentration on the morphology of vertically standing MoS2 nanoflakes

Vertically standing MoS₂ nanoflakes are favourable in applications such as energy storage devices, hydrogen evolution reactions, and gas sensors due to their large surface area and high density of exposed edges. In this work, we report the effect of Mo vapor concentration on the morphology of vertical MoS₂ nanoflakes prepared by chemical vapor deposition at atmospheric pressure. A series of MoS₂ samples were grown under different Mo vapor concentrations by varying the separation distance (x) between the MoO₃ source and the substrate. Field emission scanning electron microscopy showed the sample grown at x = 1 cm had a high density of vertical flakes (7 vertical flakes µm^-2) with an average flake length of ~770 nm and thickness of ~10 nm. As x increased to 4 cm, the average flake length was reduced to ~150 nm while the flake orientation changed from vertical to lateral. That is, high Mo vapor concentration favours the formation of large and vertical MoS₂ nanoflakes. However, oversupply of Mo vapor results in significantly thicker flakes. Raman spectra of all samples showed two main peaks at 380 and 407 cm^-1 that correspond to the E¹ _{2 g} and A_{1 g} vibrational peaks of MoS₂. As x decreased from 4 to 1, the peak intensity ratio (E¹ _2g/A_{1 g}) reduced from 0.58 to 0.42, suggesting greater dominance of vertical flakes at low x. X-ray diffraction data showed a prominent peak at 14.4°, which corresponded to the (002) diffraction peak of 2H MoS₂. Transmission electron microscopy verified the flakes consist of eight layers with an interlayer spacing of 0.62 nm. Based on hydrogen evolution reaction measurements, samples with thin flakes have high catalytic activity. This work highlights the importance of optimizing Mo vapor concentration to obtain a high density of thin, large, and vertically standing MoS₂ nanoflakes.

An Electrically Modulated Single-Color/Dual-Color Imaging Photodetector

An electrically modulated single-/dual-color imaging photodetector with fast response speed is developed based on a small molecule (CO_i 8DFIC)/perovskite (CH₃ NH₃ PbBr₃ ) hybrid film. Owing to the type-I heterojunction, the device can facilely transform dual-color images to single-color images by applying a small bias voltage. The photodetector exhibits two distinct cut-off wavelengths at ≈544 nm (visible region) and ≈920 nm (near-infrared region), respectively, without any power supply. Its two peak responsivities are 0.16 A W^-1 at ≈525 nm and 0.041 A W^-1 at ≈860 nm with a fast response speed (≈10² ns). Under 0.6 V bias, the photodetector can operate in a single-color mode with a peak responsivity of 0.09 A W^-1 at ≈475 nm, showing a fast response speed (≈10² ns). A physical model based on band energy theory is developed to illustrate the origin of the tunable single-/dual-color photodetection. This work will stimulate new approaches for developing solution-processed multifunctional photodetectors for imaging photodetection in complex circumstances.

High-performance position-sensitive detector based on the lateral photoelectrical effect of two-dimensional materials

Two-dimensional (2D) materials such as graphene and transition-metal chalcogenides have been extensively studied because of their superior electronic and optical properties. Recently, 2D materials have shown great practical application in position-sensitive detectors (PSDs), originating from the lateral photoelectrical effect of the materials or junctions. The high position sensitivity and ultrafast photoresponse of PSDs based on 2D materials, especially compatibility with Si technology, may enable diverse optoelectronic applications. In this review, recent studies of PSDs based on 2D materials are summarized, providing a promising route for high-performance PSDs.

Lateral bipolar photoresistance effect in the CIGS heterojunction and its application in position sensitive detector and memory device

Cu(In,Ga)Se₂ (CIGS) based multilayer heterojunction, as one of the best high efficiency thin film solar cells, has attracted great interest due to its outstanding features. However, the present studies are primarily focused on the structure optimization and modulation in order to enhance the photoelectric conversion efficiency. Here, we exploit another application of this multilayer heterostructure in photoresistance-modulated position sensitive detector by introducing lateral photoresistance effect. The lateral photoresistance measurements show that this multilayer heterojunction exhibits a wide spectral response (~330 to ~1150 nm) and excellent bipolar photoresistance performances (position sensitivity of ~63.26 Ω/mm and nonlinearity <4.5%), and a fast response speed (rise and fall time of ~14.46 and ~14.42 ms, respectively). More importantly, based on the lateral photoresistance effect, the CIGS heterostructure may also be developed as a position-dependent resistance memory device, which can be modulated by changing laser intensity, wavelength, and bias voltage with excellent stability and repeatability, and the position resolution reaches up to 1 μm. These results can be well explained by considering the diffusion and the drift model of carriers in the CIGS multilayer heterojunction. This work provides a new approach of achieving novel photoelectric sensors and memory devices based on the traditional photovoltaic heterostructures.

Large Area Vertically Oriented Few-Layer MoS2 for Efficient Thermal Conduction and Optoelectronic Applications

Large area growth of MoS₂ can show great advances in optoelectronic devices due to its unique optical and electronic properties. Here, we directly grow vertically oriented and interconnected few-layer MoS₂ over 1 × 1 cm² of p-type Si substrate using CVD technique. We report for the first time the thermal conductivity of vertically oriented few-layer (VFL) MoS₂ using the optothermal Raman technique. The reduced phonon-defect scattering due to minimal defects and strains in VFL MoS₂ results in excellent thermal conductivity of 100 ± 14 W m^-1 K^-1 at room temperature. The photoluminescence and DFT study confirm the semiconducting behavior of VFL-MoS₂. The VFL-MoS₂/Si photodiode shows high photoresponsivity of 7.37 A W^-1 at -2.0 V bias under 0.15 mW cm^-2 intensity of 532 nm laser. The enhanced light trapping and highly exposed edges of VFL MoS₂ due to vertical orientation, formation of efficient p-n junction at the MoS₂/Si interface and effective charge separation leads to the excellent performance of grown VFL-MoS₂ for optoelectronic applications.

Maskless Micro/Nanopatterning and Bipolar Electrical Rectification of MoS2 Flakes Through Femtosecond Laser Direct Writing

Molybdenum disulfide (MoS₂) micro/nanostructures are desirable for tuning electronic properties, developing required functionality, and improving the existing performance of multilayer MoS₂ devices. This work presents a useful method to flexibly microprocess multilayer MoS₂ flakes through femtosecond laser pulse direct writing, which can directly fabricate regular MoS₂ nanoribbon arrays with ribbon widths of 179, 152, 116, 98, and 77 nm, and arbitrarily pattern MoS₂ flakes to form micro/nanostructures such as single nanoribbon, labyrinth array, and cross structure. This method is mask-free and simple and has high flexibility, strong controllability, and high precision. Moreover, numerous oxygen molecules are chemically and physically adsorbed on laser-processed MoS₂, attributed to roughness defect sites and edges of micro/nanostructures that contain numerous unsaturated edge sites and highly active centers. In addition, electrical tests of the field-effect transistor fabricated from the prepared MoS₂ nanoribbon arrays reveal new interesting features: output and transfer characteristics exhibit a strong rectification (not going through zero and bipolar conduction) of drain-source current, which is supposedly attributed to the parallel structures with many edge defects and p-type chemical doping of oxygen molecules on MoS₂ nanoribbon arrays. This work demonstrates the ability of femtosecond laser pulses to directly induce micro/nanostructures, property changes, and new device properties of two-dimensional materials, which may enable new applications in electronic devices based on MoS₂ such as logic circuits, complementary circuits, chemical sensors, and p-n diodes.

High sensitivity Si-based photodetection with nanoscale protective layer based on interface states

A large lateral photovoltaic effect has been observed at the interface of SiO₂/p-Si/SiO₂ structure. Different from the traditional Schottky junction or PN junction device, this photovoltage is mainly dominated by the interface states existing at SiO₂/p-Si interface, where the covered nanoscale SiO₂ layer brings this device a stable and high photoelectric performance. These interface states can be explained as built-in field caused by the band bending at interface, which regulates the generation and diffusion of photo induced carriers. In this study, we discuss clearly the factors that impact greatly on the photovoltage output and sensitivity, including the oxide thickness, resistivity and tunneling effect. We believe this simple but efficient device will be beneficial for the exploring in photoelectric detection.

Toward a Fast and Highly Responsive SnSe2-Based Photodiode by Exploiting the Mobility of the Counter Semiconductor

In photodetection, the response time is mainly controlled by the device architecture and electron/hole mobility, while the absorption coefficient and the effective separation of the electrons/holes are the key parameters for high responsivity. Here, we report an approach toward the fast and highly responsive infrared photodetection using an n-type SnSe₂ thin film on a p-Si(100) substrate keeping the overall performance of the device. The I- V characteristics of the device show a rectification ratio of ∼147 at ±5 V and enhanced optoelectronic properties under 1064 nm radiation. The responsivity is 0.12 A/W at 5 V, and the response/recovery time constants were estimated as ∼57 ± 25/34 ± 15 μs, respectively. Overall, the response times are shown to be controlled by the mobility of the constituent semiconductors of a photodiode. Further, our findings suggest that n-SnSe₂ can be integrated with well-established Si technology with enhanced optoelectronic properties and also pave the way in the design of fast response photodetectors for other wavelengths as well.

High Response, Self-Powered Photodetector Based on the Monolayer MoS2/P-Si Heterojunction with Asymmetric Electrodes

Here, a self-powered photodetector based on the monolayer MoS₂/P-Si heterojunction with asymmetric electrodes was fabricated. The MoS₂/p-Si heterojunction photodetector with asymmetric electrodes offers the advantages over the conventional heterojunction photodetector on optoelectronic applications in terms of strong built-in electric field and fast photogenerated carrier separation and transport. Significantly, the MoS₂/P-Si heterojunction exhibited an obvious photovoltaic effect, which can be used as the self-powered photodetector operating without any bias voltage. At a voltage bias of 0 V, the photocurrent of the detector is 23 nA, and its photoresponse/recovery time is 84 ms/136 ms. When at bias, the detector shows a ratio of photocurrent to dark current up to 3120, high responsivity of 117 A W^-1, and fast photoresponse/recovery time of 74 ms/115 ms. Our work illustrates the great potential of the MoS₂/P-Si heterojunction device with asymmetric electrodes on photovoltaic applications.

High-performance photodetector based on hybrid of MoS2 and reduced graphene oxide

2D materials are a promising new class of materials for next generation optoelectronic devices owing to their appealing optical and electrical properties. Pristine molybdenum disulfide (MoS₂) is widely used in next generation photovoltaic and optoelectronic devices, but its low photo-dark current ratio prevents its use in highly efficient photo detection applications. Here, we decorated crumpled reduced graphene oxide (rGO) particles on a large-area vertically aligned MoS₂ flake network to enhance the performance of the MoS₂-based photodetector by forming multiple nanoscale p-n heterojunctions. The rGO/MoS₂ device exhibited a significantly improved photoresponsivity of ∼2.10 A W^-1 along with a good detectivity of ∼5 × 10¹¹ Jones (Jones = cm Hz^1/2/W) compared to that of the pristine MoS₂ photodetector in ambient atmosphere. Moreover, the rGO/MoS₂ photodetector showed a fast response of ∼18 ms with excellent stability and reproducibility in ambient air even after three months. The high performance of the photodetector is attributed to enhanced photoexcited carrier density and suppressed photo generated electron-hole recombination due to the strong local built-in electric field developed at the rGO/MoS₂ interface. Our results showed that integration of rGO with MoS₂ provides an efficient platform for photo detection applications.