2D material broadband photodetectors

Recent advances in bismuth oxychalcogenide nanosheets for sensing applications

This review offers insights into the fundamental properties of bismuth oxychalcogenides Bi2O2X (X = S, Se, Te) (BOXs), concentrating on recent advancements primarily from studies published over the past five years. It examines the physical characteristics of these materials, synthesis methods, and their potential as critical components for gas sensing, biosensing, and optical sensing applications. Moreover, it underscores the implications of these advancements for the development of military, environmental, and health monitoring devices.

Self-Assembled BiGaSeAs Composite Superlattice-Structured Nanowire for Broad-Band Photodetection

Photodetectors with a broad-band response range are widely used in many fields and are regarded as pivotal components of the modern miniaturized electronics industry. However, commercial broad-band photodetectors composed of traditional bulk semiconductor materials are still limited by complex preparation techniques, high costs, and a lack of mechanical strength and flexibility, which are difficult to satisfy the increasing demand for flexible and wearable optoelectronics. Therefore, researchers have been devoted to finding new strategies to obtain flexible, stable, and high-performance broad-band photodetectors. In this work, a novel self-assembled BiGaSeAs composite superlattice-structured nanowire was developed with a simple chemical vapor deposition method for easy fabrication. After the device assembling, the photodetector showed outstanding performance in terms of obvious Ion/Ioff (13.9), broad-band photoresponse (365-940 nm), excellent responsivity (1007.67 A/W), high detectivity (9.38 × 109 Jones), and rapid response (21 and 23 ms). The formation of microheterojunctions among various materials inside the nanowires also contributed to their extended broad-spectrum response and outstanding detection ability. These results indicate that the BiGaSeAs nanowires have potential applications in the field of flexible and wearable electronics.

Electrically tunable interlayer recombination and tunneling behavior in WSe2/MoS2 heterostructure for broadband photodetector

Electrically tunable band structure and light-matter interaction are of great importance in designing novel devices and constructing high-integrated and high-performance photodetector systems in the future. However, tunable mechanisms on the layered semiconductor, especially the heterojunction, are still unclear. Herein, the WSe2/MoS2 phototransistor with dual-gated configuration is fabricated, and its electrical and photoelectrical conversion has been studied to show large tunability. It was found that conduction and rectification characteristics can be tuned by dual gates showing four states, p-i, p-n, i-n, and n-n, as a result of the charging and depletion of WSe2 and MoS2. The rectifying ratio can be modulated across a large range from 102.5 to 10-3.2. Its photoelectronic characteristics were observed to exhibit bipolar and wavelength-dependent behaviors. The interlayer recombination of charge carriers dominates the photoresponse of the device under the illumination of visible light, while it is dominated by interlayer tunneling under the illumination of near-infrared wavelengths. This bipolar photoresponse is associated with different states of band alignment, which can be switched by dual-gating modulation. Finally, by tuning the gate voltage, responsivities reach 27 445 A W-1 and 2827 A W-1 at wavelengths of 400 and 1010 nm at room temperature, respectively, which directly extends the response region from visible light to near-infrared.

Giant optical absorption of a PtSe2-on-silicon waveguide in mid-infrared wavelengths

Low-dimensional platinum diselenide (PtSe2) is a promising candidate for high-performance optoelectronics in the short-wavelength mid-infrared band due to its high carrier mobility, excellent stability, and tunable bandgap. However, light usually interacts moderately with low-dimensional PtSe2, limiting the optoelectronic responses of PtSe2-based devices. Here we demonstrated a giant optical absorption of a PtSe2-on-silicon waveguide by integrating a ten-layer PtSe2 film on an ultra-thin silicon waveguide. The weak mode confinement in the ultra-thin waveguide dramatically increases the waveguide mode overlap with the PtSe2 film. Our experimental results show that the absorption coefficient of the PtSe2-on-silicon waveguide is in the range of 0.0648 dB μm-1 to 0.0704 dB μm-1 in a spectral region of 2200 nm to 2300 nm wavelengths. Furthermore, we also studied the optical absorption in an ultra-thin silicon microring resonator. Our study provides a promising approach to developing PtSe2-on-silicon hybrid optoelectronic integrated circuits.

Solution-Processed Sb2S3-Based Heterojunction for Self-Powered Broad Band Weak Light Detection

Antimony sulfide (Sb2S3) has recently regained the attention of photovoltaic researchers as a promising solar absorber; however, its application for the detection of white light remains relatively unexplored. Herein, we report on the self-powered heterojunction photodetector based on a device-grade Sb2S3 film made at low temperature with solution processing. The Sb2S3 absorber film was prepared by single-step spin coating of a novel precursor ink using antimony trichloride as the antimony source along with the low melting thioacetamide as the sulfur source in 2-methoxyethanol, a low boiling environmentally friendly solvent. A simple TiO2/Sb2S3 heterojunction device made by using the film shows a power conversion efficiency of 1.22% without any hole transporting layer. Interestingly, the self-powered photodetector performance of the device under white light exhibits a high on/off ratio of 2.2 × 104 under 1 sun illumination. Moreover, this optical filter-free ultraviolet-visible absorbing near-infrared blind photodetector is equally capable of detecting both strong and weak white light, with a response time of 98 ms. Further, an example of the real-life application of the device is successfully demonstrated by constructing a weak light-detecting sunlight tracking system.

Self-powered semitransparent WS2/LaVO3vertical-heterostructure photodetectors by employing interfacial hexagonal boron nitride

Two-dimensional (2D) semiconductor and LaVO3materials with high absorption coefficients in the visible light region are attractive structures for high-performance photodetector (PD) applications. Insulating 2D hexagonal boron nitride (h-BN) with a large band gap and excellent transmittance is a very attractive material as an interface between 2D/semiconductor heterostructures. We first introduce WS2/h-BN/LaVO3semitransparent PD. The photo-current/dark current ratio of the device exhibits a delta-function characteristic of 4 × 105at 0 V, meaning 'self-powered'. The WS2/h-BN/LaVO3PD shows up to 0.27 A W-1responsivity (R) and 4.6 × 1010cm Hz1/2W-1detectivity (D*) at 730 nm. Especially, it was confirmed that theD* performance improved by about 5 times compared to the WS2/LaVO3device at zero bias. Additionally, it is suggested that the PD maintains 87% of its initialRfor 2000 h under the atmosphere with a temperature of 25 °C and humidity of 30%. Based on the above results, we suggest that the WS2/h-BN/LaVO3heterojunction is promising as a self-powered optoelectronic device.

Functionalizing nanophotonic structures with 2D van der Waals materials

The integration of two-dimensional (2D) van der Waals materials with nanostructures has triggered a wide spectrum of optical and optoelectronic applications. Photonic structures of conventional materials typically lack efficient reconfigurability or multifunctionality. Atomically thin 2D materials can thus generate new functionality and reconfigurability for a well-established library of photonic structures such as integrated waveguides, optical fibers, photonic crystals, and metasurfaces, to name a few. Meanwhile, the interaction between light and van der Waals materials can be drastically enhanced as well by leveraging micro-cavities or resonators with high optical confinement. The unique van der Waals surfaces of the 2D materials enable handiness in transfer and mixing with various prefabricated photonic templates with high degrees of freedom, functionalizing as the optical gain, modulation, sensing, or plasmonic media for diverse applications. Here, we review recent advances in synergizing 2D materials to nanophotonic structures for prototyping novel functionality or performance enhancements. Challenges in scalable 2D materials preparations and transfer, as well as emerging opportunities in integrating van der Waals building blocks beyond 2D materials are also discussed.

Recent Advances in the Preparation and Application of Two-Dimensional Nanomaterials

Two-dimensional nanomaterials (2D NMs), consisting of atoms or a near-atomic thickness with infinite transverse dimensions, possess unique structures, excellent physical properties, and tunable surface chemistry. They exhibit significant potential for development in the fields of sensing, renewable energy, and catalysis. This paper presents a comprehensive overview of the latest research findings on the preparation and application of 2D NMs. First, the article introduces the common synthesis methods of 2D NMs from both "top-down" and "bottom-up" perspectives, including mechanical exfoliation, ultrasonic-assisted liquid-phase exfoliation, ion intercalation, chemical vapor deposition, and hydrothermal techniques. In terms of the applications of 2D NMs, this study focuses on their potential in gas sensing, lithium-ion batteries, photodetection, electromagnetic wave absorption, photocatalysis, and electrocatalysis. Additionally, based on existing research, the article looks forward to the future development trends and possible challenges of 2D NMs. The significance of this work lies in its systematic summary of the recent advancements in the preparation methods and applications of 2D NMs.

Integrated Graphene Heterostructures in Optical Sensing

Graphene-an outstanding low-dimensional material-exhibited many physics behaviors that are unknown over the past two decades, e.g., exceptional matter-light interaction, large light absorption band, and high charge carrier mobility, which can be adjusted on arbitrary surfaces. The deposition approaches of graphene on silicon to form the heterostructure Schottky junctions was studied, unveiling new roadmaps to detect the light at wider-ranged absorption spectrums, e.g., far-infrared via excited photoemission. In addition, heterojunction-assisted optical sensing systems enable the active carriers' lifetime and, thereby, accelerate the separation speed and transport, and then they pave new strategies to tune high-performance optoelectronics. In this mini-review, an overview is considered concerning recent advancements in graphene heterostructure devices and their optical sensing ability in multiple applications (ultrafast optical sensing system, plasmonic system, optical waveguide system, optical spectrometer, or optical synaptic system) is discussed, in which the prominent studies for the improvement of performance and stability, based on the integrated graphene heterostructures, have been reported and are also addressed again. Moreover, the pros and cons of graphene heterostructures are revealed along with the syntheses and nanofabrication sequences in optoelectronics. Thereby, this gives a variety of promising solutions beyond the ones presently used. Eventually, the development roadmap of futuristic modern optoelectronic systems is predicted.

Synergistic effects of extrinsic photoconduction and photogating in a short-wavelength ZrS3 infrared photodetector

Two-dimensional (2D) material-based photodetectors, especially those working in the infrared band, have shown great application potential in the thermal imaging, optical communication, and medicine fields. Designing 2D material photodetectors with broadened detection band and enhanced responsivity has become an attractive but challenging research direction. To solve this issue, we report a zirconium trisulfide (ZrS₃) infrared photodetector with enhanced and broadened response with the assistance of the synergistic effects of extrinsic photoconduction and photogating effect. The ZrS₃ photodetectors can detect infrared light up to 2 μm by extrinsic photoconduction and exhibit a responsivity of 100 mA W^-1 under 1550 nm illumination. Furthermore, the ZrS₃ infrared photodetectors with an oxide layer show a triple enhanced responsivity due to the photogating effect. Additionally, the infrared imaging capability of the ZrS₃ infrared photodetectors is also demonstrated. This work provides a potential way to extend the response range and improve the responsivity for nanomaterial-based photodetectors at the same time.

Mid-infrared circular-polarization-sensitive photodetector based on a chiral metasurface with a photothermoelectric effect

Photothermoelectric conversion in chiral metasurfaces with thermoelectric material provides an effective way to achieve circular polarization recognition. In this paper, we propose a circular-polarization-sensitive photodetector in a mid-infrared region, which is mainly composed of an asymmetric silicon grating, a film of gold (Au), and the thermoelectric B i ₂ T e ₃ layer. The asymmetric silicon grating with the Au layer achieves high circular dichroism absorption due to a lack of mirror symmetry, which results in a different temperature increasing on the surface of the B i ₂ T e ₃ layer under right-handed circularly polarized (RCP) and left-handed circularly polarized (LCP) excitation. Then the chiral Seebeck voltage and output power density are obtained, thanks to the thermoelectric effect of B i ₂ T e ₃. All the works are based on the finite element method, and the simulation results are conducted by the Wave Optics module of COMSOL, which is coupled with the Heat Transfer module and Thermoelectric module of COMSOL. When the incident flux is 1.0W/c m ², the output power density under RCP (LCP) light reaches 0.96m W/c m ² (0.01m W/c m ²) at a resonant wavelength, which achieves a high capability of detecting circular polarization. Besides, the proposed structure shows a faster response time than that of other plasmonic photodetectors. Our design provides a novel, to the best of our knowledge, method for chiral imaging, chiral molecular detection, and so on.

Chemical Vapor Deposition Growth of Few-Layer β12-Borophane on Copper Foils toward Broadband Photodetection

Borophene has drawn tremendous attention in the past decade for a wide range of potential applications owing to its unique structural, optical, and electronic properties. However, applications of borophene toward next-generation nanodevices are mostly theoretical predictions, while experimental realization is still lacking due to rapid oxidation of intrinsic borophene in an air environment. Here, we have successfully prepared structurally stable and transferrable few-layer β₁₂-borophane on copper foils by a typical two-zone chemical vapor deposition method, where bis(triphenylphosphine)copper tetrahydroborate was used as the boron source in a hydrogen-rich atmosphere to stabilize its structure through hydrogenation. The crystal structure of the as-prepared β₁₂-borophane is in good agreement with previous reports. A fabricated photodetector based on β₁₂-borophane-silicon (n-type) Schottky junction shows good photoelectric responses to light excitations in a wide wavelength range from 365 to 850 nm. Especially, the photodetector exhibits a good photoresponsivity of around 0.48 A W^-1, a high specific detectivity of 4.39 × 10¹¹ jones, a high external quantum efficiency of 162%, and short response and recovery times of 115 and 121 ms under an ultraviolet light with the wavelength of 365 nm at a reverse bias of 5 V. The results show great potential applications of borophane in next-generation nanophotonic and nanoelectronic devices.

Wafer-Scale Patterning Synthesis of Two-Dimensional WSe2 Layers by Direct Selenization for Highly Sensitive van der Waals Heterojunction Broadband Photodetectors

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) exhibit promising potential in fabricating highly sensitive photodetectors due to their unique electrical and optoelectrical characteristics. However, micron-sized 2D materials produced by conventional chemical vapor deposition (CVD) and mechanical exfoliation methods fail to satisfy the demands for applications in integrated optoelectronics and systems given their poor controllability and repeatability. Here, we propose a simple selenization approach to grow wafer-scale (2 in.) 2D p-WSe₂ layers with high uniformity and customized patterns. Furthermore, a self-driven broadband photodetector with a p-WSe₂/n-Si van der Waals heterojunction has been in situ fabricated with a satisfactory responsivity of 689.8 mA/W and a large specific detectivity of 1.59 × 10¹³ Jones covering from ultraviolet to short-wave infrared. In addition, a remarkable nanosecond response speed has been recorded under 0.5% duty cycle of the input light. The proposed selenization approach on the growth of 2D WSe₂ layers demonstrates an effective route to fabricate highly sensitive broadband photodetectors used for integrated optoelectronic systems.

Fast, Multi-Bit, and Vis-Infrared Broadband Nonvolatile Optoelectronic Memory with MoS2 /2D-Perovskite Van der Waals Heterojunction

Nonvolatile optoelectronic memory (NVOM) integrating the functions of optical sensing and long-term memory can efficiently process and store a large amount of visual scene information, which has become the core requirement of multiple intelligence scenarios. However, realizing NVOM with vis-infrared broadband response is still challenging. Herein, the room temperature vis-infrared broadband NVOM based on few-layer MoS₂ /2D Ruddlesden-Popper perovskite (2D-RPP) van der Waals heterojunction is realized. It is found that the 2D-RPP converts the initial n-type MoS₂ into p-type and facilitates hole transfer between them. Furthermore, the 2D-RPP rich in interband states serves as an effective electron trapping layer as well as broadband photoresponsive layer. As a result, the dielectric-free MoS₂ /2D-RPP heterojunction enables the charge to transfer quickly under external field, which enables a large memory window (104 V), fast write speed of 20 µs, and optical programmable characteristics from visible light (405 nm) to telecommunication wavelengths (i.e., 1550 nm) at room temperature. Trapezoidal optical programming can produce up to 100 recognizable states (>6 bits), with operating energy as low as 5.1 pJ per optical program. These results provide a route to realize fast, low power, multi-bit optoelectronic memory from visible to the infrared wavelength.

Locally Thinned, Core-Shell Nanowire-Integrated Multi-gate MoS2 Transistors for Active Control of Extendable Logic

Field-effect transistor (FET) devices with multi-gate coupled structures usually exhibit special electrical properties and are suitable for fabricating multifunctional devices. Among them, the 1D nanowire gate configuration has become a promising gate design to tailor 2D FET performances. However, due to possible short circuiting induced by nanowire contact and the high requirement for precision manipulation, the integration of multi-nanowires as gates in a single 2D electronic system remains a grand challenge. Herein, local laser--thinned multiple core-shell SiC@SiO₂ nanowires are successfully integrated into MoS₂ transistors as multi-gates for active control of extendable logic applications. Nanowire gates (NGs) locally enhance the carrier transportation, and the use of multiple NGs can achieve designed band structures to tune the performance of the device. For core-shell structures, a semiconducting core is used to introduce a gate bias, and the insulating shell provides protection against short circuiting between NGs, facilitating nanowire assembly. Furthermore, a global control gate is introduced to co-tune the overall electrical characteristics, while active control of logic devices and extendable inputs are achieved based on this model. This work proposes a novel nanowire multi-gate configuration, which provides possibilities for localized, precise control of band structures and the fabrication of highly integrated, multifunctional, and controllable nano-devices.

High-Responsivity Multiband and Polarization-Sensitive Photodetector Based on the TiS3/MoS2 Heterojunction

Two-dimensional (2D) material photodetectors have received considerable attention in optoelectronics as a result of their extraordinary properties, such as passivated surfaces, strong light-matter interactions, and broad spectral responses. However, single 2D material photodetectors still suffer from low responsivity, large dark current, and long response time as a result of their atomic-level thickness, large binding energy, and susceptibility to defects. Here, a transition metal trichalcogenide TiS₃ with excellent photoelectric characteristics, including a direct bandgap (1.1 eV), high mobility, high air stability, and anisotropy, is selected to construct a type-II heterojunction with few-layer MoS₂, aiming to improve the performance of 2D photodetectors. An ultrahigh photoresponsivity of the TiS₃/MoS₂ heterojunction of 48 666 A/W at 365 nm, 20 000 A/W at 625 nm, and 251 A/W at 850 nm is achieved under light-emitting diode illumination. The response time and dark current are 2 and 3 orders of magnitude lower than those of the current TiS₃ photodetector with the highest photoresponsivity (2500 A/W), respectively. Furthermore, polarized four-wave mixing spectroscopy and polarized photocurrent measurements verify its polarization-sensitive characteristics. This work confirms the excellent potential of TiS₃/MoS₂ heterojunctions for air-stable, high-performance, polarization-sensitive, and multiband photodetectors, and the excellent type-II TiS₃/MoS₂ heterojunction system may accelerate the design and fabrication of other 2D functional devices.

Menezes L, Tittl A, Ren H, Maier SA. Optical Metasurfaces for Energy Conversion

Nanostructured surfaces with designed optical functionalities, such as metasurfaces, allow efficient harvesting of light at the nanoscale, enhancing light-matter interactions for a wide variety of material combinations. Exploiting light-driven matter excitations in these artificial materials opens up a new dimension in the conversion and management of energy at the nanoscale. In this review, we outline the impact, opportunities, applications, and challenges of optical metasurfaces in converting the energy of incoming photons into frequency-shifted photons, phonons, and energetic charge carriers. A myriad of opportunities await for the utilization of the converted energy. Here we cover the most pertinent aspects from a fundamental nanoscopic viewpoint all the way to applications.

High-Performance Broad-Band Photodetection Based on Graphene-MoS2xSe2(1-x) Alloy Engineered Phototransistors

The concept of alloy engineering has emerged as a viable technique toward tuning the band gap as well as engineering the defect levels in two-dimensional transition-metal dichalcognides (TMDCs). The possibility of synthesizing these ultrathin TMDC materials through a chemical route has opened up realistic possibilities to fabricate hybrid multifunctional devices. By synthesizing nanosheets with different composites of MoS_2xSe_2(1-x) (x = 0 - 1) using simple chemical methods, we systematically investigate the photoresponse properties of three terminal hybrid devices by decorating large-area graphene with these nanosheets (x = 0, 0.5, 1) in 2D-2D configurations. Among them, the graphene-MoSSe hybrid phototransistor exhibits optoelectronic properties superior to those of its binary counterparts. The device exhibits extremely high photoresponsivity (>10⁴ A/W), low noise equivalent power (∼10^-14 W/Hz^0.5), and higher specific detectivity (∼10¹¹ jones) in the wide UV-NIR (365-810 nm) range with excellent gate tunability. The broad-band light absorption of MoSSe, ultrafast charge transport in graphene, and controllable defect engineering in MoSSe makes this device extremely attractive. Our work demonstrates the large-area scalability with the wafer-scale production of MoS_2xSe_2(1-x) alloys, having important implications toward the facile and scalable fabrication of high-performance optoelectronic devices and providing important insights into the fundamental interactions between van der Waals materials.

Influence of metal-semiconductor junction on the performances of mixed-dimensional MoS2/Ge heterostructure avalanche photodetector

The two-dimensional/three-dimensional van der Waals heterostructures provide novel optoelectronic properties for the next-generation of information devices. Herein, MoS₂/Ge heterojunction avalanche photodetectors are readily obtained. The device with an Ag electrode at MoS₂ side exhibits more stable rectification characteristics than that with an Au electrode. The rectification radio greater than 10³ and a significant avalanche breakdown are observed in the device. The responsivity of 170 and 4 A/W and the maximum gain of 320 and 13 are obtained under 532 and 1550 nm illumination, respectively. Such photoelectric properties are attributed to the carrier multiplication at a Ge/MoS₂ junction due to an avalanche breakdown. The mechanism is confirmed by the Sentaurus TCAD-simulated I-V characteristics.

Emerging Two-Dimensional Tellurene and Tellurides for Broadband Photodetectors

As with all stylish 2D functional materials, tellurene and tellurides possessing excellent physical and chemical properties such as high environmental stability, tunable narrow bandgap, and lower thermal conductivity, have aroused the great interest of the researchers. These properties of such materials also form the basis for relatively newfangled scholarly fields involving advanced topics, especially for broadband photodetectors. Integrating the excellent properties of many 2D materials, tellurene/telluride-based photodetectors show great flexibility, higher frequency response or faster time response, high signal-to-noise ratio, and so on, which make them leading the frontier of photodetector research. To fully understand the excellent properties of tellurene/tellurides and their optoelectronic applications, the recent advances in tellurene/telluride-based photodetectors are maximally summarized. Benefiting from the solid research in this field, the challenges and opportunities of tellurene/tellurides for future optoelectronic applications are also discussed in this review, which might provide possibilities for the realization of state-of-the-art high-performance tellurene/telluride-based devices.

Tuning the Electronic and Optical Properties of the Novel Monolayer Noble-Transition-Metal Dichalcogenides Semiconductor β-AuSe via Strain: A Computational Investigation

The strain-controlled structural, electronic, and optical characteristics of monolayer β-AuSe are systematically studied using first-principles calculations in this paper. For the strain-free monolayer β-AuSe, the structure is dynamically stable and maintains good stability at room temperature. It belongs to the indirect band gap semiconductor, and its valence band maximum (VBM) and conduction band minimum (CBM) consist of hybrid Au-d and Se-p electrons. Au–Se is a partial ionic bond and a partial polarized covalent bond. Meanwhile, lone-pair electrons exist around Se and are located between different layers. Moreover, its optical properties are anisotropic. As for the strained monolayer β-AuSe, it is susceptible to deformation by uniaxial tensile strain. It remains the semiconductor when applying different strains within an extensive range; however, only the biaxial compressive strain is beyond −12%, leading to a semiconductor–semimetal transition. Furthermore, it can maintain relatively stable optical properties under a high strain rate, whereas the change in optical properties is unpredictable when applying different strains. Finally, we suggest that the excellent carrier transport properties of the strain-free monolayer β-AuSe and the stable electronic properties of the strained monolayer β-AuSe originate from the p–d hybridization effect. Therefore, we predict that monolayer β-AuSe is a promising flexible semiconductive photoelectric material in the high-efficiency nano-electronic and nano-optoelectronic fields.

Broadband, Ultra-High-Responsive Monolayer MoS2/SnS2 Quantum-Dot-Based Mixed-Dimensional Photodetector

Atomically thin two-dimensional (2D) materials have gained significant attention from the research community in the fabrication of high-performance optoelectronic devices. Even though there are various techniques to improve the responsivity of the photodetector, the key factor limiting the performance of the photodetectors is constrained photodetection spectral range in the electromagnetic spectrum. In this work, a mixed-dimensional 0D/2D SnS₂-QDs/monolayer MoS₂ hybrid is fabricated for high-performance and broadband (UV-visible-near-infrared (NIR)) photodetector. Monolayer MoS₂ is deposited on SiO₂/Si using chemical vapor deposition (CVD), and SnS₂-QDs are prepared using a low-cost solution-processing method. The high performance of the fabricated 0D/2D photodetector is ascribed to the band bending and built-in potential created at the junction of SnS₂-QDs and MoS₂, which enhances the injection and separation efficiency of the photoexcited charge carriers. The mixed-dimensional structure also suppresses the dark current of the photodetector. The decorated SnS₂-QDs on monolayer MoS₂ not only improve the performance of the device but also extends the spectral range to the UV region. Photoresponsivity of the device for UV, visible, and NIR region is found to be ∼278, ∼ 435, and ∼189 A/W, respectively. Fabricated devices showed maximum responsivity under the visible region attributed to the high absorbance of monolayer MoS₂. The response time of the fabricated device is measured as ∼100 ms. These results reveal that the development of a mixed-dimensional (0D/2D) SnS₂-QDs/MoS₂-based high-performance and broadband photodetector is technologically promising for next-generation optoelectronic applications.

Self-powered topological insulator Bi2Te3/Ge heterojunction photodetector driven by long-lived excitons transfer

Due to the wide spectral absorption and ultrafast electron dynamical response under optical excitation, topological insulator (TI) was proposed to have appealing application in next-generation photonic and optoelectronic devices. Whereas, the bandgap-free speciality of Dirac surface states usually leads to a quick relaxation of photoexcited carriers, making the transient excitons difficult to manipulate in isolated TIs. Growth of TI Bi₂Te₃/Ge heterostructures can promote the specific lifetime and quantity of long-lived excitons, offering the possibility of designing original near-infrared optoelectronic devices, however, the construction of TI Bi₂Te₃/Ge heterostructures has yet to be investigated. Herein, the high-quality Bi₂Te₃/Ge heterojunction with clear interface was prepared by physical vapor deposition strategy. A significant photoluminescence quenching behaviour was observed by experiments, which was attributed to the spontaneous excitation transfer of electrons at heterointerface via theoretical analysis. Then, a self-powered heterostructure photodetector was fabricated, which demonstrated a maximal detectivity of 1.3 × 10¹¹Jones, an optical responsivity of 0.97 A W^-1, and ultrafast photoresponse speed (12.1μs) under 1064 nm light illumination. This study offers a fundamental understanding of the spontaneous interfacial exciton transfer of TI-based heterostructures, and the as-fabricated photodetectors with excellent performance provided an important step to meet the increasing demand for novel optoelectronic applications in the future.

A stretchable ultraviolet-to-NIR broad spectral photodetector using organic-inorganic vertical multiheterojunctions

Stretchable broadband photodetectors (PDs) are attractive for applications in wearable optoelectronics and personal healthcare. However, the development of stretchable broadband PDs is limited by difficulties in obtaining materials, designing device structures, and finding reliable fabrication processes. Here, we report stretchable broadband PDs by forming organic-inorganic vertical multiheterojunctions on a three-dimensionally micro-patterned stretchable substrate (3D-MPSS). The stress-adaptable 3D-MPSS structure allows all layers of the PD coated on it to sustain tensile strains. Generation of photovoltage in the vertical hybrid structure of PbS quantum dots/ZnO nanorods as a photo-responsive material on poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) as a transport channel is considred to be the mechanism of the device response to UV-Vis-NIR. The fabricated PDs present responsivity to UV (365 nm), Vis (565 nm and 660 nm), and NIR (880 nm and 970 nm) light, as well as reliable electrical performance under applied stretching up to 30%.

A Study to Improve the Performance of Mixed Cation-Halide Perovskite-Based UVC Photodetectors

Photodetectors convert optical signals into electrical signals and demonstrate application potential in various fields, such as optical communication, image detection, environmental monitoring, and optoelectronics. In this study, a mixed cation-halide perovskite-based ultraviolet C photodetector was fabricated using a solution process. The higher the mobility of the perovskite carrier, which is one of the factors affecting the performance of electronic power devices, the better the carrier diffusion. The on/off ratio and responsivity indicate the sensitivity of the response, and together with the detectivity and external quantum efficiency, these parameters demonstrate the performance of the detector. The detector fabricated in this study exhibited a mobility of 202.2 cm2/Vs and a high on/off ratio of 105% at a -2 V bias, under 254 nm light irradiation with an intensity of 0.6 mW/cm2. The responsivity, detectivity, and external quantum efficiency of the as-fabricated detector were 5.07 mA/W, 5.49 × 1011 Jones, and 24.8%, respectively. These findings demonstrate that the solution process employed in this study is suitable for the fabrication of mixed cation-halide perovskites which show immense potential for use as photodetectors.

2D Heterostructures for Ubiquitous Electronics and Optoelectronics: Principles, Opportunities, and Challenges

A grand family of two-dimensional (2D) materials and their heterostructures have been discovered through the extensive experimental and theoretical efforts of chemists, material scientists, physicists, and technologists. These pioneering works contribute to realizing the fundamental platforms to explore and analyze new physical/chemical properties and technological phenomena at the micro-nano-pico scales. Engineering 2D van der Waals (vdW) materials and their heterostructures via chemical and physical methods with a suitable choice of stacking order, thickness, and interlayer interactions enable exotic carrier dynamics, showing potential in high-frequency electronics, broadband optoelectronics, low-power neuromorphic computing, and ubiquitous electronics. This comprehensive review addresses recent advances in terms of representative 2D materials, the general fabrication methods, and characterization techniques and the vital role of the physical parameters affecting the quality of 2D heterostructures. The main emphasis is on 2D heterostructures and 3D-bulk (3D) hybrid systems exhibiting intrinsic quantum mechanical responses in the optical, valley, and topological states. Finally, we discuss the universality of 2D heterostructures with representative applications and trends for future electronics and optoelectronics (FEO) under the challenges and opportunities from physical, nanotechnological, and material synthesis perspectives.

High-Responsivity Gate-Tunable Ultraviolet-Visible Broadband Phototransistor Based on Graphene-WS2 Mixed-Dimensional (2D-0D) Heterostructure

Recent progress in the synthesis of highly stable, eco-friendly, cost-effective transition-metal dichalcogenide (TMDC) quantum dots (QDs) with their broadband absorption spectra and wavelength selectivity features have led to their increasing use in broadband photodetectors. With the solution-based processing, we demonstrate a superlarge (∼0.75 mm²), ultraviolet-visible (UV-vis) broadband (365-633 nm) phototransistor made of WS₂ QDs-decorated chemical vapor deposited (CVD) graphene as the active channel with extraordinary stability and durability under ambient conditions (without any degradation of photocurrent until 4 months after fabrication). Here, colloidal zero-dimensional (0D) WS₂ QDs are used as the photoabsorbing material, and graphene acts as the conducting channel. A high photoresponsivity (3.1 × 10² A/W), moderately high detectivity (∼8.9 × 10⁸ Jones), and low noise equivalent power (∼9.7 × 10^-11 W/Hz^0.5) are obtained at a low bias voltage (V_ds = 1 V) at an illumination of 365 nm with optical power as low as ∼0.8 μW/cm², which can be further tuned by modulating the gate bias. While comparing the photocurrent between two different morphologies of WS₂ [QDs and two-dimensional (2D) nanosheets], a significant enhancement of photocurrent is observed in the case of QD-based devices. Ab initio density functional theory (DFT)-based calculations further support our observation, revealing the role of quantum confinement in enhanced photoresponse. Our work reveals a strategy toward developing a scalable, cost-effective, high-performance hybrid mixed-dimensional (2D-0D) photodetector with graphene-WS₂ QDs for next-generation optoelectronic applications.

2D Layered Material Alloys: Synthesis and Application in Electronic and Optoelectronic Devices

2D layered materials (2DLMs) have come under the limelight of scientific and engineering research and broke new ground across a broad range of disciplines in the past decade. Nevertheless, the members of stoichiometric 2DLMs are relatively limited. This renders them incompetent to fulfill the multitudinous scenarios across the breadth of electronic and optoelectronic applications since the characteristics exhibited by a specific material are relatively monotonous and limited. Inspiringly, alloying of 2DLMs can markedly broaden the 2D family through composition modulation and it has ushered a whole new research domain: 2DLM alloy nano-electronics and nano-optoelectronics. This review begins with a comprehensive survey on synthetic technologies for the production of 2DLM alloys, which include chemical vapor transport, chemical vapor deposition, pulsed-laser deposition, and molecular beam epitaxy, spanning their development, as well as, advantages and disadvantages. Then, the up-to-date advances of 2DLM alloys in electronic devices are summarized. Subsequently, the up-to-date advances of 2DLM alloys in optoelectronic devices are summarized. In the end, the ongoing challenges of this emerging field are highlighted and the future opportunities are envisioned, which aim to navigate the coming exploration and fully exert the pivotal role of 2DLMs toward the next generation of electronic and optoelectronic devices.

Synthesis of vertically-aligned large-area MoS2nanofilm and its application in MoS2/Si heterostructure photodetector

Van der Waals heterostructures based on the combination of 2D transition metal dichalcogenides and conventional semiconductors offer new opportunities for the next generation of optoelectronics. In this work, the sulfurization of Mo film is used to synthesize vertically-aligned MoS₂nanofilm (V-MoS₂) with wafer-size and layer controllability. The V-MoS₂/n-Si heterojunction was fabricated by using a 20 nm thickness V-MoS₂, and the self-powered broadband photodetectors covering from deep ultraviolet to near infrared is achieved. The device shows superior responsivity (5.06 mA W^-1), good photodetectivity (5.36 × 10¹¹Jones) and high on/off ratioI_on/I_off(8.31 × 10³at 254 nm). Furthermore, the V-MoS₂/n-Si heterojunction device presents a fast response speed with the rise time and fall time being 54.53 ms and 97.83 ms, respectively. The high photoelectric performances could be attributed to the high-quality heterojunction between the V-MoS₂and n-Si. These findings suggest that the V-MoS₂/n-Si heterojunction has great potential applications in the deep ultraviolet-near infrared detection field, and might be used as a part of the construction of integrated optoelectronic systems.

Mechanism, Material, Design, and Implementation Principle of Two-Dimensional Material Photodetectors

Two-dimensional (2D) materials may play an important role in future photodetectors due to their natural atom-thin body thickness, unique quantum confinement, and excellent electronic and photoelectric properties. Semimetallic graphene, semiconductor black phosphorus, and transition metal dichalcogenides possess flexible and adjustable bandgaps, which correspond to a wide interaction spectrum ranging from ultraviolet to terahertz. Nevertheless, their absorbance is relatively low, and it is difficult for a single material to cover a wide spectrum. Therefore, the combination of phototransistors based on 2D hybrid structures with other material platforms, such as quantum dots, organic materials, or plasma nanostructures, exhibit ultra-sensitive and broadband optical detection capabilities that cannot be ascribed to the individual constituents of the assembly. This article provides a comprehensive and systematic review of the recent research progress of 2D material photodetectors. First, the fundamental detection mechanism and key metrics of the 2D material photodetectors are introduced. Then, the latest developments in 2D material photodetectors are reviewed based on the strategies of photocurrent enhancement. Finally, a design and implementation principle for high-performance 2D material photodetectors is provided, together with the current challenges and future outlooks.

A defect-induced broadband photodetector based on WS2/pyramid Si 2D/3D mixed-dimensional heterojunction with a light confinement effect

Broadband photodetection is of vital importance for both civil and technological applications. The widespread use of commercial photodiodes based on traditional semiconductors (e.g. GaN, Si, and InGaAs) is limited to the relatively narrow response range. In this work, we have demonstrated a self-driven and broadband photodetector based on WS₂/pyramid Si 2D/3D mixed-dimensional van der Waals (vdW) heterojunction, which is assembled by directly transferring 2D WS₂ film on 3D pyramid Si. Thanks to the enhanced light absorption with the pyramid Si structure, the defect-induced narrowed bandgap of the WS₂ film, and high-quality vdW heterojunction, impressive device performances in terms of a large responsivity of 290 mA W^-1, a high specific detectivity of up to 2.6 × 10¹⁴ Jones and an ultrabroad response spectrum ranging from 265 nm to 3.0 μm are achieved at zero bias. Importantly, the photodetector can function as an infrared imaging cell with a high spatial resolution. The totality of these excellent features confirms that the demonstrated WS₂/pyramid Si 2D/3D mixed-dimensional vdW heterojunction device may hold great promise for applications in high-performance broadband infrared photodetection and imaging.

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.

Self-Powered MXene/GaN van der Waals Heterojunction Ultraviolet Photodiodes with Superhigh Efficiency and Stable Current Outputs

A self-powered, high-performance Ti₃ C₂ T_x MXene/GaN van der Waals heterojunction (vdWH)-based ultraviolet (UV) photodiode is reported. Such integration creates a Schottky junction depth that is larger than the UV absorption depth to sufficiently separate the photoinduced electron/hole pairs, boosting the peak internal quantum efficiency over the unity and the external quantum efficiency over 99% under weak UV light without bias. The proposed Ti₃ C₂ T_x /GaN vdWH UV photodiode demonstrates pronounced photoelectric performances working in self-powered mode, including a large responsivity (284 mA W^-1 ), a high specific detectivity (7.06 × 10¹³ Jones), and fast response speed (rise/decay time of 7.55 µs/1.67 ms). Furthermore, the remarkable photovoltaic behavior leads to an impressive power conversion efficiency of 7.33% under 355 nm UV light illumination. Additionally, this work presents an easy-processing spray-deposition route for the fabrication of large-area UV photodiode arrays that exhibit highly uniform cell-to-cell performance. The MXene/GaN photodiode arrays with high-efficiency and self-powered ability show high potential for many applications, such as energy-saving communication, imaging, and sensing networks.

Ultrabroadband and High-Detectivity Photodetector Based on WS2/Ge Heterojunction through Defect Engineering and Interface Passivation

Broadband photodetectors are of great importance for numerous optoelectronic applications. Two-dimensional (2D) tungsten disulfide (WS₂), an important family member of transition-metal dichalcogenides (TMDs), has shown great potential for high-sensitivity photodetection due to its extraordinary properties. However, the inherent large bandgap of WS₂ and the strong interface recombination impede the actualization of high-sensitivity broadband photodetectors. Here, we demonstrate the fabrication of an ultrabroadband WS₂/Ge heterojunction photodetector through defect engineering and interface passivation. Thanks to the narrowed bandgap of WS₂ induced by the vacancy defects, the effective surface modification with an ultrathin AlO_x layer, and the well-designed vertical n-n heterojunction structure, the WS₂/AlO_x/Ge photodetector exhibits an excellent device performance in terms of a high responsivity of 634.5 mA/W, a large specific detectivity up to 4.3 × 10¹¹ Jones, and an ultrafast response speed. Significantly, the device possesses an ultrawide spectral response spanning from deep ultraviolet (200 nm) to mid-wave infrared (MWIR) of 4.6 μm, along with a superior MWIR imaging capability at room temperature. The detection range has surpassed the WS₂-based photodetectors in previous reports and is among the broadest for TMD-based photodetectors. Our work provides a strategy for the fabrication of high-performance ultrabroadband photodetectors based on 2D TMD materials.

Reduced graphene oxide on silicon-based structure as novel broadband photodetector

Heterojunction photodetector based on reduced graphene oxide (rGO) has been realized using a spin coating technique. The electrical and optical characterization of bare GO and thermally reduced GO thin films deposited on glass substrate has been carried out. Ultraviolet-visible-infrared transmittance measurements of the GO and rGO thin films revealed broad absorption range, while the absorbance analysis evaluates rGO band gap of about 2.8 eV. The effect of GO reduction process on the photoresponse capability is reported. The current-voltage characteristics and the responsivity of rGO/n-Si based device have been investigated using laser diode wavelengths from UV up to IR spectral range. An energy band diagram of the heterojunction has been proposed to explain the current versus voltage characteristics. The device demonstrates a photoresponse at a broad spectral range with a maximum responsivity and detectivity of 0.20 A/W and 7 × 1010 cmHz/W, respectively. Notably, the obtained results indicate that the rGO based device can be useful for broadband radiation detection compatible with silicon device technology.

Interface Engineering Ti3 C2 MXene/Silicon Self-Powered Photodetectors with High Responsivity and Detectivity for Weak Light Applications

Interfacial engineering and heterostructures designing are two efficient routes to improve photoelectric characteristics of a photodetector. Herein, a Ti₃ C₂ MXene/Si heterojunction photodetector with ultrahigh specific detectivity (2.03 × 10¹³ Jones) and remarkable responsivity (402 mA W^-1 ) at zero external bias without decline as with increasing the light power is reported. This is achieved by chemically regrown interfacial SiO_x layer and the control of Ti₃ C₂ MXene thickness to suppress the dark noise current and improve the photoresponse. The photodetector demonstrates a high light on/off ratio of over 10⁶ , an outstanding peak external quantum efficiency (EQE) of 60.3%, while it maintains an ultralow dark current at 0 V bias. Moreover, the device holds high performance with EQE of over 55% even after encapsulated with silicone, trying to resolve the air stability issue of Ti₃ C₂ MXene. Such a photodetector with high detectivity, high responsivity, and self-powered capability is particularly applicable to detect weak light signal, which presents high potential for imaging, communication and sensing applications.

Planar Multilayered 2D GeAs Schottky Photodiode for High-Performance Visible-Near-Infrared Photodetection

Novel group IV - V 2D semiconductors (e.g., GeAs and SiAs) have arisen as an attractive candidate for broad-band photodetection and optoelectronic applications. This 2D family has a wide tunable band gap, excellent thermodynamic stability, and strong in-plane anisotropy. However, their photonic and optoelectronic properties have not been extensively explored so far. This work demonstrates a broadband back-to-back metal-semiconductor-metal (MSM) Schottky photodiode with asymmetric contact geometries based on multilayered 2D GeAs. The photodetector exhibited a Schottky barrier height (SBH) in the range of 0.40-0.49 eV. Additionally, it showed a low dark current of 1.8 nA with stable, reproducible, and excellent broadband spectral response from UV to optical communication wavelengths. The highest measured responsivity in the visible is 905 A/W at 660 nm wavelength and 98 A/W for 1064 nm near-infrared at an applied voltage of -3 V and zero back gate. Most notably, the planner configuration of this GeAs photodetector showed a low detector capacitance below 1.2 pf and low voltage operation (<1 V). The stability and broadband response of the device are promising for this 2D material's application in advanced optoelectronic devices.

Construction of PtSe2/Ge heterostructure-based short-wavelength infrared photodetector array for image sensing and optical communication applications

In this work, we present the construction of a multilayered PtSe2/Ge heterostructure-based photodetector array comprising 1 × 10 device units operating in the short-wavelength infrared (SWIR) spectrum region. The as-fabricated heterostructures show an obvious photovoltaic effect, providing the devices with the ability to work as self-driven photodetectors. Upon 1550 nm illumination, a typical photodetector exhibits prominent photoresponse performance with the current on/off ratio, responsivity, external quantum efficiency and specific detectivity reaching 1.08 × 103, 766 mA W-1, 61.3% and 1.1 × 1011 Jones, respectively. The device also has a fast response speed with rise/fall times of 54.9 μs/56.6 μs. Thanks to the respectable homogeneity in device performance, the photodetector array can reliably record an image of a "diode symbol" produced by SWIR irradiation. What is more, the photodetector is successfully integrated into a SWIR optical communication system serving as an optical receiver to transmit a text signal. The above results imply a huge possibility of the present heterostructure-based photodetector array for some optoelectronic purposes such as SWIR image sensing and optical communication applications.

2D Silicon-Based Semiconductor Si2 Te3 toward Broadband Photodetection

Silicon-based semiconductor materials dominate modern technology for more than half a century with extraordinary electrical-optical performance and mutual processing compatibility. Now, 2D materials have rapidly established themselves as prospective candidates for the next-generation semiconductor industry because of their novel properties. Considering chemical and processing compatibility, silicon-based 2D materials possess significant advantages in integrating with silicon. Here, a systematic study is reported on the structural, electrical, and optical performance of silicon telluride (Si₂ Te₃ ) 2D material, a IV-VI silicon-based semiconductor with a layered structure. The ultrawide photoluminescence (PL) spectra in the range of 550-1050 nm reveals the intrinsic defects in Si₂ Te₃ . The Si₂ Te₃ -based field-effect transistors (FETs) and photodetectors show a typical p-type behavior and a remarkable broadband spectral response in the range of 405-1064 nm. Notably, the photoresponsivity and detectivity of the photodetector device with 13.5 nm in thickness and upon 405 nm illumination can reach up to 65 A W^-1 and 2.81 × 10¹² Jones, respectively, outperforming many traditional broadband photodetectors. It is believed this work will excite interests in further exploring the practical application of 2D silicon-based materials in the field of optoelectronics.

Evolution of low-dimensional material-based field-effect transistors

Field-effect transistors (FETs) have tremendous applications in the electronics industry due to their outstanding features such as small size, easy fabrication, compatibility with integrated electronics, high sensitivity, rapid detection and easy measuring procedures. However, to meet the increasing demand of the electronics industry, efficient FETs with controlled short channel effects, enhanced surface stability, reduced size, and superior performances based on low-dimensional materials are desirable. In this review, we present the developmental roadmap of FETs from conventional to miniaturized devices and highlight their prospective applications in the field of optoelectronic devices. Initially, a detailed study of the general importance of bulk and low-dimensional materials is presented. Then, recent advances in low-dimensional material heterostructures, classification of FETs, and the applications of low-dimensional materials in field-effect transistors and photodetectors are presented in detail. In addition, we also describe current issues in low-dimensional material-based FETs and propose potential approaches to address these issues, which are crucial for developing electronic and optoelectronic devices. This review will provide guidelines for low-dimensional material-based FETs with high performance and advanced applications in the future.

Benchmark Investigation of Band-Gap Tunability of Monolayer Semiconductors under Hydrostatic Pressure with Focus-On Antimony

In this paper, the band-gap tunability of three monolayer semiconductors under hydrostatic pressure was intensively investigated based on first-principle simulations with a focus on monolayer antimony (Sb) as a semiconductor nanomaterial. As the benchmark study, monolayer black phosphorus (BP) and monolayer molybdenum disulfide (MoS2) were also investigated for comparison. Our calculations showed that the band-gap tunability of the monolayer Sb was much more sensitive to hydrostatic pressure than that of the monolayer BP and MoS2. Furthermore, the monolayer Sb was predicted to change from an indirect band-gap semiconductor to a conductor and to transform into a double-layer nanostructure above a critical pressure value ranging from 3 to 5 GPa. This finding opens an opportunity for nanoelectronic, flexible electronics and optoelectronic devices as well as sensors with the capabilities of deep band-gap tunability and semiconductor-to-metal transition by applying mechanical pressure.

Ultrathin High-Quality SnTe Nanoplates for Fabricating Flexible Near-Infrared Photodetectors

This work demonstrates a controlled van der Waals growth of two-dimensional SnTe nanoplates on mica substrates and their applications in flexible near-infrared photodetectors. The growth of nonlayered rock-salt structured SnTe crystals into two-dimensional SnTe nanoplate structures is mainly caused by the two-dimensional nature of the mica surface, which also results in the ultrathin nanoplates obtained (3.6 nm, equivalent to 6 monolayers). Furthermore, it is found that the shape of the SnTe nanoplates can be well engineered by changing their growth temperature due to the competition between the surface energy of the {100} crystallographic plane and that of the {111} plane. As a result of the favorable physical properties of topological crystalline insulators such as metallic surface (high electron mobility) and narrow bandgap, near-infrared photodetectors based on single SnTe nanoplate with the thickness of 3.6 nm present excellent device performance with a responsivity of 698 mA/W, a specific detectivity of 3.89 × 10⁸ jones, and an external quantum efficiency of 88.5% under the illumination of a 980 nm laser at room temperature (300 K) without applying a gate voltage (V_g). Upon increasing the gate voltage from -30 to 30 V, the detector responsivity increases from 2.96 to 723 mA/W and the detector detectivity increases from 2.4 × 10⁶ to 5.3 × 10⁸ jones. Furthermore, upon increasing the thickness of SnTe nanoplate from 3.6 to 35 nm, the detector responsivity increases from 0.698 to 1.468 A/W. The device performance measured after bending for 300 times as well as after bending with different radii presents no obvious degradation, which exhibits the excellent flexibility of the SnTe nanoplate detectors. These results not only contribute to a deep understanding of the mechanisms of the van der Waals growth of nonlayered materials into two-dimensional structure but also demonstrate the immense potential of SnTe nanoplates to be used in flexible near-infrared detectors.

Novel Self-Powered Photodetector with Binary Photoswitching Based on SnSx/TiO2 Heterojunctions

Binary photoresponse characteristics can help realize optical signal processing and logic operations. UV photodetectors (PDs) with SnS_x nanoflakes and TiO₂ nanorod arrays (NRs) show a novel binary photoswitching behavior (change in current from positive to negative) by manipulating the light wavelength without an external power source, utilizing the interfacial recombination of the photogenerated carriers in the type-I SnS_x/TiO₂ heterojunctions. The enhanced responsivity (R*), detectivity (D^*), and fast photoresponse time for self-powered SnS_x/TiO₂PDs can be achieved by adjusting the phase ratio of SnS and SnS₂ nanoflakes. The binary photoswitching in the self-powered UV PDs can be applied in the encrypted optical signal processing and imaging in some special conditions without external bias.

Thermal Localization Enhanced Fast Photothermoelectric Response in a Quasi-One-Dimensional Flexible NbS3 Photodetector

Ultra-broadband photodetection is crucial for various applications like imaging and sensing and has become a hot research topic in recent years. However, most of the reported ultra-broadband photodetectors can only cover the range from ultraviolet to infrared, which is insufficient. Herein, a photothermoelectric (PTE) detector made of NbS₃ is reported. The device shows a considerable performance from ultraviolet to terahertz. For all examined wavelengths, the photoresponsivities are all larger than 1 V W^-1 while the response time is less than 10 ms, much shorter than the reported ultra-broadband photodetectors made of millimetric scale graphene, ternary chalcogenide single crystal, and other materials. The extraordinary performance is fully discussed and can be attributed to the thermal localization enhanced PTE effect. Because of the short thermal decay length and low thermal loss, the heat generated by the illumination is localized in only a micrometer scale along the channel, and thus a strong PTE response is produced. In addition, the fabricated device also demonstrates robust flexibility and stability. Thanks to the quasi-one-dimensional (quasi-1D) structure, the NbS₃ crystal is easy to be scaled down and thus intrinsically facilitate the integration of detectors. With these favorable merits, the quasi-1D NbS₃ crystal holds a promising potential in high-performance, ultra-broadband photodetectors.