Promoting Photosensitivity and Detectivity of the Bi/Si Heterojunction Photodetector by Inserting a WS2 Layer

Can 2D Semiconductors Be Game-Changers for Nanoelectronics and Photonics?

2D semiconductors have interesting physical and chemical attributes that have led them to become one of the most intensely investigated semiconductor families in recent history. They may play a crucial role in the next technological revolution in electronics as well as optoelectronics or photonics. In this Perspective, we explore the fundamental principles and significant advancements in electronic and photonic devices comprising 2D semiconductors. We focus on strategies aimed at enhancing the performance of conventional devices and exploiting important properties of 2D semiconductors that allow fundamentally interesting device functionalities for future applications. Approaches for the realization of emerging logic transistors and memory devices as well as photovoltaics, photodetectors, electro-optical modulators, and nonlinear optics based on 2D semiconductors are discussed. We also provide a forward-looking perspective on critical remaining challenges and opportunities for basic science and technology level applications of 2D semiconductors.

High-Performance and Polarization-Sensitive Imaging Photodetector Based on WS2 /Te Tunneling Heterostructure

Next-generation imaging systems require photodetectors with high sensitivity, polarization sensitivity, miniaturization, and integration. By virtue of their intriguing attributes, emerging 2D materials offer innovative avenues to meet these requirements. However, the current performance of 2D photodetectors is still below the requirements for practical application owing to the severe interfacial recombination, the lack of photoconductive gain, and insufficient photocarrier collection. Here, a tunneling dominant imaging photodetector based on WS₂ /Te heterostructure is reported. This device demonstrates competitive performance, including a remarkable responsivity of 402 A W^-1 , an outstanding detectivity of 9.28 × 10¹³ Jones, a fast rise/decay time of 1.7/3.2 ms, and a high photocurrent anisotropic ratio of 2.5. These outstanding performances can be attributed to the type-I band alignment with carrier transmission barriers and photoinduced tunneling mechanism, allowing reduced interfacial trapping effect, effective photoconductive gains, and anisotropic collection of photocarriers. Significantly, the constructed photodetector is successfully integrated into a polarized light imaging system and an ultra-weak light imaging system to illustrate the imaging capability. These results suggest the promising application prospect of the device in future imaging systems.

Research Process on Photodetectors based on Group-10 Transition Metal Dichalcogenides

Rapidly evolving group-10 transition metal dichalcogenides (TMDCs) offer remarkable electronic, optical, and mechanical properties, making them promising candidates for advanced optoelectronic applications. Compared to most TMDCs semiconductors, group-10-TMDCs possess unique structures, narrow bandgap, and influential physical properties that motivate the development of broadband photodetectors, specifically infrared photodetectors. This review presents the latest developments in the fabrication of broadband photodetectors based on conventional 2D TMDCs. It mainly focuses on the recent developments in group-10 TMDCs from the perspective of the lattice structure and synthesis techniques. Recent progress in group-10 TMDCs and their heterostructures with different dimensionality of materials-based broadband photodetectors is provided. Moreover, this review accounts for the latest applications of group-10 TMDCs in the fields of nanoelectronics and optoelectronics. Finally, conclusions and outlooks are summarized to provide perspectives for next-generation broadband photodetectors based on group-10 TMDCs.

Femtosecond laser upgrading the quality of bismuth films to enhance ultra-broadband photodetection

Topological insulator bismuth has attracted considerable attention for the fabrication of room-temperature, wide bandwidth, and high-performance photodetectors due to the gapless edge state and insulating bulk state properties. However, both the photoelectric conversion and carrier transportation of the bismuth films are extremely affected by the surface morphology and grain boundaries to limit optoelectronic properties further. Here, we demonstrate a strategy of femtosecond laser treatment for upgrading the quality of bismuth films. After the treatment with proper laser parameters, the measurement of average surface roughness can be reduced from Ra = 44 nm to 6.9 nm, especially with accompany of the evident grain boundary elimination. Consequently, the photoresponsivity of the bismuth films increases approximately 2 times within an ultra-broad spectrum range from the visible to mid-infrared. This investigation suggests that the femtosecond laser treatment can help to benefit the performance of topological insulator ultra-broadband photodetectors.

A review on bismuth-based nanocomposites for energy and environmental applications

Bismuth, a heavy metal which is found to be inexpensive and at a reduced cost, is utilized in the synthesis of different nanomaterials with novel structure, remarkable physical and chemical properties, adjustable bandgap, notable efficiency for photothermal conversion. These characteristics have made this element desirable for various applications such as storage and conversion of energy, electronics, sensors, photocatalysis, and other biomedical applications. These review papers are the vital points for the students, this report guides them to the research papers which focus on the impressive development in the area of bismuth and similar nanostructures. The purpose of the present review is to discuss the various synthesis routes of bismuth-based nanomaterials along with green synthesis, different nanostructures of bismuth, their significant properties, diverse applications and directions for the upcoming research. Therefore, with these different tuneable synthesis methods of bismuth-based nanomaterials combined with their novel properties, would elucidate on the future devices based on various nanostructures of bismuth.

Solution Processed Photodetectors with PVK-WS2 Nanotube/Nanofullerene Organic-Inorganic Hybrid Films

Organic-inorganic hybrid photodetectors have attracted increased interest due to their exceptional properties, such as flexibility, transparency, and low cost for many promising applications. Low-dimensional tungsten disulfide (WS₂) nanostructures have outstanding electrical and optical properties, making them ideal candidates for ultrasensitive photodetector devices. In this paper, photodetectors were fabricated with hybrid thin films containing two different WS₂ nanomaterials, one-dimensional (1D) WS₂ nanotubes (WS₂-NTs) and a zero-dimensional (0D) WS₂ nanofullerene (WS₂-FLs) hybrid with poly(N-vinyl carbazole) (PVK). The electrical responses of the devices under visible-light illuminations were studied. The photodetector devices with 0D WS₂-FLs/PVK hybrid thin films have relatively higher sensitivity and stable voltage responses to visible light. Besides, the hybrid film shows a strong surface-enhanced Raman effect (SERS). These materials and new strategies enable the creation of a new class of processed photodetectors for practical applications.

Type-I Heterostructure Based on WS2/PtS2 for High-Performance Photodetectors

van der Waals (vdW) heterodiodes composed of two-dimensional (2D) layered materials led to a new prospect in photoelectron diodes and photovoltaic devices. Existing studies have shown that Type-I heterostructures have great potential to be used as photodetectors; however, the tunneling phenomena in Type-I heterostructures have not been fully revealed. Herein, a highly efficient nn⁺ WS₂/PtS₂ Type-I vdW heterostructure photodiode is constructed. The device shows an ultrahigh reverse rectification ratio of 10⁵ owing to the transmission barrier-induced low reverse current. A unilateral depletion region is formed on WS₂, which inhibits the recombination of carriers at the interface and makes the external quantum efficiency (EQE) of the device reach 67%. Due to the tunneling mechanism of the device, which allows the co-existence of a large photocurrent and a low dark current, this device achieves a light on/off ratio of over 10⁵. In addition, this band design allows the device to maintain a high detectivity of 4.53 × 10¹⁰ Jones. Our work provides some new ideas for exploring new high-efficiency photodiodes.

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.

Highly Sensitive, Ultrafast, and Broadband Photo-Detecting Field-Effect Transistor with Transition-Metal Dichalcogenide van der Waals Heterostructures of MoTe2 and PdSe2

Recently, van der Waals heterostructures (vdWHs) based on transition-metal dichalcogenides (TMDs) have attracted significant attention owing to their superior capabilities and multiple functionalities. Herein, a novel vdWH field-effect transistor (FET) composed of molybdenum ditelluride (MoTe2 ) and palladium diselenide (PdSe2 ) is studied for highly sensitive photodetection performance in the broad visible and near-infrared (VNIR) region. A high rectification ratio of 6.3 × 105 is obtained, stemming from the sharp interface and low Schottky barriers of the MoTe2 /PdSe2 vdWHs. It is also successfully demonstrated that the vdWH FET exhibits highly sensitive photo-detecting abilities, such as noticeably high photoresponsivity (1.24 × 105 A W-1 ), specific detectivity (2.42 × 1014 Jones), and good external quantum efficiency (3.5 × 106 ), not only due to the intra-TMD band-to-band transition but also due to the inter-TMD charge transfer (CT) transition. Further, rapid rise (16.1 µs) and decay (31.1 µs) times are obtained under incident light with a wavelength of 2000 nm due to the CT transition, representing an outcome one order of magnitude faster than values currently in the literature. Such TMD-based vdWH FETs would improve the photo-gating characteristics and provide a platform for the realization of a highly sensitive photodetector in the broad VNIR region.

A reasonably designed 2D WS2 and CdS microwire heterojunction for high performance photoresponse

Heterojunctions based on low-dimensional materials can combine the superiorities of each component and realize novel properties. Herein, a mixed-dimensional heterojunction comprising multilayer WS₂, CdS microwire, and few-layer WS₂ has been demonstrated. The working mechanism and its application in a photodetector are investigated. The multilayer WS₂ and CdS microwire are utilized to provide efficient light absorption, while the few-layer WS₂ is utilized to passivate interfacial impurity scattering. In addition, based on the reasonable band alignment of the components, three built-in electric fields are formed, which efficiently separate the photo-generated carriers and enhance the photocurrent. In particular, the photo-generated electrons are trapped in CdS, while the photo-generated holes circulate in the external circuit, leading to a high photoconductivity gain. Motivated by these, we constructed a device that exhibits a photoresponsivity of ∼4.7 A W^-1, a response/recovery time of 13.7/15.8 ms, and a detectivity of 3.4 × 10¹² Jones, which are much better than the counterparts. All of these clearly demonstrate the importance of advanced device designs for realizing high performance optoelectronic devices.

A highly efficient bilayer graphene/ZnO/silicon nanowire based heterojunction photodetector with broadband spectral response

This paper presents three self-powered photodetectors namely, p⁺-bilayer graphene (BLG)/n⁺-ZnO nanowires (NWs), p⁺-BLG/n⁺-Si NWs/p^--Si and p⁺-BLG/n⁺-ZnO NWs/p^--Si. The Silvaco Atlas TCAD software is utilized to characterize the optoelectronic properties of all the devices and is validated by analytical modeling. The proposed dual-junction photodetectors cover broadband spectral response varying from ultraviolet to near-infrared wavelengths. The dual-heterojunction broadband photodetector exhibits photocurrent switching with the rise and fall time of 1.48 and 1.27 ns, respectively. At -0.5 V bias, the highest external quantum efficiency, photocurrent responsivity, specific detectivity, and the lowest noise equivalent power of 71%, 0.28 A W^-1, 4.2 × 10¹² cmHz^1/2 W^-1, and 2.59 × 10^-17 W, respectively, are found for the dual-heterojunction device with a wavelength of 480 nm at 300 K. The proposed nanowires based photodetectors offer great potential to be utilized as next-generation optoelectronic devices.

Breaking symmetry in device design for self-driven 2D material based photodetectors

The advent of graphene and other two-dimensional (2D) materials offers great potential for optoelectronic applications. Various device structures and novel mechanisms have been proposed to realize photodetectors with unique detecting properties. In this minireview, we focus on a self-driven photodetector that has great potential for low-power or even powerless operation required in the internet of things and wearable electronics. To address the general principle of self-driven properties, we propose and elaborate the concept of symmetry breaking in 2D material based self-driven photodetectors. We discuss various mechanisms of breaking symmetry for self-driven photodetectors, including asymmetrical contact engineering, field-induced asymmetry, PN homojunctions, and PN heterostructures. Typical device examples based on these mechanisms are reviewed and compared. The performance of current self-driven photodetectors is critically assessed and future directions are discussed towards the target application fields.

The Rise of 2D Photothermal Materials beyond Graphene for Clean Water Production

Water shortage is one of the most concerning global challenges in the 21st century. Solar-inspired vaporization employing photothermal nanomaterials is considered to be a feasible and green technology for addressing the water challenge by virtue of abundant and clean solar energy. 2D nanomaterials aroused considerable attention in photothermal evaporation-induced water production owing to their large absorption surface, strong absorption in broadband solar spectrum, and efficient photothermal conversion. Herein, the recent progress of 2D nanomaterials-based photothermal evaporation, mainly including emerging Xenes (phosphorene, antimonene, tellurene, and borophene) and binary-enes (MXenes and transition metal dichalcogenides), is reviewed. Then, the optimization strategies for higher evaporation performance are summarized in terms of modulation of the intrinsic photothermal performance of 2D nanomaterials and design of the complete evaporation system. Finally, the challenges and prospective of various kinds of 2D photothermal nanomaterials are discussed in terms of the photothermal performance, stability, environmental influence, and cost. One important principle is that solutions for water challenges should not introduce new environmental and social problems. This Review aims to highlight the role of 2D photothermal nanomaterials in solving water challenges and provides a viable scheme toward the practical use in photothermal materials selection, design, and evaporation systems building.

2D material broadband photodetectors

Our review provides a comprehensive overview of the latest evolution of broadband photodetectors (BBPDs) based on 2D materials (2DMs). We begin with BBPDs built on various 2DM channels, including narrow-bandgap 2DMs, 2D topological semimetals, 2D charge density wave compounds, and 2D heterojunctions. Then, we introduce defect-engineered 2DM BBPDs, including vacancy engineering, heteroatom incorporation, and interfacial engineering. Subsequently, we summarize 2DM based mixed-dimensional (0D-2D, 1D-2D, 2D-3D, and 0D-2D-3D) BBPDs. Finally, we provide several viewpoints for the future development of this burgeoning field.

Oxygen-incorporated and layer-by-layer stacked WS2 nanosheets for broadband, self-driven and fast-response photodetection

Two-dimensional (2D) layered WS2 nanosheets have been regarded as exciting and emerging candidate materials in constructing high performance photodetectors. In this work, we develop a facile solvothermal method to synthesize oxygen-doped WS2 microrods composed of layer-by-layer stacked nanosheets. The WS2 microrods exhibit an obvious bandgap of 1.2 eV, together with a broad near-infrared (NIR) absorption after 1100 nm. The unique absorption can be ascribed to the oxygen-incorporation-induced localized surface plasmon resonance (LSPR) effect. A hybrid WS2/Si heterojunction, which allows the combination of the WS2 microrods with a mature silicon platform, is then constructed by a facile spin-coating fabrication process to investigate the photoresponse properties. Benefitting from the remarkable photovoltaic performance, the WS2/Si heterojunction acts as a self-driven photodetector with outstanding characteristics. The photodetector exhibits a decent responsivity (R) of 1.5 A W-1, a high specific detectivity (D*) of ∼2 × 1012 Jones, fast response speeds with rise/fall times of 2.0/7.2 μs, and good ambient stability (2 months) at zero bias. Notably, the photodetector is still sensitive at a broadband wavelength in the NIR region (1100-2000 nm). The broadband response is attributed to the LSPR effect of the oxygen-incorporated WS2. These results suggest great potential of the oxygen-incorporated WS2/Si heterojunctions in NIR light detection.

Ultrasensitive 2D/3D Heterojunction Multicolor Photodetectors: A Synergy of Laterally and Vertically Aligned 2D Layered Materials

In this work, a p-type 2D SnS nanofilm containing both laterally and vertically aligned components was successfully deposited on an n-type Si substrate through pulsed-laser deposition. Energy band analysis demonstrates a typical type-II band alignment between SnS and Si, which is beneficial to the separation of photogenerated carriers. The as-fabricated p-SnS/n-Si heterojunction photodetector exhibits multicolor photoresponse from ultraviolet to near-infrared (370-1064 nm). Importantly, the device manifests a high responsivity of 273 A/W, a large external quantum efficiency of 4.2 × 10⁴%, and an outstanding detectivity of 7× 10¹³ Jones (1 Jones = 1 cm Hz^1/2 W^-1), which far outperforms state-of-the-art 2D/3D heterojunction photodetectors incorporating either laterally or vertically aligned 2D layered materials (2DLMs). The splendid performance is ascribed to lateral SnS's dangling-bond-free interface induced efficient carrier separation, vertical SnS's high-speed carrier transport, and collision ionization induced carrier multiplication. In sum, the current work depicts a unique landscape for revolutionary design and advancement of 2DLM-based heterojunction photodetectors.

Nanobismuth: Fabrication, Optical, and Plasmonic Properties—Emerging Applications

Along the twentieth century, the electronic properties of bismuth have been widely studied, especially in relation with its magnetoresistive and thermoelectric responses. In this context, a particular emphasis has been made on electronic confinement effects in bismuth nanostructures (or nanobismuth). In the recent years, the optical properties of bismuth nanostructures are focusing a growing interest. An increasing number of reports point at the potential of such nanostructures to support plentiful optical resonances over an ultrabroad spectral range: “interband plasmonic” resonances in the ultraviolet, visible, and near-infrared; dielectric Mie resonances in mid- and far-infrared; and conventional free-carrier plasmonic resonances in the far-infrared and terahertz. With the aim to provide a comprehensive basis for exploiting the full optical potential of bismuth nanostructures, we review the current progress in their controlled fabrication, the trends reported (from theoretical calculations and experimental observations) for their optical and plasmonic response, and their emerging applications, including photocatalysis and switchable metamaterials.

An ultra-broadband perovskite-PbS quantum dot sensitized carbon nanotube photodetector

Organic-inorganic perovskites have been hailed as promising candidates for optoelectronic and photovoltaic devices, but their operation remains limited to the visible spectrum. Here, we combine single-wall carbon nanotubes, PbS quantum dots and a perovskite to synthesize hybrid devices suitable for operation in both the visible and near-infrared. The photodetectors thus fabricated show responsivities as high as 0.5 A W-1 and 0.35 A W-1 at 500 nm and at 1300 nm, respectively, with an applied bias of 1 V. Moreover, the incorporation of nanotubes within the perovskite matrix facilitates the carrier extraction, resulting in response time under 250 μs, a gain-bandwidth product of 0.1 MHz and detectivities of 1.4 × 1011 Jones and 0.9 × 1011 Jones at 500 nm and at 1300 nm, respectively. This unique approach opens new pathways for the development of low-cost, high-speed and broadband perovskite-based optoelectronic devices for large-scale manufacturing.

Growth of Wafer-Scale Standing Layers of WS2 for Self-Biased High-Speed UV-Visible-NIR Optoelectronic Devices

This work describes the wafer-scale standing growth of (002)-plane-oriented layers of WS₂ and their suitability for use in self-biased broad-band high-speed photodetection. The WS₂ layers are grown using large-scale sputtering, and the effects of the processing parameters such as the deposition temperature, deposition time, and sputtering power are studied. The structural, physical, chemical, optical, and electrical properties of the WS₂ samples are also investigated. On the basis of the broad-band light absorption and high-speed in-plane carrier transport characteristics of the WS₂ layers, a self-biased broad-band high-speed photodetector is fabricated by forming a type-II heterojunction. This WS₂/Si heterojunction is sensitive to ultraviolet, visible, and near-infrared photons and shows an ultrafast photoresponse (1.1 μs) along with an excellent responsivity (4 mA/W) and a specific detectivity (∼1.5 × 10¹⁰ Jones). A comprehensive Mott-Schottky analysis is performed to evaluate the parameters of the device, such as the frequency-dependent flat-band potential and carrier concentration. Further, the photodetection parameters of the device, such as its linear dynamic range, rising time, and falling time, are evaluated to elucidate its spectral and transient characteristics. The device exhibits remarkably improved transient and spectral photodetection performances as compared to those of photodetectors based on atomically thin WS₂ and two-dimensional materials. These results suggest that the proposed method is feasible for the manipulation of vertically standing WS₂ layers that exhibit high in-plane carrier mobility and allow for high-performance broad-band photodetection and energy device applications.

Self-Assembly High-Performance UV-vis-NIR Broadband β-In2Se3/Si Photodetector Array for Weak Signal Detection

The emergence of a rich variety of layered materials has attracted considerable attention in recent years because of their exciting properties. However, the applications of layered materials in optoelectronic devices are hampered by the low light absorption of monolayers/few layers, the lack of p-n junction, and the challenges for large-scale production. Here, we report a scalable production of β-In₂Se₃/Si heterojunction arrays using pulsed-laser deposition. Photodetectors based on the as-produced heterojunction array are sensitive to a broadband wavelength from ultraviolet (370 nm) to near-infrared (808 nm), showing a high responsivity (5.9 A/W), a decent current on/off ratio (∼600), and a superior detectivity (4.9 × 10¹² jones), simultaneously. These figures-of-merits are among the best values of the reported heterojunction-based photodetectors. In addition, these devices can further enable the detection of weak signals, as successfully demonstrated with weak light sources including a flashlight, lighter, and fluorescent light. Device physics modeling shows that their high performance is attributed to the strong light absorption of the relatively thick β-In₂Se₃ film (20.3 nm) and the rational energy band structures of β-In₂Se₃ and Si, which allows efficient separation of photoexcited electron-hole pairs. These results offer a new insight into the rational design of optoelectronic devices from the synergetic effect of layered materials as well as mature semiconductor technology.

Highly Efficient Deep-UV Light-Emitting Diodes Using AlN-Based Deep-UV-Transparent Glass Electrodes

Many studies have set out to develop electrodes that are both highly conductive and transparent across a wide spectral region, from visible to deep UV (DUV). However, few solutions have been proposed because these two properties are mutually exclusive. In this paper, an AlN-based glass electrode film with a conducting filament formed by the application of an ac pulse is proposed as a solution, which exhibits a high transmittance in the DUV region (over 95.6% at 280 nm) and a low contact resistance with a p-Al_0.4Ga_0.6N layer (ρ_c = 3.2 × 10^-2 Ω·cm²). The Ohmic conduction mechanism at the interface between the AlN film and the p-Al_0.4Ga_0.6N layers is fully examined using various analytical tools. This AlN film is finally applied to a 280 nm top-emitting light-emitting diode, to verify the validity of the method, which exhibits very stable operations with a forward voltage of 7.7 V at 20 mA, a light output power of 7.49 mW at 100 mA, and, most importantly, a record high external quantum efficiency of 2.8% after packaging.

Enhanced broadband photoresponse of a self-powered photodetector based on vertically grown SnS layers via the pyro-phototronic effect

Here, we demonstrate the broadband photoresponse from ultraviolet (365 nm) to near-infrared (850 nm) wavelengths from a photodetector based on vertically grown SnS layers. Particularly, the photoinduced current density of the device increased from 100 to 470 μA cm^-2 with a wavelength of 760 nm and an intensity of 7 mW cm^-2 by utilizing the pyro-phototronic potential. In addition, the photodetector demonstrated ultrafast response rates of ∼12 μs for the rise and ∼55 μs for the decay times over the studied range. Moreover, a good photoresponsivity of 13 mA W^-1 and a high photodetectivity of 3 × 10¹⁴ Jones at a wavelength of 760 nm with an intensity of 7 mW cm^-2 were measured, representing enhancements of 340% and 3960%, respectively, with the pyroelectric potential. This excellent broadband performance was attributed to the photon-induced pyroelectric effect in the vertically grown SnS layers, which also modulated the optoelectronic processes. This novel approach will open a new avenue to design a broadband ultrafast device for advanced optoelectronics.

A flexible, transparent and high-performance gas sensor based on layer-materials for wearable technology

Gas sensors play a vital role among a wide range of practical applications. Recently, propelled by the development of layered materials, gas sensors have gained much progress. However, the high operation temperature has restricted their further application. Herein, via a facile pulsed laser deposition (PLD) method, we demonstrate a flexible, transparent and high-performance gas sensor made of highly-crystalline indium selenide (In₂Se₃) film. Under UV-vis-NIR light or even solar energy activation, the constructed gas sensors exhibit superior properties for detecting acetylene (C₂H₂) gas at room temperature. We attribute these properties to the photo-induced charger transfer mechanism upon C₂H₂ molecule adsorption. Moreover, no apparent degradation in the device properties is observed even after 100 bending cycles. In addition, we can also fabricate this device on rigid substrates, which is also capable to detect gas molecules at room temperature. These results unambiguously distinguish In₂Se₃ as a new candidate for future application in monitoring C₂H₂ gas at room temperature and open up new opportunities for developing next generation full-spectrum activated gas sensors.

Hybrid WSe2-In2O3 Phototransistor with Ultrahigh Detectivity by Efficient Suppression of Dark Currents

Photodetectors based on low-dimensional materials have attracted tremendous attention because of their high sensitivity and compatibility with conventional semiconductor technology. However, up until now, developing low-dimensional phototransistors with high responsivity and low dark currents over broad-band spectra still remains a great challenge because of the trade-offs in the potential architectures. In this work, we report a hybrid phototransistor consisting of a single In₂O₃ nanowire as the channel material and a multilayer WSe₂ nanosheet as the decorating sensitizer for photodetection. Our devices show high responsivities of 7.5 × 10⁵ and 3.5 × 10⁴ A W^-1 and ultrahigh detectivities of 4.17 × 10¹⁷ and 1.95 × 10¹⁶ jones at the wavelengths of 637 and 940 nm, respectively. The superior detectivity of the hybrid architecture arises from the extremely low dark currents and the enhanced photogating effect in the depletion regime by the unique design of energy band alignment of the channel and sensitizer materials. Moreover, the visible to near-infrared absorption properties of the multilayer WSe₂ nanosheet favor a broad-band spectral response for the devices. Our results pave the way for developing ultrahigh-sensitivity photodetectors based on low-dimensional hybrid architectures.

Broadband ultrafast photovoltaic detectors based on large-scale topological insulator Sb2Te3/STO heterostructures

Topological insulators (TIs) are new states of quantum matter in which the spin-momentum-locked surface states reside in the bulk insulating gap and have triggered extensive investigations on fundamental properties and potential applications. Herein, we report scalable, broadband photovoltaic detectors based on the topological insulator Sb₂Te₃/strontium titanate (STO) heterostructure. Large-scale (2 mm × 5 mm), high crystalline quality p-type Sb₂Te₃ films were fabricated on an n-type STO substrate by the molecular beam epitaxy (MBE) method. The Sb₂Te₃/STO heterostructures exhibited pronounced photovoltaic behavior in a wide range of temperatures as a result of a strong built-in field at the hetero-interface. Superior performances of broadband (from visible to infrared, 405 nm-1550 nm) and ultrafast (rise time ∼30 μs, fall time ∼95 μs) photoresponses were achieved under ambient conditions. The prominent repeatability and stability indicated that our photodetectors can operate effectively in harsh circumstances. These results show that stacking the topological insulator thin films on a strongly correlated oxide substrate using the MBE approach holds great promise for high performance optoelectronic applications.

Self-Assembly of the Lateral In2Se3/CuInSe2 Heterojunction for Enhanced Photodetection

Layered materials have been found to be promising candidates for next-generation microelectronic and optoelectronic devices due to their unique electrical and optical properties. The p-n junction is an elementary building block for microelectronics and optoelectronics devices. Herein, using the pulsed-laser deposition (PLD) method, we achieve pure In₂Se₃-based photodetectors and In₂Se₃/CuInSe₂-based photodetectors with a lateral p-n heterojunction. In comparison to that of the pure In₂Se₃-based photodetector, the photodetectors based on the In₂Se₃/CuInSe₂ heterojunction exhibit a tremendous promotion of photodetection performance and obvious rectifying behavior. The photoresponsivity and external quantum efficiency of the fabricated heterojunction-based device under 532 nm light irradiation are 20.1 A/W and 4698%, respectively. These values are about 7.5 times higher than those of our fabricated pure In₂Se₃-based devices. We attribute this promotion of photodetection to the suitable band structures of In₂Se₃ and CuInSe₂, which greatly promote the separation of photoexcited electron-hole pairs. This work suggests an effective way to form lateral p-n junctions, opening up a new scenario for designing and constructing high-performance optoelectronic devices.

Ultrasensitive Near-Infrared Photodetectors Based on a Graphene-MoTe2-Graphene Vertical van der Waals Heterostructure

Graphene and other layered materials, such as transition metal dichalcogenides, have rapidly established themselves as exceptional building blocks for optoelectronic applications because of their unique properties and atomically thin nature. The ability to stack them into van der Waals (vdWs) heterostructures with new functionality has opened a new platform for fundamental research and device applications. Nevertheless, near-infrared (NIR) photodetectors based on layered semiconductors are rarely realized. In this work, we fabricate a graphene-MoTe₂-graphene vertical vdWs heterostructure on a SiO₂/p⁺-Si substrate by a facile and reliable site-controllable transfer method and apply it for photodetection from the visible to NIR wavelength range. Compared to the layered semiconductor photodetectors reported thus far, the graphene-MoTe₂-graphene photodetector has a superior performance, including high photoresponsivity (∼110 mA W^-1 at 1064 nm and 205 mA W^-1 at 473 nm), high external quantum efficiency (EQE; ∼12.9% at 1064 nm and ∼53.8% at 473 nm), rapid response and recovery processes (a rise time of 24 μs and a fall time of 46 μs under 1064 nm illumination), and free from an external source-drain power supply. We have employed scanning photocurrent microscopy to investigate the photocurrent generation in this heterostructure under various back-gate voltages and found that the two Schottky barriers between the graphenes and MoTe₂ play an important role in the photocurrent generation. In addition, the vdWs heterostructure has a uniform photoresponsive area. The photoresponsivity and EQE of the photodetector can be modulated by the back-gate (p⁺-Si) voltage. We compared the responsivities of thin and thick flakes and found that the responsivity had a strong dependence on the thickness. The heterostructure has promising applications in future novel optoelectronic devices, enabling next-generation high-responsivity, high-speed, flexible, and transparent NIR devices.

Midrefractive Dielectric Modulator for Broadband Unidirectional Scattering and Effective Radiative Tailoring in the Visible Region

Nanoantennas have found many applications in ultrasmall sensors, single-molecule detection, and all-optical communication. Conventional nanoantennas are based on noble-metal plasmonic structures, but suffer from large ohmic loss and only possess dipolar plasmon modes. This has driven an intense search for all-dielectric materials beyond noble metals. Here, we propose midrefractive nanospheres as a novel all-dielectric material to realize broadband unidirectional radiation and effective radiative tailoring in the visible region. Midrefractive all-dielectric materials such as boron nanospheres possess broad and overlapping electric and magnetic dipole modes. The internal interaction between these two modes can route the radiation almost on the one side covering the whole visible range. Unlike the elaborate design in plasmonic nanostructures to obtain strong coupled broad and narrow modes, the bright mode in boron nanospheres is intrinsic, independent, and easily coupled with adjacent narrow modes. So the strong interaction in boron-based heterodimer is able to realize an independent and precise tailoring of the radiant and subradiant states by simply changing the particle sizes, respectively. Our findings imply midrefractivity materials like boron are excellent building blocks to support electromagnetic coupling operation in nanoscale devices, which will lead to a variety of emerging applications such as nanoantennas with directing exciton emission, ultrasensitive nanosensors, or even potential new construction of photonic metamaterials.

Stable, Fast UV-Vis-NIR Photodetector with Excellent Responsivity, Detectivity, and Sensitivity Based on α-In2Te3 Films with a Direct Bandgap

Photoelectric conversion is of great importance to extensive applications. However, thus far, photodetectors integrated with high responsivity, excellent detectivity, large phototo-dark current ratio, fast response speed, broad spectral range, and good stability are rarely achieved. Herein, we deposited large-scale and high-quality polycrystalline indium sesquitelluride (α-In2Te3) films via pulsed-laser deposition. Then, we demonstrated that the photodetectors made of the prepared α-In2Te3 films possess stable photoswitching behavior from 370 to 1064 nm and short response time better than ca. 15 ms. At a source-drain voltage of 5 V, the device achieves a high responsivity of 44 A/W, along with an outstanding detectivity of 6 × 10(12) cm H(1/2) W(-1) and an excellent sensitivity of 2.5 × 10(5) cm(2)/W. All of these figures-of-merit are the best among those of the reported α-In2Te3 photodetectors. In fact, they are comparable to the state-of-the-art commercial Si and Ge photodetectors. For the first time, we established the theoretical evidence that α-In2Te3 possesses a direct bandgap structure, which reasonably accounts for the superior photodetection performances above. Importantly, the device exhibits a good stability against the multiple photoswitching operation and ambient environment, along with no obvious voltage-scan hysteresis. These excellent figures-of-merit, together with the broad spectral range and good stability, underscore α-In2Te3 as a promising candidate material for next-generation photodetection.

Synergistic Effect of Hybrid Multilayer In2Se3 and Nanodiamonds for Highly Sensitive Photodetectors

Layered materials have rapidly established themselves as intriguing building blocks for next-generation photodetection platforms in view of their exotic electronic and optical attributes. However, both relatively low mobility and heavier electron effective mass limit layered materials for high-performance applications. Herein, we employed nanodiamonds (NDs) to promote the performance of multilayer In2Se3 photodetectors for the first time. This hybrid NDs-In2Se3 photodetector showed a tremendous promotion of photodetection performance in comparison to pristine In2Se3 ones. This hybrid devices exhibited remarkable detectivity (5.12 × 10(12) jones), fast response speed (less than 16.6 ms), and decent current on/off ratio (∼2285) simultaneously. These parameters are superior to most reported layered materials based photodetectors and even comparable to the state-of-the-art commercial photodetectors. Meanwhile, we attributed this excellent performance to the synergistic effect between NDs and the In2Se3. They can greatly enhance the broad spectrum absorption and promote the injection of photoexcited carrier in NDs to In2Se3. These results actually open up a new scenario for designing and fabricating innovative optoelectronic systems.

Promoting the Performance of Layered-Material Photodetectors by Alloy Engineering

The successful peeling of graphene heralded the era of van der Waals material (vdWM) electronics. However, photodetectors based on semiconducting transition metal dichalcogenides (TMDs), formulated as MX2 (M = Mo, W; X = S, Se), often suffer either poor responsivity or long response time because of their high density of deep-level defect states (DLDSs). Alloy engineering, which can shift the DLDSs to shallow-level defect states, is proposed to be an efficient strategy to solve this problem. However, proof-of-concept is still lacking, which is probably because of the absence of a facile technology to grow high-quality alloyed TMDs. Here, we report the growth of large-scale and high-quality Mo0.5W0.5S2 alloy films via pulsed laser deposition (PLD). We demonstrate that the resulting Mo0.5W0.5S2 photodetector possesses a stable photoresponse from 370 to 1064 nm. The photocurrent exhibits positive dependence on both the source-drain voltage and incident power density, providing good tunability for multifunctional photoelectrical applications. We also establish that, because of the suppression of DLDSs with alloy engineering, the Mo0.5W0.5S2 photodetector achieves a good responsivity of 5.8 A/W and a response time shorter than 150 ms. The working mechanism for the suppression of DLDSs in Mo0.5W0.5S2 is unveiled by qualitatively analyzing the alloying-dressed band structure. In conclusion, the excellent performance of the PLD-grown Mo0.5W0.5S2 photodetector may pave the way for next-generation photodetection. The approach shown here represents a fundamental and universal scenario for the development of alloyed TMDs.