Sandwiched WS2/MoTe2/WS2 Heterostructure with a Completely Depleted Interlayer for a Photodetector with Outstanding Detectivity.

Photodetectors based on two-dimensional van der Waals (2D vdW) heterostructures with high detectivity and rapid response have emerged as promising candidates for next-generation imaging applications. However, the practical application of currently studied 2D vdW heterostructures faces challenges related to insufficient light absorption and inadequate separation of photocarriers. To address these challenges, we present a sandwiched WS2/MoTe2/WS2 heterostructure with a completely depleted interlayer, integrated on a mirror electrode, for a highly efficient photodetector. This well-designed structure enhances light-matter interactions while facilitating effective separation and rapid collection of photocarriers. The resulting photodetector exhibits a broadband photoresponse spanning from deep ultraviolet to near-infrared wavelengths. When operated in self-powered mode, the device demonstrates an exceptional response speed of 22/34 µs, along with an impressive detectivity of 8.27 × 1010 Jones under 635 nm illumination. Additionally, by applying a bias voltage of -1 V, the detectivity can be further increased to 1.49 × 1012 Jones, while still maintaining a rapid response speed of 180/190 µs. Leveraging these outstanding performance metrics, high-resolution visible-near-infrared light imaging has been successfully demonstrated using this device. Our findings provide valuable insights into the optimization of device architecture for diverse photoelectric applications.

2D Reconfigurable van der Waals Heterojunction for Logic Gate Circuits and Wide-Spectrum Photodetectors via Sulfur Substitution and Band Matching.

The attractive physical properties of two-dimensional (2D) semiconductors in group IVA-VIA have been fully revealed in recent years. Combining them with 2D ambipolar materials to construct van der Waals heterojunctions (vdWHs) can offer tremendous opportunities for designing multifunctional electronic and optoelectronic devices, such as logic switching circuits, half-wave rectifiers, and broad-spectrum photodetectors. Here, an optimized SnSe0.75S0.25 is grown to design a SnSe0.75S0.25/MoTe2 vdWH for logic operation and wide-spectrum photodetection. Benefiting from the excellent gate modulation under the appropriate sulfur substitution and type-II band alignment, the device exhibits reconfigurable antiambipolar and ambipolar transfer behaviors at positive and negative source-drain voltage (Vds), enabling stable XNOR logic operation. It also features a gate-modulated positive and negative rectifying behavior with rectification ratios of 265:1 and 1:196, confirming its potential as half-wave logic rectifiers. Besides, the device can respond from visible to infrared wavelength up to 1400 nm. Under 635 nm illumination, the maximum responsivity of 1.16 A/W and response time of 657/500 µs are achieved at the Vds of -2 V. Furthermore, due to the strong in-plane anisotropic structure of SnSe0.75S0.25-alloyed nanosheet and narrow bandgap of 2H-MoTe2, it shows a broadband polarization-sensitive function with impressive photocurrent anisotropic ratios of 15.6 (635 nm), 7.0 (808 nm), and 3.7 (1310 nm). The direction along the maximum photocurrent can be reconfigurable depending on the wavelengths. These results indicate that our designed alloyed SnSe0.75S0.25/MoTe2 vdWH has reconfigurable logic operation and broadband photodetection capabilities in 2D multifunctional integrated circuits.

Two-Dimensional GeS/SnSe2 Tunneling Photodiode with Bidirectional Photoresponse and High Polarization Sensitivity.

A two-dimensional (2D) broken-gap (type-III) p-n heterojunction has a unique charge transport mechanism because of nonoverlapping energy bands. In light of this, type-III band alignment can be used in tunneling field-effect transistors (TFETs) and Esaki diodes with tunable operation and low consumption by highlighting the advantages of tunneling mechanisms. In recent years, 2D tunneling photodiodes have gradually attracted attention for novel optoelectronic performance with a combination of strong light-matter interaction and tunable band alignment. However, an in-depth understanding of the tunneling mechanisms should be further investigated, especially for developing electronic and optoelectronic applications. Here, we report a type-III tunneling photodiode based on a 2D multilayered p-GeS/n+-SnSe2 heterostructure, which is first fabricated by the mechanical exfoliation and dry transfer method. Through the Simmons approximation, its various tunneling transport mechanisms dependent on bias and light are demonstrated as the origin of excellent bidirectional photoresponse performance. Moreover, compared to the traditional p-n photodiode, the device enables bidirectional photoresponse capability, including maximum responsivity values of 43 and 8.7 A/W at Vds = 1 and -1 V, respectively, with distinctive photoactive regions from the scanning photocurrent mapping. Noticeably, benefiting from the in-plane anisotropic structure of GeS, the device exhibits an enhanced photocurrent anisotropic ratio of 9, driven by the broader depletion region at Vds = -3 V under 635 nm irradiation. Above all, the results suggest that our designed architecture can be potentially applied to CMOS imaging sensors and polarization-sensitive photodetectors.

2D Free-Standing GeS1-xSex with Composition-Tunable Bandgap for Tailored Polarimetric Optoelectronics.

Germanium-based monochalcogenides (i.e., GeS and GeSe) with desirable properties are promising candidates for the development of next-generation optoelectronic devices. However, they are still stuck with challenges, such as relatively fixed electronic band structure, unconfigurable optoelectronic characteristics, and difficulty in achieving free-standing growth. Herein, it is demonstrated that two-dimensional (2D) free-standing GeS1-xSex (0 ≤ x ≤ 1) nanoplates can be grown by low-pressure rapid physical vapor deposition (LPRPVD), fulfilling a continuously composition-tunable optical bandgap and electronic band structure. By leveraging the synergistic effect of composition-dependent modulation and free-standing growth, GeS1-xSex-based optoelectronic devices exhibit significantly configurable hole mobility from 6.22 × 10-4 to 1.24 cm2V-1s⁻1 and tunable responsivity from 8.6 to 311 A W-1 (635 nm), as x varies from 0 to 1. Furthermore, the polarimetric sensitivity can be tailored from 4.3 (GeS0.29Se0.71) to 1.8 (GeSe) benefiting from alloy engineering. Finally, the tailored imaging capability is also demonstrated to show the application potential of GeS1-xSex alloy nanoplates. This work broadens the functionality of conventional binary materials and motivates the development of tailored polarimetric optoelectronic devices.

Activation of the Photosensitive Potential of 2D GaSe by Interfacial Engineering.

Two-dimensional (2D) gallium selenide (GaSe) holds great promise for pioneering advancements in photodetection due to its exceptional electronic and optoelectronic properties. However, in conventional photodetectors, 2D GaSe only functions as a photosensitive layer, failing to fully exploit its inherent photosensitive potential. Herein, we propose an ultrasensitive photodetector based on out-of-plane 2D GaSe/MoSe2 heterostructure. Through interfacial engineering, 2D GaSe serves not only as the photosensitive layer but also as the photoconductive gain and passivation layer, introducing a photogating effect and extending the lifetime of photocarriers. Capitalizing on these features, the device exhibits exceptional photodetection performance, including a responsivity of 28 800 A/W, specific detectivity of 7.1 × 1014 Jones, light on/off ratio of 1.2 × 106, and rise/fall time of 112.4/426.8 µs. Moreover, high-resolution imaging under various wavelengths is successfully demonstrated using this device. Additionally, we showcase the generality of this device design by activating the photosensitive potential of 2D GaSe with other transition metal dichalcogenides (TMDCs) such as WSe2, WS2, and MoS2. This work provides inspiration for future development in high-performance photodetectors, shining a spotlight on the potential of 2D GaSe and its heterostructure.

Polarization-Sensitive Self-Powered Schottky Photodetector with High Photovoltaic Performance Induced by Geometry-Asymmetric Contacts.

Polarization-sensitive photodetectors have attracted considerable attention owing to their potential application prospects in navigation, optical switching, and communication. However, it remains challenging to develop a facile and effective strategy to simultaneously meet the demands of low power consumption, high performance, and excellent polarization sensitivity. Herein, a series of low-symmetry two-dimensional (2D) ReSe2 Schottky photodetectors with geometry-asymmetric contacts are constructed. These devices exhibit excellent photoelectrical performance and impressive polarization sensitivity in the self-powered mode owing to the difference in the Schottky barrier height induced by the asymmetric contact areas, interfacial states, and thickness difference. Particularly, an outstanding responsivity of 379 mA/W, a decent specific detectivity of 6.8 × 1011 Jones, and a high light on/off ratio (Ilight/Idark) of over 105 under 635 nm light illumination are achieved. Scanning photocurrent mapping (SPCM) measurements further confirm that the ReSe2/drain overlapped region (corresponding to the smaller contact area side) with a higher Schottky barrier height plays a dominant role in the generation of photocurrent. Furthermore, the proposed device displays impressive polarization ratios (PRs) of 3.1 and 3.6 at zero bias under 635 and 808 nm irradiation, respectively. The high-resolution single-pixel imaging capability is also demonstrated. This work reveals the great potential of the ReSe2 Schottky photodetector with geometry-asymmetric contacts for high-performance, self-powered, and polarization-sensitive photodetection.

Ideal Photodetector Based on WS2/CuInP2S6 Heterostructure by Combining Band Engineering and Ferroelectric Modulation.

Two-dimensional van der Waals (2D vdW) heterostructure photodetectors have garnered significant attention for their potential applications in next-generation optoelectronic systems. However, current 2D vdW photodetectors inevitably encounter compromises between responsivity, detectivity, and response time due to the absence of multilevel regulation for free and photoexcited carriers, thereby restricting their widespread applications. To address this challenge, we propose an efficient 2D WS2/CuInP2S6 vdW heterostructure photodetector by combining band engineering and ferroelectric modulation. In this device, the asymmetric conduction and valence band offsets effectively block the majority carriers (free electrons), while photoexcited holes are efficiently tunneled and rapidly collected by the bottom electrode. Additionally, the ferroelectric CuInP2S6 layer generates polarization states that reconfigure the built-in electric field, reducing dark current and facilitating the separation of photocarriers. Moreover, photoelectrons are trapped during long-distance lateral transport, resulting in a high photoconductivity gain. Consequently, the device achieves an impressive responsivity of 88 A W-1, an outstanding specific detectivity of 3.4 × 1013 Jones, and a fast response time of 37.6/371.3 µs. Moreover, the capability of high-resolution imaging under various wavelengths and fast optical communication has been successfully demonstrated using this device, highlighting its promising application prospects in future optoelectronic systems.

Polarization- and Gate-Tunable Optoelectronic Reverse in 2D Semimetal/Semiconductor Photovoltaic Heterostructure.

Polarimetric photodetector can acquire higher resolution and more surface information of imaging targets in complex environments due to the identification of light polarization. To date, the existing technologies yet sustain the poor polarization sensitivity (<10), far from market application requirement. Here, the photovoltaic detectors with polarization- and gate-tunable optoelectronic reverse phenomenon are developed based on semimetal 1T'-MoTe2 and ambipolar WSe2 . The device exhibits gate-tunable reverse in rectifying and photovoltaic characters due to the directional inversion of energy band, yielding a wide range of current rectification ratio from 10-2 to 103 and a clear object imaging with 100 × 100 pixels. Acting as a polarimetric photodetector, the polarization ratio (PR) value can reach a steady state value of ≈30, which is compelling among the state-of-the-art 2D-based polarized detectors. The sign reversal of polarization-sensitive photocurrent by varying the light polarization angles is also observed, that can enable the PR value with a potential to cover possible numbers (1→+∞/-∞→-1). This work develops a photovoltaic detector with polarization- and gate-tunable optoelectronic reverse phenomenon, making a significant progress in polarimetric imaging and multifunction integration applications.

Polarization-sensitive UV photodetector based on ReSe2/GaN mixed-dimensional heterojunction.

Polarization-sensitive photodetectors in the ultraviolet (UV) region have been favored for their great meaning in the field of military and civilian. UV photodetectors based on GaN have aroused much attention due to high photocurrent and high sensitivity. However, the dependence on external power sources and the limited sensitivity to polarized UV light significantly impede the practical application of these photodetectors in UV-polarized photodetection. Herein, a polarization-sensitive UV photodetector based on ReSe2/GaN mixed-dimensional van der Waals (vdWs) heterojunction is proposed. Owing to the high-quality junction and type-II band alignment, the responsivity and specific detectivity reach values of 870 mA/W and 6.8 × 1011 Jones, under 325 nm illumination, respectively. Furthermore, thanks to the strong in-plane anisotropy of ReSe2, the device is highly sensitive to polarized UV light with a photocurrent anisotropic ratio up to 6.67. The findings are expected to bring new opportunities for the development of highly sensitive, high-speed and energy-efficient polarization-sensitive photodetectors.

Experimental Study on the Dilatancy and Energy Evolution Behaviors of Red-Bed Rocks under Unloading Conditions.

Surrounding rock deformation and consequent support failure are the most prominent issues in red-bed rock tunnel engineering and are mainly caused by the effects of unloading, rheology, and swelling. This study investigated the mechanical responses of two kinds of red-bed mudstone and sandstone under unloading conditions via laboratory observation. Volume dilation was observed on the rocks during unloading, and the dilatancy stress was linear with the initial confining pressure. However, the ratios of dilatancy stress to peak stress of the two rocks kept at a range from 0.8 to 0.9, regardless of confining pressures. Both the elastic strain energy and the dissipated energy evolved synchronously with the stress-strain curve and exhibited conspicuous confining pressure dependence. Special attention was paid to the evolution behavior of the dilatancy angle. The dilatancy angle changed linearly during unloading. When the confining pressure was 10 MPa, the dilatancy angle of mudstone decreased from 26.8° to 12.5° whereas the dilatancy angle of sandstone increased from 34.6° to 51.1°; when the confining pressure rose to 25 MPa, the dilatancy angle of mudstone and sandstone decreased from 45.8° to 17.4° and increased from 21.7° to 39.5°, respectively. To further understand the evolution of the dilatancy angle, we discussed the links between the variable dilatancy angle and the processes of rock deformation and energy dissipation.

Quantum tailoring for polarization-discriminating Bi2S3 nanowire photodetectors and their multiplexing optical communication and imaging applications.

In this study, cost-efficient atmospheric pressure chemical vapor deposition has been successfully developed to produce well-aligned high-quality monocrystalline Bi2S3 nanowires. By virtue of surface strain-induced energy band reconstruction, the Bi2S3 photodetectors demonstrate a broadband photoresponse across 370.6 to 1310 nm. Upon a gate voltage of 30 V, the responsivity, external quantum efficiency, and detectivity reach 23 760 A W-1, 5.55 × 106%, and 3.68 × 1013 Jones, respectively. The outstanding photosensitivity is ascribed to the high-efficiency spacial separation of photocarriers, enabled by synergy of the axial built-in electric field and type-II band alignment, as well as the pronounced photogating effect. Moreover, a polarization-discriminating photoresponse has been unveiled. For the first time, the correlation between quantum confinement and dichroic ratio is systematically explored. The optoelectronic dichroism is established to be negatively correlated with the cross dimension (i.e., width and height) of the channel. Specifically, upon 405 nm illumination, the optimized dichroic ratio reaches 2.4, the highest value among the reported Bi2S3 photodetectors. In the end, proof-of-concept multiplexing optical communications and broadband lensless polarimetric imaging have been implemented by exploiting the Bi2S3 nanowire photodetectors as light-sensing functional units. This study develops a quantum tailoring strategy for tailoring the polarization properties of (quasi-)1D material photodetectors whilst depicting new horizons for the next-generation opto-electronics industry.

Interfacial Engineering of In2Se3/h-BN/CsPb(Br/I)3 Heterostructure Photodetector and Its Application in Automatic Obstacle Avoidance System.

Driven by the rapid development of autonomous vehicles, ultrasensitive photodetectors with high signal-to-noise ratio and ultraweak light detection capability are urgently needed. Due to its intriguing attributes, the emerging van der Waals material, indium selenide (In2Se3), has attracted extensive attention as an ultrasensitive photoactive material. However, the lack of an effective photoconductive gain mechanism in individual In2Se3 inhibits its further application. Herein, we propose a heterostructure photodetector consisting of an In2Se3 photoactive channel, a hexagonal boron nitride (h-BN) passivation layer, and a CsPb(Br/I)3 quantum dot gain layer. This device manifests a signal-to-noise ratio of 2 × 106 with responsivity of 2994 A/W and detectivity of 4.3 × 1014 Jones. Especially, it enables the detection of weak light as low as 0.03 µW/cm2. These performance characteristics are ascribed to the interfacial engineering. In2Se3 and CsPb(Br/I)3 with type-II band alignment promote the separation of photocarriers, while h-BN passivates the impurities on CsPb(Br/I)3 and promises a high-quality carrier transport interface. Furthermore, this device is successfully integrated into an automatic obstacle avoidance system, demonstrating promising application prospects in autonomous vehicles.

Bi2O2Se Nanowire/MoSe2 Mixed-Dimensional Polarization-Sensitive Photodiode with a Nanoscale Ultrafast-Response Channel.

In recent years, polarization-sensitive photodiodes based on one-dimensional/two-dimensional (1D/2D) van der Waals (vdWs) heterostructures have garnered significant attention due to the high specific surface area, strong orientation degree of 1D structures, and large photo-active area and mechanical flexibility of 2D structures. Therefore, they are applicable in wearable electronics, electrical-driven lasers, image sensing, optical communication, optical switches, etc. Herein, 1D Bi2O2Se nanowires have been successfully synthesized via chemical vapor deposition. Impressively, the strongest Raman vibration modes can be achieved along the short edge (y-axis) of Bi2O2Se nanowires with high crystalline quality, which originate from Se and Bi vacancies. Moreover, the Bi2O2Se/MoSe2 photodiode designed with type-II band alignment demonstrates a high rectification ratio of 103. Intuitively, the photocurrent peaks are mainly distributed in the overlapped region under the self-powered mode and reverse bias, within the wavelength range of 400-nm. The resulting device exhibits excellent optoelectrical performances, including high responsivities (R) and fast response speed of 656 mA/W and 350/380 µs (zero bias) and 17.17 A/W and 100/110 µs (-1 V) under 635 nm illumination, surpassing the majority of reported mixed-dimensional photodiodes. The most significant feature of our photodiode is its highest photocurrent anisotropic ratio of ∼2.2 (-0.8 V) along the long side (x-axis) of Bi2O2Se nanowires under 635 nm illumination. The above results reveal a robust and distinctive correlation between structural defects and polarized orientation for 1D Bi2O2Se nanowires. Furthermore, 1D Bi2O2Se nanowires appear to be a great potential candidate for high-performance rectifiers, polarization-sensitive photodiodes, and phototransistors based on mixed vdWs heterostructures.

Self-Powered Photodetector with High Efficiency and Polarization Sensitivity Enabled by WSe2/Ta2NiSe5/WSe2 van der Waals Dual Heterojunction.

Self-powered photodetectors have triggered widespread attention because of the requirement of Internet of Things (IoT) application and low power consumption. However, it is challenging to simultaneously implement miniaturization, high quantum efficiency, and multifunctionalization. Here, we report a high-efficiency and polarization-sensitive photodetector enabled by two-dimensional (2D) WSe2/Ta2NiSe5/WSe2 van der Waals (vdW) dual heterojunctions (DHJ) along with a sandwich-like electrode pair. On account of enhanced light collection efficiency and two opposite built-in electric fields at the hetero-interfaces, the DHJ device achieves not only a broadband spectral response of 400-1550 nm but outstanding performance under 635 nm light illumination including an ultrahigh external quantum efficiency (EQE) of 85.5%, a pronounced power conversion efficiency (PCE) of 1.9%, and a fast response speed of 420/640 µs, which is much better than that of the WSe2/Ta2NiSe5 single heterojunction (SHJ). Significantly, based on the strong in-plane anisotropy of 2D Ta2NiSe5 nanosheets, the DHJ device shows competitive polarization sensitivities of 13.9 and 14.8 under 635 and 808 nm light, respectively. Furthermore, an excellent self-powered visible imaging capability based on the DHJ device is demonstrated. These results pave a promising platform for realizing self-powered photodetectors with high performance and multifunctionality.

Reconfigurable ultra-broadband mode converter based on a two-mode fiber with pressure-loaded phase-shifted long-period alloyed waveguide grating.

We present a reconfigurable ultra-broadband mode converter, which consists of a two-mode fiber (TMF) and pressure-loaded phase-shifted long-period alloyed waveguide grating. We design and fabricate the long-period alloyed waveguide gratings (LPAWG) with SU-8, chromium, and titanium via the photo-lithography and electric beam evaporation technique. With the help of the pressure loaded or released from the LPAWG onto the TMF, the device can realize reconfigurable mode conversion between the LP01 mode and the LP11 mode in the TMF, which is weak sensitive to the state of polarization. The mode conversion efficiency larger than 10 dB can be achieved with operation wavelength range of about 105 nm, which ranges from 1501.9 nm to 1606.7 nm. The proposed device can be further used in the large bandwidth mode division multiplexing (MDM) transmission and optical fiber sensing system based on few-mode fibers.

Integration of Self-Passivated Topological Electrodes for Advanced 2D Optoelectronic Devices.

With the rapid development of two-dimensional semiconductor technology, the inevitable chemical disorder at a typical metal-semiconductor interface has become an increasingly serious problem that degrades the performance of 2D semiconductor optoelectronic devices. Herein, defect-free van der Waals contacts have been achieved by utilizing topological Bi2 Se3 as the electrodes. Such clean and atomically sharp contacts avoid the consumption of photogenerated carriers at the interface, enabling a markedly boosted sensitivity as compared to counterpart devices with directly deposited metal electrodes. Typically, the device with 2D WSe2 channel realizes a high responsivity of 20.5 A W-1 , an excellent detectivity of 2.18 × 1012  Jones, and a fast rise/decay time of 41.66/38.81 ms. Furthermore, high-resolution visible-light imaging capability of the WSe2 device is demonstrated, indicating its promising application prospect in future optoelectronic systems. More inspiringly, the topological electrodes are universally applicable to other 2D semiconductor channels, including WS2 and InSe, suggesting its broad applicability. These results open fascinating opportunities for the development of high-performance electronics and optoelectronics.

Type-II Bi2O2Se/MoTe2 van der Waals Heterostructure Photodetectors with High Gate-Modulation Photovoltaic Performance.

In recent years, two-dimensional (2D) nonlayered Bi2O2Se-based electronics and optoelectronics have drawn enormous attention owing to their high electron mobility, facile synthetic process, stability to the atmosphere, and moderate narrow band gaps. However, 2D Bi2O2Se-based photodetectors typically present large dark current, relatively slow response speed, and persistent photoconductivity effect, limiting further improvement in fast-response imaging sensors and low-consumption broadband detection. Herein, a Bi2O2Se/2H-MoTe2 van der Waals (vdWs) heterostructure obtained from the chemical vapor deposition (CVD) approach and vertical stacking is reported. The proposed type-II staggered band alignment desirable for suppression of dark current and separation of photoinduced carriers is confirmed by density functional theory (DFT) calculations, accompanied by strong interlayer coupling and efficient built-in potential at the junction. Consequently, a stable visible (405 nm) to near-infrared (1310 nm) response capability, a self-driven prominent responsivity (R) of 1.24 A·W-1, and a high specific detectivity (D*) of 3.73 × 1011 Jones under 405 nm are achieved. In particular, R, D*, fill factor, and photoelectrical conversion efficiency (PCE) can be enhanced to 4.96 A·W-1, 3.84 × 1012 Jones, 0.52, and 7.21% at Vg = -60 V through a large band offset originated from the n+-p junction. It is suggested that the present vdWs heterostructure is a promising candidate for logical integrated circuits, image sensors, and low-power consumption detection.

Ultrabroadband Imaging Based on Wafer-Scale Tellurene.

High-resolution imaging is at the heart of the revolutionary breakthroughs of intelligent technologies, and it is established as an important approach toward high-sensitivity information extraction/storage. However, due to the incompatibility between non-silicon optoelectronic materials and traditional integrated circuits as well as the lack of competent photosensitive semiconductors in the infrared region, the development of ultrabroadband imaging is severely impeded. Herein, the monolithic integration of wafer-scale tellurene photoelectric functional units by exploiting room-temperature pulsed-laser deposition is realized. Taking advantage of the surface plasmon polaritons of tellurene, which results in the thermal perturbation promoted exciton separation, in situ formation of out-of-plane homojunction and negative expansion promoted carrier transport, as well as the band bending promoted electron-hole pair separation enabled by the unique interconnected nanostrip morphology, the tellurene photodetectors demonstrate wide-spectrum photoresponse from 370.6 to 2240 nm and unprecedented photosensitivity with the optimized responsivity, external quantum efficiency and detectivity of 2.7 × 107  A W-1 , 8.2 × 109 % and 4.5 × 1015  Jones. An ultrabroadband imager is demonstrated and high-resolution photoelectric imaging is realized. The proof-of-concept wafer-scale tellurene-based ultrabroadband photoelectric imaging system depicts a fascinating paradigm for the development of an advanced 2D imaging platform toward next-generation intelligent equipment.

Three-dimensional mode multiplexer based on adiabatic-tapered waveguides forming vertical directional couplers over C + L band and beyond.

We present a mode multiplexer based on vertical directional couplers that are formed by adiabatic-tapered waveguides. We design and fabricate the device via the micro-fabrication processing to (de)multiplex the E11, E21, and E12 modes from the few-mode bus waveguide. Our experimental device shows a coupling ratio higher than 98.6% and 97.0% for the E21 and E12 modes, respectively, over the C + L band and beyond. The modal cross talk of this device can be lower than -17.1 dB, -18.4 dB, and -15.1 dB caused by the unintended E11, E21, and E12 modes, respectively. This mode multiplexer can work over a broader wavelength range with weak polarization sensitivity, which could be used in the mode-division-multiplexing systems where mode (de)multiplexing is required in the expanded communication wavelength window other than the C-band.

Integration of photovoltaic and photogating effects in a WSe2/WS2/p-Si dual junction photodetector featuring high-sensitivity and fast-response.

Two-dimensional (2D) material-based van der Waals (vdW) heterostructures with exotic semiconducting properties have shown tremendous potential in next-generation photovoltaic photodetectors. Nevertheless, these vdW heterostructure devices inevitably suffer from a compromise between high sensitivity and fast response. Herein, an ingenious photovoltaic photodetector based on a WSe2/WS2/p-Si dual-vdW heterojunction is demonstrated. First-principles calculations and energy band profiles consolidate that the photogating effect originating from the bottom vdW heterojunction not only strengthens the photovoltaic effect of the top vdW heterojunction, but also suppresses the recombination of photogenerated carriers. As a consequence, the separation of photogenerated carriers is facilitated and their lifetimes are extended, resulting in higher photoconductive gain. Coupled with these synergistic effects, this WSe2/WS2/p-Si device exhibits both high sensitivity (responsivity of 340 mA W-1, a light on/off ratio greater than 2500, and a detectivity of 3.34 × 1011 Jones) and fast response time (rise/decay time of 657/671 µs) under 405 nm light illumination in self-powered mode. Finally, high-resolution visible-light and near-infrared imaging capabilities are demonstrated by adopting this dual-heterojunction device as a single pixel, indicating its great application prospects in future optoelectronic systems.