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

High-Spike Barrier Photodiodes Based on 2D Te/WS2 Heterostructures

Two-dimensional (2D) van der Waals (vdWs) heterojunctions have been actively investigated in low-power-consumption and fast-response photodiodes owing to their atomically smooth interfaces and ultrafast interfacial charge transfer. However, achieving ultralow dark current and ultrafast photoresponse in the reported photovoltaic devices remains a challenge as the large built-in electric field in a heterojunction can not only speed up photocarrier transport but also increase the minority-carrier dark current. Here, we propose a high-spike barrier photodiode that can achieve both an ultralow dark current and an ultrafast response. The device is fabricated by the Te/WS2 heterojunction, while the band alignment can transition from type-II to type-I with a high electron barrier and a large hole built-in electronic field. The high electron barrier can greatly reduce the drift current of minority carriers and the generation current of the thermal carriers, while the large built-in electronic field can still speed up the photocarrier transport. The designed Te/WS2 vdWs photodiode yields an ultralow dark current of 8 × 10-14 A and an ultrafast photoresponse of 10/13 μs. Furthermore, a high-performance visible-light imager with a pixel resolution of 100 × 40 is demonstrated using the Te/WS2 vdWs photodiode. This work provides a comprehensive understanding of designing 2D-material-based photovoltaics with excellent overall performance.

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.

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.

Strong Covalent Coupling in Vertically Layered SnSe2/PTAA Heterojunctions Enabled High Performance Inorganic-Organic Hybrid Photodetectors

Controllable large-scale integration of two-dimensional (2D) materials with organic semiconductors and the realization of strong coupling between them still remain challenging. Herein, we demonstrate a wafer-scale, vertically layered SnSe2/PTAA heterojunction array with high light-trapping ability via a low-temperature molecular beam epitaxy method and a facile spin-coating process. Conductive probe atomic force microscopy (CP-AFM) measurements reveal strong rectification and photoresponse behavior in the individual SnSe2 nanosheet/PTAA heterojunction. Theoretical analysis demonstrates that vertically layered SnSe2/PTAA heterojunctions exhibit stronger C-Se covalent coupling than that of the conventional tiled type, which could facilitate more efficient charge transfer. Benefiting from these advantages, the SnSe2/PTAA heterojunction photodetectors with an optimized PTAA concentration show high performance, including a responsivity of 41.02 A/W, an external quantum efficiency of 1.31 × 104%, and high uniformity. The proposed approach for constructing large-scale 2D inorganic-organic heterostructures represents an effective route to fabricate high-performance broadband photodetectors for integrated optoelectronic systems.

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.

A high-performance and self-powered polarization-sensitive photoelectrochemical-type Bi2O2Te photodetector based on a quasi-solid-state gel electrolyte

Among the two-dimensional (2D) Bi2O2X (X = S, Se, and Te) series, Bi2O2Te has the smallest effective mass and the highest carrier mobility. However, Bi2O2Te has rarely been investigated, most likely due to the lack of feasible methods to synthesize 2D Bi2O2Te. Herein, 2D Bi2O2Te nanosheets are successfully synthesized by low-temperature oxidation of Bi2Te3 nanosheets synthesized using a solvothermal method. The performance of a quasi-solid-state photoelectrochemical-type (PEC-type) photodetector based on 2D Bi2O2Te nanosheets is systematically investigated. Remarkably, the device has a high responsivity of 20.5 mA W-1 (zero bias) and fast rise/fall times of 6/90 ms under 365 nm illumination, which is superior to the majority of PEC-type photodetectors based on bismuth-based compounds. More importantly, due to the strong anisotropy of 2D Bi2O2Te nanosheets, the device achieves a dichroic ratio as high as 52, which belongs to the state-of-the-art polarized photodetectors. Besides, the capacity of 2D Bi2O2Te for high-resolution polarization imaging is demonstrated. This work provides a promising strategy for the synthesis of 2D Bi2O2Te nanosheets to fabricate a high-performance and polarization-sensitive photodetector.

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-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.

High-Performance Photoinduced Tunneling Self-Driven Photodetector for Polarized Imaging and Polarization-Coded Optical Communication based on Broken-Gap ReSe2 /SnSe2 van der Waals Heterojunction

Novel 2D materials with low-symmetry structures exhibit great potential applications in developing monolithic polarization-sensitive photodetectors with small volume. However, owing to the fact that at least half of them presented a small anisotropic factor of ≈2, comprehensive performance of present polarization-sensitive photodetectors based on 2D materials is still lower than the practical application requirements. Herein, a self-driven photodetector with high polarization sensitivity using a broken-gap ReSe2 /SnSe2 van der Waals heterojunction (vdWH) is demonstrated. Anisotropic ratio of the photocurrent (Imax /Imin ) could reach 12.26 (635 nm, 179 mW cm-2 ). Furthermore, after a facile combination of the ReSe2 /SnSe2 device with multilayer graphene (MLG), Imax /Imin of the MLG/ReSe2 /SnSe2 can be further increased up to13.27, which is 4 times more than that of pristine ReSe2 photodetector (3.1) and other 2D material photodetectors even at a bias voltage. Additionally, benefitting from the synergistic effect of unilateral depletion and photoinduced tunneling mechanism, the MLG/ReSe2 /SnSe2 device exhibits a fast response speed (752/928 µs) and an ultrahigh light on/off ratio (105 ). More importantly, MLG/ReSe2 /SnSe2 device exhibits excellent potential applications in polarized imaging and polarization-coded optical communication with quaternary logic state without any power supply. This work provides a novel feasible avenue for constructing next-generation smart polarization-sensitive photodetector with low energy consumption.

Low-Dimensional-Materials-Based Photodetectors for Next-Generation Polarized Detection and Imaging

The vector characteristics of light and the vectorial transformations during its transmission lay a foundation for polarized photodetection of objects, which broadens the applications of related detectors in complex environments. With the breakthrough of low-dimensional materials (LDMs) in optics and electronics over the past few years, the combination of these novel LDMs and traditional working modes is expected to bring new development opportunities in this field. Here, the state-of-the-art progress of LDMs, as polarization-sensitive components in polarized photodetection and even the imaging, is the main focus, with emphasis on the relationship between traditional working principle of polarized photodetectors (PPs) and photoresponse mechanisms of LDMs. Particularly, from the view of constitutive equations, the existing works are reorganized, reclassified, and reviewed. Perspectives on the opportunities and challenges are also discussed. It is hoped that this work can provide a more general overview in the use of LDMs in this field, sorting out the way of related devices for "more than Moore" or even the "beyond Moore" research.

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.

CMOS-Compatible Tellurium/Silicon Ultra-Fast Near-Infrared Photodetector

High-quality photodetectors are always the main way to obtain external information, especially near-infrared sensors play an important role in remote sensing communication. However, due to the limitation of Silicon (Si) wide bandgap and the incompatibility of most near infrared photoelectric materials with traditional integrated circuits, the development of high performance and wide detection spectrum near infrared detectors suitable for miniaturization and integration is still facing many obstacles. Herein, the monolithic integration of large area tellurium optoelectronic functional units is realized by magnetron sputtering technology. Taking advantage of the type II heterojunction constructed by tellurium (Te) and silicon (Si), the photogenerated carriers are effectively separated, which prolongs the carrier lifetime and improves the photoresponse by several orders of magnitude. The tellurium/silicon (Te/Si) heterojunction photodetector demonstrates excellent detectivity and ultra-fast turn-on time. Importantly, an imaging array (20 × 20 pixels) based on the Te/Si heterojunction is demonstrated and high-contrast photoelectric imaging is realized. Because of the high contrast obtained by the Te/Si array, in comparison with the Si arrays, it significantly improve the efficiency and accuracy of the subsequent processing tasks when the electronic pictures are applied to artificial neural network (ANN) to simulate the artificial vision system.

Air-Stable Violet Phosphorus/MoS2 van der Waals Heterostructure for High-Responsivity and Gate-Tunable Photodetection

Violet phosphorus (VP), a newly emerging elemental 2D semiconductor, with attractive properties such as tunable bandgap, high carrier mobility, and unusual structural anisotropy, offers significant opportunities for designing high-performance electronic and optoelectronic devices. However, the study on fundamental property and device application of 2D VP is seriously hindered by its inherent instability in ambient air. Here, a VP/MoS2 van der Waals heterostructure is constructed by vertically staking few-layer VP and MoS2 , aiming to utilize the synergistic effect of the two materials to achieve a high-performance 2D photodetector. The strong optical absorption of VP combining with the type-II band alignment of VP/MoS2 heterostructure make VP play a prominent photogating effect. As a result, the VP/MoS2 heterostructure photodetector achieves an excellent photoresponse performances with ultrahigh responsivity of 3.82 × 105  A W-1 , high specific detectivity of 9.17 × 1013 Jones, large external quantum efficiency of 8.91 × 107 %, and gate tunability, which are much superior to that of individual MoS2 device or VP device. Moreover, the VP/MoS2 heterostructure photodetector indicates superior air stability due to the effective protection of VP by MoS2 encapsulation. This work sheds light on the future study of the fundamental property and optoelectronic device application of VP.

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.

Strong interlayer coupling in p-Te/n-CdSe van der Waals heterojunction for self-powered photodetectors with fast speed and high responsivity

Self-driven photodetectors, which can detect optical signals without external voltage bias, are highly attractive in the field of low-power wearable electronics and internet of things. However, currently reported self-driven photodetectors based on van der Waals heterojunctions (vdWHs) are generally limited by low responsivity due to poor light absorption and insufficient photogain. Here, we report p-Te/n-CdSe vdWHs utilizing non-layered CdSe nanobelts as efficient light absorption layer and high mobility Te as ultrafast hole transporting layer. Benefiting from strong interlayer coupling, the Te/CdSe vdWHs exhibit stable and excellent self-powered characteristics, including ultrahigh responsivity of 0.94 A W^-1, remarkable detectivity of 8.36 × 10¹² Jones at optical power density of 1.18 mW cm^-2 under illumination of 405 nm laser, fast response speed of 24 µs, large light on/off ratio exceeding 10⁵, as well as broadband photoresponse (405-1064 nm), which surpass most of the reported vdWHs photodetectors. In addition, the devices display superior photovoltaic characteristics under 532 nm illumination, such as large V_oc of 0.55 V, and ultrahigh I_sc of 2.73 µA. These results demonstrate the construction of 2D/non-layered semiconductor vdWHs with strong interlayer coupling is a promising strategy for high-performance and low-power consumption devices.