Silicon/2D-material photodetectors: from near-infrared to mid-infrared

Simulating and Implementing Broadband van der Waals Artificial Visual Synapses Based on Photoconductivity and Pyroconductivity Mechanisms

With advancements in artificial neural networks and information processing technology, a variety of neuromorphic synaptic devices have been proposed to emulate human sensory systems, with vision being a crucial information source. Moreover, as practical applications become increasingly complex, the need for multifunctional visual synapses to expand the application range becomes urgent. This study introduces a MoS2/WSe2 van der Waals (vdW) heterojunction and utilizes it to replicate artificial visual synapses by harnessing the cooperative effect of photoconductivity and pyroconductivity mechanisms. By adjusting the optical power, pulse width, and pulse number of the optical stimulus, the heterojunction effectively simulates synaptic properties. Under the combined action of an external electric field and the built-in electric field (Ebi), the heterojunction exhibits broadband synaptic properties in the visible to near-infrared spectrum (405-1550 nm) while consuming low power of 0.3-1.1 pJ per spike. The heterojunction can detect ultraweak optical signals at 660 nm with an optical power intensity of 14 μW/cm2, displaying a high specific detectivity (D*) of 3.98 × 1011 Jones. Furthermore, at 405, 808, 1064, and 1550 nm, the D* of the heterojunction is 4.16 × 1011, 3.61 × 109, 4.96 × 107, and 1.64 × 107 Jones, respectively. Visual synaptic devices based on the MoS2/WSe2 vdW heterojunction hold significant promise for the future development of integrated sensing and memory processing devices.

Ultra-smooth processing of lithium niobate for outstanding mid-infrared transmittance

The fabrication of anti-reflection (AR) subwavelength structures (SWSs) of lithium niobate (LN) is a challenging but rewarding task in mid-infrared LN laser systems. However, there are still some issues with the high-quality processing and fabrication of bifacial AR SWSs. Herein, a novel, to the best of our knowledge, approach to the fabrication of SWSs was proposed, which includes femtosecond laser ablation followed by wet etching and thermal annealing. The fabricated structures exhibit high surface quality (Ra = 0.08 nm) and uniformity. According to the experimental and simulated results, the transmittance of the mid-infrared AR SWSs with a period of 1.8 µm could be improved from 78% to 87% in the 3.6-5 µm band. Furthermore, the double-sided construction enabled a transmittance of up to 90%. The results have great potential in the promotion of the development of mid-infrared laser systems and LN-based photonics.

2D compounds with heterolayered architecture for infrared photodetectors

Compounds with heterolayered architecture, as a family of two-dimensional (2D) materials, are composed of alternating positive and negative layers. Their physical properties are determined not only by the charged constituents, but also by the interaction between the two layers. This kind of material has been widely used for superconductivity, thermoelectricity, energy storage, etc. In recent years, heterolayered compounds have been found as an encouraging choice for infrared photodetectors with high sensitivity, fast response, and remarkable reliability. In this review, we summarize the research progress of heterolayered materials for infrared photodetectors. A simple development history of the materials with three-dimensional (3D) or 2D structures, which are suitable for infrared photodetectors, is introduced firstly. Then, we compare the differences between van der Waals layered 2D materials and heterolayered 2D cousins and explain the advantages of heterolayered 2D compounds. Finally, we present our perspective on the future direction of heterolayered 2D materials as an emerging class of materials for infrared photodetectors.

Atomic-Thin WS2 Kirigami for Bidirectional Polarization Detection

The assembly and patterning engineering in two-dimensional (2D) materials hold importance for chip-level designs incorporating multifunctional detectors. At present, the patterning and stacking methods of 2D materials inevitably introduce impurity instability and functional limitations. Here, the space-confined chemical vapor deposition method is employed to achieve state-of-the-art kirigami structures of self-assembled WS2, featuring various layer combinations and stacking configurations. With this technique as a foundation, the WS2 nano-kirigami is integrated with metasurface design, achieving a photodetector with bidirectional polarization-sensitive detection capability in the infrared spectrum. Nano-kirigami can eliminate some of the uncontrollable factors in the processing of 2D material devices, providing a freely designed platform for chip-level multifunctional detection across multiple modules.

Room-Temperature Band-Aligned Infrared Heterostructures for Integrable Sensing and Communication

The demand for miniaturized and integrated multifunctional devices drives the progression of high-performance infrared photodetectors for diverse applications, including remote sensing, air defense, and communications, among others. Nonetheless, infrared photodetectors that rely solely on single low-dimensional materials often face challenges due to the limited absorption cross-section and suboptimal carrier mobility, which can impair sensitivity and prolong response times. Here, through experimental validation is demonstrated, precise control over energy band alignment in a type-II van der Waals heterojunction, comprising vertically stacked 2D Ta2NiSe5 and the topological insulator Bi2Se3, where the configuration enables polarization-sensitive, wide-spectral-range photodetection. Experimental evaluations at room temperature reveal that the device exhibits a self-powered responsivity of 0.48 A·W-1, a specific directivity of 3.8 × 1011 cm·Hz1/2·W-1, a response time of 151 µs, and a polarization ratio of 2.83. The stable and rapid photoresponse of the device underpins the utility in infrared-coded communication and dual-channel imaging, showing the substantial potential of the detector. These findings articulate a systematic approach to developing miniaturized, multifunctional room-temperature infrared detectors with superior performance metrics and enhanced capabilities for multi-information acquisition.

Silicon Waveguide-Integrated Platinum Telluride Midinfrared Photodetector with High Responsivity and High Speed

The detection of mid-infrared light, covering a variety of molecular vibrational spectra, is critical for both civil and military purposes. Recent studies have highlighted the potential of two-dimensional topological semimetals for mid-infrared detection due to their advantages, including van der Waals (vdW) stacking and gapless electronic structures. Among them, mid-infrared photodetectors based on type-II Dirac semimetals have been less studied. In this paper, we present a silicon waveguide integrated type-II Dirac semimetal platinum telluride (PtTe2) mid-infrared photodetector, and further improve detection performance by using PtTe2-graphene heterostructure. For the fabricated silicon waveguide-integrated PtTe2 photodetector, with an external bias voltage of -10 mV and an input optical power of 86 nW, the measured responsivity is 2.7 A/W at 2004 nm and a 3 dB bandwidth of 0.6 MHz is realized. For the fabricated silicon waveguide-integrated PtTe2-graphene photodetector, as the external bias voltage and input optical power are 0.5 V and 0.13 μW, a responsivity of 5.5 A/W at 2004 nm and a 3 dB bandwidth of 35 MHz are obtained. An external quantum efficiency of 119% can be achieved at an input optical power of 0.376 μW.

All-Optic Logical Operations Based on the Visible-Near Infrared Bipolar Optical Response

The burgeoning need for extensive data processing has sparked enthusiasm for the development of a novel optical logic gate platform. In this study, junction field-effect phototransistors based on molybdenum disulfide/Germanium (MoS2/Ge) heterojunctions are constructed as optical logic units. This device demonstrates a positive photoresponse that is attributed to the photoconductivity effect occurring upon irradiation with visible (Vis) light. Under the illumination of near-infrared (NIR) optics with wavelengths within the communication band, the device shows a negative photoresponse, which is associated with the interlayer Coulomb interactions. The current state of the device can be effectively modulated as different logical states by precisely tuning the wavelength and power density of the optical. Within a 3 × 3 MoS2/Ge phototransistor array, five essentially all-optical logic gates ("AND," "OR," "NAND," "NOT," and "NOR") can be achieved in every signal unit. Furthermore, three complex all-optical logical operations are demonstrated by integrating two MoS2/Ge phototransistors in series. Compared to electronic designs, these all-optical logic devices offer a significant reduction in transistor number, with savings of 50-94% when implementing the above-mentioned functions. These results present opportunities for the development of photonic chips with low power consumption, high fidelity, and large volumes.

Experimental Study on Damage Effect of Mid-Infrared Pulsed Laser on Charge Coupled Device (CCD) and HgCgTe Detectors

As the weak link in electro-optical imaging systems, photodetectors have always faced the threat of laser damage. In this paper, we experimentally investigated the damage mechanism of the photodetector induced by the out-of-band laser. The damage thresholds of the mid-infrared pulsed laser for Charge Coupled Device (CCD) and HgCdTe detectors were determined through damage experiments. The analysis of the damage phenomena and data for both CCD and HgCdTe detectors clearly demonstrated that out-of-band mid-infrared pulsed lasers could entirely incapacitate CCD and HgCdTe detectors. Our analysis of the damage process and data revealed that the primary mechanism of damage to CCD and HgCdTe detectors by mid-infrared pulsed lasers was primarily thermal. This study serves as a reference for further research on the mid-infrared pulsed laser damage mechanisms of CCD and HgCdTe detectors, as well as for laser protection and performance optimization in imaging systems.

Template-assisted growth of Ga-based nanoparticle clusters on Si: effect of post-annealing process on the Ga ion beam exposed 2D arrays fabricated by focused ion beam nanolithography

We demonstrate template-assisted growth of gallium-based nanoparticle clusters on silicon substrate using a focused ion beam (FIB) nanolithography technique. The nanolithography counterpart of the technique steers a focussed 30 kV accelerated gallium ion beam on the surface of Si to create template patterns of two-dimensional dot arrays. Growth of the nanoparticles is governed by two vital steps namely implantation of gallium into the substrate via gallium beam exposure and formation of the stable nanoparticles on the surface of the substrate by subsequent annealing at elevated temperature in ammonia atmosphere. The growth primarily depends on the dose of implanted gallium which is in the order of 107atoms per spot and it is also critically influenced by the temperature and duration of the post-annealing treatment. By controlling the growth parameters, it is possible to obtain one particle per spot and particle densities as high as 109particles per square centimetre could be achieved in this case. The demonstrated growth process, utilizing the advantages of FIB nanolithography, is categorized under the guided organization approach as it combines both the classical top-down and bottom-up approaches. Patterned growth of the particles could be utilized as templates or nucleation sites for the growth of an organized array of nanostructures or quantum dot structures.

A 1T'-MoTe2/GaN van der Waals Schottky junction for self-powered UV imaging and optical communication

Schottky-type self-powered UV photodetectors are promising for next-generation imaging systems. Nevertheless, conventional device fabrication using high-energy metal deposition brings unintentional interface defects, leading to deteriorated device performance and inhomogeneities. Emerging two-dimensional (2D) metallic materials offer an alternative pathway to overcoming such limitations because of their naturally passivated surfaces and the ease of combining with mature bulk semiconductors via van der Waals (vdW) integration. Here, we report the controllable preparation of MoTe2 in the pure 1T' phase and the fabrication of a high-performance 1T'-MoTe2/GaN vdW Schottky photodiode. With the reduced interface states and suppressed dark current as low as 20 pA at zero bias, the photodiode exhibits a remarkable UV-to-visible (R350/R400) rejection ratio of 1.6 × 104, a stable photoresponsivity of ∼50 mA W-1 and a detectivity of 3.5 × 1012 Jones under 360 nm illumination. The photocurrent ON/OFF ratio reaches ∼4.9 × 106 under 10.5 mW irradiation (360 nm). In particular, the 1T'-MoTe2/GaN Schottky diode shows excellent weak-light detection capability, which could detect a 3 nW 360 nm laser and the light emission from a lighter with a pronounced Ilight/Idark ratio of ∼2. Finally, the applications of the device in self-powered UV imaging and optical communication are demonstrated. These results reveal the great prospects of 2D/3D integration in multifunctional optoelectronics, which may inspire novel 2D-related devices and expand their applications in widespread fields.

Demonstration of a low power and high-speed graphene/silicon heterojunction near-infrared photodetector

The structure and process of the graphene/Si heterojunction near-infrared photodetector were optimized to enhance the operating speed limit. The introduction of a well-designed structure improved the rise time from 12.6 μs to 115 ns, albeit at the expense of the responsivity, which decreased from 1.25 A W-1 to 0.56 A W-1. Similarly, the falling time was improved from 38 μs to 288 ns with a sacrifice in responsivity from 1.25 A W-1 to 0.29 A W-1, achieved through the introduction of Ge-induced defect-recombination centers within the well. Through a judicious well design and the introduction of recombination defect centers, the minimum pulse width could be improved from 50.6 μs to 435 ns, facilitating 2 MHz operation. This represents more than 100 times increase compared to previously reported graphene and graphene/Si hybrid photodetectors.

Graphene photodetectors integrated with silicon and perovskite quantum dots

Photodetectors (PDs) play a crucial role in imaging, sensing, communication systems, etc. Graphene (Gr), a leading two-dimensional material, has demonstrated significant potential for photodetection in recent years. However, its relatively weak interaction with light poses challenges for practical applications. The integration of silicon (Si) and perovskite quantum dots (PQDs) has opened new avenues for Gr in the realm of next-generation optoelectronics. This review provides a comprehensive investigation of Gr/Si Schottky junction PDs and Gr/PQD hybrid PDs as well as their heterostructures. The operating principles, design, fabrication, optimization strategies, and typical applications of these devices are studied and summarized. Through these discussions, we aim to illuminate the current challenges and offer insights into future directions in this rapidly evolving field.

Type-printable photodetector arrays for multichannel meta-infrared imaging

Multichannel meta-imaging, inspired by the parallel-processing capability of neuromorphic computing, offers considerable advancements in resolution enhancement and edge discrimination in imaging systems, extending even into the mid- to far-infrared spectrum. Currently typical multichannel infrared imaging systems consist of separating optical gratings or merging multi-cameras, which require complex circuit design and heavy power consumption, hindering the implementation of advanced human-eye-like imagers. Here, we present printable graphene plasmonic photodetector arrays driven by a ferroelectric superdomain for multichannel meta-infrared imaging with enhanced edge discrimination. The fabricated photodetectors exhibited multiple spectral responses with zero-bias operation by directly rescaling the ferroelectric superdomain instead of reconstructing the separated gratings. We also demonstrated enhanced and faster shape classification (98.1%) and edge detection (98.2%) using our multichannel infrared images compared with single-channel detectors. Our proof-of-concept photodetector arrays simplify multichannel infrared imaging systems and offer potential solutions in efficient edge detection in human-brain-type machine vision.

Design and simulation of a high performance Ag3CuS2 jalpaite-based photodetector

This work provides a comprehensive investigation by using simulations and performance analysis of a high performance and narrowband Ag3CuS2 photodetector (PD) that operates in the near-infrared (NIR) region and is built using WS2 and BaSi2 semiconductors. Across its operational wavelength range, a comprehensive assessment of the device's electrical and optical properties such as photocurrent, open-circuit voltage, quantum efficiency, responsivity and detectivity is methodically carried out. Furthermore, a thorough investigation has been conducted into the impact of many parameters, including width, carrier density and defects of various layers. Also, the intricate interactions between WS2/Ag3CuS2 and Ag3CuS2/BaSi2 interface properties of the photodetector are explored. The Ag3CuS2-based PD remarkably produces the best outcomes with an open-circuit voltage of 0.74 V, current of 43.79 mA/cm2, responsivity of 0.79 AW-1 and detectivity of 4.73 × 1014 Jones and over 90 % QE in the NIR range for the Ag3CuS2 PD. The results showcase this jalpaite material as a promising one in the field of PD.

High-speed carbon nanotube photodetector based on a planarized silicon waveguide

The integration of silicon waveguides with low-dimensional materials with excellent optoelectronic properties can enable compact and highly integrated optical devices with multiple advantages for multiple fields. A carbon nanotube (CNT) photodetector integrated on the silicon waveguide has the potential to meet on-chip high-speed optical interconnection systems, based on the outstanding properties of CNTs such as picosecond-level intrinsic photoresponse time, high charge carrier mobility, broad spectral response, high absorption coefficient, and so on. However, the thermal stability of the device may be compromised due to the local suspension in the channel for the height difference between the WG and the substrate. Here, we report a low-cost and low-optical-loss method to achieve the planarized silicon waveguide. After that, the CNT photodetectors integrated on the original and planarized waveguide with asymmetric palladium (Pd)-hafnium (Hf) metal contacts are fabricated. The influence of this planarization method on the performance of devices is analyzed via comparing the dark leakage current, the leakage current rectification ratio (CRR), the series resistances (R S), and the photoelectric response. Finally, a CNT photodetector based on the planarized waveguide with a photocurrent (I p h ) ∼510.84n A, a photoresponsivity (R I) ∼51.04m A/W, the dark current ∼0.389µA, as well as a 3 dB bandwidth ∼34G H z at the large reverse voltage -3V is shown.

Spatially selective p-type doping for constructing lateral WS2 p-n homojunction via low-energy nitrogen ion implantation

The construction of lateral p-n junctions is very important and challenging in two-dimensional (2D) semiconductor manufacturing process. Previous researches have demonstrated that vertical p-n junction can be prepared simply by vertical stacking of 2D materials. However, interface pollution and large area scalability are challenges that are difficult to overcome with vertical stacking technology. Constructing 2D lateral p-n homojunction is an effective strategy to address these issues. Spatially selective p-type doping of 2D semiconductors is expected to construct lateral p-n homojunction. In this work, we have developed a low-energy ion implantation system that reduces the implanted energy to 300 eV. Low-energy implantation can form a shallow implantation depth, which is more suitable for modulating the electrical and optical properties of 2D materials. Hence, we utilize low-energy ion implantation to directly dope nitrogen ions into few-layer WS2 and successfully realize a precise regulation for WS2 with its conductivity type transforming from n-type to bipolar or even p-type conduction. Furthermore, the universality of this method is demonstrated by extending it to other 2D semiconductors, including WSe2, SnS2 and MoS2. Based on this method, a lateral WS2 p-n homojunction is fabricated, which exhibits significant rectification characteristics. A photodetector based on p-n junction with photovoltaic effect is also prepared, and the open circuit voltage can reach to 0.39 V. This work provides an effective way for controllable doping of 2D semiconductors.

Magnetic transverse unidirectional scattering and longitudinal displacement sensing in silicon nanodimer

Unidirectional scattering, crucial for manipulating light at the nanoscale, has wide-ranging applications from optical manipulation to sensing. While traditionally achieved through interactions between electric multipoles or between electric and magnetic multipoles, reports on unidirectional scattering driven purely by magnetic multipoles are limited. In this study, we undertake a theoretical exploration of transverse unidirectional scattering induced by magnetic multipoles, employing tightly focused azimuthally polarized beams (APBs) in interaction with a silicon nanodimer comprising two non-concentric nanorings. Through numerical simulations and theoretical analysis, we validate the transverse unidirectional scattering, predominantly governed by magnetic dipolar and quadrupolar resonances. Moreover, the directionality of this unidirectional scattering shows a strong correlation with the longitudinal displacement of the nanodimer within a specific range, showcasing its potential for longitudinal displacement sensing. Our study advances optical scattering control in nanostructures and guides the design of on-chip longitudinal displacement sensors.

Customizable Organic Charge-Transfer Cocrystals for the Dual-Mode Optoelectronics in the NIR (II) Window

Organic molecules have been regarded as ideal candidates for near-infrared (NIR) optoelectronic active materials due to their customizability and ease of large-scale production. However, constrained by the intricate molecular design and severe energy gap law, the realization of optoelectronic devices in the second near-infrared (NIR (II)) region with required narrow band gaps presents more challenges. Herein, we have originally proposed a cocrystal strategy that utilizes intermolecular charge-transfer interaction to drive the redshift of absorption and emission spectra of a series BFXTQ (X = 0, 1, 2, 4) cocrystals, resulting in the spectra located at NIR (II) window and reducing the optical bandgap to ∼0.98 eV. Significantly, these BFXTQ-based optoelectronic devices can exhibit dual-mode optoelectronic characteristics. An investigation of a series of BFXTQ-based photodetectors exhibits detectivity (D*) surpassing 1013 Jones at 375 to 1064 nm with a maximum of 1.76 × 1014 Jones at 1064 nm. Moreover, the radiative transition of CT excitons within the cocrystals triggers NIR emission over 1000 nm with a photoluminescence quantum yield (PLQY) of ∼4.6% as well as optical waveguide behavior with a low optical-loss coefficient of 0.0097 dB/μm at 950 nm. These results promote the advancement of an emerging cocrystal approach in micro/nanoscale NIR multifunctional optoelectronics.

High-Performance Visible to Mid-Infrared Photodetectors Based on HgTe Colloidal Quantum Dots under Room Temperature

HgTe colloidal quantum dots (CQDs) are one of few materials that can realize near-to-midwave infrared photodetection. And the quality of HgTe CQD directly affects the performance of photodetection. In this work, we optimize the method of synthesizing HgTe CQDs to reduce the defect concentration, therefore improving the photoelectric properties. The photodetector based on HeTe CQD can respond to the light from the visible to mid-infrared band. Notably, a photoresponse to 4000 nm light at room temperature is realized. The responsivity and detectivity are 90.6 mA W-1 and 6.9 × 107 Jones under 1550 nm light illumination, which are better than these of most reported HgTe CQD photodetectors. The response speed reaches a magnitude of microseconds with a rising time of τr = 1.9 μs and a falling time of τf = 1.5 μs at 10 kHz under 1550 nm light illumination.

Technology and Integration Roadmap for Optoelectronic Memristor

Optoelectronic memristors (OMs) have emerged as a promising optoelectronic Neuromorphic computing paradigm, opening up new opportunities for neurosynaptic devices and optoelectronic systems. These OMs possess a range of desirable features including minimal crosstalk, high bandwidth, low power consumption, zero latency, and the ability to replicate crucial neurological functions such as vision and optical memory. By incorporating large-scale parallel synaptic structures, OMs are anticipated to greatly enhance high-performance and low-power in-memory computing, effectively overcoming the limitations of the von Neumann bottleneck. However, progress in this field necessitates a comprehensive understanding of suitable structures and techniques for integrating low-dimensional materials into optoelectronic integrated circuit platforms. This review aims to offer a comprehensive overview of the fundamental performance, mechanisms, design of structures, applications, and integration roadmap of optoelectronic synaptic memristors. By establishing connections between materials, multilayer optoelectronic memristor units, and monolithic optoelectronic integrated circuits, this review seeks to provide insights into emerging technologies and future prospects that are expected to drive innovation and widespread adoption in the near future.

Locally Strained 2D Materials: Preparation, Properties, and Applications

2D materials are promising for strain engineering due to their atomic thickness and exceptional mechanical properties. In particular, non-uniform and localized strain can be induced in 2D materials by generating out-of-plane deformations, resulting in novel phenomena and properties, as witnessed in recent years. Therefore, the locally strained 2D materials are of great value for both fundamental studies and practical applications. This review discusses techniques for introducing local strains to 2D materials, and their feasibility, advantages, and challenges. Then, the unique effects and properties that arise from local strain are explored. The representative applications based on locally strained 2D materials are illustrated, including memristor, single photon emitter, and photodetector. Finally, concluding remarks on the challenges and opportunities in the emerging field of locally strained 2D materials are provided.

Top-Emitting Quantum Dot Light-Emitting Diodes: Theory, Optimization, and Application

The superior optical properties of colloidal quantum dots (QDs) have garnered significant broad interest from academia and industry owing to their successful application in self-emitting QD-based light-emitting diodes (QLEDs). In particular, active research is being conducted on QLEDs with top-emission device architectures (TQLEDs) owing to their advantages such as easy integration with conventional backplanes, high color purity, and excellent light extraction. However, due to the complicated optical phenomena and their highly sensitive optoelectrical properties to experimental variations, TQLEDs cannot be optimized easily for practical use. This review summarizes previous studies that have investigated top-emitting device structures and discusses ways to advance the performance of TQLEDs. First, theories relevant to the optoelectrical properties of TQLEDs are introduced. Second, advancements in device optimization are presented, where the underlying theories for each are considered. Finally, multilateral strategies for TQLEDs to enable their wider application to advanced industries are discussed. This work believes that this review can provide valuable insights for realizing commercial TQLEDs applicable to a broad range of applications.

2D Materials in Flexible Electronics: Recent Advances and Future Prospectives

Flexible electronics have recently gained considerable attention due to their potential to provide new and innovative solutions to a wide range of challenges in various electronic fields. These electronics require specific material properties and performance because they need to be integrated into a variety of surfaces or folded and rolled for newly formatted electronics. Two-dimensional (2D) materials have emerged as promising candidates for flexible electronics due to their unique mechanical, electrical, and optical properties, as well as their compatibility with other materials, enabling the creation of various flexible electronic devices. This article provides a comprehensive review of the progress made in developing flexible electronic devices using 2D materials. In addition, it highlights the key aspects of materials, scalable material production, and device fabrication processes for flexible applications, along with important examples of demonstrations that achieved breakthroughs in various flexible and wearable electronic applications. Finally, we discuss the opportunities, current challenges, potential solutions, and future investigative directions about this field.

Room-Temperature Plasmon-Assisted Resonant THz Detection in Single-Layer Graphene Transistors

Frequency-selective or even frequency-tunable terahertz (THz) photodevices are critical components for many technological applications that require nanoscale manipulation, control, and confinement of light. Within this context, gate-tunable phototransistors based on plasmonic resonances are often regarded as the most promising devices for the frequency-selective detection of THz radiation. The exploitation of constructive interference of plasma waves in such detectors promises not only frequency selectivity but also a pronounced sensitivity enhancement at target frequencies. However, clear signatures of plasmon-assisted resonances in THz detectors have been revealed only at cryogenic temperatures so far and remain unobserved at application-relevant room-temperature conditions. In this work, we demonstrate the sought-after room-temperature resonant detection of THz radiation in short-channel gated photodetectors made from high-quality single-layer graphene. The survival of this intriguing resonant regime at room temperature ultimately relies on the weak intrinsic electron-phonon scattering in monolayer graphene, which avoids the damping of the plasma oscillations present in the device channel.

Ferroelectricity-Driven Self-Powered Weak Temperature and Broadband Light Detection in MoS2/CuInP2S6/WSe2 van der Waals Heterojunction Nanoarchitectonics

Two-dimensional ferroelectric materials enrich the modulation degrees of freedom in self-powered van der Waals temperature/light detectors by incorporating pyroelectric and bulk photovoltaic effects. However, in addition to the low polarization, the practical applications of these materials are limited due to the significant challenge posed by their ultrathin nature, which affects their polarization stability. In this report, we introduce a design for a dual heterostructure-stabilized van der Waals heterojunction that addresses this challenge by improving the performance and extending the operational lifetime of self-powered van der Waals temperature/light detectors. The design is demonstrated using the MoS2/CuInP2S6 (CIPS)/WSe2 van der Waals heterojunction, which exhibits sensitivity to small temperature changes induced by weak light across the ultraviolet to mid-infrared spectrum. It can generate a noticeable pyroelectric current without the need for an external voltage, and its pyroelectric coefficient exceeds 130 and 978 μC/m2 K for 45 and 70 nm CIPS, respectively. The heterojunction offers high detection accuracy, with a temperature variation sensitivity as small as 0.1 K and an optical power intensity detection range from low to 1 μW/cm2. Additionally, the heterojunction exhibits exceptional detectivity (D*) for different light wavelengths. Remarkably, the self-powered detection performance remains stable for months without obvious degradation in the natural environment. These results offer a promising solution for high-performance, self-sustaining temperature/light detection applications and pave the way for the development of future ferroelectricity-driven photodetection technologies.

Optical Enhancement of Indirect Bandgap 2D Transition Metal Dichalcogenides for Multi-Functional Optoelectronic Sensors

The unique electrical and optical properties of transition metal dichalcogenides (TMDs) make them attractive nanomaterials for optoelectronic applications, especially optical sensors. However, the optical characteristics of these materials are dependent on the number of layers. Monolayer TMDs have a direct bandgap that provides higher photoresponsivity compared to multilayer TMDs with an indirect bandgap. Nevertheless, multilayer TMDs are more appropriate for various photodetection applications due to their high carrier density, broad spectral response from UV to near-infrared, and ease of large-scale synthesis. Therefore, this review focuses on the modification of the optical properties of devices based on indirect bandgap TMDs and their emerging applications. Several successful developments in optical devices are examined, including band structure engineering, device structure optimization, and heterostructures. Furthermore, it introduces cutting-edge techniques and future directions for optoelectronic devices based on multilayer TMDs.

Broadband high-performance vertical WS1.08Se0.92/Si heterojunction photodetector with MXene electrode

Vertical semiconductor van der Waals heterojunctions are essential for fabricating high-performance photodetectors. However, the range of the spectral response and defect states of semiconductor materials are two critical factors affecting the performance of photodetectors. In this work, the spectral response range of WS2was changed through WS2band gap regulation, and a self-powered vertical WS1.08Se0.92/Si heterojunction photodetector with MXene electrode was prepared by synthesizing WS1.08Se0.92film on Si substrate and vertically stacking Ti3C2TxMXene on the film. Due to the electron collection of MXene and the wonderful junction quality of WS1.08Se0.92/Si, the photodetector can detect near-infrared light in the range of 980-1310 nm, which exceed the detection limit of WS1.08Se0.92. And the device had high sensitivity in the broadband. The responsivity was 4.58 A W-1, the specific detectivity was 4.58 × 1011Jones, the on/off ratio was 4.95 × 103, and the fast response time was 9.81/9.03μs. These properties are superior to previously reported WS2-based photodetectors. Vertical structure, Energy band tuning, and MXene electrode provide a new idea for preparing broadband high-performance and self-powered photodetector.

Aqueous-Phase Formation of Two-Dimensional PbI2 Nanoplates for High-Performance Self-Powered Photodetectors

The process of the aqueous synthesis of nanomaterials has gained considerable interest due to its ability to eliminate the need for complex organic solvents, which aligns with the principles of green chemistry. Fabricating nanostructures in aqueous solutions has gained recognition for its potential to develop ultrasensitive, low-energy, and ultrafast optoelectronic devices. This study focuses on synthesizing lead iodide (PbI2) nanoplates (NPs) using a water-based solution technique and fabricating a planar photodetector. The planar photodetectors (ITO/PbI2 NPs/Au) demonstrated a remarkable photosensitivity of 3.9 × 103 and photoresponsivity of 0.51 mA/W at a wavelength of 405 nm. Further, we have carried-out analytical calculations for key performance parameters including open-circuit voltage (Voc), short-circuit current (Isc), on-off ratio, responsivity (R), and specific detectivity (D*) at zero applied bias, while photodetector operating in self-powered mode. These values are as follows: Voc = 0.103 V, Isc = 1.93 × 10-8, on-off ratio = 103, R = 4.0 mA/W, and D* = 3.3 × 1011 Jones. Particularly, the asymmetrical output properties of ITO/PbI2 NPs/Au detector provided additional evidence of the effective creation of a Schottky contact. Therefore, the photodetector exhibited a photo-response even at 0 V bias (rise/decay time ~1 s), leading to the realization of self-powered photodetectors. Additionally, the device exhibited a rapid photo-response of 0.23/0.38 s (-5 V) in the visible range. This study expands the scope of aqueous-phase synthesis of PbI2 nanostructures, enabling the large-area fabrication of high-performance photodetectors.

High-Responsivity and Broadband MoS2 Photodetector Using Interfacial Engineering

Combining MoS2 with mature silicon technology is an effective method for preparing high-performance photodetectors. However, the previously studied MoS2/silicon-based heterojunction photodetectors cannot simultaneously demonstrate high responsivity, a fast response time, and broad spectral detection. We constructed a broad spectral n-type MoS2/p-type silicon-based heterojunction photodetector. The SiO2 dielectric layer on the silicon substrate was pretreated with soft plasma to change its thickness and surface state. The pretreated SiO2 dielectric layer and the silicon substrate constitute a multilayer heterostructure with a high carrier concentration and responsiveness. Taking silicon-based and n-type MoS2 heterojunction photodetectors as examples, its responsivity can reach 4.05 × 104 A W1- at 637 nm wavelength with a power density of 2 μW mm-2, and the detectable spectral range is measured from 447 to 1600 nm. This pretreated substrate was proven applicable to other n-type TMDCs, such as MoTe2, ReS2, etc., with certain versatility.

PbS QD-Coated Si Micro-Hole Array/Graphene vdW Schottky Near-Infrared Photodiode for PPG Heart Rate Measurement

Near-infrared (NIR) photodetectors (PDs) have attracted much attention for use in noninvasive medical diagnosis and treatments. In particular, self-filtered NIR PDs are in high demand for a wide range of biomedical applications due to their ability for wavelength discrimination. In this work, we designed and then fabricated a Si micro-hole array/Graphene (Si MHA/Gr) van der Waals (vdW) Schottky NIR photodiode using a PbS quantum dot (QD) coating. The device exhibited a unique self-filtered NIR response with a responsivity of 0.7 A/W at -1 V and a response speed of 61 μs, which is higher than that seen without PbS QD coating and even in most previous Si/Gr Schottky photodiodes. The light trapping of the Si MHA and the PbS QD coating could be attributed to the high responsivity of the vdW photodiode. Furthermore, the presented NIR photodiode could also be integrated in photoplethysmography (PPG) for real-time heart rate (HR) monitoring. The extracted HR was in good accord with the values measured with the patient monitor-determined by analyzing the Fourier transform of the stable and reliable fingertip PPG waveform-suggesting its potential for practical applications.

Metamaterial graphene photodetector with bandwidth exceeding 500 gigahertz

Although graphene has met many of its initially predicted optoelectronic, thermal, and mechanical properties, photodetectors with large spectral bandwidths and extremely high frequency responses remain outstanding. In this work, we demonstrate a >500 gigahertz, flat-frequency response, graphene-based photodetector that operates under ambient conditions across a 200-nanometer-wide spectral band with center wavelengths adaptable from <1400 to >4200 nanometers. Our detector combines graphene with metamaterial perfect absorbers with direct illumination from a single-mode fiber, which breaks with the conventional miniaturization of photodetectors on an integrated photonic platform. This design allows for much higher optical powers while still allowing record-high bandwidths and data rates. Our results demonstrate that graphene photodetectors can outperform conventional technologies in terms of speed, bandwidth, and operation across a large spectral range.

Perovskite sensitized 2D photodiodes

A new type of perovskite sensitized programmable WSe₂ photodiode is constructed based on MAPbI₃/WSe₂ heterojunction, presenting flexible reconfigurable characteristics and prominent optoelectronic performances.

Integrated Graphene Heterostructures in Optical Sensing

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

Broadband transverse unidirectional scattering and large range nanoscale displacement measuring based on the interaction between a tightly focused azimuthally polarized beam and a silicon hollow nanostructure

We theoretically propose a broadband transverse unidirectional scattering scheme based on the interaction between a tightly focused azimuthally polarized beam (APB) and a silicon hollow nanostructure. When the nanostructure is located at a specific position in the focal plane of the APB, the transverse scattering fields can be decomposed into contributions from transverse components of the electric dipoles, longitudinal components of magnetic dipoles and magnetic quadrupole components. In order to satisfy the transverse Kerker conditions for these multipoles within a wide infrared spectrum, we design a novel nanostructure with hollow parallelepiped shape. Through numerical simulations and theoretical calculations, this scheme exhibits efficient transverse unidirectional scattering effects in the wavelength range of 1440 nm to 1820 nm (380 nm). In addition, by adjusting the position of the nanostructure on the x-axis, efficient nanoscale displacement sensing with large measuring ranges can be achieved. After analyses, the results prove that our research may have potential applications in the field of high-precision on-chip displacement sensors.

The Adsorption Effect of Methane Gas Molecules on Monolayer PbSe with and without Vacancy Defects: A First-Principles Study

In this paper, the adsorption effect of methane (CH₄) gas molecular on monolayer PbSe with and without vacancy defects is studied based on first-principles calculations. The effects of the adsorption of methane molecular on monolayer PbSe and on the Se vacancy (V_Se) and Pb vacancy (V_Pb) of monolayer PbSe are also explored. Our results show that methane molecules exhibit a good physical adsorption effect on monolayer PbSe with and without vacancy defects. Moreover, our simulations indicate that the adsorption capacity of CH₄ molecules on monolayer PbSe can be enhanced by applying strain. However, for the monolayer PbSe with Vse, the adsorption capacity of CH₄ molecules on the strained system decreases sharply. This indicates that applying strain can promote the dissociation of CH₄ from V_Se. Our results show that the strain can be used as an effective means to regulate the interaction between the substrate material and the methane gas molecules.

Applications of remote epitaxy and van der Waals epitaxy

Epitaxy technology produces high-quality material building blocks that underpin various fields of applications. However, fundamental limitations exist for conventional epitaxy, such as the lattice matching constraints that have greatly narrowed down the choices of available epitaxial material combinations. Recent emerging epitaxy techniques such as remote and van der Waals epitaxy have shown exciting perspectives to overcome these limitations and provide freestanding nanomembranes for massive novel applications. Here, we review the mechanism and fundamentals for van der Waals and remote epitaxy to produce freestanding nanomembranes. Key benefits that are exclusive to these two growth strategies are comprehensively summarized. A number of original applications have also been discussed, highlighting the advantages of these freestanding films-based designs. Finally, we discuss the current limitations with possible solutions and potential future directions towards nanomembranes-based advanced heterogeneous integration.

Fast-Response Micro-Phototransistor Based on MoS2/Organic Molecule Heterojunction

Over the past years, molybdenum disulfide (MoS₂) has been the most extensively studied two-dimensional (2D) semiconductormaterial. With unique electrical and optical properties, 2DMoS₂ is considered to be a promising candidate for future nanoscale electronic and optoelectronic devices. However, charge trapping leads to a persistent photoconductance (PPC), hindering its use for optoelectronic applications. To overcome these drawbacks and improve the optoelectronic performance, organic semiconductors (OSCs) are selected to passivate surface defects, tune the optical characteristics, and modify the doping polarity of 2D MoS₂. Here, we demonstrate a fast photoresponse in multilayer (ML) MoS₂ by addressing a heterojunction interface with vanadylphthalocyanine (VOPc) molecules. The MoS₂/VOPc van der Waals interaction that has been established encourages the PPC effect in MoS₂ by rapidly segregating photo-generated holes, which move away from the traps of MoS₂ toward the VOPc molecules. The MoS₂/VOPc phototransistor exhibits a fast photo response of less than 15 ms for decay and rise, which is enhanced by 3ordersof magnitude in comparison to that of a pristine MoS₂-based phototransistor (seconds to tens of seconds). This work offers a means to realize high-performance transition metal dichalcogenide (TMD)-based photodetection with a fast response speed.

Silicon Waveguide-Integrated Carbon Nanotube Photodetector with Low Dark Current and 48 GHz Bandwidth

Low-dimensional materials with excellent optoelectronic properties and complementary metal-oxide-semiconductor (CMOS) process compatibility have the potential to construct high-performance photodetectors used in a cost-efficient monolithic or hybrid integrated optical communication system. Carbon nanotubes (CNTs) have attracted a lot of attention due to special geometric structure and broad band response, high optical absorption coefficient, ps-level intrinsic light response, high carrier mobility and wafer-scaled production process. Here, we demonstrated a high-performance waveguide-integrated CNT photodetector with asymmetric palladium (Pd) and hafnium (Hf) contact electrodes. The ideal photodetector structure was realized via comparing with simulation and experimental results, where the optimized device achieved a high 3 dB bandwidth ∼48 GHz at 0 V, as well as a responsivity ∼73.62 mA/W and dark current ∼0.157 μA at -2 V bias voltage. This waveguide-integrated CNT photodetector with low dark current and high bandwidth is helpful for next-generation optical communication and high-speed optical interconnects.

Ferroelectrically Modulated and Enhanced Photoresponse in a Self-Powered α-In2Se3/Si Heterojunction Photodetector

Photodetectors have been applied to pivotal optoelectronic components of modern optical communication, sensing, and imaging systems. As a room-temperature ferroelectric van der Waals semiconductor, 2D α-In₂Se₃ is a promising candidate for a next-generation optoelectronic material because of its thickness-dependent direct bandgap and excellent optoelectronic performance. Previous studies of photodetectors based on α-In₂Se₃ have been rarely focused on the modulated relationship between the α-In₂Se₃ intrinsic ferroelectricity and photoresponsivity. Herein, a simple integrated process and high-performance photodetector based on an α-In₂Se₃/Si vertical hybrid-dimensional heterojunction was constructed. Our photodetector in the ferroelectric polarization up state accomplishes a self-powered, highly sensitive photoresponse with an on/off ratio of 4.5 × 10⁵ and detectivity of 1.6 × 10¹³ Jones, and it also shows a fast response time with 43 μs. The depolarization field generated by the remanent polarization of ferroelectrics in α-In₂Se₃ provides a strategy for enhancement and modulation of photodetection. The negative correlation was discovered because the enhancement photoresponsivity factor of ferroelectric modulation competes with the photovoltaic behavior within the α-In₂Se₃/Si heterojunction. Our research highlights the great potential of the high-efficiency heterojunction photodetector for future object recognition and photoelectric imaging.

A two-dimensional mid-infrared optoelectronic retina enabling simultaneous perception and encoding

Infrared machine vision system for object perception and recognition is becoming increasingly important in the Internet of Things era. However, the current system suffers from bulkiness and inefficiency as compared to the human retina with the intelligent and compact neural architecture. Here, we present a retina-inspired mid-infrared (MIR) optoelectronic device based on a two-dimensional (2D) heterostructure for simultaneous data perception and encoding. A single device can perceive the illumination intensity of a MIR stimulus signal, while encoding the intensity into a spike train based on a rate encoding algorithm for subsequent neuromorphic computing with the assistance of an all-optical excitation mechanism, a stochastic near-infrared (NIR) sampling terminal. The device features wide dynamic working range, high encoding precision, and flexible adaption ability to the MIR intensity. Moreover, an inference accuracy more than 96% to MIR MNIST data set encoded by the device is achieved using a trained spiking neural network (SNN).

Sensitive photodetection below silicon bandgap using quinoid-capped organic semiconductors

High-sensitivity organic photodetectors (OPDs) with strong near-infrared (NIR) photoresponse have attracted enormous attention due to potential applications in emerging technologies. However, few organic semiconductors have been reported with photoelectric response beyond ~1.1 μm, the detection limit of silicon detectors. Here, we extend the absorption of organic small-molecule semiconductors to below silicon bandgap, and even to 0.77 eV, through introducing the newly designed quinoid-terminals with high Mulliken-electronegativity (5.62 eV). The fabricated photodiode-type NIR OPDs exhibit detectivity (D^*) over 10¹² Jones in 0.41 to 1.2 μm under zero bias with a maximum of 2.9 × 10¹² Jones at 1.02 μm, which is the highest D^* for reported OPDs in photovoltaic-mode with response spectra beyond 1.1 μm. The high D^* in 0.9 to 1.2 μm is comparable to those of commercial InGaAs photodetectors, despite the detection limit of our OPDs is shorter than InGaAs (~1.7 μm). A spectrometer prototype with a wide measurable region (0.4 to 1.25 μm) and NIR imaging under 1.2-μm illumination are demonstrated successfully in OPDs.

Infrared Photodetection from 2D/3D van der Waals Heterostructures

An infrared photodetector is a critical component that detects, identifies, and tracks complex targets in a detection system. Infrared photodetectors based on 3D bulk materials are widely applied in national defense, military, communications, and astronomy fields. The complex application environment requires higher performance and multi-dimensional capability. The emergence of 2D materials has brought new possibilities to develop next-generation infrared detectors. However, the inherent thickness limitations and the immature preparation of 2D materials still lead to low quantum efficiency and slow response speeds. This review summarizes 2D/3D hybrid van der Waals heterojunctions for infrared photodetection. First, the physical properties of 2D and 3D materials related to detection capability, including thickness, band gap, absorption band, quantum efficiency, and carrier mobility, are summarized. Then, the primary research progress of 2D/3D infrared detectors is reviewed from performance improvement (broadband, high-responsivity, fast response) and new functional devices (two-color detectors, polarization detectors). Importantly, combining low-doped 3D and flexible 2D materials can effectively improve the responsivity and detection speed due to a significant depletion region width. Furthermore, combining the anisotropic 2D lattice structure and high absorbance of 3D materials provides a new strategy in high-performance polarization detectors. This paper offers prospects for developing 2D/3D high-performance infrared detection technology.

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

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

Narrow-bandgap Sn-Pb mixed perovskite single crystals for high-performance near-infrared photodetectors

Narrow-bandgap Sn-Pb mixed perovskite single crystals are highly promising as photoactive materials for efficient and low-cost near-infrared (NIR) photodetectors. However, because of the significant difference in the crystallization velocities for Pb- and Sn-based perovskites, Sn-Pb mixed perovskites are peculiarly prone to phase separation during the crystallization process, causing the degradation of the optical and electronic properties of materials. Herein, we propose a low-temperature space-confined technique (LT-SCT) that simultaneously reduces the crystallization velocities of pure Sn and Pb perovskites, enabling the fabrication of pure-phase (FASnI₃)_0.1(MAPbI₃)_0.9 single crystals. The resulting (FASnI₃)_0.1(MAPbI₃)_0.9 single crystals exhibit excellent crystallinity with a high hole mobility of 7.44 × 10³ cm² V^-1 s^-1 and a low surface trap density of 1.88 × 10⁹ cm^-2. These properties benefit the application of (FASnI₃)_0.1(MAPbI₃)_0.9 single crystals in self-powered NIR photodetectors and yield outstanding comprehensive performance, especially with a broad linear dynamic range of up to 163.5 dB, a large responsivity (R) of 0.53 A W^-1, and a fast response speed of 22.78 μs in the NIR spectral region (750-860 nm). Furthermore, high-quality NIR imaging and wearable health monitoring are achieved by employing high-performance and self-driven NIR photodetectors. This work contributes to developing Sn-Pb mixed perovskite single crystals and provides a promising candidate for efficient and low-cost NIR photodetection.

Near-infrared polarization-sensitive photodetection via interfacial symmetry engineering of an Si/MAPbI3 heterostructural single crystal

Methylammonium lead iodide (MAPbI₃) single crystals (SCs) have drawn particular attention in the optoelectronics field, due to their outstanding photoelectric performance. However, the structures of those MAPbI₃ SCs are isotropic, which limits the further application of the materials for polarization-sensitive photodetection. Here, we propose a strategy of symmetry modulation by heterogeneously integrating large-sized MAPbI₃ SCs with silicon (Si) wafers and we give the first demonstration of self-powered near-infrared (NIR) polarization-sensitive photodetection using MAPbI₃ SCs. Created via a delicate solution method, the MAPbI₃/Si heterostructures show a high crystalline quality and a solid interfacial connection. More importantly, the built-in electric field resulting from the band bending at the MAPbI₃/Si heterostructure interface generates polar symmetry, which enables directional transport of photogenerated carriers, making the MAPbI₃/Si heterostructures highly polarization-sensitive. Consequently, in the self-powered mode, NIR photodetectors of MAPbI₃/Si heterostructures exhibit large polarization ratios of 3.3 at 785 nm and 2.8 at 940 nm. Moreover, a high detectivity of 7.35 × 10¹² Jones of the present devices is also achieved. Our work gives the first demonstration of self-powered polarization-sensitive photodetection of MAPbI₃ SCs and provides a strategy to design polarization-sensitive materials beyond the conventional limitations induced by isotropic structures.

Photodetection Enhancement via Graphene Oxide Deposition on Poly 3-Methyl Aniline

A graphene oxide (GO)/poly 3-methyl aniline (P3MA) photodetector has been developed for light detection in a broad optical region: UV, Vis, and IR. The 3-methyl aniline was initially synthesized via radical polymerization using an acid medium, i.e., K₂S₂O₈ oxidant. Consequently, the GO/P3MA composite was obtained through the adsorption of GO into the surface of P3MA. The chemical structure and optical properties of the prepared materials have been illustrated via XRD, FTIR, SEM, and TEM analysis. The absorbance measurements demonstrate good optical properties in the UV, Vis, and near-IR regions, although a decrease in the bandgap from 2.4 to 1.6 eV after the composite formation was located. The current density (J_ph) varies between 0.29 and 0.68 mA·cm^-2 (at 2.0 V) under dark and light, respectively. The photodetector has been tested using on/off chopped light at a low potential, in which the produced J_ph values decrease from 0.14 to 0.04 µA·cm^-2, respectively. The GO/P3MA photodetector exhibits excellent R (and D) values of 4 and 2.7 mA·W^-1 (0.90 × 10⁹ and 0.60 × 10⁹ Jones) in the UV (340 nm) and IR (730 nm) regions, respectively. The R and D values obtained here make the prepared photodetector a promising candidate for future light detection instruments.

All-silicon microring avalanche photodiodes with a >65 A/W response

We report an all-Si microring (MRR) avalanche photodiode (APD) with an ultrahigh responsivity (R) of 65 A/W, dark current of 6.5 µA, and record gain-bandwidth product (GBP) of 798 GHz at -7.36 V. The mechanisms for the high responsivity have been modelled and investigated. Furthermore, open eye diagrams up to 20 Gb/s are supported at 1310 nm at -7.36 V. The device is the first, to the best of our knowledge, low cost all-Si APD that has potential to compete with current commercial Ge- and III-V-based photodetectors (PDs). This shows the potential to make the all-Si APD a standard "black-box" component in Si photonics CMOS foundry platform component libraries.

Mid-infrared single-pixel imaging at the single-photon level

Single-pixel cameras have recently emerged as promising alternatives to multi-pixel sensors due to reduced costs and superior durability, which are particularly attractive for mid-infrared (MIR) imaging pertinent to applications including industry inspection and biomedical diagnosis. To date, MIR single-pixel photon-sparse imaging has yet been realized, which urgently calls for high-sensitivity optical detectors and high-fidelity spatial modulators. Here, we demonstrate a MIR single-photon computational imaging with a single-element silicon detector. The underlying methodology relies on nonlinear structured detection, where encoded time-varying pump patterns are optically imprinted onto a MIR object image through sum-frequency generation. Simultaneously, the MIR radiation is spectrally translated into the visible region, thus permitting infrared single-photon upconversion detection. Then, the use of advanced algorithms of compressed sensing and deep learning allows us to reconstruct MIR images under sub-Nyquist sampling and photon-starving illumination. The presented paradigm of single-pixel upconversion imaging is featured with single-pixel simplicity, single-photon sensitivity, and room-temperature operation, which would establish a new path for sensitive imaging at longer infrared wavelengths or terahertz frequencies, where high-sensitivity photon counters and high-fidelity spatial modulators are typically hard to access.

Achieving High Responsivity and Detectivity in a Quantum-Dot-in-Perovskite Photodetector

This work reports on quantum dots (QDs) in perovskite photodetectors showing high optoelectronic performance via quantum-dot-assisted charge transmission. The self-powered broad-band photodetector constructed with SnS QDs in FAPb_0.5Sn_0.5I₃ perovskite can capture incoming optical signals directly at zero bias. The QDs-in-perovskite photodetector exhibits a high sensitivity in the wavelength range from 300 to 1000 nm. Its responsivity at 850 nm reaches 521.7 mA W^-1, and a high specific detectivity of 2.57 × 10¹² jones can be achieved, which is well beyond the level of previous self-powered broad-band photodetectors. The capability of quantum-dot-in-perovskite photodetectors as data receivers has been further demonstrated in a visible-light communication application.

Nanostructured doping of WSe2via block copolymer patterns and its self-powered photodetector application

Transition metal dichalcogenides (TMDs), e.g., MoS₂, MoSe₂, ReS₂, and WSe₂, are effective materials for advanced optoelectronics owing to their intriguing optical, structural, and electrical properties. Various approaches for manipulating the surface of the TMDs have been suggested to unleash the optoelectronic potential of the TMDs. Herein, we employed the self-assembly of the poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymer (BCP) to prepare a nanoporous pattern and generate nanostructured charge-transfer p-doping on the WSe₂ surface, maximizing the depletion region in the absorber layer. After the spin coating and thermal annealing of PS-b-PMMA, followed by the selective etching of PMMA cylindrical microdomains using oxygen reactive-ion plasma, nanopatterned WO_x with high electron affinity was grown on the WSe₂ surface, forming a three-dimensional homojunction. The nanopatterned WO_x significantly expanded the depletion region in the WSe₂ layer, thus enhancing optoelectronic performance and self-powered photodetection. The proposed approach based on the nanostructured doping of the TMDs via BCP nanolithography can help create a promising platform for highly functional optoelectrical devices.