Ultrasensitive Photodetectors Research Articles

Next-Generation Self-Powered Photodetectors using 2D Bismuth Oxide Selenide Crystals.

The concept of self-powered photodetectors has attracted significant attention due to their versatile applications in areas such as intelligent systems and hazardous substance detection. Among these, p-n junction and Schottky junction photodetectors are the most widely studied types; however, their fabrication processes are often complex and costly. To overcome these challenges, we focused on the emerging self-powered, ultrasensitive photodetector platform based on photoelectrochemical (PEC) principles. This platform leverages the unique properties of the emerging material bismuth oxide selenide (Bi2O2Se), which features a wide bandgap (∼2 eV) and a high absorption coefficient. We utilized chemical exfoliation to obtain thin layers of Bi2O2Se, enabling highly efficient photodetection. The device characterization demonstrated impressive performance metrics, including a responsivity of 97.1 μA W-1 and a specific detectivity of 2 × 108 cm Hz 1/2 W-1. The PEC photodetector also exhibits broad-spectrum sensitivity, from blue to infrared wavelengths, and features an ultrafast response time of ∼82 ms and a recovery time of ∼86 ms, highlighting its practical potential. Moreover, these self-powered photodetectors show excellent stability in electrochemical environments, positioning them promising candidates for integration into future high-efficiency devices.

An Ultrasensitive Bi2O2Se/In2S3 Photodetector with Low Detection Limit and Fast Response toward High-Precision Unmanned Driving.

The machine vision utilized in unmanned driving systems must possess the ability to accurately perceive scenes under low-light illumination conditions. To achieve this, photodetectors with low detection limits and a fast response are essential. Current systems rely on avalanche diodes or lidars, which come with the drawbacks of increased energy consumption and complexity. Here, we present an ultrasensitive photodetector based on a two-dimensional (2D) Bi2O2Se/In2S3 heterostructure, incorporating a homotype unilateral depletion band design. This innovative architecture effectively modulates the transport of both free and photoexcited carriers, suppressing the dark current and facilitating the rapid and efficient separation of photocarriers. Owing to these features, this device exhibits a responsivity of 144 A/W, a specific detectivity of 1.2 × 1014 Jones, and a light on/off ratio of 1.1 × 105. These metrics rank among the top values reported for state-of-the-art 2D devices. Moreover, this device also demonstrates a fast response time of 170/296 μs and a low noise equivalent power of 0.57 fW/Hz1/2, attributes that endow it with ultraweak light imaging capabilities. Furthermore, we have successfully integrated this device into an unmanned driving system, providing a perspective on the design and fabrication of future 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.

Polarizable Nonvolatile Ferroelectric Gating in Monolayer MoS2 Phototransistors.

Given the requirements for power and dimension scaling, modulating channel transport properties using high gate bias is unfavorable due to the introduction of severe leakages and large power dissipation. Hence, this work presents an ultrathin phototransistor with chemical-vapor-deposition-grown monolayer MoS2 as the channel and a 10.2 nm thick Al:HfO2 ferroelectric film as the dielectric. The proposed device is meticulously modulated utilizing an Al:HfO2 nanofilm, which passivates traps and suppresses charge Coulomb scattering with Al doping, efficiently improving carrier transport and inhibiting leakage current. Furthermore, a bipolar pulses excitable polarization method is developed to induce a nonvolatile electrostatic field. The MoS2 channel is fully depleted by the switchable and stable floating gate originating from remanent polarization, leading to a high detectivity of 2.05 × 1011 Jones per nanometer of gating layer (Jones nm-1) and photocurrent on/off ratio >104 nm-1, which are superior to the state-of-the-art phototransistors based on two-dimensional (2D) materials and ferroelectrics. The proposed polarizable nonvolatile ferroelectric gating in a monolayer MoS2 phototransistor promises a potential route toward ultrasensitive photodetectors with low power consumption that boast of high levels of integration.

Controlled Synthesis of a High‐Mobility Bi3O2.5Se2 Semiconductor by Oxidation of Bi2Se3 for Fast and Highly Sensitive Photodetectors

AbstractThe search of new high‐mobility two‐dimensional (2D) semiconductors is crucial for the development of next‐generation photodetectors, since current photodetectors based on single 2D semiconductors usually cannot simultaneously own ultrafast response rate and ultrahigh sensitivity. Here, using a facial method of sequentially oxidizing Bi2Se3 at optimal O content, a series of bismuth oxyselenide semiconductors (Bi3O2.5Se2, Bi2O2Se, Bi2SeO5) with appealing electronic applications are successfully synthesized. The crystal and band structures of a superlattice‐free Bi3O2.5Se2 phase are resolved by 3D electron diffraction and density functional theory calculations, showing a unique non‐neutral layered structure, moderate band gap, and small effective mass. More importantly, the concept of Bi2Se3 + O2 can be extended to synthesize the superlattice‐free Bi3O2.5Se2 ultrathin films by chemical vapor deposition, whose room‐temperature mobility can be as high as ≈150 cm2 V−1 s−1 based on Hall measurements. The ultrathin Bi3O2.5Se2 photodetectors with a simple device configuration simultaneously own ultrafast response time (≈31 µs), ultrahigh responsivity (≈8 × 104 A/W), and large detectivity (≈8 × 1013 Jones). This work not only introduces a facile way to regulate the phase in the bismuth oxyselenide family, but also provides an alternative candidate for ultrafast and ultrasensitive photodetectors.

Progress in the preparation of high-quality wafer-scale monolayer and multilayer MS2 (M = Mo; W) films by CVD

MS2 (M = Mo; W), with natural atomic thickness, are typical two-dimensional (2D) semiconductor materials, which have excellent electronic/optoelectronic properties and mechanical flexible properties. With the development of semiconductor device miniaturization, much attention has been brought to MS2, especially in large-scale integrated circuits, ultra-sensitive photodetectors, and flexible electronic devices. Here, we present the recent research progress on the controllable synthesis of high-quality, wafer-scale, uniform monolayer and multilayer MS2 films by chemical vapor deposition methods, focusing on the most concerning grain orientation control and defect modulation in whole wafer, besides the pursuit of more larger wafer size in MS2 films’ preparation. We also discuss some critical issues in the process of MS2 films growth and give a brief outlook in the controllable preparation of high-quality MS2 films for device application later on.

Two-dimensional vertical-lateral hybrid heterostructure for ultrasensitive photodetection and image sensing

Constructing heterostructures of two-dimensional (2D) materials is critical for boosting their photoelectric performances, enabling a promising route to meet the harsh requirement of next-generation optoelectronic devices. However, the practical application of currently-studied lateral and vertical heterostructures is usually limited by poor photocarrier generation and transport abilities, primarily due to their inherent imbalance of depletion region and interface area. To solve this obstacle, we herein report a novel 2D hybrid heterostructure of bismuth selenide/oxyselenide with the coexistence of lateral and vertical interfaces. The unique hybrid structure provides the heterostructure with a huge interface area and a wide depletion region for sufficient photocarrier generation and separation, significantly improving the overall optoelectronic performances of the device. Specifically, the resultant photodetectors exhibit a remarkably decreased dark current and ultrafast photoresponse rate (τrise = 50 μs and τdecay = 20 μs). Moreover, our photodetector demonstrates outstanding image sensing capability for recording various complex patterns with high resolution over a wide spectral range from ultraviolet, visible to near-infrared regions. Our research provides a highly promising route for designing and fabricating novel geometries of 2D heterostructures to realize diverse photoelectric applications.

Ultrasensitive photodetector based on 2D WS2/AgInGaS quantum dots heterojunction with interfacial charge transfer

Tungsten disulfide (WS2), as a typical member of transition metal chalcogenides (TMDs), has attracted extensive research interest in optoelectronics, especially photodetectors. However, the performance of photodetectors based on monolayer WS2 is restricted to weak light absorption. Here, AgInGaS quantum dots (AIGS-QDs) with a large absorption coefficient and high quantum efficiency are integrated onto WS2 atomic layers to achieve excellent photoelectric performance. Notably, the observed photoluminescence (PL) quenching and the reduction of the decay time of PL in the WS2/AIGS-QDs heterojunction confirm the interfacial charge transfer from AIGS-QDs to WS2 layer. The results show that type II energy band arrangement leads to the efficient separation of photoexcited carriers at the interface between WS2 and AIGS-QDs. This WS2/AIGS-QDs photodetector achieves an ultrahigh responsivity (R) of 3.3 × 103 A W−1, an external quantum efficiency (EQE) of 7.8 × 106% and a detectivity (D*) of 1.3 × 1013 Jones. Our work provides promising potential for future high-performance monolayer TMD-based photodetectors.

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.

Molybdenum Disulfide Nanoribbons with Enhanced Edge Nonlinear Response and Photoresponsivity.

MoS2 nanoribbons have attracted increased interest due to their properties, which can be tailored by tuning their dimensions. Herein, the growth of MoS2 nanoribbons and triangular crystals formed by the reaction between films of MoOx (2<x<3)grown by pulsed laser deposition and NaF in a sulfur-rich environment is demonstrated. The nanoribbons can reach up to 10µm in length, and feature single-layeredges, forming a monolayer-multilayer junction enabled by the lateral modulation in thickness. The single-layer edges show a pronounced second harmonic generation due to the symmetry breaking, in contrast to the centrosymmetric multilayer structure, which is unsusceptible to the second-order nonlinear process. A splitting of the Raman spectra is observed in MoS2 nanoribbons arising from distinct contributions from the single-layer edges and multilayer core. Nanoscale imaging reveals a blue-shifted exciton emission of the monolayer edge compared to the isolated MoS2 monolayers due to built-in local strain and disorder. Wefurther report on an ultrasensitive photodetector made of a single MoS2 nanoribbon with a responsivity of 8.72×102 AW-1 at 532nm, among the highest reported up-to-date for single-nanoribbon photodetectors. These findings can inspire the design of MoS2 semiconductors with tunable geometries for efficient optoelectronic devices.

Broad-spectrum and ultrasensitive photodetectors based on GeSe/SnS2 heterostructures with type-III band alignment

Two-dimensional (2D) van der Waals heterostructures (vdWHs) show great potential as building blocks for electronic and optoelectronic devices due to their unique band alignments at the contact interface, which can be tailored to achieve specific electronic and optical properties. The most studied 2D vdWHs have type-I and type-II band alignment, while for type-III band alignment vdWHs, carriers are transported through band-to-band tunneling, which have great potential for applications in low-power devices. Herein, we utilize the band structure alignment properties of GeSe and SnS2 to create GeSe/SnS2 vdWHs with type-III band alignment by all-dry transfer process. The GeSe/SnS2 vdWHs demonstrate an intriguing anti-ambipolar behavior attributed to their type-III alignment of electronic band structures. They also exhibit excellent photoresponse properties with broadband photoresponse from ultraviolet C (255 nm) to near-infrared (1920 nm), a competitive detectivity of 1.09 × 1010 Jones, a large responsivity of 50.7 A/W, and a response speed of 2.1 ms, which are superior to the pure GeSe (the spectral range of about 255–808 nm, the responsivity of 20.8 A/W, and τrise ≈ 20 ms), SnS2 (the spectral range of about 255–660 nm, the responsivity of 22 A/W, and τrise ≈ 50 ms), and the reported GeSe/SnS2 vdWHs.

TiS3 Nanoribbons: A Novel Material for Ultra-Sensitive Photodetection across Extreme Temperature Ranges.

Photodetectors that can operate over a wide range of temperatures, from cryogenic to elevated temperatures, are crucial for a variety of modern scientific fields, including aerospace, high-energy science, and astro-particle science. In this study, we investigate the temperature-dependent photodetection properties of titanium trisulfide (TiS3)- in order to develop high-performance photodetectors that can operate across a wide range of temperatures (77 K-543 K). We fabricate a solid-state photodetector using the dielectrophoresis technique, which demonstrates a quick response (response/recovery time ~0.093 s) and high performance over a wide range of temperatures. Specifically, the photodetector exhibits a very high photocurrent (6.95 × 10-5 A), photoresponsivity (1.624 × 108 A/W), quantum efficiency (3.3 × 108 A/W·nm), and detectivity (4.328 × 1015 Jones) for a 617 nm wavelength of light with a very weak intensity (~1.0 × 10-5 W/cm2). The developed photodetector also shows a very high device ON/OFF ratio (~32). Prior to fabrication, the TiS3 nanoribbons were synthesized using the chemical vapor technique and characterized according to their morphology, structure, stability, and electronic and optoelectronic properties; this was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and a UV-Visible-NIR spectrophotometer. We anticipate that this novel solid-state photodetector will have broad applications in modern optoelectronic devices.

Gate-controlled photoresponse improvement in b-AsP/WSe2 heterostructures with type-I band alignment

As a promising two-dimensional (2D) layered material, black arsenic phosphorus (b-AsP) alloys have received growing attention due to their unique properties and their ability for high-performance broadband photodetection. However, high dark current and slow response speed have already become bottlenecks for further development. Manual vertical van der Waals heterojunctions made of different 2D materials offer opportunities to alleviate such bottlenecks in a simple and low-energy way. The rational design of band alignment can facilitate device performance. In this work, we design and achieve a type-I vertically stacked WSe2/b-As0.084P0.916 device, which exhibits a rectification ratio of 102 along with an unusual backward current as low as 10−12 A. As such, this device can function as an ultrasensitive photodetector, which shows excellent photoresponse properties from the visible to near-infrared region (275–850 nm), with a responsivity of 244 A/W, a specific detectivity of 2.27 × 1012 Jones, and a fast response speed of τrise ≈ 5.1 ms and τdecay ≈ 4 ms. Compared to the dark state, the hole mobility under light stimulation is raised more than ten times (from 1.1 to 12.1 cm2 V−1 s−1), which contributes to numerous excited electron–hole pair transfers from WSe2 to b-As0.084P0.916. The responsivity and detectivity increase by 5 and 3 orders of magnitude, respectively, after applying gate voltage, indicating remarkable gate-controlled properties. These results suggest that the WSe2/b-As0.084P0.916 heterostructure is a promising candidate for future electronic and optoelectronic applications.

High-performance and ultra-sensitive ultraviolet photodetector based on surface passivated α-Fe2O3 thin film

Nanostructured α-Fe2O3 is a versatile material and has attracted extensive attention due to its promising electrochemical and photoelectrochemical properties, which are widely investigated in water splitting, photoelectrochemical devices, gas sensors, and catalysis. Moreover, its band gap (Eg = 2.0 eV) allows it to absorb visible light, but due to poor charge carrier mobility, ultrafast recombination of the photo-generated carriers, and surface oxygen vacancy defects its application as a photodetector got restricted. Herein with a surface passivated α-Fe2O3 film deposited on the glass substrate, the ultraviolet photodetector is demonstrated. The surface passivated photodetector is sensitive to ultraviolet light, showing a substantial enhancement in the photo-responsivity of 1.41 A/W, the external quantum efficiency of 515%, the photo-sensitivity of 1650%, and a reduction in response time of 0.06 ms (for 340 nm at a bias of +30 V) as compared with the device before surface passivation (0.228 A/W, 83%, 34%, and 1.6 ms), respectively. These improved properties are observed due to the suppression of surface defects via surface passivation, which increases free carrier concentration transport across the film. The surface passivated α-Fe2O3 thin film-based photodetector with high photo-responsivity, photo-sensitivity, high speed, and ultraviolet photoresponse is promising for practical applications, and this platform opens up new avenues for the development of low-cost, and highly efficient ultraviolet photodetectors.

Atomically Thin Twisted Heterostructure Optoelectronics Enhanced via vdW Interface Engineering

AbstractTwo‐dimensional (2D) heterostructures have sparked widespread interest in physics and device applications. The interfacial band alignment engineering of 2D heterostructures opens promising routes for high‐performance electronics and optoelectronics. In this study, a 2D Te/MoS2 interface is engineered by tailoring the lattice mismatch and distance, which changed the band alignment. The photocurrent is significantly increased by optimizing the interface alignment. The corresponding device is designed to function as an ultrasensitive photodetector with a light on/off ratio of 104, responsivity of ≈1047 A W−1, and detectivity of &gt;5 × 1012 Jones, as well as a spectral detection capability of up to 1550 nm. The proposed methods are robust and versatile and can be used to produce desired electronics; hence, this study may broaden the scope of 2D heterostructure optoelectronics.

Epitaxial CsPbBr3 /CdS Janus Nanocrystal Heterostructures for Efficient Charge Separation.

Epitaxial heterostructures of colloidal lead halide perovskite nanocrystals (NCs) with other semiconductors, especially the technologically important metal chalcogenides, can offer an unprecedented level of control in wavefunction design and exciton/charge carrier engineering. These NC heterostructures are ideal material platforms for efficient optoelectronics and other applications. Existing methods, however, can only yield heterostructures with random connections and distributions of the two components. The lack of epitaxial relation and uniform geometry hinders the structure-function correlation and impedes the electronic coupling at the heterointerface. This work reports the synthesis of uniform, epitaxially grown CsPbBr3 /CdS Janus NC heterostructures with ultrafast charge separation across the electronically coupled interface. Each Janus NC contains a CdS domain that grows exclusively on a single {220} facet of CsPbBr3 NCs. Varying reaction parameters allows for precise control in the sizes of each domain and readily modulates the optical properties of Janus NCs. Transient absorption measurements and modeling results reveal a type II band alignment, where photoexcited electrons rapidly transfer (within ≈9picoseconds) from CsPbBr3 to CdS. The promoted charge separation and extraction in epitaxial Janus NCs leadsto photoconductors with drastically improved (approximately three orders of magnitude) responsivity and detectivity, whichispromising for ultrasensitive photodetection.

Effects of post-transfer annealing and substrate interactions on the photoluminescence of 2D/3D monolayer WS2/Ge heterostructures.

The ultraflat and dangling bond-free features of two-dimensional (2D) transition metal dichalcogenides (TMDs) endow them with great potential to be integrated with arbitrary three-dimensional (3D) substrates, forming mixed-dimensional 2D/3D heterostructures. As examples, 2D/3D heterostructures based on monolayer TMDs (e.g., WS2) and bulk germanium (Ge) have become emerging candidates for optoelectronic applications, such as ultrasensitive photodetectors that are capable of detecting broadband light from the mid-infrared (IR) to visible range. Currently, the study of WS2/Ge(100) heterostructures is in its infancy and it remains largely unexplored how sample preparation conditions and different substrates affect their photoluminescence (PL) and other optoelectronic properties. In this report, we investigated the PL quenching effect in monolayer WS2/Ge heterostructures prepared via a wet transfer process, and employed PL spectroscopy and atomic force microscopy (AFM) to demonstrate that post-transfer low-pressure annealing improves the interface quality and homogenizes the PL signal. We further studied and compared the temperature-dependent PL emissions of WS2/Ge with those of as-grown WS2 and WS2/graphene/Ge heterostructures. The results demonstrate that the integration of WS2 on Ge significantly quenches the PL intensity (from room temperature down to 80 K), and the PL quenching effect becomes even more prominent in WS2/graphene/Ge heterostructures, which is likely due to synergistic PL quenching effects induced by graphene and Ge. Density functional theory (DFT) and Heyd-Scuseria-Ernzerhof (HSE) hybrid functional calculations show that the interaction of WS2 and Ge is stronger than in adjacent layers of bulk WS2, thus changing the electronic band structure and making the direct band gap of monolayer WS2 less accessible. By understanding the impact of post-transfer annealing and substrate interactions on the optical properties of monolayer TMD/Ge heterostructures, this study contributes to the exploration of the processing-properties relationship and may guide the future design and fabrication of optoelectronic devices based on 2D/3D heterostructures of TMDs/Ge.

Nucleation-controlled growth of high-quality CsPbBr3 single crystals for ultrasensitive weak-light photodetectors

High-quality cuboid-shaped CsPbBr3 single crystals have been grown using a solution refinement modified inverse temperature crystallization method for high-performance photodetectors with a low detection limit of 2.25 nW cm−2.

Self-driven and ultrasensitive room-temperature terahertz photodetector based on graphene-Ta2NiSe5 van der Waals heterojunction

Self-driven and ultrasensitive room-temperature terahertz photodetector based on graphene-Ta2NiSe5 van der Waals heterojunction

An enhanced ultrasensitive solar-blind UV photodetector based on an asymmetric Schottky junction designed with graphene/β-Ga2O3/Ag

The device has a dark current of 12.09 pA and achieves an outstanding responsivity of 44.09 A W−1, a high detectivity of 5.84 × 1012 Jones.