Atomically Thin Oxyhalide Solar-Blind Photodetectors

Review on synthetic approaches and PEC activity performance of bismuth binary and mixed-anion compounds for potential applications in marine engineering

Photoelectrochemical (PEC) technology in marine engineering holds significant importance due to its potential to address various challenges in the marine environment. Currently, PEC-type applications in marine engineering offer numerous benefits, including sustainable energy generation, water desalination and treatment, photodetection, and communication. Finding novel efficient photoresponse semiconductors is of great significance for the development of PEC-type techniques in the marine space. Bismuth-based semiconductor materials possess suitable and tunable bandgap structures, high carrier mobility, low toxicity, and strong oxidation capacity, which gives them great potential for PEC-type applications in marine engineering. In this paper, the structure and properties of bismuth binary and mixed-anion semiconductors have been reviewed. Meanwhile, the recent progress and synthetic approaches were discussed from the point of view of the application prospects. Finally, the issues and challenges of bismuth binary and mixed-anion semiconductors in PEC-type photodetection and hydrogen generation are analyzed. Thus, this perspective will not only stimulate the further investigation and application of bismuth binary and mixed-anion semiconductors in marine engineering but also help related practitioners understand the recent progress and potential applications of bismuth binary and mixed-anion compounds.

Two-Dimensional Oxide Crystals for Device Applications: Challenges and Opportunities

Atomically thin two-dimensional (2D) oxide crystals have garnered considerable attention because of their remarkable physical properties and potential for versatile applications. In recent years, significant advancements have been made in the design, preparation, and application of ultrathin 2D oxides, providing many opportunities for new-generation advanced technologies. This review focuses on the controllable preparation of 2D oxide crystals and their applications in electronic and optoelectronic devices. Based on their bonding nature, the various types of 2D oxide crystals are first summarized, including both layered and nonlayered crystals, as well as their current top-down and bottom-up synthetic approaches. Subsequently, in terms of the unique physical and electrical properties of 2D oxides, recent advances in device applications are emphasized, including photodetectors, field-effect transistors, dielectric layers, magnetic and ferroelectric devices, memories, and gas sensors. Finally, conclusions and future prospects of 2D oxide crystals are presented. It is hoped that this review will provide comprehensive and insightful guidance for the development of 2D oxide crystals and their device applications.

Polarization-Sensitive Photodetector Based on High Crystallinity Quasi-1D BiSeI Nanowires Synthesized via Chemical Vapor Deposition

Bismuth chalcohalides (BiSeI and BiSI), a class of superior light absorbers, have recently garnered great attention owing to their promise in constructing next-generation optoelectronic devices. However, to date, the photodetection application of bismuth chalcohalides is still limited due to the challenge in controllable preparation. Herein, the synthesis of large-scale quasi-1D BiSeI nanowires via chemical vapor deposition growth is reported. By precisely tuning the growth temperature and the Se supply, it can effectively control the growth thermodynamics and kinetics of BiSeI crystal, and thus achieve high purity quasi-1D BiSeI nanowires with high crystal quality, uniform diameter, and tunable domain length. Theory and optical characterizations of the quasi-1D BiSeI nanowires reveal an indirect bandgap of 1.57 eV with prominent optical linear dichroism. As a result, the quasi-1D BiSeI nanowire-based photodetector demonstrates a broadband photoresponse (400-800 nm) with high responsivity of 5880 mA W-1 , fast response speed of 0.11 ms and superior air stability. More importantly, the photodetector displays strong polarization sensitivity (anisotropic ratio = 1.77) under the 532 nm light irradiation. This work will provide important guides to the synthesis of other quais-1D metal chalcohalides and shed light on their potential in constructing novel multifunctional optoelectronic devices.

Enhancing UV-C Photoelectron Lifetimes for Avalanche-like Photocurrents in Carbon-Doped Bi3O4Cl Nanosheets

Interlayer electric fields in two-dimensional (2D) materials create photoelectron protecting barriers useful to mitigate electron-hole recombination. However, tuning the interlayer electric field remains challenging. Here, carbon-doped Bi₃O₄Cl (C:Bi₃O₄Cl) nanosheets are synthesized using a gas phase protocol, and n-type carriers are acquired as confirmed by the transconductance polarity of nanosheet field effect transistors. Thin C:Bi₃O₄Cl nanosheets show excellent 266 nm photodetector figures of merit, and an avalanche-like photocurrent is demonstrated. Decaying behaviors of photoelectrons pumped by a 266 nm laser pulse (266 nm photoelectrons) are observed using transient absorption spectroscopy, and a significant 266 nm photoelectron lifetime quality in C:Bi₃O₄Cl is presented. Built C:Bi₃O₄Cl models suggest that the interlayer electric field can be boosted by two different carbon substitutions at the inner and outer bismuth sites. This work reports a facile approach to increase the interlayer electric field in Bi₃O₄Cl for future UV-C photodetector applications.

Ultrahigh-Sensitivity and Fast-Speed Solar-Blind Ultraviolet Photodetector Based on a Broken-Gap van der Waals Heterodiode

Broad-bandgap semiconductor-based solar-blind ultraviolet (SBUV) photodetectors have attracted considerable research interest because of their broad applications in missile plume tracking, flame detectors, environmental monitoring, and optical communications due to their solar-blind nature and high sensitivity with low background radiation. Owing to its high light absorption coefficient, abundance, and wide tunable bandgap of 2-2.6 eV, tin disulfide (SnS₂) has emerged as one of the most promising compounds for application in UV-visible optoelectronic devices. However, SnS₂ UV detectors have some undesirable properties such as slow response speed, high current noise level, and low specific detectivity. This study reports a metal mirror-enhanced Ta_0.01W_0.99Se₂/SnS₂ (TWS) van der Waals heterodiode-based SBUV photodetector with an ultrahigh photoresponsivity (R) of ∼1.85 × 10⁴ AW^-1 and a fast speed with rising time (τ_r) of 3.3 μs and decay time (τ_d) of 3.4 μs. Notably, the TWS heterodiode device exhibits a significantly low noise equivalent power of ∼1.02 × 10^-18 W Hz^-1/2 and a high specific detectivity of ∼3.65 × 10¹⁴ cm Hz^1/2 W^-1. This study provides an alternative method for designing fast-speed SBUV photodetectors with enormous potential in applications.

2D Ultrawide Bandgap Semiconductors: Odyssey and Challenges

2D ultrawide bandgap (UWBG) semiconductors have aroused increasing interest in the field of high-power transparent electronic devices, deep-ultraviolet photodetectors, flexible electronic skins, and energy-efficient displays, owing to their intriguing physical properties. Compared with dominant narrow bandgap semiconductor material families, 2D UWBG semiconductors are less investigated but stand out because of their propensity for high optical transparency, tunable electrical conductivity, high mobility, and ultrahigh gate dielectrics. At the current stage of research, the most intensively investigated 2D UWBG semiconductors are metal oxides, metal chalcogenides, metal halides, and metal nitrides. This paper provides an up-to-date review of recent research progress on new 2D UWBG semiconductor materials and novel physical properties. The widespread applications, i.e., transistors, photodetector, touch screen, and inverter are summarized, which employ 2D UWBG semiconductors as either a passive or active layer. Finally, the existing challenges and opportunities of the enticing class of 2D UWBG semiconductors are highlighted.

Thermally Stable Organic Field-Effect Transistors Based on Asymmetric BTBT Derivatives for High Performance Solar-Blind Photodetectors

High-performance solar-blind photodetectors are widely studied due to their unique significance in military and industrial applications. Yet the rational molecular design for materials to possess strong absorption in solar-blind region is rarely addressed. Here, an organic solar-blind photodetector is reported by designing a novel asymmetric molecule integrated strong solar-blind absorption with high charge transport property. Such alkyl substituted [1]benzothieno[3,2-b][1]-benzothiophene (BTBT) derivatives Cn-BTBTN (n = 6, 8, and 10) can be easily assembled into 2D molecular crystals and perform high mobility up to 3.28 cm² V^-1 s^-1 , which is two orders of magnitude higher than the non-substituted core BTBTN. Cn-BTBTNs also exhibit dramatically higher thermal stability than the symmetric alkyl substituted C8-BTBT. Moreover, C10-BTBTN films with the highest mobility and strongest solar-blind absorption among the Cn-BTBTNs are applied for solar-blind photodetectors, which reveal record-high photosensitivity and detectivity up to 1.60 × 10⁷ and 7.70 × 10¹⁴ Jones. Photodetector arrays and flexible devices are also successfully fabricated. The design strategy can provide guidelines for developing materials featuring high thermal stability and stimulating such materials in solar-blind photodetector application.

Strain-controlled synthesis of ultrathin hexagonal GaTe/MoS2 heterostructure for sensitive photodetection

Ultrathin hexagonal GaTe, with relatively high charge density, holds great potential in the field of optoelectronic devices. However, the thermodynamical stability limits it fabrications as well as applications. Here, by introducing two-dimensional MoS2 as the substrate, we successfully realized the phase-controlled synthesis of ultrathin h-GaTe, leading to high-quality h-GaTe/MoS2 heterostructures. Theoretical calculation studies reveal that GaTe with hexagonal phase is more thermodynamically stable on MoS2 templates, which can be attributed to the strain stretching and the formation energy reduction. Based on the achieved p-n heterostructures, optoelectronic devices are designed and probed, where remarkable photoresponsivity (32.5 A/W) and fast photoresponse speed (<50 μs) are obtained, indicating well-behaved photo-sensing behaviors. The study here could offer a good reference for the controlled growth of the relevant materials, and the achieved heterostructure will find promising applications in future integrated electronic and optoelectronic devices and systems.

Cross-Substitution Promoted Ultrawide Bandgap up to 4.5 eV in a 2D Semiconductor: Gallium Thiophosphate

Exploring 2D ultrawide bandgap semiconductors (UWBSs) will be conductive to the development of next-generation nanodevices, such as deep-ultraviolet photodetectors, single-photon emitters, and high-power flexible electronic devices. However, a gap still remains between the theoretical prediction of novel 2D UWBSs and the experimental realization of the corresponding materials. The cross-substitution process is an effective way to construct novel semiconductors with the favorable parent characteristics (e.g., structure) and the better physicochemical properties (e.g., bandgap). Herein, a simple case is offered for rational design and syntheses of 2D UWBS GaPS₄ by employing state-of-the-art GeS₂ as a similar structural model. Benefiting from the cosubstitution of Ge with lighter Ga and P, the GaPS₄ crystals exhibit sharply enlarged optical bandgaps (few-layer: 3.94 eV and monolayer: 4.50 eV) and superior detection performances with high responsivity (4.89 A W^-1 ), high detectivity (1.98 × 10¹² Jones), and high quantum efficiency (2.39 × 10³ %) in the solar-blind ultraviolet region. Moreover, the GaPS₄ -based photodetector exhibits polarization-sensitive photoresponse with a linear dichroic ratio of 1.85 at 254 nm, benefitting from its in-plane structural anisotropy. These results provide a pathway for the discovery and fabrication of 2D UWBS anisotropic materials, which become promising candidates for future solar-blind ultraviolet and polarization-sensitive sensors.

Multiple-Dimensionally Controllable Nucleation Sites of Two-Dimensional WS2/Bi2Se3 Heterojunctions Based on Vapor Growth

Two-dimensional (2D) heterojunctions have attracted great attention due to their excellent optoelectronic properties. Until now, precisely controlling the nucleation density and stacking area of 2D heterojunctions has been of critical importance but still a huge challenge. It hampers the progress of controlled growth of 2D heterojunctions for optoelectronic devices because the potential relation between numerous growth parameters and nucleation density is always poorly understood. Herein, by cooperatively controlling three parameters (substrate temperature, gas flow rate, and precursor concentration) in modified vapor deposition growth, the nucleation density and stacking area of WS₂/Bi₂Se₃ vertical heterojunctions were successfully modulated. High-quality WS₂/Bi₂Se₃ vertical heterojunctions with various stacking areas were effectively grown from single and multiple nucleation sites. Moreover, the potential nucleation mechanism and efficient charge transfer of WS₂/Bi₂Se₃ vertical heterojunctions were systematically studied by utilizing the density functional theory and photoluminescence spectra. This modified vapor deposition strategy and the proposed mechanism are helpful in controlling the nucleation density and stacking area of other heterojunctions, which plays a key role in the preparation of electronic and optoelectronic nanodevices.

Recent Advances in 2D Group VB Transition Metal Chalcogenides

2D materials have received considerable research interest owing to their abundant material systems and remarkable properties. Among them, 2D group VB transition metal chalcogenides (GVTMCs) stand out as emerging 2D metallic materials and significantly broaden the research scope of 2D materials. 2D GVTMCs have great advantages in electrical transport, 2D magnetism, charge density wave, sensing, catalysis, and charge storage, making them attractive in the fields of functional devices and energy chemistry. In this review, the recent progress of 2D GVTMCs is summarized systematically from fundamental properties, growth methodologies to potential applications. The challenges and prospects are also discussed for future research in this field.

Atomic-Thin ZnO Sheet for Visible-Blind Ultraviolet Photodetection

The atomic-thin 2D semiconductors have emerged as plausible candidates for future optoelectronics with higher performance in terms of the scaling process. However, currently reported 2D photodetectors still have huge shortcomings in ultraviolet and especially visible-blind wavelengths. Here, a simple and nontoxic surfactant-assisted synthesis strategy is reported for the controllable growth of atomically thin (1.5 to 4 nm) ZnO nanosheets with size ranging from 3 to 30 µm. Benefit from the short carbon chains and the water-soluble ability of sodium dodecyl sulfate (SDS), the synthesized ZnO nanosheets possess high crystal quality and clean surface, leading to good compatibility with traditional micromanufacturing technology and high sensitivity to UV light. The photodetectors constructed with ZnO demonstrate the highest responsivity (up to 2.0 × 10⁴ A W^-1 ) and detectivity (D* = 6.83 × 10¹⁴ Jones) at a visible-blind wavelength of 254 nm, and the photoresponse speed is optimized by the 400 °C annealing treatment (τ_R  = 3.97 s, τ_D  = 5.32 s), thus the 2D ZnO can serve as a promising material to fill in the gap for deep-UV photodetection. The method developed here opens a new avenue to controllably synthesize 2D nonlayered materials and accelerates their applications in high-performance optoelectronic devices.