Broadband GaAsSb Nanowire Array Photodetectors for Filter-Free Multispectral Imaging

Improved UV Photoresponse Performance of ZnO Nanowire Array Photodetector via Effective Pt Nanoparticle Coupling

Ultraviolet (UV) photodetectors (PDs) based on nanowire (NW) hold significant promise for applications in fire detection, optical communication, and environmental monitoring. As optoelectronic devices evolve towards lower dimensionality, multifunctionality, and integrability, multicolor PDs have become a research hotspot in optics and electronic information. This study investigates the enhancement of detection capability in a light-trapping ZnO NW array through modification with Pt nanoparticles (NPs) via magnetron sputtering and hydrothermal synthesis. The optimized PD exhibits superior performance, achieving a responsivity of 12.49 A/W, detectivity of 4.07 × 1012 Jones, and external quantum efficiency (EQE) of 4.19 × 103%, respectively. In addition, the Pt NPs/ZnO NW/ZnO PD maintains spectral selectivity in the UV region. These findings show the pivotal role of Pt NPs in enhancing photodetection performance through their strong light absorption and scattering properties. This improvement is associated with localized surface plasmon resonance induced by the Pt NPs, leading to enhanced incident light and interfacial charge separation for the specialized configurations of the nanodevice. Utilizing metal NPs for device modification represents a breakthrough that positively affects the preparation of high-performance ZnO-based UV PDs.

Filter-Less Color-Selective Photodetector Derived from Integration of Parallel Perovskite Photoelectric Response Units

Color-selective photodetectors (PDs) play an indispensable role in spectral recognition, image sensing, and other fields. Nevertheless, complex filters and delicate optical paths in such devices significantly increase their complexity and size, which subsequently impede their integration in smart optoelectronic chips for universal applications. This work demonstrates the successful fabrication of filter-less color-selective perovskite PDs by integrating three perovskite units with different photoresponse on a single chip. The variation in photoresponse is attributed to different quantities of SnO2 nanoparticles, synthesized through controlled ultrasonic treatment on the surface of the electron transportation layer SnS2, which selectively absorb short-wavelength light, thus increasing the relative transmittance of long-wavelength light and enhancing the photoresponse of the units to long wavelengths. By integrating any two units and deriving the formula for the wavelength to the responsivity ratio, a wavelength sensor is developed which can accurately identify incident light in the range of 400-700 nm with a minimum error <3 nm. Furthermore, the device integrating three units with different photoresponse can identify red, green and blue in polychromatic light to achieve color imaging with a relative error <6%. This work provides valuable insights into wavelength identification and color imaging of perovskite PDs.

Recent progress of group III-V materials-based nanostructures for photodetection

Due to the suitable bandgap structure, efficient conversion rates of photon to electron, adjustable optical bandgap, high electron mobility/aspect ratio, low defects, and outstanding optical and electrical properties for device design, III-V semiconductors have shown excellent properties for optoelectronic applications, including photodiodes, photodetectors, solar cells, photocatalysis, etc. In particular, III-V nanostructures have attracted considerable interest as a promising photodetector platform, where high-performance photodetectors can be achieved based on the geometry-related light absorption and carrier transport properties of III-V materials. However, the detection ranges from Ultraviolet to Terahertz including broadband photodetectors of III-V semiconductors still have not been more broadly development despite significant efforts to obtain the high performance of III-V semiconductors. Therefore, the recent development of III-V photodetectors in a broad detection range from Ultraviolet to Terahertz, and future requirements are highly desired. In this review, the recent development of photodetectors based on III-V semiconductor with different detection range is discussed. First, the bandgap of III-V materials and synthesis methods of III-V nanostructures are explored, subsequently, the detection mechanism and key figures-of-merit for the photodetectors are introduced, and then the device performance and emerging applications of photodetectors are provided. Lastly, the challenges and future research directions of III-V materials for photodetectors are presented.

Sb-saturated high-temperature growth of extended, self-catalyzed GaAsSb nanowires on silicon with high quality

Ternary GaAsSb nanowires (NW) are key materials for integrated high-speed photonic applications on silicon (Si), where homogeneous, high aspect-ratio dimensions and high-quality properties for controlled absorption, mode confinement and waveguiding are much desired. Here, we demonstrate a unique high-temperature (high-T >650 °C) molecular beam epitaxial (MBE) approach to realize self-catalyzed GaAsSb NWs site-selectively on Si with high aspect-ratio and non-tapered morphologies under antimony (Sb)-saturated conditions. While hitherto reported low-moderate temperature growth processes result in early growth termination and inhomogeneous morphologies, the non-tapered nature of NWs under high-T growth is independent of the supply rates of relevant growth species. Analysis of dedicated Ga-flux and growth time series, allows us to pinpoint the microscopic mechanisms responsible for the elimination of tapering, namely concurrent vapor-solid, step-flow growth along NW side-facets enabled by enhanced Ga diffusion under the high-T growth. Performing growth in an Sb-saturated regime, leads to high Sb-content in VLS-GaAsSb NW close to 30% that is independent of Ga-flux. This independence enables multi-step growth via sequentially increased Ga-flux to realize uniform and very long (>7μm) GaAsSb NWs. The excellent properties of these NWs are confirmed by a completely phase-pure, twin-free zincblende (ZB) crystal structure, a homogeneous Sb-content along the VLS-GaAsSb NW growth axis, along with remarkably narrow, single-peak low-temperature photoluminescence linewidth (<15 meV) at wavelengths of ∼1100-1200 nm.

A molecular pyroelectric enabling broadband photo-pyroelectric effect towards self-driven wide spectral photodetection

Broadband spectral photoresponse has shown bright prospects for various optoelectronic devices, while fulfilling high photoactivity beyond the material bandgap is a great challenge. Here, we present a molecular pyroelectric, N-isopropylbenzylaminium trifluoroacetate (N-IBATFA), of which the broadband photo-pyroelectric effects allow for self-driven wide spectral photodetection. As a simple organic binary salt, N-IBATFA possesses a large polarization (~9.5 μC cm-2), high pyroelectric coefficient (~6.9 μC cm-2 K-1) and figures-of-merits (FV = 187.9 × 10-2 cm2 μC-1; FD = 881.5 × 10-5 Pa-0.5) comparable to the state-of-art pyroelectric materials. Particularly, such intriguing attributes endow broadband photo-pyroelectric effect, namely, transient currents covering ultraviolet (UV, 266 nm) to near-infrared (NIR, 1950 nm) spectral regime, which breaks the restriction of its optical absorption and thus allows wide UV-NIR spectral photodetection. Our finding highlights the potential of molecular system as high-performance candidates toward self-powered wide spectral photodetection.

Visualizing the intellectual structure and evolution of carbon neutrality research: a bibliometric analysis

Carbon neutrality is a research hotspot and achieves increasing interests in recent years. In this paper, utilizing the Web of Science database as the data resource, we conduct a series of analyses for the carbon neutrality-related literature from the past decade based on CiteSpace, including the visualization analysis for the research hotspots and trends, discovery of intellectual structure and influential directions, as well as the cooperation analysis for representative researchers, organizations, and countries. The findings demonstrate that (a) the relationship between carbon emissions and economic growth has achieved increasing academic interests in recent years. (b) There are mainly four knowledge groups at present in this area including renewable energy and carbon emissions; international energy cooperation and investment; energy regulations and policies of different countries; technological innovation and economic growth. (c) Cooperations exist widely within various authors, institutions, as well as countries, with academic clusters developed towards the goals of energy transitions, environmental sustainability, city development, etc.

Ternary GePdS3: 1D van der Waals Nanowires for Integration of High-Performance Flexible Photodetectors

One-dimensional (1D) van der Waals (vdW) materials are anticipated to leverage for high-performance, giant polarized, and hybrid-dimension photodetection owing to their dangling-bond free surface, intrinsic crystal structure, and weak vdW interaction. However, only a few related explorations have been conducted, especially in the field of flexible and integrated applications. Here, high-quality 1D vdW GePdS₃ nanowires were synthesized and proven to be an n-type semiconductor. The Raman vibration and band gap (1.37-1.68 eV, varying from bulk to single chain) of GePdS₃ were systemically studied by experimental and theoretical methods. The photodetector based on a single GePdS₃ nanowire possesses fast photoresponse at a broadband spectrum of 254-1550 nm. The highest responsivity and detectivity reach up to ∼219 A/W and ∼2.7 × 10¹⁰ Jones (under 254 nm light illumination), respectively. Furthermore, an image sensor with 6 × 6 pixels based on GePdS₃ nanowires is integrated on a flexible polyethylene terephthalate (PET) substrate and exhibits sensitive and homogeneous detection at 808 nm light. These results indicate that the ternary noble metal chalcogenides show great potential in flexible and broadband optoelectronics applications.

A neuromorphic bionic eye with filter-free color vision using hemispherical perovskite nanowire array retina

Spherical geometry, adaptive optics, and highly dense network of neurons bridging the eye with the visual cortex, are the primary features of human eyes which enable wide field-of-view (FoV), low aberration, excellent adaptivity, and preprocessing of perceived visual information. Therefore, fabricating spherical artificial eyes has garnered enormous scientific interest. However, fusing color vision, in-device preprocessing and optical adaptivity into spherical artificial eyes has always been a tremendous challenge. Herein, we demonstrate a bionic eye comprising tunable liquid crystal optics, and a hemispherical neuromorphic retina with filter-free color vision, enabled by wavelength dependent bidirectional synaptic photo-response in a metal-oxide nanotube/perovskite nanowire hybrid structure. Moreover, by tuning the color selectivity with bias, the device can reconstruct full color images. This work demonstrates a unique approach to address the color vision and optical adaptivity issues associated with artificial eyes that can bring them to a new level approaching their biological counterparts.

Perovskite photodetector-based single pixel color camera for artificial vision

Narrowband red, green, blue self-filtering perovskite photodetectors and a broadband white photodetector are incorporated into a single pixel imaging camera to mimic the long-, medium-, and short-wavelength cone cells and rod cells in human visual system, leading to the demonstration of high-resolution color images in diffuse mode.

Flexible Microspectrometers Based on Printed Perovskite Pixels with Graded Bandgaps

Miniaturized spectrometers have attracted much attention due to their capability to detect spectral information within a small size. However, such technology still faces challenges including large-scale preparation and performance repeatability. In this work, we overcome these challenges by demonstrating a microspectrometer constructed with a series of pixelized graded-bandgap perovskite photodetectors fabricated with inkjet printing. High-quality perovskite films with minimal pinholes and large grains are deposited by optimizing printing conditions including substrate temperature and surface modification. The resulting perovskite photodetectors show decent photosensing performance, and the different photodetectors based on perovskite films with different bandgaps exhibit various spectral responsivities with different cutoff wavelength edges. Microspectrometers are then constructed with the array of the pixelized graded-bandgap perovskite photodetectors, and incident spectra are algorithmically reconstructed by combining their output currents. The reconstruction performance of the miniaturized spectrometer is evaluated by comparing the results to the spectral curve measured with a commercial bulky spectrometer, indicating a reliable spectral reconstruction with a resolution of around 10 nm. More significantly, the miniaturized spectrometers are successfully fabricated on polymer substrates, and they demonstrate excellent mechanical flexibility. Therefore, this work provides a flexible miniaturized spectrometer with large-scale fabricability, which is promising for emerging applications including wearable devices, hyperspectral imaging, and internet of things.

Broadband Photoresponses from Ultraviolet to Near-Infrared (II) Region through Light-induced Pyroelectric Effects in a Hybrid Perovskite

Broadband photodetection has shown a great promise for diverse applications, while the realization of plateau photoresponse from ultraviolet (UV) to near-infrared (NIR) spectral region is very challenging. Herein, we exploit photoexcited pyroelectric effect in a chiral hybrid perovskite, (N, N-dimethylcyclohexylammonium)PbBr₃ (1), serving as a new pathway to drive broadband photoactivities. It is a room-temperature pyroelectric with large polarization of ≈6.4 μC cm^-2 and high pyroelectric figure-of-merits (F_V =1.0×10^-2  cm²   μC^-1 and F_D =7.1×10^-5  Pa^-1/2 ). Strikingly, light-induced pyroelectric effect arising from spontaneous polarization is observed in 1, which cover UV (266 nm) to NIR-II (1950 nm) full spectral region. The broadband photoresponses actualized by pyroelectricity break the limit of optical band gap. As the first demonstration of photo-pyroelectricity covering UV-to-NIR spectral region in hybrid perovskites, this work paves a pathway to assemble high-performance smart devices.

Random color filters based on an all-dielectric metasurface for compact hyperspectral imaging

Metasurface filters are a compact, lightweight, and inexpensive solution for the miniaturized hyperspectral imaging system. However, the emerging applicability of these filters is limited by the trade-off between spatial and spectral resolutions. In this study, we establish and experimentally demonstrate a compact hyperspectral photodetection method using random all-dielectric metasurface filters that are directly integrated on the detectors. Based on compressive sensing algorithms, the compact photodetectors can accurately reconstruct the incident spectrum in the visible range. The minimum full width at half maximum (FWHM) of the spectrum reconstructed is 4.8 nm, which fully satisfies the requirements of hyperspectral imaging. The proposed method may be applied in the design, development, and measurement of compact hyperspectral imaging systems.

Investigation of light-matter interaction in single vertical nanowires in ordered nanowire arrays

Quasi one-dimensional semiconductor nanowires (NWs) in either arrays or single free-standing forms have shown unique optical properties (i.e., light absorption and emission) differently from their thin film or bulk counterparts, presenting new opportunities for achieving enhanced performance and/or functionalities for optoelectronic device applications. However, there is still a lack of understanding of the absorption properties of vertically standing single NWs within an array environment with light coupling from neighboring NWs within certain distances, due to the challenges in fabrication of such devices. In this article, we present a new approach to fabricate single vertically standing NW photodetectors from ordered InP NW arrays using the focused ion beam technique, to allow direct measurements of optical and electrical properties of single NWs standing in an array. The light-matter interaction and photodetector performance are investigated using both experimental and theoretical methods. The consistent photocurrent and simulated absorption mapping results reveal that the light absorption and thus photoresponse of single NWs are strongly affected by the NW array geometry and related light coupling from their surrounding dielectric environment, due to the large absorption cross section and/or strong light interaction. While the highest light concentration factor (∼19.64) was obtained from the NW in an array with a pitch of 1.5 μm, the higher responsivity per unit cell (equivalent to NW array responsivity) of a single vertical NW photodetector was achieved in an array with a pitch of 0.8 μm, highlighting the importance of array design for practical applications. The insight from our study can provide important guidance to evaluate and optimize the device design of NW arrays for a wide range of optoelectronic device applications.