Ag Nanowire-Plasmonic-Assisted Charge Separation in Hybrid Heterojunctions of Ppy-PEDOT:PSS/GaN Nanorods for Enhanced UV Photodetection

Optimization of Si doping in GaN nanowires for high-performance photoelectrochemical photodetectors

Photoelectrochemical-type photodetectors (PEC PDs) have received extensive attention owing to their low cost, simple fabrication process, and high photoresponse adjustability. Here, we fabricated GaN nanowires with different Si-doping concentrations by changing the temperature of the silicon cell in plasma-assisted molecular beam epitaxy.  The influence of Si-doping concentration on the PEC PD performance of GaN-based nanowire photoelectrodes was studied. The experimental results show that the photoresponse performance of the PEC PD can be significantly improved by adjusting the Si-doping concentration of GaN nanowire. When Tsi = 1120°C, the doped GaN nanowires photoelectrode exhibited the maximum photoresponse, which was 20 times greater than that of undoped GaN nanowire photoelectrode.

Wafer-Scale Vertical 1D GaN Nanorods/2D MoS2/PEDOT:PSS for Piezophototronic Effect-Enhanced Self-Powered Flexible Photodetectors

van der Waals (vdW) heterostructures constructed by low-dimensional (0D, 1D, and 2D) materials are emerging as one of the most appealing systems in next-generation flexible photodetection. Currently, hand-stacked vdW-type photodetectors are not compatible with large-area-array fabrication and show unimpressive performance in self-powered mode. Herein, vertical 1D GaN nanorods arrays (NRAs)/2D MoS2/PEDOT:PSS in wafer scale have been proposed for self-powered flexible photodetectors arrays firstly. The as-integrated device without external bias under weak UV illumination exhibits a competitive responsivity of 1.47 A W-1 and a high detectivity of 1.2 × 1011 Jones, as well as a fast response speed of 54/71 µs, thanks to the strong light absorption of GaN NRAs and the efficient photogenerated carrier separation in type-II heterojunction. Notably, the strain-tunable photodetection performances of device have been demonstrated. Impressively, the device at - 0.78% strain and zero bias reveals a significantly enhanced photoresponse with a responsivity of 2.47 A W-1, a detectivity of 2.6 × 1011 Jones, and response times of 40/45 µs, which are superior to the state-of-the-art self-powered flexible photodetectors. This work presents a valuable avenue to prepare tunable vdWs heterostructures for self-powered flexible photodetection, which performs well in flexible sensors.

Metal-semiconductor-metal solar-blind ultraviolet photodetector based on Al0.55Ga0.45N/Al0.4Ga0.6N/Al0.65Ga0.35N heterostructures

We have designed a metal-semiconductor-metal (MSM) solar-blind ultraviolet (UV) photodetector (PD) by utilizing Al0.55Ga0.45N/Al0.4Ga0.6N/Al0.65Ga0.35N heterostructures. The interdigital Ni/Au metal stack is deposited on the Al0.55Ga0.45N layer to form Schottky contacts. The AlGaN hetero-epilayers with varying Al content contribute to the formation of a two-dimensional electron gas (2DEG) conduction channel and the enhancement of the built-in electric field in the Al0.4Ga0.6N absorption layer. This strong electric field facilitates the efficient separation of photogenerated electron-hole pairs. Consequently, the fabricated PD exhibits an ultra-low dark current of 1.6 × 10-11 A and a broad spectral response ranging from 220 to 280 nm, with a peak responsivity of 14.08 A/W at -20 V. Besides, the PD demonstrates an ultrahigh detectivity of 2.28 × 1013 Jones at -5 V. Furthermore, to investigate the underlying physical mechanism of the designed solar-blind UV PD, we have conducted comprehensive two-dimensional device simulations.

Plasmonic Nanostructure Engineering with Shadow Growth

Physical shadow growth is a vacuum deposition technique that permits a wide variety of 3D-shaped nanoparticles and structures to be fabricated from a large library of materials. Recent advances in the control of the shadow effect at the nanoscale expand the scope of nanomaterials from spherical nanoparticles to complex 3D shaped hybrid nanoparticles and structures. In particular, plasmonically active nanomaterials can be engineered in their shape and material composition so that they exhibit unique physical and chemical properties. Here, the recent progress in the development of shadow growth techniques to realize hybrid plasmonic nanomaterials is discussed. The review describes how fabrication permits the material response to be engineered and highlights novel functions. Potential fields of application with a focus on photonic devices, biomedical, and chiral spectroscopic applications are discussed.

A highly sensitive electrochemical sensor by growing Ag nanoparticles on the surface of PPy@PEDOT:PSS film for detecting sodium hydroxymethanesulfinate molecules

A high-sensitivity electrochemical sensor was fabricated via in situ growth of Ag nanoparticles (AgNPs) on the surface of a polypyrrole@poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PPy@PEDOT:PSS) film for detecting sodium hydroxymethanesulfinate (SHF) molecules in milk and rice flour samples. The sensor fabrication process involved randomly decorating Ag seed points on the porous PPy@PEDOT:PSS film via a chemical reduction process using a AgNO₃ solution. Next, AgNPs were anchored on the PPy@PEDOT:PSS film surface using an electrochemical deposition method to prepare a sensor electrode. Under optimal conditions, the sensor exhibits a good linear relation within a range of 1-130 ng/mL for real milk and rice flour samples and its limit-of-detection values were up to 0.58 and 0.29 ng/mL, respectively. Additionally, Raman spectroscopy was used to identify the byproducts of the chemical reaction, such as formaldehyde. This AgNP/PPy@PEDOT:PSS film-based electrochemical sensor offers a simple and rapid method for detecting SHF molecules in food products.

One Stone Two Birds: Utilization of Solar Light for Simultaneous Selective Phenylcarbinol Oxidation and H2 Production over 0D/2D-3D Pt/In2S3 Schottky Junction

Precise regulation and control solar-light-driven charges photoexcited on photocatalysts for separation-transfer and target redox reactions is an attractive and challenging pathway toward sustainability. Herein, 0D/2D-3D Pt/In2S3 Schottky junction was fabricated for simultaneous selective phenylcarbinol conversion into value-added aldehydes and production of clean energy H2 by directly utilizing photoexcited holes and electrons in one reaction system under mild reaction conditions. In contrast to pure water splitting and pure In2S3, the reaction thermodynamics and kinetics of H2 evolution on the Pt/In2S3 were significantly enhanced. The optimized 0.3% Pt/In2S3 exhibited the highest and most stable photocatalytic activity with 22.1 mmol g−1 h−1 of H2 production rate and almost 100% selectivity of benzaldehyde production. Notably, this dual-function photocatalysis also exhibited superiority in contrast to sacrificial-agent H2 evolution reactions such as lactic acid, Na2S, methanol and triethanolamine. The turnover frequency (TOF) could reach up to ~2394 h−1. The Pt clusters anchored at the electron location and strong metal-support interactions (SMSI) between Pt and In2S3 synergistically improved the spatial charge separation and directional transportation (~90.1% of the charge transport efficiency could be achieved over the Pt/In2S3 hybrid), and thus result in significant enhancement of photocatalytic H2 evolution with simultaneous benzaldehyde production.

An Internal-Electrostatic-Field-Boosted Self-Powered Ultraviolet Photodetector

Self-powered photodetectors are of significance for the development of low-energy-consumption and environment-friendly Internet of Things. The performance of semiconductor-based self-powered photodetectors is limited by the low quality of junctions. Here, a novel strategy was proposed for developing high-performance self-powered photodetectors with boosted electrostatic potential. The proposed self-powered ultraviolet (UV) photodetector consisted of an indium tin oxide and titanium dioxide (ITO/TiO₂) heterojunction and an electret film (poly tetra fluoroethylene, PTFE). The PTFE layer introduces a built-in electrostatic field to highly enhance the photovoltaic effect, and its high internal resistance greatly reduces the dark current, and thus remarkable performances were achieved. The self-powered UV photodetector with PTFE demonstrated an extremely high on-off ratio of 2.49 × 10⁵, a responsivity of 76.87 mA/W, a response rise time of 7.44 ms, and a decay time of 3.75 ms. Furthermore, the device exhibited exceptional stability from room temperature to 70 °C. Compared with the conventional ITO/TiO₂ heterojunction without the PTFE layer, the photoresponse of the detector improved by 442-fold, and the light-dark ratio was increased by 8.40 × 10⁵ times. In addition, the detector is simple, easy to fabricate, and low cost. Therefore, it can be used on a large scale. The electrostatic modulation effect is universal for various types of semiconductor junctions and is expected to inspire more innovative applications in optoelectronic and microelectronic devices.

Ultraviolet Photodetector Based on Poly(3,4-Ethylenedioxyselenophene)/ZnO Core-Shell Nanorods p-n Heterojunction

In this work, we successfully assembled an organic-inorganic core-shell hybrid p-n heterojunction ultraviolet photodetector by the electropolymerization deposition of poly(3,4-ethylenedioxyselenophene) (PEDOS) on the surface of zinc oxide nanoarrays (ZnO NRs). The structures of composite were confirmed by FTIR, UV-Vis, XRD and XPS. Mott-Schottky analysis was used to study the p-n heterojunction structure. The photodetection properties of ZnO NRs/PEDOS heterojunction ultraviolet photodetector were systematically investigated current-voltage (I-V) and current-time (I-t) analysis under different bias voltages. The results showed that PEDOS films uniformly grew on ZnO NRs surface and core-shell structure was formed. The p-n heterojunction structure was formed with strong built-in electric field between ZnO NRs and PEDOS. Under the irradiation of UV light, the device showed a good rectification behavior. The responsivity, detection rate and the external quantum efficiency of the ultraviolet photodetector reached to 247.7 A/W, 3.41 × 10¹² Jones and 84,000% at 2 V bias, respectively. The rise time (τ_r) and fall time (τ_f) of ZnO NRs/PEDOS UV photodetector were obviously shortened compared to ZnO UV photodetector. The results show that the introduction of PEDOS effectively improves the performance of the UV photodetector.

Edge-enriched MoS2 nanosheets modified porous nanosheet-assembled hierarchical In2O3 microflowers for room temperature detection of NO2 with ultrahigh sensitivity and selectivity

Nitrogen dioxide (NO₂) is one of the most hazardous toxic pollutants to human health and the environment. However, deficiencies of low sensitivity and poor selectivity at room temperature (RT) restrain the application of NO₂ sensors. Herein, the edge-enriched MoS₂ nanosheets modified porous nanosheets-assembled three-dimensional (3D) In₂O₃ microflowers have been synthesized to improve the sensitivity and selectivity of NO₂ detection at RT. The results show that the In₂O₃/MoS₂ composite sensor exhibits a response as high as 343.09-5 ppm NO₂, which is 309 and 72.5 times higher than the sensors based on the pristine MoS₂ and In₂O₃. The composite sensor also shows short recovery time (37 s), excellent repeatability and long-term stability. Furthermore, the response of the In₂O₃/MoS₂ sensor to NO₂ is at least 30 times higher than that of other gases, proving the ultrahigh selectivity of the sensor. The outstanding sensing performance of the In₂O₃/MoS₂ sensor can be attributed to the synergistic effect and abundant active sites originating from the p-n heterojunction, exposed edge structures and the designed 2D/3D hybrid structure. The strategy proposed herein is expected to provide a useful reference for the development of high-performance RT NO₂ sensors.

Biodegradable Polymer Composites for Electrophysiological Signal Sensing

Electrophysiological signals are collected to characterize human health and applied in various fields, such as medicine, engineering, and pharmaceuticals. Studies of electrophysiological signals have focused on accurate signal acquisition, real-time monitoring, and signal interpretation. Furthermore, the development of electronic devices consisting of biodegradable and biocompatible materials has been attracting attention over the last decade. In this regard, this review presents a timely overview of electrophysiological signals collected with biodegradable polymer electrodes. Candidate polymers that can constitute biodegradable polymer electrodes are systemically classified by their essential properties for collecting electrophysiological signals. Moreover, electrophysiological signals, such as electrocardiograms, electromyograms, and electroencephalograms subdivided with human organs, are discussed. In addition, the evaluation of the biodegradability of various electrodes with an electrophysiology signal collection purpose is comprehensively revisited.

Flexible assembly of the PEDOT: PSS/ exfoliated β-Ga2O3 microwire hybrid heterojunction for high-performance self-powered solar-blind photodetector

Motivated by the goals of fabricating highly reliable, high performance, and cost-efficient self-powered photodetector (PD) for numerous scientific research and civil fields, an organic-inorganic hybrid solar-blind ultraviolet (UV) PD based on PEDOT: PSS/exfoliated β-Ga₂O₃ microwire heterojunction was fabricated by a flexible and cost-effective assembly method. Benefiting from the heterojunction constructed by the highly crystalline β-Ga₂O₃ and the excellent hole transport layer PEDOT: PSS, the device presents a high responsivity of 39.8 mA/W at 250 nm and a sharp cut-off edge at 280 nm without any power supply. Additionally, the ultra-high normalized photo-to-dark current ratio (> 10⁴ mW^-1cm²) under reverse bias and the superior detectivity of 2.4×10¹² Jones at zero bias demonstrate the excellent detection capabilities. Furthermore, the hybrid PD exhibits a rapid rise time (several milliseconds) and high rejection ratio (R₂₅₀/R₃₆₅: 5.8 × 10³), which further highlights its good spectral selectivity for solar-blind UV. The prominent performance is mainly ascribed to the efficient separation of the photogenerated carriers by the large built-in electric field of the advanced heterojunction. This flexible assembly strategy for solar-blind UV PD combines the advantages of high efficiency, low cost and high performance, providing more potential for PD investigation and application in the future.

High performance langasite based SAW NO2 gas sensor using 2D g-C3N4@TiO2 hybrid nanocomposite

Nitrogen dioxide (NO₂) gas has emerged as a severe air pollutant that causes damages to the environment, human life and global ecosystems etc. However, the currently available NO₂ gas sensors suffers from insufficient selectivity, sensitivity and long response times that impeding their practical applicability for room temperature (RT) gas sensing. Herein, we report a high performance langasite (LGS) based surface acoustic wave (SAW) RT NO₂ gas sensor using 2-dimensional (2D) g-C₃N₄@TiO₂ nanoplates (NP) with {001} facets hybrid nanocomposite as a chemical interface. The g-C₃N₄@TiO₂ NP/LGS SAW device showed a significant negative frequency shift (∆f) of ~19.8 kHz which is 2.4 fold higher than that of the pristine TiO₂ NP/LGS SAW sensor toward 100 ppm of NO₂ at RT. In addition, the hybrid SAW device fascinatingly exhibited a fast response/recovery time with a low detection limit, high selectivity, and an effective long term stability toward NO₂ gas. It also exhibited an enhanced and robust negative frequency shifts under various relative humidity conditions ranging from 20% to 80% for 100 ppm of NO₂ gas. The high performance of the g-C₃N₄ @TiO₂ NP/LGS SAW gas sensor can be attributed to the enhanced mass loading effect which was assisted by the large surface area, oxygen vacancies, OH and amine functional groups of the n-n hybrid heterojunction of g-C₃N₄@TiO₂ NP that provide abundant active sites for the adsorption and diffusion of NO₂ gas molecules. These results emphasize the significance of the integration of 2D materials with metal oxides for SAW based RT gas sensing technology holds great promise in environmental protection.

Self-Powered Organometal Halide Perovskite Photodetector with Embedded Silver Nanowires

Metal-semiconductor-metal (MSM) configuration of perovskite photodetectors (PPDs) suggests easy and low-cost manufacturing. However, the basic structures of MSM PPDs include vertical and lateral configurations, which require the use of expensive materials such as transparent conductive oxides or/and sophisticated fabrication techniques such as lithography. Integrating metallic nanowire-based electrodes into the perovskite photo-absorber layer to form one-half of the MSM PPD structure could potentially resolve the key issues of both configurations. Here, a manufacturing of solution-processed and self-powered MSM PPDs with embedded silver nanowire electrodes is demonstrated. The embedding of silver nanowire electrode into the perovskite layer is achieved by treating the silver nanowire/perovskite double layer with a methylamine gas vapor. The evaporated gold layer is used as the second electrode to form MSM PPDs. The prepared MSM PPDs show a photoresponsivity of 4 × 10-5 AW-1 in the UV region and 2 × 10-5 AW-1 in the visible region. On average, the devices exhibit a photocurrent of 1.1 × 10-6 A under white light (75 mW cm-2) illumination with an ON/OFF ratio of 83.4. The results presented in this work open up a new method for development and fabrication of simple, solution-processable MSM self-powered PPDs.

Surmounting the interband threshold limit by the hot electron excitation of multi-metallic plasmonic AgAuCu NPs for UV photodetector application

Sharply improved photoresponse characteristics are demonstrated by the multi-metallic AgCu, AuCu and AgAuCu NP based UV-PDs through the superior photo carrier injection by the strong elemental composition-dependent hot electrons and localized surface plasmon resonance (LSPR).

A Spiro-MeOTAD/Ga2O3/Si p-i-n Junction Featuring Enhanced Self-Powered Solar-Blind Sensing via Balancing Absorption of Photons and Separation of Photogenerated Carriers

Solar blind ultraviolet (SBUV) self-powered photodetectors (PDs) have a great number of applications in civil and military exploration. Ga₂O₃ is a prospective candidate for SBUV detection owing to its reasonable bandgap corresponding to the SBUV waveband. Nevertheless, the previously reported Ga₂O₃ photovoltaic devices had low photoresponse performance and were still far from the demands of practical application. Herein, we propose an idea of using spiro-MeOTAD (spiro) as the SBUV transparent conductive layer to construct p-i-n PDs (p-spiro/Ga₂O₃/n-Si). With the aid of double built-in electric fields, the designed p-i-n PDs could operate without any external power source. Furtherly, the influence of spiro thickness on improving the photoelectric performance of devices is investigated in detail and the optimum device is achieved, translating to a peak responsivity of 192 mA/W upon a weak 254 nm light illumination of 2 μW/cm² at zero bias. In addition, the I-t curve of our PD shows binary response characteristics and a four-stage current response behavior under a small forward bias, and also, its underlying working mechanism is analyzed. In sum, this newly developed device presents great potential for booming the high energy-efficient optoelectronic devices in the short run.

Study of Normally-Off AlGaN/GaN HEMT with Microfield Plate for Improvement of Breakdown Voltage

In this paper, we introduce a new type of AlGaN/GaN high electron mobility transistor (HEMT) with microfield plate (FP). We use Silvaco-ATLAS two-dimensional numerical simulation to calculate the performance of conventional HEMT and HEMT with micro-FP and analyze its principle. By studying a new charge balance method provided by HEMTs and micro-FPs, the physical mechanism of FP adjusting the HEMT potential distribution and channel electric field distribution is analyzed. The new FP structure consists of a drain field plate (D-FP), a source field plate (S-FP) and several micro-gate field plates (G-FP) to improve the output characteristics of HEMTs. By adjusting the distribution of potential and channel electric field, a wider and more uniform channel electric field can be obtained, and the breakdown voltage can be increased to 1278 V. Although the on-resistance of the HEMT is slightly increased to 5.24 Ω mm, it is still lower than other reference values. These results may open up a new and effective method for manufacturing high-power devices for power electronics applications.

Plasmon-Enhanced Photoresponse of Self-Powered Si Nanoholes Photodetector by Metal Nanowires

In this work, we report the development of self-powered photodetectors that integrate silicon nanoholes (SiNHs) and four different types of metal nanowires (AgNWs, AuNWs, NiNWs, PtNWs) applied on the SiNHs’ surface using the solution processing method. The effectiveness of the proposed architectures is evidenced through extensive experimental and simulation analysis. The AgNWs/SiNHs device showed the highest photo-to-dark current ratio of 2.1 × 10⁻⁴, responsivity of 30 mA/W and detectivity of 2 × 10¹¹ Jones along with the lowest noise equivalent power (NEP) parameter of 2.4 × 10⁻¹² WHz^−1/2 in the blue light region. Compared to the bare SiNHs device, the AuNWs/SiNHs device had significantly enhanced responsivity up to 15 mA/W, especially in the red and near-infrared spectral region. Intensity-modulated photovoltage spectroscopy (IMVS) measurements revealed that the AgNWs/SiNHs device generated the longest charge carrier lifetime at 470 nm, whereas the AuNWs/SiNHs showed the slowest recombination rate at 627 nm. Furthermore, numerical simulation confirmed the local field enhancement effects at the MeNWs and SiNHs interface. The study demonstrates a cost-efficient and scalable strategy to combine the superior light harvesting properties of SiNHs with the plasmonic absorption of metallic nanowires (MeNWs) towards enhanced sensitivity and spectral-selective photodetection induced by the local surface plasmon resonance effects.