Flexible Self-Powered GaN Ultraviolet Photoswitch with Piezo-Phototronic Effect Enhanced On/Off Ratio

Piezoelectricity in wide bandgap semiconductor 2D crystal GaN nanosheets

Gallium nitride (GaN) exhibits various potential applications in optics and optoelectronics due to its outstanding physical characteristics, including a wide direct bandgap, strong deep-ultraviolet emission, and excellent electron transport properties. However, research on the piezoelectric and related properties of GaN nanosheets are scarce, as previous small-scale GaN investigations have mainly concentrated on nanowires and nanotubes. Here, we report a strategy for growing 2D GaN nanosheets using chemical vapor deposition on Ga/W liquid-phase substrates. Additionally, utilizing scanning probe techniques, it has been observed that 700 nm-thick GaN nanosheets demonstrate a piezoelectric constant of deff33 = 1.53 ± 0.21 pm V-1 and possess the capability to effectively modulate the Schottky barrier. The piezoelectric characteristics of 2D GaN are offering new options for innovative applications in various fields, including energy harvesting, electronics, sensing, and communications.

Recent Advances in Antimony Selenide Photodetectors

Photodetectors (PDs) rapidly capture optical signals and convert them into electrical signals, making them indispensable in a variety of applications including imaging, optical communication, remote sensing, and biological detection. Recently, antimony selenide (Sb2Se3) has achieved remarkable progress due to its earth-abundant, low toxicity, low price, suitable bandgap width, high absorption coefficient, and unique structural characteristics. Sb2Se3 has been extensively studied in solar cells, but there's a lack of timely updates in the field of PDs. A literature review based on Sb2Se3 PDs is urgently warranted. This review aims to provide a concise understanding of the latest progress in Sb2Se3 PDs, with a focus on the basic characteristics and the performance optimization for Sb2Se3 photoconductive-type and photodiode-type detectors, including nanostructure regulation, process optimization, and stability improvement of flexible devices. Furthermore, the application progresses of Sb2Se3 PDs in heart rate monitoring, and monolithic-integrated matrix images are introduced. Finally, this review presents various strategies with potential and feasibility to address challenges for the rapid development and commercial application of Sb2Se3 PDs.

Integrating ultraviolet sensing and memory functions in gallium nitride-based optoelectronic devices

Optoelectronic devices present a promising avenue for emulating the human visual system. However, existing devices struggle to maintain optical image information after removing external stimuli, preventing the integration of image perception and memory. The development of optoelectronic memory devices offers a feasible solution to bridge this gap. Simultaneously, the artificial vision for perceiving and storing ultraviolet (UV) images is particularly important because UV light carries information imperceptible to the naked eye. This study introduces a multi-level UV optoelectronic memory based on gallium nitride (GaN), seamlessly integrating UV sensing and memory functions within a single device. The embedded SiO2 side-gates around source and drain regions effectively extend the lifetime of photo-generated carriers, enabling dual-mode storage of UV signals in terms of threshold voltage and ON-state current. The optoelectronic memory demonstrates excellent robustness with the retention time exceeding 4 × 104 s and programming/erasing cycles surpassing 1 × 105. Adjusting the gate voltage achieves five distinct storage states, each characterized by excellent retention, and efficiently modulates erasure times for rapid erasure. Furthermore, the integration of the GaN optoelectronic memory array successfully captures and stably stores specific UV images for over 7 days. The study marks a significant stride in optoelectronic memories, showcasing their potential in applications requiring prolonged retention.

Self-powered photodetectors: a device engineering perspective

Nanoscale self-powered photodetectors that can work without any external source of energy are required for future applications. There is potential demand for these devices in areas like wireless surveillance, weather forecasting, remote monitoring, and places where the availability of power is scarce. This study provides an overview of state of the art research trends and improvements in self-powered photodetectors. A device engineering perspective for improvement in the figures of merit has been presented along with a description of additional effects like pyro-phototronic, piezo-phototronic, and surface plasmonics.

Optically pumped flexible GaN-based ultraviolet VCSELs

Flexible optoelectronic platforms, which integrate optoelectronic devices on a flexible substrate, are promising in more complex working environments benefiting from the mechanical flexibility. Herein, for the first time to the best of our knowledge, a flexible GaN-based vertical cavity surface-emitting laser (VCSEL) in the ultraviolet A (UVA) range was demonstrated by using a thin-film transfer process based on laser lift-off (LLO) and spin-coating of a flexible substrate. The lasing wavelength is 376.5 nm with a linewidth of 0.6 nm and threshold energy of 98.4 nJ/pulse, corresponding to a threshold energy density of 13.9 mJ/cm2. The flexible substrate in this study is directly formed by spin-coating of photosensitive epoxy resin, which is much simplified and cost-effective, and a 2-in. wafer scale GaN-based membrane can be successfully transferred to a flexible substrate through this method. Such flexible UVA VCSELs are promising for the development of next-generation flexible and wearable technologies.

Polarity reversal and strain modulation of Janus MoSSe/GaN polar semiconductor heterostructures

Beyond three-dimensional (3D) architectures, polar semiconductor heterostructures are developing in the direction of two-dimensional (2D) scale with mix-dimensional integration for novel properties and multifunctional applications. Herein, we stacked 2D Janus MoSSe and 3D wurtzite GaN polar semiconductors to construct MoSSe/GaN polar heterostructures by polarity configurations. The structural stability was enhanced as binding energy changed from -0.08 eV/-0.17 eV in the N polarity to -0.24 eV/-0.42 eV in the Ga polarity. In particular, the polarity reversal of GaN in contact with Janus MoSSe not only determined the charge transfer direction but also significantly increased the electrostatic potential difference from 0.71 eV/0.78 eV in the N polarity to 3.13 eV/2.24 eV in the Ga polarity. In addition, strain modulation was further utilized to enhance interfacial polarization and tune the electronic energy band profiles of Janus MoSSe/GaN polar heterostructures. By applying in-plane biaxial strains, the AA and AA' polarity configurations induced band alignment transition from type I (tensile) to type II (compressive). As a result, both the polarity reversal and strain modulation provide effective ways for the multifunctional manipulation and facile design of Janus MoSSe/III-nitrides polar heterostructures, which broaden the Janus 2D/3D polar semiconducting devices in advanced electronics, optoelectronics, and energy harvesting applications.

Broadband ultraviolet plasmonic enhanced AlGaN/GaN heterojunction photodetectors with close-packed Al nanoparticle arrays

Plasmonic metallic nanostructures could concentrate optical fields into nanoscale volumes and support efficient light scattering and absorption, which therefore stimulates the continuing development of advanced plasmonic-assisted semiconductor photodetectors. In this work, by fabricating Al nanoparticle (NP) arrays in AlGaN surface using the AAO template transferring method, significant broadband ultraviolet (UV) photoresponse enhancement was demonstrated on AlGaN/GaN heterojunction photodetectors. By deliberately designing the close-packed Al NP arrays, the broadband UV plasmonic resonance with large optical field absorption and strong interface field enhancement are enabled, hence, the highest responsivity exceeding 8.1 A W-1 and maximum external quantum efficiency of 3500% was obtained at the resonance wavelength 292 nm, revealing more than 80 times the excellent enhancement in responsivity. Specifically, owing to coupling among NPs at the Al/AlGaN interface, the smaller size Al NP array exhibits an excellent photoresponse enhancement encompassing the entire UV band compared to the relatively larger size Al NP array. In addition, different photoresponse enhancements depending on the applied bias were observed. The Al NPs detector also demonstrates a fast photoresponse with a rise time of around 60 ms and a relatively long fall time of 1.42 s. This work could be of great significance for gaining a low and efficient approach to achieve plasmonic-empowered heterojunction broadband UV detectors.

InGaN micro-LED array with integrated emission and detection functions for color detection application

InGaN-based micro-LEDs can detect and emit optical signals simultaneously, owing to their overlapping emission and absorption spectra, enabling color detection. In this paper, we fabricated a green InGaN-based micro-LED array with integrated emission and detection functions. On the back side of the integrated device, when the 80 μm micro-LED emitted light, the 200 μm LED could receive reflected light to accomplish color detection. The spacing between the 80 μm and the 200 μm micro-LEDs was optimized to be 1 mm to reduce the effect of the direct light transmitted through the n-GaN layer without reflection. The integrated device shows good detection performance for different colors and skin colors, even in a dark environment. In addition, light can be emitted from the top side of the device. Utilization of light from both sides of the integrated device provides the possibility of its application in display, communication, and detection on the different sides.

Emerging Trends in 2D TMDs Photodetectors and Piezo-Phototronic Devices

The piezo-phototronic effect shows promise with regards to improving the performance of 2D semiconductor-based flexible optoelectronics, which will potentially open up new opportunities in the electronics field. Mechanical exfoliation and chemical vapor deposition (CVD) influence the piezo-phototronic effect on a transparent, ultrasensitive, and flexible van der Waals (vdW) heterostructure, which allows the use of intrinsic semiconductors, such as 2D transition metal dichalcogenides (TMD). The latest and most promising 2D TMD-based photodetectors and piezo-phototronic devices are discussed in this review article. As a result, it is possible to make flexible piezo-phototronic photodetectors, self-powered sensors, and higher strain tolerance wearable and implantable electronics for health monitoring and generation of piezoelectricity using just a single semiconductor or vdW heterostructures of various nanomaterials. A comparison is also made between the functionality and distinctive properties of 2D flexible electronic devices with a range of applications made from 2D TMDs materials. The current state of the research about 2D TMDs can be applied in a variety of ways in order to aid in the development of new types of nanoscale optoelectronic devices. Last, it summarizes the problems that are currently being faced, along with potential solutions and future prospects.

Soft Fiber Electronics Based on Semiconducting Polymer

Fibers, originating from nature and mastered by human, have woven their way throughout the entire history of human civilization. Recent developments in semiconducting polymer materials have further endowed fibers and textiles with various electronic functions, which are attractive in applications such as information interfacing, personalized medicine, and clean energy. Owing to their ability to be easily integrated into daily life, soft fiber electronics based on semiconducting polymers have gained popularity recently for wearable and implantable applications. Herein, we present a review of the previous and current progress in semiconducting polymer-based fiber electronics, particularly focusing on smart-wearable and implantable areas. First, we provide a brief overview of semiconducting polymers from the viewpoint of materials based on the basic concepts and functionality requirements of different devices. Then we analyze the existing applications and associated devices such as information interfaces, healthcare and medicine, and energy conversion and storage. The working principle and performance of semiconducting polymer-based fiber devices are summarized. Furthermore, we focus on the fabrication techniques of fiber devices. Based on the continuous fabrication of one-dimensional fiber and yarn, we introduce two- and three-dimensional fabric fabricating methods. Finally, we review challenges and relevant perspectives and potential solutions to address the related problems.

Transferable Ga2O3 Membrane for Vertical and Flexible Electronics via One-Step Exfoliation

Transferable Ga₂O₃ thin film membrane is desirable for vertical and flexible solar-blind photonics and high-power electronics applications. However, Ga₂O₃ epitaxially grown on rigid substrates such as sapphire, Si, and SiC hinders its exfoliation due to the strong covalent bond between Ga₂O₃ and substrates, determining its lateral device configuration and also hardly reaching the ever-increasing demand for wearable and foldable applications. Mica substrate, which has an atomic-level flat surface and high-temperature tolerance, could be a good candidate for the van der Waals (vdW) epitaxy of crystalline Ga₂O₃ membrane. Beyond that, benefiting from the weak vdW bond between Ga₂O₃ and mica substrate, in this work, the Ga₂O₃ membrane is exfoliated and transferred to arbitrary flexible and adhesive tape, allowing for the vertical and flexible electronic configuration. This straightforward exfoliation method is verified to be consistent and reproducible by the transfer and characterization of thick (∼380 nm)/thin (∼95 nm) κ-phase Ga₂O₃ and conductive n-type β-Ga₂O₃. Vertical photodetectors are fabricated based on the exfoliated Ga₂O₃ membrane, denoting the peak response at ∼250 nm. Through the integration of Ti/Au Ohmic contact and Ni/Ag Schottky contact electrode, the vertical photodetector exhibits self-powered photodetection behavior with a responsivity of 17 mA/W under zero bias. The vdW-bond-assisted exfoliation of the Ga₂O₃ membrane demonstrated here could provide enormous opportunities in the pursuit of vertical and flexible Ga₂O₃ electronics.

Lead-Free Perovskite Cs3Bi2I9-Derived Electroactive PVDF Composite-Based Piezoelectric Nanogenerators for Physiological Signal Monitoring and Piezo-Phototronic-Aided Strain Modulated Photodetectors

In recent years, lead-free perovskite materials are exponentially emerging in photovoltaic and optoelectronic applications due to their low toxicity and superior optical properties. On the other hand, the demand for flexible, wearable, and lightweight optoelectronic devices is significantly growing in sensor and actuator technologies. In this scenario, lead-free perovskite-based flexible piezoelectric polymer composites have sparked considerable attention in this field due to their excellent piezo-, pyro-, ferroelectric, and photovoltaic properties. Thus, in this work, a long-term stable lead-free Cs₃Bi₂I₉-PVDF composite is introduced. The in situ growth of the Cs₃Bi₂I₉ perovskite induces 92% yield of the electroactive phase in the PVDF matrix. The possible mechanism behind the electroactive β-phase transformation is presented via interfacial interactions of PVDF moieties with the Cs₃Bi₂I₉ (CBI) perovskite, which also give rise to long-term environmental stability. Next, a piezoelectric nanogenerator (PNG) has been fabricated with the Cs₃Bi₂I₉-PVDF composite for mechanical energy harvesting, biophysiological motion monitoring, and voice recognitions that have potential utility in the health-care sector. Furthermore, a photodetector is developed to realize the piezo-phototronic effect. It exhibits a fast photoswitching behavior with rise and decay times of 141 and 278 ms, respectively. Thus, it is confirmed that the flexible Cs₃Bi₂I₉-PVDF composite has shown tremendous potential to be used as an optical signal-modulated piezo-responsive wearable sensor.

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.

Flexible 1.3 μm photodetector fabricated with InN nanowires and graphene on overhead projector transparency sheet

We report the first demonstration of flexible photodetectors, operating at the wavelength window of 1.3 μm, fabricated with InN nanowires (NWs) and graphene on an overhead projector transparency (OHP) sheet. The InN NWs, used as an absorption medium for the device, were formed on a Si substrate and exhibited strong emission with a peak wavelength of 1.3 μm at room temperature. They were randomly and horizontally embedded in the graphene sandwich structure functioned as a carrier channel. The photocurrent and photoresponsivity of the flexible photodetector were found to be 1.17 mA and 0.48 A W^-1, respectively, at a voltage of 1 V and a light intensity of 60 mW cm^-2 of a xenon lamp. The photocurrent measured when the photodetector was bent under a strain of 3% was 1.15 mA, which corresponds to 98.3% compared to that before bending. Moreover, the photocurrent and photoresponsivity of the flexible photodetector measured after the 200 cyclic-bending tests are comparable to those measured before bending.

Mitigating the Negative Piezoelectricity in Organic/Inorganic Hybrid Materials for High-performance Piezoelectric Nanogenerators

The conversion of ecofriendly waste energy into useable electrical energy is of significant interest for energy harvesting technologies. Piezoelectric nanogenerators based on organic/inorganic hybrid materials are a key promising technology for harvesting mechanical energy due to their high piezoelectric coefficient and good mechanical flexibility. However, the negative piezoelectric effect of the polymer component in composite devices severely undermines its overall piezoelectricity, compromising the output performance of PVDF-based piezoelectric hybrid nanogenerators. Here, to conquer this, we report a two-step poling schedule to orient the dipoles of organic and inorganic components in the same direction. The optimized nanogenerator delivers a combination of high piezoelectric coefficient, great output performance, and remarkable stability. The isotropic piezoelectricity in the composite device collaborates to output a maximum voltage of 110 V and a power density of 7.8 μW cm^-2. This strategy is also applied to elevate the piezoelectricity of other organic/inorganic-hybrid-based nanogenerators, substantiating its universal applicability for composite piezoelectric nanogenerators. This study presents a feasible strategy for enhancing the effective output capability of composite nanogenerator technologies.

Sensitive Silicon Nanowire Ultraviolet B Photodetector Induced by Leakage Mode Resonances

Ultraviolet photodetectors (UVPDs) have played an important role both in civil and military applications. While various studies have shown that traditional UVPDs based on wide-band-gap semiconductors (WBSs) have excellent device performances, it is, however, undeniable that the practical application of WBS-based UVPDs is largely limited by the relatively high fabrication cost. In this work, we propose a new silicon nanowire (Si NW) UVPD that is very sensitive to UVB light illumination. The Si NWs with a diameter of about 36 nm are fabricated by a metal-assisted chemical etching method. Performance analysis revealed that the Si NW device was only sensitive to UVB light and almost blind to illumination in the visible and near-infrared regions. Such abnormal spectral selectivity was associated with the leakage mode resonances (LMRs) of the small diameter, according to our theoretical simulation. Under 300 nm illumination, the responsivity, external quantum efficiency, and specific detectivity were estimated to be 10.2 AW^-1, 4.22 × 10³%, and 2.14 × 10¹⁰ Jones, respectively, which were comparable to or even higher than those of some WBS-based UVPDs. These results illustrate that the small dimension Si NWs are potential building blocks for low-cost and high-performance UVPDs in the future.

High Performance, Stable, and Flexible Piezoelectric Nanogenerator Based on GaN:Mg Nanowires Directly Grown on Tungsten Foil

Rapid development of micro-electromechanical systems increases the need for flexible and durable piezoelectric nanogenerators (f-PNG) with high output power density. In this study, a high-performance, flexible, and highly stable f-PNG is prepared by directly growing the Mg-doped semi-insulating GaN nanowires (NWs) on a 30-µm-thick tungsten foil using vapor-liquid-solid growth mechanism. The direct growth of NWs on metal foil extends the overall lifetime of the f-PNG. The semi-insulating GaN NWs significantly enhance the piezoelectric performance of the f-PNG by reducing free electron density. Additionally, the direct integration of NWs on the tungsten foil improves the conductivity, resulting in current enhancement (2.5 mA) with an output power density of 13 mW cm^-2 . The piezoelectric performance of the f-PNG is investigated under several bending angles, actuation frequencies, continuous vibrations, and airflow velocities. The maximum output voltage exhibited by the f-PNG is 20 V at a bending angle of 155°. The f-PNG is connected to the backside of an index finger to monitor finger bending behavior by changing the current density. Depending on its flexibility and sensitivity, the f-PNG can be used as a health-monitoring sensor to be mounted on joints (fingers, hands, elbows, and knees) to monitor their repeated bending and relaxation.

Advances in Self-Powered Ultraviolet Photodetectors Based on P-N Heterojunction Low-Dimensional Nanostructures

Self-powered ultraviolet (UV) photodetectors have attracted considerable attention in recent years because of their vast applications in the military and civil fields. Among them, self-powered UV photodetectors based on p-n heterojunction low-dimensional nanostructures are a very attractive research field due to combining the advantages of low-dimensional semiconductor nanostructures (such as large specific surface area, excellent carrier transmission channel, and larger photoconductive gain) with the feature of working independently without an external power source. In this review, a selection of recent developments focused on improving the performance of self-powered UV photodetectors based on p-n heterojunction low-dimensional nanostructures from different aspects are summarized. It is expected that more novel, dexterous, and intelligent photodetectors will be developed as soon as possible on the basis of these works.

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).

Recent Advances in Flexible Tactile Sensors for Intelligent Systems

Tactile sensors are an important medium for artificial intelligence systems to perceive their external environment. With the rapid development of smart robots, wearable devices, and human-computer interaction interfaces, flexible tactile sensing has attracted extensive attention. An overview of the recent development in high-performance tactile sensors used for smart systems is introduced. The main transduction mechanisms of flexible tactile sensors including piezoresistive, capacitive, piezoelectric, and triboelectric sensors are discussed in detail. The development status of flexible tactile sensors with high resolution, high sensitive, self-powered, and visual capabilities are focused on. Then, for intelligent systems, the wide application prospects of flexible tactile sensors in the fields of wearable electronics, intelligent robots, human-computer interaction interfaces, and implantable electronics are systematically discussed. Finally, the future prospects of flexible tactile sensors for intelligent systems are proposed.

The effect of electrode shape on Schottky barrier and electric field distribution of flexible ZnO photodiode

In this study, the effect of electrode shape difference on the height of the Schottky barrier and the electric field in flexible photodiodes (PDs) has been investigated. For this purpose, three different electrode designs were prepared on three flexible FR4 layers that were coated with Zinc Oxide (ZnO). The printing circuit board (PCB) method was used to create these copper electrodes. The asymmetry of the PD electrodes and the difference in the height of the Schottky barrier has led to the creation of self-powered PDs. The effect of the amount and shape of the distribution of internal electric fields generated in the PDs and its effect on the parameters of the PDs has been investigated with the help of simulations performed in COMSOL software. The photocurrent of the sample with circular and rectangular electrodes was equal to 470 µA in 15 V bias, which was twice as good as a sample with an interdigitated MSM structure. Also, this sample had the best response time among these three samples, which was equal to 440 ms.

High Performance Flexible Visible-Blind Ultraviolet Photodetectors with Two-Dimensional Electron Gas Based on Unconventional Release Strategy

Interdigitated photodetectors (IPDs) based on the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface have gained prominence as high sensitivity ultraviolet (UV) PDs due to their excellent optoelectronic performance. However, most 2DEG-IPDs have been built on rigid substrates, thus limiting the use of 2DEG-IPDs in flexible and wearable applications. In this paper, we have demonstrated high performance flexible AlGaN/GaN 2DEG-IPDs using AlGaN/GaN 2DEG heterostructure membranes created from 8 in. AlGaN/GaN on insulator (AlGaN/GaNOI) substrates. The interdigitated AlGaN/GaN heterostructure has been engineered to reduce dark current by disconnecting the conductive channel at the heterostructure interface. Photocurrent has been also boosted by the escaped carriers from the 2DEG layer. Therefore, the utilization of a 2DEG layer in transferrable AlGaN/GaN heterostructure membranes offers great promises for high performance flexible 2DEG-IPDs for advanced UV detection systems that are critically important in myriad biomedical and environmental applications.

Fabrication of GaN nano-towers based self-powered UV photodetector

The fabrication of unique taper-ended GaN-Nanotowers structure based highly efficient ultraviolet photodetector is demonstrated. Hexagonally stacked, single crystalline GaN nanocolumnar structure (nanotowers) grown on AlN buffer layer exhibits higher photocurrent generation due to high quality nanotowers morphology and increased surface/volume ratio which significantly enhances its responsivity upon ultraviolet exposure leading to outstanding performance from the developed detection device. The fabricated detector display low dark current (~ 12 nA), high I_Light/I_Dark ratio (> 10⁴), fast time-correlated transient response (~ 433 µs) upon ultraviolet (325 nm) illumination. A high photoresponsivity of 2.47 A/W is achieved in self-powered mode of operation. The reason behind such high performance could be attributed to built-in electric field developed from a difference in Schottky barrier heights will be discussed in detail. While in photoconductive mode, the responsivity is observed to be 35.4 A/W @ − 3 V along with very high external quantum efficiency (~ 10⁴%), lower noise equivalent power (~ 10^–13 WHz^−1/2) and excellent UV–Vis selectivity. Nanotower structure with lower strain and dislocations as well as reduced trap states cumulatively contributed to augmented performance from the device. The utilization of these GaN-Nanotower structures can potentially be useful towards the fabrication of energy-efficient ultraviolet photodetectors.

Stretchable Inorganic GaN-Nanowire Photosensor with High Photocurrent and Photoresponsivity

To effectively implement wearable systems, their constituent components should be made stretchable. We successfully fabricated highly efficient stretchable photosensors made of inorganic GaN nanowires (NWs) as light-absorbing media and graphene as a carrier channel on polyurethane substrates using the pre-strain method. When a GaN-NW photosensor was stretched at a strain level of 50%, the photocurrent was measured to be 0.91 mA, corresponding to 87.5% of that (1.04 mA) obtained in the released state, and the photoresponsivity was calculated to be 11.38 A/W. These photosensors showed photocurrent and photoresponsivity levels much higher than those previously reported for any stretchable semiconductor-containing photosensor. To explain the superior performances of the stretchable GaN-NW photosensor, it was approximated as an equivalent circuit with resistances and capacitances, and in this way, we analyzed the behavior of the photogenerated carriers, particularly at the NW-graphene interface. In addition, the buckling phenomenon typically observed in organic-based stretchable devices fabricated using the pre-strain method was not observed in our photosensors. After a 1000-cycle stretching test with a strain level of 50%, the photocurrent and photoresponsivity of the GaN-NW photosensor were measured to be 0.96 mA and 11.96 A/W, respectively, comparable to those measured before the stretching test. To evaluate the potential of our stretchable devices in practical applications, the GaN-NW photosensors were attached to the proximal interphalangeal joint of the index finger and to the back of the wrist. Photocurrents of these photosensors were monitored during movements made about these joints.

Toward Large-Scale Ga2O3 Membranes via Quasi-Van Der Waals Epitaxy on Epitaxial Graphene Layers

Epitaxial growth using graphene (GR), weakly bonded by van der Waals force, is a subject of interest for fabricating technologically important semiconductor membranes. Such membranes can potentially offer effective cooling and dimensional scale-down for high voltage power devices and deep ultraviolet optoelectronics at a fraction of the bulk-device cost. Here, we report on a large-area β-Ga₂O₃ nanomembrane spontaneous-exfoliation (1 cm × 1 cm) from layers of compressive-strained epitaxial graphene (EG) grown on SiC, and demonstrated high-responsivity flexible solar-blind photodetectors. The EG was favorably influenced by lattice arrangement of SiC, and thus enabled β-Ga₂O₃ direct-epitaxy on the EG. The β-Ga₂O₃ layer was spontaneously exfoliated at the interface of GR owing to its low interfacial toughness by controlling the energy release rate through electroplated Ni layers. The use of GR templates contributes to the seamless exfoliation of the nanomembranes, and the technique is relevant to eventual nanomembrane-based integrated device technology.

Epitaxial Lift-Off of Flexible GaN-Based HEMT Arrays with Performances Optimization by the Piezotronic Effect

High-electron-mobility transistors (HEMTs) are a promising device in the field of radio frequency and wireless communication. However, to unlock the full potential of HEMTs, the fabrication of large-size flexible HEMTs is required. Herein, a large-sized (> 2 cm²) of AlGaN/AlN/GaN heterostructure-based HEMTs were successfully stripped from sapphire substrate to a flexible polyethylene terephthalate substrate by an electrochemical lift-off technique. The piezotronic effect was then induced to optimize the electron transport performance by modulating/tuning the physical properties of two-dimensional electron gas (2DEG) and phonons. The saturation current of the flexible HEMT is enhanced by 3.15% under the 0.547% tensile condition, and the thermal degradation of the HEMT was also obviously suppressed under compressive straining. The corresponding electrical performance changes and energy diagrams systematically illustrate the intrinsic mechanism. This work not only provides in-depth understanding of the piezotronic effect in tuning 2DEG and phonon properties in GaN HEMTs, but also demonstrates a low-cost method to optimize its electronic and thermal properties.

Hybrid Device Architecture Using Plasmonic Nanoparticles, Graphene Quantum Dots, and Titanium Dioxide for UV Photodetectors

In this work, a nanoscale device architecture is demonstrated for a UV photodetector application on sapphire (0001), incorporating the plasmonic hybrid nanoparticles (HNPs), graphene quantum dots (GQDs), and titanium oxide (TiO₂) for the first time. The hybrid GQDs/TiO₂/HNPs photodetector exhibits the photocurrent of 1.58 × 10^-5 A under the 1.64 mW/mm² of 275 nm illumination at 10 V, which is around two order increase from the bare TiO₂ device. The proposed architecture demonstrates a low dark current of ∼1 × 10^-10 A at 10 V and thus the device demonstrates an excellent photo to dark current ratio along with the improved rise and fall time on the order of several hundred millisecond. The enhanced performance of device architecture is attributed to the efficient utilization of localized surface plasmon resonance (LSPR) induced hot carriers as well as scattered photons from the plasmonic HNPs that are fully encapsulated by the photoactive TiO₂ layers. Furthermore, the addition of GQDs on the TiO₂ can offer an additional photon absorption pathway. The proposed hybrid architecture of GQDs/TiO₂/HNPs demonstrates the integration of the photon absorption and carrier transfer properties of plasmonic HNPs, GQDs, and TiO₂ for an enhanced ultraviolet (UV) photoresponse. The photocurrent enhancement mechanisms of the hybrid device architecture are thoroughly investigated based on the finite-difference time domain (FDTD) simulation along with the energy band analysis. This work demonstrates a great potential of the hybrid device architecture for high-performance UV photodetectors.

Tailoring of a visible-light-absorbing biaxial ferroelectric towards broadband self-driven photodetection

In terms of strong light-polarization coupling, ferroelectric materials with bulk photovoltaic effects afford a promising avenue for optoelectronic devices. However, due to severe polarization deterioration caused by leakage current of photoexcited carriers, most of ferroelectrics are merely capable of absorbing 8-20% of visible-light spectra. Ferroelectrics with the narrow bandgap (<2.0 eV) are still scarce, hindering their practical applications. Here, we present a lead-iodide hybrid biaxial ferroelectric, (isopentylammonium)₂(ethylammonium)₂Pb₃I₁₀, which shows large spontaneous polarization (~5.2 μC/cm²) and a narrow direct bandgap (~1.80 eV). Particularly, the symmetry breaking of 4/mmmFmm2 species results in its biaxial attributes, which has four equivalent polar directions. Accordingly, exceptional in-plane photovoltaic effects are exploited along the crystallographic [001] and [010] axes directions inside the crystallographic bc-plane. The coupling between ferroelectricity and photovoltaic effects endows great possibility toward self-driven photodetection. This study sheds light on future optoelectronic device applications.

A reduced-dimensional polar hybrid perovskite for self-powered broad-spectrum photodetection

Polar hybrid perovskites have been explored for self-powered photodetection benefitting from prominent transport of photo-induced carriers and the bulk photovoltaic effect (BPVE). However, these self-powered photodetection ranges are relatively narrow depending on their intrinsic wide bandgaps (>2.08 eV), and the realization of broad-spectrum self-powered photodetection is still a difficult task. Herein, we successfully obtained a polar multilayered perovskite, (I-BA)2(MA)2Pb3I10 (IMP, MA+ = methylammonium and I-BA+ = 4-iodobutylammonium), via rational dimension reduction of CH3NH3PbI3. It features the narrowest bandgap of 1.71 eV in a BPV material. As a consequence, the integration of narrow bandgap and BPVE causes the self-powered photodetection to extend to 724 nm for IMP, and a repeatable photovoltaic current reaching 1.0 μA cm-2 is acquired with a high "on/off" ratio of ∼103 and photodetectivity (∼109 Jones) at zero bias. This innovative research provides a foothold for adjusting the physical properties of hybrid perovskites and will expand their potential for self-powered broad-spectrum detection.

Epitaxial growth mechanisms of single-crystalline GaN on single-crystalline graphene

Dangling bonds, an AlN nucleation layer and high selectivity of AlN nucleation are prerequisites for the epitaxy of single-crystalline GaN on a single-crystalline graphene template.

Multieffect Coupled Nanogenerators

With the advent of diverse electronics, the available energy may be light, thermal, and mechanical energies. Multieffect coupled nanogenerators (NGs) exhibit strong ability to harvest ambient energy by integrating various effects comprising piezoelectricity, pyroelectricity, thermoelectricity, optoelectricity, and triboelectricity into a standalone device. Interaction of multitype effects can promote energy harvesting and conversion by modulating charge carriers' behaviour. Multieffect coupled NGs stand for a vital group of energy harvesters, supporting the advances of an electronic device and promoting the resolution of energy crisis. The matchless versatility and high reliability of multieffect coupled NGs make them main candidates for integration in complicated arrays of the electronic device. Multieffect coupled NGs can also be employed as a variety of self-powered sensors due to their rapid response, high accuracy, and high responsivity. This article reviews the latest achievements of multieffect coupled NGs. Fundamentals mainly including basic theory and materials of interest are covered. Advanced device design and output characteristics are introduced. Potential applications are described, and future development is discussed.

Aluminum Plasmonics Enriched Ultraviolet GaN Photodetector with Ultrahigh Responsivity, Detectivity, and Broad Bandwidth

Plasmonics have been well investigated on photodetectors, particularly in IR and visible regimes. However, for a wide range of ultraviolet (UV) applications, plasmonics remain unavailable mainly because of the constrained optical properties of applicable plasmonic materials in the UV regime. Therefore, an epitaxial single-crystalline aluminum (Al) film, an abundant metal with high plasma frequency and low intrinsic loss is fabricated, on a wide bandgap semiconductive gallium nitride (GaN) to form a UV photodetector. By deliberately designing a periodic nanohole array in this Al film, localized surface plasmon resonance and extraordinary transmission are enabled; hence, the maximum responsivity (670 A W-1) and highest detectivity (1.48 × 1015 cm Hz1/2 W-1) is obtained at the resonance wavelength of 355 nm. In addition, owing to coupling among nanoholes, the bandwidth expands substantially, encompassing the entire UV range. Finally, a Schottky contact is formed between the single-crystalline Al nanohole array and the GaN substrate, resulting in a fast temporal response with a rise time of 51 ms and a fall time of 197 ms. To the best knowledge, the presented detectivity is the highest compared with those of other reported GaN photodetectors.

Tailoring Artificial Mode to Enable Cofired Integration of Shear-type Piezoelectric Devices

Low-temperature cofired ceramic technology is the prerequisite for producing advanced integrated piezoelectric devices that enable modern micro-electromechanical systems because of merits such as high level of compactness and ultralow drive voltage. However, piezoceramic structure with shear-type outputs, as a most fundamental functional electronic element, has never been successfully fabricated into multilayer form by the cofired method for decades. Technical manufacture requirements of parallel applied electric fields and polarization are theoretically incompatible with intrinsically orthogonal orientations in naturally occurring shear modes. Herein, inspired by the philosophy of building metamaterial from identical unit cells, an artificial prototype device with distinctive patterned electrodes and arrayed piezoceramic subunits is designed and fabricated, which is proved to perfectly generate synthetic face shear deformation. At the same drive voltage, an enhanced shear-type displacement output by over an order of magnitude is observed beyond previous d15-mode bulk elements. Further results of guided wave-based structural health monitoring and force sensing confirm that the methodology wipes out a tough piezoelectric technique barrier, and promises to fundamentally enlighten advances of integrated shear-mode piezoelectric devices for augmented actuation, sensing, and transduction applications.

Strain-Controlled Flexible Graphene/GaN/PDMS Sensors Based on the Piezotronic Effect

Using simple graphene transfer and the laser lift-off process for a non-centrosymmetric GaN layer on a flexible polydimethylsiloxane (PDMS) substrate, the piezotronic effect by strain-induced current-voltage measurements at the two end points is studied. By inducing compressive strain on the flexible graphene/GaN/PDMS sensor, the Schottky barrier between the graphene and GaN/PDMS heterojunction can be electro-mechanically modulated by the piezotronic effect. It is observed that the flexible graphene/GaN/PDMS sensor is sensitive to various applied compressive and tensile strains in the positive/negative bias scans. The sensor is extremely sensitive to a compressive strain of -0.1% with a gauge factor of 13.48, which is 3.7 times higher than that of a standard metal strain gauge. Furthermore, the sharp response of the flexible graphene/GaN/PDMS sensor under the -0.1% compressive strain is also investigated. The results of this study herald the development of commercially viable large-scale flexible/wearable strain sensors based on the strain-controlled piezotronic effect in future investigations.

Visible or Near-Infrared Light Self-Powered Photodetectors Based on Transparent Ferroelectric Ceramics

Transparent ferroelectrics, with promising prospects in transparent optoelectronic devices, have unique advantages in self-powered photodetection. The self-powered photodetectors based on the photovoltaic effect have quicker responses and higher stability compared with those based on the pyroelectric effect. However, the ferroelectric ceramics previously applied are always opaque and have no infrared light-stimulated photovoltaic effect. Thus, it would be very meaningful to design photodetectors based on infrared light-stimulated photovoltaic effect and/or transparent ferroelectric ceramics. In this work, highly optical transparent pristine lead lanthanum zirconate titanate (PLZT) and band gap-engineered Ni-doped PLZT ceramics with excellent piezoelectric/ferroelectric properties were prepared by hot-pressing sintering. Stable and excellent photovoltaic performance was obtained for pristine PLZT and band gap-engineered PLZT. The value of short-circuit current density is at least 2 orders of magnitude larger than those in PLZT reported in previous works. The transparent PLZT and Ni-doped PLZT ferroelectric ceramics are applied as self-powered photodetectors for the first time for 405 nm and near-infrared light, respectively. The devices based on PLZT under 405 nm light exhibit high detectivity (7.15 × 10⁷ Jones) and quick response (9.5 ms for rise and 11.5 ms for decay), and those devices based on Ni-doped PLZT, under near-infrared light filtered from AM 1.5 G simulated sunlight, also exhibit high detectivity (6.86 × 10⁷ Jones) and short response time (8.5 ms), both presenting great potential for future transparent photodetectors.

Flexible Self-Powered Real-Time Ultraviolet Photodetector by Coupling Triboelectric and Photoelectric Effects

The portable UV photodetector is used to timely remind humans of overexposure to UV radiation. However, the traditional UV photodetector cannot meet the practical demands, and the power supply problem hinders its further development. In this work, we demonstrated a flexible, transparent, and self-powered UV photodetector by coupling of triboelectric and photoelectric effects. The device integrates a flexible ZnO nanoparticle (NP) UV photodetector, a transparent- and flexible-film-based TENG (TFF-TENG), commercial chip resistors, and LEDs on the PET thin film. The TFF-TENG could harvest mechanical energy from finger tapping and sliding motion and power the ZnO NP UV photodetector to realize self-powered detection. The voltage of the constant resistors connected with the UV photodetector in series changes from 0.5 to 19 V under the UV light with power intensities increasing from 0.46 to 21.8 mW/cm², and the voltage variation is reflected by the number of LEDs directly. The excellent flexibility and transparency of the device could extend its application scenarios; for example, such a portable device could be applied to real-time monitoring of the UV radiation to remind humans of intense UV light.

Improved Photoresponse of UV Photodetectors by the Incorporation of Plasmonic Nanoparticles on GaN Through the Resonant Coupling of Localized Surface Plasmon Resonance

Very small metallic nanostructures, i.e., plasmonic nanoparticles (NPs), can demonstrate the localized surface plasmon resonance (LSPR) effect, a characteristic of the strong light absorption, scattering and localized electromagnetic field via the collective oscillation of surface electrons upon on the excitation by the incident photons. The LSPR of plasmonic NPs can significantly improve the photoresponse of the photodetectors. In this work, significantly enhanced photoresponse of UV photodetectors is demonstrated by the incorporation of various plasmonic NPs in the detector architecture. Various size and elemental composition of monometallic Ag and Au NPs, as well as bimetallic alloy AgAu NPs, are fabricated on GaN (0001) by the solid-state dewetting approach. The photoresponse of various NPs are tailored based on the geometric and elemental evolution of NPs, resulting in the highly enhanced photoresponsivity of 112 A W-1, detectivity of 2.4 × 1012 Jones and external quantum efficiency of 3.6 × 104% with the high Ag percentage of AgAu alloy NPs at a low bias of 0.1 V. The AgAu alloy NP detector also demonstrates a fast photoresponse with the relatively short rise and fall time of less than 160 and 630 ms, respectively. The improved photoresponse with the AgAu alloy NPs is correlated with the simultaneous effect of strong plasmon absorption and scattering, increased injection of hot electrons into the GaN conduction band and reduced barrier height at the alloy NPs/GaN interface.

Nested Inverse Opal Perovskite toward Superior Flexible and Self-Powered Photodetection Performance

Flexible and self-powered perovskite photodetectors have attracted tremendous research interests due to their applications in wearable and portable devices. However, the conventional planar structured photodetectors are always accompanied with limited device performance and undesired mechanical stability. Herein, a nested inverse opal (NIO) structured perovskite photodetector via a facile template-assisted spin-coating method is reported. The coupling effect of enhanced light capture, increased carrier transport, and improved perovskite film quality enables NIO device to exhibit superior photoresponse performance. The NIO photodetector exhibits a high responsivity of 473 mA W^-1 and detectivity up to 1.35 × 10¹³ Jones at 720 nm without external bias. The NIO structure can efficiently release mechanical stress during the bending process and the photocurrent has no degradation even after 500 cycles of bending. Moreover, the unencapsulated NIO device can operate for over 16 d under ambient conditions, presenting a significantly enhanced environmental stability compared to the planar device. This work demonstrates that deliberate structural design is an effective avenue for constructing self-powered, flexible, and stable optoelectronic devices.

Photo- and Thermosensitive Polymer Membrane with a Tunable Microstructure Doped with Graphene Oxide Nanosheets and Poly(N-isopropylacrylamide) for the Application of Light-Cleaning

Traditional polymer membranes exhibit a constant structure that makes adjustment of the filtration process difficult, such as flux changing and contaminant cleaning. Inspired by the automatically closing behavior of leaf stomata under strong light, we prepared a membrane with thermo- and photosensitivities, whose microstructure, as well as filtration properties, could be controlled by adjusting the light condition. The membrane was fabricated by the immersion phase inversion method with a casting solution of polyvinylidene fluoride-g-poly(N-isopropylacrylamide) (PVDF-g-PNIPAAm) and graphene oxide (GO) nanosheets. Additionally, the membrane could be heated to a high temperature in a short time under illumination, causing shrinkage of its PNIPAAm chains and expansion of its membrane pores. On the basis of the reversible photoinduced structural transformation, the membrane exhibited a high water gating ratio under the switching of light on/off. Moreover, we proposed a novel and simple method to clear the contaminant from the pores of the membrane via light, which we named "light-cleaning". Light-cleaning had a flux recovery rate of 99.2%, substantially higher than that of back-washing (62%). This work not only extends the controllability and functionality of the polymer membrane but also develops a new membrane cleaning system.

Bioinspired Fluffy Fabric with In Situ Grown Carbon Nanotubes for Ultrasensitive Wearable Airflow Sensor

Recently, electronic skin and smart textiles have attracted considerable attention. Flexible sensors, as a kind of indispensable components of flexible electronics, have been extensively studied. However, wearable airflow sensors capable of monitoring the environment airflow in real time are rarely reported. Herein, by mimicking the spider's fluff, an ultrasensitive and flexible all-textile airflow sensor based on fabric with in situ grown carbon nanotubes (CNTs) is developed. The fabric decorated with fluffy-like CNTs possesses exceptionally large contact area, endowing the airflow sensor with superior properties including ultralow detection limit (≈0.05 m s^-1 ), multiangle airflow differential response (0°-90°), and fast response time (≈1.3 s). Besides, the fluffy fabric airflow sensor can be combined with a pristine fabric airflow sensor to realize highly sensitive detection in a wide airflow range (0.05-7.0 m s^-1 ). Its potential applications including transmitting information according to Morse code by blowing the sensors, monitoring increasing and decreasing airflow velocity, and alerting blind people walking outside about potential hazard induced by nearby fast-moving objects are demonstrated. Furthermore, the airflow sensor can be directly integrated into clothing as stylish designs without sacrificing comfortness. It is believed that the ultrasensitive all-textile airflow sensor holds great promise for applications in smart textiles and wearable electronics.

Ultrasensitive Fiber-Based ZnO Nanowire Network Ultraviolet Photodetector Enabled by the Synergism between Interface and Surface Gating Effects

A flexible UV photodetector with a high on/off ratio is extremely important for environmental sensing, optical communication, and flexible optoelectronic devices. In this work, a flexible fiber-based UV photodetector with an ultrahigh on/off ratio is developed by utilizing the synergism between interface and surface gating effects on a ZnO nanowire network structure. The synergism between two gating effects is realized by the interplay between surface band bending and the Fermi level through the nanowire network structure, which is proved through the control experiments between the ZnO micro/nanowire photodetector and micro/nanowire junction photodetector, and the corresponding Kelvin probe force microscopy (KPFM) measurements. The on/off ratio of the fiber-based ZnO nanowire network UV photodetector reaches 1.98 × 10⁸ when illuminated by 1.0 mW cm^-2 UV light, which is 20 times larger than the largest reported result under the same UV illumination. This new UV sensor also has a high resolution to UV light intensity change in the nW cm^-2 range. Furthermore, when the fiber-based photodetector is curved, it still shows excellent performance as above. This work gives a new effective route for the development of a high-performance UV photodetector or other optoelectronic detection devices.

High photosensitivity and external quantum efficiency photosensors achieved by a cable like nanoarchitecture

The poor intrinsic flexibility of semiconducting ceramic materials hinders their applications in wearable electronics. Here, we present a highly efficient photosensor with extreme levels of bending and repeatable resilience based on cable-like structure. The ZnO@TiO₂ cable-like photosensor demonstrates an ultra-high external quantum efficiency (2.82 × 10⁶%) and photosensitivity (1.27 × 10⁵) upon UV light illumination at 254 nm, and a stability of 85% at the small curvature radius of 0.5 mm. Moreover, the ZnO@TiO₂ photodetector demonstrates extremely stable flexibility over 1000 bending cycles. This specific nanoscale architecture has future potential applications for soft integrated electronics.

Review on Quasi One-Dimensional CdSe Nanomaterials: Synthesis and Application in Photodetectors

During the past 15 years, quasi one-dimensional (1D) Cadmium Selenide (CdSe) nanomaterials have been widely investigated for high-performance electronic and optoelectronic devices, due to the unique geometrical and physical properties. In this review, recent advancements on diverse synthesis methods of 1D CdSe nanomaterials and the application in photodetectors have been illustrated in detail. First, several bottom-up synthesis methods of 1D CdSe nanomaterials have been introduced, including the vapor-liquid-solid method, the solution-liquid-solid method, and electrochemical deposition, etc. Second, the discussion on photodetectors based on 1D CdSe nanomaterials has been divided into three parts, including photodiodes, photoconductors, and phototransistors. Besides, some new mechanisms (such as enhancement effect of localized surface plasmon, optical quenching effect of photoconductivity, and piezo-phototronic effect), which can be utilized to enhance the performance of photodetectors, have also been elaborated. Finally, some major challenges and opportunities towards the practical integration and application of 1D CdSe nanomaterials in photodetectors have been discussed, which need to be further investigated in the future.

Polarization-Driven Self-Powered Photodetection in a Single-Phase Biaxial Hybrid Perovskite Ferroelectric

Self-powered photodetection driven by ferroelectric polarization has shown great potential in next-generation optoelectronic devices. Hybrid perovskite ferroelectrics that combine polarization and semiconducting properties have a promising position within this portfolio. Herein, we demonstrate the realization of self-powered photodetection in a new developed biaxial ferroelectric, (EA)₂ (MA)₂ Pb₃ Br₁₀ (1, EA is ethylammonium and MA is methylammonium), which displays high Curie temperature (375 K), superior spontaneous polarization (3.7 μC cm^-2 ), and unique semiconducting nature. Strikingly, without an external energy supply, 1 exhibits an direction-selectable photocurrent with fascinating attributes including high photocurrent density (≈4.1 μA cm^-2 ), high on/off switching ratio (over 10⁶ ), and ultrafast response time (96/123 μs); such merits are superior to those of the most active ferroelectric oxide BiFeO₃ . Further studies reveal that strong inversion symmetry breaking in 1 provides a desirable driving force for carrier separation, accounting for such electrically tunable self-powered photoactive behaviors. This work sheds light on exploring new multifunctional hybrid perovskites and advancing the design of intelligent photoelectric devices.

Improved Current Extraction of Cu/Si Nanowire Heterojunctions for Self-Powered Photodetecting with Insertion of MoO x Quantum Dots Film

MoO _x quantum dots were inserted between the Si nanowires (SiNWs) and Cu contacts to form the MoO _x /SiNW heterojunctions via the low-temperature solution process. The common Schottky heterojunction of Cu/SiNWs is used as the referred device, and the photoelectric characteristics of Cu/MoO _x /Si structures are detailedly investigated. The results indicate that the inset of MoO _x between Cu and SiNWs obviously enhances photoelectric conversion efficiency from 1.58 to 3.92%, and photodetection characteristics have also improved compared to the referred device. We attribute these experimental findings to the fact that the incorporation of MoO _x quantum dots into the Cu/Si heterojunction could enhance the transport of holes and inhibit the injection of electrons from Si into the top Cu electrode. In addition, it is believed that such an improved performance also comes from the improved optical absorption as well as the optimized carrier transfer and collection capability of MoO _x /SiNW radial heterojunctions.

Piezotronics and Piezo-phototronics of Third Generation Semiconductor Nanowires

With the fast development of nanoscience and nanotechnology in the last 30 years, semiconductor nanowires have been widely investigated in the areas of both electronics and optoelectronics. Among them, representatives of third generation semiconductors, such as ZnO and GaN, have relatively large spontaneous polarization along their longitudinal direction of the nanowires due to the asymmetric structure in their c-axis direction. Two-way or multiway couplings of piezoelectric, photoexcitation, and semiconductor properties have generated new research areas, such as piezotronics and piezo-phototronics. In this review, an in-depth discussion of the mechanisms and applications of nanowire-based piezotronics and piezo-phototronics is presented. Research on piezotronics and piezo-phototronics has drawn much attention since the effective manipulation of carrier transport, photoelectric properties, etc. through the application of simple mechanical stimuli and, conversely, since the design of new strain sensors based on the strain-induced change in semiconductor properties.