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The piezotronics effect utilizes a piezopotential to modulate and control current in piezo-semiconductors. Ferroelectric materials, as a type of piezoelectric materials, possess piezoelectric coefficients that are significantly larger than those found in conventional piezoelectric materials. Here, we propose a strain modulated ferroelectric field-effect transistor (St-FeFET) utilizing external strain instead of gate voltage to achieve ferroelectric modulation, which eliminates the need for gate voltage. By applying a very small strain (0.01%), the St-FeFET can achieve a maximum on-off current ratio of 1250% and realizes a gauge factor (GF) of 1.19 × 106, which is much higher than that of conventional strain sensors. This work proposes a new method for realizing highly sensitive strain sensors and presents innovative approaches to the operation methods of ferroelectric field-effect transistors as well as potential applications for coupling of strain sensors and various devices across different fields. [ABSTRACT FROM AUTHOR]

Recently, a great deal of interest has been focused on developing sensors that can measure both pressure and light. However, traditional sensors are difficult to integrate into silicon (Si)-based integrated circuits. Therefore, it is particularly important to design a sensor that operates on a new principle. In this paper, junction piezotronic transistor (JPT) arrays based on zinc oxide (ZnO) nanowire are demonstrated. And the JPT arrays show high spatial resolution pressure and light mapping with 195 dpi. Because ZnO nanowires are arranged vertically above the p-type Si channel's center of the transistor, the width of the heterojunction depletion region is constricted by the positive piezoelectric potential generated by strained ZnO. In addition, photogenerated charge carriers can be created in the Si channel when JPT is stimulated by light, which increases its electrical conductivity. Consequently, the external pressure and light distribution information can be obtained from the variation in the output current of the device. The prepared JPT arrays can be compatible with Si transistors, which make them highly competitive and make it possible to incorporate both pressure and light sensors into large integrated circuits. This work will contribute to many applications, such as intelligent clothing, human–computer interaction, and electronic skin. [ABSTRACT FROM AUTHOR]

Nitrides are the leading semiconductor material used for the fabrication of high electron mobility transistors (HEMTs). They exhibit piezoelectric properties, which, coupled with their high mechanical stiffness, expand their versatile applications into the fabrication of piezoelectric devices. Today, due to advances in device technology that result in a reduction in the size of individual transistor elements and due to increased structural complexity (e.g., multi-gate transistors), the integration of piezoelectric materials into HEMTs leads to an interesting occurrence, namely acoustic emission from the transistor gate due to piezoelectric effects. This could affect the device's performance, reliability, and durability. However, this phenomenon has not yet been comprehensively described. This paper aims to examine this overlooked aspect of AlGaN/GaN HEMT operation, that is, the acoustic emission from the gate region of the device induced by piezoelectric effects. For this purpose, dedicated test structures were designed, consisting of two narrow 1.7 μm-wide metallization strips placed at distances ranging from 5 μm to 200 μm fabricated in AlGaN/GaN heterostructures to simulate and examine the gate behavior of the HEMT transistor. For comparison, the test device structures were also fabricated on sapphire, which is not a piezoelectric material. Measurements of acoustic and electrical interactions in the microwave range were carried out using the "on wafer" method with Picoprobe's signal–ground–signal (SGS)-type microwave probes. The dependence of reflectance |S11| and transmittance |S21| vs. frequency was investigated, and the coupling capacitance was determined. An equivalent circuit model of the test structure was developed, and finite element method simulation was performed to study the distribution of the acoustic wave in the nitride layers and substrate for different frequencies using Comsol Multiphysics software. At frequencies up to 2–3 GHz, the formation of volume waves and a surface wave, capable of propagating over long distances (in the order of tens of micrometers) was observed. At higher frequencies, the resulting distribution of displacements as a result of numerous reflections and interferences was more complicated. However, there was always the possibility of a surface wave occurrence, even at large distances from the excitation source. At small gate distances, electrical interactions dominate. Above 100 µm, electrical interactions are comparable to acoustic ones. With further increases in distance, weakly attenuated surface waves will dominate. [ABSTRACT FROM AUTHOR]

Recently, a great deal of interest has been focused on developing sensors that can measure both pressure and light. However, traditional sensors are difficult to integrate into silicon (Si)-based integrated circuits. Therefore, it is particularly important to design a sensor that operates on a new principle. In this paper, junction piezotronic transistor (JPT) arrays based on zinc oxide (ZnO) nanowire are demonstrated. And the JPT arrays show high spatial resolution pressure and light mapping with 195 dpi. Because ZnO nanowires are arranged vertically above the p-type Si channel’s center of the transistor, the width of the heterojunction depletion region is constricted by the positive piezoelectric potential generated by strained ZnO. In addition, photogenerated charge carriers can be created in the Si channel when JPT is stimulated by light, which increases its electrical conductivity. Consequently, the external pressure and light distribution information can be obtained from the variation in the output current of the device. The prepared JPT arrays can be compatible with Si transistors, which make them highly competitive and make it possible to incorporate both pressure and light sensors into large integrated circuits. This work will contribute to many applications, such as intelligent clothing, human–computer interaction, and electronic skin.

This study investigates the piezoelectric and piezotronic properties of a novel composite material comprising polyvinylidene fluoride (PVDF) and antimony sulphoiodide (SbSI) nanowires. The material preparation method is detailed, showcasing its simplicity and reproducibility. The material's electrical resistivity, piezoelectric response, and energy-harvesting capabilities are systematically analyzed under various deflection conditions and excitation frequencies. The piezoelectric response is characterized by the generation of charge carriers in the material due to mechanical strain, resulting in voltage output. The fundamental phenomena of charge generation, along with their influence on the material's resistivity, are proposed. Dynamic strain testing reveals the composite's potential as a piezoelectric nanogenerator (PENG), converting mechanical energy into electrical energy. Comparative analyses highlight the composite's power density advantages, thereby demonstrating its potential for energy-harvesting applications. This research provides insights into the interplay between piezoelectric and piezotronic phenomena in nanocomposites and their applicability in energy-harvesting devices. [ABSTRACT FROM AUTHOR]

Herein, the influence of stresses on parameters of 2D electron gas (2DEG) in AlGaN/GaN high‐electron‐mobility transistor‐type heterostructures grown on sapphire substrate by metal–organic vapor‐phase epitaxy technique is presented. The as‐grown heterostructures as well as Schottky diodes fabricated in them are subjected to compressive stress. The custom stressing system induces a homogeneous state of compressive stress in the samples without causing electrical side effects. Time‐dependent heterostructures characteristics of electron concentration, electron mobility, and bandgap width are measured. Additionally, in the case of the Schottky diodes, current–voltage characteristics and charge flow in the contact are measured. The measurements are performed in cycles with and without applied stresses to determine the repeatability of effects and to separate the influence of thermal and electrical factors. Additionally, electrical simulations are performed using APSYS software package. The obtained results lead to conclusions that are different to those reported in existing literature, especially in regard to the time dependence of the measured effects, that is essential to proper explanation. It is also shown that a key role in the change of 2DEG parameters is played by deep surface states and interlayer piezoelectric effects. Finally, the anisotropic character of the derived relations is demonstrated. [ABSTRACT FROM AUTHOR]

Piezoelectricity is the electric charge which accumulates in certain materials in response to mechanical stimuli, while piezoelectric nanogenerators (PENGs) converting mechanical energy into electricity can be widely used for energy harvesting and self-powered systems. The group IV–VI monochalcogenides may exhibit strong piezoelectricity because of their puckered C2v symmetry and electronic structure, making them promising for flexible PENG. Herein, we investigated the synthesis and piezoelectric properties of multilayer SnSe nanosheets grown by chemical vapor deposition (CVD). The SnSe nanosheets exhibited high single-crystallinity, large area, and good stability. The strong layer-dependent in-plane piezoelectric coefficient of SnSe nanosheets showed a saturated trend to be ∼ 110 pm/V, which overcomes the weak piezoelectric response or odd-even effects in other layered nanosheets. A high energy conversion efficiency of 9.3% and a maximum power density of 538 mW/cm2 at 1.03% strain have been demonstrated in a SnSe-based PENG. Based on the enhanced piezoelectricity of SnSe and attractive output performance of the nanogenerator, a self-powered sensor for human motion monitoring is further developed. These results demonstrate the strong piezoelectricity in high quality CVD-grown SnSe nanosheets, allowing for application in flexible smart piezoelectric sensors and advanced microelectromechanical devices. [ABSTRACT FROM AUTHOR]

Driven by the urgent demands for information technology, energy, and intelligent industry, third-generation semiconductor GaN has emerged as a pivotal component in electronic and optoelectronic devices. Fundamentally, piezoelectric polarization is the most essential feature of GaN materials. Incorporating piezotronics and piezo-phototronics, GaN materials synergize mechanical signals with electrical and optical signals, thereby achieving multi-field coupling that enhances device performance. Piezotronics regulates the carrier transport process in micro–nano devices, which has been proven to significantly improve the performance of devices (such as high electron mobility transistors and microLEDs) and brings many novel applications. This review examines GaN material properties and the theoretical foundations of piezotronics and phototronics. Furthermore, it delves into the fabrication and integration processes of GaN devices to achieve state-of-the-art performance. Additionally, this review analyzes the impact of introducing three-dimensional stress and regulatory forces on the electrical and optical output performance of devices. Moreover, it discusses the burgeoning applications of GaN devices in neural sensing, optoelectronic output, and energy harvesting. The potential of piezotronic-controlled GaN devices provides valuable insights for future research and the development of multi-functional, diversified electronic devices.

With the arrival of the era of artificial intelligence (AI) and big data, the explosive growth of data has raised higher demands on computer hardware and systems. Neuromorphic techniques inspired by biological nervous systems are expected to be one of the approaches to breaking the von Neumann bottleneck. Piezotronic neuromorphic devices modulate electrical transport characteristics by piezopotential and directly associate external mechanical motion with electrical output signals in an active manner, with the capability to sense/store/process information of external stimuli. In this review, we have presented the piezotronic neuromorphic devices (which are classified into strain-gated piezotronic transistors and piezoelectric nanogenerator-gated field effect transistors based on device structure) and discussed their operating mechanisms and related manufacture techniques. Secondly, we summarized the research progress of piezotronic neuromorphic devices in recent years and provided a detailed discussion on multifunctional applications, including bionic sensing, information storage, logic computing, and electrical/optical artificial synapses. Finally, in the context of future development, challenges, and perspectives, we have discussed how to modulate novel neuromorphic devices with piezotronic effects more effectively. It is believed that the piezotronic neuromorphic devices have great potential for the next generation of interactive sensation/memory/computation to facilitate the development of the Internet of Things, AI, biomedical engineering, etc.

Piezotronic and piezo-phototronic effects can effectively modulate the Schottky barrier height (SBH) of the metal-semiconductor contact and the built-in electric field. Most models focus on the built-in electric field of perovskite solar cells, and polarization-modulated SBH is missing. We investigated piezotronic and piezo-phototronic effects on the Schottky barrier and built-in electric field of perovskite solar cells. A model of the surface potential induced by polarization was developed. The analytical and numerical results are calculated for perovskite solar cells. We found that the piezo-phototronic effect can significantly increase the performance of perovskite solar cells by reducing the height of the Schottky barrier. This model not only provides a fundamental physical picture of the piezotronic and piezo-phototronic effect on perovskite solar cells, but also paves a new path to develop high-efficiency perovskite solar cells. [Display omitted] • Piezotronic and piezo-phototronic effect can improve the performance of perovskite solar cells. • The model of piezotronics and piezo-phototronics on perovskite solar cells was proposed. • This model provides a basic physics picture for piezotronic and piezo-phototronic effect on perovskite solar cell. [ABSTRACT FROM AUTHOR]

Abstract Introducing polarization field of piezoelectric materials is an effective strategy to improve photocatalytic performance. In this study, a new type of BaTiO3/CuO heterostructure catalyst was designed and synthesized to achieve high piezo-photocatalytic activity through the synergy of heterojunction and piezoelectric effect. The BaTiO3/CuO heterostructure shows a significantly enhanced piezo-photocatalytic degradation efficiency of organic pollutants compared with the individual BaTiO3 nanowires (NWs) and CuO nanoparticles (NPs). Under the co-excitation of ultrasonic vibration and ultraviolet radiation, the optimal degradation reaction rate constant k of polarized BaTiO3/CuO heterostructure on methyl orange (MO) dye can reach 0.05 min− 1, which is 6.1 times of photocatalytic rate and 7 times of piezocatalytic rate. The BaTiO3/CuO heterostructure with remarkable piezo-photocatalytic behavior provides a promising strategy for the development of high-efficiency catalysts for wastewater purification, and it also helps understand the coupling mechanism between piezoelectric effect and photocatalysis.

Mechanical characterization of quasi one-dimensional nanostructures is essential for the design of novel nanoelectromechanical systems. However, the results obtained on basic mechanical quantities, such as Young's modulus and fracture strength, show significant standard deviation in the literature. This is partly because of diversity in the quality of the nanowire, and partly because of inappropriately performed mechanical tests and simplified mechanical models. Here we present orientation-controlled bending and fracture studies on wet chemically grown vertical ZnO nanowires, using lateral force microscopy. The lateral force signal of the atomic force microscope was calibrated by a diamagnetic levitation spring system. By acquiring the bending curves of 14 nanowires, and applying a two-segment mechanical model, an average bending modulus of 108 ± 17 GPa was obtained, which was 23% lower than the Young's modulus of bulk ZnO in the [0001] direction. It was also found that the average fracture strain and stress inside the nanowire was above 3.1 ± 0.3 % and 3.3 ± 0.3 GPa, respectively. However, the fracture of the nanowires was governed by the quality of the nanowire/substrate interface. The demonstrated technique is a relatively simple and productive way for the accurate mechanical characterization of vertical nanowire arrays. [ABSTRACT FROM AUTHOR]

This study investigates the piezoelectric and piezotronic properties of a novel composite material comprising polyvinylidene fluoride (PVDF) and antimony sulphoiodide (SbSI) nanowires. The material preparation method is detailed, showcasing its simplicity and reproducibility. The material’s electrical resistivity, piezoelectric response, and energy-harvesting capabilities are systematically analyzed under various deflection conditions and excitation frequencies. The piezoelectric response is characterized by the generation of charge carriers in the material due to mechanical strain, resulting in voltage output. The fundamental phenomena of charge generation, along with their influence on the material’s resistivity, are proposed. Dynamic strain testing reveals the composite’s potential as a piezoelectric nanogenerator (PENG), converting mechanical energy into electrical energy. Comparative analyses highlight the composite’s power density advantages, thereby demonstrating its potential for energy-harvesting applications. This research provides insights into the interplay between piezoelectric and piezotronic phenomena in nanocomposites and their applicability in energy-harvesting devices.

Metal‐halide perovskites have emerged as versatile materials for various electronic and optoelectronic devices such as diodes, solar cells, photodetectors, and sensors due to their interesting properties of high absorption coefficient in the visible regime, tunable bandgap, and high power conversion efficiency. Recently, metal‐free organic perovskites have also emerged as a particular class of perovskites materials for piezoelectric applications. This broadens the chemical variety of perovskite structures with good mechanical adaptability, light‐weight, and low‐cost processability. Despite these achievements, the fundamental understanding of the underlying phenomenon of piezoelectricity in metal‐free perovskites is still lacking. Therefore, this perspective emphasizes the overview of piezoelectric properties of metal‐halide, metal‐free perovskites, and their recent progress which may encourage material designs to enhance their applicability towards practical applications. Finally, challenges and outlooks of piezoelectric metal‐free perovskites are highlighted for their future developments. [ABSTRACT FROM AUTHOR]

• The piezotronic fields in non-uniform piezo-semiconductive fibers are solved using a power series expansion method. • The convergence and correctness of the method are proved. • The antisymmetry of the electromechanical fields is broken due to the contoured profile. • A necking heterogeneous piezoelectric semiconductor PN junction is more conveniently modulated. In order to evidently improve the working performance of piezotronic devices, non-uniform piezoelectric semiconductor fibers with contoured profiles are designed. However, apart from the finite element method, it's hard to achieve analytical descriptions of the electromechanical fields in these non-uniform piezoelectric semiconductor fibers because of the governing equations with variable coefficients. For solving this bottleneck and exploring improved performance and new phenomena caused by the non-uniform profile, a power series expansion method is proposed based on the framework of the one-dimensional linearized model and is further applied to analyze the piezotronic performances of n-type non-uniform piezoelectric semiconductor fibers and PN junctions. It is revealed via systematical numerical simulations that the antisymmetry of the electromechanical fields in piezoelectric semiconductor fibers is broken because of the contoured profile and the piezotronic coupling. Meanwhile, the barrier configuration in a non-uniform PN junction is sensitive to the variation of cross-sectional area. Furthermore, the current-voltage relation of a necking heterogeneous piezoelectric semiconductor PN junction can be manipulated more conveniently by external mechanical loadings, meaning that the sensitivity of the device is improved. Not limited by non-uniform piezoelectric semiconductor fibers with contoured profiles, this method exhibits broad applicability, which is still available for solving multiple-coupled properties of functional graded piezoelectric semiconductor media. [ABSTRACT FROM AUTHOR]

Abstract Metal‐halide perovskites have emerged as versatile materials for various electronic and optoelectronic devices such as diodes, solar cells, photodetectors, and sensors due to their interesting properties of high absorption coefficient in the visible regime, tunable bandgap, and high power conversion efficiency. Recently, metal‐free organic perovskites have also emerged as a particular class of perovskites materials for piezoelectric applications. This broadens the chemical variety of perovskite structures with good mechanical adaptability, light‐weight, and low‐cost processability. Despite these achievements, the fundamental understanding of the underlying phenomenon of piezoelectricity in metal‐free perovskites is still lacking. Therefore, this perspective emphasizes the overview of piezoelectric properties of metal‐halide, metal‐free perovskites, and their recent progress which may encourage material designs to enhance their applicability towards practical applications. Finally, challenges and outlooks of piezoelectric metal‐free perovskites are highlighted for their future developments.

Mechanical characterization of quasi one-dimensional nanostructures is essential for the design of novel nanoelectromechanical systems. However, the results obtained on basic mechanical quantities, such as Young’s modulus and fracture strength, show significant standard deviation in the literature. This is partly because of diversity in the quality of the nanowire, and partly because of inappropriately performed mechanical tests and simplified mechanical models. Here we present orientation-controlled bending and fracture studies on wet chemically grown vertical ZnO nanowires, using lateral force microscopy. The lateral force signal of the atomic force microscope was calibrated by a diamagnetic levitation spring system. By acquiring the bending curves of 14 nanowires, and applying a two-segment mechanical model, an average bending modulus of 108 ± 17 GPa was obtained, which was 23% lower than the Young’s modulus of bulk ZnO in the [0001] direction. It was also found that the average fracture strain and stress inside the nanowire was above 3.1 ± 0.3 % and 3.3 ± 0.3 GPa, respectively. However, the fracture of the nanowires was governed by the quality of the nanowire/substrate interface. The demonstrated technique is a relatively simple and productive way for the accurate mechanical characterization of vertical nanowire arrays.

• A new Kirchhoff–Love composite piezoelectric semiconductor shell is established. • The principle of virtual work is applied for the governing equations. • Static bending and forced vibration analyses are analytically conducted. • Coupling relations between mechanical deformation and charge behavior are obtained. • New structures and analytical solutions are helpful for sensing and energy harvesting. We study electromechanical effects and piezotronic behaviors in a Kirchhoff–Love laminated composite piezoelectric semiconductor circular cylindrical thin shell, which is composed of a non-piezoelectric semiconductor core and two piezoelectric dielectric layers. A second-order assumption for electric potentials and carrier concentration perturbations is utilized to capture accurate descriptions of the electric field and charge distributions within the composite shell, where the zeroth-order, first-order, and second-order forms represent constant, antisymmetric, and symmetric distributions along the thickness, respectively. The field equations and boundary conditions are simultaneously derived through a principle of virtual work and the fundamental lemma of the calculus of variation. The new governing equations derived show a new coupling relation between mechanical deformation and charge behavior in the composite shell, where all mechanical deformations (extension, bending of the shell) and all distribution forms of electric potential (zeroth-, first-, second-order electric potentials) are coupled, which is different from piezoelectric semiconductor beams and plates. Then, the numerical results of electromechanical effects and piezotronic behaviors in static bending and forced vibration problems of the shell are conducted with the derived theoretical model. Numerical studies of static bending graphically show some fundamental coupling relations between mechanical forces and charge distributions in deformed piezoelectric semiconductor shells. The new results from the forced vibration analysis given by the current model show that the deflection amplitude and the electric potential distribution in the thin shell are frequency-dependent and can be adjusted by controlling the excitation frequency. In addition, the semiconducting properties (dependence of mechanical behavior on doping level) are studied in both static and dynamic problems. The mechanically controlled charge distribution suggests that shell-shaped piezoelectric semiconductor shells could serve as an effective means of sensing or energy harvesting by converting mechanical energy into electricity. [ABSTRACT FROM AUTHOR]

Piezotronics and piezo-phototronics are two emerging fields that involve high performance piezoelectric semiconductor devices. The nonuniform strain can create nonlinear piezopotential even in nonpiezoelectric materials such as silicon. Here, we propose theory of quantum piezotronics under nonuniform strain using a typical example of the interaction between independently trapped charges under nonlinear piezopotential. The trapped-ion motional frequency along the x direction can increase from 4 MHz to 25 MHz, and the electric-field noise can decrease by 15 times under nonuniform strain. This piezotronic harmonic oscillator based on trapping wells not only provides a good understanding of quantum piezotronics but also a guide for developing peizotronic devices for quantum computing. [Display omitted] • The nonuniform strain can create quadratic piezo-potential to control the axis motional frequency of trapped ions qubit. • The trapped-ion motional frequency along the x direction can reach up to 25 MHz under nonuniform strain. • The surface electric-field noise is decreased by 15 times under nonuniform strain. [ABSTRACT FROM AUTHOR]

The properties of spin and valley transport of piezotronics valley transistor is studied based on a normal/ferromagnetic/normal (NFN) structure of monolayer (ML) transition metal dichalcogenides (TMDs). Rabi frequency reach up to 4200 MHz based on piezotronics effect, which is about 1000 times higher than that of ZnO/CdO quantum well devices. Strain-induced strong polarization can control properties of spin and valley transport in piezo-phototronic transistor. The strong polarization can be applied on the modulation of the valley qubit. The spin and valley conductance and the spin and valley polarizability are calculated theoretically. The strong polarization can be applied on the manipulation of valley qubit, which paves a new way to quantum computing applications based on piezotronic valley transistors. [Display omitted] • Quantum piezotronic devices have high Rabi frequency based on polarization-driven spin and valley transport. • Piezotronic effect on spin and valley transport is an effective way to manipulate valley qubit. • Strong polarization can pave a new way to quantum computing applications based on piezotronic valley transistors. [ABSTRACT FROM AUTHOR]

Straintronics of two-dimensional (2D) materials offers enormous promise for both fundamental research and smart technologies. Strain engineering of 2D materials has recently witnessed an upsurge of interest, driven by the growing demands of building flexible semiconductor devices under miniaturization. 2D materials have received considerable attention to tune their fascinating electrical, optical, and vibrational properties for flexible electronics due to their high stretchability and flexibility. For this, a variety of controllable straining techniques have been developed by mimicking either natural phenomena or mechanical processes. In the literature, strained nano-/microstructures of 2D materials have been extensively reviewed for highlighting their potential in tunable electronics, however a systematic assessment of the straining techniques utilized to create such strained structures is still lacking. In this review, we provide detailed one-to-one assessments of the straining methods used to create diverse strained structures of 2D materials and their limitations, covering recent advancements and in-depth discussions. In addition, the importance and advantages of applying straining techniques to improve the performance of flexible straintronic devices have also been covered. These will open pathways for exploiting the straining techniques for their meticulous applications. [Display omitted] • Straining techniques to create strained nano-/microstructures of 2D materials. • One-to-one analyses of all existing straining techniques are presented. • Straining techniques for upgrading 2D material-based flexible straintronic devices. [ABSTRACT FROM AUTHOR]

Remote epitaxy has been developed recently as a new method for synthesising zinc oxide (ZnO) nanowires (NWs) with unique structural and physical properties. In this paper, the piezopotential properties and piezotronic behaviours of ZnO NWs epitaxially grown on monolayer graphene and molybdenum disulfide (MoS 2) i.e., graphene-ZnO and MoS 2 –ZnO NWs are studied through a multiscale simulation technique. It is shown that compression is the only type of force that can efficiently trigger the piezopotential in ZnO NWs grown by remote epitaxy, since their ZnO and two-dimensional (2D) material components are weakly connected at the interfaces. Although compressed MoS 2 –ZnO and graphene-ZnO NWs are found to have different piezopotential distributions due to the unique polarity inversion behaviour in MoS 2 –ZnO NWs, the local piezopotential distribution in both ZnO NWs can be similarly modified by changing the location of 2D interlayer material. Moreover, the graphene-ZnO NWs are found to possess a much larger global piezopotential difference than conventional ZnO NWs, though both ZnO NWs have the similar piezopotential distribution. Due to the unique local piezopotential property and the existence of additional peak barriers or Schottky barriers at the interfaces between ZnO NW and 2D interlayer material components, ZnO NWs grown by remote epitaxy, especially MoS 2 –ZnO NWs exhibit a distinct piezotronic behaviour that is significantly different from that of their conventional counterparts. [ABSTRACT FROM AUTHOR]

As obtaining flexible tactile sensors with high sensitivity, waterproofness and breathability at the same time is still a huge challenge, which limits their application in advanced fields such as human prosthetics and robotic arms. Herein, a fully flexible piezoelectric tactile sensor with high-performance, energy-efficient, waterproof, and breathable was constructed by capacitive coupling the β-PVDF nanofiber membrane (NM) with electro-mechanical conversion function and organic field effect transistor (OFET) device with signal amplification function. The inherent waterproofed β-phase PVDF NM was fabricated by advanced electrospinning process, such morphology with thousands of micropores not only gives the device excellent breathability, but also increases the deformation tolerance and accelerates the respond/recovery time, so that the obtained device can be bent at will without affecting its performance. At the same time, under the guidance of pizotronics, the charge generated by PVDF membrane based on piezoelectric effect polarization was sufficient to drive the OFET device, the as-fabricated sensor shows great sensing performance in monitoring human physiological signals without applying a gate voltage. Such device exhibits excellent pressure sensitivity, detection limit, and response time of 7.94 KPa-1, 48.54 Pa and 105 ms, respectively, which may become promising device in smart electronic skins, human motion detection, and human−machine interaction. [Display omitted] • The natural hydrophobic characteristics of the PVDF combined with electrospinning to achieve a flexibility, waterproofness and breathability sensor. • Under the guidance of piezotronics, the PVDF NM and OFET are capacitively coupled to construct a high-performance tactile sensor. • The tactile sensor with high performance and comfort can realize real-time monitoring of human physiological signals. [ABSTRACT FROM AUTHOR]

2D metal oxides have aroused increasing attention in the field of electronics and optoelectronics due to their intriguing physical properties. In this review, an overview of recent advances on synthesis of 2D metal oxides and their electronic applications is presented. First, the tunable physical properties of 2D metal oxides that relate to the structure (various oxidation-state forms, polymorphism, etc.), crystallinity and defects (anisotropy, point defects, and grain boundary), and thickness (quantum confinement effect, interfacial effect, etc.) are discussed. Then, advanced synthesis methods for 2D metal oxides besides mechanical exfoliation are introduced and classified into solution process, vapor-phase deposition, and native oxidation on a metal source. Later, the various roles of 2D metal oxides in widespread applications, i.e., transistors, inverters, photodetectors, piezotronics, memristors, and potential applications (solar cell, spintronics, and superconducting devices) are discussed. Finally, an outlook of existing challenges and future opportunities in 2D metal oxides is proposed., (© 2023 Wiley-VCH GmbH.)

Piezotronic and piezophototronic sensors have potential application to biological detection and human-computer interaction due to converting mechanical signals into electrical signals. Strain-induced polarization can manipulate avalanche multiplication process in the junction of the piezotronic and piezophototronic avalanche diode and field effect transistor. The gauge factor of piezotronic and piezophototronic avalanche devices can reach 106-107. The ultrafast piezotronic and piezophototronic avalanche devices can be developed because the response time can be reduced by strain-induced polarization. This study can provide guidance for ultrafast and ultrahigh sensitivity piezotronic and piezophototronic strain sensors and photodetectors. Piezotronic avalanche diode was studied based on GaN with ultra-high gauge factor (106-107). Strain-induced polarization control the avalanche multiplication process effectively. The transient time is improved obviously by dynamical applied strain. [Display omitted] • Piezotronic avalanche diode has been demonstrated based on the model of avalanche multiplication process. • The sensitivity of piezotronic avalanche devices can reach 106-107 with transient time of 10−14 s. • This study provides a novel design for ultrafast piezotronic and piezophototronic avalanche devices. [ABSTRACT FROM AUTHOR]

Piezoelectricity in two-dimensional (2D) materials have received particular attention because of their great potential in realizing nanoscale piezotronic devices. However, most 2D layered piezoelectric materials found so far possess only in-plane piezoelectricity and require the induction of stress by bending flexible substrate, which limits their integration with conventional rigid substrates such as silicon wafer. CuInP 2 S 6 is a promising 2D layered material that has attracted widespread devotion due to its diverse excellent properties including out-of-plane ferroelectricity and high stability at room-temperature. However, comprehensive investigation of piezoelectric effect in 2D CuInP 2 S 6 and its relevant piezoelectric device application is still at an initial stage compared to the extensive investigation of its ferroelectricity. Herein, we perform a quantitative analysis of the large out-of-plane piezoelectricity in multilayer CuInP 2 S 6 and therefore demonstrate the device application for 2D piezoelectric nanogenerator (PENG). Few-layer CuInP 2 S 6 nanosheet shows a high d 33 piezoelectric coefficient of 17.4 pm/V, outperforming other 2D layered piezoelectrics currently reported. Moreover, the PENG based on a single CuInP 2 S 6 nanoflake illustrates a maximum piezoelectric current and voltage responses of 1.7 nA and 12 mV, respectively. The experimental results are discussed based on the piezotronic effect. The strong piezoelectric response achieved in 2D CuInP 2 S 6 nanosheets warrants their potential to be adopted for future strain-modulable nanoelectronic and piezotronic devices integrated with silicon-based chips. [Display omitted] • A large d 33 piezoelectric coefficient of 17.4 pm/V is reported in few-layer CuInP 2 S 6 nanosheet investigated by PFM. • 2D CuInP 2 S 6 -based piezotronic device is explored and its working principle is understood based on piezotronic effect. • We firstly present a single 2D CuInP 2 S 6 nanosheet-based vertical piezoelectric nanogenerator integrated with silicon wafer. [ABSTRACT FROM AUTHOR]

Piezo-phototronic spin lasers are studied based on wurtzite quantum wells. The strain-induced polarization changes the gain spectrum and gain asymmetry at room temperature. In this work, the gain properties of piezo-phototronic spin lasers based on InGaN/GaN quantum wells can be modulated by strain-induced polarization. This work not only paves a new way for the room-temperature applications of quantum piezotronic and piezo-phototronic devices, but also provides new method of regulation for wurtzite spin lasers by strain-induced polarization. The active region of piezo-phototronic spin laser based on In 0.1 Ga 0.9 N/GaN quantum wells is studied. The electronic structure and microscopic gain can be regulated by strain-induced polarization. This is a new device design to develop quantum piezotronic and piezo-phototronic devices at room-temperature. [Display omitted] • Piezo-phototronic spin lasers based on wurtzite piezoelectric semiconductor has been investigated. • Strain induced polarization regulate gain spectrum and gain asymmetry of spin laser. • GaN quantum well spin laser provide a new design for piezotronic and piezophototronic quantum devices at room-temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • We achieved ultrathin flexible AZO electrodes with low resistivities (less than100 μΩ•cm). • We demonstrated the mechanical robustness of ultrathin flexible AZO electrodes. • We discovered abnormally high carrier concentrations in strained epitaxial AZO. Aluminum-doped zinc oxide (AZO) thin films are popular transparent electrodes for optoelectronics and photovoltaics. However, next generation flexible devices demand not only high conductivities but also low thicknesses in AZO electrodes to stay robust against deformations. The two requirements contradict each other due to the scattering of carriers at grain boundaries in polycrystalline AZO electrodes. Herein, this work develops ultrathin, highly conductive, single-crystalline, and mechanically robust AZO electrodes on flexible Hastelloy substrates. The epitaxial growth of AZO on polycrystalline Hastelloy is empowered by an advanced buffer architecture topped with a biaxially-textured MgO layer. Thereby, a c -axis epitaxial strain is generated in the AZO electrodes and then regulated by varying the thickness of the electrodes. Abnormally high carrier concentrations are detected in the AZO electrodes likely caused by the piezopotential generated by the epitaxial strain. While the highest resistivity value of the epitaxial AZO electrodes is within the mainstream values of AZO electrodes on various substrates, a resistivity as low as ~22 μΩ•cm is demonstrated in the ultrathin electrode with a thickness of ~28 nm. The mechanical durability of the ultrathin AZO electrode is validated by bending tests of 1000 cycles. [ABSTRACT FROM AUTHOR]

The gallium nitride (GaN) nanowires (NWs) in piezotronic applications are usually under cyclic loading, which thus may inevitably suffer the mechanical fatigue. In this paper, the fatigue behaviours of defective GaN NWs are investigated by using molecular dynamics (MD) simulations. Our results show no significant changes in the molecular structures of GaN NWs until their final failure during the fatigue process. The final fracture occurring in the GaN NWs under fatigue loading is triggered by the crack that unusually initiates from the NW surface. The GaN NW with a smaller defect concentration or under the fatigue load with a smaller amplitude is found to possess a longer fatigue life. In addition, the ultimate fatigue strain of GaN NWs can be significantly increased by reducing the defect concentration of NWs. The material parameters including elastic constants, piezoelectric coefficients, and dielectric constants of GaN NWs in the fatigue test are evaluated through MD simulations, all of which are found to keep almost unchanged during the fatigue process. These material parameters together with the band gaps of GaN NWs extracted from first-principles calculations are employed in finite element calculations to investigate the piezopotential properties of GaN NWs under fatigue loading. No significant changes are found in the piezopotential properties of GaN NWs during the fatigue process, which indicates the long-term dynamic reliability of GaN NWs in piezotronic applications., (© 2021 IOP Publishing Ltd.)