Piezoelectric Field Research Articles

Enhanced piezocatalytic and piezo-photocatalytic dye degradation via S-scheme mechanism with photodeposited nickel oxide nanoparticles on PbBiO2Br nanosheets

The fabrication of an S-scheme heterojunction demonstrates as an efficient strategy for achieving efficient charge separation and enhancing catalytic activity of piezocatalysts. In this study, a new S-scheme heterojunction was fabricated on the PbBiO2Br surface through the photo-deposition of NiO nanoparticles. It was then employed in the piezoelectric catalytic degradation of Rhodamine B (RhB). The results demonstrate that the NiO/PbBiO2Br composite exhibits efficient performance in piezocatalytic RhB degradation. The optimal sample is the NiO/PbBiO2Br synthesized after 2 h of irradiation, achieving a RhB degradation rate of 3.11 h−1, which is 12.4 times higher than that of pure PbBiO2Br. Simultaneous exposure to visible light and ultrasound further increases in the RhB degradation rate, reaching 4.60 h−1, highlighting the synergistic effect of light and piezoelectricity in the NiO/PbBiO2Br composite. A comprehensive exploration of the charge migration mechanism at the NiO/PbBiO2Br heterojunction was undertaken through electrochemical analyses, theoretical calculations, and in-situ X-ray photoelectron spectroscopy analysis. The outcomes reveal that p-type semiconductor NiO and n-type semiconductor PbBiO2Br possess matching band structures, establishing an S-scheme heterojunction structure at their interface. Under the combined effects of band bending, interface electric fields, and Coulomb attraction, electrons and holes migrate and accumulate on the conduction band of PbBiO2Br and valence band of NiO, respectively, thereby achieving effective spatial separation of charge carriers. The catalyst’s synergistic photo-piezoelectric catalysis effect can be ascribed to its role in promoting the generation and separation of charge carriers under both light irradiation and the piezoelectric field. The results of this investigation offer valuable insights into the development and production of catalytic materials that exhibit outstanding performance through the synergy of piezocatalysis and photocatalysis.

Highly-efficient photocatalytic hydrogen evolution enabled by piezotronic effects in SrTiO3/BaTiO3 nanofiber heterojunctions

The synergistic effect between piezoelectric and photocatalytic behaviors presents an interesting avenue to enhance the water-splitting processes for hydrogen production. Through a combination of experimental findings and theoretical calculations, we propose that the piezoelectric field inherent in these materials may decrease the bandgap of piezo-photocatalysts, while the Z-scheme heterojunction structure facilitates electron transfer. Leveraging the synergistic effects of heterojunction formation and piezoelectric assistance, we demonstrate that the incorporated piezoelectric BaTiO3 significantly enhances the hydrogen evolution rate of hybrid SrTiO3/BaTiO3 nanofibers to 1950.2 μmol·g–1·h–1. This surpasses the rates achieved by pure SrTiO3 and BaTiO3 counterparts by 2.4 and 4.1 times, respectively, and notably exceeds those of perovskite-based piezo-photocatalysts ever reported. The present work offers a valuable pathway for piezoelectric-assisted photocatalytic mechanism insight and sustainable hydrogen production, toward a remarkable advancement in pursuit of efficient and environmentally-friendly energy solutions.

Low parasitic carrier reservoir of AlGaN-based DUV-LED via controlled-polarization step-graded superlattice electron blocking layer for high luminescence lighting

Achieving high luminescence intensity of deep-ultraviolet light-emitting diode (DUV-LED) is generally performed through the implementation of electron blocking layer (EBL) on the chip’s epilayers. However, the issue of parasitic carrier reservoir that originated from the uncontrolled piezoelectric field polarization has restricted the performance of DUV-LED by reducing the radiative recombination in the active region. This work reports on the numerical computation analysis of the DUV-LED with different types of EBL designs which are reference EBL, conventional superlattice EBL and step-graded superlattice EBL. The analysis of the DUV-LED focuses on the band diagram, carrier concentration at the EBL interfaces, current density of the carrier in the active region, radiative recombination rates, and luminescence spectrum. Remarkably, it is found that the DUV-LED step-graded superlattice EBL provides the polarization-controlled band diagram and emits 272 nm UVC-wavelength in which it is superior in performance compared to the other structures, specifically in terms of its radiated intensity. The parasitic electron and hole reservoir have been reduced by 30% and 60%, respectively. The luminescence intensity was also enhanced by 11% compared with the reference EBL and the IQE obtained by the DUV-LED with step-graded superlattice EBL is 50.12%.

Construction of PVDF-HKUST-1/BiVO4 hybrid electrospun flexible fiber membrane for enhanced piezo-photocatalytic reduction performance of Cr(VI)

For the practical implementation of Cr(Ⅵ) removal, effective and recyclable water treatment technology is essential. Polarized electric fields inside piezoelectric materials have proved to be a promising technique for facilitating photogenerated charge separation. In this work, Z-scheme heterojunction photocatalyst HKUST-1/BiVO4 and organic piezoelectric material PVDF were combined through electrospinning to create a novel flexible fiber PVDF-HKUST-1/BiVO4 (PVDF-HV) piezo-photocatalyst membrane. When the amount of HKUST-1/BiVO4 powder was 2.4% and the diameter of the obtained fiber film was 10 cm, the optimal reduction efficiency can be achieved by the piezoelectric photocatalytic reduction in solution with initial pH=2, and the piezo-photocatalytic efficiency of PVDF-HV reached up to 85.33% within 120 min, which was about 1.35 times and 2.19 times greater than that of single photocatalysis and piezoelectric catalysis, respectively. It successfully promoted photo charge separation based on the piezoelectric field in PVDF and the heterojunction produced between HKUST-1 and BiVO4. This research developed an efficient strategy for multi-path collection and exploitation of natural solar energy and vibration energy to boost photoactivity.

Enhanced vertical piezoelectricity in nano-switch diamane structures by super-dipole-moment effect

The lack of the vertical piezoelectricity and the corresponding internal physical mechanism of diamanes limit their applications in the piezoelectric field. The vertical piezoelectricity of the diamane doped with Si/Ge atoms is studied systematically by the first principles calculation. These monolayer diamanes can be regarded as the vertical piezoelectric nano-switches with a moderate barrier. Based on the 25 kinds of monolayers' data, the super-dipole-moment effect is found as the internal mechanism of larger vertical piezoelectricity based on the ordered phase of Born effective charges. It may deepen the understanding of the internal physical mechanism about the piezoelectricity.

Construction of piezoelectric photocatalyst Au/BiVO4 for efficient degradation of tetracycline and studied at single-particle level

Piezopotential-assisted catalysis has been proven to be a low-cost and high-efficiency environmental purification process. Herein, Au/bismuth vanadate (BiVO4) piezoelectric photocatalysts are prepared by modifying highly dispersed Au nanoparticles (AuNPs) on piezoelectric BiVO4 microcrystal by a deposition-precipitation approach. Under visible light irradiation and assisted ultrasound excitation, the removal rate of tetracycline was 95% within 60 min, demonstrating the optimum photocatalytic performance over 3Au/BiVO4. The significantly enhanced photocatalytic performance is due to the synergistic coupling of plasmonic and piezotronic effect based on facet engineering. Single-particle spectroscopy technology can provide photoluminescence (PL) lifetime and PL spectra information in the micro-/nano regions, thereby exploring the charge transfer behavior of heterostructures. Single-particle PL images revealed a significant attenuation of PL emission and shortened PL lifetime of 3Au/BiVO4, compared with BiVO4, indicating that high-density dispersed AuNPs promote charge transfer. In situ monitoring of individual BiVO4 and 3Au/BiVO4 particles before and after polarization treatment confirms that the piezoelectric field of the BiVO4 decahedron further promotes separation of photogenerated carriers induced by plasmonic effect. Driven by the piezoelectric potential induced by ultrasonic vibration near the heterostructures, high-energy hot electrons excited on plasmonic AuNPs can be effectively extracted to BiVO4. This work provides new choices for designing high-performance pollutant treatment catalysts.

Polymorphic transformation from metastable β to stable α phase in MnTe flake

Manganese telluride (MnTe) is an intriguing polymorphic semiconductor. Among them, the metastable β-MnTe phase, characterized by a wurtzite-type structure, has been successfully fabricated as a sputtered film on substrates. However, bulk or free-standing β-MnTe without substrates has never been realized. In this study, we fabricated a β-MnTe flake using a lift-off process. Notably, the X-ray diffraction patterns of the flake sample approached the predicted peak positions of bulk β-MnTe, indicating strain relaxation. This study represents a pioneering experimental success in demonstrating a bulk-like β-MnTe. Furthermore, we conducted thermal analyses associated with the β→α transformation through differential scanning calorimetry. The β-MnTe flake exhibited a lower transformation temperature than films, suggesting diminished thermal stability of the β phase. The enthalpy change was quantitatively determined as −45.1 kJ mol−1, which arises from the substantial volume change. These experimental demonstrations are expected to contribute to the application of free-standing β-MnTe in optoelectronic and piezoelectric fields.

Cascade charge transfer mechanism optimization of g-C3N4/Bi@Bi2WO6 for efficient 2,4-DCP piezo-photocatalytic degradation

The technique of ultrasonically mediated piezo-photocatalysis shows promising prospects in the fields of environment and energy. However, a more detailed exploration is needed to understand its underlying mechanisms. The present study demonstrates the successful enhancement of piezo-photocatalytic efficiency in a g-C3N4/Bi@Bi2WO6 (ωCBBW) composite by employing a bifunctional strategy. Approximately 91 % of the 2,4-dichlorophenol (2,4-DCP) is degraded by the cooperative interaction of ultrasonic and illumination, which is 1.7 times higher than that under photocatalytic and 2.1 times greater than under piezoelectric. The negative shifted flat band in Mott-Schottky is attributed to the regulation of the internal electric field by the piezoelectric effect, indicating the shielding of the Schottky barrier by the piezoelectric field. The strongest photocurrent density of 7.18 μA/cm2 shows a significant charge conduction behavior. Additionally, the Charge density difference suggests a preferential electron transfer from Bi to Bi2WO6 rather than g-C3N4. Based on work function and ESR spectroscopy, a novel mechanism is proposed for the transition from Type-II to S-scheme charge transfer in the piezo-photocatalytic system. This study establishes the profound influence of heterojunction materials, exhibiting both LSPR and piezoelectric properties, on photon conversion efficiency in piezo-photocatalytic systems, characterized by an augmented photocurrent density.

Enhanced metal-free photocatalyst performance by synergistic Coupling of internal magnetic field and piezoelectric field

Graphitic carbon nitride (g-C3N4) is a promising metal-free photocatalyst; however, its high carrier recombination rate and insufficient redox capacity limit its degradation effect on antibiotics. In order to overcome these shortcomings, the photocatalytic activity is improved by regulating the spin polarization state, constructing the internal electric field, and applying the external piezoelectric field. In this paper, the chlorine-doped and nitrogen-deficient porous carbon nitride composite carbon quantum dots (Nv-Cl/UPCN@CQD) has been synthesized successfully. The doping position of chlorine and spin polarization properties are verified by DFT calculation. The key intermediates *O2− and *OOH for the synthesis of reactive oxygen species were detected by in-situ infrared testing, which promotes the production of •O2− and H2O2. The degradation rate constant of Nv-Cl/UPCN@CQD for removal of tetracycline is 8.45 times higher than that of g-C3N4. The active oxygen production and degradation efficiency of piezoelectric photocatalysis under the synergistic effect of intense stirring and vis-light irradiation are much higher than those of photocatalysis and piezoelectric catalysis, and the conversion of H2O2 to •OH is promoted by piezoelectric field. This paper provides a reliable way to improve the performance of piezoelectric photocatalysts by adjusting their energy band, electronic structure and piezoelectric force.

The Interaction between Surface Acoustic Wave and Quantum Hall Effects

Abstract Surface Acoustic Wave (SAW) is a powerful technique for investigating quantum phases appearing in two-dimensional electron systems. The electrons respond to the piezoelectric field of SAW through screening, attenuating its amplitude and shifting its velocity, which is described by the relaxation model. In this work, we systematically study this interaction using orders of magnitude lower SAW amplitude than that in previous studies. At high magnetic fields when electrons form highly correlated states such as the quantum Hall effect, we observe an anomalously large attenuation of SAW while the acoustic speed remains considerably high, inconsistent with the conventional relaxation model. This anomaly exists only when the SAW power is sufficiently low.

Piezocatalytic property of PVDF/Graphene self-assembling piezoelectric membrane for environmental remediation

In recent years, industrial pollution has become an inescapable global issue. The catalytic degradation processes driven by environmental sources, such as photocatalysis and piezocatalysis, are among the effective solutions. However, the difficulty in recycling catalysts leads to secondary pollution, limiting their practical application. This study develops a graphene-based self-assembled piezocatalytic membrane. Through Non-solvent Induced Phase Separation (NIPS), polyvinylidene fluoride (PVDF)/graphene asymmetrical membrane was prepared. The addition of graphene induced the self-assembly of PVDF crystalline phases into piezoelectric β phase. The membrane generates the ROS species to degrade the pollutant by the screen charge from material surface under a piezoelectric field. The optimal membrane exhibits the highest Vpp value of 4.26 V, and significant degradation efficiency of 80.2 % and 85.6 % for methylene blue (MnB) and crystal violet (CV), respectively, which are positively charged dyes. Meanwhile, the degradation efficiency within 2 h reached 73.8 % for negatively charged methyl orange (MO) and 96.1 % for toxic rhodamine B (RhB). This study successfully developed a crystalline self-assembled piezocatalytic membrane, providing fundamental insights into its piezoelectric response and various pollutant degradation. It introduces new directions and possibilities for the future development of membrane-based piezocatalysis.

Li-diffusion in lithium niobate - tantalate solid solutions

Among the class of ferroelectric crystals, the lithium-niobate-tantalate (LiNb1-xTaxO3) system attracts growing attention for applications in the field of nonlinear optics, functional electronics and piezoelectrics. The self-diffusion of the ionic constituents, especially Li, is important for the overall electric conductivity. The aim of this investigation is to figure out how Li diffusion in lithium niobate-tantalate solid solution crystals behaves as a function of the Ta content. Specially grown LiNb1-xTaxO3 single crystals with different niobium to tantalum ratios are used for this purpose. Li tracer self-diffusion is analysed using secondary ion mass spectrometry after applying an isotope-enriched 6LiNbO3 tracer layer and subsequent annealing. All investigations are carried out at 250 and 600 °C, respectively. Despite of the theoretically predicted non-linear variation of the volume of the unit cell between the values of the end compounds, the results indicate no significant modification of Li diffusivities within error limits in the whole solid solution range.

Piezo-photodynamic therapy of Au@PEG-ZnO nanostructures enabled with a battery-free wireless cancer therapeutic dot

Cancer remains a global health concern, necessitating advanced therapeutic strategies to address its fatal challenges. Conventional treatments, such as radiotherapy and chemotherapy, often lack tumor specificity and may induce systemic toxicity. Photodynamic therapy (PDT) and sonodynamic therapy (SDT) have emerged as promising alternatives, demonstrating high specificity and minimal side effects. In this study, we propose a novel piezo-photodynamic therapy (PPDT) enabled with battery-free wireless cancer therapeutic dot, in which the nanocomposites of gold nanoparticles (Au NPs), zinc oxide nanorods (ZnO NRs) and hydrophilic polyethylene glycol (PEG) can enhance reactive oxygen species (ROS) generation and effectively inhibit tumor growth. The therapeutic dot is implanted directly inside the tissue around the tumor and wirelessly controlled by ultrasound (US), allowing dual activation of electron-hole pairs from the nanocomposites via US and ultraviolet light (UV). The internally generated piezoelectric field minimizes electron-hole recombination, maximizing ROS induction within tumor cells. This PPDT approach surpasses the efficacy of conventional PDT and SDT, showcasing a synergistic therapeutic effect. The study further elucidates the detailed mechanism of Au@PEG-ZnO NRs catalysts, providing insights into their piezoelectric-photocatalytic action. The battery-free wireless control and minimally invasive implantation of the therapeutic dot with inorganic piezo-photocatalyst open new perspectives in cancer therapy.

Ultrasound-driven radical chain reaction and immunoregulation of piezoelectric-based hybrid coating for treating implant infection

The poor efficiency of US-responsive coatings on implants restricts their practical application. Immunotherapy that stimulates immune cells to enhance their antibacterial activity is expected to synergize with sonodynamic therapy for treating implant infection effectively and safely. Herein, US-responsive hybrid coatings composed of the oxygen-deficient BaTiO3 nanorod arrays and l-arginine (BaTiO3-x/LA) are designed and prepared on titanium implants for sonocatalytic therapy-cooperated immunotherapy to treat Methicillin-resistant Staphylococcus aureus (MRSA) infection. BaTiO3-x/LA can generate more oxidizing reactive oxygen species (ROS, hydroxyl radical (·OH)) and reactive nitrogen species (RNS, peroxynitrite anion (ONOO−)). The construction of nanorod arrays and oxygen defects balances the piezoelectric properties and sonocatalytic capability during US treatment. The generated piezoelectric electric field provides a sufficient driving force to separate electrons and holes, and the oxygen defects attenuate the electron-hole recombination efficiency, consequently increasing the yield of ROS during the US treatment. Moreover, nitric oxide (NO) released by l-arginine reacts with the superoxide radical (·O2−) to produce ONOO−. Since, this radical chain reaction improves the oxidizing ability between bacteria and radicals, the cell membrane (argB, secA2) and DNA (dnaBGXN) are destroyed. The bacterial self-repair mechanism indirectly accelerates bacterial death based on the transcriptome analysis. In addition to participating in the radical chain reaction, NO positively affects macrophage M1 polarization to yield potent phagocytosis to MRSA. As a result, without introducing an extra sonosensitizer, BaTiO3-x/LA exhibits excellent antibacterial activity against MRSA after the US treatment for 15 min. Furthermore, BaTiO3-x/LA facilitates macrophage M2 polarization after implantation and improves osteogenic differentiation. The combined effects of sonodynamic therapy and immunoregulation lead to an effective and safe treatment method for implant-associated infections.

Anisotropic Strain-Tailoring Nonlinear Optical Response in van der Waals NbOI2.

Two-dimensional (2D) NbOI2 demonstrates significant second-harmonic generation (SHG) with a high conversion efficiency. To unlock its full potential in practical applications, it is desirable to modulate the SHG behavior while utilizing the intrinsic lattice anisotropy. Here, we demonstrate direction-specific modulation of the SHG response in NbOI2 by applying anisotropic strain with respect to the intrinsic lattice orientations, where more than 2-fold enhancement in the SHG intensity is achieved under strain along the polar axis. The strain-driven SHG evolution is attributed to the strengthened built-in piezoelectric field (polar axis) and the enlarged Peierls distortions (nonpolar axis). Moreover, we provide quantifications of the correlation between strain and SHG intensity in terms of the susceptibility tensor. Our results demonstrate the effective coupling of orientation-specific strain to the anisotropic SHG response through the intrinsic polar order in 2D nonlinear optical crystals, opening a new paradigm toward the development of functional devices.

Efficient hydrogen recovery from wastewater treatment by piezo-photocatalytic heterostructure

Hydrogen (H2) recovery during wastewater treatment has been considered as a promising direction to accomplish environmental sustainability. However, the effective H2 evolution in contaminants degradation process was still a major challenge. In this research, an advanced piezo-photocatalytic induced hydro-energy system is proposed, in consideration of improving the separation and transfer efficiency of photogenerated electrons and holes. As expected, the catalytic performance was significantly enhanced under the stress of ultrasound-induced piezoelectric field (major nitenpyram degradation within 60 min, H2 evolution was 746.56 μmol g−1 h−1). Experiments and density functional theory calculations illustrated that the introduced piezoelectric field directionally tuned the energy band structure of heterostructure, triggering a change in the electron transfer path within the heterostructure, which facilitated the major electrons transferred to zinc oxide (H2 evolution) and holes accumulated in molybdenum sulfide (hydroxyl radical generation), further accelerating contaminants degradation and H2 evolution. Furthermore, the in-depth mechanism of contaminants degradation and H2 evolution under the influence of piezoelectric field was further explored. The piezo-photocatalytic system of this work first accomplished H2 recovery in wastewater treatment on heterostructure, providing a constructive strategy for the design of environmentally sustainable catalytic systems.

Layered perovskite piezoelectric Bi3TiNbO9 as a piezo-photocatalyst: Synergistically enhanced catalytic activity and mechanism

Photocatalysis is considered as a green and efficient technology for dealing with water pollution problems, but there exists serious carrier recombination in photocatalysis. Introducing a piezoelectric electric field to reduce carrier recombination and accelerate carrier separation and migration is a recognized as an effective approach, while it remains testing for exploitation for high-performance catalysts with light and stress dual response as well as the coupling catalytic mechanism. In this work, we report a novel layered perovskite structure piezo-photocatalyst Bi3TiNbO9 and conducted an analysis of potential piezo-photocatalytic mechanisms. The piezoelectric force microscopy (PFM) and COMSOL finite element analysis prove that the Bi3TiNbO9 is a piezoelectric with strong piezoelectricity. In the degradation of tetracycline hydrochloride, Bi3TiNbO9 exhibits significantly better piezo-photocatalysis performance compared to piezocatalysis and photocatalysis. It is owing to that the ultrasound results in piezoelectric polarization accompanied by the generation of piezo-potential, which can induce piezocatalysis and facilitate the separation and transfer of photo-generated carriers. Electron paramagnetic resonance (EPR) technique and electrochemical tests are carried out under different excitation sources to identify the dominant active species involved in the reaction and to disclose the origin for the high performance of piezo-photocatalysis from the perspective of carriers. This study adds a new member to the family of piezo-photocatalytic material system, and provides further understanding on the synergistic piezo-photocatalysis mechanism.

Internal piezoelectric field produced by tri-component (FTO: Sb-ZnO/MoS2) thin film for enhanced photocatalytic degradation of organic pollutants and antibacterial activity

The detection of organic dyes, pharmaceuticals, and microorganisms in the water environment continues to be a major concern worldwide. Hence, we report a novel method whereby a tri-component (Sb-ZnO/MoS2) immobilized on Fluorine-doped Tin Oxide (FTO) substrate for piezo-photocatalytic degradation of organic contaminants and bacterial disinfection. To determine the optical, electrochemical, physical, and chemical properties of the Sb-ZnO/MoS2, the following methods were applied, SEM & EDS, TEM, XRD, BET, UV-Vis DRS, PL, EIS and chronoamperometry. The SEM and TEM results showed long ZnO nanorods on the surface of stacked MoS2 nanosheets. Chronoamperometry studies showed that the Sb-ZnO/MoS2 tri-component exhibited a piezoelectric effect under ultrasonic vibration, indicating an internal piezoelectric field for inhibition of electrons and holes from recombination. According to PL studies, Sb-ZnO/MoS2 tri-component had a lower PL emission peak intensity, which suggests a better separation of electrons and holes. The developed tri-component was investigated for its catalytic degradation of methylene blue (MB), methyl orange (MO), and ciprofloxacin (CIP) under light and ultrasonic vibration. The coupling of light (photocatalysis) and ultrasonic irradiation (piezocatalysis) showed greater degradation efficiencies of 95, 82, and 72% for MB, MO, and CIP, respectively. The degree of mineralisation was recorded from total organic carbon (TOC) as 76, 70, and 52% for MB, MO, and CIP, respectively. In addition, Sb-ZnO/MoS2 tri-component was shown to have antibacterial activity against both E. coli and S. aureus bacterial strains. Therefore, this study reveals that the prepared Sb-ZnO/MoS2 tri-component can be applied for the simultaneous removal of dyes, pharmaceuticals, and disinfection of wastewater pollutants.

A Self‐Powered Wound Dressing Based on “Lock‐ON/OFF” Drug Release Combined Electric Stimulus Therapy for Accelerated Infected Wound Healing

AbstractTo facilitate the on‐demand release of hydrophilic antibiotics for accelerated repair of infected wounds, a self‐powered wound dressing incorporating a “Lock‐ON/OFF” electric field (EF)‐driven drug release mechanism combined with electrical stimulation (ES) therapy is presented. When subjected to mechanical stress, the drug exhibits controlled, slow‐release behavior, achieving a remarkable cumulative release rate of 88.57%—89 times higher than the non‐mechanical stress group. Conversely, in the absence of mechanical stress, the drug remains unreleased, maintaining a 0% cumulative release rate in a fully closed state. The dressing utilizes its piezoelectric effect to establish an electric field, enabling precise control of hydrophilic drug release by regulating the electrostatic balance between the drug carrier and the drug. Moreover, the piezoelectric field acts as an exogenous electric field, remodeling the endogenous electric field of the wound, and accelerating wound closure. Combining EF‐driven drug release with ES result in a 1.26 fold improvement in wound healing compared to ES alone. This study addresses precision therapy limitations in fully automated diagnosis and treatment, paving the way for advancements in remote diagnosis, wireless therapy, and on‐demand precision medicine.

Anisotropic structural and optical properties of semi-polar (20–21) InGaN/GaN multiple quantum wells grown on patterned sapphire substrates

Semi-polar orientation owns the advantage of reduced internal piezoelectric fields by tilting the growth direction away from the conventional c-direction. The crystal symmetry and the balanced biaxial stress in growth plane are inevitably broken in the semi-polar orientation, leading to the appearance of anisotropic properties in both structural and optical performance. This report has investigated the structural and optical properties of semi-polar (20–21) InGaN/GaN multiple quantum wells overgrown on patterned sapphire substrates with a wide wavelength range from 415 nm to 521 nm. Polarization switching was not observed on these semi-polar (20–21) samples. The polarization ratio monotonically increases from 0.18 to 0.43 with increasing the emission wavelength, and the energy difference simultaneously increases from 17 meV to 29 meV. As increasing the excitation laser power, the polarization ratio drops slightly while the energy difference remains stable, indicating a saturation of the recombination to the topmost valence subband. These results help exploit the anisotropic structural and optical properties of semi-polar nitrides and promote the development of highly polarized light source for the application in the fields of display and communication.