To date, semiconductor light emitters have been developed to exceed 50% efficiency across the entire visible region. [6,7] However, the performance of AlGaNbased ultraviolet light-emitting diodes (LEDs) has been severely limited by the extremely inefficient strain-induced polarization fields and prohibitively large defect densities. Various approaches, including sputtered AlN nucleation layer, polarization doping, patterned sapphire substrate (PSS), AlGaN superlattices, and non-/ semipolars have been studied to improve the efficiency of LEDs in the ultraviolet region. [1,[8][9][10][11][12] Due to low magnesium (Mg)doping efficiency and large Mg activation energy, [13][14][15] AlGaN-based LEDs usually exhibit very high threshold voltages in the deep ultraviolet range. [13,16] Furthermore, the lattice mismatch between AlGaN materials and the substrate materials induces high dislocations and stacking faults with thermal stress in the Al-rich AlGaN epitaxial layers. [14] The AlGaN multiple quantum wells (MQWs) grown along a polar [0001] orientation suffer from inherent spontaneous and piezoelectric polarizations. The total polarization fields result in the spatial separation of the electron and hole wave functions and thus in restricting the radiative recombination efficiency, known as the quantum-confined Stark effect (QCSE). [17,18] As a result, because of the poor material quality and the polarization-induced electric field, it is still difficult to achieve internal quantum efficiency (IQE) in AlGaN epitaxial structures. This poor internal quantum efficiency eventually leads to extremely low output power of AlGaN-based LEDs operating in the UVA-C bands.Such critical issues can be potentially addressed by employing 1D nanowire structures and nonpolar core-shell heterostructures. [1,12] GaN-based nanowire structures have been intensively studied in the past decade. [19][20][21] Recent reports have shown that such nanowires can drastically reduce the dislocation densities due to efficient surface strain relaxation, and also can significantly enhance the p-type current conduction due to reduced Mg-dopant formation energy in p-Al(Ga)N structures. [22,23] With the use of nonpolar structures grown along m-plane direction in GaN structure, the improved light output power and electrical performance have been demonstrated in InGaN-based quantum well LEDs with the absence of polarization. [12,24,25] Therefore, it is expected that the incorporation of the nonpolar core-shell and the nanowire structures can significantly improve the internal quantum efficiency, p-contact Highly efficient nonpolar AlGaN nanowire ultraviolet light-emitting diode is developed, wherein core-shell AlGaN multiple quantum well layers are incorporated in the nonpolar active regions. It is confirmed that the core-shell light-emitting diode (LED) heterostructures are uniformly grown on the nonpolar surfaces of hexagonal GaN nanowires by metalorganic chemical vapor deposition (MOCVD) technique. At room temperature, the nearly defect-free core-shell AlGaN...

Recent studies are actively contributing to the implementation of the use of five human senses in electronic skins. In order to achieve this, it is critical to develop sensors with the ability to heal after being subjected to stretching or damage; this should be achieved without any significant deterioration in performance, as is possible for human skin. This study investigates the potential for producing stretchable, cuttable, and healable photodetectors. To this end, a reversibly cross‐linkable silicone polymer, polydimethylsiloxane (rcPDMS), is synthesized via a Diels–Alder reaction; subsequently, ZnS:Cu particles are dispersed therein to form a composite film. Ag nanowires (AgNWs) are formed on both the surfaces of the film to realize a three‐layer sandwich structured capacitor, namely: AgNWs/ZnS:Cu‐rcPDMS/AgNWs. Light irradiation of the film induces the photodielectric effect in ZnS:Cu particles and the dielectric response of photoinduced dipole moments composed of localized photoactive carriers results in a change in the capacitance of the film. Based on this, a photodetector is developed that is stretchable, healable, and demonstrates no reduction in the device performance even before and after cutting as well as healing.

the changes in electrical parameters (such as conductivity and impedance) or the geometry of a specific material produced by small mechanical deformations. [22] Here, general requirements for an excellent mechanical sensor usually refer to a high gauge factor (the ratio of the relative changes in the measured property to the mechanical strain), but in the case of a stretchable strain and pressure sensor, some other conditions must also be satisfied. The implementation of stretchable sensors means that the sensor must be elastic enough to be stretched or shrunk beyond a certain level, the performance of the sensor should not be degraded even when it is stretched, and the sensor should be able to withstand repeated stretch-and-release.Capacitive sensors, which transduce a physical contact with a conductive object (such as human finger) into a change in capacitance, have been used in commercial touch sensors as they have a short response time, a simple read-out mechanism, and high sensitivity even under extremely weak interactions with an external conductive object. [23] The capacitive sensory mechanism has also been employed to obtain pressure sensors by using a layer of soft dielectric polymer sandwiched between two flexible transparent electrode layers, where the capacitance is formed. [22,24] When pressure is applied to the sensor, the thickness of the inserted dielectric layer between the two electrodes is reduced, resulting in an increase in capacitance, which can be used as a sensing parameter. In order for the pressure sensor to have stretchability, all elements constituting the sensor, that is, the upper and lower substrate, the centering dielectric layer, and the electrodes, should have large elasticity or sufficient conductivity even in the stretched state. Furthermore, the interface between each layer in the pressure sensor should be chemically robust so that delamination or severe plastic deformation at the interface can be prevented after repeated stretch-and-release.In this respect, the most ideal sensor structure is that all components except the electrodes are formed of the same material, or at least share equivalent physical/mechanical properties. Unfortunately, most stretchable pressure sensors reported so far have been fabricated by bonding two elastic polymer substrates with an adhesive [25][26][27] or by coating a liquid oligomer on a pre-cured polymer film to form a multilayer [28] ; thus, it is A typical capacitive mechanical sensor implemented using a layer of soft dielectric polymer sandwiched between two flexible electrodes, where the capacitance is formed, suffers from unintended buckling instability upon repeated stretch-and-release owing to different mechanical characteristics of constituent materials and unstable interfaces. Here, a stretchable, healable, and transparent strain/pressure-sensitive capacitor is successfully fabricated by hybridizing Ag nanowires (AgNWs) with a polydimethylsiloxane containing maleimide-derived Diels-Alder (DA) adducts as reversible crosslinkers. AgNWs for...