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Quasi‐two‐dimensional (quasi‐2D) perovskite light‐emitting diodes (PeLEDs) are considered as one of the most potential candidates in electroluminescence territory owing to their unique quantum confinement effect and excellent thermal stability of the light. Nevertheless, heterogeneous energy domain distribution leads to severe non‐radiative recombination in the process of energy transfer, which enormously hinders the performance and application of PeLEDs. Herein, an ambipolar amino acid, 5‐aminovaleric acid (5AVA), is demonstrated to be able to coordinate lead and halides simultaneously with its carboxyl and amidogen groups. The coordinated ambipolar molecule not only reconstitutes energy domains of perovskites but also minimizes the interfacial defects of PeLEDs. Accordingly, the presence of 5AVA in perovskite precursors leads to dramatic suppression of the n = 1 and n = 2 phases and accelerates energy transfer from wide bandgap domains to narrow bandgap ones. As a result, maximum external quantum efficiency (EQE) of 19.3% (18.20% ± 1.10%) is achieved in quasi‐2D green PeLEDs with current efficiency of 61.7 cd A−1. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) with MgZnO/ZnO/MgZnO double heterojunction structure have been fabricated and the room temperature electroluminescence (EL) spectra have been studied. With the help of double heterostructure, LEDs show better visible EL performance than that of LED with ordinary p-i-n structure. By replacing ZnO film with ZnO nanorod arrays in this double heterostructure, strong ultraviolet EL emission around 380 nm was achieved. The ZnO-nanorod-based double heterostructured light-emitting diode exhibits superior stability with an intensity degradation of less than 3% over 8 h. The EL mechanisms were discussed in terms of carrier confinement and carrier transport based on semiconductor heterojunction theory. [ABSTRACT FROM AUTHOR]

In this paper, layered ZnO nanowall networks were directly grown on Al substrates using a hydrothermal method without predepositing seed layers. The individual ZnO nanowalls with a thickness of several nanometers and a size of several hundred nanometers were (002) surface dominated, in which the preferential growth direction of ZnO was suppressed. White electroluminescence devices were fabricated based on Au/polymethylmethacrylate/ZnOnanowall (metal-insulator-semiconductor) structures. The chromaticity coordinate of the electroluminescence spectrum for the optimal device was calculated as (0.27, 0.34), which is close to (0.33, 0.33) of standard white light. [ABSTRACT FROM AUTHOR]

Abstract: Reproducible near-ultraviolet (near-UV) light-emitting diodes composed of ZnO nanorods (NRs) and p-GaN film using direct-bonding (DB) structure have been demonstrated and characterized. It is revealed that numerous p–n heterojunctions are formed between the ZnO NR top tips and GaN film after the thermal treatment. Dominant near-UV electroluminescence (EL) centered at 400nm was observed and green–orange defect-related light emissions were absent, which is probably due to the formation of high-quality p–n heterojunctions where the EL is stimulated. The EL origination and related carrier transport mechanism were discussed qualitatively in terms of photoluminescence results and energy band diagram. It''s hoped that the DB structure may serve as a feasible way in the future solid lighting applications. [Copyright &y& Elsevier]

n-ZnO/p-Si heterojunction light emitting devices with and without a NiO intermediate layer were fabricated using a radio frequency magnetron sputtering system. Electroluminescence measurements revealed that the device with the NiO intermediate layer exhibits a sharper and stronger orange emission peaks at ∼670 nm compared with that of the device without the NiO layer. And the light output-current characteristic of the n-ZnO/NiO/p-Si heterojunction device follows a nearly linear relationship (L ∝ I) rather than the superlinear relationship (L ∝ I1.5) for the n-ZnO/p-Si heterojunction device. This work indicates that the NiO intermediate layer could effectively improve the performance of the n-ZnO/p-Si heterojunction light emitting device. [ABSTRACT FROM AUTHOR]

n-ZnO/HfO2/p-GaN based heterojunction light emitting diodes were fabricated using a radio frequency magnetron sputtering system. The electroluminescence measurements revealed that dominant violet emissions centered at around 415 nm were emitted and improved performances were observed for the devices with the HfO2 intermediate layer; the color of the devices could be tuned from violet (0.18, 0.10) to cold white (0.22, 0.20) by varying the Ar/O2 flow ratio during the deposition of HfO2, which are probably ascribed to the deep level emission bands in ZnO. The results were studied by peak-deconvolution with Gaussian functions and were discussed in terms of band diagram of the heterojunctions. [ABSTRACT FROM AUTHOR]

We fabricate an ultraviolet (UV)/orange bicolor light emitting diode (LED) based on an n-ZnO/n-GaN isotype heterojunction, which presents a sharp ultraviolet emission centered at 367 nm and a broad orange emission centered at 640 nm under forward and reverse biases, respectively. Time dependence electroluminescence (EL) measurements reveal that this device shows good stability. The electroluminescence mechanism of the bicolor light emitting diode is discussed in terms of the material properties of the interfacial layer and the luminescence properties of the device in this work. [ABSTRACT FROM AUTHOR]

We report an \n-Mn0.04\Zn0.96\O\!(\MZO)\! \/\i-ZnGa2\O4\!\/\break\n-GaN structure both as a light-emitting diode and as an ultraviolet (UV) photodetector at forward and reverse biases, respectively. The n-MZO films were prepared on n-GaN coated sapphire substrates, followed by postdeposition thermal annealing treatment at 700 ^\circ\C, and an \i-ZnGa2\O4 interface layer was formed at the MZO/GaN interface after the annealing treatment. We found that the electroluminescence characteristics showed a transition from visible- to UV-dominant mode when the deposition temperature of the MZO film is from 100 ^ \circ\C to 300 ^\circ\C. For the UV detection performance, the devices based on the low-temperature deposition (100 ^\circ\C) of the MZO film showed the lowest dark current and the biggest ratio of photocurrent to dark current with a selectivity detectivity for 365 nm around light. [ABSTRACT FROM PUBLISHER]

There are still challenges in growth of transferable large area orientated ultrathin high‐melting‐point metal oxide single crystals with conventional methods. Herein, a new pathway to produce high quality single‐crystal ZnO nanoplates with more than 400 µm crystal size is revealed by using the van der Waals epitaxy (vdWE) combined with pulsed laser deposition (PLD) method on fluorophlogopite mica. The quasi‐2D ZnO plates as thin as 5 nm on fluorophlogopite mica without transition layer are achieved, showing an excellent thickness and orientation control while maintaining the excellent crystalline. ZnO nanoplates grown on conducting graphite and insulating hexagonal boron nitride (h‐BN) 2D substrates are also obtained through PLD assisted vdWE. The transfer of 15 nm thick quasi‐2D ZnO plates with 8 mm × 8 mm area onto a SiO2/Si substrate is successfully demonstrated. Based on the ZnO nanoplates, semitransparent self‐powered ultraviolet (UV) photodetectors and light‐emitting diodes centered at 400 nm UV region are demonstrated. This research highlights that the PLD assisted vdWE method is a fascinating way to fabricate high coverage ultrathin 2D ZnO plates with precisely thickness control for optoelectronic applications and may have enormous inspiration for other 2D nanomaterials growth. [ABSTRACT FROM AUTHOR]

[Display omitted] Despite their excellent environmental stability, low defect density, and high carrier mobility, large- n quasi-two-dimensional halide perovskites (quasi-2DHPs) feature a limited application scope because of the formation of self-assembled multiple quantum wells (QWs) due to the similar thermal stabilities of large- n phases. However, large- n quasi-phase-pure 2DHPs (quasi-PP-2DHPs) can solve this problem perfectly. This review discusses the structures, formation mechanisms, and photoelectronic and physical properties of quasi-PP-2DHPs, summarises the corresponding single crystals, thin films, and heterojunction preparation methods, and presents the related advances. Moreover, we focus on applications of large- n quasi-PP-2DHPs in solar cells, photodetectors, lasers, light-emitting diodes, and field-effect transistors, discuss the challenges and prospects of these emerging photoelectronic materials, and review the potential technological developments in this area. [ABSTRACT FROM AUTHOR]

Abstract: We have fabricated a fully transparent ultraviolet (UV)/violet dual-color electroluminescence (EL) device based on n-ZnO single crystal and p-GaN via a simple direct-contact method. The device presents dual-color EL under forward and reverse biases—an intense violet emission centered at 400nm from ZnO and a sharp UV emission peaked at 365nm from GaN, respectively. The reason for dual color emissions is proposed in terms of the energy band theory and the transmission spectra of ZnO single crystal and p-GaN. [Copyright &y& Elsevier]

Light-emitting diodes based on p -SnO 2 / i -MgZnO/ n -ZnO heterojunction have been fabricated. The material properties and the performance of heterojunction device are characterized. Current-voltage characteristics of the device show a diode-like rectifying behavior. Under forward bias, two prominent emission peaks located at 589 nm and 722 nm in the visible region and a weak ultraviolet emission are observed from p -SnO 2 / i -MgZnO/ n -ZnO heterojunction device. As the device is under reverse bias, a broad visible emission band dominates the electroluminescence spectrum at a high current. Furthermore, the emission mechanism has been discussed in terms of energy band structures of the device under forward and reverse biases. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) based on ZnO were fabricated on a p -Si substrate by using a pulsed laser deposition system. Significant electroluminescence (EL) improvement was demonstrated with the insertion of an HfO 2 electron blocking layer (EBL) in n -ZnO/ p -Si heterojunctions. Distinct near-band-edge emission at around 392 nm accompanying by a broadly strong visible emission was achieved when a proper thickness of HfO 2 EBL was used. Current-voltage and capacitance-voltage measurements confirmed that a proper thickness of the HfO 2 EBL can effectively balance the injection of electrons and holes, resulting in an increase of radiative recombination in the ZnO active layer and thus enhancing the EL performance of the devices. Five independent emissions corresponding to five different transition processes were proposed to clarify the EL origination of the n -ZnO/HfO 2 / p -Si heterojunction LEDs by Gaussian deconvolutions. It is hoped that results in this work should be helpful for the development of ZnO-based LEDs that can integrate ZnO with the Si planar technology. [ABSTRACT FROM AUTHOR]