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Abstract An ultraviolet-infrared (UV-IR) dual-wavelength photodetector (PD) based on a monolayer (ML) graphene/GaN heterostructure has been successfully fabricated in this work. The ML graphene was synthesized by chemical vapor deposition (CVD) and subsequently transferred onto GaN substrate using polymethylmethacrylate (PMMA). The morphological and optical properties of the as-prepared graphene and GaN were presented. The fabricated PD based on the graphene/GaN heterostructure exhibited excellent rectify behavior by measuring the current–voltage (I– V) characteristics under dark conditions, and the spectral response demonstrated that the device revealed an UV-IR dual-wavelength photoresponse. In addition, the energy band structure and absorption properties of the ML graphene/GaN heterostructure were theoretically investigated based on density functional theory (DFT) to explore the underlying physical mechanism of the two-dimensional (2D)/three-dimensional (3D) hybrid heterostructure PD device. This work paves the way for the development of innovative GaN-based dual-wavelength optoelectronic devices, offering a potential strategy for future applications in the field of advanced photodetection technology. Graphical Abstract

Highlights The main effects of deformation of flexible catalytic materials on the catalytic hydrogen evolution reaction performance are discussed, and a series of novel strategies to design highly active catalysts based on the mechanical flexibility of low-dimensional nanomaterials are summarized in detail. This review provides a strategic choice for the rational design of low-cost and high-performance industrialized electrocatalysts.

Micro-LED is considered an emerging display technology with significant potential for high resolution, brightness, and energy efficiency in display applications. However, its decreasing pixel size and complex manufacturing process create challenges for its integration with driving units. Recently, researchers have proposed various methods to achieve highly integrated micro-structures with driving unit. Researchers take advantage of the high performance of the transistors to achieve low power consumption, high current gain, and fast response frequency. This paper gives a review of recent studies on the new integration methods of micro-LEDs with different types of transistors, including the integration with BJT, HEMT, TFT, and MOSFET.

GaN-based micro light-emitting diode (LED) has gradually become one of the promising light sources for visible light communication (VLC), of which high modulation bandwidth has been demonstrated. In order to acquire high speed and high brightness for VLC application, the modulation bandwidth and optical performance of micro-LEDs were investigated in series and parallel in this work. The electrical characteristics, optical characteristics and communication characteristics of single-pixel, 2-pixel, 4-pixel series and parallel green micro-LEDs with different pixel sizes were systematically tested. High modulation bandwidth as much as 1.4 GHz was acquired by using 10 μm micro-LEDs with 4-pixel in parallel. It is found that parallel micro-LED array can achieve higher modulation bandwidth, higher brightness and higher stability as well, which can be used as the preferred mode for the development of micro-LED based VLC.

Micro-light-emitting diodes (micro-LEDs) with high modulation rates and low power consumption could attract growing attention as visible light communication (VLC) technology advances. The designed and fabricated semi-polar micro-LEDs have achieved high bandwidth at low current injection due to the reduced quantum-confined Stark effect (QCSE), which was significantly greater than that of typical c-plane at the same current injection. Semi-polar green micro-LEDs got a −3 dB bandwidth that surpasses 500 MHz and 1 GHz at low current densities of 43.8 A/cm2 and 120.6 A/cm2, while blue micro-LEDs exceed 500 MHz at low current densities of 76.6 A/cm2, respectively. Additionally, the free space VLC system has shown semi-polar blue and green micro-LED transmission data rates of 3.495 Gbps (433 A/cm2) and 3.483 Gbps (402 A/cm2) respectively. Semi-polar micro-LEDs, which can achieve low power consumption and high bandwidth, are anticipated to play a significant role in the development of energy-efficient VLC in the future.

In recent years, the rapid progress in the field of GaN-based power devices has led to a smaller chip size and increased power usage. However, this has given rise to increasing heat aggregation, which affects the reliability and stability of these devices. To address this issue, diamond substrates with nanostructures were designed and investigated in this paper. The simulation results confirmed the enhanced performance of the device with diamond nanostructures, and the fabrication of a diamond substrate with nanostructures is demonstrated herein. The diamond substrate with square nanopillars 2000 nm in height exhibited optimal heat dissipation performance. Nanostructures can effectively decrease heat accumulation, resulting in a reduction in temperature from 121 °C to 114 °C. Overall, the simulation and experimental results in this work may provide guidelines and help in the development of the advanced thermal management of GaN devices using diamond micro/nanostructured substrates.

GaN-based Micro-LED has been widely regarded as the most promising candidate for next generation of revolutionary display technology due to its advantages of high efficiency, high brightness and high stability. However, the typical micro-fabrication process would leave a great number of damages on the sidewalls of LED pixels, especially for Micro-LEDs, thus reducing the light emitting efficiency. In this paper, sidewall passivation methods were optimized by using acid-base wet etching and SiO2 layer passivation. The optical and electrical characteristics of optimized Micro-LEDs were measured and analyzed. The internal quantum efficiency (IQE) of Micro-LED was increased to 85.4%, and the reverse leakage current was reduced down to 10−13 A at −5 V. Optimized sidewall passivation can significantly reduce the non-radiative recombination centers, improving the device performance and supporting the development of high-resolution Micro-LED display.

GaN-based blue micro-light-emitting diodes (μ-LEDs) with different structures were designed, of which the effect of quantum well (QW) structure on modulation bandwidth was numerically explored. By using trapezoidal QWs, the quantum-confined Stark effect (QCSE) can be reduced, leading to an enhanced electron-hole wave function overlap, thereby increasing the recombination rate and reducing the differential carrier lifetime. In addition, the improved hole transport also creates favorable conditions for shortening the differential carrier lifetime. Furthermore, by comparing with traditional μ-LEDs with different thicknesses of QW, the modulation bandwidth of μ-LEDs with trapezoidal QWs exhibits a large advantage at lower current densities of below 2 kA/cm2.

GaN-based μLEDs with superior properties have enabled outstanding achievements in emerging micro-display, high-quality illumination, and communication applications, especially white-light visible light communication (WL-VLC). WL-VLC systems can simultaneously provide white-light solid-state lighting (SSL) while realizing high-speed wireless optical communication. However, the bandwidth of conventional white-light LEDs is limited by the long-lifetime yellow yttrium aluminum garnet (YAG) phosphor, which restricts the available communication performance. In this paper, white-light GaN-μLEDs combining blue InGaN-μLEDs with green/red perovskite quantum dots (PQDs) are proposed and experimentally demonstrated. Green PQDs (G-PQDs) and red PQDs (R-PQDs) with narrow emission spectrum and short fluorescence lifetime as color converters instead of the conventional slow-response YAG phosphor are mixed with high-bandwidth blue InGaN-μLEDs to generate white light. The communication and illumination performances of the WL-VLC system based on the white-light GaN-based μLEDs are systematically investigated. The VLC properties of monochromatic light (green/red) from G-PQDs or R-PQDs are studied in order to optimize the performance of the white light. The modulation bandwidths of blue InGaN-μLEDs, G-PQDs, and R-PQDs are up to 162 MHz, 64 MHz, and 90 MHz respectively. Furthermore, the white-light bandwidth of 57.5 MHz and the Commission Internationale de L’Eclairage (CIE) of (0.3327, 0.3114) for the WL-VLC system are achieved successfully. These results demonstrate the great potential and the direction of the white-light GaN-μLEDs with PQDs as color converters to be applied for VLC and SSL simultaneously. Meanwhile, these results contribute to the implementation of full-color micro-displays based on μLEDs with high-quality PQDs as color-conversion materials.

Oxygen vacancy (OV) states are the most prevalent chemical defects in metal oxides without extrinsic dopants, which govern the regime of photoelectrochemical (PEC) kinetics. So far, although tremendous strategies are developed to overcome the negative effects from OV, the threshold at which OV plays a positive role has not been specifically studied. Furthermore, the kinetics of stoichiometry changes as well as their effects on the charge transport aroused from manipulating OV distribution are still in confusion. Here, taking α-Ga2O3 nanorod arrays as the model, we show the evolution mechanism about the changes in OV distribution during vacancy engineering. Since the O diffusion flow into bulk is regulated by the surface OV-assisted migration mechanism, the surface OV concentration decreased first and recovered slightly after a period of time. This is deviated from the common sense that the longtime O2 annealing should bring about monotonical OV decrease at the surface. After PEC characterization and theory calculation, the results show that OV plays to the score in the PEC process, depending on its own spatial distribution. The optimized engineering strategy of OV spatial distribution is proposed to establish the efficient carrier separation nanoarchitectures for high-performance UV photodetection. This work provides an insight for clarifying fundamental rules for defect engineering in the PEC field. [ABSTRACT FROM AUTHOR]

Clubroot disease has spread explosively in recent years, posing a serious threat to cruciferous crop production. Take rapeseed for example, according to the statistics, until year 2022 the incidence of the clubroot has exceeded 1.33 million hectares in China. Breeding for resistant cultivars is considered as the most efficient and economical way to prevent clubroot disease spreading. However, the current CR cultivars mostly used CR loci of PbBa8.1 or CRb. Due to the complexity and diversity of Plasmodiophora brassicae from different locations, resources for resistant germplasm need to be explored. In this study, 14 clubroot-resistant Chinese cabbages were characterized using different clubroot pathogens and molecular markers for known CR loci. We found that among them, five materials, DG117, ZS105, SG01, SR06 and JQ07 did not contain CRb locus, and their disease resistance were stronger than Huashuang5R/Huayouza5R. At last, KL02 containing the CRb locus showed stronger resistance to PbXM (strain from Xinmin) than 409R, therefore it may contain other novel loci leading to better resistance. These six Chinese cabbage resources can be considerd as new resistance resources and could be utilized in future breeding work for CR Brassica napus. [ABSTRACT FROM AUTHOR]