Article
Chemistry, Physical
Yu Yin, Renfeng Chen, Rui He, Yiwei Duo, Hao Long, Weiguo Hu, Junyi Zhai, Caofeng Pan, Zihui Zhang, Junxi Wang, Jinmin Li, Tongbo Wei
Summary: This study demonstrates the dual-wavelength InGaN/GaN multiple-quantum-wells (MQWs) micro light emitting diode (Micro-LED) with color response under mechanical stimulation by piezo-phototronic effect. The change in the intensity and integral ratio of green and blue light leads to a significant display color shift. The different piezoelectric modulation between green QW and blue QW is revealed by experiments and APSYS simulation. This study is of high significance for the development of optical-based stress sensor with strain visualization and high spatial resolution.
Article
Engineering, Electrical & Electronic
Jack I. H. Haggar, Yuefei Cai, Jie Bai, Suneal Ghataora, Tao Wang
Summary: This paper demonstrates the feasibility of using (11-22) semipolar LEDs for long-wavelength VLC and the potential for monolithic integration to produce a single white light RGB chip. By utilizing high-performance semipolar InGaN/GaN LEDs, the research team successfully achieved high-speed data transmission for green, yellow, and amber LEDs.
ACS APPLIED ELECTRONIC MATERIALS
(2021)
Article
Chemistry, Multidisciplinary
Chaoqiang Zhang, Ke Gao, Fei Wang, Zhiming Chen, Philip Shields, Sean Lee, Yanqin Wang, Dongyan Zhang, Hongwei Liu, Pingjuan Niu
Summary: This paper investigates the edge strain relaxation of InGaN/GaN MQW micro-pillars. The results show a significant peak wavelength shift between micro-pillar arrays caused by a high range of strain relaxation. Raman spectrum observation and finite element method simulation provide effective verification of the strain relaxation analysis, offering references for the design and analysis of small-size micro-LED devices.
APPLIED SCIENCES-BASEL
(2022)
Article
Optics
D. S. Arteev, A. Sakharov, A. E. Nikolaev, W. Lundin, A. F. Tsatsulnikov
Summary: Research on temperature-dependent luminescent properties of dual-wavelength blue-cyan LEDs based on InGaN quantum wells revealed that the thickness of the interwell GaN layer had a significant impact on the spectra, especially at room temperature. Differences in the temperature behavior of above-bandgap PL spectra can be explained by variations in carrier collection regions for samples with different interwell barrier thickness. An anomalous increase in above-bandgap PL intensity was observed at temperatures around 120-150 K, which was absent in below-bandgap excitation cases.
JOURNAL OF LUMINESCENCE
(2021)
Review
Chemistry, Physical
Johanna Meier, Gerd Bacher
Summary: This review discusses the progress in device processing and analysis of LED devices based on three-dimensional core-shell microrods, emphasizing the potential of the 3D device architecture from an applications point of view.
Article
Optics
Vikas Pendem, Pratim Kumar Saha, Shonal Chouksey, Swaroop Ganguly, Dipankar Saha
Summary: In this study, nanosecond electrical pulsed-bias actuation was shown to induce a chirp in the emission spectra of strained InGaN quantum well light emitting diodes (LEDs), allowing for a broad tunable emission. The emission wavelength can be tuned not only by the amplitude, but also by the on-time of the pulse, while optical power can be adjusted solely by the on-time of the pulse. The chirp effect is a result of the dominance of the quantum confined Stark effect over junction temperature, with various factors such as polarization charges, applied bias, and carrier dynamics considered for accurate design of the pulsed-bias.
JOURNAL OF LUMINESCENCE
(2021)
Article
Materials Science, Multidisciplinary
C. K. Huang, C. Cheng, W. H. Lai, C. C. Chung, P. J. Chang, C. Y. Liu
Summary: An approach has been developed to measure the internal electrical field (Einternal) in InGaN quantum wells of GaN LEDs, with a linear relation established between forward voltage change and stressing voltage. By inducing a large reverse bias in the GaN LEDs, the initial compressive stress in MQWs was converted to a tensile state, reaching a stress-free condition at the transition point. The calculated Einternal across the In0.15Ga0.85N quantum wells was found to be in agreement with reported values.
MATERIALS CHEMISTRY AND PHYSICS
(2021)
Article
Optics
Xianhe Liu, Yi Sun, Yakshita Malhotra, Ayush Pandey, Ping Wang, Yuanpeng Wu, Kai Sun, Zetian Mi
Summary: This study addresses the issue of efficiency reduction in conventional quantum well light-emitting diodes (LEDs) with reduced areal size by utilizing N-polar InGaN nanowires. The epitaxy and performance characteristics of N-polar InGaN nanowire LEDs were studied, achieving a maximum external quantum efficiency of around 11% for LEDs with lateral dimensions as small as 750 nm directly on wafer without any packaging. The impact of electron overflow and Auger recombination on device performance was also investigated.
PHOTONICS RESEARCH
(2022)
Article
Physics, Applied
Axel R. R. Persson, Anders Gustafsson, Zhaoxia Bi, Lars Samuelson, Vanya Darakchieva, Per O. A. Persson
Summary: In this study, we investigated the optical properties of InGaN platelets with a quantum well structure for nano-LEDs emitting red light and their correlation with the atomic structure. Using cathodoluminescence measurements and a spectroscopy-thinning-imaging method, we observed how stacking mismatch boundaries intersect with the quantum well in plan-view and result in diminished cathodoluminescence intensity. The findings emphasize the significance of avoiding stacking mismatch in small LED structures due to the presence of relatively large non-radiative recombination regions caused by the mismatch boundaries.
APPLIED PHYSICS LETTERS
(2023)
Article
Nanoscience & Nanotechnology
Jumpei Yamada, Ai Mizuno, Tatsuya Honda, Keigo Yoshida, Rie Togashi, Ichirou Nomura, Tomohiro Yamaguchi, Tohru Honda, Katsumi Kishino
Summary: This study investigated the growth behavior of Indium gallium nitride (InGaN)-based nanocolumn arrays and fabricated red emission nanocolumn micro-light emitting diodes (μ-LEDs). The internal structure of the InGaN/GaN superlattice (SL) layer under the multiple-quantum-well (MQW) active layers was evaluated using scanning transmission electron microscopy (STEM) analysis. It was found that the crystal plane at the top of the nanocolumn changed as the number of SL pairs increased, and the growth of the semipolar (10-11) plane InGaN active layers was observed. Red nanocolumn μ-LEDs with an φ12μm emission window were fabricated, achieving an external quantum efficiency of 1.01% at 51 A cm(-2).
Article
Multidisciplinary Sciences
Geoffrey Avit, Yoann Robin, Yaqiang Liao, Hu Nan, Markus Pristovsek, Hiroshi Amano
Summary: GaN nanorods with axial InGaN/GaN MQWs insertions were synthesized using a cost-effective nanoimprint-lithography process. By controlling the diameter, luminescence with a blueshift up to 0.26 eV was achieved without significant degradation of the recombination rate. This process enables multiple single-color emissions from a single uniform InGaN/GaN MQWs layer, addressing color mixing issues in InGaN-based nanorods LED devices.
SCIENTIFIC REPORTS
(2021)
Article
Chemistry, Physical
Yu Zhang, Xiaolu Zhu, Lei Ao, Zhihua Xiong
Summary: The indium gallium nitride (InGaN)-based micro-LEDs hold great promise for future displays, but the low efficiency of InGaN-based red LEDs is a major obstacle for their development. This study investigates the effects of substrate-induced strain on the behavior of In atoms on GaN surfaces using first-principles calculations. The results show that applying slight tensile strain enhances In adsorption and promotes In incorporation in the GaN surface. Additionally, using substrates with larger lattice constants can stabilize the InGaN system and suppress phase separation.
JOURNAL OF PHYSICAL CHEMISTRY C
(2023)
Article
Computer Science, Information Systems
Zbigniew Lisik, Ewa Raj, Jacek Podgorski
Summary: This paper introduces a new electro-thermal model for LEDs, which allows for parametric analysis under steady-state conditions and has been validated through simulations using ANSYS software. The model offers a simple and low computational cost solution, aiding in the optimization of LED structures.
Article
Physics, Condensed Matter
Rui Li, Mingsheng Xu, Chengxin Wang, Shangda Qu, Kaiju Shi, Changfu Li, Xiangang Xu, Ziwu Ji
Summary: Experimental results show that different growth temperatures of InGaN/GaN multiple quantum wells can affect the structure and performance of LEDs, reducing the growth temperature can alter the structure and enhance the luminous efficiency.
SUPERLATTICES AND MICROSTRUCTURES
(2021)
Article
Physics, Applied
Abu Bashar Mohammad Hamidul Islam, Tae Kyoung Kim, Dong-Soo Shin, Jong-In Shim, Joon Seop Kwak
Summary: This study investigates the effect of current stress on InGaN/GaN multiple-quantum-well flip-chip blue micro light-emitting diodes (mu-LEDs) and reveals the mechanisms of defect aggregation and generation that cause changes in the optoelectronic performance of the devices. The aging test shows that the improvement in crystal quality due to defect aggregation initially enhances the light output power and external quantum efficiency (EQE), but the generation of sidewall point defects eventually leads to performance degradation. The findings highlight the importance of both defect aggregation and generation in understanding the degradation mechanisms of mu-LEDs.
APPLIED PHYSICS LETTERS
(2022)
Article
Environmental Sciences
Dongjun Lin, Xing Yuan, Binghao Jia, Peng Ji
Summary: This study analyzed the surface soil moisture products over the Qinghai-Tibet Plateau and found that the CSSPv2 high-resolution product performed the best, while other global products may overestimate the surface soil moisture dynamics. From 2009 to 2017, the soil moisture products of ESA CCI, ERA5, and CSSPv2 all showed an increasing trend, with wetting in the west and drying in the east.
Article
Meteorology & Atmospheric Sciences
Chunyu Shao, Xing Yuan, Feng Ma
Summary: Seasonal precipitation and temperature predictions based on global climate models developed from ocean-atmosphere interactions play a crucial role in water resources management and hazard mitigation. However, the skill of real-time forecasts and the impact of decadal variability on prediction remain uncertain. In this study, the forecast skill of precipitation and temperature in the Yangtze River basin was evaluated using hindcast and real-time forecast data from the North American multi-model ensemble (NMME). The results showed that real-time prediction skills were lower than hindcast skills, with a decrease in anomaly correlation and an increase in error, particularly at longer lead-times. The failure to accurately represent the decadal variations of ocean-atmospheric teleconnection, especially Indian Ocean surface temperature, during the real-time forecast period may explain the decline in prediction skills. This study highlights the importance of understanding decadal variability for improving real-time climate predictions.
Article
Geosciences, Multidisciplinary
Feng Ma, Xing Yuan
Summary: The Yangtze River basin experienced unprecedented heat in 2022. By considering duration and intensity, we found that the heatwaves of 2022 were much larger than historical averages, occurring once every 64 years. Without mitigation efforts, this record-breaking heat would become normal by the 2050s, affecting 70% of the basin's land and projected population before a 3 degrees C temperature increase. However, reducing warming levels could delay and minimize these impacts, with a 60% reduction in affected area at 2 degrees C and avoidance of emergence at 1.5 degrees C. Urgent mitigation efforts are necessary to reduce the risk of compound heat extremes.
GEOPHYSICAL RESEARCH LETTERS
(2023)
Article
Engineering, Civil
Enda Zhu, Yaqiang Wang, Xing Yuan
Summary: A reliable estimation of long-term change in terrestrial water storage (TWS) is critical for managing freshwater resources. In this study, a hybrid model combining land surface model simulation, human activities, and land properties with machine learning is developed to analyze TWS anomalies (TWSA). The model is applied to reconstruct historical TWSA in China from 1981 to 2020, showing reliable results and consistent patterns with independent datasets. Climate variation affects TWSA in humid regions, while human interventions dominate TWSA decline in arid and semi-arid areas. The potential of using artificial intelligence to represent human interventions is highlighted.
JOURNAL OF HYDROLOGY
(2023)
Article
Environmental Sciences
Jiayuan Li, Xing Yuan
Summary: Medium-range streamflow forecasts are largely dependent on accurate meteorological forecasts, but due to errors in precipitation forecasts, most streamflow forecasts only rely on historical data. In this study, a cascade LSTM model is used to forecast daily streamflow over 49 watersheds in the Yangtze River basin up to 15 days. The results show that the cascade LSTM model provides skillful streamflow forecasts, with the performance improving with increasing drainage area. The implementation of the cascade LSTM model leads to increased streamflow Kling-Gupta efficiency in 61-88% of the watersheds, especially at longer lead times.
Article
Meteorology & Atmospheric Sciences
Shiyu Zhou, Xing Yuan
Summary: The summer temperatures in 2022 have exceeded historical records over the Northern Hemisphere, leading to compound extreme events of droughts and heat waves with rapid intensification. By using a Lagrangian model to track the air mass trajectory during the heat waves, researchers found that upwind droughts enhance 21% of the heat waves over East China. Flash droughts, which have faster onset speeds, have a greater impact on heat waves than slowly evolving droughts. Flash droughts are a critical precursor for extreme heat waves in the downwind region.
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES
(2023)
Article
Meteorology & Atmospheric Sciences
Zhongwei Huang, Xing Yuan, Siao Sun, Guoyong Leng, Qiuhong Tang
Summary: Many countries are facing the challenge of groundwater depletion, and it is difficult to accurately estimate the long-term trend and inter-annual variation of groundwater depletion due to limited observations and uncertainties. In this study, a flux-based approach was used to estimate the groundwater depletion rate in China from 1965 to 2016, based on survey data and water availability datasets. The results showed that the groundwater depletion rate in China was 20.4 km(3) year(-1) on average during this period, with a significant increasing trend. Climate variability, especially precipitation, played a significant role in the inter-annual variation of groundwater depletion, and its influence has been increasing over time.
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES
(2023)
Article
Water Resources
Zhongwei Huang, Xing Yuan, Xingcai Liu, Qiuhong Tang
Summary: Study in the northern part of China has shown that the trend of water scarcity has changed from positive to negative after 2001. While increased water withdrawal was the main factor exacerbating water scarcity before 2001, climate change, with its increased precipitation, has become the major contributor to alleviating water scarcity from 2001 to 2020. Future projections also indicate that climate change will further alleviate water scarcity in the region by increasing water availability. These findings highlight the growing significance of climate change in influencing water scarcity and have important implications for regional water policy-making.
JOURNAL OF HYDROLOGY-REGIONAL STUDIES
(2023)
Article
Biodiversity Conservation
Abubaker Omer, Xing Yuan, Alexandra Gemitzi
Summary: Landscape transitions in the Nile River basin will likely accelerate due to socioeconomic developments and climate change, leading to significant changes in land use/land cover (LULC) and their impact on water resources. Using geospatial-hydrological models, this study projected future LULC changes in the Nile basin and its tributaries, identifying drivers and projected hydrological impacts under different socioeconomic pathways (SSPs). The results show increased forested areas in the upstream regions, reducing downstream river discharge, while unused land in the Atbara River sub-catchment is expected to decrease, resulting in a decrease in river flow during the rainy season. These findings emphasize the need for adaptive LULC planning and conservation measures in the Nile basin.
ECOLOGICAL INDICATORS
(2023)
Article
Water Resources
Haoyu Yang, Feng Ma, Xing Yuan
Summary: Meteorological droughts can lead to hydrological droughts and cause damage to agriculture and society. The impact of human activities on the propagation of droughts has been analyzed in the Heihe River Basin. The results show that human activities have a significant impact on drought propagation in the midstream area, while the impact is negligible in the upstream area.
HYDROLOGICAL PROCESSES
(2023)
Article
Meteorology & Atmospheric Sciences
Feng Ma, Xing Yuan, Xinyue Liu
Summary: This study examines the changes in characteristics of meteorological and hydrological droughts, as well as the propagation of droughts, under different climate change scenarios. It finds that climate warming leads to increased severity of both meteorological and hydrological droughts, but the impact of drought propagation varies across regions.
INTERNATIONAL JOURNAL OF CLIMATOLOGY
(2023)
Article
Environmental Sciences
Miaoling Liang, Xing Yuan, Shiyu Zhou, Zhanshan Ma
Summary: In this study, a three-dimensional meteorological flash drought index based on the percentile of 15-day moving average precipitation minus evapotranspiration (P-ET) is developed to investigate the spatiotemporal evolution of a mega-flash drought in the Yangtze River basin. The results show that the index can effectively capture the drought's evolution, and the nowcast of the P-ET index by the China Meteorological Administration global medium-range ensemble forecast system (CMA-GFS) roughly captures the drought's evolution. This study demonstrates the potential of using the index and nowcast for flash drought early warnings and water resource management.
Article
Environmental Sciences
Miaoling Liang, Xing Yuan, Wenyan Wang
Summary: The GRAPES_GFS is a new generation numerical weather forecast model developed by the China Meteorological Administration (CMA), but it has biases in the forecasts of surface latent heat fluxes and surface air temperature. These biases affect the forecasts of atmospheric dynamics and the application of GRAPES_GFS. Various modifications, such as adding a soil resistance term and considering the effect of salinity, have been made to reduce these biases and improve the performance of GRAPES_GFS. This paper highlights the importance of the representations of land/ocean surface and boundary layer processes in forecasting surface heat fluxes and 2 m air temperature.
Article
Geosciences, Multidisciplinary
Yuxin Li, Sisi Chen, Jun Yin, Xing Yuan
Summary: The rapid development of flash droughts can have serious impacts on agriculture, ecosystems, human health, and society. However, the current definition of flash droughts using pentad-averaged soil moisture may lead to low accuracy in assessing their occurrence and hinder the analysis of factors influencing their formation. In this study, we used a stochastic water balance framework to quantify the probability structure of soil moisture declining rapidly from a higher level to a lower one. By applying this framework to global datasets, we obtained global maps of drought development time and flash drought risks.
HYDROLOGY AND EARTH SYSTEM SCIENCES
(2023)
Article
Geosciences, Multidisciplinary
Yumiao Wang, Xing Yuan
Summary: The Yangtze River Basin experienced a severe flash drought in the summer of 2022, with precipitation deficit being the main trigger and high temperature intensifying the drought conditions.
GEOPHYSICAL RESEARCH LETTERS
(2023)
