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Spectral analysis is a widely used method for monitoring photosynthetic capacity. However, vegetation indices-based linear regression exhibits insufficient utilization of spectral information, while full spectra-based traditional machine learning has limited representational capacity (partial least squares regression) or uninterpretable (convolution). In this study, we proposed a deep learning model with enhanced interpretability based on attention and vegetation indices calculation for global spectral feature mining to accurately estimate photosynthetic capacity. We explored the ability of the model to uncover the optimal vegetation indices form and illustrated its advantage over traditional methods. Furthermore, we verified that power compression was an effective method for spectral processing. Our results demonstrated that the new model outperformed traditional models, with an increase in the coefficient of determination (R2) of 0.01-0.43 and a decrease in root mean square error (RMSE) of 1.58-12.48 μmol m-2 s-1. The best performance of our model in R2 was 0.86 and 0.81 for maximum carboxylation rate (Vcmax) and maximum electron transport rate (Jmax), respectively. The photosynthesis-sensitive spectral bands identified by our model were predominantly in the visible range. The most sensitive vegetation indices form discovered by our model was Reflectancenear−infrared+Reflectancegreen/blueReflectancenear−infrared×Reflectancered. Our model provides a new framework for interpreting spectral information and accurately estimating photosynthetic capacity.

The monolithically integrated self-driven photoelectric detector (PD) with the light-emitting diode (LED) epitaxial structure completely relies on the built-in electric field in the multi-quantum wells region to separate the photogenerated carriers. Here, we propose a novel superlattices–electron barrier layer structure to expand the potential field region and enhance the detection capability of the integrated PD. The PD exhibits a record-breaking photo-to-dark current ratio of 5.14 × 107, responsivity of 110.3 A/W, and specific detectivity of 2.2 × 1013 Jones at 0 V bias, respectively. A clear open-eyed diagram of the monolithically integrated chip, including the PD, LED, and waveguide, is realized under a high-speed communication rate of 150 Mbps. The obtained transient response (rise/decay) time of 2.16/2.28 ns also illustrates the outstanding transient response capability of the integrated chip. The on-chip optical communication system is built to achieve the practical video signals transmission application, which is a formidable contender for the core module of future large-scale photonic integrated circuits.

Abstract The realization of high quality (0001) GaN on Si(100) is paramount importance for the monolithic integration of Si‐based integrated circuits and GaN‐enabled optoelectronic devices. Nevertheless, thorny issues including large thermal mismatch and distinct crystal symmetries typically bring about uncontrollable polycrystalline GaN formation with considerable surface roughness on standard Si(100). Here a breakthrough of high‐quality single‐crystalline GaN film on polycrystalline SiO2/Si(100) is presented by quasi van der Waals epitaxy and fabricate the monolithically integrated photonic chips. The in‐plane orientation of epilayer is aligned throughout a slip and rotation of high density AlN nuclei due to weak interfacial forces, while the out‐of‐plane orientation of GaN can be guided by multi‐step growth on transfer‐free graphene. For the first time, the monolithic integration of light‐emitting diode (LED) and photodetector (PD) devices are accomplished on CMOS‐compatible SiO2/Si(100). Remarkably, the self‐powered PD affords a rapid response below 250 µs under adjacent LED radiation, demonstrating the responsivity and detectivity of 2.01 × 105 A/W and 4.64 × 1013 Jones, respectively. This work breaks a bottleneck of synthesizing large area single‐crystal GaN on Si(100), which is anticipated to motivate the disruptive developments in Si‐integrated optoelectronic devices.

The prediction of crop growth and nitrogen status is essential for agricultural development and food security under climate change scenarios. Crop models are powerful tools for simulating crop growth and their responses to environmental variables, but accurately capturing the dynamic changes in crop nitrogen remains a considerable challenge. Data assimilation can reduce uncertainties in crop models by integrating observations with model simulations. However, current data assimilation research is primarily focused on a limited number of observational variables, and insufficiently utilizes nitrogen observations. To address these challenges, this study developed a new multivariable data assimilation system, ORYZA-EnKF, that is capable of simultaneously integrating multivariable observations (including development stage, DVS; leaf area index, LAI; total aboveground dry matter, WAGT; and leaf nitrogen concentration, LNC). Then, the system was tested through three consecutive years of field experiments from 2021 to 2023. The results revealed that the ORYZA-EnKF model significantly improved the simulations of crop growth compared to the ORYZA2000 model. The relative root mean squared error (RRMSE) for LAI simulations decreased from 23–101% to 16–47% in the three-year experiment. Moreover, the incorporation of LNC observations enabled more accurate predictions of rice nitrogen dynamics, with RRMSE for LNC simulations reduced from 16–31% to 14–26%. And, the RRMSE decreased from 32–50% to 30–41% in the simulations of LNC under low-nitrogen conditions. The multivariable data assimilation system demonstrated its effectiveness in improving crop growth simulations and nitrogen status predictions, providing valuable insights for precision agriculture.

Accurate estimation of gross primary production (GPP) of paddy rice fields is essential for understanding cropland carbon cycles, yet remains challenging due to spatial heterogeneity. In this study, we integrated high-resolution unmanned aerial vehicle (UAV) imagery into a leaf biochemical properties-based model for improving GPP estimation. The key parameter, maximum carboxylation rate at the top of the canopy (Vcmax,025), was quantified using various spatial information representation methods, including mean (μref) and standard deviation (σref) of reflectance, gray-level co-occurrence matrix (GLCM)-based features, local binary pattern histogram (LBPH), and convolutional neural networks (CNNs). Our models were evaluated using a two-year eddy covariance (EC) system and UAV measurements. The result shows that incorporating spatial information can vastly improve the accuracy of Vcmax,025 and GPP estimation. CNN methods achieved the best Vcmax,025 estimation, with an R of 0.94, an RMSE of 19.44 μmol m−2 s−1, and an MdAPE of 11%, and further produced highly accurate GPP estimates, with an R of 0.92, an RMSE of 6.5 μmol m−2 s−1, and an MdAPE of 23%. The μref-GLCM texture features and μref-LBPH joint-driven models also gave promising results. However, σref contributed less to Vcmax,025 estimation. The Shapley value analysis revealed that the contribution of input features varied considerably across different models. The CNN model focused on nir and red-edge bands and paid much attention to the subregion with high spatial heterogeneity. The μref-LBPH joint-driven model mainly prioritized reflectance information. The μref-GLCM-based features joint-driven model emphasized the role of GLCM texture indices. As the first study to leverage the spatial information from high-resolution UAV imagery for GPP estimation, our work underscores the critical role of spatial information and provides new insight into monitoring the carbon cycle.

Abstract Background In this study, we intend to retrospectively analyze the clinical data of postoperative neuroblastoma children, including the results of follow-up examinations and laboratory tests, to explore the clinical value of combined serum Carbohydrate antigen 125 (CA125), neuron-specific enolase (NSE) and 24-hour urine vanillylmandelic acid (VMA) levels at baseline for the prediction of recurrence in children with neuroblastoma. Methods 265 children with neuroblastoma were successfully followed up, including 163 cases without recurrence (non-recurrence group) and 102 cases with recurrence (recurrence group). The levels of 24-hour urine VMA were determined using spectrophotometric methods. Additionally, the serum levels of CA125 and NSE were measured using electrochemiluminescence immunoassay. Results The serum CA125, NSE and 24-hour urine VMA levels were significantly higher in the recurrence group than in the non-recurrence group. It demonstrated a significant positive correlation between the levels of serum CA125, NSE, and 24-hour urine VMA in all children with neuroblastoma. All children in stage IV of neuroblastoma had the highest level of serum CA125, NSE and 24-hour urine VMA and vice versa. The combined CA125, NSE and VMA had significantly better sensitivity and specificity than an individual marker. Conclusions Combined serum CA125, NSE and 24-hour urine VMA had the potential to predict neuroblastoma recurrence more effectively.

Abstract As an emerging single crystals growth technique, the 2D-material-assisted epitaxy shows excellent advantages in flexible and transferable structure fabrication, dissimilar materials integration, and matter assembly, which offers opportunities for novel optoelectronics and electronics development and opens a pathway for the next-generation integrated system fabrication. Studying and understanding the lattice modulation mechanism in 2D-material-assisted epitaxy could greatly benefit its practical application and further development. In this review, we overview the tremendous experimental and theoretical findings in varied 2D-material-assisted epitaxy. The lattice guidance mechanism and corresponding epitaxial relationship construction strategy in remote epitaxy, van der Waals epitaxy, and quasi van der Waals epitaxy are discussed, respectively. Besides, the possible application scenarios and future development directions of 2D-material-assisted epitaxy are also given. We believe the discussions and perspectives exhibited here could help to provide insight into the essence of the 2D-material-assisted epitaxy and motivate novel structure design and offer solutions to heterogeneous integration via the 2D-material-assisted epitaxy method. Graphical Abstract

This work successfully achieves a strain-free AlN film with low dislocation density for DUV-LED through graphene-driving strain-pre-store engineering and present the unique mechanism of strain-relaxation in QvdW epitaxy.

The study of the three-dimensional(3D) distribution characteristics of ore-forming element geochemical field in Jinqingding gold deposit, Mouping-Rushan metallogenic belt, Shandong Province, summarizes the metallogenic law and establishes a 3D comprehensive prospecting model. It provides richer information for deep prediction and guides the direction of mine production and development. In this study, 3D modelling of the deposit and its geochemical field was carried out. Guided by the prospecting model of this deposit, the 3D geological bodies and 3D geochemical model of ore bodies were built up in this study based on comprehensive analysis upon the geological and geochemical data in this deposit, by using 3D modelling visualization technology and geostatistics. These models reveal the ore bodies features and geochemical characterization of this deposit. In order to reduce the uncertainty of the deep prospecting information, the 3D modelling of the Jinqingding gold deposit was carried out by the comprehensive information analysis and prediction of geology and geochemistry in the study area. The 3D model of the ore body shows that the ore body is wide in the middle and narrow at ends, and tends to narrow and disappear to the deep. The distribution characteristics of the geochemical field show that the elements and combination factors of Au, As, Sb, Hg, Cu, W, Sn, Co, Ni are distributed in the shallow part of the ore bodies, showing a decreasing trend of element-field strength to the deep. The characteristics of Mo and Bi are distributed deep in the ore bodies. The characteristics of Ag, Pb, and Zn are more scattered and there are multiple metallogenic centers. The 3D model of the combination geochemical field shows that the metallogenesis of gold occurred in the shallow area of the ore bodies, while it weakened in the deep. The results show that guided by the comprehensive prospecting model, the display, extraction and comprehensive analysis of 3D geological and geochemical anomaly information based on the 3D geochemical field model effectively evaluate the potential of deep prospecting and provide the evidences for deep prospecting prediction. The comprehensive analysis results show that the prospecting potential of the No.2 orebody of the Jinqingding gold deposit below -1 200 m is low-expected, and it is inappropriate to continue deep exploration massively.

Abstract Background Renal cancer is a common malignant tumor with an increasing incidence rate. Methods In this study, based on the gene expression profiles, we analyzed the compositions of tumor-infiltrating immune cells (TIICs) in renal cancer and paracancerous samples using CIBERSORT. The proportions of 22 TIICs subsets in 122 paired renal carcinoma and paracancerous samples, and 224 Wilms tumor (WT) samples varied between intragroup and intergroup. Results After analyzed the difference of TIICs composition between renal cancer and paired paracancerous samples, we found that M0 macrophages and CD8 T cells were significantly elevated, while naive B cells were significantly decreased in renal cancer samples compared with paracancerous samples. Survival analysis showed that high overall TIICs proportion, the low proportion of resting mast cells and the high proportion of activated memory CD4 T cells were associated with poor prognosis of renal cancer patients. In addition, 3 clusters were identified by hierarchical clustering analysis, and they presented a distinct prognosis. Cluster 1 had superior survival outcomes, while cluster 2 had an inferior survival outcome. Conclusions Our study indicated that overall TIICs proportion, certain TIICs subset proportion, including resting mast cells and activated memory CD4 T cells, and distinct cluster patterns were associated with the prognosis of renal cancer, which was significant for the clinical surveillance and treatment of renal cancer.

Hexagonal boron nitride (h-BN) is one promising material class for applications in DUV optoelectronics due to the layered structure and ultra-wide bandgap. The synthesis of h-BN with smooth surface morphology and high quality on dielectric substrates is the key to construct efficient functional devices thereon. In this study, we reported wafer-scale h-BN on c-plane sapphire substrates by metal organic chemical vapor deposition utilizing the flow modulation epitaxy (FME) with growth interruptions. The effect of the growth interruption location within FME on the surface morphology and crystalline quality of h-BN films was systematically investigated. The interruption after the TEB injection could promote the mobility of B adatoms, and the interruption after the NH3 injection could further relieve the passivation of N terminal growth fronts and mitigate the parasitic gas-phase reaction between growth precursors. By simultaneously employing interruptions after TEB and NH3 injections, the growth rate of h-BN increased significantly from 0.16 nm/min to 4.76 nm/min, and the surface roughness of 2-nm-thick h-BN was reduced to 0.587 nm. In addition, h-BN grown with an interruption solely after the NH3 injection presented the best crystallinity because the relatively slow growth rate reduced the possibility of impurity incorporation.

Visible light communication (VLC) has attracted widespread attention for wireless communications. The popularity of GaN‐based light‐emitting diodes (LEDs) has also laid a solid foundation for the application of VLC. As the light source of VLC, LED's modulation bandwidth directly determines the speed of communication. Herein, reviewing progress on modulation bandwidth improvement schemes of GaN LEDs transmitter is reviewed, covering aspects from epitaxial to devices. Epitaxial approaches include c‐polar facet epitaxial optimization, non/semipolar facet epitaxial growth, and chip scheme such as micro‐LEDs, nano‐LEDs, resonant cavity‐LEDs (RC‐LEDs), plasmon, and metacavity LEDs. In terms of white LEDs, approaches to tackle the slow Stokes transfer and long carrier life for conventional phosphors including new color‐conversion materials (CCMs) and new energy transfer routes are reviewed. This review promotes the development of GaN‐based LEDs as the transmitter for high‐speed VLC.

One-dimensional, direct, and narrow band gap indium arsenide (InAs) nanowires (NWs) have been emerging with great potentials for the next-generation wide-spectrum photodetectors. In this study, metal–semiconductor–metal (MSM) structure InAs NW-based photodetectors were fabricated by transferring MBE-grown NWs onto a sapphire substrate via a mechanical stamping method. These NW detectors exhibit strong negative photoconductive (NPC) effects, which are likely caused by the carrier dynamics in the “core-shell” structure of the NWs. Specifically, under the irradiation of a 405 nm violet laser, the maximum Idark/Ilight ratio reaches ∼102 and the NPC gain reaches 105 at a low bias voltage of 0.2 V. At room temperature, the rise and decay times of InAs NW devices are 0.005 and 2.645 s, respectively. These InAs NW devices with a high Idark/Ilight ratio and NPC gain can be potentially used in the field of vis/near-IR light communication in the future.

Metal-assisted chemical etching plays a critical role in synthesizing GaN nanowires. In this work, GaN films grown on Si(111) substrates are immersed in CuSO4/HF etchant under UV illumination to fabricate nanowires. These GaN nanowires are much more homogeneous than those synthesized in AgNO3/HF etchant. During the etching process, Cu and Ag particles appear primarily at the cracks in GaN films where the atoms are more reactive. After that, Cu accumulates continuously at the cracks, while Ag dendrites are formed and spread all over the whole GaN surface. These phenomena are ascribed to the different nucleation rates and diffusion rates of Ag and Cu. The metal particles thus formed block out ultraviolet illumination, and suppress the etching of GaN. It is the orderly accumulation of Cu particles that enables uniform photochemical etching. Our work proposes a novel metal-assisted photochemical etching method for synthesizing uniform GaN nanowires and reveals the physical distribution of the metal during etching. This method has the potential for rapid preparation of GaN nanowires. Keywords: Metal-assisted chemical etching, GaN nanowires, Ag dendrites, Cu particles

Constant advance in improving the luminous efficacy (ηL) of nitride-based light-emitting diodes (LEDs) plays a critical role for saving measurable amounts of energy. Further development is motivated to approach the efficiency limit for this material system while reducing the costs. In this work, strategies of using thin AlN prebuffer and transitional-refraction-index patterned sapphire substrate (TPSS) were proposed, which pushed up the efficiency of white LEDs (WLEDs). The AlN prebuffer was obtained through physical vapor deposition (PVD) method and TPSS was fabricated by dry-etched periodic silica arrays covered on sapphire. Devices in mass production confirmed that PVD AlN prebuffer was able to improve the light output power (φe) of blue LEDs (BLEDs) by 2.53% while increasing the productivity by ~8% through shortening the growth time. Additionally, BLEDs on TPSS exhibited an enhanced top ηext of 5.65% in contrast to BLEDs on the conventional PSS through Monte Carlo ray-tracing simulation. Consequently, φe of BLEDs was experimentally enhanced by 10% at an injected current density (Jin) of 40 A/cm2. A peak ηL of 295.2 lm/W at a Jin of 0.9 A/cm2 and the representative ηL of 282.4 lm/W at a Jin of 5.6 A/cm2 for phosphor-converted WLEDs were achieved at a correlated color temperature of 4592 K.

Abstract Efficient and low‐cost production of high‐quality aluminum nitride (AlN) films during heteroepitaxy is the key for the development of deep ultraviolet light‐emitting diodes (DUV‐LEDs). Here, the quasi‐2D growth of high‐quality AlN film with low strain and low dislocation density on graphene (Gr) is presented and a high‐performance 272 nm DUV‐LED is demonstrated. Guided by first‐principles calculations, it is found that AlN grown on Gr prefers lateral growth both energetically and kinetically, thereby resulting in a Gr‐driven quasi‐2D growth mode. The strong lateral growth mode enables most of dislocations to annihilate each other at the AlN/Gr interface, and therefore the AlN epilayer can quickly coalesce and flatten the nanopatterned sapphire substrate. Based on the high quality and low strain of AlN film grown on Gr, the as‐fabricated 272 nm DUV‐LED shows a 22% enhancement of output power than that with low‐temperature AlN buffer, following a negligible wavelength shift under high current. This facile strategy opens a pathway to drastically improve the performance of DUV‐LEDs.

In this study, we demonstrate the phosphor-free hybrid white LED devices with the combination of the truncated-hexagonal-pyramid (THP) structures and quantum dots (QDs) (THPQD). In the THP structures, it is noted that the broad spectrum can be obtained from different microfacets. Moreover, the THP structures make the far-field viewing angle decrease by ~45.4° and improve the light extraction efficiency compared with the traditional LED. The simulations also show that the light extraction efficiency of the THP LED is as approximately seven times as high as that of the traditional LED. Furthermore, by controlling the selective area growth (SAG) and adding QDs, the white emission can be realized from the THPQD LED with high color-rendering index (CRI). The CRI of the THPQD LED is from 71.2 up to 87.2 with the change of driving different current and its correlated color temperature covers the scope from 4845 to 5877 K.

AlGaN-based deep UV (DUV) LEDs generally employ a p-type electron blocking layer (EBL) to suppress electron overflow. However, Al-rich III-nitride EBL can result in challenging p-doping and large valence band barrier for hole injection as well as epitaxial complexity. As a result, wall plug efficiency (WPE) can be compromised. Our systematic studies of band diagram and carrier concentration reveal that carrier concentrations in the quantum well and electron overflow can be significantly impacted because of the slope variation of the quantum barrier (QB) conduction and valence bands, which in turn influence radiative recombination and optical output power. Remarkably, grading the Al composition from 0.60 to 0.70 for the 12-nm-thick AlGaN QB of the DUV LED without the EBL can lead to 13.5% higher output power and similar level of overflown electron concentration (~1 × 1015/cm3) as opposed to the conventional DUV LED with the p-type EBL. This paradigm is significant for the pursuit of higher WPE or shorter emission wavelength for DUV LEDs and lasers, as it provides a new direction for addressing electron overflow and hole injection issues.

With the development of wireless optical communication and solid-state lighting, the high efficiency, large bandwidth, and high uniform white light source becomes more and more important. In this paper, a white light source generated by red, green, and blue laser diodes (RGB LDs) was synthetized according to the calculated power ratio of RGB LDs based on the chromaticity theory. The high coherence of the lasers normally leads to the nonuniform white light. Thus, it is to improve the illumination quality of the lighting source by employing micro lens for the purpose of homogenization. The simulation results showed that the uniformity of the white light incoherent radiation was above 90% which proves that the coherence of the lasers was destroyed. In addition, the photoelectric parameters of the RGB-LD mixed white light after homogenization was characterized. Meanwhile, the modulation bandwidth of RGB LDs before and after homogenization was analyzed, respectively, and it shows that the bandwidth was more than 1 GHz, which is limited by the photodetector cut-off frequency. Such a high-uniformity and high-speed RGB-LD mixed white light can be deployed for illumination and wireless communication simultaneously.

The light extraction efficiency (LEE) of different polarization modes have been simulated by FDTD solutions for three photonic crystal (PhC) structures, which are spherical-PhC LED, cylindrical-PhC LED and compound-PhC LED. The TE-and TM-mode LEE are simulated seperately. It shows that the discontinuity of the structure from the propagation direction will cause decrease of TE-mode and TM-mode LEE. TE and TM mode are enhanced by 60% and 40% in cylindrical-PhC LED, in which the single nanorod act as light waveguide. Finally, a multi-layer-compound-PhC-LED is proposed. Results show that the TM-mode LEE based on this structure is increased by 1.45 times at a wavelength of 532 nm, and the TM-mode illuminous intensity will be larger than that of TE mode, and then polarization inversion occurs. Keywords: Photonic crystals, Polarization, GaN-based LED, Light extraction efficiency

Conventionally, Cu is preferred over Al to fabricate integrated inductors with higher quality factors on either silicon or sapphire substrates, profiting from its lower resistivity. However, after investigating and comparing these two kinds of metal multilayers in terms of fabrication process, electrical conductivity, in-depth profile analysis and performance of actual inductors, the Al-based metal multilayer exhibits competitive ability in fabricating thin-film inductors on sapphire compared to Cu-based multilayers. This is attributed to the degradation in electrical conductivity out of oxidation of Cu-based metal sublayers or forming alloys between them. Furthermore, in order to avoid complicated de-embedding procedures in the characterization of the on-chip inductors, a six-element equivalent physical model, which takes the parasitic effect of radio-frequency (RF) test structures into account, is proposed and validated by matching well with embedded measurement results.

InGaN-based micro-structured light-emitting diodes (µLEDs) play a critical role in the field of full-color display. In this work, selected area growth (SAG) of a micro-pyramid LED array was performed on a 2-inch wafer-scale patterned SiO2 template (periodicity: 4 µm diameter), by which a uniform periodic µLED array was achieved. The single-element pyramid-shaped LED exhibited 6 equivalent semipolar {1-101} planes and a size of about 5 µm, revealing a good crystalline quality with screw and edge dislocation densities of 8.27 × 107 and 4.49 × 108 cm−2. Due to the stress–relaxation out of the SAG, the as-built compressive strain was reduced to 0.59 GPa. The µLED array demonstrated a stable emission, confirmed by a small variation of electroluminescence (EL) peak wavelength over a wide range of current density up to 44.89 A/cm2, as well as tiny fluctuations (within 1.9 nm) in the EL full width at half maximum. The photoluminescence peak wavelength exhibits a good uniformity throughout the whole wafer with a discrete probability of only 0.25%.

Versatile applications call for InGaN-based light-emitting diodes (LEDs) to operate at ultra-high current densities with high quantum efficiency. In this work, we investigated the size-dependent effects of the electrical and optical performance of LEDs as increasing the current density up to 100 A/cm2, which demonstrated that mini-strip flip-chip LEDs were superior option to achieve better performance. In detail, at a current density of 100 A/cm2, the light output power density of these mini-strip LEDs was improved by about 6.1 W/cm2, leading to an improvement in the wall-plug efficiency by 4.23%, while the operating temperature was reduced by 11.3 °C, as compared with the large-sized LEDs. This could be attributed to the increase in the sidewall light extraction, alleviated current crowding effect, and improved heat dissipation. This work suggests an array of mini-strip LEDs would provide an option in achieving higher luminescent efficiency at ultrahigh current injection conditions for various applications.

Large-scale two-dimensional air-gap photonic crystals (PhCs) were embedded in an n-type GaN layer to enhance the light emission of GaN-based light-emitting diodes (LEDs). The embedded-PhCs were obtained through overgrowth on n-GaN templates, which had air holes array previously fabricated by using nanosphere lithography technology. The effects of the distance D from active region to PhCs on the light extraction efficiency (LEE) of LEDs are investigated by experiments and finite difference-time domain simulation. The PhC LEDs with D = 2370 nm showed an improved light output power by 80.8% on average at forward current of 350 mA without degradation of electrical performance compared to conventional LEDs. It is mainly attributed to the improved LEE by enhancing the interaction of the guided modes and the embedded air-gap PhCs.

The growth of nitride on large-size and low-cost amorphous substrates has attracted considerable attention for applications in large-scale optoelectronic devices. In this paper, we reported the growth of GaN-based light-emitting diodes (LEDs) on amorphous SiO2 substrate with the use of nanorods and graphene buffer layers by metal organic chemical vapor deposition (MOCVD). The effect of different growth parameters on the morphology and vertical-to-lateral aspect ratio of nanorods was discussed by analyzing growth kinetics. Furthermore, we tuned nanorod coalescence to obtain continuous GaN films with a blue-LED structure by adjusting growth conditions. The GaN films exhibited a hexagonal wurtzite structure and aligned c-axis orientation demonstrated by X-ray diffractometer (XRD), Raman, and transmission electron microscopy (TEM) results. Finally, five-pair InGaN/GaN multi-quantum-wells (MQWs) were grown. The photoluminescence (PL) showed an intense emission peak at 475 nm, and the current–voltage (I-V) curve shows a rectifying behavior with a turn-on voltage of 5.7 V. This work provides a promising fabrication method for the large-area and low-cost GaN-based devices on amorphous substrates and opens up the further possibility of nitride integration with Si (100) complementary metal oxide semiconductor (CMOS) electronics.

Electron-leakage is a deep-rooted problem for nitride-based light-emitting diodes (LEDs), particularly for AlGaN-based deep-ultraviolet (DUV) LEDs. In this paper, a specific design for the electron-blocking structure in AlGaN DUV LEDs, increasing the Al composition of the last quantum barrier to the same value as that of the electron-blocking layer accompanied with composition-graded p-AlGaN layer, is proposed to reduce electron leakage. Simulation results demonstrate that this design can effectively reduce electron leakage and hence increase internal quantum efficiency. Furthermore, fabricated devices with at an emitting wavelength of 292 nm verify remarkably enhanced light-output power. At 20-mA injection current, the proposed structure achieved a light-output increment as high as 98%, compared with the conventional structure.

We report on the maskless epitaxial lateral overgrowth (ELOG) of the AlN layer on trench-patterned AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). With a two-phase growth of different V/III ratio at a relatively low growth temperature of 1250 °C, up to a 7.3-μm-thick high-quality crack-free AlN film with a threading dislocation density of 8 × 108 cm-2 was obtained. Compared with the 0.9-μm AlN film grown on a planar sapphire substrate, the ELOG-AlN film has a lower dislocation density and a much better strain state, regardless of its 7.3-μm thickness. Compared with the single low V/III ratio growth, the two-phase growth method can lead to a coherent coalescence at the second growth stage and hence suppress new dislocations generating at the coalescence fronts. Stimulated emission was observed from Al(Ga)N multi-quantum-wells laser grown on the ELOG-AlN template with low dislocation density. The deep-ultraviolet laser (DUV) on these templates exhibited lasing at 263.3 nm with the spectral linewidth of 1.29 nm and threshold pumping power density of 2.7 MW/cm2 at room temperature.

In this paper, isoelectronic doping with indium (In) in p-GaN is investigated on the basis of the thermal quenching of ultraviolet luminescence (UVL) band. A phenomenological rate-equation model is proposed as a nondestructive diagnostic technique to acquire the dopant ionization energy of p-GaN. In terms of this model, we analyze the evolution of the ionization energy of p-GaN samples grown with different trimethyindium flow rate and find that isoelectronic doping with appropriate In incorporation is able to significantly reduce the ionization energy of the acceptor from 245 to 112 meV, which are consistent with the results of the variable temperature Hall-effect measurements. The comparison between the samples' full width at half maximum of the UVL band indicates that excessive In incorporation will degenerate the conductivity of p-GaN.

In this paper, we experimentally demonstrated a novel approach known as electroless silver plating (ESP) for the fabrication of Ag-only reflectors on vertical light-emitting diodes (VLEDs). The Ag reflector that was obtained through the ESP approach shows a higher reflectance of 83% and a lower contact resistivity of 6 * 10-3 Ω · cm2 with p-GaN, compared with that fabricated through the conventional electron beam (EB) approach, which shows a reflectance of 75% and a contact resistivity of 6.2 * 10-2 Ω · cm2, respectively. Improvements in the light output intensity-current (L-I) and current-voltage (I-V) results in VLEDs, which originated from the high reflectance and low-contact resistivity of the incorporated ESP-Ag reflector. Our result opens up an alternative and promising way to substitute the traditional EB approach for Ag-based reflector fabrication and, thus, is practically meaningful in real device fabrication, such as with VLEDs.

A 365-nm UV LED was fabricated based on embedded nanoporous AlGaN distributed Bragg reflectors (DBR) by electrochemical etching. The porous DBR had a reflectance of 93.5% at the central wavelength of 365 nm; this is the highest value of porous AlGaN DBRs below 370 nm which has been reported so far. An innovative two-step etching method with a SiO2 sidewall protection layer (SPL) was proposed to protect the n-AlGaN layer and active region of UV LED from being etched by the electrolyte. The DBR-LED with SPL showed 54.3% improvement of maximal external quantum efficiency (EQE) and 65.7% enhancement of optical power at 100 mA without any degeneration in electrical properties, compared with the un-etched standard LED sample. This work has paved the way for the application of electrically-pumped UV LEDs and VCSELs based on nanoporous AlGaN DBRs.

β-Ga2O3, characterized with high n-type conductivity, little lattice mismatch with III-Nitrides, high transparency (>80%) in blue, and UVA (400–320 nm) as well as UVB (320–280 nm) regions, has great potential as the substrate for vertical structure blue and especially ultra violet LEDs (light emitting diodes). Large efforts have been made to improve the quality of III-Nitrides epilayers on β-Ga2O3. Furthermore, the fabrication of vertical blue LEDs has been preliminarily realized with the best result that output power reaches to 4.82 W (under a current of 10 A) and internal quantum efficiency (IQE) exceeds 78% by different groups, respectively, while there is nearly no demonstration of UV-LEDs on β-Ga2O3. In this review, with the perspective from materials to devices, we first describe the basic properties, growth method, as well as doping of β-Ga2O3, then introduce in detail the progress in growth of GaN on (1 0 0) and (−2 0 1) β-Ga2O3, followed by the epitaxy of AlGaN on gallium oxide. Finally, the advances in fabrication and performance of vertical structure LED (VLED) are presented.

In this work, efficiency droop of InGaN/GaN multiple-quantum-well LEDs with super wide well (WW) is discussed by comparing the external quantum efficiency (EQE) of GaN grown on sapphire and FS-GaN substrates. The luminescence and electrical characteristics of these WW LEDs are also experimentally and theoretically analyzed. With the increase of well width from 3 nm to 6 nm, high V-pits density and more strain relaxation are found in WW LED on sapphire, which exhibits greatly reduced peak efficiency but almost negligible droop behavior. In contrast, despite a larger polarization field, WW LED on FS-GaN shows obviously enhanced peak efficiency and comparable droop compared to the counterpart with 3-nm well. The Auger recombination probably dominates the mechanism of efficiency droop rather than defect-related nonradiative recombination or polarization effect in the WW LED on both sapphire and FS-GaN, especially at high current density.

High-resistive layers were obtained by periodic growth and in situ annealing of InGaN. The effect of the annealing temperature of InGaN on the indium content and the material sheet resistive was investigated. The indium content decreased as the increase of in situ annealing temperature. Additionally, the material sheet resistance increased with the increase of the in situ annealing temperature for the annealed samples and reached 2 × 1010Ω/sq in the light and 2 × 1011Ω/sq in the dark when the in situ annealing temperature reached 970∘C. The acquirement of high-resistive layers is attributed to the generation of indium vacancy-related defects. Introducing indium vacancy-related defects to compensate background carriers can be an effective method to grow high-resistance material.

GaN-based flip-chip light-emitting diodes (FC-LEDs) grown on nanopatterned sapphire substrates (NPSS) are fabricated using self-assembled SiO2 nanospheres as masks during inductively coupled plasma etching. By controlling the pattern spacing, epitaxial GaN can be grown from the top or bottom of patterns to obtain two different GaN/substrate interfaces. The optoelectronic characteristics of FC-LED chips with different GaN/sapphire interfaces are studied. The FC-LED with an antireflective interface layer consisting of a NPSS with GaN in the pattern spacings demonstrates better optical properties than the FC-LED with an interface embedded with air voids. Our study indicates that the two types of FC-LEDs grown on NPSS show higher crystal quality and improved electrical and optical characteristics compared with those of FC-LEDs grown on conventional planar sapphire substrates.

The degradation behaviors of high power GaN-based vertical blue LEDs on Si substrates were measured using in-situ accelerated life test. The results show that the dominant failure mechanism would be different during the operation. Besides that, the corresponding associated failure mechanisms were investigated systematically by using different analysis technologies, such as Scan Electron Microscopy, Reflectivity spectroscopy, Transient Thermal Analysis, Raman Spectra, etc. It is shown that initially, the failure modes were mainly originated from the semiconductor die and interconnect, while afterwards, the following serious deterioration of the radiant fluxes was attributed to the package. The interface material and quality, such as die attach and frame, play an important role in determining the thermal performance and reliability. In addition, the heating effect during the operation will also release the compressive strain in the chip. These findings will help to improve the reliability of GaN-based LEDs, especially for the LEDs with vertical structure.

To evaluate electron leakage in InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs), analytic models of ballistic and quasi-ballistic transport are developed. With this model, the impact of critical variables effecting electron leakage, including the electron blocking layer (EBL), structure of multiple quantum wells (MQWs), polarization field, and temperature are explored. The simulated results based on this model shed light on previously reported experimental observations and provide basic criteria for suppressing electron leakage, advancing the design of InGaN/GaN LEDs.

In this work, a novel carrier concentration adjusting insertion layer for InGaN/GaN multiple quantum wells light-emitting diodes was proposed to mitigate the efficiency droop and improve optical output properties at high current density. The band diagrams and carrier distributions were investigated numerically and experimentally. The results indicate that due to the newly formed electron barrier and the adjusted built-in field near the active region, the hole injection has been improved and a better radiative recombination can be achieved. Compared to the conventional LED, the light output power of our new structure with the carrier concentration adjusting layers is enhanced by 127% at 350 mA , while the efficiency only droops to be 88.2% of its peak efficiency.

In this work, novel double Electron Blocking Layers for InGaN/GaN multiple quantum wells light-emitting diodes were proposed to mitigate the efficiency droop at high current density. The band diagram and carriers distributions were investigated numerically. The results indicate that due to a newly formed holes stack in the p-GaN near the active region, the hole injection has been improved and an uniform carriers distribution can be achieved. As a result, in our new structure with double Electron Blocking Layers, the efficiency droop has been reduced to 15.5 % in comparison with 57.3 % for the LED with AlGaN EBL at the current density of 100 A/cm2.

Large-scale Ag nanodisks (NDs) arrays fabricated using nanospherical-lens lithography (NLL) are embedded in p-GaN layer of an InGaN/GaN light-emitting diode (LED) for generating localized surface plasmon (LSP) coupling with the radiating dipoles in the quantum-well (QWs). Based on the Ag NDs with the controlled surface coverage, LSP leads to the improved crystalline quality of regrowth p-GaN, increased photoluminescence (PL) intensity, reduced PL decay time, and enhanced output power of LED. Compared with the LED without Ag NDs, the optical output power at a current of 350 mA of the LSP-enhanced LEDs with Ag NDs having a distance of 20 and 35 nm to QWs is increased by 26.7% and 31.1%, respectively. The electrical characteristics and optical properties of LEDs with embedded Ag NPs are dependent on the distance of between Ag NPs and QWs region. The LED with Ag NDs array structure is also found to exhibit reduced emission divergence, compared to that without Ag NDs.

Self-assembly SiO2 nanosphere monolayer template is utilized to fabricate nanopatterned sapphire substrates (NPSSs) with 0-nm, 50-nm, and 120-nm spacing, receptively. The GaN growth on top of NPSS with 0-nm spacing has the best crystal quality because of laterally epitaxial overgrowth. However, GaN growth from pattern top is more difficult to get smooth surface than from pattern bottom. The rougher surface may result in a higher work voltage. The stimulation results of finite-difference time-domain (FDTD) display that too large or too small spacing lead to the reduced light extracted efficiency (LEE) of LEDs. Under a driving current 350 mA, the external quantum efficiencies (EQE) of GaN-based LEDs grown on NPSSs with 0-nm, 50-nm, and 120-nm spacing increase by 43.3%, 50.6%, and 39.1%, respectively, compared to that on flat sapphire substrate (FSS). The optimized pattern spacing is 50 nm for the NPSS with 600-nm pattern period.

The InGaN multiple quantum well light-emitting diodes (LEDs) with different sizes of indium-tin-oxide (ITO) nanobowl photonic crystal (PhC) structure has been fabricated using self-assembled monolayer nanosphere lithography. The light output power (LOP) of PhC LEDs (at 350 mA) has been enhanced by 63.5% and the emission divergence exhibits a 28.8° reduction compared to conventional LEDs without PhC structure. Current-Voltage curves have shown that these PhC structures on ITO layer will not degrade the LED electrical properties. The finite-difference time-domain simulation (FDTD) has also been performed for light extraction and emission characteristics, which is consistent with the experimental results.