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The efficiency of multiple quantum well (QW) light emitting diodes (LEDs) to a large degree depends on uniformity of hole distribution between the QWs. Typically, transport between the QWs takes place via carrier capture into and thermionic emission out of the QWs. In InGaN/GaN QWs, the thermionic hole transport is hindered by the high quantum confinement and polarization barriers. To overcome this drawback, hole injection through semipolar QWs located at sidewalls of V-defects had been proposed. However, in the case of the V-defect injection, strong lateral emission variations take place. In this work, we explore the nature of these variations and the impact of the V-defects on the emission spectra and carrier dynamics. The study was performed by mapping electroluminescence (EL) and photoluminescence (PL) with a scanning near-field optical microscope in LEDs that contain a deeper well that can only be populated by holes through the V-defects. Applying different excitation schemes (electrical injection and optical excitation in the far- and near-field), we have shown that the EL intensity variations are caused by the lateral nonuniformity of the hole injection. We have also found that, in biased structures, the PL intensity and decay time in the V-defect regions are only moderately lower that in the V-defect-free regions thus showing no evidence of an efficient Shockley-–Read–Hall recombination. In the V-defect regions, the emission spectra experience a red shift and increased broadening, which suggests an increase of the In content and well width in the polar QWs close to the V-defects. [ABSTRACT FROM AUTHOR]

Micro-light-emitting diodes (µLEDs) are gathering significant interest as a technology for emerging micro-displays. However, µLEDs encounter numerous obstacles, including size-dependent efficiency loss, poor efficiency of red µLEDs, and challenges associated with the mass transfer and integration of full-color µLEDs. These issues become more acute in ultra-small µLEDs (<5 µm), which were required by the augmented reality (AR) displays. Here, we discuss the principal challenges faced by µLEDs and explore the possible solutions. We highlight recent advances in InGaN-based RGB µLEDs tailored for AR displays. In particular, we discuss the advancements in ultra-small InGaN µLEDs scaled down to 1 µm, the developments in InGaN red µLEDs, and the implementation of tunnel junction-based cascaded InGaN µLEDs for monolithic integration. [ABSTRACT FROM AUTHOR]

V-defects are morphological defects that typically form on threading dislocations during epitaxial growth of (0001) -oriented GaN layers. A V-defect is a hexagonal pyramid-shaped depression with six { 10 1 ¯ 1 } -oriented sidewalls. These semipolar sidewalls have a lower polarization barrier than the polarization barriers present between the polar c-plane quantum wells and quantum barriers and can laterally inject carriers directly into quantum wells in GaN-based light emitting diodes (LEDs). This is especially important, as the high polarization field in c-plane GaN is a significant factor in the high forward voltage of GaN LEDs. The optimal V-defect density for efficient lateral carrier injection in a GaN LED (∼109 cm−2) is typically an order of magnitude higher than the threading dislocation density of GaN grown on patterned sapphire substrates (∼108 cm−2). Pure-edge dislocation loops have been known to exist in GaN, and their formation into large V-defects via low-temperature growth with high Si-doping has recently been studied. Here, we develop a method for pure-edge threading dislocation half-loop formation and density control via disilane flow, growth temperature, and thickness of the half-loop generation layer. We also develop a method of forming the threading dislocation half-loops into V-defects of comparable size to those originating from substrate threading dislocations. [ABSTRACT FROM AUTHOR]

The efficiency of operation of GaN-based light emitting diodes (LEDs) to a large degree relies on realization of a uniform hole distribution between multiple quantum wells (QWs) of the active region. Since the direct thermionic transport between the QWs is inefficient, the hole injection through semipolar 10 1 ¯ 1 QWs that form on the facets of V-defects has been suggested as an alternative approach. However, for an efficient LED operation, the carrier distribution should be uniform not only vertically, between the QWs but also laterally, within individual QWs. In this work, the lateral carrier distribution in long wavelength InGaN/GaN QW LEDs is studied by the scanning near-field optical microscopy. The measurements have shown that emission is concentrated around the V-defect injectors. At high currents, the diffusion length of holes in polar QWs was found to be ∼0.6–1 μm and the hole diffusion coefficient ∼0.6 cm2/s. The obtained data should aid design of the V-defect injectors for a laterally uniform carrier distribution in the active region QWs. [ABSTRACT FROM AUTHOR]

Metasurface‐based optical elements offer a wide design space for miniature and lightweight optical applications. Typically, metasurface optical elements transform an incident light beam into a desired output waveform. Recent demonstrations of light‐emitting metasurfaces highlight the potential for directly producing desired output waveforms via metasurface‐mediated spontaneous emission. In this work, reciprocal finite‐difference time‐domain (FDTD) simulations and machine learning are used to enable the inverse design of highly unidirectional photoluminescent III‐Nitride quantum well metasurfaces capable of directive p‐, s‐, or combined p‐ and s‐ polarized emission at arbitrary angles. In comparison with previous intuition‐guided designs using the same quantum well architectures, the inverse design approach enables new polarization capabilities and experimentally demonstrated improvements in directivity of 54%. An analysis of ways in which the inverse design both validates and contradicts previous intuition‐guided design heuristics is presented. Ultimately, the combination of reciprocal simulations and efficient global optimization (EGO) grants remarkable improvements in emission directivity and results in full control over the polarization and momentum of emitted light, including simultaneous directional emission of s‐ and p‐polarized light. [ABSTRACT FROM AUTHOR]

The large polarization barriers between the quantum wells and quantum barriers in long-wavelength GaN-based light-emitting diodes (LEDs) inhibit their performance by requiring excess driving voltages to reach standard operating current densities. Lateral injection of carriers directly into quantum wells is required to circumvent this issue. V-defects are naturally occurring inverted hexagonal defects with semipolar 10 1 ¯ 1 -plane sidewalls generated on surface depressions from threading dislocations. LEDs engineered to intentionally generate V-defects below the active region of the LED can achieve lateral carrier injection through the V-defect sidewalls and have already been able to demonstrate world record wall-plug efficiencies for LEDs in the green-red wavelengths. V-defects can be enlarged during kinetically limited growth where the growth rate of the c-plane GaN is faster than that of their sidewalls, leaving them unfilled. We report on the metal organic chemical vapor deposition growth conditions required to fill in V-defects with p-GaN during epitaxial growth of the LED post the active region. Circular transmission length measurements of Pd/Au contacts processed on p-GaN surfaces with various amounts of unfilled V-defects showed no significant difference in their sheet resistance and specific contact resistance. J–V measurements of LEDs grown with varying unfilled V-defect densities showed no significant difference in the forward bias regime. However, in the reverse bias regime, catastrophic breakdown occurred at markedly lower voltages for samples with larger unfilled V-defect densities. This suggests that unfilled V-defects may act as hotspots for device failure, and planarizing LED surfaces may help prevent early degradation of LED devices. [ABSTRACT FROM AUTHOR]

Nanoparticles (NPs) have attracted significant attention as carriers for the delivery of drugs, genes, and macromolecules for biomedical and therapeutic applications. These technologies require NPs to be delivered to the interior of the cell. However, this translocation is unlikely because of the presence of a cell membrane composed of phospholipids, cholesterol, proteins, and glycans. The cell membrane composition can influence its rigidity; thus, membrane composition is a crucial factor in determining the translocation of NPs across the cell membrane. Here, we focus on cholesterol, which is an essential component of biological cell membranes, and investigate NP translocation across membranes containing cholesterol under an applied electric field using a coarse-grained molecular dynamics simulation. We found that NPs could translocate directly across cholesterol-containing membranes without irreversible membrane disruption. This unique translocation was induced by two key phenomena. Before NP translocation, a phospholipid-rich/cholesterol-poor domain was formed at the NP–membrane contact interface. Second, a smaller transmembrane pore was formed in the cholesterol-containing membrane during membrane crossing of the NP. Our findings imply that the delivery of NPs to the cell interior across the cholesterol-containing membrane can be achieved by appropriately controlling the strength of the applied electric field, depending on the cholesterol content in the membrane. [ABSTRACT FROM AUTHOR]

Background: Preservation of renal function is an important goal in renal cell carcinoma-related surgery. Although several case-dependent techniques for renal pedicle clamping and hemostasis have been used, their effects on long-term renal function are controversial. Methods: The clinical records of 114 patients who underwent off-clamp non-renorrhaphy open partial nephrectomy at our hospital were retrospectively reviewed. Perioperative estimated glomerular filtration rate (eGFR) preservation was calculated, and predictors of eGFR decline 12 months post-surgery and overtime deterioration of renal function were identified using a multivariate regression analysis. Results: The median patient age was 65 years, and the median tumor size was 27 mm. The mean eGFR preservation at 1, 3, and 12 months post-surgery were 90.1%, 89.0%, and 86.9%, respectively. eGFR decline at 1 and 3 months were associated with poor eGFR preservation at 12 months with the odds ratio (95% confidence interval (CI)) of 1.97 and 3.157, respectively. Multivariate regression analyses revealed that tumor size was an independent predictor of eGFR decline at 12 months. Among 65 patients with eGFR preservation over 90% at 1 month post-surgery, eGFR value of 28 patients deteriorated below 90% at 12 months post-surgery compared with preoperative eGFR. Tumor size and eGFR preservation at 1 month were independent predictors of long-term renal function deterioration. Conclusion: Tumor size predicted eGFR decline 12 months post-surgery. Only a mild decline in eGFR was observed between 3 and 12 months after open partial nephrectomy. Tumor size and eGFR preservation at 1 month predicted the deterioration of renal function over time. [ABSTRACT FROM AUTHOR]

Artificial night-time lights (ANTL) pose environmental, economic, and social problems. To effectively manage this issue, it is important to understand the sources that contribute to it. Previous research has presented conflicting views on the relative importance of streetlamps and spill-over light from buildings as contributors to ANTL. In this study, we used satellite images, ground surveys of streetlamps and buildings in the city of Hobart, Tasmania, Australia, to determine the major contributing sources of ANTL. Imagery from the Visible Infrared Imaging Radiometer Suite (VIIRS) satellite was used to map ANTL. We developed a predictive random forest regression (RFR) model and found that streetlamps were the major contributor, followed by the building footprint area. We also found that an increase in both the number of streetlamps and buildings leads to an increase in ANTL observable in VIIRS satellite data. The RFR model performed well with an R² of 0.94 and a median normalised root mean square error of 6.25%. [ABSTRACT FROM AUTHOR]