In this work, we investigate carrier recombination dynamics and defect-related emission behavior in high-indium content InGaN platelets containing a single quantum well (QW) and a transition layer (TL) using temperature-dependent monochromatic cathodoluminescence (CL) imaging and time-resolved CL (TRCL). At low temperature, monochromatic CL imaging reveals expanded apparent emitting area of both layers and reduced effective width of dark lines associated with stacking mismatch boundaries, indicating suppressed non-radiative recombination and enhanced alloy-induced carrier localization. The TRCL data reveal distinct temperature-dependent carrier recombination mechanisms governing both layers. At low temperature, carrier localization supports longer lifetimes (tau) in the QW of about 1.4 ns and the TL displays multiple recombination channels due to its structural complexity. At room temperature, thermal carrier diffusion enables efficient capture by defects, resulting in pronounced tau quenching to about 0.22 and 0.07 ns in the two layers, respectively.

We investigate heat conduction and energy relaxation in an InAs semiconductor nanowire using a hybrid semiconductor-superconductor architecture. Local electronic temperatures are measured with an in-situ grown quantum dot thermometer, while controlled Joule heating is applied at different locations along the wire to probe temperature gradients at sub-kelvin temperatures. With a onedimensional heat transport model, we calculate an electron-phonon heat flow that scales as Q_e-ph ∝T^2.6, which is in close agreement with the T^3 dependence predicted for a clean one-dimensional electron gas coupled to a phonon bath. We further estimate a characteristic length l_eq = 370 nm, beyond this length scale, phonon-mediated heat transport dominates over heat conduction in our nanowire. Our results provide a quantitative measure of energy relaxation mechanisms in a onedimensional semiconductor and provide a framework for studying heat flow in low-dimensional nanostructures.

InP quantum dots have emerged as a promising ecofriendly alternative to cadmium-based QDs for next-generation display applications. However, red-emitting InP QDs synthesized via aminophosphine precursors still suffer from broad emission spectra and limited stability. In this study, we present a strain-engineered InP/ZnSe/ZnSexS1-x/ZnS QD structure featuring a gradient alloyed ZnSexS1-x shell that effectively mitigates lattice mismatch, reduces strain accumulation, and enhances shell uniformity. Through systematic analysis, we elucidate the strain distribution profiles across different shell architectures and the corresponding defect types induced by strain. This approach enables the controlled growth of a thick ZnS shell, improving passivation and minimizing nonradiative recombination. As a result, the optimized QDs exhibit a narrow full width at half-maximum of 45 nm, a high photoluminescence quantum yield of ≥80%, and significantly enhanced photochemical stability. This work highlights the critical role of strain management in achieving high-performance InP QDs for practical applications.

We present a bottom-up technology for producing dislocation-free, strain-relaxed InGaN microLEDs in the form of sub-micron scale hexagonal platelets. The use of InGaN barrier material enables high indium-content quantum wells with peak emission tunable from blue to deep red (> 670 nm). These platelets do not suffer from plasma induced damage and exhibit internal quantum efficiency values up to 60% for deep red emitting quantum wells. We further show red microLEDs exhibiting dominant wavelengths above 630 nm for drive currents up to 50 A/cm2, which is well suited for wide color gamut, and ultra-high brightness displays.

Micro‐LEDs have emerged as a hot research topic due to their potential for next‐generation display and lighting applications, necessitating advanced characterization techniques to optimize their performance. This study demonstrates the advantage of cathodoluminescence in the scanning electron microscope to be a critical tool for the optical characterization of InGaN platelets with red quantum well emission. Emission spectra revealed red‐shifted quantum well peaks with respect to the barrier emission corresponding to quantum well emission, confirming an increased indium incorporation and a reduced bandgap, enabling deep red InGaN QW‐emission. However, dark line defects, identified as stacking mismatch boundaries, and pinholes were observed, acting as non‐radiative recombination centers, and reducing emission intensity. Monochromatic cathodoluminescence imaging at varying acceleration voltages provided insights into defect propagation and spatial distribution by probing different layers in the sample, revealing inhomogeneities and compositional variations.

Nanowires are promising structures for next-generation photonic devices due to their superior structural, optical, and electronic properties compared to thin films. In this study, unexpected electrostatic potential wells across the non-polar m-plane and at the core/shell interface in n-type GaN core/shell nanowires, grown via metal-organic vapor phase epitaxy, are reported. Using advanced electron microscopy, including off-axis electron holography, electrostatic potential distributions are mapped and shallow quantum wells are identified at the core/shell interface and core center. High-resolution transmission electron microscopy ruled out planar and line defects, implicating point defects as their source. Valence electron energy loss spectroscopy revealed localized bandgap narrowing due to strain from concentrated point defects. Hyperspectral cathodoluminescence linked lower potential in the core to CN defects, while the absence of related luminescence at the core/shell interface suggests VGaON defect complexes as plausible causes. These findings highlight the critical role of point defects in GaN nanowires, with significant implications for device performance.

Colloidal quantum dots (QDs) possess size/shape/surface-tunable optical and electronic properties, making them promising building blocks for optoelectronic applications. However, the fluorescence intermittency, also known as "blinking," observed in individual QDs is a pervasive phenomenon. The dark state (trion state) in blinking experiences non-radiative recombination processes, such as trap-mediated recombination and Auger-Meitner recombination, which significantly diminish the quantum efficiency of the QDs. Despite efforts to mitigate blinking phenomena through chemical engineering of QDs structures and their environments, blinking continues to impede the application of single QDs, particularly in single photon sources. This study demonstrates that F & ouml;rster resonance energy transfer (FRET) from green QDs (donor) to individual red QDs (acceptor) can effectively suppress fluorescence intermittency. The findings indicate that FRET facilitates the removal of excess charges from the charged state (dark state, trion state), allowing the QDs to transition from the lower quantum yield trion state to the higher quantum yield single-exciton state (bright state). Our research confirms that FRET can inhibit fluorescence intermittency by deactivating the charged state.

Direct thermal-to-electric energy converters typically operate in the linear regime, where the ratio of actual maximum power relative to the ideal maximum power, the so-called fill factor (FF), is 0.25. By increasing the FF one can potentially increase maximum power by up to four times, but this is only possible in the nonlinear regime of transport and has previously rarely been considered. Here we show, based on fundamental symmetry considerations, that the leading order non-linear terms that can increase the FF require devices with broken spatial symmetry. To experimentally demonstrate such a system, we study nonlinear, thermoelectric transport across an asymmetric energy barrier epitaxially defined in a single semiconductor nanowire. We find in both experiment and theory that we can increase the FF above the linear-response limit of 0.25, accompanied by a drastic increase in short circuit current, open-circuit voltage and maximum power. Our results show that geometric symmetry breaking combined with the design of nonlinear behaviour represent a design strategy for increasing the performance of thermal-to-electric energy converters such as in hot-carrier photovoltaics, thermophotovoltaics or in anisotropic thermoelectric materials.

A study of submicron-sized InGaN containing a single quantum well, intended for use as nano-light-emitting diodes in high-resolution display based on direct emission, is presented. Herein, the structures are grown by a bottom-up method from holes in a masked GaN/sapphire substrate and are intended for red emission. Many of the platelets show dark lines in cathodoluminescence images, previously identified as stacking mismatch boundaries. These introduce local shifts in the reduced emission, perhaps related to local strain. However, the total emission position stays unaffected, just reduced in intensity. Due to an unintended variation in the size of the c-facet, there is a gradient in the indium content which, in turn, leads to a significant shift in the peak position of the quantum well emission. With increasing probe current there is a slight blueshift, likely a result of the quantum confined Stark effect.

We have investigated the optical properties of heterostructured InGaN platelets aiming at red emission, intended for use as nano-scaled light-emitting diodes. The focus is on the presence of non-radiative emission in the form of dark line defects. We have performed the study using hyperspectral cathodoluminescence imaging. The platelets were grown on a template consisting of InGaN pyramids, flattened by chemical mechanical polishing. These templates are defect free, whereas the dark line defects are introduced in the lower barrier and tend to propagate through all the subsequent layers, as revealed by the imaging of different layers in the structure. We conclude that the dark line defects are caused by stacking mismatch boundaries introduced by multiple seeding and step bunching at the edges of the as-polished, dome shaped templates. To avoid these defects, we suggest that the starting material must be flat rather than dome shaped.

We demonstrate experimentally nonequilibrium transport in unipolar quasi-1D hot electron devices reaching the ballistic limit at room temperature. The devices are realized with heterostructure engineering in nanowires to obtain dopant- and dislocation-free 1D-epitaxy and flexible bandgap engineering. We show experimentally the control of hot electron injection with a graded conduction band profile and the subsequent filtering of hot and relaxed electrons with rectangular energy barriers. The number of electrons passing the barrier depends exponentially on the transport length with a mean-free path of 200-260 nm, and the electrons reach the ballistic transport regime for the shortest devices with 70% of the electrons flying freely through the base electrode and the barrier reflections limiting the transport to the collector.

InP quantum dots (QDs) are the most competitive in terms of environmentally friendly QDs. However, the synthesis of InP QDs requires breakthroughs in low-cost and safe phosphorus precursors such as tri(dimethylamino)phosphine [(DMA)3P]. It is found that even if the oxygen is completely avoided, there are still oxidation state defects at the core/shell interface of InP QDs. Herein, the record-breaking (DMA)3P-based red InP QDs were synthesized with the assist of HF processing to eliminate the InPOx defect and improve the fluorescence efficiency. The maximum photoluminescence quantum yield was 97.7%, which is the highest of the red InP QDs synthesized by the aminophosphine. The external quantum efficiency and brightness of the QD light-emitting diode device are also improved accordingly from 0.6% and 1276 cd·m-2 to 3.5% and 2355 cd·m-2, respectively.

Miniaturization of light-emitting diodes (LEDs) with sizes down to a few micrometers has become a hot topic in both academia and industry due to their attractive applications on self-emissive displays for high-definition televisions, augmented/mixed realities and head-up displays, and also on optogenetics, high-speed light communication, etc. The conventional top-down technology uses dry etching to define the LED size, leading to damage to the LED side walls. Since sizes of microLEDs approach the carrier diffusion length, the damaged side walls play an important role, reducing microLED performance significantly from that of large area LEDs. In this paper, we review our efforts on realization of microLEDs by direct bottom-up growth, based on selective area metal–organic vapor phase epitaxy. The individual LEDs based on either GaN nanowires or InGaN platelets are smaller than 1 μm in our approach. Such nano-LEDs can be used as building blocks in arrays to assemble microLEDs with different sizes, avoiding the side wall damage by dry etching encountered for the top-down approach. The technology of InGaN platelets is especially interesting since InGaN quantum wells emitting red, green and blue light can be grown on such platelets with a low-level of strain by changing the indium content in the InGaN platelets. This technology is therefore very attractive for highly efficient microLEDs of three primary colors for displays.

III-Nitride based light-emitting diodes based on InGaN active layers formed on GaN, are fine for the blue and green emitting LEDs. However, the large lattice mis-match between red-emitting active layers and the GaN substrate still limits the efficiencies to very low values, typically <5%. We propose to use seeding techniques originally developed for nanowire growth, to seed the formation of ternary InGaN pyramids which later are converted to thin c-facet platelets of InGaN. I will in this presentation show that such relaxed, and dislocation-free, InGaN platelets with In-composition about 20%, have the potential as ideal templates for red-emitting microLEDs. Of special significance is the fact that our technology provides all three RGB microLED sources with one and the same InGaN technology, and with the same efficiency and with the maintained efficiency down to pixel sizes of just 1-2 µm in diameter.

Structural defects are detrimental to the efficiency and quality of optoelectronic semiconductor devices. In this work, we study InGaN platelets with a quantum well structure intended for nano-LEDs emitting red light and how their optical properties, measured with cathodoluminescence, relate to the corresponding atomic structure. Through a method of spectroscopy–thinning–imaging, we demonstrate in plan-view how stacking mismatch boundaries intersect the quantum well in a pattern correlated with the observed diminished cathodoluminescence intensity. The results highlight the importance of avoiding stacking mismatch in small LED structures due to the relatively large region of non-radiative recombination caused by the mismatch boundaries.