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Time-resolved cathodoluminescence is a key tool with high temporal and spatial resolution. However, optical spectroscopic information can be also extracted using synchrotron pulses in a hard X-ray nanoprobe, exploiting a phenomenon called X-ray excited optical luminescence. Here, with 20 ps time resolution and 80 nm lateral resolution, we applied this time-resolved X-ray microscopy technique to individual core-shell InGaN/GaN multiple quantum well heterostructures deposited on GaN wires. Our findings suggest that the m -plane related multiple quantum well states govern the carrier dynamics. Likewise, our observations support not only the influence of In incorporation in the recombination rates, but also carrier localization phenomena at the hexagon wire apex. In addition, our experiment calls for further investigations of the spatiotemporal domain on the underlying mechanisms of optoelectronic nanodevices. Its great potential becomes more valuable when time-resolved X-ray excited optical luminescence microscopy is used in operando with other methods, such as X-ray absorption spectroscopy.

Thin-wall tubes composed of nitride semiconductors (III-N compounds) based on GaN/InAlN multiple quantum wells (MQWs) are fabricated by metal-organic vapor-phase epitaxy in a simple and full III-N approach. The synthesis of such MQW-tubes is based on the growth of N-polar c-axis vertical GaN wires surrounded by a core-shell MQW heterostructure followed by in situ selective etching using controlled H 2 /NH 3 annealing at 1010 °C to remove the inner GaN wire part. After this process, well-defined MQW-based tubes having nonpolar m-plane orientation exhibit UV light near 330 nm up to room temperature, consistent with the emission of GaN/InAlN MQWs. Partially etched tubes reveal a quantum-dotlike signature originating from nanosized GaN residuals present inside the tubes. The possibility to fabricate in a simple way thin-wall III-N tubes composed of an embedded MQW-based active region offering controllable optical emission properties constitutes an important step forward to develop new nitride devices such as emitters, detectors or sensors based on tubelike nanostructures.

We demonstrate large area fully flexible blue LEDs based on core/shell InGaN/GaN nanowires grown by MOCVD. The fabrication relies on polymer encapsulation, nanowire lift-off and contacting using silver nanowire transparent electrodes. The LEDs exhibit rectifying behavior with a light-up voltage around 3 V. The devices show no electroluminescence degradation neither under multiple bending down to 3 mm curvature radius nor in time for more than one month storage in ambient conditions without any protecting encapsulation. Fully transparent flexible LEDs with high optical transmittance are also fabricated. Finally, a two-color flexible LED emitting in the green and blue spectral ranges is demonstrated combining two layers of InGaN/GaN nanowires with different In contents.

We report the fabrication of a photonic platform consisting of single wire light-emitting diodes (LED) and photodetectors optically coupled by waveguides. MOVPE-grown (metal-organic vapor-phase epitaxy) InGaN/GaN p-n junction core-shell nanowires have been used for device fabrication. To achieve a good spectral matching between the emission wavelength and the detection range, different active regions containing either five narrow InGaN/GaN quantum wells or one wide InGaN segment were employed for the LED and the detector, respectively. The communication wavelength is ∼400 nm. The devices are realized by means of electron beam lithography on Si/SiO2 templates and connected by ∼100 μm long nonrectilinear SiN waveguides. The photodetector current trace shows signal variation correlated with the LED on/off switching with a fast transition time below 0.5 s.

A single nanoscale object containing a set of InGaN/GaN nonpolar multiple-quantum wells has been analyzed by microphotoluminescence spectroscopy (μPL), high-resolution scanning transmission electron microscopy (HR-STEM) and atom probe tomography (APT). The correlated measurements constitute a rich and coherent set of data supporting the interpretation that the observed μPL narrow emission lines, polarized perpendicularly to the crystal c-axis and with energies in the interval 2.9-3.3 eV, are related to exciton states localized in potential minima induced by the irregular 3D In distribution within the quantum well (QW) planes. This novel method opens up interesting perspectives, as it will be possible to apply it on a wide class of quantum confining emitters and nano-objects.

Nonpolar InGaN/GaN multiple quantum wells (MQWs) grown on the {11-00} sidewalls of c-axis GaN wires have been grown by organometallic vapor phase epitaxy on c-sapphire substrates. The structural properties of single wires are studied in detail by scanning transmission electron microscopy and in a more original way by secondary ion mass spectroscopy to quantify defects, thickness (1-8 nm) and In-composition in the wells (∼16%). The core-shell MQW light emission characteristics (390-420 nm at 5 K) were investigated by cathodo- and photoluminescence demonstrating the absence of the quantum Stark effect as expected due to the nonpolar orientation. Finally, these radial nonpolar quantum wells were used in room-temperature single-wire electroluminescent devices emitting at 392 nm by exploiting sidewall emission.

Quantitative structural information about epitaxial arrays of nanowires are reported for a InAs/InP longitudinal heterostructure grown by chemical beam epitaxy on an InAs (111)B substrate. Grazing incidence X-ray diffraction allows the separation of the nanowire contribution from the substrate overgrowth and gives averaged information about crystallographic phases, epitaxial relationships (with orientation distribution), and strain. In-plane strain inhomogeneities, intrinsic to the nanowires geometry, are measured and compared to atomistic simulations. Small-angle X-ray scattering evidences the hexagonal symmetry of the nanowire cross-section and provides a rough estimate of size fluctuations.