Core–Shell Nanorods as Ultraviolet Light-Emitting Diodes

Abstract

Existing barriers to efficient deep ultraviolet (UV) light-emitting diodes (LEDs) may be reduced or overcome by moving away from conventional planar growth and toward three-dimensional nanostructuring. Nanorods have the potential for enhanced doping, reduced dislocation densities, improved light extraction efficiency, and quantum wells free from the quantum-confined Stark effect. Here, we demonstrate a hybrid top-down/bottom-up approach to creating highly uniform AlGaN core–shell nanorods on sapphire repeatable on wafer scales. Our GaN-free design avoids self-absorption of the quantum well emission while preserving electrical functionality. The effective junctions formed by doping of both the n-type cores and p-type caps were studied using nanoprobing experiments, where we find low turn-on voltages, strongly rectifying behaviors and significant electron-beam-induced currents. Time-resolved cathodoluminescence measurements find short carrier liftetimes consistent with reduced polarization fields. Our results show nanostructuring to be a promising route to deep-UV-emitting LEDs, achievable using commercially compatible methods.

Low-Leakage Current Core–Shell AlGaN Nanorod LED Device Operating in the Ultraviolet-B Band

“…However, other studies on nanorod-based UV LEDs with similar structures utilize top-down and bottom-up processes to create the same structures. This additional process increases the LED manufacturing cost and there is a risk of degrading the optical characteristics of the LED due to various resistances generated during the manufacturing process. , In contrast, the deposition process developed in our research can be considered a suitable and promising structure for LED manufacturing, as it can produce LEDs with minimal resistance without the need for additional processes like the existing ones. Figure c displays the electroluminescence (EL) spectrum comparison data, showing the maximum emission peaks of both the conventional core–shell structure and top-separated core–shell structure under an injection current of 10 mA.…”

Cathodoluminescence Nanoscopy: State of the Art and Beyond

“…Using a gold photocathode driven by laser pulses and a streak camera for time-resolved detection, they revealed the correlation of local carrier dynamics in GaAs nanostructures with the surface morphology. In parallel with the developments in the laser-driven cathode, advances in ultrafast beam blankers promise a flexible and easily integrated method to generate electron pulses with a broad range of pulse widths and repetition rates, while keeping a good spatial resolution with a typical duration of tens of picoseconds. , In recent years, time-resolved CL with pulsed electron beams in SEM has enabled the dynamic study of exciton diffusion, ,, carrier relaxation, ,− and excited states of DNA . Currently, time-resolved CL studies performed in TEM have also been reported, , making progress toward elucidating structure–function relations at atomic scales.…”

“…Beyond panchromatic and hyperspectral 2D CL imaging, which has been the dominant historical application, more degrees of freedom in CL emission are exploited in nanophotonic research. Polarization-resolved CL has been introduced such that the degree of linear and circular polarization of the emitted CL light can be determined. − In addition, the momentum distribution of CL emission, i.e., the direction in which light is emitted, can be recorded by angle-resolved CL. − By combining these two techniques and performing polarization studies in momentum space, it is viable to fully define the polarization state of CL emission and explore polarization-dependent phenomena with great spatial and angular resolution. − With the advent of ultrafast electron microscopy, time-resolved CL has emerged as a powerful technique for fundamental studies of the dynamics of electron–matter interaction with simultaneous nm–ps–meV space–time–energy resolution, for which it is appealing in the research of exciton/carrier dynamics − and single-photon sources. − On the basis of the synchronized laser and ultrafast electron pulse excitation, the prototypical pump–probe CL spectroscopy has also been reported, enabling analyses of the electron–light–material energy-transfer process. Furthermore, conventional space-resolved CL imaging and spectroscopy have made impressive advances in cathodoluminescence excitation spectroscopy, delocalized imaging, 3D tomography, , and nanothermometry for semiconductors …”