While hot carrier generation from surface plasmon decay at the surface of a nanostructured metal offers a distinctive concept for boosting photoelectrocatalytic reactions, the nature of the plasmonic hot hole transfer based on the sizes of metallic nanomaterials has not been investigated in depth experimentally. Here, we report direct photoelectrochemical (PEC) experimental proof that the injection of plasmonic hot holes depends on the size of the metallic nanostructures. PEC results clearly indicate that a plasmonic template with smaller Au nanoprisms exhibits higher external and internal quantum efficiencies, leading to a significant enhancement of both oxygen evolution and hydrogen evolution reactions. We verified that these outcomes stemmed from the enhanced hot hole generation with higher energy and transfer efficiency driven by enhanced field confinement. These findings provide a facile strategy by which futuristic photocatalysis and solar energy conversion applications based on plasmonic hot holes can be expedited.

We demonstrate the first InGaN/GaN blue light emitting diodes (LEDs) on freestanding GaN grown using a Si substrate. Transmission electron microscopy and X-ray diffraction analysis revealed that the InGaN/GaN multi quantum wells (MQWs) on freestanding GaN grown using Si substrates have excellent structural properties suitable for high-performance optical devices. Photoluminescence measurements confirm the high crystal quality of the InGaN/GaN MQWs and remarkable emission wavelength uniformity with a standard deviation of 0.68%. Light−current−voltage characteristics indicate that the InGaN/GaN LEDs on freestanding GaN grown using a Si substrate exhibit a forward voltage of 3.75 V at a current of 20 mA and rectifying characteristics with very low leakage current and high breakdown voltage. Furthermore, they provide stable blue electroluminescence (λ = 460 nm) with a small variation in the emission wavelength of 0.2% over a 2 in. area. The internal quantum efficiency of InGaN/GaN LEDs on freestanding GaN grown using Si substrates is remarkable at ∼80%. Despite using Si substrates as the support, the optoelectronic properties of the InGaN/GaN LEDs are outstanding. We believe that the InGaN/GaN LEDs based on freestanding GaN crystals extracted from Si substrates are promising for the development of GaN-based high-performance devices.

Nonradiative surface plasmon decay produces highly energetic electron-hole pairs with desirable characteristics, but the measurement and harvesting of nonequilibrium hot holes remain challenging due to ultrashort lifetime and diffusion length. Here, the direct observation of LSPR-driven hot holes created in a Au nanoprism/p-GaN platform using photoconductive atomic force microscopy (pc-AFM) is demonstrated. Significant enhancement of photocurrent in the plasmonic platforms under light irradiation is revealed, providing direct evidence of plasmonic hot hole generation. Experimental and numerical analysis verify that a confined |E|-field surrounding a single Au nanoprism spurs resonant coupling between localized surface plasmon resonance (LSPR) and surface charges, thus boosting hot hole generation. Furthermore, geometrical and size dependence on the extraction of LSPR-driven hot holes suggests an optimized pathway for their efficient utilization. The direct visualization of hot hole flow at the nanoscale provides significant opportunities for harnessing the underlying nature and potential of plasmonic hot holes.

Artificial synaptic platforms are promising for next-generation semiconductor computing devices; however, state-of-the-art optoelectronic approaches remain challenging, owing to their unstable charge trap states and limited integration. We demonstrate wide-band-gap (WBG) III–V materials for photoelectronic neural networks. Our experimental analysis shows that the enhanced crystallinity of WBG synapses promotes better synaptic characteristics, such as effective multilevel states, a wider dynamic range, and linearity, allowing the better power consumption, training, and recognition accuracy of artificial neural networks. Furthermore, light-frequency-dependent memory characteristics suggest that artificial optoelectronic synapses with improved crystallinity support the transition from short-term potentiation to long-term potentiation, implying a clear emulation of the psychological multistorage model. This is attributed to the charge trapping in deep-level states and suppresses fast decay and nonradiative recombination in shallow traps. We believe that the fingerprints of these WBG synaptic characteristics provide an effective strategy for establishing an artificial optoelectronic synaptic architecture for innovative neuromorphic computing.

We report forward tunneling characteristics of InGaN/GaN blue light emitting diodes (LEDs) on freestanding GaN detached from a Si substrate using temperature-dependent current–voltage (T-I-V) measurements. T-I-V analysis revealed that the conduction mechanism of InGaN/GaN LEDs using the homoepitaxial substrate can be distinguished by tunneling, diffusion and recombination current, and series resistance regimes. Their improved crystal quality, inherited from the nature of homoepitaxy, resulted in suppression of forward leakage current. It was also found that the tunneling via heavy holes in InGaN/GaN LEDs using the homoepitaxial substrate can be the main transport mechanism under low forward bias, consequentially leading to the improved forward leakage current characteristics.