Rie Togashi

Red emission remains a major bottleneck for practical full-color micro-light-emitting diodes (microLEDs) because the quantum efficiencies of InGaN decrease in the long-wavelength region. To enhance red emission, this study developed a honeycomb-latticed InGaN/GaN nanocolumn array integrated with an Ag-based plasmonic LED structure. Finite-difference time-domain simulations were used to optimize the lattice parameters, identifying a = 220 nm and D = 190 nm as the optimal geometries. This design provided an electric-field enhancement of approximately 4.5 at λ = 623 nm, indicating strong surface plasmon polariton coupling in the red region. A device fabricated with the same parameters exhibited up to a 6.3-fold photoluminescence enhancement under surface excitation, outperforming the 5.9-fold enhancement previously achieved under backside excitation. These results demonstrate that honeycomb-latticed plasmonic engineering is effective for boosting red emission in InGaN-based structures and offers a promising route to high-efficiency red microLEDs.

InGaN-based light-emitting diodes (LEDs) exhibit excellent emission efficiency in the blue spectral region but experience severe degradation of external quantum efficiency in the red region, primarily due to lattice strain and increased defect density. To address this limitation, we introduced surface plasmon polaritons into InGaN/GaN nanocolumn (NC) arrays arranged in a honeycomb lattice to enhance red-light emission. Deposition of Ag films on the photonic crystal NCs generated plasmonic crystals that allowed precise control of photonic–plasmonic band interactions. Angle-resolved photoluminescence measurements combined with electromagnetic field analysis revealed that strong coupling occurs when photonic and plasmonic field modes are spectrally and spatially matched. Rabi splitting was observed due to the strong coupling between photonic and plasmonic band states, and a 9.6-fold enhancement in red emission was achieved through the combined effects of strong and weak coupling. This controllable strong coupling between photonic and plasmonic band states provides a promising approach for overcoming the intrinsic efficiency limitations of InGaN-based red LEDs while simultaneously enhancing their optical functionality.

Abstract Thermodynamic analysis of β -Ga ₂ O ₃ growth by oxide vapor-phase epitaxy using Ga ₂ O and H ₂ O precursors was conducted, supported by preliminary growth experiments. Calculations clarify practical growth windows as functions of temperature, the H ₂ mole fraction in the carrier gas, the input VI/III ratio, and the input partial pressure of Ga ₂ O ( ). The analysis revealed that sustained β -Ga ₂ O ₃ growth above 1000 °C requires careful control of the H ₂ mole fraction to balance precursor generation and thermodynamically driven etching. Phase diagrams were constructed as functions of temperature, , and input VI/III ratio, which delineate the growth and etching regimes. β -Ga ₂ O ₃ was grown on (0001) sapphire substrates, and the experimentally derived driving forces agree well with the thermodynamic predictions. The results demonstrate that β -Ga ₂ O ₃ growth using Ga ₂ O and H ₂ O can be effectively controlled based on thermodynamics, offering a chloride-free, safer alternative for power-device-grade drift layers.

Using nanotemplate selective‐area growth methods, InGaN/GaN nanocolumn arrays with bulk‐InGaN active layers are fabricated on AlN/Si(111) substrates by varying the nanocolumn period ( L = 200–400 nm) and InGaN growth time ( t _InGaN = 5–20 min). For t _InGaN = 12 and 20 min, the photoluminescence emission peak wavelength ( λ ) increases with L . Red emission is observed over a wide range of L (220–300 nm) at t _InGaN = 12 min, and the emission color shifts from green to red at t _InGaN = 20 min as L increases from 200 to 320 nm. In contrast, for t _InGaN = 5 and 8 min, λ shifts toward shorter wavelengths with increasing L . Specifically, at t _InGaN = 8 min, three distinct emission regions—red, green, and blue—are achieved within the bulk InGaN, with the emission switching from red to green to blue as L increases, where high‐purity red ( λ = 622 nm), green (544 nm), and blue (477 nm) emissions are obtained for L = 200, 300, and 400 nm, respectively. Notably, red–green–blue‐emitting nanocolumn arrays are achieved in a single‐growth process, with red emission realized even in thin nanocolumns where the nanocrystalline effect is pronounced.

Abstract The integration of red-green-blue (RGB) light sources is essential for the development of high-resolution micro-light-emitting diode (micro-LED) displays. In this study, we propose a color-tunable device based on self-assembled InGaN-based nanocolumn LEDs without a patterning process. The nanocolumn LEDs exhibited a color shift from red to orange-yellow, pale green, and further to blue as the driving voltage increased. Micro-electroluminescence measurements revealed that a small wavelength shift was observed within individual nanocolumn regions. Instead, emission spots sequentially turned on, transitioning from red to blue (660-435 nm), elucidating the mechanism of color tuning. Combined with pulse-width-modulation driving, these findings open the pathway for the realization of novel monolithic RGB-LED devices.