Session Index

Deep ultraviolet LDs and LEDs around 260 nm, which are absorbed by the RNA and DNA of viruses and bacteria, are expected to be useful. To enhance the emission efficiency of these optical devices, controlling the flatness of the heterointerface at the atomic level is essential. In this study, we investigated the relationship between the device fabrication process, specifically the growth temperature of thin films, and the flatness of the heterointerface using a computational approach.

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Far-ultraviolet C (Far-UVC) light-emitting diodes (LEDs) operating near 230 nm are emerging as promising sources for safe and effective disinfection, including inactivation of airborne pathogens and viruses. However, their external quantum efficiency (EQE) remains below 1% @ 230nm emission wavelength, primarily due to poor light extraction efficiency (LEE) and point defects. In this talk, we present recent theoretical and experimental progress at RIKEN in collaboration with National Yang Ming Chiao Tung University (Taiwan) toward overcoming this limitation through nano-patterned sapphire substrates (nanoPSS) and photonic crystal (PhC) structures. Finite-difference time-domain (FDTD) simulations reveal that optimized nanoPSS and reflective PhCs can synergistically enhance LEE by up to 6.7× compared to flat substrates. Experimentally, nanoPSS-based devices demonstrated a two-fold increase in EQE—from 0.15% to 0.32%—and doubled emission power. The experimental results of both the nanoPSS and PhC based LED will be revealed later. Furthermore, our 230 nm far-UVC LED modules successfully inactivated Dengue Virus (DENV), HIV-1, Influenza-A Virus (IAV), and SarsCoV-2 confirming their potential for real-world sterilization applications. Ongoing work aims to integrate optimized PhC designs with nanoPSS to achieve EQE >2% @ 230nm emission wavelength, paving the way for high-performance far-UVC LEDs for healthcare and environmental safety.

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High-frequency quaternary InAlGaN/GaN high electron mobility transistors (HEMTs) are demonstrated with fT = 101 GHz and fmax = 120 GHz. Small-signal modeling of 0.2 µm-gate devices extracts intrinsic parameters and analyzes performance-limiting factors. Using these insights, RF scaling across multiple device sizes is validated, showing reduced gate capacitances and minimized parasitics central to enhanced fT/fmax. The results provide a systematic evaluation of frequency-scaling trends and highlight the potential of InAlGaN/GaN HEMTs for next-generation RF and millimeter-wave applications.


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This work aims to enhance the unity current gain cutoff frequency (f_T) of AlInGaN/GaN high-electron-mobility transistor (HEMT). To reduce the gate capacitance (C_g) while maintaining sufficient control over the channel, the gate length (L_g) was scaled down to 40 nm, and the channel thickness was set to 40 nm. In addition, the source to drain spacing (L_{sd}) was reduced to 1.84 μm to improve the transconductance (g_m). Finally, when the contact resistance (R_c) is decreased to 0.15 Ω⋅mm, the device achieved an f_T of 254 GHz.

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We design a vertical GaN MOSFET with Ion around 90 A/cm2 and Vth > ~10 V and the device has a clear saturation and transfer characteristics. Thermal characterization shows the drain current density is a up to ∼90A/cm² at VG=20V, corresponding to a thermal resistance Rth ~0.01−0.02 K⋅cm2/W. The current flow path and peak electric field versus drain voltage have been studied. The different current crowding effects may lead to different thermal effects even with the same power density. The simulation result provides the information for the device optimization in achieving a high breakdown voltage.

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Unified studies on material gain and internal field screening in wide polar InGaN and AlGaN quantum wells are presented. Numerical results reveal a transition from quantum-confined to bulk-like behavior, governed by the well width and carrier-induced polarization screening. In wide wells, the optical gain is dominated by excited-state transitions, while in thin wells, it is primarily due to ground-state transitions. The analysis provides a comprehensive framework for understanding gain formation in III-nitride emitters and offers design strategies to mitigate the dead-width effect, enabling efficient light emission in both the visible and deep-UV spectral regions using wide quantum wells.

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