Session Index

This study focuses on minimizing the emission divergence angle of resonant cavity light-emitting diodes (RCLEDs) through the implementation of multilayer distributed Bragg reflectors (DBRs) and integrated microlens (ML) structures. By employing staggered multiple quantum wells (SMQWs) and nanoporous DBRs, the effects of varying DBR periods and microlens incorporation are systematically examined. The findings demonstrate a notable reduction in angular dispersion, along with improved spectral stability and overall device efficiency. These enhancements make the proposed RCLED design highly suitable for applications demanding precise beam control, including optical interconnects, micro-LED displays, and augmented reality systems.

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We evaluate the optical characteristics of p-side-up InGaN/GaN photonic crystal surface-emitting lasers (PCSELs) with air holes in different geometries. Three-dimensional finite element method simulations reveal that the B-mode dominates lasing behavior. PCSELs with right-angled isosceles triangle air holes possess a higher slope efficiency than those with circular ones due to higher out-coupling efficiency, and the optimal fill factor is around 11%. The experimental results agree with the optical simulations, with the least threshold energy density of 16 mJ/cm2.

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We show recent progress in development of tunnel junctions (TJs) for efficient carrier conversion between electrons and holes in nitride-based devices by plasma assisted molecular beam epitaxy (PAMBE). We discuss growth conditions for low resistance TJs enabling vertical integration of multicolor LDs and LEDs. The TJs allows to control the current path in distributed-feedback LDs and micro-LEDs. It also opens the possibility to design new architecture of nitride devices like bi-directional light emitting device, which is shining light from the same single quantum well for positive and negative voltage bias.

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We report the observation of quasi-saturation behavior in GaN vertical MOSFETs with a sidewall-gate layout. The drain current roll-off and negative transconductance are linked to space charge modulation near the gate–drift interface. Electrical measurements and TCAD simulations provide insights into the role of gate geometry on carrier injection and current crowding.

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This study investigates the impact of different In compositions (18.5%, 20%, and 21%) on the performance of AlInN-HEMT devices. The results indicate that a higher In composition reduces contact resistance (Rc) but simultaneously decreases two-dimensional electron gas (2DEG) density, affecting the on-resistance (Ron). The maximum current density (JDS) peaks at an In composition of 20%. Overall, an In composition of 20% provides an optimal balance between contact resistance, current density, and switching characteristics.

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Micro-LED displays are an emerging technology, but their micron-scale LED chip size suffers from significant efficiency degradation. The low light output efficiency is mainly attributed to an increased weighting of sidewall nonradiative recombination with the perimeter-area ratio of smaller chip size. To prevent this, we introduce insulting regions in the mesa sidewall by oxidizing the metal components in the epi-structures. Our results show that steam oxidation technique efficiently suppresses sidewall nonradiative recombination, with more significant suppression observed in smaller mesa sizes. These results highlight the potential of sidewall oxidation in overcoming efficiency degradation for micro-red LEDs in displays.

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We will present a comprehensive structural and optical characterization of a fully processed red-emitting InGaN/GaN
LED using cathodoluminescence spectroscopy at low temperature directly performed in a scanning transmission
electron microscope. The nanoscale luminescence investigations give detailed insight into the lateral inhomogeneity of
InGaN multiple quantum well luminescence. The local carrier density is quantified as 6*10^18 cm-3, and the capture
length of excess carriers into the active region is determined to be 28 nm. The transport processes of excess carriers
into the active region are quantified. Additionally, the threading dislocation density approximately 10^9
cm-2. The different types of dislocations are identified.

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With its wide bandgap and high breakdown field, β-Ga₂O₃ is a promising candidate for high-voltage devices. The recess etch process often damage the semiconductor-oxide interface. This study adopts a non-recess etch process and TEGa-based UID layer growth to enhance breakdown voltage and device performance for power applications.

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This study demonstrates the use of 50-nanometer Nickel Oxide (NiOx) as a p-type gate material to enable enhancement-mode (E-mode) operation in InAlN-barrier high electron mobility transistors (HEMTs). By incorporating both partially and fully recessed gate structures, the fabricated devices exhibit positive threshold voltages (Vₜ) of 0.56 V and 0.74 V, respectively, as defined at a drain current density of 1 mA/mm. The combined effect of the high work-function NiO and optimized gate recess effectively modulates the channel potential, validating the feasibility of oxide-based p-type gate designs for normally-off HEMT applications.

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In this work, a novel “step-free” μLED structure was proposed to eliminate the mesa height difference between anode and cathode, a key issue in integrating driving circuits. Devices based on this architecture were evaluated through cross-sectional SEM for structural analysis and emission pattern and J–V–L measurements for performance. The step-free structure μLEDs demonstrated performance comparable to conventional mesa structure devices, confirming uniform current injection and reliable operation. These results highlight the potential of the step-free structure as a promising solution for improving fabrication yield and enabling practical use of monolithic μLEDs in next-generation VR/AR displays.

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We report a high wall-plug efficiency (WPE) for AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) emitting at 275 nm, achieved using a micro-mesh p-electrode integrated with scattering nanostructures. The micro-mesh p-electrode was designed to minimize DUV light absorption while maintaining high electrical efficiency. Scattering nanostructures were employed to redirect guided light out of the device. This configuration resulted in a 1.7-fold enhancement in WPE compared to conventional DUV-LEDs, reaching 9.1% after encapsulation. Although the micro-mesh p-electrode reduced contact area, a high electrical efficiency of 90% was maintained, with a drive voltage as low as 5.0 V at 20 mA.

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The photonic field distributions of InGaN-based U-shaped micro LEDs are characterized via a proximity photodetector. The comparison between traditional and U-shape devices showed the wider distribution at a close range from the latter design.

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We investigated the dependence of hole concentration on the AlN mole fraction in
polarization-doped graded AlGaN layers without Mg doping, grown on AlN by Hall effect
measurements. By employing an AlGaN contact layer without lattice relaxation, we achieved p-type
conductivity in polarization-doped AlGaN without Mg doping. The measured hole concentration
showed good agreement with the calculation value based on charge neutrality condition. The resistivity
was approximately 2 Ω·cm, and the hole mobility was found to be governed by alloy scattering. These
results provide insights into polarization doping in high AlN mole fraction AlGaN.

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The thermally oxidized AlxGa2−xO3 sidewall was introduced to deep ultraviolet micro-light-emitting diodes (DUV micro-LEDs) to improve optoelectronic performance. The thickness of the thermally oxidized AlxGa2−xO3 sidewall results in an increase in Vf and dynamic resistance in all DUV micro-LEDs. The light output power densities and transverse magnetic polarized light emission of all DUV micro-LEDs were enhanced by introducing the thermally oxidized AlxGa2−xO3 sidewall, and the light extraction efficiency could be improved. The light output power density was also enhanced by thickening the thermally oxidized AlxGa2−xO3 sidewall.

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In red-emission InGaN-based nanocolumn LED crystals, defects of the p-GaN cladding layer were generated on the uneven surface of the p-AlGaN electron blocking layer (EBL). To address this issue, p-AlGaN EBL was grown with the shutter control method at a higher growth temperature by 100 °C against the previous condition; the surface migration of Al and Ga is promoted. The improved surface roughness of p-AlGaN EBL reduced the dislocations generated from the p-AlGaN EBL surface.




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We fabricated square-shaped GaN-based ultraviolet LEDs with cross-shaped metal contacts, incorporating an ALD process, and designed three different device sizes: 25 μm, 50 μm, and 75 μm. The current–voltage characteristics were measured, along with the optical and spectral properties under both room-temperature and low-temperature conditions. Finally, the external quantum efficiency (EQE) was analyzed based on the measurement results.

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An N-polar GaN/AlGaN/AlN HEMT was fabricated on a 2degree off c-plane sapphire substrate using MOVPE. The device showed clear pinch-off behavior and low leakage current up to 600 °C, demonstrating excellent thermal stability. At temperatures above 700 °C, ID significantly decreased and leakage current increased. The results suggest that the AlN buffer layer contributes to reduced leakage and stable GaN channel properties, enabling high-temperature operation.

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In this work, precise gate etching was applied to p and n-channel AlGaN/GaN HEMTs to achieve enhancement-mode operation, enabling the integration of GaN CMOS logic circuits
on a single substrate. The threshold voltages of the n-channel and p-channel devices were 0.5 V
and -0.5 V, respectively. At a supply voltage of 2 V, the GaN CMOS logic circuit exhibited an
output swing of 1.949 V, a logic-low noise margin of 0.3789 V, a logic-high noise margin of
1.31 V, a transition window of 0.26 V, and a high voltage gain of 12.8 V/V.

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The developments towards higher wall-plug efficiency GaN-based VCSELs at Meijo University are described. By using high-quality AlInN/GaN DBR, lateral optical/current confinement, and in situ cavity length control, our GaN-based VCSELs show a WPE of 27% at 413 nm under RT CW operation.

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We investigated reducing operating voltage to improve the wall-plug efficiency (WPE) of GaN-based VCSELs. We fabricated and evaluated the VCSEL and analyzed the components of the differential resistance. The resistances of ITO and n-GaN were more than half of the total resistance. We fabricated a micro LED with a thicker n-GaN and a low-resistivity ITO. As expected from calculations, the operating voltage and the differential resistance decreased to 4.8 V and 65 Ω. If such a low operating voltage is achieved in a VCSEL, the WPE is expected to be 30% in VCSELs.

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This work investigates the impact of a body trench structure on the electrical performance and field distribution of vertical GaN MOSFETs. Devices with and without a body trench were fabricated and characterized through current-voltage (I-V) and capacitance-voltage (C-V) measurements, and further analyzed via TCAD simulations.

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Laser Lift Off (LLO) is expected to apply to improve light extraction efficiency of ultraviolet-C (UV-C) light-emitting diodes (LEDs).
In this study, we achieved substrate delamination of a 1 mm × 1 mm sapphire substrate was successfully achieved by four sequential
laser irradiations.
While a photoluminescence (PL) peak wavelengths before and after delamination were the same at 278 nm, PL peak intensity after roughening was 1.6 times higher than that before delamination.
These results suggest that LLO via laser scanning enable delamination without causing serious damage to the active layer, making it a promising technique toward high-efficiency UV-C LEDs.

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We present a GaInN-based monolithic stacked RGB μLED array with a fully step-free electrode structure. By introducing conductive vias from each LED layer to the top surface, all anode and cathode electrodes are formed on the same planar level. This eliminates vertical steps between red, green, and blue subpixels, enabling direct integration with drive circuits without bump bonding or height compensation. Independent emissions from each color were demonstrated with uniform current injection and accurate etching control. This structure offers a highly practical solution for full-color micro displays in AR/VR systems.

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230-nm band far-ultraviolet (UV) light sources can offer effective disinfection and sterilization capabilities to human tissue. AlN has large optical nonlinearity and is transparent in the far-UV region, thus it is suitable as a material that generates far-UV light by second harmonic generation (SHG). Compared to a vertical polarity inverted AlN bilayer waveguide, a four-layer polarity inverted AlN waveguide can be expected to provide 7.8 times the SH power. We have fabricated a four-layer polarity inverted AlN channel waveguide, and the SH light measured by a photomultiplier tube peaked at a pump wavelength of 458.7 nm.

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We fabricated AlGaN based light emitting diodes (LEDs) with AlGaN homojunction tunnel junctions (TJs). The AlGaN TJ was successfully formed with Mg and Si profiles very close to those of the low-resistivity GaN TJ. However, The AlGaN TJ LED exhibited a much higher forward voltage, and a slightly lower light output than the standard LED. The operating voltage of 18.4 V at 57 A/cm2. Further developments toward low-resistivity AlGaN TJs are necessary.

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In this work, we report a fully CMOS back-end-of-line (BEOL) compatible fabrication process for GaN-on-Si monolithic microwave integrated circuits (MMICs) on 200-mm wafers. Using this platform, AlInGaN/GaN HEMTs were successfully fabricated on 8-inch GaN-on-Si substrates, demonstrating state-of-the-art performance. Devices with a 150 nm gate length achieved fT/fMAX values of 82/150 GHz, along with excellent large-signal characteristics. The incorporation of an AlInGaN barrier further enabled a high output power density of 1.86 W/mm and a peak power-added efficiency (PAE) of 6.68% at 60 GHz.

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