Session Index

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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