We demonstrate the fabrication of blue, green, and amber InGaN/GaN light-emitting diodes (LEDs) on semipolar {11-22} bulk GaN substrates. The {11-22}GaN substrates used in this study are produced by cutting out from a c-oriented GaN bulk crystal grown by hydride vapor epitaxy. The LEDs have a dimension of 320 ×320 µm2 and are packed in an epoxide resin. The output power and external quantum efficiency (EQE) at a driving current of 20 mA are 1.76 mW and 3.0%, respectively, for the blue LED, 1.91 mW and 4.1% for the green LED, and 0.54 mW and 1.3% for the amber LED. The maximum output powers obtained with a maximum current of 200 mA are 19.0 mW (blue), 13.4 mW (green), and 1.9 mW (amber), while the maximum EQEs are 4.0% at 140 mA (blue), 4.9% at 0.2 mA (green), and 1.6% at 1 mA (amber). It is confirmed that the emission light is polarized along the [1-100] direction, reflecting the low crystal symmetry of the {11-22} plane.

We realized room-temperature lasing of blue and green GaN-based vertical-cavity surface-emitting lasers (VCSELs), for the first time, by current injection. The blue GaN-based VCSEL had a threshold current of 1.5 mA and a threshold voltage of 3.3 V under continuous-wave operation. Its maximum output power was 0.70 mW and its laser emission wavelength was 451 nm. The green GaN-based VCSEL had a threshold current of 22 mA and a threshold voltage of 6.3 V under pulsed current operation. Its maximum output power was estimated to be over 0.80 mW and the laser emission wavelength was 503 nm.

We fabricated high-output-power 255 and 280 nm light-emitting diodes (LEDs) using direct bonding. The LED chips were bonded to sapphire lenses at room temperature using either atomic diffusion bonding or surface-activated bonding. The LEDs with lenses had a higher light extraction efficiency than conventionally structured LEDs. As a result, at a forward current of 350 mA, the output power of the 255 nm LED increased by a factor of 2.8, reaching 73.6 mW, while that of the 280 nm LED increased by a factor of 2.3, reaching 153 mW.

255/280/310 nm deep ultraviolet light-emitting diodes (DUV LEDs) suitable for high-current operation are reported. Newly developed 1 mm sized chips are installed in a commercial package with a two-series configuration. At a forward current of 350 mA, we measured powers of 45.2, 93.3, and 65.8 mW for the 255, 280, and 310 nm LEDs, respectively. The corresponding external quantum efficiencies per serial circuit were 1.3, 3.0, and 2.4%, and successful chip scalability was demonstrated. The 50% lifetime of the 280 nm LED die was estimated to be 3000 h at a junction temperature of 30 • C.

We reviewed the structural and optical properties of high output power 255 and 280 nm light-emitting diodes (LEDs) bonded with hemispherical lenses made of inorganic materials. [This is described as a full paper (and not a review). Is this your intended meaning?][This is my intended] The optimal LED structure with a lens to improve the output power for deep ultraviolet LEDs was designed using Monte Carlo simulation. The LED chips were bonded to sapphire lenses at room temperature using either atomic diffusion bonding or surface activated bonding. The bonding of the lenses to the LEDs is experimentally shown to improve the light extraction efficiency, and the light output power of the LEDs with lenses was significantly higher than that of conventional structure LEDs. The output power of a 255 nm LED with a lens was 2.8 times larger than that without a lens, with a maximum external quantum efficiency of 4.56%, and that of the 280 nm LED with a lens was larger by a factor of 2.3.

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