240 nm AlGaN-based micro-LEDs with different sizes are designed and fabricated. Then, the external quantum efficiency (EQE) and light extraction efficiency (LEE) are systematically investigated by comparing size and edge effects. Here, it is revealed that the peak optical output power increases by 81.83% with the size shrinking from 50.0 to 25.0 μm. Thereinto, the LEE increases by 26.21% and the LEE enhancement mainly comes from the sidewall light extraction. Most notably, transverse-magnetic (TM) mode light intensifies faster as the size shrinks due to the tilted mesa side-wall and Al reflector design. However, when it turns to 12.5 μm sized micro-LEDs, the output power is lower than 25.0 μm sized ones. The underlying mechanism is that even though protected by SiO₂ passivation, the edge effect which leads to current leakage and Shockley-Read-Hall (SRH) recombination deteriorates rapidly with the size further shrinking. Moreover, the ratio of the p-contact area to mesa area is much lower, which deteriorates the p-type current spreading at the mesa edge. These findings show a role of thumb for the design of high efficiency micro-LEDs with wavelength below 250 nm, which will pave the way for wide applications of deep ultraviolet (DUV) micro-LEDs.

Efficient and eco-friendly disinfection of air-borne human respiratory RNA viruses is pursued in both public environment and portable usage. The AlGaN-based deep ultraviolet (DUV) light-emission diode (LED) has high practical potentials because of its advantages of variable wavelength, rapid sterilization, environmental protection, and miniaturization. Therefore, whether the emission wavelength has effects on the disinfection as well as whether the device is feasible to sterilize various respiratory RNA viruses under portable conditions is crucial. Here, we fabricate AlGaN-based DUV LEDs with different wavelength on high-temperature-annealed (HTA) AlN/Sapphire templates and investigate the inactivation effects for several respiratory RNA viruses. The AlN/AlGaN superlattices are employed between the template and upper n-AlGaN to release the strong compressive stress (SCS), improving the crystal quality and interface roughness. DUV LEDs with the wavelength of 256, 265, and 278 nm, corresponding to the light output power of 6.8, 9.6, and 12.5 mW, are realized, among which the 256 nm-LED shows the most potent inactivation effect in human respiratory RNA viruses, including SARS-CoV-2, influenza A virus (IAV), and human parainfluenza virus (HPIV), at a similar light power density (LPD) of ~0.8 mW/cm² for 10 s. These results will contribute to the advanced DUV LED application of disinfecting viruses with high potency and broad spectrum in a portable and eco-friendly use.

AlGaN solar-blind ultraviolet (SBUV) detectors have potential application in fire monitoring, corona discharge monitoring, or biological imaging. With the promotion of application requirements, there is an urgent demand for developing a high-performance vertical detector that can work at low bias or even zero bias. In this work, we have introduced a photoconductive gain mechanism into a vertical AlGaN SBUV detector and successfully realized it in a p-i-n photodiode via inserting a multiple-quantum-well (MQW) into the depletion region. The MQW plays the role of trapping holes and increasing carrier lifetime due to its strong hole confinement effect and quantum confinement Stark effect. Hence, the electrons can go through the detector multiple times, inducing unipolar carrier transport multiplication. Experimentally, an AlGaN SBUV detector with a zero-bias peak responsivity of about 0.425 A/W at 233 nm is achieved, corresponding to an external quantum efficiency of 226%, indicating the existence of internal current gain. When compared with the device without MQW structure, the gain is estimated to be about 103 in magnitude. The investigation provides an alternative and effective approach to obtain high current gain in vertical AlGaN SBUV detectors at zero bias.

Due to the bandwidth limitation of the ultraviolet-C (UV-C) optical communication system and strong channel attenuation, it is difficult to transmit high-frequency signals. In this paper, the temporal ghost imaging (TGI) algorithm was first applied to the UV-C communication experimentally, and we realized the transmission of a 4 GHz signal through 95.34 MHz system bandwidth. The study indicates that the TGI algorithm can significantly improve the signal-to-noise ratio (SNR) compared with the on–off keying method. Our research provides a new approach for alleviating transmission frequency limitation due to poor SNR and insufficient hardware bandwidth.

In this work, a self-powered GaN-based metal-semiconductor-metal photodetector (MSM PD) with high responsivity has been proposed and fabricated. The proposed MSM PD forms an asymmetric feature by using the polarization effect under one electrode, such that we adopt an AlGaN/GaN heterojunction to produce the electric field, and by doing so, an asymmetric energy band between the two electrodes can be obtained even when the device is unbiased. The asymmetric feature is proven by generating the asymmetric current-voltage characteristics both in the dark and the illumination conditions. Our results show that the asymmetric energy band enables the self-powered PD, and the peak responsivity wavelength is 240 nm with the responsivity of 0.005 A/W. Moreover, a high responsivity of 13.56 A/W at the applied bias of 3 V is also achieved. Thanks to the very strong electric field in the charge transport region, when compared to the symmetric MSM PD, the proposed MSM PD can reach an increased photocurrent of 100 times larger than that for the conventional PD, even if the illumination intensity for the light source becomes increased.

AlGaN solar-blind ultraviolet detectors have great potential in many fields, although their performance has not fully meet the requirements until now. Here, we proposed an approach to utilize the inherent polarization effect of AlGaN to improve the detector performance. AlGaN heterostructures were designed to enhance the polarization field in the absorption layer, and a high built-in field and a high electron mobility conduction channel were formed. As a result, a high-performance solar-blind ultraviolet detector with a peak responsivity of 1.42 A/W at 10 V was achieved, being 50 times higher than that of the nonpolarization-enhanced one. Moreover, an electron reservoir structure was proposed to further improve the performance. A higher peak responsivity of 3.1 A/W at 30 V was achieved because the electron reservoir structure could modulate the electron concentration in the conduction channel. The investigation presented here provided feasible approaches to improve the performance of the AlGaN detector by taking advantage of its inherent property.