The development of semiconductors is always accompanied by the progress in controllable doping techniques. Taking AlGaN-based ultraviolet (UV) emitters as an example, despite a peak wall-plug efficiency of 15.3% at the wavelength of 275 nm, there is still a huge gap in comparison with GaN-based visible light-emitting diodes (LEDs), mainly attributed to the inefficient doping of AlGaN with increase of the Al composition. First, p-doping of Al-rich AlGaN is a long-standing challenge and the low hole concentration seriously restricts the carrier injection efficiency. Although p-GaN cladding layers are widely adopted as a compromise, the high injection barrier of holes as well as the inevitable loss of light extraction cannot be neglected. While in terms of n-doping the main issue is the degradation of the electrical property when the Al composition exceeds 80%, resulting in a low electrical efficiency in sub-250 nm UV-LEDs. This review summarizes the recent advances and outlines the major challenges in the efficient doping of Al-rich AlGaN, meanwhile the corresponding approaches pursued to overcome the doping issues are discussed in detail.

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.

In this letter, high power density AlGaN/GaN high electron-mobility transistors (HEMTs) on a freestanding GaN substrate are reported. An asymmetric Γ-shaped 500-nm gate with a field plate of 650 nm is introduced to improve microwave power performance. The breakdown voltage (BV) is increased to more than 200 V for the fabricated device with gate-to-source and gate-to-drain distances of 1.08 and 2.92 μm. A record continuous-wave power density of 11.2 W/mm@10 GHz is realized with a drain bias of 70 V. The maximum oscillation frequency (f_max) and unity current gain cut-off frequency (f_t) of the AlGaN/GaN HEMTs exceed 30 and 20 GHz, respectively. The results demonstrate the potential of AlGaN/GaN HEMTs on free-standing GaN substrates for microwave power applications.

利用磁控溅射和金属有机化学气相沉积方法在c面蓝宝石衬底上生长了深紫外Al_0.38Ga_0.62N/Al_0.55Ga_0.45N多量子阱结构，并对其荧光（PL）谱进行了测量。其PL谱的激发密度依赖性测量结果表明，该量子阱的辐射过程包含了局域载流子的散射、极化场的屏蔽和局域态的填充效应；其PL谱的温度依赖性测量结果则表明，该量子阱的辐射过程包含了局域载流子的弛豫、局域载流子的热激发和自由载流子的常规热化效应。这个现象（即多种辐射复合过程的存在）在低温和弱激发测试条件下尤为显著，并且表现出该量子阱结构具有显著的局域深度非均一性和载流子的局域效果，是浅局域载流子的散射效应和深局域态的载流子填充效应共同作用所致。在较低的温度范围内，随着温度升高，该量子阱的辐射过程是由浅局域载流子的弛豫效应和深局域载流子的热激发效应共同作用的结果。这些行为被归因于阱宽起伏所诱发的局域深度的非均一性和载流子的局域效果。

氮化镓功率器件凭借优异性能被抗辐照应用领域重点关注，为探究氮化镓功率器件抗γ射线辐照损伤能力，明确其辐射效应退化机制，针对增强型AlGaN/GaN高电子迁移率晶体管（High Electron Mobility Transistor，HEMT）器件开展不同偏置（开态、关态和零偏置）条件下的γ射线辐照与不同温度的退火试验，分析器件电学性能同偏置条件和退火环境之间的响应规律。结果表明：随着γ射线辐照剂量的增加，器件阈值电压负漂，跨导峰值、饱和漏电流和反向栅泄漏电流逐渐增加，且在开态偏置条件下器件的电学特性退化更加严重；此外，高温环境下退火会导致器件的电学性能恢复更加明显。分析认为γ射线辐照剂量越高，产生的辐照缺陷越多，同时栅极偏压会降低辐照引发的电子-空穴对的初始复合率，逃脱初始复合的空穴数量增多，进一步增加了缺陷电荷的浓度；而高温环境会导致器件发生隧穿退火或热激发退火，有助于器件性能恢复。氮化镓功率器件的辐照损伤过程及机理研究，为其空间环境应用的评估验证提供了数据支撑。

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.

随着AlGaN基深紫外发光二极管(DUV LED)的发展，其不仅在杀菌消毒领域得到广泛应用，在日盲紫外光通信领域的应用也受到越来越多的关注。这主要是由于相比其他的紫外光源（如汞灯、激光），其具有功耗低、设计灵活且调制带宽高的优势。而DUV LED的带宽严重依赖于器件尺寸，器件尺寸越小，其带宽越高。但是，随着深紫外微型发光二极管(μLED)的尺寸减少，尽管其带宽得到提高，但是其光功率却急剧下降，这严重限制了深紫外μLED在光通信中的应用。文中主要总结了深紫外μLED作为日盲紫外光通信光源的研究现状和综合分析尺寸效应引起器件性能的变化及其机理；并分析出低的光提取效率和严重的自热效应是影响深紫外μLED光功率的两个主要因素。进而综述了各种提高深紫外μLED光提取效率和改善热学特性的方法。文中将为从事深紫外μLED研究的工作者提供一定的研究方向指导。

A physics-based analytical expression that predicts the charge, electrical field and potential distributions along the gated region of the GaN HEMT channel has been developed. Unlike the gradual channel approximation (GCA), the proposed model considers the non-uniform variation of the concentration under the gated region as a function of terminal applied voltages. In addition, the model can capture the influence of mobility and channel temperature on the charge distribution trend. The comparison with the hydrodynamic (HD) numerical simulation showed a high agreement of the proposed model with numerical data for different bias conditions considering the self-heating and quantization of the electron concentration. The analytical nature of the model allows us to reduce the computational and time cost of the simulation. Also, it can be used as a core expression to develop a complete physics-based transistor Ⅳ model without GCA limitation.