240 nm AlGaN-based deep ultraviolet micro-LEDs:size effect versus edge effect

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 25.0μm.Thereinto,the LEE increases by 26.21%and the LEE enhancement mainly comes from the sidewall light extraction.Most notably,transversemagnetic(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 12.5μm sized micro-LEDs,the output power is lower than 25.0μm 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.

Rapid inactivation of human respiratory RNA viruses by deep ultraviolet irradiation from light-emitting diodes on a high-temperatureannealed AlN/Sapphire template

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.

Nonvolatile and reconfigurable two-terminal electro-optic duplex memristor based on Ⅲ-nitride semiconductors

With the fast development of artificial intelligence(AI),Internet of things(IOT),etc,there is an urgent need for the technology that can efficiently recognize,store and process a staggering amount of information.The AlScN material has unique advantages including immense remnant polarization,superior temperature stability and good latticematch to other III-nitrides,making it easy to integrate with the existing advanced III-nitrides material and device technologies.However,due to the large band-gap,strong coercive field,and low photo-generated carrier generation and separation efficiency,it is difficult for AlScN itself to accumulate enough photo-generated carriers at the surface/interface to induce polarization inversion,limiting its application in in-memory sensing and computing.In this work,an electro-optic duplex memristor on a GaN/AlScN hetero-structure based Schottky diode has been realized.This twoterminal memristor shows good electrical and opto-electrical nonvolatility and reconfigurability.For both electrical and opto-electrical modes,the current on/off ratio can reach the magnitude of 104,and the resistance states can be effectively reset,written and long-termly stored.Based on this device,the“IMP”truth table and the logic“False”can be successfully reproduced,indicating the huge potential of the device in the field of in-memory sensing and computing.

Construction of van der Waals substrates for largely mismatched heteroepitaxy systems using first principles

The high density of defects induced by large strains in largely mismatched heteroepitaxy systems, such as AlN and GaN, because of the large lattice and thermal mismatch between substrates and epilayers is the bottleneck problem. Graphene-assisted van der Waals(vdW) heteroepitaxy offers a new opportunity to resolve this problem. However, it suffers from the difficulty of nucleation. Here we theoretically assess the effects of five 2D materials for vdW heteroepitaxy of AlN and GaN, including graphene, hBN, MoS2, gC3N, and gC3N4, and provide physical insights using first-principle calculations. MoS2 and gC3N exhibit significant potential to overcome the shortcomings of graphene owing to their appropriate binding strengths and Al(or Ga)diffusion barriers. Moreover, the interface behavior between the epilayers and the substrates are carefully analyzed. Our findings are helpful not only for obtaining high-quality AlN and GaN films but also for developing new criterions to discover effective 2D materials for vdW heteroepitaxy.

Polarization-enhanced AlGaN solar-blind ultraviolet detectors

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 at30 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.

Prediction of network public opinion based on bald eagle algorithm optimized radial basis function neural network

Purpose-In the new era of highly developed Internet information,the prediction of the development trend of network public opinion has a very important reference significance for monitoring and control of public opinion by relevant government departments.Design/methodology/approach-Aiming at the complex and nonlinear characteristics of the network public opinion,considering the accuracy and stability of the applicable model,a network public opinion prediction model based on the bald eagle algorithm optimized radial basis function neural network(BES-RBF)is proposed.Empirical research is conducted with Baidu indexes such as“COVID-19”,“Winter Olympic Games”,“The 100th Anniversary of the Founding of the Party”and“Aerospace”as samples of network public opinion.Findings-The experimental results show that the model proposed in this paper can better describe the development trend of different network public opinion information,has good stability in predictive performance and can provide a good decision-making reference for government public opinion control departments.Originality/value-A method for optimizing the central value,weight,width and other parameters of the radial basis function neural network with the bald eagle algorithm is given,and it is applied to network public opinion trend prediction.The example verifies that the prediction algorithm has higher accuracy and better stability.