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Understanding the Role of Existing Technology in the Fight Against COVID-19
Published in Ram Shringar Raw, Vishal Jain, Sanjoy Das, Meenakshi Sharma, Pandemic Detection and Analysis Through Smart Computing Technologies, 2022
In order to develop the mechanism of disinfection using UV light, the technology involved in the process needs to be understood. The UV-C used in the UVGI is produced by a lamp which emits short-wavelength radiations. The conventional lamps are usually made of mercury vapors enclosed in a fused quartz tube. The mercury vapors are either at low or high pressure depending on the requirement. The low-pressure lamps are similar to fluorescent lamps, but do not contain fluorescent phosphorus. Moreover, the quartz tube is used instead of the glass because the latter absorbs the UV radiations. Whereas the low-pressure mercury lamps give off 253.7 nm radiations, a broader emission may be obtained by using high-pressure mercury lamps, which work on the principle of arc discharge lamps. Since mercury is toxic in nature, alternative technology such as excimer lamps and light-emitting diodes (LEDs) are being used. In an excimer lamp, diatomic molecules are used which are excited from the ground state to the excited state using electric discharge method. The excited electrons come back spontaneously to the ground state emitting photons in the UV region. A wide range of radiation lamps may be made using different excimers. The LED technology is also mercury-free and uses solid-state semiconductor materials such as aluminum gallium nitride (AlGaN). The semiconductor LEDs are tunable for specific needs by doping or chemical modification of the active material. The advantages of LED lamps lie in its compact size; however, much work is needed to optimize its efficiency, device lifetime, and cost as compared to conventional methods.
Current Collapse in AlGaN/GaN HEMTs
Published in D. Nirmal, J. Ajayan, Handbook for III-V High Electron Mobility Transistor Technologies, 2019
Group III-V nitride compound semiconductors such as Gallium Nitride (GaN) and Aluminum Gallium Nitride (AlGaN) exhibit distinctive combination of properties like high breakdown field, large energy band gap, good thermal conductivity, high mobility and high saturation velocity. Due to these properties, GaN-based devices outperform existing Si- and SiC-based devices for power electronic applications. There has been a rapid progress in the design and development of GaN-based devices and circuits since the demonstration of first GaN-based transistor [1]. Since early 1990s, Ga-N has been considered as a very interesting and highly promising material for both optical and high power microwave applications. Owing to the high defect density present in native GaN material, early studies of GaN and related compounds showed uncertainty on whether devices based on this material could ever be used for practical applications. Nevertheless, with better understanding of effect of these defects on device performance along with improvement in the epitaxial growth technology, GaN-based technology has been successfully in use for high-power applications. Trapping related reliability issues still remain a major obstacle for AlGaN/GaN High Electron mobility Transistors (HEMT), thus preventing them from being adopted widely for high-voltage and high-temperature applications. It is essential to analyze and study trapping effects in AlGaN/GaN HEMTs because of two important reasons. First, they limit DC and RF performance of the device. Secondly, they also play an important role in reliability of the device in high-power applications. The device performance severely degrades when it operates at high voltage as the electrons get trapped in various locations in the device. It has also been seen that the trapping effects rise after device degradation. Performance and thus reliability of the device thus greatly reduces by increased trapping [2–5].
Metal nitride-based nanostructures for electrochemical and photocatalytic hydrogen production
Published in Science and Technology of Advanced Materials, 2022
Harpreet Singh Gujral, Gurwinder Singh, Arun V. Baskar, Xinwei Guan, Xun Geng, Abhay V. Kotkondawar, Sadhana Rayalu, Prashant Kumar, Ajay Karakoti, Ajayan Vinu
Template-induced synthesis of mixed MNs is an effective method for generating tunable porous features that are crucial for their catalytic activity [152–154]. Fischer et al. developed a reactive hard templating approach for the fabrication of aluminium gallium nitride (AlGaN) and titanium vanadium nitride (TiVN) particles with diameters smaller than 10 nm, as demonstrated in Figure 7d [155]. Due to the confinement effect of the carbon nitride matrix, the composition of the resulting MN could be easily adjusted by changing the concentration of the preceding precursor solution. Thus, ternary MN nanoparticles with continuously tunable metal composition were successfully produced. Robins et al. presented ordered mixed titanium-niobium nitrides with gyroidal network structures synthesized from triblock terpolymer structure-directed mixed oxides [156]. The materials retained both macroscopic integrity and mesoscale ordering despite heat treatment up to 600°C without a rigid carbon framework as support. The gyroidal lattice parameters were varied by changing polymer molar mass. This kind of synthesis strategy may prove useful in generating a variety of monolithic ordered mesoporous mixed oxides and nitrides for electrode and catalyst materials.
Strain-enhanced high Q-factor GaN micro-electromechanical resonator
Published in Science and Technology of Advanced Materials, 2020
Liwen Sang, Meiyong Liao, Xuelin Yang, Huanying Sun, Jie Zhang, Masatomo Sumiya, Bo Shen
Silicon-based nano- and micro-electromechanical systems (NEMS/MEMS) are reaching their limits for sensing in harsh conditions, a matter that has received extensive attentions in recent years. With the increasing requirement for MEMS/NEMS regarding novel functionalities, the wide-bandgap semiconductors are attracting more attentions due to their higher mechanical and thermal stability, biocompatibility, miniaturization, and facile integration [1–3]. Among all the wide-bandgap material systems, gallium nitride (GaN) intrinsically has a direct bandgap, superior mechanical properties, high thermal stability, and chemical inertness [4,5]. Especially, the high crystalline-quality GaN has been achieved on the silicon (Si) substrates in recent years. The GaN-on-Si technology enables the monolithic integration of MEMS/NEMS with the existing CMOS circuits, which is beyond GaN-on-sapphire or silicon carbide (SiC) technology [6]. The well-developed power electronic devices and high-frequency devices based on aluminium gallium nitride/gallium nitride (AlGaN/GaN) high electron mobility transistors (HEMTs) on Si substrates can be combined or integrated into MEMS to produce novel smart devices and systems [7–10]. However, compared to the well-developed optoelectronic devices, the GaN-based MEMS/NEMS technology is still in its infancy. For example, the reported quality (Q) factors of all the GaN or HEMT MEMS/NEMS systems are only on the order of 102–103, which are much lower than those of Si or SiC resonators [1,4,5].