barrier thickness
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Crystals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 114
Author(s):  
Huan Xu ◽  
Xin Hou ◽  
Lan Chen ◽  
Yang Mei ◽  
Baoping Zhang

Optical properties of wurtzite violet InGaN/GaN quantum well (QW) structures, with the same well-plus-barrier thickness, grown by metal-organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates, were investigated using temperature-dependent photoluminescence (TDPL) and excitation-power-dependent photoluminescence (PDPL). Two samples were compared: one had a thicker well (InGaN/GaN 3/5 nm); the other had a thicker barrier (InGaN/GaN 2/6 nm). It was found that the GaN barrier thickness in the InGaN/GaN MQWs plays an important role in determining the optical characteristics of the MQWs. The peak energy of the two samples varied with temperature in an S-shape. The thicker-barrier sample had a higher turning point from blueshift to redshift, indicating a stronger localization effect. From the Arrhenius plot of the normalized integrated PL intensity, it was found that the activation energy of the nonradiative process also increased with a thicker barrier thickness. The radiation recombination process was dominated in the sample of the thicker barrier, while the non-radiation process cannot be negligible in the sample of the thicker well.


Micromachines ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 537
Author(s):  
Tuan-Anh Vuong ◽  
Ho-Young Cha ◽  
Hyungtak Kim

AlGaN/GaN HEMT hydrogen gas sensors were optimized by AlGaN barrier thickness in the gate-source connected configuration demonstrated high response and robust stability up to 500 °C. First, we found that the hydrogen sensing performance of a conventional normally-on HEMT-based sensor was enhanced when zero voltage was applied on the gate in comparison with a floating-gate condition due to a reduced level of the base current. In the next step, to take advantage of the response increase by VGS = 0 V, a new type of sensor with a source-connected gate (SCG) was fabricated to utilize the normally-on operation of the GaN HEMT sensor as a two-terminal device. AlGaN barrier thickness was thinned by the dry-etching process to gain higher transconductance at a zero-gate bias with the reduction of the distance from the 2DEG channel to the AlGaN surface, thereby significantly improve the hydrogen response. The SCG GaN sensor with an ultra-thin AlGaN barrier (9 nm) exhibited responses of 85% and 20% at 200 and 500 °C, respectively, onto 4%-hydrogen gas, which demonstrates a promising ability for harsh environment applications.


Author(s):  
I. Maamoun ◽  
◽  
O. Falyouna ◽  
R. Eljamal ◽  
K. Bensaida ◽  
...  

Hexavalent chromium is one of the highly toxic heavy metals which could lead to severe health issues when it is discharged into aquifers as industrial wastewater. In the current study nFe0/Cu was successfully employed in PRB technology for Cr(VI) removal from groundwater. Batch and column experiments confirmed the high reactive performance of nFe0/Cu towards Cr(VI) removal by around 85% removal efficiency. The main pathways for Cr-species removal by nFe0/Cu were determined as the reduction of Cr(VI) to Cr(III) by both nFe0 and Cu0 and the precipitation/co-precipitation of Cr(III) with the released iron oxides on the nFe0/Cu surface. The developed 3D-surface response optimization model confirmed the reciprocal relation between the residence time, barrier thickness and hydraulic conductivity. The interaction and sensitivity analysis between the model’s parameters were significantly crucial for defining the optimal design conditions of the nFe0/Cu-PRB. Generally, the current study could represent a great contribution in scaling-up the PRB technology towards the real field applications.


2020 ◽  
Vol 28 (16) ◽  
pp. 23796
Author(s):  
Yi Chao Chow ◽  
Changmin Lee ◽  
Matthew S. Wong ◽  
Yuh-Renn Wu ◽  
Shuji Nakamura ◽  
...  

AIP Advances ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 065126
Author(s):  
Han-Sol Jun ◽  
Jin-Young Choi ◽  
Kei Ashiba ◽  
Sun-Hwa Jung ◽  
Miri Park ◽  
...  

2020 ◽  
Vol 67 (3) ◽  
pp. 828-833 ◽  
Author(s):  
Qi Zhou ◽  
Wei Xiong ◽  
Xiu Yang ◽  
Liyang Zhu ◽  
Kuangli Chen ◽  
...  

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