scholarly journals Ultra-weak emission and microcurrents instabilities in blue GaN LEDs at different stages of degradation

2021 ◽  
pp. 74-82
Author(s):  
Sergei Ekhanin ◽  
Alexander Tomashevich
Keyword(s):  
Quantum Wells ◽  
High Sensitivity ◽  
Multiple Quantum ◽  
Defect States ◽  
Destructive Testing ◽  
Potential Wells ◽  
Current Voltage ◽  
Recombination Processes ◽  
Non Destructive ◽  
Weak Luminescence

It is found that the ultra-weak luminescence observed in microcurrents mode in blue GaN LEDs with multiple quantum wells is due to tunnel-recombination processes with the participation of defect states and local potential wells of various depths, which arise as a result of planar fluctuations of indium in the InGaN layers of the active region. Digital photographs were obtained and patterns of ultra-weak luminescence of the surface of LED crystals were analyzed. It is shown that the patterns of luminescence, along with the current-voltage characteristic, demonstrate significant changes after testing even at the initial stages of degradation, which indicates a high sensitivity of these parameters to degradation processes and the possibility of their use in diagnostic and non-destructive testing methods.

Radiative recombination processes of the many-body states in multiple quantum wells

1990 ◽  
Vol 42 (5) ◽  
pp. 2893-2903 ◽  
Author(s):  
R. Cingolani ◽  
K. Ploog ◽  
A. Cingolani ◽  
C. Moro ◽  
M. Ferrara
Keyword(s):  
Quantum Wells ◽  
Radiative Recombination ◽  
Multiple Quantum Wells ◽  
Multiple Quantum ◽  
Many Body ◽  
Recombination Processes ◽  
The Many

Ultraviolet light emitting diodes using non-polar A-plane AlGaN multiple quantum wells

2006 ◽  
Vol 955 ◽  
Author(s):  
Ramya Chandrasekaran ◽  
Anirban Bhattacharyya ◽  
Ryan France ◽  
Christos Thomidis ◽  
Adrian Williams ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Ultraviolet Light ◽  
Light Emitting Diodes ◽  
Multiple Quantum Well ◽  
Multiple Quantum ◽  
Light Emitting ◽  
Current Voltage ◽  
Uv Leds ◽  
Ultraviolet Light Emitting Diodes ◽  
Electro Luminescence

ABSTRACTIn this paper, we report the growth and fabrication of non-polar A-plane AlGaN multiple quantum well based ultraviolet light emitting diodes (UV-LEDs). The LEDs were grown on R-plane sapphire substrates using molecular beam epitaxy (MBE). The Current-voltage characteristics of the fabricated devices demonstrated rectifying behavior with a series resistance of 38 ohms. An electro-luminescence emission at 338 nm was obtained.

scholarly journals Magnetic Flux Leakage Course of Inner Defects and Its Detectable Depth

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Jianbo Wu ◽  
Wenqiang Wu ◽  
Erlong Li ◽  
Yihua Kang
Keyword(s):  
Magnetic Flux ◽  
Steel Structure ◽  
High Sensitivity ◽  
Magnetic Flux Leakage ◽  
Non Destructive Testing ◽  
Destructive Testing ◽  
Near Surface ◽  
Testing Method ◽  
Non Destructive ◽  
Flux Leakage

AbstractAs a promising non-destructive testing (NDT) method, magnetic flux leakage (MFL) testing has been widely used for steel structure inspection. However, MFL testing still faces a great challenge to detect inner defects. Existing MFL course researches mainly focus on surface-breaking defects while that of inner defects is overlooked. In the paper, MFL course of inner defects is investigated by building magnetic circuit models, performing numerical simulations, and conducting MFL experiments. It is found that the near-surface wall has an enhancing effect on the MFL course due to higher permeability of steel than that of air. Further, a high-sensitivity MFL testing method consisting of Helmholtz coil magnetization and induction coil with a high permeability core is proposed to increase the detectable depth of inner defects. Experimental results show that inner defects with buried depth up to 80.0 mm can be detected, suggesting that the proposed MFL method has the potential to detect deeply-buried defects and has a promising future in the field of NDT.

scholarly journals Feasibility of Digital Image Correlation for Fatigue Cracks Detection under Dynamic Loading

Sensors ◽  
2021 ◽  
Vol 21 (19) ◽  
pp. 6457
Author(s):  
Vladimir V. Bardakov ◽  
Artem Yu. Marchenkov ◽  
Anton Yu. Poroykov ◽  
Alexander S. Machikhin ◽  
Milana O. Sharikova ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Dynamic Loading ◽  
Digital Image ◽  
Fatigue Cracks ◽  
High Sensitivity ◽  
Image Correlation ◽  
Stress Distributions ◽  
Non Destructive Testing ◽  
Destructive Testing ◽  
Non Destructive

We address non-contact detection of defects in the railway rails under their dynamic loading and propose to combine digital image correlation (DIC) and finite element modeling (FEM). We show that accurate model of defect-free rail operating at the same loading conditions as the inspected one provides a reliable reference for experimental data. In this study, we tested the rail samples with artificial and fatigue defects under cyclic loading, calculated displacement and stress distributions at different locations of the cracks via DIC and validated the obtained results by FEM. The proposed DIC-FEM approach demonstrates high sensitivity to fatigue cracks and can be effectively used for remote control of rails as well as for non-destructive testing of various other objects operating under dynamic loads.

scholarly journals Damage Identification and Quantification in Beams Using Wigner-Ville Distribution

Sensors ◽  
2020 ◽  
Vol 20 (22) ◽  
pp. 6638
Author(s):  
Andrzej Katunin
Keyword(s):  
Damage Identification ◽  
Boundary Effect ◽  
Parametric Method ◽  
High Sensitivity ◽  
Non Destructive Testing ◽  
Destructive Testing ◽  
Novel Method ◽  
Local Stiffness ◽  
Non Destructive ◽  
Identification And Quantification

The paper presents the novel method of damage identification and quantification in beams using the Wigner-Ville distribution (WVD). The presented non-parametric method is characterized by high sensitivity to a local stiffness decrease due to the presence of damage, comparable with the sensitivity of the wavelet-based approaches, however the lack of selection of the parameters of the algorithm, like wavelet type and its order, and the possibility of reduction of the boundary effect make this method advantageous with respect to the mentioned wavelet-based approaches. Moreover, the direct relation between the energy density resulting from the application of WVD to modal rotations make it possible to quantify damage in terms of its width and depth. The results obtained for the numerical modal rotations of a beam presented in this paper, simulating the results of non-destructive testing achievable with the shearography non-destructive testing method, confirm high accuracy in localization of a damage as well as quantification of its dimensions. It was shown that the WVD-based method is suitable for detection of damage represented by the stiffness decrease of 1% and can be identified and quantified with a high precision. The presented results of quantification allowed extracting information on damage width and depth.

The piezotronic effect on carrier recombination processes in InGaN/GaN multiple quantum wells microwire

Nano Energy ◽  
2021 ◽  
pp. 106145
Author(s):  
Xianshao Zou ◽  
Jianqi Dong ◽  
Kang Zhang ◽  
Weihua Lin ◽  
Meiyuan Guo ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Multiple Quantum Wells ◽  
Multiple Quantum ◽  
Carrier Recombination ◽  
Piezotronic Effect ◽  
Recombination Processes
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