1,871,531 research outputs found
Pulsed operation and performance of commercial GaN HEMTs
No full textThe present study investigates the behaviour and performance of commercially available GaN HEMTs provided by Cree Inc. The gain and power variations at pulse repetition frequencies (PRFs) in the range 100–400 kHz are presented. Rise and fall times are also investigated at different PRFs and power levels. The pulsed RF waveforms are obtained by switching the gate bias of the transistor on and completely off to ensure that the device goes through full transients for every pulse. The RF frequency at which the study is conducted is 3.5 GHz. The aim of the study is to assess the suitability of commercial GaN HEMTs to pulsed RF applications such as Radar.The present study investigates the behaviour and performance of commercially available GaN HEMTs provided by Cree Inc. The gain and power variations at pulse repetition frequencies (PRFs) in the range 100-400 kHz are presented. Rise and fall times are also investigated at different PRFs and power levels. The pulsed RF waveforms are obtained by switching the gate bias of the transistor on and completely off to ensure that the device goes through full transients for every pulse. The RF frequency at which the study is conducted is 3.5 GHz. The aim of the study is to assess the suitability of commercial GaN HEMTs to pulsed RF applications such as Radar
Dynamic Transconductance Dispersion Characterization of Channel Hot-Carrier Stressed 0.25<i>μ</i>m AlGaN/GaN HEMTs
Get PDFUsing the dynamic transconductance frequency dispersion technique, we characterize unstressed and hot-electron stressed short-channel AlGaN/GaN high-electron-mobility transistors. The results reported in this letter demonstrate that the stress-induced degradation in dc and pulsed characteristics is unlikely to be ascribable to sizable trap generation at the AlGaN/GaN interface
Zonghan-Barry-Gan/public-axriv: 220812-Update-to-Pro-Abdulhamit-GAN-BHI
No full textThis release is an update and discussion to Prof Abdulhamit. It use GAN to generate breast histopathology images, which will be later used as image enhancement to train models
This notebook is based on Chris Deotte's notebook on 2019 using GAN for dog images. reference show hear "Dog Memorizer GAN". 2019. Deotte, C. Accessed August 12 2022. https://www.kaggle.com/code/cdeotte/dog-memorizer-gan
Intentionally Carbon-Doped AlGaN/GaN HEMTs:Necessity for Vertical Leakage Paths
Get PDFDynamic ON-resistance (RON) in heavily carbon doped AlGaN/GaN high electron mobility transistors is shown to be associated with the semi-insulating carbon-doped buffer region. Using transient substrate bias, differences in RON dispersion between transistors fabricated on nominally identical epilayer structures were found to be due to the band-to-band leakage resistance between the buffer and the 2DEG. Contrary to normal expectations, suppression of dynamic RON dispersion in these devices requires a high density of active defects to increase reverse leakage current through the depletion region allowing the floating weakly p-type buffer to remain in equilibrium with the 2DEG
Behavioral modeling of GaN-based power amplifiers: impact of electrothermal feedback on the model accuracy and identification
Get PDFIn this article, we discuss the accuracy of behavioral models in simulating the intermodulation distortion (IMD) of microwave GaN-based high-power amplifiers in the presence of strong electrothermal (ET) feedback. Exploiting an accurate self-consistent ET model derived from measurements and thermal finite-element method simulations, we show that behavioral models are able to yield accurate results, provided that the model identification is carried out with signals with wide bandwidth and large dynamics
AlN/GaN-based MOS-HEMT technology: processing and device results
Get PDFProcess development of AlN/GaN MOS-HEMTs is presented, along with issues and problems concerning the fabrication processes. The developed technology uses thermally grown Al<sub>2</sub>O<sub>3</sub> as a gate dielectric and surface passivation for devices. Significant improvement in device performance was observed using the following techniques: (1) Ohmic contact optimisation using Al wet etch prior to Ohmic metal deposition and (2) mesa sidewall passivation. DC and RF performance of the fabricated devices will be presented and discussed in this paper
LCT-GAN - Improving the efficiency of tabular data synthesis via latent embeddings
No full textIn the past decade data-driven approaches have been at the core of many business and research models. In critical domains such as healthcare and banking, data privacy issues are very stringent. Synthetic tabular data is an emerging solution to privacy guarantee concerns. Generative Adversarial Networks (GANs) are one of the emerging solutions for synthesizing data. However in order to capture all relevant relationships between columns, tabular data needs to be numerically encoded. As columns might be of different types, this is a challenging task as proven by recent approaches. Throughout this paper, we focus on the dimensionality explosion problem, which leads to high-dimensional datasets alongside computational overhead and increase in training time. We introduce a novel synthesis pipeline - LCT-GAN - an improvement to the current state-of-the-art in tabular data synthesis CTAB-GAN. Our approach addresses the dimensionality explosion problem by introducing a low-dimensional embedding step via an autoencoder prior to training. It is then combined with a novel conditional GAN architecture, operating in latent space. After thorough evaluation, we observe that our solution achieves more than 30\% improvement in certain statistical metrics in comparsion to CTAB-GAN, accompanied by 5 fold decrease in size and 150 times speedup in training time for a single epoch. We successfully show that it is possible to embed data using autoencoders, and that GANs are able to learn complex relationships in latent space in the context of tabular data.CSE3000 Research ProjectComputer Science and Engineerin
FCT-GAN: Fourier Neural Operator for Global Relation Enhancement in Tabular Data Synthesizing using Generative Adversarial Networks
No full textSince the regularization of data privacy (e.g., GDPR), the effectiveness of data sharing has decreased. A promising technique to circumvent this problem is tabular data synthesis (i.e., the generation of fake tabular data that statistically resembles the original data). However, the state-of-the-art tabular data synthesis model, CTAB-GAN, fails at robustly imitating global data dependencies and underperforms when column orders get permuted. CTAB-GAN internally uses Convolutional Neural Networks (CNN) which limits the model’s performance due to a strictly non-global data perspective during iterative training phases. To address this limitation, this paper proposes FCT-GAN which leverages the Fourier Neural Operator to learn global dependencies in the frequency domain. Specifically, it enhances CTAB-GAN by replacing the CNN of the discriminator with a four-layered two-dimensional Fourier Neural Operator. As a consequence of FCT-GAN’s global nature and cross-column relation robustness, it outperforms CTAB-GAN and additionally offers the column permutation invariant property. The evaluation of FCT-GAN on five datasets shows that the generated data, remarkably resembles the real data and reveals an increase in accuracy, by up to 19% for five machine learning algorithms independent of data column order, compared to CTAB-GAN.CSE3000 Research ProjectComputer Science and Engineerin
InGaN/GaN quantum wells grown on polar and nonpolar GaN substrates
No full textNonpolar (m-plane or a-plane) gallium nitride (GaN) is predicted to be a potential substrate material to improve luminous efficiencies of nitride-based quantum wells (QWs). Numerical calculations indicated that the spontaneous emission rate in a single In0.15Ga0.85N/GaN QW could be improved by ~2.2 times if the polarization-induced internal field was avoided by epitaxial deposition on nonpolar substrates.
A challenge for nonpolar GaN is the limited size (less than 10×10 mm2) of substrates, which was addressed by expansion during the regrowth by Hydride Vapor Phase Epitaxy (HVPE). Subsurface damage in GaN substrates were reduced by annealing with NH3 and N2 at 950 ºC for 60 minutes. It was additionally found that the variation of m-plane QWs’ emission properties was significantly increased when the substrate miscut toward a-axis was increased from 0º to 0.1º.
InGaN/GaN QWs were grown by Metalorganic Chemical Vapor Deposition (MOCVD) on c-plane and m-plane GaN substrates. The QWs were studied by cathodoluminescence spectroscopy with different incident electron beam probe currents (0.1 nA ~ 1000 nA). Lower emission intensities and longer peak wavelengths from c-plane QWs were attributed to the Quantum-confined Stark Effect (QCSE). The emission intensity ratios of m-plane QWs to c-plane QWs decreased from 3.04 at 1 nA to 1.53 at 1000 nA. This was identified as the stronger screening effects of QCSE at higher current densities in c-plane QWs.
To further investigate these effects in a fabricated structure, biased photoluminescence measurements were performed on m-plane InGaN/GaN QWs. The purpose was to detect the possible internal fields induced by the dot-like structure in the InGaN layer through the response of these internal fields under externally applied fields. No energy shifts of the QWs were observed, which was attributed to strong surface leakage currents
Coincident electron channeling and cathodoluminescence studies of threading dislocations in GaN
No full textWe combine two scanning electron microscopy techniques to investigate the influence of dislocations on the light emission from nitride semiconductors. Combining electron channeling contrast imaging and cathodoluminescence imaging enables both the structural and luminescence properties of a sample to be investigated without structural damage to the sample. The electron channeling contrast image is very sensitive to distortions of the crystal lattice, resulting in individual threading dislocations appearing as spots with black–white contrast. Dislocations giving rise to nonradiative recombination are observed as black spots in the cathodoluminescence image. Comparison of the images from exactly the same micron-scale region of a sample demonstrates a one-to-one correlation between the presence of single threading dislocations and resolved dark spots in the cathodoluminescence image. In addition, we have also obtained an atomic force microscopy image from the same region of the sample, which confirms that both pure edge dislocations and those with a screw component (i.e., screw and mixed dislocations) act as nonradiative recombination centers for the Si-doped c-plane GaN thin film investigated
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