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Gate Conduction Mechanisms and Lifetime Modeling of p-Gate AlGaN/GaN High-Electron-Mobility Transistors
摘要： The gate conduction mechanisms in p-gallium nitride (GaN)/AlGaN/GaN enhancement mode transistors are investigated using temperature-dependent dc gate current measurements. In each of the different gate voltage regions, a physical model is proposed and compared to experiment. At negative gate bias, Poole–Frenkel emission (PFE) occurs within the passivation dielectric from gate to source. At positive gate bias, the p-GaN/AlGaN/GaN “p-i-n” diode is in forward operation mode, and the gate current is limited by hole supply at the Schottky contact. At low gate voltages, the current is governed by thermionic emission with Schottky barrier lowering in dislocation lines. Increasing the gate voltage and temperature results in thermally assisted tunneling (TAT) across the same barrier. An improved gate process reduces the gate current in the positive gate bias region and eliminates the onset of TAT. However, at high positive gate bias, a sharp increase in current is observed originating from PFE at the metal/p-GaN interface. Using the extracted conduction mechanisms for both devices, accurate lifetime models are constructed. The device fabricated with the novel gate process exhibits a maximum gate voltage of 7.2 V at t1% = 10 years.
关键词： time-dependent breakdown (TDB),p-GaN gate,high-electron-mobility transistor (HEMT),enhancement mode,gallium nitride (GaN),Conduction mechanism
更新于2025-09-23 15:21:21
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Design of a Compact GaN MMIC Doherty Power Amplifier and System Level Analysis With X-Parameters for 5G Communications
摘要： This paper presents a monolithic microwave integrated circuit Doherty power amplifier (DPA) operating at sub-6 GHz for 5G communication applications by a 0.25-μm gallium nitride high-electron mobility transistor process. A compact impedance inverter and output matching of the DPA are achieved using a transmission line network and shunt capacitors. Also, the size ratio of power cells in the main and auxiliary amplifiers is optimized for a high efficiency at output power backoff (OPBO). The measured peak output power (Pout) and the 1-dB compression point (P1 dB) are 38.7 and 32.1 dBm, respectively, at 5.9 GHz. The power-added efficiency at 6-dB OPBO is up to 49.5%. Without digital predistortion (DPD), the DPA can deliver an average Pout of 23.5 dBm with error vector magnitude (EVM) <?28 dB and 21.5 dBm with EVM <?32 dB for 64-quadrature amplitude modulation (QAM) and 256-QAM signals, respectively. The measured X-parameters are employed to further investigate the DPA nonlinear characteristics and verify the accuracy of conventionally used power amplifier characterization/measurement methods for system-level design and testing applications. The simulated results based on the X-parameters also indicate that the average output power can be enhanced up to 25.7 dBm with DPD for 256-QAM.
关键词： 5G communication,monolithic microwave integrated circuit (MMIC),X-parameters,power-added efficiency (PAE),power amplifier (PA),Doherty,gallium nitride (GaN)
更新于2025-09-23 15:21:21
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Early prediction of revascularisation by angiomotin-targeting positron emission tomography
摘要： This study aimed to develop a PET imaging agent of angiomotin (AMOT) expression, a potential biomarker of functional tissue regeneration in post-ischaemic conditions. Methods: Hindlimb ischaemia was induced by ligature and resection of the right femoral artery in mice, and clinical score and limb perfusion were evaluated up to 30 days after surgery. AMOT expression was evaluated by histology and Western blot analysis. NODAGA-conjugates of AMOT ligand, sCD146, were designed, synthesised and radiolabelled with gallium-68. 68Ga-sCD146 microPET/CT imaging was performed from day 1 to day 30 after ischaemia. 68Ga-sCD146 specificity for AMOT was evaluated by autoradiography. Results: Immunohistochemistry showed a significant endothelial overexpression of AMOT from day 5 up to day 10 in the ischaemic hindlimb. 68Ga-sCD146 PET signal intensity correlated significantly with AMOT immunohistochemistry evaluation. 68Ga-sCD146 PET imaging showed a significant uptake in the ischaemic hindlimb from day 2 to day 15, peaking on day 5 (ipsi/contralateral ratio?=?2.4?±?1.3, P?=?0.0005) and significantly decreased after pharmacological blocking (62.57?±?11% decrease in PET signal P?=?0.032). Finally, we observed a significant correlation between day 5 68Ga-sCD146 PET signal intensity and clinical recovery (day 28) or hindlimb perfusion recovery (day 30). Conclusions: This work reports for the first time an early and sustained increase in AMOT expression after hindlimb ischaemia in mice. We therefore developed an AMOT-targeting imaging agent, 68Ga-sCD146, and showed its specific uptake up to 21 days after ischaemic hindlimb using microPET imaging. Correlation of early post-ischaemic PET signal with both delayed perfusion recovery and clinical outcome allows us to postulate that 68Ga-sCD146 represents a promising radiotracer for tissue angiogenesis assessment.
关键词： sCD146,Gallium,angiomotin,ischaemia,angiogenesis
更新于2025-09-23 15:21:21
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Surfactant-free stable SnS2 nanoparticles dispersion for deposition of device-quality films
摘要： Tin sulfide (SnS2) has recently attracted considerable attention due to its layered structure that may form two dimensional morphologies. It is an n-type semiconductor with band gap and electron affinity similar to CdS and In2S3; therefore can be regarded as an alternative for these materials in thin film solar cells. Here, we synthesis of SnS2 nanoparticles with different morphology in different ratio of water-ethanol mixed solution by solvothermal method, and observe that more ethanol leads to large sheet like morphologies, while water based synthesis results in very small nanosheets. A challenge in wet deposition of device-quality thin films of SnS2 is the requirement for highly dispersed particles/sheets. We found highly polar dimethylformamide (DMF) as the right dispersing medium, yielding highly stable dispersions. Very uniform nanocrystalline thin films with [001] preferred orientation and good adhesion to substrate are simply deposited by drop casting and spin coating a 0.5 wt% DMF sol of SnS2 at 2000 rpm for 1 min. Electron affinity and band gap of the films are 4.33 eV and 2.27 eV, which is well aligned for copper indium gallium sulfo-selenide (CIGS) solar cells.
关键词： Two dimensional structures,Surfactant-free dispersion,copper indium gallium sulfo-selenide solar cells,SnS2 thin film,Dimethylformamide,Buffer layer
更新于2025-09-23 15:21:21
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Highly Enhanced Photocatalytic Water-splitting Activity of Gallium Zinc Oxynitride Derived from Flux-assisted Zn/Ga Layered Double Hydroxides
摘要： The Ga/Zn-oxynitride solid solution [(GaN)1-x(ZnO)x] is one of the promising visible-light harvesting photocatalysts for overall water-splitting. A series of (GaN)1-x(ZnO)x (0.11 ≤ x ≤ 0.33) are synthesized by calcining the carbonate-type Zn/Ga-LDH precursor with and without sodium carbonate flux at 850 oC for 8 - 14 h under a NH3 gas-flow. The solid solutions without flux are determined to be low in crystallinity but plate-like in morphology with preferred orientation could be observed. On the other hand, those with flux turn out to be better in crystallinity, and eventually exhibit significantly higher photocatalytic activity for overall water splitting under visible-light irradiation than those without flux. In addition, the bandgap energies can also be engineered from 2.57 eV to 2.72 eV by changing the synthetic parameter such as nitridation time. It is, therefore, suggested that the present new approach can offer new opportunities for designing the next generation photocatalytic systems.
关键词： Overall water splitting,Photocatalyst,Gallium Zinc Oxynitride,Layered double hydroxides,Flux
更新于2025-09-23 15:21:21
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Demonstrating the GaInP/GaAs Three-Terminal Heterojunction Bipolar Transistor Solar Cell
摘要： The three-terminal heterojunction bipolar transistor solar cell (HBTSC) concept enables the realization of a monolithic double-junction device with individual current extraction. We present an HBTSC realized by a heterojunction of GaInP and GaAs. The one-sun open-circuit voltage (VOC ) of the top and bottom junctions are 1.33 V and 0.99 V, respectively, while ?ll factors (FF) are above 80%. At one-sun illumination, reducing one junction’s bias from VOC to maximum power point degrades the performance of the other junction only slightly (< 0.5% ef?ciency loss). These results demonstrate the potential of the HBTSC concept to produce high-ef?ciency independently connected double-junction solar cells.
关键词： photovoltaic cells,independent current,multi terminal,gallium indium phosphide,gallium arsenide,double junction
更新于2025-09-23 15:21:01
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[IEEE 2018 IEEE 5G World Forum (5GWF) - Silicon Valley, CA, USA (2018.7.9-2018.7.11)] 2018 IEEE 5G World Forum (5GWF) - Packaged High Power Frond-End Module for Broadband 24GHz & 28GHz 5G solutions
摘要： This paper presents realization and characteristics of broadband plastic low cost packaged 5G High Power Frond-End (HPFE) operating in 24-31GHz bandwidth. This demonstrator includes a Transmit and Receive paths realized on mixed technologies: 150nm Gallium Nitride on Silicon Carbide (AlGaN/GaN on SiC) and 150nm Gallium Arsenide (GaAs). Continuous Wave (CW) measured power results of the Transmit path (Tx) demonstrates a maximum output power (POUT,Tx) higher than 2W (33.5dBm) with 25% drain efficiency (DE), 24% power added efficiency (PAE), and 36dB of insertion gain (GI,Tx) in the 24-31GHz bandwidth. The receiver path (Rx) presents an maximum output power (POUT,Rx) of 30mW (15.5dBm) and an average Noise Figure (NF) of 3.6dB with an associated Insertion Gain (GI,Rx) of 20dB in the same bandwidth. The HPFE/Tx linearity has been investigated with several M-QAM modulation signals with 25/50 and 100MHz channel spacing and using Digital Pre-Distortion (DPD) leading to 48dBc Adjacent Channel Leakage Ratio (ACLR) and 40dB Mean Squared Error (MSE) for average output powers ranging from linearity performances have been 17dBm to 25dBm. The compared to the ones obtained with two other linear GaAs amplifiers to point telecommunications application: the HPFE presents similar linearity performances associated to a higher efficiency. Thanks to the mixed technologies approach, an optimized trade-off in terms of integration, electrical performances and cost has been demonstrated.
关键词： MMIC,PHEMT,Gallium Arsenide,Plastic packaging,Transmit/Receive path,Low Noise Amplifier,Gallium Nitride,Power Amplifier,Switch
更新于2025-09-23 15:21:01
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Photovoltaic anodes for enhanced thermionic energy conversion
摘要： Thermionic energy converters are heat engines based on the direct emission of electrons from a hot cathode towards a colder anode. Since the thermionic emission is unavoidably accompanied by photonic emission, radiative energy transfer is a significant source of losses in these devices. In this letter, we provide the experimental demonstration of a hybrid thermionic-photovoltaic device that is able to produce electricity not only from the electrons, but also from the photons that are emitted by the cathode. Thermionic electrons are injected in the valence band of a gallium arsenide semiconducting anode, then pumped to the conduction band by the photovoltaic effect, and finally extracted from the conduction band to produce useful energy before they are re-injected in the cathode. We show that such a hybrid device produces a voltage boost of ~ 1V with respect to a reference thermionic device made of the same materials and operating under the same conditions. This proof of concept paves the way to the development of efficient thermionic and photovoltaic devices for the direct conversion of heat into electricity.
关键词： thermionic energy conversion,photovoltaic,hybrid device,voltage boost,gallium arsenide
更新于2025-09-23 15:21:01
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Extremely Low Dark Current and Detection Range Extension of Ga2O3 UV Photodetector using Sn Alloyed Nanostructures
摘要： A unique metal-semiconductor-metal (MSM) photodetector has been fabricated using Sn incorporation in Ga2O3 forming SnxGa1-xO nanostructures (Ns) with platinum (Pt) metal as contacts. The mixed nanostructures (MNs) has been attributed to an increment in the detection range of UV (254 – 302 nm) with ultra-low dark current, hence a potential device in the field of long range deep-UV detector. SnxGa1-xO (Ns) are deposited on c-plane sapphire using low-pressure chemical vapour deposition (LPCVD). From the X-ray diffraction results, existence both SnxGa1-xO and tetragonal SnO2 MNs are confirmed. The XRD peak shifts in SnxGa1-xO is attributed to the integration of Sn with Ga forming SnxGa1-xO alloy with x to be ~7.3% determined from the Vegard’s law. The FESEM images show the thick diameter wire-shaped nanostructures. The absorption spectra show a trace of two absorption edges corresponding to both SnxGa1-xO and SnO2 Ns. Photo to dark current ratio (PDCR) of the fabricated photodetector is large (103) at 2 V bias with fast fall time of 0.18 s. The detector reveals self-powered behaviour also with PDCR > 104 at 0 V bias. The dark current is ultra-low (13 pA at 5 V) due to high barrier height of Pt and the UV detection range has been extended from 254 – 302 nm with a very small drop in PDCR owing to incorporation of Sn.
关键词： LPCVD,Nanostructures,Photodetector,Gallium Oxide
更新于2025-09-23 15:21:01
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The fox and the hound: in-depth and in-grain Na doping and Ga grading in Cu(In,Ga)Se <sub/>2</sub> solar cells
摘要： Cu(In,Ga)(S,Se)2 (CIGS) thin film solar cells require appropriate depth and lateral distributions of alkali metal dopants and gallium to attain world record photovoltaic energy conversion. The two requirements are interdependent because sodium is known to hamper In/Ga interdiffusion in polycrystalline films. However, such a fact is challenged by recent findings where sodium appears to enhance In/Ga interdiffusion in monocrystalline films. This contribution reviews closely the two cases to the benefits of grain boundary engineering in CIGS. A computational model reveals why Na induces In accumulation at CIGS grain boundaries, confining Ga to grain interiors. The positive technological implications for wider gap chalcopyrites are stressed.
关键词： sodium doping,gallium grading,CIGS,solar cells,grain boundary engineering
更新于2025-09-23 15:21:01