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Degradation of GaN-on-GaN vertical diodes submitted to high current stress
摘要： GaN-on-GaN vertical devices are expected to ?nd wide application in power electronics, thanks to the high current densities, the low on-resistance and the high breakdown voltage. So far, only few papers on the reliability of GaN-on-GaN vertical devices have been published in the literature. This paper investigates the degradation of GaN-on-GaN pn diodes submitted to stress at high current density. The study was carried out by means of electrical characterization and electroluminescence (EL) measurements. We demonstrate that: (i) when submitted to stress at high current density, the devices show signi?cant changes in the electrical characteristics: an increase in on-resistance/turn-on voltage, an increase in the generation/recombination components, the creation of shunt-paths. (ii) the increase in on-resistance is strongly correlated to the decrease in the EL signal emitted by the diodes. (iii) the degradation kinetics have a square-root dependence on time, indicative of a di?usion process. The results are interpreted by considering that stress induces a di?usion of hydrogen from the highly-p-type doped surface towards the pn junction. This results in a decrease in hole concentration, due to the creation of MgeH bonds, and in a lower hole injection. As a consequence, on-resistance increases while EL signal shows a correlated decrease.
关键词： Wide band gap semiconductors,Bulk GaN substrates,Vertical diodes,pn junction,Di?usion,Gallium nitride,Hydrogen,Degradation
更新于2025-09-09 09:28:46
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Diode Parameters of Heterojunctions Comprising <i>p</i> -Type Ultrananocrystalline Diamond Films and <i>n</i> -Type Si Substrates
摘要： In the current research, heterojunctions comprising p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films and n-type Si substrates were formed via pulsed laser deposition. To extract their junction parameters via thermionic emission (TE) theory and Norde model, the measurement of dark current density–voltage curves was carried out under various temperatures ranging from 300 to 60 K. Through TE theory, the ideality factor values at 300 K and 60 K were 2.70 and 8.66, respectively. This justified that a heavy recombination process occurs at the junction interface in addition to another tunneling process at 300 K. The tunneling process is predominant at low temperatures. The barrier height values were 0.78 eV and 0.18 eV at 300 K and 60 K, respectively. The values for series resistance (Rs) at 300 K and 60 K were 275.24 Ω and 78.66 kΩ, respectively. The increment of Rs at low temperatures was likely due to the decrease of carrier concentration in the B-doped UNCD/a-C:H films when temperature was decreased.
关键词： PLD,Thin Films,UNCD/a-C:H,Heterojunction,Junction Parameters
更新于2025-09-09 09:28:46
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KOH-Modified Ni/LaTiO2N Schottky Junction Efficiently Reducing CO2 to CH4 under Visible Light Irradiation
摘要： Efficiency of solar-driven CO2 into fuels is largely limited by the sluggish reaction kinetics resulting from high activation barriers and poor electron-hole separation. Here, a synergistic strategy was proposed to overcome these obstacles. As a prototype, KOH-modified Ni/LaTiO2N photocatalyst afforded a high performance in CO2 reduction with a generation rate of 9.69 μmol g-1 for CH4 and 0.31 μmol g-1 for CO, about 5 times higher than the catalytic activities of LaTiO2N. The prominent enhancement results in the following effects: (1) Schottky barrier at Ni/LaTiO2N interface boosts separation of electron-hole pairs. (2) The OH- of KOH as basic sites favors activation of CO2 into CO3 2- species, significantly improving the reaction kinetics of CO2 reduction. (3) The OH- also functions as hole acceptor, boosting the proton release from H2O oxidation.
关键词： molecule activation,Schottky junction,CO2 reduction,charge separation
更新于2025-09-09 09:28:46
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Non-equilibrium photoexcited carrier effects in a graphene-based Josephson junction
摘要： We studied the superconducting proximity effect under photoexcitation by illuminating a superconductor/monolayer graphene/superconductor (SGS) Josephson junction with monochromatic light at a wavelength of 1.31 lm. Although the critical current Ic can be controlled by the irradiation power P, its variation cannot be explained by modi?cation of the carrier density, which has been reported for semiconductor-based Josephson junctions. The estimated electron temperature of gra- phene is proportional to Pd, where d ’ 1=3. This relation clearly indicates that photogenerated non- equilibrium carrier dynamics are responsible for the variation of Ic with P. We suggest that the SGS junction can directly mediate interactions between the optical ?eld and the superconducting state.
关键词： electron temperature,photoexcitation,critical current,graphene,Josephson junction,superconducting proximity effect
更新于2025-09-09 09:28:46
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Gate voltage and temperature dependent Ti-graphene junction resistance toward straightforward p-n junction formation
摘要： High-quality metal-graphene contact is crucial for the fabrication of high-performance graphene transistors. Although Ti has been widely used as metal electrodes in graphene-based devices owing to its excellent adhesive capability, contact resistance (Rc) for Ti/graphene (Ti/Gr) is typically high and varies largely by three orders of magnitude from ～103 to 106 Ω μm. Here, we have systematically investigated the effects of gate voltage (VG) and temperature (T) on Rc in the Ti/Gr interface. Besides significant VG dependence, Rc in the n branch is always larger than that in the p branch, indicating a Ti induced n-doping in graphene. In addition, Rc exhibits an anomalous temperature dependence and drops significantly as the temperature decreases, reaching ～234 Ω μm at 20 K. Such Ti/Gr contact can adjust the Fermi energy of up to 0.15 eV and can also directly form a well-defined sharp p-n junction without extra gates or chemical doping. These findings pave the way to develop the next generation of graphene-based electronic and optoelectronic devices.
关键词： gate voltage,temperature dependence,Ti-graphene junction,p-n junction,graphene,contact resistance
更新于2025-09-04 15:30:14
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Steering Charge Transfer for Boosting Photocatalytic H2 Evolution: Integration of Two-dimensional Semiconductor Superiorities and Noble-Metal-free Schottky Junction Effect
摘要： Sunlight-driven photocatalysis holds great promise for alleviating the energy and environmental crises. For the visible-light-driven bare semiconductor, there is an irreconcilable contradiction between the light absorption and strong redox capabilities. Here, we reported a predictable design for improving the photocatalytic performance via regulating the bandgap and accelerating the charge kinetics of the semiconductor. Taken together, utilize two-dimensional (2D) structure to essentially increase the bandgap of the semiconductor for gaining the higher transfer and separation of the photogenerated electron-hole pairs and the stronger redox capabilities; and accelerate charge kinetics via the driving force from the Schottky junction. Meanwhile, the Schottky barrier prevents the photogenerated electrons trapped by a noble-metal-free electron acceptor from dually recombining. Additionally, the energy transfer process of the photocatalytic reaction was also researched in detail, aligning well with the photocatalytic mechanism.
关键词： photocatalytic H2 evolution,2D materials,Schottky junction
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) - Singapore (2018.7.16-2018.7.19)] 2018 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) - Characterization of Bandgap Engineering on Operative Transistor Devices by Spectral Photon Emission
摘要： In modern IC technologies, it is very common to use germanium enriched silicon in order to increase field effect transistor (FET) channel carrier mobility for high performance. The germanium content modifies the effective semiconductor band gap EG. Thus, the bandgap energy EG is an important technology performance parameter. EG can be obtained in an LED-like operation of electronic devices, requiring forward biased p-n junctions. P-n junctions in FETs are source or drain to body diodes, usually grounded or reversely biased. This investigation applies a bias to the body that can trigger parasitic forward operation of the source/drain to body p-n junction in any FET. Spectral photon emission (SPE) is taken here as non-destructive in operative method to characterize engineered bandgaps transistor devices, while the device remains fully functional. Proving this technique with the nominal silicon bandgap on an (unstrained) 120nm technology FET, the characterization capability for bandgap engineering is successfully demonstrated using SiGe:C HBT. In IC technology, Ge enriched silicon is recently often used to increase channel carrier mobility. As a next step, 14/16nm p-type FinFET devices have been investigated by applying a bias voltage to the body and thereby activating one of the body/diffusion p-n junctions in forward bias. By measuring the spectral distribution of emission intensity through the backside of the operating device with an InGaAs detector, EG of the engineered bandgap can be determined in the FinFETs as well, in case of the investigated p-type FinFETs to 0.84 eV. This opens a new path for contactless fault isolation by quantitative local determination of bandgap engineering.
关键词： Bandgap engineering,body diode,heterojunction bipolar transistor,body bias voltage,contactless fault isolation,parasitic operation,FinFET,germanium,MOSFET,p-n junction,bandgap characterization,spectral photon emission,SiGe,HBT
更新于2025-09-04 15:30:14
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Visible light induced H2 evolution on the hetero-junction Ag/NiO prepared by nitrate route
摘要： The photo-electrochemical study of the hetero-junction Ag/NiO (5/95 wt%) prepared in situ by nitrate route was investigated to assess its photoactivity for the hydrogen production upon visible light. The X-ray diffraction pattern shows narrow peaks of Ag and NiO. The direct optical gap of the sensitizer NiO (1.51 eV) is well matched to the solar spectrum. It acts as n-type semiconductor and the potential of its conduction band (?0.35 VSCE), determined from the capacitance measurement, is more negative than the H2O/H2 level (～?0.3 VSCE), yielding water reduction under visible light; the photoactivity peaks at pH ～ 13. The excited electrons are transferred to Ag clusters, to reduce water into gaseous hydrogen owing to the low H2-over-voltage (～160 μmol). A quantum conversion efficiency of 0.11% is reported under visible light (3.42 × 1018 photons s?1) within ～10 min with an evolution rate of 96 μmol h?1 mg?1. The catalyst was tested for several successive photocatalytic cycles, a de-activation effect of ～7% per cycle is observed, thus proving its stability and repeatability. The heating of the catalyst under dynamic vacuum at 250 °C restores the initial photoactivity.
关键词： Hetero-junction Ag/NiO,Hydrogen,Semiconductor,Photo-electrochemical
更新于2025-09-04 15:30:14
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Twist-angle Dependent Optoelectronics in a few-layer Transition-Metal Dichalcogenides Heterostructure
摘要： Lattice matching has been supposed to play an important role in the coupling between two materials in vertical heterostructure (HS). To investigate this role, we fabricated a heterojunction device with a few layers of p-type WSe2 and n-type MoSe2 with different crystal orientation angles. The crystal orientations of WSe2 and MoSe2 were estimated by using high-resolution X-ray diffraction. Heterojunction devices were fabricated with twist angles of 0?, 15? and 30?. The I-V curve of the sample with the twist angle of 0° under the dark condition showed a diode-like behavior. The strong coupling due to lattice matching caused a well-established p-n junction. In cases of 15° and 30° samples, the van der Waals gap was built due to lattice mismatching, which resulted in the formation of a potential barrier. However, when the LED light of 365 nm (3.4 eV) was illuminated, excited electrons and holes were possible to jump beyond the potential barrier and the current flowed well in both forward and reverse directions. The effects of the twist angle were analyzed by spectral responsivity and external quantum efficiency, where it was found that the untwisted HS exhibited higher sensitivity under IR illumination while the twisting effect was not noticeable under UV illumination. From the photoluminescence and Raman spectroscopy, it was confirmed that the twisted HS showed a weak coupling due to the lattice mismatch.
关键词： p-n junction,optoelectronics,transition-metal dichalcogenides,heterostructure,a few-layer TMD,twist angle
更新于2025-09-04 15:30:14
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Comprehensive Pyro‐Phototronic Effect Enhanced Ultraviolet Detector with ZnO/Ag Schottky Junction
摘要： As a coupling effect of pyroelectric and photoelectric effect, pyro-phototronic effect has demonstrated an excellent tuning role for fast response p–n junction photodetectors (PDs). Here, a comprehensive pyro-phototronic effect is utilized to design and fabricate a self-powered and flexible ultraviolet PD based on the ZnO/Ag Schottky junction. By using the primary pyroelectric effect, the maximal transient photoresponsivity of the self-powered PDs can reach up to 1.25 mA W?1 for 325 nm illumination, which is improved by 1465% relative to that obtained from the steady-state signal. The relative persistent secondary pyroelectric effect weakens the height of Schottky barrier, leading to a reduction of the steady-state photocurrent with an increase in the power density. When the power density is large enough, the steady-state photocurrent turns into a reverse direction. The corresponding tuning mechanisms of the comprehensive pyro-phototronic effect on transient and steady-state photocurrent are revealed based on the bandgap diagrams. The results may help us to further clarify the mechanism of the pyro-phototronic effect on the photocurrent and also provide a potential way to optimize the performance of self-powered PDs.
关键词： ultraviolet photodetector,Schottky junction,secondary pyroelectric effect,pyro-phototronic effect,self-powered
更新于2025-09-04 15:30:14