In this letter,high power density AlGaN/GaN high electron-mobility transistors(HEMTs)on a freestanding GaN substrate are reported.An asymmetricΓ-shaped 500-nm gate with a field plate of 650 nm is introduced to improv...In this letter,high power density AlGaN/GaN high electron-mobility transistors(HEMTs)on a freestanding GaN substrate are reported.An asymmetricΓ-shaped 500-nm gate with a field plate of 650 nm is introduced to improve microwave power performance.The breakdown voltage(BV)is increased to more than 200 V for the fabricated device with gate-to-source and gate-to-drain distances of 1.08 and 2.92μm.A record continuous-wave power density of 11.2 W/mm@10 GHz is realized with a drain bias of 70 V.The maximum oscillation frequency(f_(max))and unity current gain cut-off frequency(f_(t))of the AlGaN/GaN HEMTs exceed 30 and 20 GHz,respectively.The results demonstrate the potential of AlGaN/GaN HEMTs on freestanding GaN substrates for microwave power applications.展开更多
This work demonstrates high-performance NiO/β-Ga_(2)O_(3) vertical heterojunction diodes(HJDs)with double-layer junc-tion termination extension(DL-JTE)consisting of two p-typed NiO layers with varied lengths.The bott...This work demonstrates high-performance NiO/β-Ga_(2)O_(3) vertical heterojunction diodes(HJDs)with double-layer junc-tion termination extension(DL-JTE)consisting of two p-typed NiO layers with varied lengths.The bottom 60-nm p-NiO layer fully covers theβ-Ga_(2)O_(3) wafer,while the geometry of the upper 60-nm p-NiO layer is 10μm larger than the square anode elec-trode.Compared with a single-layer JTE,the electric field concentration is inhibited by double-layer JTE structure effectively,resulting in the breakdown voltage being improved from 2020 to 2830 V.Moreover,double p-typed NiO layers allow more holes into the Ga_(2)O_(3) drift layer to reduce drift resistance.The specific on-resistance is reduced from 1.93 to 1.34 mΩ·cm^(2).The device with DL-JTE shows a power figure-of-merit(PFOM)of 5.98 GW/cm^(2),which is 2.8 times larger than that of the conven-tional single-layer JTE structure.These results indicate that the double-layer JTE structure provides a viable way of fabricating high-performance Ga_(2)O_(3) HJDs.展开更多
Ga_2O_3 metal–oxide–semiconductor field-effect transistors(MOSFETs) with high-breakdown characteristics were fabricated on a homoepitaxial n-typed β-Ga_2O_3 film, which was grown by metal organic chemical vapor dep...Ga_2O_3 metal–oxide–semiconductor field-effect transistors(MOSFETs) with high-breakdown characteristics were fabricated on a homoepitaxial n-typed β-Ga_2O_3 film, which was grown by metal organic chemical vapor deposition(MOCVD) on an Fedoped semi-insulating(010) Ga_2O_3 substrate. The structure consisted of a 400 nm unintentionally doped(UID) Ga_2O_3 buffer layer and an 80 nm Si-doped channel layer. A high k HfO_2 gate dielectric film formed by atomic layer deposition was employed to reduce the gate leakage. Moreover, a source-connected field plate was introduced to enhance the breakdown characteristics. The drain saturation current density of the fabricated device reached 101 mA/mm at V_(gs) of 3 V. The off-state current was as low as 7.1 ×10^(-11) A/mm, and the drain current I_(ON)/I_(OFF) ratio reached 10~9. The transistors exhibited three-terminal off-state breakdown voltages of 450 and 550 V, corresponding to gate-to-drain spacing of 4 and 8 μm, respectively.展开更多
Two-inch semi-insulating SiC bulk crystals with resistivity higher than 1×106 Ωcm were achieved by vanadium doping during sublimation. Secondary-ion-mass-spectrometry (SIMS) was employed to determine the concen-...Two-inch semi-insulating SiC bulk crystals with resistivity higher than 1×106 Ωcm were achieved by vanadium doping during sublimation. Secondary-ion-mass-spectrometry (SIMS) was employed to determine the concen-tration of impurities in the crystals, such as B, Al, V and N. These results indicated that the concentration of nitrogen and aluminum kept on decreasing and the concentration of B and V was almost constant during the whole growth. An inner crucible was used to control the exhausting of vanadium, which made the uniformity of the high resistivity (>1×106 Ωcm) in the wafer up to 80%. High-performance AlGaN/GaN high-electron-mobility-transistor (HEMT) materials and devices were grown and fabricated on semi-insulating 6H-SiC sub-strates. The two-dimensional electron gas (2DEG) mobility at room-temperature was 1795 cm2/V·s. The charge carrier concentration of the substrate determined by capacitance-voltage (C-V) test was 7.3×1015 cm-3. The device with a gate width of 1 mm exhibits a maximum output power of 5.5 W at 8 GHz, which proves the semi-insulating property of the substrates indirectly.展开更多
In this work,we investigate the influence of defect concentration of the diamond substrates on the performance of hydrogen-terminated diamond field-effect transistors by Raman spectra,pulsed I–V characteristics analy...In this work,we investigate the influence of defect concentration of the diamond substrates on the performance of hydrogen-terminated diamond field-effect transistors by Raman spectra,pulsed I–V characteristics analysis,and radio frequency performances measurements.It is found that a sample with higher defect concentration shows larger drain-lag effect and lower large-signal output power density.Defects in the diamond act as traps in the carrier transport and have a considerable influence on the large-signal output power density of diamond field-effect transistors.This work should be helpful for further performance improvement of the microwave power diamond devices.展开更多
Downy mildew is a serious disease in cucumber production worldwide,which is caused by Pseudoperonospora cubensis(Berk.&Curt.)Rostov.Underlying the mechanism of cucumber response to downy mildew infection is import...Downy mildew is a serious disease in cucumber production worldwide,which is caused by Pseudoperonospora cubensis(Berk.&Curt.)Rostov.Underlying the mechanism of cucumber response to downy mildew infection is important for breeding improvement and production;however,the research remains largely elusive.A comparative proteomic approach was used to reveal the differential accumulation of the proteomes from leaves of cucumber(susceptible line and resistant line)that were inoculated with P.cubensis or not by two-dimensional electrophoresis and MALDI-TOF/TOF MS.A total of 76 protein spots were successfully identified with significant changes in abundance(>2-fold,P<0.05)in downy mildew infected or not leaves for the susceptible line and resistant line.By the functional annotation,these proteins were classified into 8 groups including photosynthesis(29%),energy and metabolism(29%),cell rescue and defense(17%),and protein biosynthesis,folding and degradation(13%),unclassified(7%),nucleotide metabolism(3%),signal transduction(1%)and cellular process(1%).Among the 17 differentially expressed proteins between the resistant and susceptible cucumber line,most of the protein spots were concentrated in cell rescue and defense(4)and energy and metabolism(4).Moreover,a schematic diagram containing majority of the metabolic pathways of cucumber leaves in response to downy mildew was proposed.This network revealed the positive effect of several functional components in cucumber seedlings’resistant to downy mildew such as accumulation of energy supply and resistance-related proteins,hastened protein metabolism and photorespiratory,inhibited photosynthesis,and triggered photosystem repair and programmed cell death.Taken together,these results have advanced a further understanding of the key metabolic pathways of cucumber resistance to downy mildew and pathogen control in the proteomic level.展开更多
2D material of graphene has inspired huge interest in fabricating of solid state gas sensors.In this work,epitaxial graphene,quasi-free-standing graphene,and CVD epitaxial graphene samples on SiC substrates are used t...2D material of graphene has inspired huge interest in fabricating of solid state gas sensors.In this work,epitaxial graphene,quasi-free-standing graphene,and CVD epitaxial graphene samples on SiC substrates are used to fabricate gas sensors.Defects are introduced into graphene using SF6 plasma treatment to improve the performance of the gas sensors.The epitaxial graphene shows high sensitivity to NO2 with response of 105.1%to 4 ppm NO2 and detection limit of 1 ppb.The higher sensitivity of epitaxial graphene compared to quasi-free-standing graphene,and CVD epitaxial graphene was found to be related to the different doping types of the samples.展开更多
Trap-induced current collapse has become one of the critical issues hindering the improvement of Ga Nbased microwave power devices. It is difficult to study the behavior of each trapping effect separately with the exp...Trap-induced current collapse has become one of the critical issues hindering the improvement of Ga Nbased microwave power devices. It is difficult to study the behavior of each trapping effect separately with the experimental measurement. Transient simulation is a useful technique for analyzing the mechanism of current collapse. In this paper, the coeffect of surface-and bulk-trapping behaviors on the performance of Al Ga N/Ga N HEMTs is investigated based on the two-dimensional(2 D) transient simulation. In addition, the mechanism of trapping effects is analyzed from the aspect of device physics. Two simulation models with different types of traps are used for comparison, and the simulated results reproduced the experimental measured data. It is found that the final steady-state current decreases when both the surface and bulk traps are taken into account in the model.However, contrary to the expectation, the total current collapse is dramatically reduced(e.g. from 18% to 4% for the 90 nm gate-length device). The results suggest that the surface-related current collapse of Ga N-based HEMTs may be mitigated in some degree due to the participation of bulk traps with short time constant. The work in this paper will be helpful for further optimization design of material and device structures.展开更多
Ultraviolet(UV) detectors with large photosensitive areas are more advantageous in low-level UV detection applications. In this Letter, high-performance 4 H-SiC p-i-n avalanche photodiodes(APDs) with large active area...Ultraviolet(UV) detectors with large photosensitive areas are more advantageous in low-level UV detection applications. In this Letter, high-performance 4 H-SiC p-i-n avalanche photodiodes(APDs) with large active area(800 μm diameter) are reported. With the optimized epitaxial structure and device fabrication process,a high multiplication gain of 1.4 × 10^6 is obtained for the devices at room temperature, and the dark current is as low as ~10 p A at low reverse voltages. In addition, record external quantum efficiency of 85.5% at 274 nm is achieved, which is the highest value for the reported Si C APDs. Furthermore, the rejection ratio of UV to visible light reaches about 10^4. The excellent performance of our devices indicates a tremendous improvement for largearea SiC APD-based UV detectors. Finally, the UV imaging performance of our fabricated 4 H-SiC p-i-n APDs is also demonstrated for system-level applications.展开更多
Silver sintering is receiving increasing attention due to its novel die-attach technique for high-temperature power electronics.Excellent thermal conductivity,high melting point/remelting temperature and low-temperatu...Silver sintering is receiving increasing attention due to its novel die-attach technique for high-temperature power electronics.Excellent thermal conductivity,high melting point/remelting temperature and low-temperature sintering behaviors of the silver sintered attachment meet the requirements of high-temperature applications for power devices,specifically SiC devices.The merits and demerits of the existing pressure-assisted sintering and pressure-less sintering techniques using nano-scale,micro-scale and micro-nano-scale hybrid silver sintered materials are separately presented.The emerging rapid sintering approaches,such as the electric-assisted approach,are briefly introduced and the technical outlook is provided.In addition,the study highlights the importance of creating a brief resource guide on using the correct sintering methods.展开更多
To the Editor:Acute kidney injury(AKI)is a common public health problem worldwide,which can adversely affect patients’quality of life and even lead to death.^([1])Academic hospitals play an important role in admittin...To the Editor:Acute kidney injury(AKI)is a common public health problem worldwide,which can adversely affect patients’quality of life and even lead to death.^([1])Academic hospitals play an important role in admitting and providing treatment for patients with AKI,but limited data exist regarding the characteristics of patients in county-level local hospitals.Our research group initiated a comprehensive survey as part of the International Society of Nephrology’s"0 by 25"project(eliminating all deaths related to untreated AKI by 2025)for investigating the disease burden of AKI and its associated risk factors and prognosis through 22 province-level regions of China in 2013.展开更多
文摘In this letter,high power density AlGaN/GaN high electron-mobility transistors(HEMTs)on a freestanding GaN substrate are reported.An asymmetricΓ-shaped 500-nm gate with a field plate of 650 nm is introduced to improve microwave power performance.The breakdown voltage(BV)is increased to more than 200 V for the fabricated device with gate-to-source and gate-to-drain distances of 1.08 and 2.92μm.A record continuous-wave power density of 11.2 W/mm@10 GHz is realized with a drain bias of 70 V.The maximum oscillation frequency(f_(max))and unity current gain cut-off frequency(f_(t))of the AlGaN/GaN HEMTs exceed 30 and 20 GHz,respectively.The results demonstrate the potential of AlGaN/GaN HEMTs on freestanding GaN substrates for microwave power applications.
基金supported by the National Natural Science Foundation of China under Grant U21A20503.
文摘This work demonstrates high-performance NiO/β-Ga_(2)O_(3) vertical heterojunction diodes(HJDs)with double-layer junc-tion termination extension(DL-JTE)consisting of two p-typed NiO layers with varied lengths.The bottom 60-nm p-NiO layer fully covers theβ-Ga_(2)O_(3) wafer,while the geometry of the upper 60-nm p-NiO layer is 10μm larger than the square anode elec-trode.Compared with a single-layer JTE,the electric field concentration is inhibited by double-layer JTE structure effectively,resulting in the breakdown voltage being improved from 2020 to 2830 V.Moreover,double p-typed NiO layers allow more holes into the Ga_(2)O_(3) drift layer to reduce drift resistance.The specific on-resistance is reduced from 1.93 to 1.34 mΩ·cm^(2).The device with DL-JTE shows a power figure-of-merit(PFOM)of 5.98 GW/cm^(2),which is 2.8 times larger than that of the conven-tional single-layer JTE structure.These results indicate that the double-layer JTE structure provides a viable way of fabricating high-performance Ga_(2)O_(3) HJDs.
基金supported by the National Natural Science Foundation of China(Nos.61674130,61604137)
文摘Ga_2O_3 metal–oxide–semiconductor field-effect transistors(MOSFETs) with high-breakdown characteristics were fabricated on a homoepitaxial n-typed β-Ga_2O_3 film, which was grown by metal organic chemical vapor deposition(MOCVD) on an Fedoped semi-insulating(010) Ga_2O_3 substrate. The structure consisted of a 400 nm unintentionally doped(UID) Ga_2O_3 buffer layer and an 80 nm Si-doped channel layer. A high k HfO_2 gate dielectric film formed by atomic layer deposition was employed to reduce the gate leakage. Moreover, a source-connected field plate was introduced to enhance the breakdown characteristics. The drain saturation current density of the fabricated device reached 101 mA/mm at V_(gs) of 3 V. The off-state current was as low as 7.1 ×10^(-11) A/mm, and the drain current I_(ON)/I_(OFF) ratio reached 10~9. The transistors exhibited three-terminal off-state breakdown voltages of 450 and 550 V, corresponding to gate-to-drain spacing of 4 and 8 μm, respectively.
基金supported by the National Natural Sci-ence Foundation of China under grant No. 50472068 and No. 50721002the National "863" High Technology Re-search and Development Program of China under grant No. 2006AA03A145 and No. 2007AA03Z405+1 种基金the Na-tional Basic Research Program of China under grant No.2009CB930503the Cultivation Fund of the Key Scientific and Technical Innovation Project, Ministry of Education of China under grant No. 707039
文摘Two-inch semi-insulating SiC bulk crystals with resistivity higher than 1×106 Ωcm were achieved by vanadium doping during sublimation. Secondary-ion-mass-spectrometry (SIMS) was employed to determine the concen-tration of impurities in the crystals, such as B, Al, V and N. These results indicated that the concentration of nitrogen and aluminum kept on decreasing and the concentration of B and V was almost constant during the whole growth. An inner crucible was used to control the exhausting of vanadium, which made the uniformity of the high resistivity (>1×106 Ωcm) in the wafer up to 80%. High-performance AlGaN/GaN high-electron-mobility-transistor (HEMT) materials and devices were grown and fabricated on semi-insulating 6H-SiC sub-strates. The two-dimensional electron gas (2DEG) mobility at room-temperature was 1795 cm2/V·s. The charge carrier concentration of the substrate determined by capacitance-voltage (C-V) test was 7.3×1015 cm-3. The device with a gate width of 1 mm exhibits a maximum output power of 5.5 W at 8 GHz, which proves the semi-insulating property of the substrates indirectly.
基金This work was supported by the National Natural Science Foundation of China(Grant No.51702296)Excellent Youth Foundation of Hebei Scientific Committee(Grant No.F2019516002).
文摘In this work,we investigate the influence of defect concentration of the diamond substrates on the performance of hydrogen-terminated diamond field-effect transistors by Raman spectra,pulsed I–V characteristics analysis,and radio frequency performances measurements.It is found that a sample with higher defect concentration shows larger drain-lag effect and lower large-signal output power density.Defects in the diamond act as traps in the carrier transport and have a considerable influence on the large-signal output power density of diamond field-effect transistors.This work should be helpful for further performance improvement of the microwave power diamond devices.
基金This work was supported by the Hebei Province Scientific and Technological Support Program(Grant No.16226308D-4)Hebei Vegetable Innovation Projects of Modern Agricultural Industry Technology System(Grant No.HBCT2018030209)Hebei Province High Education Science and Technology Research Project(Grant No.BJ2018002).
文摘Downy mildew is a serious disease in cucumber production worldwide,which is caused by Pseudoperonospora cubensis(Berk.&Curt.)Rostov.Underlying the mechanism of cucumber response to downy mildew infection is important for breeding improvement and production;however,the research remains largely elusive.A comparative proteomic approach was used to reveal the differential accumulation of the proteomes from leaves of cucumber(susceptible line and resistant line)that were inoculated with P.cubensis or not by two-dimensional electrophoresis and MALDI-TOF/TOF MS.A total of 76 protein spots were successfully identified with significant changes in abundance(>2-fold,P<0.05)in downy mildew infected or not leaves for the susceptible line and resistant line.By the functional annotation,these proteins were classified into 8 groups including photosynthesis(29%),energy and metabolism(29%),cell rescue and defense(17%),and protein biosynthesis,folding and degradation(13%),unclassified(7%),nucleotide metabolism(3%),signal transduction(1%)and cellular process(1%).Among the 17 differentially expressed proteins between the resistant and susceptible cucumber line,most of the protein spots were concentrated in cell rescue and defense(4)and energy and metabolism(4).Moreover,a schematic diagram containing majority of the metabolic pathways of cucumber leaves in response to downy mildew was proposed.This network revealed the positive effect of several functional components in cucumber seedlings’resistant to downy mildew such as accumulation of energy supply and resistance-related proteins,hastened protein metabolism and photorespiratory,inhibited photosynthesis,and triggered photosystem repair and programmed cell death.Taken together,these results have advanced a further understanding of the key metabolic pathways of cucumber resistance to downy mildew and pathogen control in the proteomic level.
基金supported by the National Natural Science Foundation of China (61674131 and 61306006)
文摘2D material of graphene has inspired huge interest in fabricating of solid state gas sensors.In this work,epitaxial graphene,quasi-free-standing graphene,and CVD epitaxial graphene samples on SiC substrates are used to fabricate gas sensors.Defects are introduced into graphene using SF6 plasma treatment to improve the performance of the gas sensors.The epitaxial graphene shows high sensitivity to NO2 with response of 105.1%to 4 ppm NO2 and detection limit of 1 ppb.The higher sensitivity of epitaxial graphene compared to quasi-free-standing graphene,and CVD epitaxial graphene was found to be related to the different doping types of the samples.
基金supported by the National Natural Science Foundation of China(Nos.61604137,61674130)
文摘Trap-induced current collapse has become one of the critical issues hindering the improvement of Ga Nbased microwave power devices. It is difficult to study the behavior of each trapping effect separately with the experimental measurement. Transient simulation is a useful technique for analyzing the mechanism of current collapse. In this paper, the coeffect of surface-and bulk-trapping behaviors on the performance of Al Ga N/Ga N HEMTs is investigated based on the two-dimensional(2 D) transient simulation. In addition, the mechanism of trapping effects is analyzed from the aspect of device physics. Two simulation models with different types of traps are used for comparison, and the simulated results reproduced the experimental measured data. It is found that the final steady-state current decreases when both the surface and bulk traps are taken into account in the model.However, contrary to the expectation, the total current collapse is dramatically reduced(e.g. from 18% to 4% for the 90 nm gate-length device). The results suggest that the surface-related current collapse of Ga N-based HEMTs may be mitigated in some degree due to the participation of bulk traps with short time constant. The work in this paper will be helpful for further optimization design of material and device structures.
基金supported by the National Natural Science Foundation of China(Nos.61604137 and 61674130)
文摘Ultraviolet(UV) detectors with large photosensitive areas are more advantageous in low-level UV detection applications. In this Letter, high-performance 4 H-SiC p-i-n avalanche photodiodes(APDs) with large active area(800 μm diameter) are reported. With the optimized epitaxial structure and device fabrication process,a high multiplication gain of 1.4 × 10^6 is obtained for the devices at room temperature, and the dark current is as low as ~10 p A at low reverse voltages. In addition, record external quantum efficiency of 85.5% at 274 nm is achieved, which is the highest value for the reported Si C APDs. Furthermore, the rejection ratio of UV to visible light reaches about 10^4. The excellent performance of our devices indicates a tremendous improvement for largearea SiC APD-based UV detectors. Finally, the UV imaging performance of our fabricated 4 H-SiC p-i-n APDs is also demonstrated for system-level applications.
基金Supported by the National Natural Science Foundation of China(51967005)Guangxi Natural Science Foundation(2018GXNSFAA294082)Director Fund Project of Guangxi Key Lab of Manufacturing System and Advanced Manufacturing Technology(19-050-44-006Z).
文摘Silver sintering is receiving increasing attention due to its novel die-attach technique for high-temperature power electronics.Excellent thermal conductivity,high melting point/remelting temperature and low-temperature sintering behaviors of the silver sintered attachment meet the requirements of high-temperature applications for power devices,specifically SiC devices.The merits and demerits of the existing pressure-assisted sintering and pressure-less sintering techniques using nano-scale,micro-scale and micro-nano-scale hybrid silver sintered materials are separately presented.The emerging rapid sintering approaches,such as the electric-assisted approach,are briefly introduced and the technical outlook is provided.In addition,the study highlights the importance of creating a brief resource guide on using the correct sintering methods.
基金supported by grants from the National Natural Science Foundation of China(Nos.91742205,81625004,and 81860129)the Beijing Young Scientist Program(No.BJJWZYJH01201910001006)the Peking University Clinical Scientist Program by the Fundamental Research Funds for the Central Universities.
文摘To the Editor:Acute kidney injury(AKI)is a common public health problem worldwide,which can adversely affect patients’quality of life and even lead to death.^([1])Academic hospitals play an important role in admitting and providing treatment for patients with AKI,but limited data exist regarding the characteristics of patients in county-level local hospitals.Our research group initiated a comprehensive survey as part of the International Society of Nephrology’s"0 by 25"project(eliminating all deaths related to untreated AKI by 2025)for investigating the disease burden of AKI and its associated risk factors and prognosis through 22 province-level regions of China in 2013.