A Si doped AlGaN/GaN HEMT structure with high Al content (x=43%) in the barrier layer is grown on sapphire substrate by RF-MBE.The structural and electrical properties of the heterostructure are investigated by the tr...A Si doped AlGaN/GaN HEMT structure with high Al content (x=43%) in the barrier layer is grown on sapphire substrate by RF-MBE.The structural and electrical properties of the heterostructure are investigated by the triple axis X-ray diffraction and Van der Pauw-Hall measurement,respectively.The observed prominent Bragg peaks of the GaN and AlGaN and the Hall results show that the structure is of high quality with smooth interface.The high 2DEG mobility in excess of 1260cm2/(V·s) is achieved with an electron density of 1.429×10 13cm -2 at 297K,corresponding to a sheet-density-mobility product of 1.8×10 16V -1·s -1.Devices based on the structure are fabricated and characterized.Better DC characteristics,maximum drain current of 1.0A/mm and extrinsic transconductance of 218mS/mm are obtained when compared with HEMTs fabricated using structures with lower Al mole fraction in the AlGaN barrier layer.The results suggest that the high Al content in the AlGaN barrier layer is promising in improving material electrical properties and device performance.展开更多
AIGaN/GaN HEMTs are investigated by numerical simulation from the self-consistent solution of Schr6dinger-Poisson-hydrodynamic （HD） systems. The influences of polarization charge and quantum effects are considered i...AIGaN/GaN HEMTs are investigated by numerical simulation from the self-consistent solution of Schr6dinger-Poisson-hydrodynamic （HD） systems. The influences of polarization charge and quantum effects are considered in this model. Then the two-dimensional conduction band and electron distribution, electron temperature characteristics, Id versus Vd and Id versus Vg, transfer characteristics and transconductance curves are obtained. Corresponding analysis and discussion based on the simulation results are subsequently given.展开更多
The shear-induced migration of neutrally-buoyant non-colloidal circular particles in a two-dimensional circular Couette flow is investigated numerically with a distributed Lagrange multiplier based fictitious domain m...The shear-induced migration of neutrally-buoyant non-colloidal circular particles in a two-dimensional circular Couette flow is investigated numerically with a distributed Lagrange multiplier based fictitious domain method.The effects of inertia and volume fraction on the particle migration are examined.The results indicate that inertia has a negative effect on the particle migration.In consistence with the experimental observations,the rapid migration of particles near the inner cylinder at the early stage is observed in the simulation,which is believed to be related to the chain-like clustering of particles.The migration of circular particles in a plane Poiseuille flow is also examined in order to further confirm the effect of such clustering on the particle migration at early stage.There is tendency for the particles in the vicinity of outer cylinder in the Couette device to pack into concentric rings at late stage in case of high particle concentration.展开更多
Since silicon is limited by its physical properties,it is challenging and important to find candidate materials for high performance electronic devices.Two-dimensional（2D）semiconductor materials have attracted drama...Since silicon is limited by its physical properties,it is challenging and important to find candidate materials for high performance electronic devices.Two-dimensional（2D）semiconductor materials have attracted dramatically increasing interest due to their unique physical,展开更多
Two-dimensional(2D) molybdenum disulfide(MoS2 ) holds significant promise as an energy storage material, whereas the exfoliation of MoS2 into few-layer from natural molybdenites remains a challenge. An efficient elect...Two-dimensional(2D) molybdenum disulfide(MoS2 ) holds significant promise as an energy storage material, whereas the exfoliation of MoS2 into few-layer from natural molybdenites remains a challenge. An efficient electrochemical strategy was proposed for the preparation of fewlayer MoS2 through cationic intercalation. Few-layer MoS2 without the impurity phases was obtained with high yield through Raman mapping analysis, and the intermediate(TBA+)xMoS2x- was captured by in-situ Raman. Note that the charge transport kinetics of the exfoliated few-layer MoS2 was further enhanced by the introduction of graphene, which could efficiently enhance the Na+diffusion mobility, alleviate the volume change of MoS2 and stabilize the reaction products. Commendably, the exfoliated MoS2 /graphene hybrid shows a reversible specific capacity of 642.8 mA h g-1 at 0.1 A g-1, superior rate performance(447.8 and 361.9 mA h g-1 at 1 and 5 A g-1, respectively) and remarkable long-cycle stability with 328.7 mA h g-1 at 1 A g-1 after 1000 cycles for sodium-ion batteries(SIBs). Therefore, this efficient electrochemical exfoliation method can be driven to prepare other few-layer 2D materials for SIBs.展开更多
We have calculated the longitudinal acoustic phonon limited electron mobility of 14 twvo-dimensional semiconductors with composition of MX2, where M （= Mo, W, Sn, Hf, Zr and Pt） is the transition metal, and X is S, ...We have calculated the longitudinal acoustic phonon limited electron mobility of 14 twvo-dimensional semiconductors with composition of MX2, where M （= Mo, W, Sn, Hf, Zr and Pt） is the transition metal, and X is S, Se and Te. We treated the scattering matrix by the deformation potential approximation. We found that out of 14 compounds, MoTe2, HfSe2 and ZrSe2 are promising regarding to their possible high mobility and finite band gap. The phonon limited mobility can be above 2,500 cm^2·V^-1·s^-1 at room temperature.展开更多
Boron nanosheets possess unique photoelectric properties, including photosensitivity, photoresponse,and optical nonlinearity. In this article, we show the interaction between light and boron nanosheets in which concen...Boron nanosheets possess unique photoelectric properties, including photosensitivity, photoresponse,and optical nonlinearity. In this article, we show the interaction between light and boron nanosheets in which concentric rings formed in the far field, which attributed to the strong Kerr nonlinearity of boron nanosheets. Furthermore, the distortion, regulation and relationship between the Kerr nonlinearity and effective mass or carrier mobility of the diffraction rings of boron nanosheets have been investigated.Our work shows that the spatial self-phase modulation effect of boron nanosheets is indeed caused by nonlocal electronic coherence. In addition, we have implemented all-light modulation and all-light logic gates based on the prepared boron nanosheets. We believe that our results will provide a powerful demonstration of nonlinear photonic devices based on boron nanosheets and a reference for photonic devices based on two-dimensional materials.展开更多
文摘A Si doped AlGaN/GaN HEMT structure with high Al content (x=43%) in the barrier layer is grown on sapphire substrate by RF-MBE.The structural and electrical properties of the heterostructure are investigated by the triple axis X-ray diffraction and Van der Pauw-Hall measurement,respectively.The observed prominent Bragg peaks of the GaN and AlGaN and the Hall results show that the structure is of high quality with smooth interface.The high 2DEG mobility in excess of 1260cm2/(V·s) is achieved with an electron density of 1.429×10 13cm -2 at 297K,corresponding to a sheet-density-mobility product of 1.8×10 16V -1·s -1.Devices based on the structure are fabricated and characterized.Better DC characteristics,maximum drain current of 1.0A/mm and extrinsic transconductance of 218mS/mm are obtained when compared with HEMTs fabricated using structures with lower Al mole fraction in the AlGaN barrier layer.The results suggest that the high Al content in the AlGaN barrier layer is promising in improving material electrical properties and device performance.
文摘AIGaN/GaN HEMTs are investigated by numerical simulation from the self-consistent solution of Schr6dinger-Poisson-hydrodynamic （HD） systems. The influences of polarization charge and quantum effects are considered in this model. Then the two-dimensional conduction band and electron distribution, electron temperature characteristics, Id versus Vd and Id versus Vg, transfer characteristics and transconductance curves are obtained. Corresponding analysis and discussion based on the simulation results are subsequently given.
基金Supported by the National Natural Science Foundation of China （No. 10472104）.
文摘The shear-induced migration of neutrally-buoyant non-colloidal circular particles in a two-dimensional circular Couette flow is investigated numerically with a distributed Lagrange multiplier based fictitious domain method.The effects of inertia and volume fraction on the particle migration are examined.The results indicate that inertia has a negative effect on the particle migration.In consistence with the experimental observations,the rapid migration of particles near the inner cylinder at the early stage is observed in the simulation,which is believed to be related to the chain-like clustering of particles.The migration of circular particles in a plane Poiseuille flow is also examined in order to further confirm the effect of such clustering on the particle migration at early stage.There is tendency for the particles in the vicinity of outer cylinder in the Couette device to pack into concentric rings at late stage in case of high particle concentration.
基金supported by the National Key Basic Research Program of China(Grant No.2013CB632900)National Natural Science Foundation of China(Grant Nos.61390502&21373068)+1 种基金the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(Grant No.51521003)Self-Planned Task of State Key Laboratory of Robotics and System(HIT)(Grant No.SKLRS201607B)
文摘Since silicon is limited by its physical properties,it is challenging and important to find candidate materials for high performance electronic devices.Two-dimensional（2D）semiconductor materials have attracted dramatically increasing interest due to their unique physical,
基金supported by the National Natural Science Foundation of China (51622406, 21673298, and 21473258)the National Key Research and Development Program of China (2017YFB0102000 and 2018YFB0104200)the Project of Innovation Driven Plan in Central South University (2017CX004 and 2018CX005)。
文摘Two-dimensional(2D) molybdenum disulfide(MoS2 ) holds significant promise as an energy storage material, whereas the exfoliation of MoS2 into few-layer from natural molybdenites remains a challenge. An efficient electrochemical strategy was proposed for the preparation of fewlayer MoS2 through cationic intercalation. Few-layer MoS2 without the impurity phases was obtained with high yield through Raman mapping analysis, and the intermediate(TBA+)xMoS2x- was captured by in-situ Raman. Note that the charge transport kinetics of the exfoliated few-layer MoS2 was further enhanced by the introduction of graphene, which could efficiently enhance the Na+diffusion mobility, alleviate the volume change of MoS2 and stabilize the reaction products. Commendably, the exfoliated MoS2 /graphene hybrid shows a reversible specific capacity of 642.8 mA h g-1 at 0.1 A g-1, superior rate performance(447.8 and 361.9 mA h g-1 at 1 and 5 A g-1, respectively) and remarkable long-cycle stability with 328.7 mA h g-1 at 1 A g-1 after 1000 cycles for sodium-ion batteries(SIBs). Therefore, this efficient electrochemical exfoliation method can be driven to prepare other few-layer 2D materials for SIBs.
文摘We have calculated the longitudinal acoustic phonon limited electron mobility of 14 twvo-dimensional semiconductors with composition of MX2, where M （= Mo, W, Sn, Hf, Zr and Pt） is the transition metal, and X is S, Se and Te. We treated the scattering matrix by the deformation potential approximation. We found that out of 14 compounds, MoTe2, HfSe2 and ZrSe2 are promising regarding to their possible high mobility and finite band gap. The phonon limited mobility can be above 2,500 cm^2·V^-1·s^-1 at room temperature.
基金partially supported by the National Natural Science Foundation of China (61875133 and 11874269)the Science and Technology Project of Shenzhen (JCYJ20190808143801672, JCYJ20190808150803580, JCYJ20180305125036005, JCYJ20180 305124842330, and JCYJ20180305125443569)the Guangdong Natural Science Foundation (2018A030313198)。
文摘Boron nanosheets possess unique photoelectric properties, including photosensitivity, photoresponse,and optical nonlinearity. In this article, we show the interaction between light and boron nanosheets in which concentric rings formed in the far field, which attributed to the strong Kerr nonlinearity of boron nanosheets. Furthermore, the distortion, regulation and relationship between the Kerr nonlinearity and effective mass or carrier mobility of the diffraction rings of boron nanosheets have been investigated.Our work shows that the spatial self-phase modulation effect of boron nanosheets is indeed caused by nonlocal electronic coherence. In addition, we have implemented all-light modulation and all-light logic gates based on the prepared boron nanosheets. We believe that our results will provide a powerful demonstration of nonlinear photonic devices based on boron nanosheets and a reference for photonic devices based on two-dimensional materials.
