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
In this paper we study a negatively charged exciton （NCE）, which is trapped by a two-dimensional （2D） parabolic potential. By using matrix diagonalization techniques, the correlation energies of the low-lying stat...In this paper we study a negatively charged exciton （NCE）, which is trapped by a two-dimensional （2D） parabolic potential. By using matrix diagonalization techniques, the correlation energies of the low-lying states with L=0, 1, and 2 are calculated as a function of confinement strength. We find that the size effects of different states are different. This phenomenon can be explained as a hidden symmetry, which is originated purely from symmetry. Based on symmetry, the features of the low-lying states are discussed in the influence of the 2D parabolic potential well. It is found that the confinement may cause accidental degeneracies between levels with different low-excited states. It is shown that the effect of quantum confinement on the binding energy of the heavy hole is stronger than that of a light hole.展开更多
Though several theoretical models have been proposed to design electronic flat-bands, the definite experimental realization in two-dimensional atomic crystal is still lacking. Here we propose a novel and realistic fla...Though several theoretical models have been proposed to design electronic flat-bands, the definite experimental realization in two-dimensional atomic crystal is still lacking. Here we propose a novel and realistic flat-band model based on threefold degenerate p-orbitals in two-dimensional ionic materials. Our theoretical analysis and first-principles calculations show that the proposed flat-band can be realized in 1 T layered materials of alkali-metal chalogenides and metal-carbon group compounds. Some of the former are theoretically predicted to be stable as layered materials(e.g., K2 S), and some of the latter have been experimentally fabricated in previous works(e.g., Gd2 CCl2). More interestingly, the flat-band is partially filled in the heterostructure of a K2 S monolayer and graphene layers. The spin polarized nearly flatband can be realized in the ferromagnetic state of a Gd2 CCl2 monolayer, which has been fabricated in experiments. Our theoretical model together with the material predictions provide a realistic platform for the study of flat-bands and related exotic quantum phases.展开更多
This work presents a self-consistent two-dimensional(2-D) simulation method with unified physical models for different operation regimes of charge trapping memory. The simulation carefully takes into consideration the...This work presents a self-consistent two-dimensional(2-D) simulation method with unified physical models for different operation regimes of charge trapping memory. The simulation carefully takes into consideration the tunneling process, charge trapping/de-trapping mechanisms, and 2-D drift-diffusion transport within the storage layer. A string of three memory cells has been simulated and evaluated for different gate stack compositions and temperatures. The simulator is able to describe the charge transport behavior along bitline and tunneling directions under different operations. Good agreement has been made with experimental data,which hence validates the implemented physical models and altogether confirms the simulation as a valuable tool for evaluating the characteristics of three-dimensional NAND flash memory.展开更多
Confined low dimensional charges with high density such as two-dimensional electron gas(2 DEG)at interfaces and charged domain walls in ferroelectrics show great potential to serve as functional elements in future nan...Confined low dimensional charges with high density such as two-dimensional electron gas(2 DEG)at interfaces and charged domain walls in ferroelectrics show great potential to serve as functional elements in future nanoelectronics.However,stabilization and control of low dimensional charges is challenging,as they are usually subject to enormous depolarization fields.Here,we demonstrate a method to fabricate tunable charged interfaces with~77°,86°and 94°head-to-head polarization configurations in multiferroic Bi Fe O_(3) thin films by grain boundary engineering.The adjacent grains are cohesively bonded and the boundary is about 1 nm in width and devoid of any amorphous region.Remarkably,the polarization remains almost unchanged near the grain boundaries,indicating the polarization charges are well compensated,i.e.,there should be two-dimensional charge gas confined at grain boundaries.Adjusting the tilt angle of the grain boundaries enables tuning the angle of polarization configurations from 71°to 109°,which in turn allows the control of charge density at the grain boundaries.This general and feasible method opens new doors for the application of charged interfaces in next generation nanoelectronics.展开更多
Efficient charge separation and rapid interfacial reaction kinetics are crucial factors that determine the efficiency of photocatalytic hydrogen evolution.Herein,a fascinating 2D heterojunction photocatalyst with supe...Efficient charge separation and rapid interfacial reaction kinetics are crucial factors that determine the efficiency of photocatalytic hydrogen evolution.Herein,a fascinating 2D heterojunction photocatalyst with superior photocatalytic hydrogen evolution performance–holey C_(3)N_(4)nanosheets nested with TiO_(2)nanocrystals(denoted as HCN/TiO_(2))–is designed and fabricated via an in situ exfoliation and conversion strategy.The HCN/TiO_(2)is found to exhibit an ultrathin 2D heteroarchitecture with intimate interfacial contact,highly porous structures and ultrasmall TiO_(2)nanocrystals,leading to drastically improved charge carrier separation,maximized active sites and the promotion of mass transport for photocatalysis.Consequently,the HCN/TiO_(2)delivers an impressive hydrogen production rate of 282.3 lmol h^(-1)per10 mg under AM 1.5 illumination and an apparent quantum efficiency of 13.4%at a wavelength of 420 nm due to the synergetic enhancement of surface reactions and charge separation.The present work provides a promising strategy for developing high-performance 2D heterojunctions for clean energy applications.展开更多
Electronic structure and transport properties of highly defective two-dimensional （2D） sp2 graphene are investigated theoretically. Classical molecular dynamics are used to generate large graphene planes containing ...Electronic structure and transport properties of highly defective two-dimensional （2D） sp2 graphene are investigated theoretically. Classical molecular dynamics are used to generate large graphene planes containing a considerable amount of defects. Then, a tight-binding Hamiltonian validated by ab initio calculations is constructed in order to compute quantum transport within a real-space order-N Kubo-Greenwood approach. In contrast to pristine graphene, the highly defective sp2 carbon sheets exhibit a high density of states at the charge neutrality point raising challenging questions concerning the electronic transport of associated charge carriers. The analysis of the electronic wavepacket dynamics actually reveals extremely strong multiple scattering effects giving rise to mean free paths as low as 1 nm and localization phenomena. Consequently, highly defective graphene is envisioned as a remarkable prototype of 2D Anderson insulating materials.展开更多
In this work,we theoretically study hard-core bosons on a two-dimensional square optical superlattice at T = 0.First of all,we present the mean field phase diagram of this model in terms of the chemical potential μ a...In this work,we theoretically study hard-core bosons on a two-dimensional square optical superlattice at T = 0.First of all,we present the mean field phase diagram of this model in terms of the chemical potential μ and the alternating potential strength △.Besides a superfluid(SF) phase at △ = 0 and a charge density wave(CDW)phase in the large △ at half filling,we demonstrate that a supersolid(SS) phase emerges in the moderate △.Then,we focus on the μ = 0,e.g.,half filling case,using large-S semi-classical spin-wave approximation to study the SS to CDW quantum phase transition.In particular,we calculate the ground-state energy and the superfluid density at the level of1/S correction.We then compare the spin-wave results with the large scale quantum Monte Carlo(QMC) simulations using the cluster stochastic series expansion(CSSE) algorithm,and find that while the spin wave method is intuitive with clear physical pictures,the quantum critical point is quite different from that of numerical results which is believed to be accurate.We suggest that as simple as it is,this model still exhibits strong quantum fluctuations near the quantum critical point beyond the power of semiclassical spin-wave approach.展开更多
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 National Natural Science Foundation of China under Grant No.10775035
文摘In this paper we study a negatively charged exciton （NCE）, which is trapped by a two-dimensional （2D） parabolic potential. By using matrix diagonalization techniques, the correlation energies of the low-lying states with L=0, 1, and 2 are calculated as a function of confinement strength. We find that the size effects of different states are different. This phenomenon can be explained as a hidden symmetry, which is originated purely from symmetry. Based on symmetry, the features of the low-lying states are discussed in the influence of the 2D parabolic potential well. It is found that the confinement may cause accidental degeneracies between levels with different low-excited states. It is shown that the effect of quantum confinement on the binding energy of the heavy hole is stronger than that of a light hole.
基金supported by the National Basic Research Program of China(2015CB921102 and 2019YFA0308403)the National Natural Science Foundation of China(11674028 and11822407)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(XDB28000000)China Postdoctoral Science Foundation(2020M670011)。
文摘Though several theoretical models have been proposed to design electronic flat-bands, the definite experimental realization in two-dimensional atomic crystal is still lacking. Here we propose a novel and realistic flat-band model based on threefold degenerate p-orbitals in two-dimensional ionic materials. Our theoretical analysis and first-principles calculations show that the proposed flat-band can be realized in 1 T layered materials of alkali-metal chalogenides and metal-carbon group compounds. Some of the former are theoretically predicted to be stable as layered materials(e.g., K2 S), and some of the latter have been experimentally fabricated in previous works(e.g., Gd2 CCl2). More interestingly, the flat-band is partially filled in the heterostructure of a K2 S monolayer and graphene layers. The spin polarized nearly flatband can be realized in the ferromagnetic state of a Gd2 CCl2 monolayer, which has been fabricated in experiments. Our theoretical model together with the material predictions provide a realistic platform for the study of flat-bands and related exotic quantum phases.
基金supported by National Natural Science Foundation of China (Grant No. 91230107)National Basic Research Program of China (973) (Grant No. 2013CBA01604)National High Technology Research and Development Program of China (863) (Grant No. 2015AA016501)
文摘This work presents a self-consistent two-dimensional(2-D) simulation method with unified physical models for different operation regimes of charge trapping memory. The simulation carefully takes into consideration the tunneling process, charge trapping/de-trapping mechanisms, and 2-D drift-diffusion transport within the storage layer. A string of three memory cells has been simulated and evaluated for different gate stack compositions and temperatures. The simulator is able to describe the charge transport behavior along bitline and tunneling directions under different operations. Good agreement has been made with experimental data,which hence validates the implemented physical models and altogether confirms the simulation as a valuable tool for evaluating the characteristics of three-dimensional NAND flash memory.
基金supported by the National Basic Research Program of China(2016YFA0300804)the National Natural Science Foundation of China(51672007 and 11974023)+6 种基金Key Area R&D Program of Guangdong Province(2018B010109009)the Key R&D Program of Guangdong Province(2018B030327001)National Equipment Program of China(ZDYZ2015-1)the‘‘2011 Program”Peking-Tsinghua-IOP Collaborative Innovation Centre for Quantum Mattersupported by the National Basic Research Program of China(2016YFA0301004)the National Natural Science Foundation of China(51872155,52025024)the Beijing Advanced Innovation Center for Future Chip(ICFC)。
文摘Confined low dimensional charges with high density such as two-dimensional electron gas(2 DEG)at interfaces and charged domain walls in ferroelectrics show great potential to serve as functional elements in future nanoelectronics.However,stabilization and control of low dimensional charges is challenging,as they are usually subject to enormous depolarization fields.Here,we demonstrate a method to fabricate tunable charged interfaces with~77°,86°and 94°head-to-head polarization configurations in multiferroic Bi Fe O_(3) thin films by grain boundary engineering.The adjacent grains are cohesively bonded and the boundary is about 1 nm in width and devoid of any amorphous region.Remarkably,the polarization remains almost unchanged near the grain boundaries,indicating the polarization charges are well compensated,i.e.,there should be two-dimensional charge gas confined at grain boundaries.Adjusting the tilt angle of the grain boundaries enables tuning the angle of polarization configurations from 71°to 109°,which in turn allows the control of charge density at the grain boundaries.This general and feasible method opens new doors for the application of charged interfaces in next generation nanoelectronics.
基金the National Key R&D Program of China(2018YFE0201704 and 2018YFE0201701)the National Natural Science Foundation of China(21673256,21533011,2163100,and 21603036)Shanghai Rising-Star Program.
文摘Efficient charge separation and rapid interfacial reaction kinetics are crucial factors that determine the efficiency of photocatalytic hydrogen evolution.Herein,a fascinating 2D heterojunction photocatalyst with superior photocatalytic hydrogen evolution performance–holey C_(3)N_(4)nanosheets nested with TiO_(2)nanocrystals(denoted as HCN/TiO_(2))–is designed and fabricated via an in situ exfoliation and conversion strategy.The HCN/TiO_(2)is found to exhibit an ultrathin 2D heteroarchitecture with intimate interfacial contact,highly porous structures and ultrasmall TiO_(2)nanocrystals,leading to drastically improved charge carrier separation,maximized active sites and the promotion of mass transport for photocatalysis.Consequently,the HCN/TiO_(2)delivers an impressive hydrogen production rate of 282.3 lmol h^(-1)per10 mg under AM 1.5 illumination and an apparent quantum efficiency of 13.4%at a wavelength of 420 nm due to the synergetic enhancement of surface reactions and charge separation.The present work provides a promising strategy for developing high-performance 2D heterojunctions for clean energy applications.
文摘Electronic structure and transport properties of highly defective two-dimensional （2D） sp2 graphene are investigated theoretically. Classical molecular dynamics are used to generate large graphene planes containing a considerable amount of defects. Then, a tight-binding Hamiltonian validated by ab initio calculations is constructed in order to compute quantum transport within a real-space order-N Kubo-Greenwood approach. In contrast to pristine graphene, the highly defective sp2 carbon sheets exhibit a high density of states at the charge neutrality point raising challenging questions concerning the electronic transport of associated charge carriers. The analysis of the electronic wavepacket dynamics actually reveals extremely strong multiple scattering effects giving rise to mean free paths as low as 1 nm and localization phenomena. Consequently, highly defective graphene is envisioned as a remarkable prototype of 2D Anderson insulating materials.
基金Supported by the National Natural Science Foundation of China under Grant Nos.10904096,10604024,11474025the Natural Science Foundation of Beijing under Grant No.1092009
文摘In this work,we theoretically study hard-core bosons on a two-dimensional square optical superlattice at T = 0.First of all,we present the mean field phase diagram of this model in terms of the chemical potential μ and the alternating potential strength △.Besides a superfluid(SF) phase at △ = 0 and a charge density wave(CDW)phase in the large △ at half filling,we demonstrate that a supersolid(SS) phase emerges in the moderate △.Then,we focus on the μ = 0,e.g.,half filling case,using large-S semi-classical spin-wave approximation to study the SS to CDW quantum phase transition.In particular,we calculate the ground-state energy and the superfluid density at the level of1/S correction.We then compare the spin-wave results with the large scale quantum Monte Carlo(QMC) simulations using the cluster stochastic series expansion(CSSE) algorithm,and find that while the spin wave method is intuitive with clear physical pictures,the quantum critical point is quite different from that of numerical results which is believed to be accurate.We suggest that as simple as it is,this model still exhibits strong quantum fluctuations near the quantum critical point beyond the power of semiclassical spin-wave approach.
