作为常见的高迁移率直接带隙半导体,砷化镓(gallium arsenide,GaAs)的光电响应性质一直是学界研究的焦点.针对特殊结构半导体器件的光电响应方式理论上研究一般采用宏观有限元方法结合半经典理论的模拟.随着器件尺寸的小型化,微观结构...作为常见的高迁移率直接带隙半导体,砷化镓(gallium arsenide,GaAs)的光电响应性质一直是学界研究的焦点.针对特殊结构半导体器件的光电响应方式理论上研究一般采用宏观有限元方法结合半经典理论的模拟.随着器件尺寸的小型化,微观结构的重要性更加凸显.通过非平衡态格林函数结合密度泛函理论方法(non-equilibrium Green’s function method with density functional theory,NEDF-DFT)首次在原子尺度下计算了砷化镓纳米结在化学掺杂和栅极下的光响应,定性分析了材料掺杂浓度对光响应的影响.本工作对于半导体器件光电性质的模拟分析方法的拓展和器件性能的定性理解具有比较重要的意义.展开更多
We investigate the electronic and transport properties of one-dimensional armchair phosphorene nanoribbons(APNRs) containing atomic vacancies with different distributions and concentrations using ab initio density fun...We investigate the electronic and transport properties of one-dimensional armchair phosphorene nanoribbons(APNRs) containing atomic vacancies with different distributions and concentrations using ab initio density functional calculations. It is found that the atomic vacancies are easier to form and detain at the edge region rather than a random distribution through analyzing formation energy and diffusion barrier. The highly local defect states are generated at the vicinity of the Fermi level, and emerge a deep-to-shallow transformation as the width increases after introducing vacancies in APNRs.Moreover, the electrical transport of APNRs with vacancies is enhanced compared to that of the perfect counterparts. Our results provide a theoretical guidance for the further research and applications of PNRs through defect engineering.展开更多
The electrical characteristics of a double-gate armchair silicene nanoribbon field-effect-transistor （DG ASiNR FET） are thoroughly investigated by using a ballistic quantum transport model based on non-equilibrium G...The electrical characteristics of a double-gate armchair silicene nanoribbon field-effect-transistor （DG ASiNR FET） are thoroughly investigated by using a ballistic quantum transport model based on non-equilibrium Green＇s function （NEGF） approach self-consistently coupled with a three-dimensional （3D） Poisson equation. We evaluate the influence of variation in uniaxial tensile strain, ribbon temperature and oxide thickness on the on-off current ratio, subthreshold swing, transconductance and the delay time of a 12-nm-length ultranarrow ASiNR FET. A novel two-parameter strain mag- nitude and temperature-dependent model is presented for designing an optimized device possessing balanced amelioration of all the electrical parameters. We demonstrate that employing HfO2 as the gate insulator can be a favorable choice and simultaneous use of it with proper combination of temperature and strain magnitude can achieve better device performance. Furthermore, a general model power （GMP） is derived which explicitly provides the electron effective mass as a function of the bandgap of a hydrogen passivated ASiNR under strain.展开更多
A theoretical study of resonant tunneling is carried out for an inverse parabolic double-barrier structure subjected to an external electric field. Tunneling transmission coefficient and density of states are analyzed...A theoretical study of resonant tunneling is carried out for an inverse parabolic double-barrier structure subjected to an external electric field. Tunneling transmission coefficient and density of states are analyzed by using the non-equilibrium Green＇s function approach based on the finite difference method. It is found that the resonant peak of the transmission coefficient, being unity for a symmetrical case, reduces under the applied electric field and depends strongly on the variation of the structure parameters.展开更多
Self assembled quantum dots have shown a great promise as a leading candidate for infrared detection at room temperature. In this paper, a theoretical model of the absorption coefficient of quantum dot devices is pres...Self assembled quantum dots have shown a great promise as a leading candidate for infrared detection at room temperature. In this paper, a theoretical model of the absorption coefficient of quantum dot devices is presented. Both of bound to bound absorption and bound to continuum absorption are taken into consideration in this model. This model is based on the effective mass theory and the Non Equilibrium Greens Function (NEGF) formalism. NEGF formalism is used to calculate the bound to continuum absorption coefficient. The results of the model have been compared with a published experimental work and a good agreement is obtained. Based on the presented model, the bound to bound absorption coefficient component is compared to the bound to continuum absorption coefficient component. In addition, the effects of the dot dimensions and electron filling on the bound to continuum absorption coefficient are also investigated. In general, increasing the dot filling increases the absorption and decreasing the dots dimensions will increase the absorption and move the absorption peak towards longer wavelengths.展开更多
The conductance stabilities of carbon atomic chains （CACs） with different lengths are investigated by performing the- oretical calculations using the nonequilibrium Green＇s function method combined with density fun...The conductance stabilities of carbon atomic chains （CACs） with different lengths are investigated by performing the- oretical calculations using the nonequilibrium Green＇s function method combined with density functional theory. Regular even-odd conductance oscillation is observed as a function of the wire length. This oscillation is influenced delicately by changes in the end carbon or sulfur atoms as well as variations in coupling strength between the chain and leads. The lowest unoccupied molecular orbital in odd-numbered chains is the main transmission channel, whereas the conductance remains relatively small for even-numbered chains and a significant drift in the highest occupied molecular orbital resonance to- ward higher energies is observed as the number of carbon atoms increases. The amplitude of the conductance oscillation is predicted to be relatively stable based on a thiol joint between the chain and leads. Results show that the current-voltage evolution of CACs can be affected by the chain length. The differential and second derivatives of the conductance are also provided.展开更多
Lead nanowire occupies a very important position in an electronic device. In this study, a genetic algorithm（GA）method has been used to simulate the Pb nanowire. The result shows that Pb nanowires are a multishell c...Lead nanowire occupies a very important position in an electronic device. In this study, a genetic algorithm（GA）method has been used to simulate the Pb nanowire. The result shows that Pb nanowires are a multishell cylinder. Each shell consists of atomic rows wound up helically side by side. The quantum electron transport properties of these structures are calculated based on the non-equilibrium Green function（NEGF） combined with the density functional theory（DFT）,which indicate that electronic transport ability increases gradually with the atomic number increase. In addition, the thickest nanowire shows excellent electron transport performance. It possesses great transmission at the Fermi level due to the strongest delocalization of the electronic state. The results provide valuable information on the relationship between the transport properties of nanowires and their diameter.展开更多
Impacts of effective oxide thickness on a symmetric double-gate MOSFET with 9-nm gate length are studied, using full quantum simulation. The simulations are based on a self-consistent solution of the two-dimensional ...Impacts of effective oxide thickness on a symmetric double-gate MOSFET with 9-nm gate length are studied, using full quantum simulation. The simulations are based on a self-consistent solution of the two-dimensional （2D） Poisson equation and the Schr6dinger equation within the non-equilibrium Green＇s function formalism. Oxide thickness and gate dielectric are investigated in terms of drain current, on-off current ratio, off current, sub-threshold swing, drain induced barrier lowering, transconductance, drain conductance, and voltage. Simulation results illustrate that we can improve the device performance by proper selection of the effective oxide thickness.展开更多
We adopt a self-consistent real space Kerker method to prevent the divergence from charge sloshing in the simulating transistors with realistic discrete dopants in the source and drain regions. The method achieves eff...We adopt a self-consistent real space Kerker method to prevent the divergence from charge sloshing in the simulating transistors with realistic discrete dopants in the source and drain regions. The method achieves efficient convergence by avoiding unrealistic long range charge sloshing but keeping effects from short range charge sloshing. Numerical results show that discrete dopants in the source and drain regions could have a bigger influence on the electrical variability than the usual continuous doping without considering charge sloshing. Few discrete dopants and the narrow geometry create a situation with short range Coulomb screening and oscillations of charge density in real space. The dopants induced quasilocalized defect modes in the source region experience short range oscillations in order to reach the drain end of the device.The charging of the defect modes and the oscillations of the charge density are identified by the simulation of the electron density.展开更多
文摘作为常见的高迁移率直接带隙半导体,砷化镓(gallium arsenide,GaAs)的光电响应性质一直是学界研究的焦点.针对特殊结构半导体器件的光电响应方式理论上研究一般采用宏观有限元方法结合半经典理论的模拟.随着器件尺寸的小型化,微观结构的重要性更加凸显.通过非平衡态格林函数结合密度泛函理论方法(non-equilibrium Green’s function method with density functional theory,NEDF-DFT)首次在原子尺度下计算了砷化镓纳米结在化学掺杂和栅极下的光响应,定性分析了材料掺杂浓度对光响应的影响.本工作对于半导体器件光电性质的模拟分析方法的拓展和器件性能的定性理解具有比较重要的意义.
基金National Natural Science Foundation of China under National Outstanding Young Scientist Award (60788402)National Science Foundation of China (60976067)Fundamental Research Funds for the Central Universities (3101033,1101001,3104009)
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11574080 and 91833302)。
文摘We investigate the electronic and transport properties of one-dimensional armchair phosphorene nanoribbons(APNRs) containing atomic vacancies with different distributions and concentrations using ab initio density functional calculations. It is found that the atomic vacancies are easier to form and detain at the edge region rather than a random distribution through analyzing formation energy and diffusion barrier. The highly local defect states are generated at the vicinity of the Fermi level, and emerge a deep-to-shallow transformation as the width increases after introducing vacancies in APNRs.Moreover, the electrical transport of APNRs with vacancies is enhanced compared to that of the perfect counterparts. Our results provide a theoretical guidance for the further research and applications of PNRs through defect engineering.
文摘The electrical characteristics of a double-gate armchair silicene nanoribbon field-effect-transistor （DG ASiNR FET） are thoroughly investigated by using a ballistic quantum transport model based on non-equilibrium Green＇s function （NEGF） approach self-consistently coupled with a three-dimensional （3D） Poisson equation. We evaluate the influence of variation in uniaxial tensile strain, ribbon temperature and oxide thickness on the on-off current ratio, subthreshold swing, transconductance and the delay time of a 12-nm-length ultranarrow ASiNR FET. A novel two-parameter strain mag- nitude and temperature-dependent model is presented for designing an optimized device possessing balanced amelioration of all the electrical parameters. We demonstrate that employing HfO2 as the gate insulator can be a favorable choice and simultaneous use of it with proper combination of temperature and strain magnitude can achieve better device performance. Furthermore, a general model power （GMP） is derived which explicitly provides the electron effective mass as a function of the bandgap of a hydrogen passivated ASiNR under strain.
文摘A theoretical study of resonant tunneling is carried out for an inverse parabolic double-barrier structure subjected to an external electric field. Tunneling transmission coefficient and density of states are analyzed by using the non-equilibrium Green＇s function approach based on the finite difference method. It is found that the resonant peak of the transmission coefficient, being unity for a symmetrical case, reduces under the applied electric field and depends strongly on the variation of the structure parameters.
文摘Self assembled quantum dots have shown a great promise as a leading candidate for infrared detection at room temperature. In this paper, a theoretical model of the absorption coefficient of quantum dot devices is presented. Both of bound to bound absorption and bound to continuum absorption are taken into consideration in this model. This model is based on the effective mass theory and the Non Equilibrium Greens Function (NEGF) formalism. NEGF formalism is used to calculate the bound to continuum absorption coefficient. The results of the model have been compared with a published experimental work and a good agreement is obtained. Based on the presented model, the bound to bound absorption coefficient component is compared to the bound to continuum absorption coefficient component. In addition, the effects of the dot dimensions and electron filling on the bound to continuum absorption coefficient are also investigated. In general, increasing the dot filling increases the absorption and decreasing the dots dimensions will increase the absorption and move the absorption peak towards longer wavelengths.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11304079,11404094,and 51201059)the Priority Scientific and Technological Project of Henan Province,China(Grant No.14A140027)+1 种基金the School Fund(Grant No.2012BS055)the Plan of Natural Science Fundamental Research of Henan University of Technology,China(Grant No.2014JCYJ15)
文摘The conductance stabilities of carbon atomic chains （CACs） with different lengths are investigated by performing the- oretical calculations using the nonequilibrium Green＇s function method combined with density functional theory. Regular even-odd conductance oscillation is observed as a function of the wire length. This oscillation is influenced delicately by changes in the end carbon or sulfur atoms as well as variations in coupling strength between the chain and leads. The lowest unoccupied molecular orbital in odd-numbered chains is the main transmission channel, whereas the conductance remains relatively small for even-numbered chains and a significant drift in the highest occupied molecular orbital resonance to- ward higher energies is observed as the number of carbon atoms increases. The amplitude of the conductance oscillation is predicted to be relatively stable based on a thiol joint between the chain and leads. Results show that the current-voltage evolution of CACs can be affected by the chain length. The differential and second derivatives of the conductance are also provided.
基金Project supported by the National Natural Science Foundation of China(Grant No.51671114)the Special Funding in the Project of the Taishan Scholar Construction Engineering and National Key Research Program of China(Grant No.2016YFB0300501)
文摘Lead nanowire occupies a very important position in an electronic device. In this study, a genetic algorithm（GA）method has been used to simulate the Pb nanowire. The result shows that Pb nanowires are a multishell cylinder. Each shell consists of atomic rows wound up helically side by side. The quantum electron transport properties of these structures are calculated based on the non-equilibrium Green function（NEGF） combined with the density functional theory（DFT）,which indicate that electronic transport ability increases gradually with the atomic number increase. In addition, the thickest nanowire shows excellent electron transport performance. It possesses great transmission at the Fermi level due to the strongest delocalization of the electronic state. The results provide valuable information on the relationship between the transport properties of nanowires and their diameter.
文摘Impacts of effective oxide thickness on a symmetric double-gate MOSFET with 9-nm gate length are studied, using full quantum simulation. The simulations are based on a self-consistent solution of the two-dimensional （2D） Poisson equation and the Schr6dinger equation within the non-equilibrium Green＇s function formalism. Oxide thickness and gate dielectric are investigated in terms of drain current, on-off current ratio, off current, sub-threshold swing, drain induced barrier lowering, transconductance, drain conductance, and voltage. Simulation results illustrate that we can improve the device performance by proper selection of the effective oxide thickness.
基金Project supported by the National Natural Science Foundation of China(Grant No.11104069)
文摘We adopt a self-consistent real space Kerker method to prevent the divergence from charge sloshing in the simulating transistors with realistic discrete dopants in the source and drain regions. The method achieves efficient convergence by avoiding unrealistic long range charge sloshing but keeping effects from short range charge sloshing. Numerical results show that discrete dopants in the source and drain regions could have a bigger influence on the electrical variability than the usual continuous doping without considering charge sloshing. Few discrete dopants and the narrow geometry create a situation with short range Coulomb screening and oscillations of charge density in real space. The dopants induced quasilocalized defect modes in the source region experience short range oscillations in order to reach the drain end of the device.The charging of the defect modes and the oscillations of the charge density are identified by the simulation of the electron density.
