Electron transport through a quantum-dot superlattice

Miniband electron transport through a laterally-confined superlattice is investigated using the balance equation approach. Up to 15 subbands with intraband and interband impurity and phonon scatterings are included. The nonlinear drift velocity and electron temperature, calculated as functions of the applied electric field for systems of varying degrees of confinement, exhibit significant subband effects, and the cross-over from one-dimensional to three-dimensional behavior.     

Controllable spin-dependent transport in silicene superlattice

Based on the transfer-matrix method, we theoretically investigate the spin-dependent transport properties in magnetic silicene superlattice in the presence of extrinsic Rashba spin–orbit interaction (RSOI). It is found that the spin transmission probability and spin conductivities can be efficiently controlled by the number of magnetic barriers. As the number of magnetic barriers increases, spin conductivities strongly decrease, and reduce to zero in the large on-site potential difference between A and B sublattices (Δ_z) region. The results indicate that a magnetic silicene superlattice exhibits a remarkable wavevector-dependent spin filtering effect. Also, the magnetoresistance (MR) ratio exhibits an oscillatory behavior with the Fermi energy. The MR ratio can be tuned by the Fermi energy, number of magnetic barriers and extrinsic RSOI. Specifically, in the presence of magnetic field the spin polarization can be observed, and increases by increasing the magnetic field.     

Electron transport across a quantum wire embedding a saw-tooth superlattice

By developing the recursive Green function method, the transport properties through a quantum wire embedding a finite-length saw-tooth superlattice are studied in the presence of magnetic field. The effects of magnetic modulation and the geometric structures of the superlattice on transmission coefficient are discussed. It is shown that resonant peak splitting of this kind of structure is different from that of ‘magnetic' and ‘electric' superlattices in two-dimensional electron gas. The transmission spectrum can be tailored to match requirements through adjusting the size of saw-tooth quantum dot and field strength.     

Effect of the charge dragging in a graphene-based superlattice under a constant electric field

The effect of a constant electric field on the charge dragging by an electromagnetic wave is studied for graphene-based superlattice. An expression is derived for the electric current density in a graphene-based superlattice under a constant electric field in an approximation of a constant time of relaxation. It is demonstrated that the current as a function of wave intensity is of a nonmonotonous character.     

Space charge dynamics in a semiconductor superlattice affected by titled magnetic field and heating

The transition between different modes of current oscillations in a semiconductor superlattice, from close-to-harmonic (near the generation onset) to relaxation oscillations, has been investigated. The transition type is shown to change with an increase in temperature. A period-doubling bifurcation is observed at low temperatures. With an increase in temperature, the period-doubling bifurcation is observed at increasingly larger values of the voltage across the superlattice. The doubling bifurcation ceases to be observed at voltages at which the generation of oscillations of the current through the semiconductor superlattice is suppressed.     

Effect of an external resonator on the space charge dynamics in a semiconductor superlattice

The dynamics of a semiconductor superlattice in an external resonator is studied. It is shown that the external electrodynamic system considerably complicates the behavior of the superlattice by exciting random oscillations and leads to additional negative differential conductivity in the I–V characteristic that is not observed in an autonomous system.     

A non-Boltzmann balance equation approach to electronic transport in a type-I superlattice

Force and energy balance equations are derived for steady state hot electron transport in a type-I superlattice composed of periodically arranged finite-width quantum wells. The scatterings by remote and background impurities and by acoustic and polar optical phonons are taken into account, together with Coulomb interactions between intralayer electrons and interlayer electrons. The carrier mobility and electron temperature are calculated as functions of drift velocity ν up to ν=3×10⁷ cm / s, showing significant nonlinearity and dependence on geometrical superlattice parameters (quantum well width and separation, etc.)     

Recent results on superlattice transport and optoelectronics applications

Recent results involving miniband transport in superlattices at millimetre (mm) wave frequencies are reviewed. The miniband negative differential conductance up to very high frequencies allows for a new kind of device, the superlattice photo-oscillator. A practical application for optical to mm-wave conversion is demonstrated. An analysis of the intrinsic limitations in the transport processes led to recent progress in the understanding of superlattices physics involving Zener inter-miniband tunneling.     

太赫兹场和倾斜磁场对超晶格电子动力学特性调控规律研究

微带超晶格在磁场和太赫兹场调控下表现出丰富而复杂的动力学行为, 研究微带电子在外场作用下的输运性质对于太赫兹器件设计与研制具有重要意义. 本文采用准经典的运动方程描述了超晶格微带电子在沿超晶格生长方向(z方向)的THz场和相对于z轴倾斜的磁场共同作用下的非线性动力学特性. 研究表明, 在太赫兹场和倾斜磁场共同作用下, 超晶格微带电子随时间的演化表现出周期和混沌等新奇的运动状态. 采用庞加莱分支图详细研究了微带电子在磁场和太赫兹场调控下的运动规律, 给出了电子运行于周期和混沌运动状态的参数区间. 在电场和磁场作用下, 微带电子将产生布洛赫振荡和回旋振荡, 形成复杂的协同耦合振荡. 太赫兹场与这些协同振荡模式之间的相互作用是导致电子表现出周期态、混沌态以及倍周期分叉等现象的主要原因.     

Electronic band gap and transport in graphene superlattice with a Gaussian profile potential voltage

We study the electronic properties for the graphene-based one-dimensional superlattices, whose potential voltages vary according to the envelope of a Gaussian function. It is found that an unusual Dirac point exists and its location is exactly associated with a zero-averaged wave number （zero-re） gap. This zero-k gap is less sensitive to incident angle and lattice constants, properties opposing those of Bragg gap. The defect mode appearing inside the zero-l gap has an effect on transmission, conductance, and shot noise, which will be useful for further investigation.     

Non-equilibrium charge transport at a first-order phase transition

We have studied penetration of a charge density disturbance cause by a moving bubble wall in relativistic plasma, using the self-consistent field approximation. We have shown that the charge density as a function of distance from the wall has a power-law tail 1/z². We find that penetration of charge in plasma is most effective when the wall velocity is close to unity. However, for wall velocities u0.7, the effective, in the integral sense, penetration length is found to be essentially equal to the static Debye radius.     

Polarizable scattering centers in a fluctuation approach to charge transport

We present a detailed derivation of the fluctuation transport theory, previously developed by Gerlach and Mycielski. The basic idea is the transformation of carrier-densities and fields into the rest frame of each type of carriers and application of the Fluctuation-Dissipation-theorem for monopolar, unscreened carrier densities. In the present paper, the theory is applied to a model system containing free electrons, rigid ions and polarizable neutral donors. We compare our results with experimental data for the polar II–VI-semiconductor Eu₁-_xSr_xS.     

Vertical transport in multilayer semiconductor structures

The judicious design of multilayer semiconductor systems, grown by MBE or MOCVD, has made possible new studies of tunnelling, hot-electron injection, avalanching, photoresponse, and other phenomena in III–V semiconductors. Some recent progress is reviewed.