对称双势垒量子阱中自旋极化输运的时间特性

电子的隧穿时间是描述量子器件动态工作范围的重要指标. 本文考虑k³ Dresselhaus 自旋轨道耦合效应对系统哈密顿量的修正, 结合转移矩阵方法和龙格-库塔法来解含时薛定谔方程, 进而讨论了电子在非磁半导体对称双势垒结构中的透射系数及隧穿寿命等问题. 研究结果发现:由于k³ Dresselhaus 自旋轨道耦合效应使自旋简并消除, 并在时间域内得到了表达, 导致自旋向上和自旋向下电子的透射峰发生了自旋劈裂; 不同自旋取向的电子构建时间和隧穿寿命不同, 这是导致自旋极化的原因之一; 电子的自旋极化在时间上趋于稳定. 关键词： 自旋极化输运 透射系数 隧穿寿命 自旋极化率     

Resonant tunneling through double-barrier structures on graphene

Quantum resonant tunneling behaviors of double-barrier structures on graphene are investigated under the tightbinding approximation. The Klein tunneling and resonant tunneling are demonstrated for the quasiparticles with energy close to the Dirac points. The Klein tunneling vanishes by increasing the height of the potential barriers to more than 300 meV. The Dirac transport properties continuously change to the Schro¨dinger ones. It is found that the peaks of resonant tunneling approximate to the eigen-levels of graphene nanoribbons under appropriate boundary conditions. A comparison between the zigzag- and armchair-edge barriers is given.     

Resonant tunneling through a double-barrier quantum well in a transverse magnetic field

We theoretically analyze the tunneling of electrons through a heterostructure with two barriers and a quantum well between them in a magnetic field perpendicular to the current. We take into account the contribution from electrons with various positions of the magnetic oscillator center to the current. The region of the Z-shaped current-voltage characteristic for the heterostructure is shown to narrow as the magnetic field strengthens. Our analysis reveals a critical magnetic field strength at which the Z-shaped current-voltage characteristic transforms into an N-shaped one. We compare our results with experimental data.     

Level width of a quasibound state in a double-barrier parabolic-well resonant tunneling structure

Taking exact Airy functions and Hermitian functions as envelope functions, we investigate in detail the level width of a quasibound state for electrons coherent resonant tunneling through symmetric and asymmetric double-barrier parabolic-well resonant tunneling structures (DBRT) with the transfer-matrix formalism. It is found that for the symmetric structure and the asymmetric structure with left barrier thicker than the right one, both the level width and the peak value vary monotonously with increasing applied bias, but for the asymmetric DBRT structure with left barrier thinner than the right one, they change nonmonotonously. The nonmonotonous variations of the level width and the peak value reflect the transition of tunneling type (i.e. first from incompletely resonant tunneling to completely resonant tunneling, and then from completely resonant tunneling back to incompletely resonant tunneling). The effects of well width, barrier thickness and barrier height on the level width and the peak value are also inspected.     

Spin-dependent tunnelling through an indirect double-barrier structure

We use the transfer matrix method to study the quantum tunnelling through an indirect-band-gap double-barrier like the GaAs/AlAs/GaAs/AlAs/GaAs heterostructures along the [001] axis, which is described by the tight-binding model. The X-valley quasi-bound state gives rise to the Fano resonance different from the direct double-barrier transition in a resonance-tunnelling diode. The quantitative calculations demonstrate that a relatively high spin-polarization of the transmission probability can be achieved as compared with the single-barrier tunnelling ease. Moreover the extension to the multi-barrier device is provided and leads to an important observation that the spin polarization increases with the number of barriers.     

Single electron on a nanodot in a double-barrier tunneling structure observed by noncontact atomic-force spectroscopy

A single electron has been observed on a nanodot in a double-barrier tunneling structure by noncontact atomic-force microscopy at fixed separation. Frequency shift-voltage dependence of an Au-coated cantilever/vacuum/1-decanethiol protected Au nanodot/1-octanethiol self-assembled monolayer/Au substrate structure deviates from the theoretical parabolic curve, which is attributed to the change in the number of quantized electrons on the Au nanodot caused by the Coulomb blockade phenomena.     

High quantum efficiency of intersubband transitions in coherent tunneling of electrons through asymmetric double-barrier structures

A converging perturbation series that can be summed analytically has been obtained for intersubband transitions of electrons coherently tunneling through the middle of a dimensionally quantized level in an asymmetric double-barrier structure in a high-frequency terahertz electric field. The possibility of a substantial increase in tunneling current accompanied by either absorption or emission of a photon has been demonstrated. The quantum efficiency of radiative transitions between dimensionally quantized levels can be up to 66%. Zh. éksp. Teor. Fiz. 112, 237–245 (July 1997)     

Current rectification through a single-barrier resonant tunneling quantum structure

We propose a simple quantum structure which exhibits resonant tunneling under one bias and simple tunneling under the opposite one, thus acting as a rectifier. The diode consists of a single laterally-indented barrier. Due to its particular conduction-band profile, electrons undergo resonant tunneling when the bias creates a band-profile triangular well which can contain a resonant state aligned to the emitter Fermi energy. A diode with an active layer of ≈ 100Å, realized by AlGaAs/GaAs, has a Rectification Ratio, calculated at the current-peak bias at resonance, of ≈ 100. This value can be enhanced by putting in series several elements of this kind.