Influence of Γ–X mixing on carrier transport and photoluminescence in GaAs/AlAs type-I superlattices

We report on the effects of field-induced Γ–X resonances on carrier transport and optical properties of GaAs/AlAs type-I short-period superlattices (SLs). We have observed an anomalously delayed photocurrent and Γ2-hh1 photoluminescence originating from X1–Γ2 mixing. These observations clearly suggest that electrical conductivity and optical properties even in type-I SLs are seriously affected by X states in the applied electric field.     

Effect of the Radiation Power on the Modification of Oscillations of the Photocurrent in Single-Barrier p–i–n GaAs/AlAs/GaAs Heterostructures with InAs Quantum Dots

JETP Letters - The effect of the power of incident light radiation on the behavior of quantum oscillations of the photocurrent in single-barrier p–i–n GaAs/AlAs heterostructures with...     

Effect of Bias Step on the I-V Curve in Double-Barrier AlGaAs/GaAs/AlGaAs Resonant-Tunnelling Devices

We investigate the non-equilibrium electron transport properties of double-barrier AlGaAs/GaAs/AlGaAs resonant- tunnelling devices in nonlinear bias using the time-dependent simulation technique. It is found that the bias step of the external bias voltage applied on the device has an important effect on the final current-voltage （I - V） curves. The results show that different bias step applied on the device can change the bistability, hysteresis and current plateau structure of the I - V curve. The current plateau occurs only in the case of small bias step. As the bias step increases, this plateau structure disappears.     

Electron Transport Properties of Two-Dimensional Electron Gas in BexZn1−xO/ZnO Heterostructures

In this study, we have numerically investigated the conduction band structures, the carrier densities and the electron probability densities of pseudomorphic grown Be_xZn_1?xO/ZnO heterostructures using self-consistent solutions of one-dimensional, non linear Schrödinger–Poisson equations. In the calculations, two-dimensional electron gas (2DEG) formations were observed in the studied heterostructures and the effects of layer thickness and Be-mole fraction (x) of Be_xZn_1?xO barrier layer on 2DEG were described. For possible transistor device applications, 10 nm Be_xZn_1?xO barrier layer structure with x = 0.08 has been suggested. For this structure, we examined the variation of electron mobility with temperature using analytical calculations. Because of the polarization-induced low carrier densities, we found that the background impurity scattering has a strong effect on total electron mobility even at room temperature.     

Strong Effect of the Wavelength of Light on Quantum Oscillations of the Photocurrent and Their Resonant Tunneling Nature in p–i–n GaAs/AlAs Heterostructures

JETP Letters - The strong effect of the wavelength of incident light λ on the fraction of the oscillatory component of the photocurrent in p–i–n GaAs/AlAs heterostructures has been...     

Effect of Connected Multi-Ring Impurity Scattering on Quantum Transport

We investigate the quantum transmission properties of connected multi-rings with impurities and analyse the effect of the impurities on the band formation in these geometric structures. It is shown that energy bands and band gaps are formed clearly while there is not any fixed band structure for the case of the single ring. The number of resonant peaks in conductance bands increases with the number of rings. Some essential differences are pointed out and magnetic properties of loop configurations in the presence of Aharonov-Bohm flux are explored as well.     

Resonant Γ–X–Γ tunneling in GaAs/AlAs/GaAs single barrier heterostructures at zero and elevated magnetic field

We report the observation of resonant tunneling and magneto-tunneling between states of different effective mass derived from zone centre (Γ) and zone edge (X) points of the Brillouin zone in single AlAs barrier diodes. The nature of the X states involved (longitudinal X_zor transverseX_xy ) is deduced from the observed resonances in the conductance versus bias characteristics at zero magnetic field (B). At finite B, the σ–V curves exhibit resonant magneto-tunneling with X_zLandau levels (LL), whilst no evidence of resonances withX_xy LLs is found. Clear observation of both LL index (in-plane momentum) conserving and non-conserving tunneling to X_zallows the transverse effective mass in AlAs to be determined. As a consequence of the different effective masses, momentum-conserving tunneling is inhibited at B = 0, but is restored when high B is applied.     

Effect of Multiple Scattering of a Relativistic Electron Beam in a Gas–Plasma Medium on the Dynamics of the Resistive Hose Instability

We consider the effect of the multiple Coulomb scattering on the spatial dynamics of the relativistic hose instability of a relativistic electron beam propagating along an Ohmic plasma channel. It is shown that the enhancement of scattering noticeably suppresses this instability.

     

Effect of Kinetic Alfvén Waves on Electron Transport in an Ion-Scale Flux Rope

At the Earth's magnetopause, the electron transport due to kinetic Alfvén waves(KAWs) is investigated in an ion-scale flux rope by the Magnetospheric Multiscale mission. Clear electron dropout around 90° pitch angle is observed throughout the flux rope, where intense KAWs are identified. The KAWs can effectively trap electrons by the wave parallel electric field and the magnetic mirror force, allowing electrons to undergo Landau resonance and be transported into more field-aligned directions. The pitch angle range for the trapped electrons is estimated from the wave analysis, which is in good agreement with direct pitch angle measurements of the electron distributions. The newly formed beam-like electron distribution is unstable and excites whistler waves,as revealed in the observations. We suggest that KAWs could be responsible for the plasma depletion inside a flux rope by this transport process, and thus be responsible for the formation of a typical flux rope.     

A “superlattice” model for a smooth GaAs/AlAs (001) heterointerface

The effect of a smooth interface potential on the electronic states in GaAs/AlAs (001) structures is investigated using the pseudopotential method. In this approach, the transition region between GaAs and AlAs is assumed to be a layer corresponding to a half-period of the (AlAs)₂(GaAs)₂ superlattice, with the potential of this layer being close to the real potential near the heterointerface. In this case, the intervalley mixing occurs at two boundaries and in the transition layer rather than at one boundary, as in the model with a sharply cut-off potential. It is shown that a smooth potential has an appreciable effect on electron tunneling in structures with thin layers. This effect is especially important in the case where short-wavelength X states are involved. For one GaAs/AlAs (001) boundary, the transition layer acts as a quantum well localizing the charge density of a mixed Γ-X state near the boundary. In structures with a layer thickness of less than 2 nm, the differences in the resonance energies obtained in the models with a smooth heterointerface and with a sharp heterointerface can be as high as ～0.1 eV. The envelopes of the wave functions associated with Γ ₁ ⁽¹⁾ , Γ ₁ ⁽²⁾ , and Γ ₃ ⁽¹⁾ superlattice valleys and with Γ₁, X ₁, and X ₃ valleys of GaAs and AlAs are analyzed. It is shown that the matching matrices for the envelope functions at the GaAs/(AlAs)₂(GaAs)₂ and (AlAs)₂(GaAs)₂/AlAs boundaries depend only weakly on the electron energy near the bottom of the conduction band and that the probability densities calculated using these functions agree with the results of many-band calculations. Therefore, these functions can be used to construct a model with a smooth interface potential in the framework of the effective-mass method.     

Linear Interaction (Transformation) of de Broglie Waves of the Γ- and X-Valleys and Intraband Optical Transitions in GaAs/AlAs Quantum-Well Heterostructures in a Lateral Electric Field

We discuss the linear interaction between the de Broglie waves of different electron valleys in heterostructures where a constant electric field is applied along the heterointerfaces (lateral field). The probabilities of phononless and dipole optical transitions of electrons between the - and X-subbands in GaAs/AlAs quantum-well heterosructures with a lateral electric field are calculated. It is shown that the electric field has a strong effect on the probabilities of phononless and direct optical dipole -X electron transitions. Moreover, a lateral electric field changes the spectrum of the intersubband -X light absorption, i.e., there is an intersubband analogue of the Franz-Keldysh effect. The considered linear interaction of de Broglie waves is compared with the well-known cases of linear wave interaction in a magnetized plasma, the Zener breakdown, and the Franz-Keldysh effect in solids.     

Effects of Relative Orientation of Molecules on Electron Transport in Molecular Devices

Effects of relative orientation of the molecules on electron transport in molecular devices are studied by the non-equilibrium Green function method based on density functional theory. In particular, two molecular devices with planar Au7 and Ag3 clusters sandwiched between the Al（100） electrodes axe studied. In each device, two typical configurations with the clusters parallel and vertical to the electrodes are considered. It is found that the relative orientation affects the transport properties of these two devices completely differently. In the Al（100）- Au7-Al（100） device, the conductance and the current of the parallel configuration are much larger than those in the vertical configuration, while in the Al（100）-Ag3-Al（100） device, an opposite conclusion is obtained.     

Effect of Small-Angle Scattering on the Integer Quantum Hall Plateau

A GaAs/AlGaAs two-dimensional electron gas （2DEG） structure with the high mobility of μ2K= 1.78 × 10^6 cm^2/Vs has been studied by low-temperature Hall and Shubnikov de Hags （SdH） measurements. Quantum lifetimes related to all-angle scattering events reduced from 0.64 ps to 0.52 ps after i11uminating by Dingle plots, and transport lifetimes related to large-angle scattering events increasing from 42.3ps to 67.8ps. These results show that small-angle scattering events become stronger. It is clear that small-angle scattering events can cause the variation of the widths of the quantum Hall plateaus.     

Temperature-Dependent Electron Transport in In0.5Ga0.5 P/GaAs Grown by MOVPE

Hall effect measurements in undoped In0.5Ga0.5 P/GaAs allo grown by metal organic vapour-phase epitaxy （MOVPE） have been carried out in the temperat.ure range 15-350K. The experimenta.1 results are analysed using a two-band model including conduction band transport calculated using an iterative solution of the Boltz- mann equation. A good agreement was obtained between theory and experiment. The impurity contents of In0.5Ga0.5 P/GaAs alloy, such as donor density ND, acceptor density NA and donor activation energy εD, were also determined.     

Effect of Magnetic Co–CoO Particles on the Carrier Transport in Monolayer Graphene

Physics of the Solid State - Electrodeposition of cobalt on monolayer graphene synthesized by chemical vapor deposition produces Co–CoO/graphene composite structures, which is accompanied by...     

Storage of Photoexcited Electron—Hole Pairs in an AlAs／GaAs Heterostructure Created by Electron Transfer in Real and κ Spaces

The storage of photoexcited electron-hole pairs is experimentally carried out and theoretically realized by transferring electrons in both real and κ spaces through resonant Γ-X in and AlAs/GaAs heterostructure,This is proven by the peculiar capacitance jump and hysteresis in the measured capacitance-voltage curves.Our structure may be used as a photonic memory cell with a long storage time and a fast retrieval of photons as well.     

Effect of Cluster Coulomb Fields on Electron Acceleration in Laser-Cluster Interaction

Single particle simulations are used to investigate electron acceleration in the laser-cluster interaction, taking into account the Coulomb fields around individual clusters. These Coulomb fields are induced from the cluster cores with positive charge when electrons escape from the cluster cores through ponderomotive push from the laser field. These Coulomb fields enable some stripped electrons to be stochastically in phases with the laser fields so that they can gain net energy from the laser efficiently. In this heating mechanism, circularly polarized lasers, larger cluster size and higher cluster densities make the acceleration more efficient.     

Magnetointersubband Oscillations of the Two-Dimensional Electron Gas in AlxGa1-xN／GaN Heterostructures

Shubnikov-de Haas (SdH) measurements are performed over a temperature range of 1.5-20 K in Al0.22 Ga0.78N/GaN heterostructures with two subbands occupied. In addition to an intermodulation between two sets of SdH oscillations from the first and second subbands, a beating in oscillatory magnetoresistance at 12K is observed, due to the mixing of the first subband SdH oscillations and ‘magnetointersubband‘ (MIS) oscillations. A phase shift of π between the SdH and MIS oscillations is also clearly identified. Our experimental results, i.e. that the SdH oscillations dominate at low temperature and MIS oscillations dominate at high temperature, fully comply with the expected behaviour of MIS oscillations.     

Effect of Nonradiative Recombination on Carrier Dynamics in GaInNAs/GaAs Quantum Wells

The nonradiative recombination effect on carrier dynamics in GalnNAs/GaAs quantum wells is studied by timeresolved photoluminescence （TRPL） and polarization-dependent TRPL at various excitation intensities. It is found that both recombination dynamics and spin relaxation dynamics strongly depend on the excitation intensity. Under moderate excitation intensities the PL decay curves exhibit unusual non-exponential behaviour. This result is well simulated by a rate equation involving both the radiative and non-radiative recombinations via the introduction of a new parameter of the effective concentration of nonradiative recombination centres in the rate equation. In the spin dynamics study, the spin relaxation also shows strong excitation power dependence. Under the high excitation power an increase of spin polarization degree with time is observed. This new finding provides a useful hint that the spin process can be controlled by excitation power in GaInNAs systems.     

(GaAs)_1(AlAs)_1(001)超晶格电子结构的从头计算

本文用密度泛函线性丸盒轨道原子球近似方法(DFT-LMTO-ASA)对(GaAs)_1(AlAs)_1(001)超晶格的电子结构进行了第一原理性计算。利用Lowdin微扰法在矩阵元中计入d态的影响,可使本文方法仅用阶数很小(32×32)的久期方程便可较满意地处理这个超晶格系统。计算并讨论了该超晶格的带隙,导带极小值处各本征态的分波特性以及GaAs和AlAs层间的价电子转移。我们的结果同最近用计算量大得多的从头算赝势法和完整势线性缀加平面波(FLAPW)法所得的结果进行了比较。结果表明,本文方法不仅具有合理的精度,而且有快速高效率的特点,更适于研究层数较多或结构更复杂的半导体超晶格,如(GaAs)m(AlAs)n等系统的电子结构性质。