InSb带间法拉第转角的振荡现象

在低温下,用连续CO激光器观察到了InSb带间法拉第转角随外磁场变化的振荡现象,振荡的产生可归结于电子相继跃迁到导带的不同朗道子能级,实验测量和理论的估算进行了比较.     

Negative FIR-photoconductivity in n-GaAs

Negative photoconductivity in n-GaAs has been observed in the far infrared spectral range between 20 and 29 cm^?1. Negative photoconductivity occurs when a magnetic field is applied to the samples and impact ionization of shallow donors by the electric bias field is the dominant mechanism of electron excitation to the conduction band. A conceivable model qualitatively explaining the experimental results is proposed, which involves optical transitions from the lowest Landau subband to higher bound states of shallow donors.     

Hot electron energy relaxation in quantizing magnetic fields

A systematic study of the radiative recombination of hot electrons between Landau levels in several n-InSb samples has been carried out as a function of the free electron concentration and the applied electric and magnetic fields (E ～ H). The magnetic field range investigated was 0.5 to 3.0 T. Electron temperatures are derived in dependence of the total electric and the magnetic field applied. The carrier heating is impeded with increasing electron concentration and also with increasing magnetic field. From the direct observation of the recombination radiation intensity on electric field response the electron lifetime in the first Landau level is found to be less than 10^?8. The results obtained are discussed in light of a new theoretical approach. We give evidence that electron-electron scattering plays an important role both for the carrier distribution established and for the electron lifetime in the first Landau level.     

磁场引起弱耦合超晶格中隧穿电流的增加

在n-型掺杂弱耦合GaAs/AlAs超晶格中,沿着垂直于超晶格平面方向加一个静态磁场,研究电子的隧穿过程.随着磁场的增加,相邻量子阱基态间的隧穿电流增加.这是由于磁场导致电子的隧穿机制发生了变化,即由低磁场下电子的非共振隧穿或跳跃电导向高磁场下电子的共振隧穿的转变.     

磁场引起弱耦合超晶格中隧穿电流的增加

在n-型掺杂弱耦合GaAs/AlAs超晶格中,沿着垂直于超晶格平面方向加一个静态磁场,研究电子的隧穿过程.随着磁场的增加,相邻量子阱基态间的隧穿电流增加.这是由于磁场导致电子的隧穿机制发生了变化,即由低磁场下电子的非共振隧穿或跳跃电导向高磁场下电子的共振隧穿的转变.     

Magnetic quantum oscillation in a monolayer insulator

The Shubnikov-de Haas(SdH)oscillation,as evidenced by the oscillating resistivity as a function of magnetic field at sufficiently low temperature,is not uncommon in metals,semi-metals and narrow gap semiconductors at their conducting state.The origin of SdH oscillation is associated with Landau quantization,at which the cyclotron orbits of electrons are quantized.In other words,electrons can only occupy dis-crete energy levels,which are called the Landau levels.As the magnetic field increases,the split,quantized Landau levels move across the Fermi level and hence the material's trans-port properties start to oscillate periodically.     

Temperature dependence of thermoelectric power in n-InSb in a transverse quantizing magnetic field

The thermoelectric power in n-InSb in a transverse quantizing magnetic field has been studied in the temperature range 67–160 K. The dependence of the electronic component of the thermoelectric power on the magnetic field is accounted for in terms of a quantum theory taking into account the spin splitting of Landau levels.     

Magnetoabsorption in narrow-gap HgCdTe epitaxial layers in the terahertz range

The magnetoabsorption and photoconductivity spectra are investigated in the terahertz (THz) range at a temperature of T = 4.2 K for n-Hg_{1 ? x} Cd _x Te bulk epitaxial layers of various compositions (both semiconductor and semimetallic) grown by molecular-beam epitaxy. Within the framework of the Kane 8 · 8 model, the electron and hole Landau levels are calculated. It is shown that, in contrast to the results of previous investigations, all observed resonance lines are related to transitions between the Landau levels of free carriers (the cyclotron resonance in the conduction band and the transitions between heavy-hole and electron Landau levels), which is evidence of the high purity and structural perfection of the samples. The possibility of using zero-gap Hg_{1 ? x} Cd _x Te solid solutions as THz photodetectors tunable by magnetic field is shown.     

Resonance modulation of electron-electron relaxation by a quantizing magnetic field

It is found that a magnetic field turns on intersubband electron relaxation as the Landau levels of the spatial quantization subbands of a single heterojunction scan the Fermi level. The observed steady decrease in intersubband relaxation time as the magnetic field increases is attributed to the addition of electron-phonon interaction to electron-electron interaction.     

Magneto-quantum oscillations of the Korringa relaxation rate of manganese ion near a two-dimensional electron gas

The Mn ion-spin relaxation rate (Korringa relaxation) in the vicinity of the two-dimensional electrons (2DEG) in a Mn-based semiconductor nanostructures in a quantizing magnetic field was calculated. The Korringa relaxation is an energy-consuming process due to the difference in magnetic moments of localized and electrons spins involved. The mechanism of energy transfer between the Mn spin and the 2DEG is exchange scattering of the Landau electrons with a transition from the e ↑ sub-band to the e ↓ sub-band accompanied by a change in the Mn spin. It was found that due to the presence of Landau levels and the spin-split mobility gap, the Korringa relaxation rate oscillates with the magnetic field resembling the oscillations of the resistivity in such systems. Our calculation offers a method of investigating the dynamics of a magnetic ion such as Mn in a 2DEG and provide new information on the exchange parameter as well as information about the 2D electrons themselves.     

平行磁场下半导体超晶格电子结构(英文)

Electron and hole subbands of superlattices in an in-plane magnetic field are investigated. Landau energy levels, subband dispersion curves and optical transition probabilities in GaAs-AlxGa1-xAs are calculated by using the effective mass theory. The variations of the binding energies of light and heavy hole excitoas as functions of quantum well width and magnetic field strength are obtained.Electronic energy levels in a magnetic field (in xy plane) with the tilting away from the growth direction (y axis) are calculated and discussed.     

Vertical transport in type-II heterojunctions with InAs/GaSb/AlSb composite quantum wells in a high magnetic field

Vertical transport in type-II heterojunctions with a two-barrier AlSb/InAs/GaSb/AlSb quantum well (QW) grown by MOVPE on an n-InAs (100) substrate is investigated in quantizing magnetic fields up to B = 14 T at low temperatures T = 1.5 and 4.2 K. The width of the QWs is selected from the formation condition of the inverted band structure. Shubnikov–de Haas oscillations are measured at two orientations of the magnetic field (perpendicular and parallel) relative to the structure plane. It is established that conduction in the structure under study is occurs via both three-dimensional (3D) substrate electrons and two-dimensional 2D QW electrons under quantum limit conditions for bulk electrons (B > 5 T). The electron concentrations in the substrate and InAs QW are determined. The g-factor for 3D carriers is determined by spin splitting of the zero Landau level. It is shown that the conductance maxima in a magnetic field perpendicular to the structure plane and parallel to the current across the structure in fields B > 9 T correspond to the resonant tunneling of 3D electrons from the emitter substrate into the InAs QW through the 2D electron states of the Landau levels.     

Effects of self-consistent electrostatic potential in quantum wells with several quantum confinement levels in high magnetic fields

The effect of self-consistent electrostatic potential on the spectrum of two-dimensional electron states in high magnetic fields is studied under the conditions where more than one quantum confinement subband is filled. The cases of magnetic field directed perpendicular to the quantum well plane and tilted magnetic field are considered. In the case of perpendicular magnetic field it is shown that two or more Landau levels that belong to different quantum confinement subbands can be degenerate in some ranges of concentrations (magnetic fields). The inclination of the magnetic field with respect to the growth direction produces opening of the energy gap between these levels; however, the gap as a function of concentration (magnetic field) remains almost constant in the same range of parameters.     

Power broadening and nonlinear FIR magneto-photoconductivity in n-GaAs

The saturation of the photoconductivity due to 1s-2p₊ shallow donor transitions in n-GaAs has been investigated using a high power cw-FIR-laser. Magnetic field strengths were chosen in such a way that 2p₊ energy levels were either below or above the N=0 conduction band Landau level. In the former case 1s-p₊ transitions are found to be inhomogeneously broadened with a saturation intensity as low as 0.84 mW/cm², giving an effective lifetime of the 2p₊ state of 1.5 μs. Above the band edge the integrated photoconductivity does not saturate though the intensity-normalized peak photosignal decreases and the linewidth increases with raising intensity. This strange behaviour is tentatively attributed to optical excitations of 2p₊ electrons to higher lying electron Landau states.     

强耦合表面磁极化子的基态能量和有效质量

采用Landau-Pekar变分理论研究强耦合表面磁极化子的性质。分别计算了强耦合表面磁极化子的基态能量和有效质量，并讨化了表面磁极化子的基态能量，振动频率和有效质量随磁场的变化关系。对KCL晶体进行了数值计算，结果表明，强耦合表面磁极化子的振动频率和有效质量随磁场的增加而增加，基态能量随磁场的增加而减少。     

Spectrum of an electron in a quantum well in high inclined magnetic field and high transverse electric field

The energy and wave functions of localized electron states in a quantum well in a high magnetic field arbitrarily oriented with respect to the layers of the structure, and a high transverse electric field are studied. The situation where the quantum-confined energy and the Landau energy are close to each other is considered. The evolution of the spectrum with varying orientation of the magnetic field over the entire angle range is studied.     

The cyclotron resonance of holes in InGaAs/GaAs heterostructures with quantum wells in quantizing magnetic fields

The spectra of the cyclotron resonance of holes in the InGaAs/GaAs selectively doped heterostructures with quantum wells are studied in pulsed magnetic fields as high as 50 T at 4.2 K. The previously observed effect of the inverted (compared with the results of the single-particle calculation of the Landau levels) ratio of the spectral weight of two split components of the line of the cyclotron resonance, which is attributed to the effects of the exchange interaction of holes, is confirmed. It is found that the ratios of intensities of the components of the line of the cyclotron resonance profoundly differ on the ascending and descending branches of the magnetic field pulse, which may be associated with a long time of the spin relaxation of holes between the two lowest Landau levels, which constitute tens of milliseconds.     

Effect of temperature on the thermodynamic density of states in a quantizing magnetic field

The dependence of the density of energy states (N _s ) on temperature in quantizing magnetic fields is studied. It is shown that, as temperature is increased, the Landau levels are blurred as a result of thermal widening and the quantities N _s are transformed into the density of states as in the absence of a magnetic field. The temperature dependence of the distribution of the density of energy states in high magnetic fields for semiconductors is considered using a mathematical model. It is shown that the continuous spectrum of density of states measured at liquid-nitrogen temperature is transformed into discrete Landau levels at lower temperatures. Mathematical simulation of the processes with the use of experimental data for the continuous spectrum of the density of states makes it possible to calculate the discrete Landau levels. Experimental results obtained for PbS are analyzed using the suggested model. The density of states at low temperatures is calculated from data on high-temperature N _s .     

Nondestructive characterization of Hg1−xCdxTe layers with n-p structures by magneto-thermoelectric measurements

The thermoelectric properties of n-type Hg_0.79Cd_0.21Te (MCT) and of MCT layers with n-p structure have been investigated in transverse (B ⊥ ∇T) and longitudinal (B ‖∇T) magnetic fields (0 ≤ B ≤ 16 kG) using the lateral gradient method at temperatures between 10 and 300K. The experimental results were analyzed by considering the contributions of electrons and holes to the magneto-thermoelectric effect and the scattering mechanisms involved. The analysis is based on a nonparabolic conduction band and Landau quantization as well as empirical relations for the band gap, the intrinsic carrier density, and the magnetoresistance. For n-type MCT at low temperatures (10 < T < 30K) and weak magnetic fields (B < 2 kG), the transverse magneto-thermoelectric effect (TME) was seen to be dominated by electron scattering on ionized defects. Longitudinal acoustic phonon drag was found to affect the TME in strong magnetic fields (B > 3 kG) at low temperatures (T < 20K). Longitudinal (LO) phonons were shown to prevail in the electron scattering at higher temperatures (T > 50K) in weak magnetic fields. With increasing magnetic fields, the effect of LO-phonon scattering decreases, and eventually the TME becomes independent of electron scattering. The longitudinal magneto-thermoelectric effect of n-type MCT was also found to exhibit magnetophonon oscillations due to LO-phonon scattering from both HgTe and CdTe phonons. The transverse magnetoresistance (TMR) of the n-type layers in the quantum region has been found to be linearly dependent on the magnetic field. Owing to the TMR of the n-type layers, the variation of the TME of p-n multiple layers with magnetic field is much larger than the variation of the Seebeck coefficient with temperature. Thus, the sensitivity to p-type layers is considerably enhanced compared to that of the Seebeck coefficient. As a result, the TME has proved to be particularly useful in determining the doping and composition of the constituent layers of MCT n-p structures.     

Band gap opening and charge modulation in AlGaAs lateral structures obtained by organized epitaxy

Quantum wires superlattices have been grown on GaAs vicinal surfaces. Their electrical resistance anisotropy, their low-field magnetoresistance (for current flow perpendicular to the wires) and, in the magnetic quantum limit, the van Hove singularities of the Landau bands, and the very sudden enhancement of the spin splitting above a critical field, all demonstrate unambiguously that a strong low-disordered periodic lateral potential modulation can be achieved as a result of significant atomic ordering by the steps.