Magnetoresistance of a two-dimensional electron gas in a parallel magnetic field

The conductivity of a two-dimensional electron gas in a parallel magnetic field is calculated. We take into account the magnetic-field-induced spin-splitting, which changes the density of states, the Fermi momentum, and the screening behavior of the electron gas. For impurity scattering, we predict a positive magnetoresistance for low electron density and a negative magnetoresistance for high electron density. The theory is in qualitative agreement with recent experimental results found for Si inversion layers and Si quantum wells.     

Mobility of two-dimensional electron gas in JFETS limited by polar-optic and impurity scattering

The theory of mobility of a two-dimentional electron gas in JFET structures limited by polar-optic phonon and impurity scattering is developed in this work. The energy level and the wave function of the lowest subband are obtained by a variational procedure. The mobility limited by polar-optic phonon scattering is obtained by solving the Boltzmann equation iteratively. The expression for the impurity scattering limited mobility is obtained by using the variational wave function. For numerical calculation, however, the electron gas is assumed to be strictly two-dimensional. It is found that for experimental range of impurity concentration in GaAs JFETs, impurity scattering is the dominant process even at 300K.     

Point impurities remove degeneracy of the Landau levels in a two-dimensional electron gas

The density of states of a two-dimensional electron gas in a magnetic field has been studied taking into account the scattering on point impurities. It is demonstrated that allowance for the electron-impurity interaction completely removes degeneracy of the Landau levels even for a small volume density of these point defects. The density of states is calculated in a self-consistent approximation taking into account all diagrams without intersections of the impurity lines. The electron density of states ρ is determined by the contribution from a cut of the one-particle Green’s function rather than from a pole. In a wide range of the electron energies ω (measured from each Landau level), the value of ρ(ω) is inversely proportional to the energy |ω| and proportional to the impurity concentration. The obtained results are applicable to various two-dimensional electron systems such as inversion layers, heterostructures, and electrons on the surface of liquid helium.     

Impact of dopants in GaN on the formation of two-dimensional electron gas in AlGaN/GaN heterostructure field-effect transistors

The two-dimensional electron gas distribution in AlGaN/GaN high electron mobility transistors is determined from the solution of the coupled Schr?dinger’s and Poisson’s equations. Considering the piezoelectric effect, the two-dimensional electron gas concentration is calculated to be as high as 7.7×10¹⁹ cm^-3. In order to obtain an understanding of how the two-dimensional electron gas distribution is influenced by dopants in GaN, we observed the two-dimensional electron gas concentration and occupation of sub-bands versus dopant concentration in the GaN layer of an AlGaN/GaN heterostructure. Our results show that the two-dimensional electron gas concentration is slightly increased at higher doping levels in GaN, while the quantum confinement in the AlGaN/GaN heterostructure is weakened with the increase of donor concentration in the GaN layer. Received: 26 May 2001 / Accepted: 23 July 2001 / Published online: 23 January 2002     

Anomalous Hall effect in a two dimensional electron gas with magnetic impurities

Magnetic impurities play an important role in many spintronics-related materials. Motivated by this fact, we study the anomalous Hall effect in the presence of magnetic impurities, focusing on two-dimensional electron systems with Rashba spin-orbit coupling. We find a highly nonlinear dependence on the impurity polarization, including possible sign changes. At small impurity magnetizations, this is a consequence of the remarkable result that the linear term is independent of the spin-orbit coupling strength. Near saturation of the impurity spins, the anomalous Hall conductivity can be resonantly enhanced, due to interference between potential and magnetic scattering.     

On the effect of far impurities on the density of states of two-dimensional electron gas in a strong magnetic field

The effect of impurities situated at different distances from a two-dimensional electron gas on the density of states in a strong magnetic field is analyzed. Based on the entire result of Brezin, Gross, and Itzykson, we calculate the density of states in the entire energy range, assuming the Poisson distribution of impurities in the bulk. It is shown that, in the case of small impurity concentration, the density of states is qualitatively different from the model case when all impurities are located in the plane of the two-dimensional electron gas.     

The conductivity of the spin-polarized two-dimensional electron gas: Exchange/correlation and strong disorder effects

The conductivity of a spin-polarized two-dimensional electron gas is calculated and compared with the conductivity of the unpolarized electron gas. Disorder effects are considered within the self-consistent current relaxation theory, which gives rise to a crossover point from metallic to insulating behavior. Many-body effects due to exchange and correlation are taken into account and are described by a local-field correction. Our calculations are in good agreement with recent experimental results on the magnetoresistance of silicon inversion layers.     

Estimation of various scattering parameters and 2-DEG mobilities from electron mobility calculations in the three conduction bands Γ, L and X of gallium arsenide

The electron drift mobility in Γ conduction band of GaAs has been calculated before, but for the first time, we have made attempts to estimate the electron mobilities in higher energy L and X minima. We have also calculated the value of mobility of two-dimensional electron gas needed to predict hetero-structure device characteristics using GaAs. Best scattering parameters have been derived by close comparison between experimental and theoretical mobilities. Room temperature electron mobilities in Γ, L and X valleys are found to be nearly 9094, 945 and 247 cm²/V-s respectively. For the above valleys, the electron masses, deformation potentials and polar phonon temperatures have been determined to be (0.067, 0.22, 0.39m ₀), (8.5, 9.5, 6.5 eV), and (416, 382, 542 K) as best values, respectively. The 2-DEG electron mobility in Γ minimum increases to 1.54 × 10⁶ from 1.59 × 10⁵ cm²/V-s (for impurity concentration of 10¹⁴ cm⁻³) at 10 K. Similarly, the 2-DEG electron mobility values in L and X minima are estimated to be 2.28 × 10⁵ and 1.44 × 10⁵ cm²/V-s at 10 K, which are about ∼4.5 and ∼3.9 times higher than normal value with impurity scattering present.      

Oscillations of the kinetic coefficients in a two-dimensional electron system with the spin-orbit interaction in an alternating magnetic field

The response of a two-dimensional electron system with the spin-orbit interaction to a measuring direct-current electric field is investigated for the case in which the system is disturbed from the equilibrium by a microwave alternating magnetic field. Point nonmagnetic impurities are considered as scattering sources. It is demonstrated that the combined transitions occurring under the action of an alternating magnetic field lead to new oscillations of the diagonal components of the electrical conductivity tensor of the two-dimensional electron gas.     

In-depth information from auger electron spectroscopy

In-depth information on impurity concentrations in the surface region of a solid can be obtained in a non-destructive way from Auger electron spectroscopy by varying the energy of the primary electrons. Examples are given for a silicon crystal covered by monolayers and multilayers of several types of impurity atoms.     

Minimum magnetocapacitance of a screened two-dimensional electron gas

A theory for the magnetocapacitance of a partially screened two-dimensional (2D) electron gas is proposed. The model investigated is sensitive to different types of screening in a 2D electron gas with an integer filling factor: the so-called conventional approach and the self-consistent approximation introduced in the present paper. The calculations point to the importance of the self-consistent treatment of the magnetocapacitance of a 2D electron gas under the conditions of an integer filling factor. The final self-consistent results are qualitatively consistent with the available experimental data. Fiz. Tverd. Tela (St. Petersburg) 39, 742–745 (April 1997)     

Collision-energy-resolved Penning ionization electron spectroscopy of toluene and chlorotoluenes

Stereodynamics in ionization of toluene and o-, p-chlorotoluenes by collision with He^*(2³S) metastable atoms were investigated by two-dimensional collision-energy/electron-energy-resolved Penning ionization electron spectroscopy. Anisotropic interactions around the molecule were studied by the collision energy dependence of partial ionization cross-sections (CEDPICS) as well as model potential calculations, and shielding effect by the methyl group was observed in CEDPICS for ionization from Cl lone-pair orbitals of o- chlorotoluene. Attractive interaction with He^*(2³S) around the π orbital region was found to be larger for toluene rather than o-, p- chlorotoluenes. Exterior electron density (EED) calculation of partial ionization cross-sections in Penning ionization and negative CEDPICS for ionization band observed in ca. 4 eV in electron energy indicated that π^-2π⁺¹ shake-up state was observed in Penning ionization electron spectroscopy of toluene.     

Off-centering of Pb and Sn impurities in GeTe induced by strong local stress

Noncentrality of large impurity atoms—Pb and Sn atoms—substituting for Ge atoms in a GeTe lattice has been discovered by means of EXAFS investigations in Ge_0.9Pb_0.1Te and Ge_0.85Sn_0.15Te samples. The transition of impurity atoms into a noncentral position under conditions of a strong local stress is explained by the participation of an unshared electron pair from the impurity atoms in the formation of the chemical bond. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 600–603 (25 April 1996)     

Low-temperature spin coulomb drag in a two-dimensional electron gas

The phenomenon of low-temperature spin Coulomb drag in a two-dimensional electron gas is investigated. The spin transresistivity coefficient is essentially enhanced in the diffusive regime, as compared to conventional predictions. The origin of this enhancement is the quantum coherence of spin-up and spin-down electrons propagating in the same random impurity potential and coupled via the Coulomb interaction. A comprehensive analysis of spin and interlayer Coulomb drag effects is presented.     

Non-Fermi-liquid behavior of compressible electron states on the lowest Landau level

Experiments show that at even denominator fractions (EDF) (7p = 1=2;3=4;3=2,...) the two-dimensional electron gas (2DEG) in a strong magnetic field becomes compressible, has no energy gap, and demonstrates the presence of an ostensible Fermi surface (FS). Since this phenomenon results from a minimization of the interaction, rather than the kinetic energy, the EDF states might well exhibit deviations from a conventional Fermi liquid (FL). We show that impurity scattering and its interference with electronelectron and electron-phonon interactions provide examples of intrinsically non-Fermi-liquid (NFL) transport at EDFs.     

Thermally induced spin polarization and thermal conductivities in a spin–orbit-coupled two-dimensional electron gas

The thermal conductivities and spin polarization induced by the temperature gradient are investigated in a Rashba spin–orbit-coupled two-dimensional electron gas. In this spin–orbit-coupled system in the presence of nonmagnetic or magnetic electron–impurity scattering, the Wiedemann–Franz law still holds. However, the spin polarization induced by the temperature gradient strongly depends on the property of impurities. The components of spin accumulation both perpendicular and parallel to the direction of the temperature gradient, and the thermally induced charge Hall conductivity may be nonzero for magnetic disorders.     

Two-dimensional electron gas at noble-metal surfaces

The electrons of the surface states on the (111) surfaces of the noble metals Au, Ag, and Cu form a quasi-two-dimensional (2D) free electron gas which is confined to the first few atomic layers at the crystal surface. They are scattered by the potential associated with surface defects, e.g. impurity atoms, adatoms, or step edges, leading to quantum-interference patterns in the local density of states around these defects. We have used the quantum-interference phenomena to quantitatively measure the electron phase-relaxation length and to probe long-range adsorbate interactions. Received: 12 October 2001 / Accepted: 23 October 2001 / Published online: 3 April 2002     

Evolution of vacancy defects in the surface layers of a metal irradiated with a pulsed electron beam

The distribution of vacancy defects in the surface layers of α-Fe after irradiation with a high-current pulsed electron beam is studied experimentally by unique nuclear-physical methods — low-energy positron annihilation, Rutherford backscattering (RBS), and proton-induced x-ray emission (PIXE). Regions with low local density, which are sources of crater formation on the surface of the irradiated sample, are observed by scanning a proton microbeam. Positron lifetime measurements reveal that as the electron beam power increases, nonequilibrium vacancies tend to be captured by carbon impurity atoms. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 618–622 (25 April 1997)     

Two-dimensional electron gas in a strong magnetic field. II

The quantum mechanical problem on the motion of electrons in a strong (quantizing the motion) magnetic field is considered, taking into account the Coulomb interaction between charges. It is shown how, on the basis of the solutions found, it is possible to obtain the fractional filling factor of the Landau levels that enters into the expression for the Hall conductivity of a two-dimensional electron gas.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 25–29, March, 1990.     

Vertex corrections to the anomalous Hall effect in spin-polarized two-dimensional electron gases with a Rashba spin-orbit interaction

We study the effect of disorder on the intrinsic anomalous Hall conductivity in a magnetic two-dimensional electron gas with a Rashba-type spin-orbit interaction. We find that anomalous Hall conductivity vanishes unless the lifetime is spin-dependent, similar to the spin Hall conductivity in the nonmagnetic system. In addition, we find that the spin Hall conductivity does not vanish in the presence of magnetic scatterers.