Martin Moško

ELECTRON CAPTURE IN QUANTUM WELLS VIA SCATTERING BY ELECTRONS, HOLES, AND OPTICAL PHONONS

Electron capture times due to the electron-electron (e-e), electron-hole (e-h) and electron-polar optical phonon (e-pop) interactions are calculated in the GaAs quantum well (QW) with electron and hole densities 10^11 cm^-2. The calculated capture times oscillate as a function of the QW width with the same period but with different amplitudes. The e-h capture time is two to four orders larger and the e-e capture time one to three orders larger than the e-pop capture time. The exceptions are the QW widths near resonance minima, where the e-e capture time is only 2-3 times larger and the e-h capture time 10-100 times larger. Different physical origin of the oscillatory behavior is demonstrated for the e-e and e-pop capture times. Effects of exchange and degeneracy on the e-e capture are analysed. The exchange effect increases the e-e capture time approximately two times while the degeneracy does not change the capture time except for the QW depths and widths near the resonance.

On the analytical approach to the real space electron transfer in GaAsAlGaAs heterostructures

Abstract Real space electron transfer (RSET) in modulation-doped heterostructures is analyzed in the frame of the analytical model for large layer widths (≥0.04 μ) proposed by Shichijo and co-workers (1980). It is shown that in high electric field parallel to the interface there is a discontinuity in electron temperature at the boundary between two materials. The model of Shichijo and co-workers (1980) is therefore modified using appropriate boundary condition for electron temperature. In order to compare the modified model with Shichijo and co-workers (1980) results their calculations are reexamined. We obtained different results which are qualitatively much closer to Monte Carlo results of Glisson and co-workers (1980). The inclusion of electron temperature discontinuity in modified model yields the results not very different from reexamined ones. Taking into account the nonparabolicity of the central valley the influence of the electron temperature discontinuity was found to be apparent. Our analytical approach is in good agreement with Monte Carlo calculations. The aptitude of the approach for heterostructures consisting of central valley dominated materials is discussed.

Carrier capture into a GaAs quantum well with a separate confinement region: comment on quantum and classical aspects

We study the optic-phonon-mediated carrier capture in a narrow GaAs quantum well with a 100 nm separate confinement region. In a standard quantum model capture means the carrier scattering from the energy subband above the quantum well into a subband in the quantum well. We use the quantum model in parallel with a classical model in which a classical carrier is captured during collisionless motion when emitting the optic phonon inside the GaAs layer. Comparison with the experiment of Blom et al (1993 Phys. Rev. B 47 2072) suggests that the quantum capture model is valid not only for electrons but also for heavy holes in the case of very narrow (2.6 nm) quantum wells. In the case of wider quantum wells the available experimental data support equally the quantum as well as classical hole capture models and do not allow us to draw a definite conclusion. Finally, the effect of the phonon confinement on the quantum capture is evaluated and discussed.

Electron–impurity scattering in free-standing quantum wires: Effect of dielectric confinement

We calculate the impurity-scattering limited mobility of the one-dimensional electron gas in a rectangular GaAs quantum wire confined in the vertical (growth) direction by n-modulation doped AlGaAs layers and free-standing along the transverse direction. The Fourier-transformed scattering potential of the ionized impurity is obtained analytically by solving the Poisson equation with z-dependent electrostatic permittivity. An abrupt permittivity change at the GaAs(AlGaAs)/air interfaces gives rise to the image charge effect which strongly modifies the unperturbed scattering potential. We show that the “image impurity” scattering tends to drastically reduce the electron mobility for sufficiently small (∼10 nm) transverse wire widths.

Energy exchange between heterostructure layers by real‐space electron transfer

Using Monte Carlo simulation we investigate electron transport in GaAs‐n‐AlxGa1−xAs heterostructure with high electric field applied parallel to the layer interface. Within a three‐dimensional electron gas model we study the energy exchange between adjacent layers caused by real‐space electron transfer (RSET). We have calculated an x‐dependent electron temperature Te(x), with x being the distance from the interface, and distribution function f(kx,x), where kx is a wave‐vector component perpendicular to the interface. Te(x) behavior clearly shows that the energy exchange between layers occurs: the electron temperature in the GaAs layer (high mobility—strong heating by field) is lower and that in the n‐AlxGa1−xAs layer (low mobility—weak heating by field) is greater than the corresponding bulk values. A peculiar feature of the electron temperature x dependence is its abrupt change at the interface. We have shown that the presence of temperature step is necessary for the energy exchange due to RSET and it sh...

Picosecond real-space electron transfer in GaAs-n-AlxGa1−xAs heterostructures with graded barriers: Monte Carlo simulation

Using Monte Carlo simulation combined with iterative solution of the Poisson equation the real‐space electron transfer (RSET) and negative differential conductivity (NDC) in GaAs–n‐AlxGa1−xAs heterostructures with electric field applied parallel to the layer interfaces have been investigated. The original Hess RSET model has been modified by considering graded AlxGa1−xAs layers with proper spatial dependence of the Al composition. Simulation results confirm that this modification enables one to avoid undesirable effects due to space‐charge fields: (1) Graded AlxGa1−xAs layers can be depleted in thermal equilibrium at higher donor concentrations than layers without compositional grading; (2) it is sufficient to use doped, but not compensated, AlxGa1−xAs layers because electron velocity in graded layers is low mainly due to electron transfer to L and X valleys; and (3) there is no confinement of cold electrons in graded AlxGa1−xAs layers due to space‐charge fields when the RSET occurs. The RSET‐induced NDC ...

Persistent current of correlated electrons in mesoscopic ring with impurity

The persistent current of correlated electrons in a continuous one-dimensional ring with a single scatterer is calculated by solving the many-body Schrodinger equation for several tens of electrons interacting via the electron-electron (e-e) interaction of finite range. The problem is solved by the configuration-interaction (CI) and diffusion Monte Carlo (DMC) methods. The CI and DMC results are in good agreement. In both cases, the persistent current I as a function of the ring length L exhibits the asymptotic dependence I α L -1-α typical of the Luttinger liquid, where the power a depends only on the e-e interaction. The numerical values of a agree with the known formula of the renormalization-group theory.

Possible persistent current in a ring made of the perfect crystalline insulator

Abstract A mesoscopic conducting ring pierced by magnetic flux is known to support the persistent electron current. Here we propose possibility of the persistent current in the ring made of the perfect crystalline insulator. We consider a ring-shaped lattice of one-dimensional “atoms” with a single energy level. We express the Bloch states in the lattice as a linear combination of atomic orbitals. The discrete energy level splits into the energy band which serves as a simple model of the valence band. We show that the insulating ring (with the valence band fully filled by electrons) supports a nonzero persistent current, because each atomic orbital overlaps with its own tail when making one loop around the ring. In the tight-binding limit only the neighboring orbitals overlap. In that limit the persistent current at full filling becomes zero which is a standard result.

States-conserving density of states for Altshuler-Aronov effect: Heuristic derivation

|E − EF | valid for |E − EF | smaller than a certain correlation energy Uco. Recent experiments have shown that at energies larger than Uco the DOS exhibits a states-conserving dependence on energy, namely, the states removed from near the Fermi level are found at energies above Uco in the energy range of about 3Uco. In this work the AA effect is studied beyond the low energy limit theoretically. We consider the AA model in which the electrons interact via the statically screened Coulomb interaction and the modification of the DOS is due to the exchange part of the electron selfenergy. We derive the states-conserving DOS heuristically. Namely, we show that the self-energy consists of a diverging part (which we skip on physical grounds) and of the small part of the order of the pair Coulomb energy. This small part gives the states-conserving DOS which is in qualitative accord with experimental observations at energies above Uco and which reproduces the AA result at energies below Uco.

Tunneling of interacting one-dimensional electrons through a single scatterer: Luttinger liquid behavior in the Hartree–Fock model

We study tunneling of weakly interacting spinless electrons at zero temperature through a single δ barrier in one-dimensional wires and rings of finite lengths. Our numerical calculations are based on the self-consistent Hartree-Fock approximation, nevertheless, our results exhibit features known from correlated many-body models. In particular, the transmission in a wire of length L at the Fermi level is proportional to L -2α with the universal power α (depending on the electron-electron interaction only, not on the strength of the δ barrier). Similarly, the persistent current in a ring of the circumference L obeys the rule I ∝ L -1-α known from the Luttinger liquid and Hubbard models. We show that the transmission at the Fermi level in the wire is related to the persistent current in the ring at the magnetic flux h/4e.