High Mobility 2D Electron Gas Research Articles

Optically detected cyclotron resonance in a high mobility 2D electron gas

We study the properties of high mobility GaAs/GaAlAs quantum well structure by monitoring the microwave induced changes in the low-temperature photoluminescence of the 2DEG as a function of the external magnetic field. The most pronounced changes are observed at cyclotron resonance conditions, but weak features are also visible at cyclotron resonance replicas. Possible observation of microwave induced shift in the Landau-level structure of magneto-photoluminescence is reported in addition to the effects of carrier heating which are conventionally bracketed together with microwave irradiation.

Magnetophonon resonance in a GaAs quantum well with AlAs/GaAs superlattice barriers at high filling factors

The magnetotransport of a high-mobility 2D electron gas in single GaAs quantum wells with AlAs/GaAs superlattice barriers is studied at high filling factors. For the selectively doped structures under study in the temperature range from 10 to 25 K, magnetoresistance oscillations periodic in the inverse magnetic field are observed with their frequency being proportional to the Fermi wave vector of the 2D electron gas. The experimental results are explained by the interaction of the 2D electron gas with leaky interface acoustic phonons.

Coherent scattering in a small quantum dot

Ballistic transport in an open small (100 nm) three-terminal quantum dot has been analyzed. The dot is based on the high-mobility 2D electron gas of the AlGaAs/GaAs heterojunction. It has been shown that the gate oscillations of the resistance of such a dot arise due to the coherent scattering of electrons on its quasidiscrete levels and these oscillations are suppressed by a weak magnetic field.

Large positive magnetoresistance in a high-mobility two-dimensional electron gas: Interplay of short- and long-range disorder

We have observed a large positive quasi-classical magneto-resistance (MR) in a high mobility 2D electron gas in AlGaAs/GaAs heterostructure. The magneto-resistance is non-saturating and increases with magnetic field as $\rho_{xx}\sim B^{\alpha} (\alpha=0.9-1.2)$. In antidot lattices a non-monotonic MR is observed. We show that in both cases this MR can be qualitatively described in terms of the theory recently advanced by Polyakov et al (PRB, 64, 205306 (2001)). Their prediction is that such behavior as we observe may be the consequence of a concurrent existence of short and long range scattering potentials.

Large positive quasi-classical magnetoresistance in high mobility 2D electron gas: interplay of short- and long-range disorder

We observed a giant positive quasi-classical magnetoresistance (MR) of high mobility 2D electron gas in AlGaAs/GaAs heterostructure. The MR is non-saturating and increases with the magnetic field as ρ xx ∼ B α ( α=0.9–1.2). In antidot lattice a non-monotonic behavior is observed. We show that the MR in both cases is well described by the recently advanced theory by Polyakov et al. (Phys. Rev. B 64 (2001) 205306) where non-saturating positive MR and non-monotonic MR in antidot lattice is predicted as the consequence of concurrent existence of short- and long-range scattering.

Conductance of a multiterminal ballistic wire

An experimental study of the two-, three-, and four-terminal resistance of a ballistic wire is carried out. The wire is fabricated on the basis of high-mobility 2D electron gas in an AlGaAs/GaAs heterojunction. Different behavior of mesoscopic fluctuations of multiterminal resistances is observed depending on the gate voltage and magnetic field. At B=0.45 T, the four-terminal resistance drops almost to zero and features resembling a ballistic conductance quantization are observed.

Magnetoresistance of a 2D electron gas caused by electron interactions in the transition from the diffusive to the ballistic regime.

On a high-mobility 2D electron gas we have observed, in strong magnetic fields (omega(c)tau>1), a parabolic negative magnetoresistance caused by electron-electron interactions in the regime of k(B)Ttau/ variant Planck's over 2pi approximately 1, which is the transition from the diffusive to the ballistic regime. From the temperature dependence of this magnetoresistance the interaction correction to the conductivity deltasigma(ee)(xx)(T) is obtained in the situation of a long-range fluctuation potential and strong magnetic field. The results are compared with predictions of the new theory of interaction-induced magnetoresistance.

A far infrared modulated photoluminescence (FIRM-PL) study of cyclotron resonance in a 2D electron gas in GaAs/AlxGa1-xAs heterojunctions

The new technique of far infrared modulated photoluminescence (FIRM-PL) has been used to study the properties of a high mobility 2D electron gas in a series of GaAs/AlGaAs heterojunctions. When the occupancy of the lowest Landau level is between 1 and 2 very large transfers of PL intensity are observed at the cyclotron resonance condition. The PL intensity is transferred from the E0 line to E1 corresponding to emission from the first two quantized electric subbands. A study of the power dependence of this signal allows us to deduce that the relative recombination efficiencies of the two lines are around five orders of magnitude different in such structures. This difference leads to a very high sensitivity of this technique for the observation of internal excitations within the electron system.

Magnetization of an incompressible two-dimensional electron gas

We have measured the magnetization of several single layer, high mobility 2D electron gases, using an ultra-sensitive torque magnetometer. Sharp diamagnetic jumps in the magnetization are observed when an integer number of Landau levels is filled. We relate these jumps to incompressibility gaps in the energy spectrum on the order of the cyclotron energy, in which a small fraction of the total number of states is present. We show that a simple hypothesis for the density of states with almost no Landau level overlap accounts for the observed shape of the magnetization oscillations. The spin-splitting of the Landau levels is observed as well, in particular at ν=1, and gives a measure of the enhancement of the g-factor.

2D lattice of coupled Sinai billiards: metal or insulator at g ≪ 1?

We investigate the transport in a two-dimensional (2D) lattice of coupled Sinai billiards fabricated on the basis of a high-mobility 2D electron gas in a GaAs/AlGaAs heterojunction in going from g>1 to g≪1 (where g=σ/(e2/h) is dimensionless conductivity). The data obtained suggest that the system studied behaves more like a metal than an insulator at g≪1 and is not described by the generally accepted picture of metal–insulator transition in 2D electron systems.

Magnetization and incompressibility of a high mobility 2D electron gas in the IQHE

We have measured the magnetization of a single layer, high mobility 2D electron gas in the quantum limit. Sharp diamagnetic jumps in the magnetization are observed when an integer number of Landau levels is filled. We relate these jumps to incompressibility gaps in the energy spectrum of the order of the cyclotron energy, in which a small fraction of the total number of states is present. The spin-splitting of the Landau levels is observed as well, in particular at ν=1, and gives a measure of the enhancement of the g-factor.

High mobility 2D electron gas in iodine modulation doped CdTe/CdMgTe heterostructures

High mobility 2D electron gas in iodine modulation doped CdTe/CdMgTe heterostructures

High mobility 2D electron gas in iodine modulation doped CdTe/CdMgTe heterostructures

We report on growth and characterization of modulation doped CdTe/Cd 1− y Mg y Te quantum well structures. Well resolved Shubnikov—de Haas oscillations and quantum Hall effect have been observed. In the best CdTe/Cd 1− y Mg y Te structures the modulation doping enabled fabrication of a two-dimensional electron gas with mobility exceeding 10 5 cm 2/V s. This is the highest mobility reported in wide-gap II–VI materials.

Magnetization and Energy Gaps of a High-Mobility 2D Electron Gas in the Quantum Limit

We have measured the magnetization of several single-layer, high-mobility 2D electron gas AlGaAs-GaAs heterostructures in the quantum limit. Abrupt jumps in the magnetization are observed when an integer number of Landau levels is filled. The width and the magnitude of the jumps identify incompressibility gaps in the energy spectrum of the order of the cyclotron energy, in which a small fraction of the total number of states is present. Sizable magnetization steps associated with the spin splitting are observed at odd filling factors (including $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$) and give a measure of the exchange enhancement of the spin splitting.

High Mobility 2D Electron Gas in CdTe/CdMgTe Heterostructures

We report on iodine doping of molecular beam epitaxy (MBE)-grown Cd(Mn)Te quasi-bulk films and modulation-doped CdTe/Cd1-yMgyTe two-dimensional (2D) single quantum well structures. Modulation doping with iodine of CdTe/Cd1y Mgy Te structures resulted in fabrication of a 2D electron gas with mobility exceeding 10 5 cm2 /(V s). This is the highest mobility reported in wide-gap II-VI materials. PACS numbers: 73.40.Hm

Effective masses in high-mobility 2D electron gas structures

Effective masses derived from the low-field Shubnikov-de Haas oscillations in high mobility GaAs/AlGaAs samples are found to decrease systematically with density. Measurements in a low-density sample show the temperature dependence does not conform to standard theory. It is argued that this is to be expected when there is extra structure, in addition to the Landau levels, in the density of states. This may be important in interpreting measurements of composite fermion effective masses.

Novel A-B type oscillations in a 2D electron gas in inhomogenous magnetic fields

We present results from a quantum and semiclassical theoretical study of the rho xy and rho xx resistivities of a high mobility 2D electron gas in the presence of a dilute random distribution of tubes with magnetic flux Phi and radius R, for arbitrary values of kfR and F=e Phi /h. We report on novel Aharonov-Bohm-type oscillations in rho xy and rho xx, related to degenerate quantum flux tube resonances, that satisfy the selection rule (kfR)2=4F(n+1/2), with n an integer. We discuss possible experimental conditions where these oscillations may be observed.

Transmitted acoustic phonon drag between parallel two-dimensional electron gases: Monte Carlo simulation

We present Monte Carlo (MC) simulation of transmitted acoustic phonon (TAP) drag between barrier-separated two-dimensional (2D) electron gases in the AlGaAs/GaAs system. Non-equilibrium acoustic phonons emitted by the hot 2D electron gas in the biased GaAs channel travel across the sample. These phonons are partially absorbed in an unbiased 2D channel where they induce a drag current. Simulation includes 2D electron-non-equilibrium acoustic phonon interaction for both deformation-potential and piezoelectric coupling. Non-equilibrium phonon distribution is calculated numerically. TAP drag is simulated at 4.2 K in a multiple quantum well containing equivalent high-mobility 2D electron gases. Drift velocities around 1000 m s-1 are found in the drag channel (2D gas without outer field), when it is driven by TAP drag from a large number (10-50) of 2D electron gases subjected to electric field of 1000 V m-1 TAP drag is mainly due to the deformation-potential coupling.

Anomalous classical diffusion of high mobility 2D electron gas in magnetic field.

It is well known that in a classically strong magnetic field, ${\mathrm{\ensuremath{\omega}}}_{\mathit{c}}$${\mathrm{\ensuremath{\tau}}}_{\mathit{t}}$\ensuremath{\gg}1 (${\mathrm{\ensuremath{\omega}}}_{\mathit{c}}$ is the cyclotron frequency and ${\mathrm{\ensuremath{\tau}}}_{\mathit{t}}$ is the transport relaxation time), the transverse conductivity is inversely proportional to magnetic field squared, ${\mathrm{\ensuremath{\sigma}}}_{\mathit{x}\mathit{x}}$=${\mathrm{\ensuremath{\sigma}}}_{0}$/(${\mathrm{\ensuremath{\omega}}}_{\mathit{c}}$${\mathrm{\ensuremath{\tau}}}_{\mathit{t}}$${)}^{2}$, wher ${\mathrm{\ensuremath{\sigma}}}_{0}$ is the conductivity without magnetic field. Such a dependence results from the lack of correlation of scattering events of an electron. This condition can be violated in a high mobility 2D gas, where the correlation length of the scattering potential is large. A strong correlation between scattering events results in an anomalous dependence of ${\mathrm{\ensuremath{\sigma}}}_{\mathit{x}\mathit{x}}$ on magnetic field.

Current switching and modulation based on electron interference in electron waveguides: a zero gap electron wave coupler

Summary form only given. The authors fabricated electron waveguide devices analogous to optical guided wave devices. Specifically, they made a zero gap electron wave coupler which demonstrated current switching and modulation based on electron interference in electron waveguides. Fabrication involves forming Schottky gate electrodes on the surface of a high-mobility 2D electron gas sample. Under appropriate reverse bias, areas under gate electrodes are depleted of electrons and conduction from one side to the other can only occur through the narrow and short channels. These channels behave as electron waveguides if their dimensions and temperature of operation are appropriate. >