The growth and physics of ultra-high-mobility two-dimensional hole gas on (311)A GaAs surface

We report on the molecular beam epitaxy growth of modulation-doped GaAs-(Ga,Al)As heterostructures on the (311)A GaAs surface using silicon as the acceptor. Two-dimensional hole gases (2DHGs) with low-temperature hole mobility exceeding 1.2×10⁶ cm² V⁻¹ s⁻¹ with carrier concentrations as low as 0.8×10¹¹ cm⁻² have been obtained. This hole mobility is the highest ever observed at such low densities by any growth technique. We also report the first observation of persistent photoconductivity in a 2DHG. An analysis of the number density and temperature dependence of the mobility leads us to conclude that the mobility is limited by phonon scattering above 4 K and interface scattering at lower temperatures.     

Experimental observation of phase coherence in bilayer systems in the absence of a magnetic field

A high narrow peak of differential interlayer tunneling conductance is observed in the absence of a magnetic field at low temperatures in heterostructures with two closely spaced electron layers. The analysis of experimental results suggests that this peak is a consequence of the interlayer phase coherence, which arises in the system owing to the Bose condensation of interlayer excitons, i.e., pairs formed by electrons and holes belonging to different layers, in accordance with the recent theoretical predictions.     

PLE studies of two-dimensional hole systems in the quantum Hall regime

We report a spectroscopic investigation of the densities of both occupied and unoccupied states of a high-quality two-dimensional hole system, in the regime of the quantum Hall effects (QHEs). Photoluminescence and photoluminescence excitation spectroscopies are used to elucidate the complicated valence band structure of the holes, and to establish their optical response to the QHEs.     

Magnetic-field-induced Fermi-edge singularity in the tunneling current through an InAs self-assembled quantum dot

The results of the investigation of tunneling transport through a GaAs/(AlGa)As/GaAs single-barrier heterostructure containing InAs self-assembled quantum dots at low temperatures are reported. An anomalous increase in the tunneling current through the quantum dots has been observed in the presence of a magnetic field both parallel and perpendicular to the current. This increase is a manifestation of a Fermi-edge singularity appearing in the current due to the interaction of a tunneling electron with the electron gas in an emitter.     

Coulomb oscillations of the current through spin-nondegenerate <Emphasis Type="Italic">p</Emphasis> states of InAs quantum dots

The electron transport is studied in split-gate structures fabricated on the basis of a modulation-doped heterostructure that contains a single quantum well and self-assembled InAs quantum dots near the 2D electron gas regions. The current passing through the channel with a denumerable set of InAs quantum dots is found to exhibit Coulomb oscillations as a function of the gate voltage. The oscillations are associated with the excited p states of InAs quantum dots, which are characterized by opposite spins and caused by lifting of the spin degeneracy of the p state due to the Coulomb interaction. The Coulomb oscillations of the current are observed up to a temperature of ～20 K. The Coulomb energy is found to be ΔE_c = 12.5 meV, which agrees well with the theoretical estimates for the p states of quantum dots in the structures under study.     

Observation of the interaction between Landau levels of different two-dimensional subbands in GaAs in a normal magnetic field

Tunnel current measurements between strongly disordered two-dimensional electron systems in a perpendicular magnetic field are presented. Two-dimensional electron accumulation layers are formed by an extremely narrow layer of Si donors (Si delta doping) in GaAs on either side of an AlGaAs tunnel barrier. Strong interaction between Landau levels of the two-dimensional subbands in each accumulation layer is observed as an anticrossing of the related peak positions in the tunnel current vs. voltage curves as a function of magnetic field. The splitting of the interacting Landau levels is about 10 meV, which cannot be explained by nonparabolicity of the conduction band in GaAs. A possible reason for the observed interaction connected with the collective excitations in the 2DES is discussed.     

One-electron spin-dependent transport in split-gate structures containing self-organized InAs quantum dots

The paper presents the results obtained in a study of electron transport in split-gate structures prepared from heterostructures with self-organizing InAs quantum dots situated close to a two-dimensional electron gas. Coulomb oscillations of current through InAs quantum dots depending on the voltage on the gate were observed. Coulomb current oscillations persisted up to about 20 K. The Coulomb energy ΔE _C = 12.5 meV corresponding to theoretical estimates for the p-states of quantum dots in our structures was determined.     

Anomalous quantum Hall effect induced by nearby quantum dots

Transport measurements in high magnetic fields have been performed on two-dimensional electron system (2DES) separated by a thin barrier layer from a layer of InAs self-assembled quantum dots (QDs). Clear feature of quantum Hall effect was observed in spite of presence of QDs nearby 2DES. However, both magnetoresistance, ρ_xx, and Hall resistance, ρ_xy, are suppressed significantly only in the magnetic field range of filling factor in 2DES ν<1 and voltage applied on a front gate . The results indicate that the electron state in QDs induces spin-flip process in 2DES.