Vladimir A. Sablikov

Charging of deep-level centers and negative persistent photoconductivity in modulationdoped AlGaAs/GaAs heterostructures

The relaxation kinetics of persistent photoconductivity in AlGaAs/GaAs modulation-doped heterostructures due to charging of EL2-and DX-centers is investigated over a wide range of temperatures and excitation photon energies. The light-induced charging of these deep centers was found to lead to accumulation of positive and negative localized charges, which give rise to positive and negative persistent photoconductivities, respectively. These positive and negative charges are accumulated in different parts of the heterostructure. Their different characteristic times, and the different temperature dependences of these times, result in nonmonotonic time and temperature dependences of the persistent photoconductivity. Charging of EL2-centers in the GaAs buffer layer leads to negative persistent conductivity in the temperature range 180–300 K, while the negative photoconductivity observed at the temperatures below 180 K is caused by excited states of DX-centers in the n+-AlGaAs.

Piled up charge effects in a ballistic transport in quantum wires

Abstract We have found that a high-field domain appears in a quantum wire with ballistic transport under far from equilibrium condition. The domain is located near the injecting electrode. The applied voltage drops mainly across the domain while the rest part of the wire remains nearly equipotential. The potential hump in the domain limits the current through the wire.

Optical reflection in semiconductor structures modulated by radio-frequency electric fields

We propose a contactless technique of modulation spectroscopy for semiconductors which is based on the AC electric field effect on the probing light beam reflection. This technique allows one to investigate the distribution of both built-in and induced electric fields as well as the electron-hole interaction effects in various layers of the semiconductor structure. The measured spectra are explained by a combination of the interband transitions in the high-field (Franz-Keldysh effect) and low-field regimes, the transitions via exciton states and the temperature effect. The model is developed which allows one to describe quantitatively the spectra observed on the modulation-doped heterostructures GaAs/AlGaAs.

Metastable-state formation as a possible mechanism for the conductance anomalies in mesoscopic structures

We study metastable-state formation in the one-dimensional model of a quantum ballistic contact, in which the contact is represented by a potential barrier with electron-electron interaction localized therein. It is shown that when the interaction parameter exceeds a critical value, a metastable state with spontaneous spin polarization of the barrier is formed. The difference between the grand potentials of the metastable and globally stable states tends to zero at the critical point; therefore, the metastable state manifests itself in transport even at low temperatures and its effect gradually increases with temperature. The main effect is a decrease in the conductance with increasing temperature, which occurs in a certain range of the barrier-region potential, similar to that observed during the formation of the well-known 0.7 conductance anomaly.

Intersubband electron interaction in 1D–2D junctions

It is shown that the electron transport through junctions between one-and a two-dimensional systems and through quantum point contacts is considerably affected by the interaction of electrons belonging to different subbands. The interaction mechanism is related to Friedel oscillations, which are produced by the electrons of the closed subbands even in smooth transitions. Because of the interaction with these oscillations, electrons of the open subbands experience a backscattering. The electron reflection coefficient has a sharp peak at the energy equal to the Fermi energy and may reach a value of about 0.1. This result allows one to explain a number of available experimental facts.

Origin of current instability in GaAs/AlGaAs heterostructures

Abstract We propose a mechanism to explain the electric instability often observed in modulation-doped heterostructures GaAs/AlGaAs when current is passed along the heterostructure layers. The instability is caused by hot electron transport in AlGaAs layer that is not only heavily doped, but also strongly compensated due to the presence of DX-centers. This layer contains a large-scale random potential of significant magnitude, which strongly affects electron transport. The heating of electrons in the percolation cluster net and electron transfer from the cluster into the random potential wells result in the appearance of latent negative differential conductivity causing the current instability. When the instability gives rise to the formation of a high electric field domain, one of the domain walls blocks the current flow through the two-dimensional electron gas. Experimental results supporting this mechanism are given.

Effect of lateral transport of photoinduced charge carriers in a heterostructure with a two-dimensional electron gas

It is shown that the nonequilibrium charge carriers produced by a local optical disturbance of the heterostructure with a two-dimensional electron gas are transported in the plane of the structure over an extremely large distance from the excitation location, which greatly exceeds the diffusion length in the bulk. The effect is attributable to the fact that the photogenerated electrons and holes are separated by the built-in electric field of the heterojunction to opposite edges of the buffer layer, where they are transported along parallel planes. The distance over which the nonequilibrium carrier density spreads reaches large values because of 1) the high conductivity of two-dimensional electrons, 2) the barrier for electron-hole recombination, and 3) hole drift in the electric field produced by the charge of nonequilibrium carriers in the plane of the structure.

Spin-polarized currents in the tunnel contact of a normal conductor and a two-dimensional topological insulator

The spin filtering of electrons tunneling from the edge states of a two-dimensional topological insulator into a normal conductor under a magnetic field (external or induced due to proximity to a magnetic insulator) is studied. Calculations are performed for a tunnel contact of finite length between the topological insulator and an electronic multimode quantum strip. It is shown that the flow of tunneling electrons is split in the strip, so that spin-polarized currents arise in its left and right branches. These currents can be effectively controlled by the contact voltage and the chemical potential of the system. The presence of a magnetic field, which splits the spin subbands of the electron spectrum in the strip, gives rise to switching of the spin current between the strip branches.

Rectification effect in a quantum contact

The rectification of current has been observed in a quasi-one-dimensional ballistic quantum channel. The effect is explained by the asymmetry of the potential profile in the channel. The dependence of the rectified current on the height of the potential barrier in the channel exhibits sharp maxima, which are associated with conductance quantization steps. A model of the rectification is proposed.

Effect of local optical excitation on semiconductor heterostructures with 2D electron gas

An effect of local illumination on layered semiconductor heterostructures with 2D electron gas is investigated by measuring the spatial distribution of the photoreflectance and photoluminescence intensity varying the distance between the excitation spot and the probing position.