Yu. N. Khanin

Resonant tunneling and photoluminescence spectroscopy in quantum wells containing self-assembled quantum dots

We investigate the optical and electrical properties of n-i-n GaAs/(AlGa)As double barrier resonant tunneling diodes (RTDs) in which a layer of InAs self-assembled quantum dots (QDs) is embedded in the center of the GaAs quantum well. A combination of photoluminescence (PL) and electrical measurements indicates that the electronic states and charge distribution in this type of RTD are strongly affected by the presence of the dots. Also, the dot PL properties depend strongly on bias, being affected by tunneling of majority (electrons) and minority (photocreated holes) carriers through the well. The measurements demonstrate nonlinear effects in the QD PL by means of resonant tunneling and the possibility of using the dot PL as a probe of carrier dynamics in RTDs.

Sensitive detection of photoexcited carriers by resonant tunneling through a single quantum dot

We show that the resonant tunnel current through a single energy level of an individual quantum dot within an ensemble of dots is strongly sensitive to photoexcited holes that become bound in the close vicinity of the dot. The presence of these holes lowers the electrostatic energy of the quantum dot state and switches the current carrying channel from fully open to fully closed with a high on/off ratio (> 50). The device can be reset by means of a bias voltage pulse. These properties are of interest for charge sensitive photon counting devices.

Nonlinear electron transport in normally pinched-off quantum wire

Nonlinear electron transport in normally pinched-off quantum wires was studied. The wires were fabricated from AlGaAs/GaAs heterostructures with high-mobility two-dimensional electron gas by electron beam lithography and following wet etching. At certain critical source-drain voltage the samples exhibited a step rise of the conductance. The differential conductance of the open wires was noticeably lower than e2/h as far as only part of the source-drain voltage dropped between source contact and saddle point of the potential relief along the wire. The latter limited the electron flow injected to the wire. At high enough source-drain voltages the decrease of the differential conductance due to the real space transfer of electrons from the wire in GaAs to the doped AlGaAs layer was found. In this regime the sign of the differential magnetoconductance was changed with reversing the direction of the current in the wire or the magnetic field, when the magnetic field lies in the heterostructure plane and is directed perpendicular to the current. The dependence of the differential conductance on the magnetic field and its direction indicated that the real space transfer events were mainly mediated by the interface scattering.

Anisotropy of electronic wave functions in self-assembled InAs dots embedded in the center of a GaAs quantum well studied by magnetotunneling spectroscopy

We present an experimental study of electron wave functions in InAs/GaAs self-assembled quantum dots by magnetotunneling spectroscopy. The electronic wave functions have a biaxial symmetry in the growth plane, with axes corresponding to the main crystallographic directions in the growth plane. Moreover, we observed the in-plane anisotropy of the subbands of the quantum well.

Magnetic field variation of tunnelling gap between disordered two-dimensional electron systems

Abstract We have investigated tunnelling between disordered two-dimensional electron systems in a magnetic field parallel to the current. At liquid-helium temperatures, the high magnetic field creates a gap in the tunnelling density of states that depends linearly on magnetic field. The temperature dependence of the magnetic field variation of the equilibrium tunnelling conductance reveals features which could be interpreted as a manifestation of the insulator-quantum Hall-insulator transition.

Magnetic-field-induced singularity in the tunneling current through an InAs quantum dot

The tunneling transport through a GaAs/(AlGa)As/GaAs single-barrier heterostructure with self-assembled InAs quantum dots is studied experimentally at low temperatures. An anomalous increase in the tunneling current through the quantum dots is observed in magnetic fields both parallel and perpendicular to the current. This result cannot be understood in the framework of the single-electron approximation. The proposed explanation of the phenomenon is based on the modified Matveev-Larkin theory, which predicts the appearance of a singularity in the tunneling current through the zero-dimensional state in a magnetic field because of the interaction between the tunneling electron and the spin-polarized three-dimensional electron gas in the emitter. The absence of spin splitting in the experimental resonance peaks is caused by the complete spin polarization of the emitter in relatively weak magnetic fields.

Probing the electronic properties of disordered two-dimensional systems by means of resonant tunnelling

We investigate resonant tunnelling in GaAs/(AlGa)As double-barrier resonant-tunnelling diodes in which a single layer of InAs self-assembled quantum dots is embedded in the centre of the GaAs quantum well. The dots provide a well-defined and controllable source of disorder in the well and we use resonant tunnelling to study the effect of this disorder on the electronic properties of the well.

Suppression of the equilibrium tunneling current between slightly disordered two-dimensional electron systems with different electron concentrations in a high magnetic field

Tunneling between parallel two-dimensional electron gases (2DEG) in accumulation layers formed on both sides of the single doped AlGaAs barrier are examined in both zero and high magnetic field. Accumulation layers are separated from highly n-doped contact regions which freely supply electrons to the 2DEGs via 80 nm thick lightly n-doped spacer layers. Strongly oscillating current with magnetic field along the 2DEGs is absent in this arrangement. Without magnetic field resonant tunneling between 2DEGs with different as grown electron concentration could be settle by application of external voltage bias. High magnetic fields (ν<1) shift resonant tunneling to zero external bias and suppresses tunneling current, creating wide gap in the tunneling density of states at the Fermi level arisen from the in-plane Coulomb interaction in the 2DEGs.

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.

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 ΔEC = 12.5 meV corresponding to theoretical estimates for the p-states of quantum dots in our structures was determined.