Evgenii Moskalenko

The charged exciton in an InGaN quantum dot on a GaN pyramid

The emission of a charged exciton in an InGaN quantum dot (QD) on top of a GaN pyramid is identified experimentally. The intensity of the charged exciton exhibits the expected competition with that of the single exciton, as observed in temperature-dependent micro-photoluminescence measurements, performed with different excitation energies. The non-zero charge state of this complex is further supported by time resolved micro-photoluminescence measurements, which excludes neutral alternatives of biexciton. The potential fluctuations in the vicinity of the QD that localizes the charge carriers are proposed to be responsible for the unequal supply of electrons and holes into the QD.

Comparative Magneto-Photoluminescence Study of Ensembles and of Individual InAs Quantum Dots

We report on magneto-photoluminescence studies of InAs/GaAs quantum dots (QDs) of considerably different densities, from dense ensembles down to individual dots. It is found that a magnetic field applied in Faraday geometry decreases the photoluminescence (PL) intensity of QD ensembles, which is not accompanied by the corresponding increase of PL signal of the wetting layer on which QDs are grown. The model suggested to explain these data assumes considerably different strengths of suppression of electron and hole fluxes by a magnetic field. This idea has been successfully checked in experiments on individual QDs, where the PL spectra allow to directly monitor the charge state of a QD and, hence, to conclude about relative magnitudes of electron and hole fluxes toward the QD. Comparative studies of different individual QDs have revealed that the internal electric field in the sample (which was altered in the experiments in a controllable way) together with an external magnetic field will determine the charge state and emission intensity of the QDs.

Anomalous influence of magnetic field on the indirect exciton in GaAs/AlGaAs double quantum wells

A study is reported of exciton luminescence in GaAs double quantum wells produced in electric and magnetic fields. It has been found that the indirect-exciton line (IX) behaves anomalously, namely, one observes a magnetic-field-induced low-energy shift of the IX line, and the onset of periodic (≈5 s) fluctuations in the IX-line intensity.

Interaction of phonons with 2D exciton gas

Abstract We give an overview of experiments in which luminescence detection of nonequilibrium phonons in semiconductors is used to study the interaction of acoustic phonons with two-dimensional excitons. Question which are specific for the 2D exciton-phonon interaction are discussed: momentum conservation in the exciton-phonon interaction; role of exciton-exciton collisions; drag of 2D excitons by phonons; 2D excitons as a phonon spectrometer.

Influence of the magnetic field and measurement temperature on the shape of microphotoluminescence spectra of Eu-Doped InGaN/GaN quantum-well structures

Based on the results of complex investigations of the influence of the magnetic field strength and measurement temperature on the shape of microphotoluminescence (micro-PL) spectra of Eu-doped InGaN/GaN quantum-well structures, the determination of the charge state of Eu impurity ions, and the change in the concentration of dopant ions, it has been shown that an increase in the magnetic field strength (0–5 T) leads to a more significant decrease in the luminescence intensity as compared to the undoped structures. An increase in the measurement temperature from 4.2 to 78 K results in an enhancement of the effect of the magnetic field on the shape of the micro-PL spectra of Eu-doped InGaN/GaN structures. It has been demonstrated that the doping of InGaN/GaN quantum-well structures with europium at a high excitation level leads to a shift in the maximum of the luminescence intensity toward the long-wavelength range of the spectrum.

Effect of nonequilibrium acoustic phonons on exciton states in interrupted grown GaAs/Al0.33Ga0.67As quantum wells

We present the first studies of the effect of heat pulses on the exciton luminescence from GaAs/Al0.33Ga0.67As quantum wells (QW) prepared using growth interrupts to reduce the interface step density. We have observed the redistribution of excitons between the main thinner part and islands one monolayer thick of the QW induced by the heat pulses. The effect strongly depends on the relative position of heater and exciton gas and is discussed in terms of the drag of free excitons produced by “phonon wind”.

Magnetoluminescence of CdTe/MnTe/CdMgTe heterostructures with ultrathin MnTe layers

CdTe/MnTe/CdMgTe quantum-well structures with one or two monolayers of MnTe inserted at CdTe/CdMgTe interfaces were fabricated. The spectra of the excitonic luminescence from CdTe quantum wells and their variation with temperature indicate that introduction of ultrathin MnTe layers improves the interface quality. The effect of a magnetic field in the Faraday configuration on the spectral position of the exciton-emission peaks indicates that frustration of magnetic moments in one-monolayer MnTe insertions is weaker than in two-monolayer insertions. The effect of a magnetic field on the exciton localization can be explained in terms of the exciton wave-function shrinkage and obstruction of the photoexcited charge-carrier motion in the quantum well.

Circularly polarized emission from ensembles of InAs/GaAs quantum dots

We present a low-temperature micro-photoluminescence (mu-PL) study of ensembles of InAs/GaAs quantum dots (QDs) with respect to its circular polarization (rho(c)) for a manifold of experimental con ...

Effect of a magnetic field on energy transfer of band states to the Mn2+ 3d shell in the CdMgTe matrix with ultrathin CdMnTe layers

The effect of external magnetic fields on two radiative (band-to-band and on-site) recombination channels in II–VI dilute magnetic semiconductors and related nanostructures has been considered. The 3d on-site emission of manganese ions in CdMgTe matrices containing periodic inclusions of CdMnTe narrow-band-gap layers with thicknesses of 0.5, 1.5, and 3.0 monolayers has been investigated in magnetic fields of up to 6 T. It has been shown that, in a magnetic field, luminescence of manganese ions weakens because of the decrease in the rate of spin-dependent excitation transfer from band states to the Mn2+ 3d shell. The maximum suppression of 3d luminescence has been observed in the matrix with a CdMnTe layer 3.0 monolayers thick. This indicates that the main factor responsible for the energy transfer is the internal field near the CdMnTe layers, which determines the magnetic splitting and spin polarization of band states.

Temperature and magnetic field effects on the transport controlled charge state of a single quantum dot.

Individual InAs/GaAs quantum dots are studied by micro-photoluminescence. By varying the strength of an applied external magnetic field and/or the temperature, it is demonstrated that the charge state of a single quantum dot can be tuned. This tuning effect is shown to be related to the in-plane electron and hole transport, prior to capture into the quantum dot, since the photo-excited carriers are primarily generated in the barrier.