Alexei Vladimirovich Platonov

Ioffe Institute | ioffe · Laboratory of Solid State Spectroscopy

Photoluminescence and polarized reflection spectra of quantum well structures with symmetric Cd0.9Zn0.1Te/CdTe/Cd0.9Zn0.1Te and asymmetric Cd0.9Zn0.1Te/CdTe/Cd0.4Mg0.6Te barriers were studied. The Stokes parameters of the reflected light from these structures were measured. In structures with asymmetric barriers, in the region of exciton resonances...

Photoluminescence and polarized reflection spectra of quantum well structures with symmetric Cd$_{0.9}$Zn$_{0.1}$Te/CdTe/Cd$_{0.9}$Zn$_{0.1}$Te and asymmetric Cd$_{0.9}$Zn$_{0.1}$Te/CdTe/Cd$_{0.4}$Mg$_{0.6}$Te barriers were studied. The Stokes parameters of the reflected light from these structures were measured. In the structures with symmetric ba...

We have studied experimentally a series of samples of layered MoS 2 flakes with thicknesses varying from 1 to 10 μm and observed their strong in-plane optical anisotropy, which we attribute to the effects of strain in combination with fluctuations in the direction of the C-axis. This optical anisotropy allows us to convert the polarization of trans...

The dependences of the exciton-polariton photoluminescence spectra on the intensity of optical excitation and external magnetic fields are investigated in cylindrical mesas based on high-quality microcavities. It was found that with an increase of the intensity of optical excitation above a certain threshold at sufficiently large magnetic field or...

Bulk inversion asymmetry (BIA) of III-V and II-VI semiconductor quantum wells is demonstrated by reflection experiments in magnetic field oriented in the structure plane. The linear in the magnetic field contribution to the reflection coefficients is measured at oblique incidence of s and p polarized light in the vicinity of exciton resonances. We...

Photoluminescence spectra of an isolated GaAs quantum dot within an AlGaAs quantum wire are studied. The examination of behavior of spectra in a magnetic field provided an opportunity to estimate the exciton binding energy in the quantum dot, which turned out to be 10 times higher than the bulk exciton binding energy in GaAs. It is demonstrated tha...

Bulk inversion asymmetry (BIA) of III-V and II-VI semiconductor quantum wells is demonstrated by reflection experiments in magnetic field oriented in the structure plane. The linear in the magnetic field contribution to the reflection coefficients is measured at oblique incidence of $s$ and $p$ polarized light in vicinity of exciton resonances. We...

Polarization conversion of light reflected from quantum wells governed by both magnetic field and light propagation direction is observed. We demonstrate that the polarization conversion is caused by the magnetospatial dispersion in quantum wells which manifests itself in the reflection coefficient contribution bilinear in the in-plane components o...

Polarization conversion of light reflected from quantum wells governed by both magnetic field and light propagation direction is observed. We demonstrate that the polarization conversion is caused by the magneto-spatial dispersion in quantum wells which manifests itself in the reflection coefficient contribution bilinear in the in-plane components...

The optical activity of crystals leads to the occurrence of ellipticity at the reflection of light which is linearly polarized in the interface plane or normally to it. The effect experimentally discovered in the investigated structures with quantum wells is due to a spin-orbit interaction and birefringence. The qualitative dependence of the effect...

We report on the observation of optical activity of quantum wells resulting in the conversion of the light polarization state controlled by the light propagation direction. The polarization conversion is detected in reflection measurements. We show that a pure $s$-polarized light incident on a quantum well is reflected as an elliptically polarized...

Light amplification by stimulated emission of radiation, well-known for revolutionising photonic science, has been realised primarily in fermionic systems including widely applied diode lasers. The prerequisite for fermionic lasing is the inversion of electronic population, which governs the lasing threshold. More recently, bosonic lasers have also...

A new magnetooptical phenomenon referred to as the parity effect is predicted and observed. This effect takes the form of a redistribution of the exciton oscillator strength between spatially even and odd states of the exciton’s center of mass quantization in a wide quantum well.

In this paper we predicted and observed a new magneto-optical effect – the “effect of parity”. The effect is manifest as a redistribution of the oscillator strengths between spatially even and odd center of mass quantized states of the exciton in the quantum well. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Picosecond acoustic pulses, generated in a thin aluminum transducer, are injected into semiconductor vertical transport devices consisting of core-shell GaAsP nanowires. The acoustic pulses induce current pulses in the device with amplitude similar to 1 mu A. The spectrum of the electrical response is sensitive to the elastic properties of the devi...

We report on a study of the photoluminescence spectra taken from quasi one-dimensional and quasi zero-dimensional semiconductor heterostructures. The structures were grown by molecular-beam epitaxy in (111) direction and were cylindrical nanowires based on AlGaAs, of 20 - 50 nm in diameter and 0.5 - 1 μm in length. Inside the nanowires contain one...

The dependence of the spectra of the polarized photoluminescence of excitons in microcavities under conditions of three-dimensional quantization on the optical-excitation intensity is investigated. The cascade relaxation of polaritons between quantized states of a polariton Bose condensate is observed.

The magnetic field effect on phase transitions in electrically neutral bosonic systems is much less studied than those in fermionic systems, such as superconducting or ferromagnetic phase transitions. Nevertheless, composite bosons are strongly sensitive to magnetic fields: both their internal structure and motion as whole particles may be affected...

We report on a numerical model of quasi-1-D and quasi-0-dimensional semiconductor heterostructures. This model is strictly based on experimental structures of cylindrical nanocolumns of AlGaAs grown by molecular-beam epitaxy in the (1 1 1) direction. The nanocolumns are of 20-50 nm in diameter and 0.5-1 μm in length and contain a single GaAs quantu...

We report on a numerical model of quasi-1-D and quasi-0-dimensional semiconductor heterostructures. This model is strictly based on experimental structures of cylindrical nanocolumns of AlGaAs grown by molecular-beam epitaxy in the (1 1 1) direction. The nanocolumns are of 20-50 nm in diameter and 0.5-1 μm in length and contain a single GaAs quantu...

We present a numerical model of quasi one-dimensional and quasi zero-dimensional semiconductor heterostructures strictly based on experimental structures of polyphorm cylindrical nanocolumns.

The photoluminescence (PL) spectra of semiconductor structures, namely, Al0.3Ga0.7As-based quasi-one-dimensional cylindrical nanowires (nanowhiskers), are measured. The diameter of a typical nanowire is 20–50 nm, and its length was 0.5–1.0 μm. Samples containing one or several GaAs-based quantum dots at the center of the quantum wire are studied. T...

The results of a study into the photoluminescence spectra of a set of quantum dots based on GaAs enclosed in AlGaAs nanowires are presented. The steady state and time resolved spectra of photoluminescence under optical excitation both from an array of quantum wires/dots and a single quantum wire/dot have been measured. In the photoluminescence spec...

We report the photoluminescence characterization of GaAs quantum dots embedded in AlGaAs nanowires. Time-integrated and time-resolved photoluminescence was measured for both arrays and single quantum dot/nanowires. The optical spectroscopy data show the influence of growth temperature on the distribution of diameters and the presence of different c...

This paper reports on a study of the exciton polariton region in reflection spectra of wide CdTe/CdZnTe quantum wells (with well width exceeding by far the exciton Bohr radius) measured in Voigt geometry in a magnetic field. In a magnetic field, forbidden exciton lines were observed to appear for each exciton quantization level. The exciton diamagn...

Anisotropy of the relaxation of electron spin in AlGaAs quantum wells with an asymmetric profile in the growth-axis direction is studied by the technique of optical orientation. It is demonstrated that the difference between the Hanle curves for [110] and [1$ \bar 1 $ \bar 1 0] orientations does originate from the spin-relaxation anisotropy rather...

We report remarkable changes in the magnetic properties of excitons as they acquire kinetic energy in wide (001) quantum wells of CdTe, ZnSe, ZnTe and GaAs. In particular, the magnetic moments (g-values) when magnetic fields are applied in the growth direction are shown to. have a strong dependence on the translational wavevector K-z. The dependenc...

This paper overviews our recent results on the magneto-optics of excitons in wide quantum wells, when the well width is much larger than the exciton Bohr radius. We have demonstrated that the magnetic moment of the exciton increases by an order of magnitude due to its motion along the magnetic field. The effect was observed for a set of quantum wel...

We have observed remarkable changes in the magnetic properties of excitons as they acquire kinetic energy. In particular, the Zeeman splittings and diamagnetic shifts of excitonic transitions when magnetic fields are applied along the growth direction of (001) wide quantum wells of CdTe, ZnSe, ZnTe and GaAs are found to to have a strong dependence...

We summarize experimental studies on the optical polarization properties of MBE-grown shape-asymmetric self-assembled CdSe/ZnSe quantum dots (QDs). The zero magnetic field fine structure splitting of excitonic transitions in structurally anisotropic QDs gives rise to an effective linear-to-circular and circular-to-linear optical polarization conver...

The paper is an overview of recent studies of the optical anisotropy of heterostructures with quantum wells, quantum wires, and quantum dots based on cubic semiconductors. This subject area is essentially an extension of the research conducted by professor A.A. Kaplyanskii in the optical anisotropy of cubic crystals.

A new physical phenomenon has been found, namely a giant enhancement of the exciton magnetic moment due to its motion. This phenomenon was observed in GaAs, CdTe and ZnSe based quantum wells with QW widths much larger than the exciton Bohr radius. Consequently, it is relevant to any crystal with zinc blende structure.

Reflectivity and transmission spectra from wide GaAs and CdTe quantum wells (L=50–1000 nm) were studied in magnetic fields in Faraday geometry. The exciton Zeeman splitting was found to increase with the index N of the exciton quantization level. Since N is related to the magnitude of the exciton wave vector K, the observed effect means there is a...

Spin relaxation times of two-dimensional electrons in asymmetrical (001) AlGaAs quantum wells are measured by means of Hanle effect. Three different spin relaxation times for spins oriented along [110], [110] and [001] crystallographic directions are extracted demonstrating anisotropy of the D'yakonov-Perel' spin relaxation mechanism. The relative...

The observation of a new physical phenomenon, a giant increase in the longitudinal magnetic moment of an exciton in motion, is reported. The effect is observed in the wide GaAs-, CdTe-, and ZnSe-based quantum wells, with a width much larger than the exciton Bohr radius, and hence relates to any crystals with a zinc-blend structure.

We report remarkable changes in the magnetic properties of excitons as they acquire kinetic energy in wide (001) quantum wells of CdTe, ZnSe, ZnTe and GaAs. In particular, the magnetic moments (g-values) when magnetic fields are applied in the growth direction are shown to. have a strong dependence on the translational wavevector K-z. The dependenc...

We report a remarkable enhancement of the magnetic moments of excitons as a result of their motion. This surprising result, which we have observed in magneto-optical studies of three distinct zinc-blende semiconductors, GaAs, CdTe, and ZnSe, becomes significant as the kinetic energy of the exciton becomes comparable with its Rydberg energy and is a...

We present an experimental data, which demonstrate a basically new mechanism of carrier radiative recombination in semiconductor heterostructures-recombination via Tamm-like interface states. Bright line was observed in photoluminescence spectra of periodical ZnSe/BeTe heterostructures at the energies, which correspond to the optical transitions be...

Spin-relaxation times of two-dimensional electrons in asymmetrical (001) AlGaAs quantum wells are measured by means of Hanle effect. Three different spin-relaxation times for spins oriented along [110], [11¯0] , and [001] crystallographic directions are extracted demonstrating anisotropy of the D'yakonov-Perel' spin relaxation mechanism. The relati...

Resonant photoluminescence and photoluminescence excitation spectroscopy have been applied to CdSe/ZnSe quantumdots where separation between the quantized levels is close to the optical phonon energy. Astrong relaxation enhancement induced by the optical phonon is observed. The fine structure of the phonon replicas is resolved. It is attributed to...

We present comprehensive studies of in-plane optical anisotropy in CdSe/ZnSe quantum dot ensembles. The anisotropy reveals itself as circular-to-linear polarization conversion and as an alignment occurring at resonant excitation without any applied magnetic fields. The variation of the anisotropy in different dots has been analyzed based on angle s...

Spin relaxation of two-dimensional electrons in asymmetrical (001) AlGaAs quantum wells are measured by means of Hanle effect. Three different spin relaxation times for spins oriented along [110], [1-10] and [001] crystallographic directions are extracted demonstrating anisotropy of D'yakonov-Perel' spin relaxation mechanism. The relative strengths...

We report circular-to-linear and linear-to-circular conversion of optical polarization by semiconductor quantum dots. The polarization conversion occurs under continuous wave excitation in the absence of any magnetic field. The effect originates from quantum interference of linearly and circularly polarized photon states, induced by the natural ani...

We report on a complex nontrivial behavior of the optical anisotropy of quantum dots that is induced by a magnetic field in the plane of the sample. We find that the optical axis either rotates in the opposite direction to that of the magnetic field or remains fixed to a given crystalline direction. A theoretical analysis based on the exciton pseud...

Temperature dependent photoluminescence and reflectivity spectra of excitons, singlet and triplet states of trions were studied in CdTe-based quantum wells at high magnetic fields. Interesting features of the exciton and trion spectral lines with altering temperatures are explained by analyzing the thermal population and the kinetics of the exciton...

Reflectivity spectra from GaAs and CdTe based wide quantum wells (widths L = 50–1000 nm) have been studied in magnetic fields in Faraday geometry. The magnitude of the exciton Zeeman splitting has been found to grow with increase of the quantization index N for the exciton energy levels. Since N is related to the magnitude of the exciton wave vecto...

We report circular-to-linear and linear-to-circular conversion of optical polarization by semiconductor quantum dots. The polarization conversion occurs under continuous wave excitation in absence of any magnetic field. The effect originates from quantum interference of linearly and circularly polarized photon states, induced by the natural anisotr...

The spectral response of the lateral optical anisotropy of periodic undoped type-II ZnSe/BeTe heterostructures with nonequivalent interfaces was studied by ellipsometry. The spectra revealed two types of features corresponding to optical transitions with energies lying in the bandgap. The position of features of the first type does not depend on th...

Photoluminescence (PL) and reflectivity spectra from modulation-doped CdTe∕CdxMg1−xTe quantum well structures containing a two-dimensional electron gas have been studied in magnetic fields up to 45 T. In high fields, the recombination from the dark triplet trion state was found to be one of the most intense PL lines. A “bright” triplet line is reve...

Spectral response of lateral optical anisotropy of periodic undoped type-II ZnSe/BeTe heterostructures with nonequivalent interfaces has been studied by spectroscopic ellipsometry. The spectra revealed two types of features corresponding to optical transitions with energies lying in the bandgap. The position of features of the first type does not d...

Photoluminescence (PL) spectra of modulation‐doped CdTe/CdMgTe quantum well structures containing two dimensional electron gases different electron concentrations have been studied in magnetic fields up to 45T. Recombination line of triplet trion state was found in the spectra. A model calculation of PL spectra in magnetic fields, which takes into...

Photoluminescence spectra of modulation-doped CdTe/CdMgTe quantum well structures containing two-dimensional electron gases of low, moderate and high electron concentrations were studied in high magnetic fields up to 45 T. The recombination line of triplet trion state was found in the spectra. A model calculation of photoluminescence spectra in mag...

The in-plane anisotropy of the refractive index and absorption coefficient in the blue-green spectral region in ZnSe/BeTe type-II heterostructures with no common atoms at the interface has been studied by ellipsometry in reflection. It was established that the relative difference (anisotropy) in the refractive index and absorption coefficient remai...

Time-resolved and time-integrated circularly-polarized photoluminescence of excitons and trions have been studied in external magnetic fields up to 10 T. ZnSe-based quantum well structures of n-type with carrier densities varied from 5×109 to 1011cm-2 were used in this study. Absence of the chemical equilibrium in the exciton–trion system has been...

We report on the subpicosecond switch-off of the emission of an electrically pumped quantum-dot (QD) laser with perturbation by a 100 fs optical pulse. The observed effect is in contrast to known ones for quantum-well laser diodes. This is explained by unique properties of the QDs, namely by the fast modal gain saturation and localization-enhanced...

Circularly and linearly polarized radiation due to spatially indirect optical transitions is studied in semimagnetic (Zn,Mn)Se/BeTe and nonmagnetic ZnSe/BeTe quantum-well structures with a type-II band alignment. Because of the giant in-plane anisotropy of the optical matrix elements related to a particular interface, complete spin orientation of p...

This paper reports on transient switch-off of the emission of an electrically pumped quantum dot laser with perturbation by a short optical pulse. This laser response is explained in terms of hot carrier absorption on intraband optical transitions leading to the transient suppression of the laser mode and, hence, to the switch-off. The switching ti...

The polarization properties of indirect photoluminescence (PL) in ZnSe/BeTe quantum well structures with a type-II band alignment were studied experimentally and analyzed theoretically. The linear polarization degree appears with increasing density of photoexcitation. It is caused by an electric field along the structure growth axis induced by a sp...

Electroluminescence (EL) spectra are studied in the type-Il ZnSe/BeTe light emitting diode (LED) based on a single heterojunction. The light emitted from the surface exhibits a strong in-plane linear polarization along [110] crystal axis. The polarization is stable in respect to an increase of the applied voltage and temperature up to 300 K. The ex...

BeTe–ZnSe heterojunctions are interesting model systems, where the interface is made of materials which are almost lattice matched, but have no common anion nor cation. As a consequence, there are two interface configurations, which are basically reflected by a “ZnTe” and a “BeSe” interfacial layer. To a certain extent, the interface configuration...

The in-plane optical anisotropy of ZnSe/BeTe multi-layered heterostructures has been studied by analyzing the linear polarization of the spatially indirect photoluminescence. A pronounced quantum-confined Pockels effect is reported in ZnSe/BeTe double-barrier structures. A tight-binding model is proposed which consistently interprets the experiment...

The electric field-induced in-plane optical anisotropy (Pockels effect) of ZnSe/BeTe multi-layered heterostructures has been studied by analysing the linear polarization of the spatially indirect photoluminescence. A pronounced quantum-confined Pockels effect was found in ZnSe/BeTe double-barrier structures. A tight-binding model is proposed which...

Time-resolved and cw photoluminescence (PL) spectra are studied in type-II ZnSe/BeTe multiple quantum wells. Samples with nonequivalent interfaces exhibit a strong in-plane linear polarization of the PL along a axis. The polarization is stable with respect to an increase in the excitation intensity by many orders of magnitude, to a raising of the t...

The quantum confined Pockels effect has been observed in type-II ZnSe/BeTe quantum well structures. In order to describe the in-plane optical anisotropy induced by the electric field in type-II heterostructures, a theoretical approach has been developed which is based on the representation of optical matrix elements in the microscopical tight-bindi...

The photoluminescence spectra of type-II ZnSe/BeTe superlattices are investigated. Giant linear polarization of the luminescence is observed with unpolarized excitation in the spatially indirect exciton region. The effect is interpreted in a model of the general optical anisotropy of heterostructures with no common atom at the interfaces.

The polarized photoluminescence from localized interface states in a GaAs/AlGaAs single heterojunction have been studied as a function of magnetic field in Faraday geometry. A theoretical model of carrier trapping into these interface states has been developed. The effect of magnetic field on the spectra is discussed in terms of the field-dependent...

We have studied the reflectivity spectra of modulation-doped CdTe/Cd0.6Mg0.4Te and Cd1−xMnxTe/Cd0.6Mg0.4Te quantum well structures with a two-dimensional electron gas of low density. The evolution of exciton and trion parameters with the magnetic field has been analyzed. A strong modification of the exciton radiative and nonradiative damping parame...

Heterostructures with ZnSe quantum wells and different barrier materials (Zn1 − xMgxS1 − ySey and Zn1 − xBexSe) are investigated by means of photoluminescence and reflectivity in external magnetic fields up to 20 T. Up to four exciton excited states are well-resolved in the photoluminescence excitation spectra of undoped structures. Model calculati...

The contribution of inelastic processes to exciton–electron scattering in quantum well (QW) structures with two-dimensional electron gas of low density has been studied. The additional exciton damping caused by exchange scattering have been found to be comparable with the exciton damping caused by direct exciton–electron scattering.

Photoluminescence spectra of type-II ZnSe/BeTe superlattices were studied. A linear polarised photoluminescence has been found in the spectral range of spatially indirect exciton transitions. This observation is interpreted in a model of optical anisotropy of heterostructures with no-common atom at interfaces.

A study of reflectance spectra from thin ZnSxSe1−x solid-solution layers in the region of excitonic resonances is reported. It has been found that an increase in sulfur concentration in the layers increases the inhomogeneous broadening of the quantized polariton lines. It has been established that the inhomogeneous line broadening in a reflectance...

We present an optical study of novel ZnSe/BeTe heterostructures with a type-II band alignment based on beryllium chalcogenides. A strong exciton transition involving a confined electron and a quasibound hole state (both in the ZnSe layer) is observed in photoluminescence, photoluminescence excitation and reflectivity spectra. This exciton state is...

The theory of resonant optical reflection from long-period multiple quantum-well structures has been extended to take into account the difference between the dielectric constant of the barrier, εb, and the nonresonant contribution, εa, to the dielectric function in the wells. The reflection spectra taken from CdTe/CdMgTe quasi-Bragg quantum wells r...

Results of an optical study of heterostructures based on new compounds, ZnSe/ZnMgSSe, are presented. The possibility of using these compounds to produce high-quality quantum-well structures having strong exciton features in optical spectra is demonstrated. An analysis of reflectance spectra has yielded the exciton parameters: the resonant frequency...

Theory of specular light reflection from long-period quantum-well structures taking into account the exciton contribution to dielectric polarization has been developed for an arbitrary relation between the background refractive index in the well, n a, and barrier-material refractive index nb. General expressions for the optical reflection and trans...

We present an optical investigation of novel heterostructures based on beryllium chalcogenides with a type-I and type-II band alignment. In the type-II quantum well structures (ZnSe/BeTe) we observed a strong exciton transition involving an electron confined in the conduction band well and a hole localized in the valence band barrier (both in ZnSe...

A method has been developed for recording and analyzing the differential magnetoreflection (magnetotransmission) spectra of semiconductor structures with quantum wells. The method was used to determine the exciton g-factor in semimagnetic CdTe/(Cd, Mn)Te heterostructures with quantum wells. In nonmagnetic structures with quantum wells containing a...

Summary Photoluminescence excitation experiments have been performed with a non-intentionally doped GaInAs/AlGaInAs superlattice lattice-matched to an InP substrate. The superlattice is the intrinsic part of a p-i-n diode. We have observed the 1s and 2s heavy-hole exciton states and the Wannier-Stark ladder associated to the light-hole exciton. Thr...

The annular dependence of reflection spectra was used to measure the dispersion of the refractive index of Zn{sub 1-x}CdâSe epitaxial layers within a broad spectral range in the transparency region at 77 and 300 K for Cd concentrations x = 0, 0.14, and 0.2. 4 refs., 3 figs., 1 tab.

An effect of optical orientation of electrons and Hanle effect was studied in GaAs-based asymmetrical quantum well structures. It has been found that the width of Hanle depolarization curve in the asymmetrical quantum well depends strongly on the orientation of magnetic field relatively to the crystallographic axes of the sample. An explanation of...