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A trion magnetic polaron formed by the exchange interaction of a positively charged exciton (trion) with localized spins of Mn$^{2+}$ ions is found experimentally in a 4\,nm wide Cd$_{0.98}$Mn$_{0.02}$Te/Cd$_{0.78}$Mn$_{0.02}$Mg$_{0.2}$Te quantum well containing resident holes. The experiment is performed at a temperature of 1.6 K using resonant excitation of the trion with circularly polarized light. The trion is formed from a resident hole, which is in a hole magnetic polaron state, and a photogenerated electron-hole pair. The dynamical evolution from the hole magnetic polaron to the trion magnetic polaron is accompanied by a spin-flip of the electron, which results in negative circular polarization of the photoluminescence. The degree of circular polarization reaches $-8\%$ at zero magnetic field and strongly decreases in transverse magnetic fields exceeding 0.2 T. Our model considerations show that different localization sizes of the resident and photogenerated holes and the resulting difference in their exchange interaction with the Mn$^{2+}$ spins maintains Mn spin polarization. The resulting exchange field of Mn acting on the electron provides a robust spin polarization of the trion magnetic polaron. We evaluate the electron exchange energy in the T$^+$MP to be 0.19~meV, and the T$^+$MP binding energy to be about 0.5 - 1 meV.

Measurements of magnetotransport in SnTe/PbTe heterojunctions grown by the MBE technique on (001) undoped CdTe substrates were performed. At low magnetic fields, quantum corrections to conductivity were observed that may be attributed to the presence of topological states at the junction interface. For a sample with 5 nm thick SnTe layer, the data analysis suggests that midgap states are actually gapped. However, the phase coherence effects in 10 nm and 20 nm SnTe/PbTe samples are fully explained assuming existence of gapless Dirac cones. Magnetotransport at higher magnetic fields is described in the framework of mobility spectrum analysis (MSA). We demonstrate that the electron- and hole-like peaks observed simultaneously for all SnTe/PbTe heterojunctions may originate from the concave and convex parts of the energy isosurface for topological states -- and not from the existence of quasiparticles both carrying negative and positive charges. This interpretation is supported by numerical calculations of conductivity tensor components for gapless (100) Dirac cones, performed within a classical model and based on the solutions of Boltzmann transport equation. Our approach shows the feasibility of MSA in application to magnetotransport measurements on topological matter.

The reflection and luminescence spectra of a CdTe/CdMgTe heterostructures doped with iodine are studied. Iodine was introduced either into a barrier layer or into a wide CdTe quantum well. It is shown how the doping method and level affect the spectra and the temperature dependence of the quantum well exciton emission intensity.

In tunnel-coupled quantum wells of different widths, it was found that the spin dynamics arising from resonant pulsed optical pumping of an exciton in the narrow well includes the dynamics of electron spin polarization in the wide well, although the electron level in the wide well is 55 meV lower than the electron level in the narrow well. An analysis of the obtained results showed that the observed effect is caused by the exchange interaction of spin-polarized electrons in the wide well with exciton states in the narrow well.

Voltage control of ferromagnetism on the nanometer scale is highly appealing for the development of novel electronic devices with low power consumption, high operation speed, reliable reversibility and compatibility with semiconductor technology. Hybrid structures based on the assembly of ferromagnetic and semiconducting building blocks are expected to show magnetic order as a ferromagnet and to be electrically tunable as a semiconductor. Here, we demonstrate the electrical control of the exchange coupling in a hybrid consisting of a ferromagnetic Co layer and a semiconductor CdTe quantum well, separated by a thin non-magnetic (Cd,Mg)Te barrier. The electric field controls the phononic ac Stark effect—the indirect exchange mechanism that is mediated by elliptically polarized phonons emitted from the ferromagnet. The effective magnetic field of the exchange interaction reaches up to 2.5 Tesla and can be turned on and off by application of 1V bias across the heterostructure., Manipulating magnetic orders by electric fields promises energy efficient spintronic applications. Here the authors demonstrate electrical control of s-p exchange interaction in a ferromagnet-semiconductor quantum well structure due to the phononic ac Stark effect.

Molecular beam epitaxy was applied to evaporate a set of Au/ZnTe:I/CdTe:I/GaAs/In heterostructures. The resulted heterostructures were examined for photovoltaic energy conversion application. Electrical characteristics were studied for understanding the relevant electrical transport mechanisms. The current–voltage (I–V) characteristics were checked under dark and light conditions. Ideality factor indicates the recombination mechanisms in the designed device; its value equals (3.22). Under various light intensities (1–140 mW cm−2), the I–V curves are affected highly by reverse voltage bias. The open-circuit voltage increases exponentially with the illumination and its values of this device increased with increasing light intensity (L), where 55 mV at 1 mW cm−2 and 465 mV at 140 mW cm−2. Electrical as well as power related parameters of the designed device were interpreted. Photosensitivity and Responsitivity of the studied device showed a high photoresponse under different light intensities. Au/ZnTe:I/CdTe:I/GaAs/In heterostructures is a promising material for photosensor and optoelectronic applications.

ZnTe/CdSe/(Zn,Mg)Te core/double-shell nanowires are grown by molecular beam epitaxy by employing the vapor-liquid-solid growth mechanism assisted with gold catalysts. A photoluminescence study of these structures reveals the presence of an optical emission in the near infrared. We assign this emission to the spatially indirect exciton recombination at the ZnTe/CdSe type II interface. This conclusion is confirmed by the observation of a significant blue-shift of the emission energy with an increasing excitation fluence induced by the electron-hole separation at the interface. Cathodoluminescence measurements reveal that the optical emission in the near infrared originates from nanowires and not from two dimensional residual deposits between them. Moreover, it is demonstrated that the emission energy in the near infrared depends on the average CdSe shell thickness and the average Mg concentration within the (Zn,Mg)Te shell. The main mechanism responsible for these changes is associated with the strain induced by the (Zn,Mg)Te shell in the entire core/shell nanowire heterostructure., Comment: 7 pages

The photoluminescence (PL) and PL excitation (PLE) spectra of CdTe/ZnTe asymmetric double quantum well (QW) structures are studied on a series of samples containing two CdTe layers with nominal thicknesses of 2 and 4 monolayers (ML) in the ZnTe matrix. The samples differ in the thickness of the ZnTe spacer between CdTe QWs which is 45, 65 and 75 ML. It has been found that at above-barrier excitation the PL from a shallow QW at sufficiently weak excitation intensities is determined by recombination of hot excitons. It is shown that under these conditions, when PL is excited by lasers with different wavelengths, the ratio of the PL intensities from shallow and deep QWs decreases exponentially with an increase of the initial kinetic energy of hot excitons. It is found that energy relaxation of hot excitons with LO phonon emission determine the shape of the PLE spectrum of shallow QW in the range of exciton kinetic energies up to more than 20 LO phonons above ZnTe bandgap. We have shown that the results obtained are well described by the model of charge and energy transfer between QWs.

We study the magnetic-field dependence of the longitudinal spin relaxation time ${T}_{1}$ of donor-bound electrons placed in the middle of an 8-nm CdTe quantum well with different doping concentrations in the range from $1\ifmmode\times\else\texttimes\fi{}{10}^{9}$ to $2.9\ifmmode\times\else\texttimes\fi{}{10}^{11}$ $\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$ and at low temperature. We use an extended photoinduced Faraday rotation technique, which expands the usual domain of the measured decays from tens of ns to $\ensuremath{\mu}\mathrm{s}$. As in high-purity bulk semiconductors, a maximum relaxation time of around ${T}_{1}\ensuremath{\sim}10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$ is observed for a residually doped sample at low magnetic field of $B=0.08\phantom{\rule{0.16em}{0ex}}\mathrm{T}$. For higher doping concentrations, the magnetic-field dependence of ${T}_{1}$ shows a nonmonotonic behavior: first a rapid increase, followed by a plateau or a decrease of ${T}_{1}$. The fast increase of ${T}_{1}$ at low magnetic fields is explained by the inhibition of the mechanisms identified at zero field---hyperfine and anisotropic exchange interactions---while the behavior at high magnetic field can be succesfully explained by a mechanism proposed by Lyubinskiy and associated to electron hops [I. S. Lyubinskiy, JETP Lett. 88, 814 (2008)]. A good agreement between experiment and theory is found for samples below the metal-insulator transition, when Dresselhaus terms of spin-orbit coupling are considered to be the dominant ones in the Hamiltonian describing the system.

Optical control of electronic spins is the basis for ultrafast spintronics: circularly polarized light in combination with spin-orbit coupling of the electronic states allows for spin manipulation in condensed matter. However, the conventional approach is limited to spin orientation along one particular orientation that is dictated by the direction of photon propagation. Plasmonics opens new capabilities, allowing one to tailor the light polarization at the nanoscale. Here, we demonstrate ultrafast optical excitation of electron spin on femtosecond time scales via plasmon to exciton spin conversion. By time-resolving the THz spin dynamics in a hybrid (Cd,Mn)Te quantum well structure covered with a metallic grating, we unambiguously determine the orientation of the photoexcited electron spins which is locked to the propagation direction of surface plasmon-polaritons. Using the spin of the incident photons as additional degree of freedom, one can orient the photoexcited electron spin at will in a two-dimensional plane., main text 23 pages, 5 figures. Supplementing material with 6 figures

We report the observation of tens of minor lines of the combinational spin-flip Raman scattering in a CdTe:Mn quantum well by means of the high-resolution optical spectroscopy. Classification of this manifold leads to four characteristic values of energy, that correspond to four different types of pair clusters of Mn ions: the nearest, second, third, etc., neighbors. All the four energies show up in a single experiment with a very high precision, providing experimental grounds for a deeper understanding of the $d\ensuremath{-}d$ exchange interactions in a diluted magnetic semiconductor and demonstrating the capacity of the employed method. The major (nearest-neighbor) exchange constant ${J}_{1}=6.15\ifmmode\pm\else\textpm\fi{}0.05$ K was found to consent with its previously reported value. Other detected characteristic energies are as follows ($\ifmmode\pm\else\textpm\fi{}0.05$ K): ${J}_{(2)}=1.80$ K, ${J}_{(3)}=1.39$ K, ${J}_{(4)}=0.81$ K.

We use the two-pulse spin-dependent photon echo technique to study the in-plane hole spin anisotropy in a 20~nm-thick CdTe/Cd$_{0.76}$Mg$_{0.24}$Te single quantum well by exciting the donor-bound exciton resonance. We take advantage of the photon echo sensitivity to the relative phase of the electron and hole spin precession and study various interactions contributing to the hole in-plane spin properties. The main contribution is found to arise from the crystal cubic symmetry described by the Luttinger parameter $q=0.095$, which is substantially larger than the one theoretically expected for CdTe or found in other quantum well structures. Another contribution is induced by the strain within the quantum well. These two contributions manifest as different harmonics of the spin precession frequencies in the photon echo experiment, when strength and orientation of the Voigt magnetic field are varied. The magnitude of the effective in-plane hole $g$ factor is found to vary in the range $|\tilde{g_h}|$=0.125--0.160 in the well plane., 7 figures

Magneto-optical phenomena such as the Faraday and Kerr effects play a central role in controlling the polarization and intensity of optical fields propagating through a medium. Intensity effects in which the direction of light emission depends on the orientation of the external magnetic field are of particular interest, as they can be harnessed for routing light. Effects known so far for accomplishing such routing all control light emission along the axis parallel to the magnetic field. Here we report a new class of emission phenomena where directionality is established perpendicular to the externally applied magnetic field for light sources located in the vicinity of a surface. As a proof of principle for this effect, which we call transverse magnetic routing of light emission, we demonstrate the routing of emission for excitons in a diluted-magnetic-semiconductor quantum well. In hybrid plasmonic semiconductor structures, we observe significantly enhanced directionality of up to 60%.

The photoluminescence (PL) spectra of CdTe/ZnTe double quantum wells (QWs) are studied on a series of samples containing two CdTe layers with nominal thicknesses of 2 and 4 monolayers (ML) in the ZnTe matrix. The QWs were grown in atomic-layer epitaxy and separated by ZnTe spacers with the thicknesses dsp =40−160 ML. The dependences of the relative intensity of shallow QW1 and deep QW2 PL bands (I1 and I2 , respectively) on the pump intensity (J) when excited by the lasers with different radiation wavelengths are investigated. It is found that in the sample with dsp=40 ML, the ratio Y(J)=I1/I2 depends on J and the shape of the Y(J) dependency changes with the excitation wavelength. In the samples with dsp > 70 ML Y(J) also changes with the excitation intensity J, but the shape of this dependence is the same for various excitation wavelengths. It is concluded that the energy relaxation in these samples is influenced not only by the tunneling of charge carriers from QW1 to QW2, but also by carrier relaxation at the nonradiative centers, for which the recombination rate is different for shallow and deep QWs.

The coherent spin dynamics of electrons in tunnel-coupled CdTe and (Cd,Mn)Te quantum wells (QWs) is studied by time-resolved pump-probe Kerr rotation. The coupled QWs have different thicknesses; the narrow one is doped by ${\mathrm{Mn}}^{2+}$ magnetic ions. A short range proximity effect between them is observed: the Zeeman splitting of electrons in the wide QW is given in addition to the intrinsic electron $g$ factor by the exchange interaction with the ${\mathrm{Mn}}^{2+}$ ions mediated by electron tunneling into the narrow QW. The exchange interaction strength scales with the ${\mathrm{Cd}}_{0.88}{\mathrm{Mg}}_{0.12}\mathrm{Te}$ barrier thickness separating the QWs. The Kerr rotation signal measured on the wide QW shows two close frequencies of electron spin Larmor precession in a transverse magnetic field. These components have very different spin dephasing times, 50 ps and 1 ns. The two frequencies originate from electrons in the wide QW being either part of an exciton or being resident. The proximity effect of the exciton electron is smaller due to the binding by Coulomb interaction, which decreases the tunneling to the narrow well. The experimental data are in good agreement with model calculations.

We study the quantum beats in the polarization of the photon echo from donor-bound exciton ensembles in semiconductor quantum wells. To induce these quantum beats, a sequence composed of a circularly polarized and a linearly polarized picosecond laser pulse in combination with an external transverse magnetic field is used. This results in an oscillatory behavior of the photon echo amplitude, detected in the $\sigma^+$ and $\sigma^-$ circular polarizations, occurring with opposite phases relative to each other. The beating frequency is the sum of the Larmor frequencies of the resident electron and the heavy hole when the second pulse is polarized along the magnetic field. The beating frequency is, on the other hand, the difference of these Larmor frequencies when the second pulse is polarized orthogonal to the magnetic field. The measurement of both beating frequencies serves as a method to determine precisely the in-plane hole $g$ factor, including its sign. We apply this technique to observe the quantum beats in the polarization of the photon echo from the donor-bound excitons in a 20-nm-thick CdTe/Cd$_{0.76}$Mg$_{0.24}$Te quantum well. From these quantum beats we obtain the in-plane heavy hole $g$ factor $g_h=-0.143\pm0.005$., Comment: 4 pages, 4 figures

International audience; The behavior of the spin relaxation time of electrons bound to donors immersed in the middle of a CdTe quantum well was measured in the range of temperatures 10-80 K, by using picosecond pump-probe Kerr rotation. Different doping concentrations spanning from isolated donors up to a concentration beyond the metal-insulator transition were considered at a fixed magnetic field; at very low temperature, in insulating regime all electrons are bound to donors but for one high concentration we had to consider that a fraction of electrons is in conduction states. By increasing the temperature, the number of conduction electrons increases. The experimental temperature dependences were explained by invoking spin exchange between electron spins localized on donors and the spin of electrons promoted to conduction states. A good agreement between experiment and theory was found and allowed us to conclude that, while the spin of localized electrons undergoes the effect of both hyperfine and anisotropic exchange interactions, the D'yakonov-Perel' mechanism governs the spin relaxation of the conduction electrons for the whole range of the studied doping concentrations. Moreover, we identified the scattering mechanisms possibly undergone by the conduction electrons at low temperature.

Spin-dependent photon echoes in combination with pump-probe Kerr rotation are used to study the microscopic electron spin transport in a CdTe/(Cd,Mg)Te quantum well in the hopping regime. We demonstrate that independent of the particular spin relaxation mechanism, hopping of resident electrons leads to a shortening of the photon echo decay time, while the transverse spin relaxation time evaluated from pump-probe transients increases due to motional narrowing of spin dynamics in the fluctuating effective magnetic field of the lattice nuclei., 11 pages, 8 figures

Low-temperature spin relaxation time of electrons localized on iodine donors placed in the middle of a 8-nm CdTe quantum well is studied by using the photoinduced Faraday rotation technique, for donor concentrations in the range from $1\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{4pt}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$ to $3.6\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{4pt}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$. A maximum relaxation time of the order of 20 ns is found at a doping concentration near the metal-insulator transition. Adapting the theoretical description developed for bulk GaAs [R. I. Dzhioev et al., Phys. Rev. B 66, 245204 (2002)] to a quantum well, we have fitted the experimental results taking as a parameter the spin-orbit constant in CdTe. A satisfactory fit is obtained with ${\ensuremath{\alpha}}_{so}=0.079\ifmmode\pm\else\textpm\fi{}0.011,$ which is also very close to the calculated theoretical value. A comparison of the experimental spin relaxation times measured previously in bulk CdTe to those predicted by the theory is done. Finally, we compare the predicted spin relaxation times in bulk CdTe to those predicted in one of the most studied bulk semiconductor materials: GaAs, and in (less studied) ZnSe.

Heterostructure p-(ZnMgTe/ZnTe:N)/CdTe/n-(CdTe:I)/GaAs was evaporated using molecular beam epitaxy and investigated for photovoltaic energy conversion application. The electrical properties of the studied heterostructure were measured and characterized in order to understand the relevant electrical transport mechanisms. Electrical properties derived from the current–voltage (I–V) characteristics of solar cells provide essential information necessary for the analysis of performance losses and device efficiency. I–V characteristics are investigated in dark conditions and under different light intensities. All the electrical and power parameters of the heterostructure were measured, calculated and explained.

A series of ZnTe matrix containing two CdTe monolayers separated by barrier layers of different thicknesses is studied. The dependences of the energies of the exciton emission bands related to the CdTe monolayers, their relative intensities, and temperature behavior on the thickness of the ZnTe barrier layer are determined. It is established that CdTe monolayers can be considered independent of each other with a barrier layer thickness of more than 30 monolayers.

We study optical pumping of resident electron spins under resonant excitation of trions in $n$-type CdTe/(Cd,Mg)Te quantum wells subject to a transverse magnetic field. In contrast to the comprehensively used time-resolved pump-probe techniques with polarimetric detection, we exploit here a single beam configuration in which the time-integrated intensity of the excitation laser light transmitted through the quantum wells is detected. The transmitted intensity reflects the bleaching of light absorption due to optical pumping of the resident electron spins and can be used to evaluate the Larmor precession frequency of the optically oriented carriers and their spin relaxation time. Application of the magnetic field leads to depolarization of the electron spin ensemble so that the Hanle effect is observed. Excitation with a periodic sequence of laser pulses leads to optical pumping in the rotating frame if the Larmor precession frequency is synchronized with the pulse repetition rate. This is manifested by the appearance of Hanle curves every 3.36 or 44.2 mT for pulse repetition rates of 75.8 or 999 MHz, respectively. From the experimental data we evaluate the $g$ factor of $|g|=1.61$ and the spin relaxation time of 14 ns for the optically pumped resident electrons, in agreement with previous time-resolved pump-probe studies.

Time-resolved Kerr-rotation microscopy explores the influence of optical doping on the persistent spin helix in a [001]-grown CdTe quantum well at cryogenic temperatures. Electron spin diffusion dynamics reveal a momentum-dependent effective magnetic field providing SU(2) spin-rotation symmetry, consistent with kinetic theory. The Dresselhaus and Rashba spin-orbit coupling parameters are extracted independently from rotating the spin helix with external magnetic fields applied parallel and perpendicular to the effective magnetic field. Most importantly, a non-uniform spatiotemporal precession pattern is observed. The kinetic theory framework of spin diffusion allows for modeling of this finding by incorporating the photocarrier density into the Rashba ($\alpha$) and the Dresselhaus ($\beta_3$) parameters. Corresponding calculations are further validated by an excitation-density dependent measurement. This work shows universality of the persistent spin helix by its observation in a II-VI compound and the ability to fine-tune it by optical doping., Comment: 5 pages, 4 figures, journal submission

n-CdTe/p-CdMnTe/p-GaAs diluted magnetic diode was grown by molecular beam epitaxy technology. The forward- and reverse-bias capacitance–voltage (C–V), conductance–voltage (G–V), series resistance–voltage (R s–V), impedance–voltage (Z–V), and phase–voltage (θ–V) characteristics of this diode have been analyzed in the frequency range of 5 kHz to 1 MHz at room temperature. Both the density of interface states (N ss) and series resistance (R s) are strongly frequency dependent and decrease with increasing frequency. The values of the built-in potential ( $$ V_{\rm{bi}} $$ ), the doping concentration ( $$ N_{\rm{d}} $$ ), and the barrier height ( $$ \varphi_{{{\rm{b}}(C - V)}} $$ ) of the diode were calculated at different frequencies. Our experimental results revealed that both the series resistance and interface state density must be taken into account in studying the impedance spectroscopy on heterojunction diodes to understand their performance for electronic and optoelectronic applications. Diluted magnetic semiconductors are promising materials for future technology.

The exchange interaction between magnetic ions and charge carriers in semiconductors is considered to be a prime tool for spin control. Here, we solve a long-standing problem by uniquely determining the magnitude of the long-range $p\ensuremath{-}d$ exchange interaction in a ferromagnet-semiconductor (FM-SC) hybrid structure where a 10-nm-thick CdTe quantum well is separated from the FM Co layer by a CdMgTe barrier with a thickness on the order of 10 nm. The exchange interaction is manifested by the spin splitting of acceptor bound holes in the effective magnetic field induced by the FM. The exchange splitting is directly evaluated using spin-flip Raman scattering by analyzing the dependence of the Stokes shift ${\mathrm{\ensuremath{\Delta}}}_{S}$ on the external magnetic field $B$. We show that in a strong magnetic field, ${\mathrm{\ensuremath{\Delta}}}_{S}$ is a linear function of $B$ with an offset of ${\mathrm{\ensuremath{\Delta}}}_{pd}=50--100\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{eV}$ at zero field from the FM induced effective exchange field. On the other hand, the $s\ensuremath{-}d$ exchange interaction between conduction band electrons and FM, as well as the $p\ensuremath{-}d$ contribution for free valence band holes, are negligible. The results are well described by the model of indirect exchange interaction between acceptor bound holes in the CdTe quantum well and the FM layer mediated by elliptically polarized phonons in the hybrid structure.

We study Rabi oscillations detected in the coherent optical response from various exciton complexes in a 20~nm-thick CdTe/(Cd,Mg)Te quantum well using time-resolved photon echoes. In order to evaluate the role of exciton localization and inhomogeneous broadening we use selective excitation with spectrally narrow ps-pulses. We demonstrate that the transient profile of the photon echo from the localized trion (X$^-$) and the donor-bound exciton (D$^0$X) transitions strongly depends on the strength of the first pulse. It acquires a non-Gaussian shape and experiences significant advancement for pulse areas larger than $\pi$ due to non-negligible inhomogeneity-induced dephasing of the oscillators during the optical excitation. Next, we observe that an increase of the area of either the first (excitation) or the second (rephasing) pulse leads to a significant damping of the photon echo signal, which is strongest for the neutral excitons and less pronounced for the donor-bound exciton complex (D$^0$X). The measurements are analyzed using a theoretical model based on the optical Bloch equations which accounts for the inhomogeneity of optical transitions in order to reproduce the complex shape of the photon echo transients. In addition, the spreading of Rabi frequencies within the ensemble due to the spatial variation of the intensity of the focused Gaussian beams and excitation-induced dephasing are required to explain the fading and damping of Rabi oscillations. By analyzing the results of the simulation for the X$^-$ and the D$^0$X complexes we are able to establish a correlation between the degree of localization and the transition dipole moments determined as $\mu($X$^-$)=73~D and $\mu($D$^0$X)=58~D., Comment: 5 figures

This paper reports on the observation of the magnetic quantum ratchet effect in (Cd,Mn)Te- and CdTe-based quantum well structures with an asymmetric lateral dual grating gate superlattice subjected to an external magnetic field ($B$), applied normal to the quantum well plane. An electric current excited by terahertz laser radiation shows 1/$B$-periodic oscillations with amplitude much larger than the photocurrent at zero magnetic field. It is shown that the photocurrent generation is due to the combined action of a spatially periodic lateral potential and the spatially modulated radiation due to the near-field effects of light diffraction. The magnitude and direction of the photocurrent are determined by the degree of the lateral asymmetry controlled by the variation of voltages applied to the individual gates. The observed magneto-oscillations with enhanced photocurrent amplitude result from Landau quantization. For (Cd,Mn)Te-based structures at low temperatures, a beating-like pattern of the oscillations is observed, caused by the interplay of Zeeman and Landau splitting. A theoretical analysis, considering the magnetic quantum ratchet effect in the framework of a semiclassical approach, describes quite well the experimental results.

The luminescence of CdTe layers with a nominal thickness of 1, 2, 4, and 8 monolayers grown by atomic layer epitaxy in ZnTe matrix was studied. It is shown that layers with a thickness of 1 and 2 monolayers are homogeneous, while layers with a nominal thickness of 4 and 8 monolayers are the planar QD arrays. The sizes of QDs and their size dispersion increase with an increase in the nominal thickness of CdTe layer. The luminescence excitation spectra of CdTe layer in the samples vary significantly. It has been shown that, depending on the energy distance between the CdTe and ZnTe exciton levels, the ratio of contributions to the energy transfer via the exciton ZnTe and charge carriers varies greatly.

Abstract Heterostructures of the CdTe/ZnTe type with ultrathin quantum wells are studied. Lines of light and heavy excitons bound to the CdTe layers are observed in the spectra. It is found that the photoluminescence intensity of the light exciton is comparable to the luminescence intensity of the heavy exciton. The temperature shifts of these lines are different, and the lines are intersected at a temperature of 65 K. The estimates of the energy and wave functions of the exciton states have made it possible to clarify parameters of some bands and excitons in such structures.

High-resolution X-ray di ractometer was used to study structural quality, lattice parameters and mis t strain in p-ZnTe/n-CdTe heterojunctions grown by the molecular-beam epitaxy technique on two di erent (001)-oriented substrates of GaAs and CdTe. The X-ray di ractometer results indicate that the CdTe layers, grown on lattice mismatched GaAs substrate, are partially relaxed, by the formation of mis t dislocations at the interface, and display residual vertical strain of the order of 10−4. The presence of threading dislocations in the layers e ectively limits the e ciency of solar energy conversion in the investigated heterojunctions. Homoepitaxially grown CdTe layers, of much better structural quality, display unexpected compressive strain in the layers and the relaxed lattice parameter larger than that of the substrate. Possible reasons for the formation of that unusual strain are discussed.

We report on the method of fabrication of a photonic microstructure that contains a single magnetic ion. Exactly one manganese ion was introduced into a self-assembled CdTe quantum dot, which was located in a ZnTe based micropillar cavity. The multistep fabrication procedure includes molecular beam epitaxy growth, optical characterization, and focused ion beam etching. Realization of the structure was confirmed by the observation of spectroscopic exciton lines split by six due to the exchange interaction with a manganese ion. The cavity mode was tuned to the quantum dot emission energy by a variation of the temperature. The presented technology is developed to be applied in optoelectronics based on solitary dopants.

The optical properties of series of CdTe/ZnTe heterostructures with two built-in planar CdTe inclusions of thickness 4.0 and 1.5 monolayers are investigated. The temperature behavior of the exciton luminescence intensity at above-barrier and under-barrier excitation depends on the ZnTe barrier thickness which varies from 15 to 55 monolayers. It occurs that the shape of exciton luminescence bands changes strongly under the increasing optical excitation. The excitation luminescence spectra are studied in the temperature range 5 – 80 K.

In tunnel-coupled quantum wells (QWs) CdTe (20 nm wide) and CdMnTe (8 nm wide) separated by Cd0.88Mg0.12Te barrier with a thickness of L B = 5, 7, 9, and 11 monolayers (MLs), the dependence of electron g-factor on the barrier thickness and temperature is investi-gated by means of the pump-probe Kerr rotation technique. The renormalization of the electron g-factor occurs due to the s–d exchange interaction of electrons with manganese ions in a magnetic QW. The most change of the electron g-factor value Δg = 0.25 is registered at the least barrier width of 5 MLs and temperature T = 5 K. In this case, the penetration of the electron wave function from the nonmagnetic QW into the magnetic one is estimated to be 0.6%.

The properties of 3 monolayers (ml) CdTe self-assembled quantum dot (SAQD) sample are investigated by means of Raman and photoluminescence (PL) spectroscopy. The PL spectrum is characterized by two main emission peaks, both connected with the existence of QDs. One presents direct deexcitation to ground state and the other one is optical phonon ( ω = 204.2 cm −1 ) assisted deexcitation. One-phonon Raman spectra at room temperature show surface-optical phonon at 201 cm −1 . At temperatures below 200 K, multiphonon processes are registered. Multiphonon maximum depends on the temperature, and laser energy.

We report on the observation and systematic study of polarization sensitive magnetic quantum ratchet effects induced by alternating electric fields in the terahertz frequency range. The effects are detected in (Cd,Mn)Te-based quantum well (QW) structures with inter-digitated dual-grating-gate (DGG) lateral superlattices. A dc electric current excited by cw terahertz laser radiation shows 1/B-periodic oscillations with an amplitude much larger than the photocurrent at zero magnetic field. Variation of gate voltages applied to individual grating gates of the DGG enables us to change the degree and the sign of the lateral asymmetry in a controllable way. The data reveal that the photocurrent reflects the degree of lateral asymmetry induced by different gate potentials. We show that the magnetic ratchet photocurrent includes the Seebeck thermoratchet effect as well as the effects of "linear" and "circular" ratchets, which are sensitive to the corresponding polarization of the driving electromagnetic force. Theoretical analysis performed in the framework of semiclassical approach and taking into account Landau quantization describes the experimental results well.

We have studied the coherent spin dynamics of excitons bound to acceptors, A0X, immersed in a CdTe quantum well by using time resolved photo-induced Faraday rotation. We have also measured the time-resolved differential transmission in order to determine a A0X lifetime of 220 ps, which is independent of the applied magnetic field. We show that at low magnetic field, the spin of A0X is completely frozen during a time, ≅ 4.5 ns, at least twenty times longer than its lifetime. We compare the spin properties of A0X with the spin properties of other charged excitons systems, and we conclude that the hyperfine interaction of the photo-created electron spin with nuclear spins is very likely to be at the origin of the observed spin dephasing times. Fil: Grinberg, Patricio. Universite Paris Sorbonne - Paris Iv; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Bernardot, F.. Universite Paris Diderot - Paris 7; Francia. Universite Paris Sorbonne - Paris Iv; Francia Fil: Eble, B.. Universite Paris Sorbonne - Paris Iv; Francia Fil: Karczewski, G.. Institute Of Physics Of The Polish Academy Of Sciences; Polonia Fil: Testelin, C.. Universite Paris Sorbonne - Paris Iv; Francia Fil: Chamarro, M.. Universite Paris Sorbonne - Paris Iv; Francia

AbstractThe exciton luminescence spectra of CdTe/ZnTe heterostructures containing two thin CdTe layers separated by barriers of different thickness were studied. The complex temperature dependence of the intensity of luminescence from these layers in its underbarrier and abovebarrier excitation led to the conclusions about the effect of the thickness of the barriers on the energy transfer between the CdTe layers and gave the possibility to observe, at specific temperatures, the implementation of a resonant-type excitation. The dependence of the shape of the exciton emission contours on the excitation level gives information about the real structure of CdTe layers with the monolayer thickness of 1.5 and 4.0 monolayers.

In the version of this Article originally published, the expression for Pc was missing a division slash; it should have read Pc = ±2dydz/(dy2 + dz2) ≈ ±2/3Δh,F/Δ1h. Also, affiliation 5 was missing ‘Institute of Physics’; it should have read ‘International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences, Warsaw, Poland’. These issues have now been corrected.

We present an approach to electrical control of the spin polarization in a diluted magnetic semiconductor (DMS) structure. A variable magnetic field induced by a micro-scale current loop magnetizes the Mn2+ ions in a CdMnTe/CdMgTe DMS quantum well, which via the sp-d exchange interaction polarizes photo-generated electron-hole pairs confined in the well. A maximum spin polarization degree of ±8.5% is obtained at 4.2 K without external magnetic field. The current-induced magnetic field and the current-generated heating of the spin system are quantitatively extracted by micro magneto-luminescence measurements.

The microstructure of ferroelectric Cd1−xZnxTe (CZT) thin films with x ≈ 0.04 grown by molecular beam epitaxy has been studied by means of cross sectional high-resolution transmission electron microscopy (HREM). High- density {1 1 1} lamellar twins are found to be the dominant defects in the films. Double-position twins with twin boundaries nearly parallel to (1 1 −2) are observed to always coexist with the (1 1 1) lamellar twins and stop the penetration of the latter. The coexistence of both kinds of twins produces complex twin structures with triple-point and quadruple-point junctions. The fact that lamellar (1 1 1) twins in the ferroelectric CZT layer are shorter than those in the Cd1−xMgxTe buffer layers is explained. The films show uniform texture direction oriented along [1 1 1] except a few regions with the habit faces of twins oblique to the surface of the films.