Cd1 xMnxTe Research Articles

Zeeman effect in Cd1-xMn xTe parabolic and half-parabolic quantum wells

We have investigated the electronic structure of Cd1_xMn xTe parabolic quantum wells and half-parabolic quantum wells heterostructures in the envelope function approximation using the k · p method. We have considered an external magnetic field applied in two different configurations: in the plane of the layer and in the growth direction. The confined states have been calculated taking into account the effective mass dependence of the Mn concentration and the strain effects. In this work we analyze the giant Zeeman splitting due to applied magnetic fields and we havecompared the energies of the excitonic transitions hh (lh) ->el for the magnetic field in the two considered configurations. Comparison of our results for the half-parabolic quantum wells with available experimental data is made.

Spectroscopic, Phototropic, and Lasing Properties of Cd1−xMnxTe Single Crystals Doped With Chromium Ions

The spectroscopic properties of Cr2+ ions in Cr:Cd1−xMnxTe (CMT) crystals are studied, and the possibility of using these impurity crystals as active media and saturable absorbers of solid‐state lasers of medium IR range is demonstrated. The bands of absorption with a maximum at 1.9 μm and of luminescence with a maximum at 2.6 μm correspond to the transitions between the levels 5T2 and 5E of the tetracoordinated Cr2+ ions with more than 1·10−18‐cm2 cross sections. The pulsed and continuous lasing modes of a Cr:CMT laser are realized in the 2.6‐μm region. The Cr:CMT crystals are characterized by effective saturation of impurity absorption. The cross sections of absorption from the ground and excited states of the Cr2+ ions at λ = 2.09 μm are determined: σgsa = 1.1·10−18 cm2; σesa/σgsa < 0.1. With the use of the Cr:CMT crystals as a passive gate the regime of Q‐switching of the Cr,Tm,Ho:YAG laser emitting at λ = 2.09 μm is obtained.

Excitonic resonant spin-flip Raman scattering in Cd 1-xMn xTe multilayers

We report the observation of resonant spin-flip Raman scattering due to localized heavy-hole excitons in quasi-bulk Cd 1-xMn xTe multilayers. The exciton- and electron spin-flip energies were compared with excitonic Zeeman splittings obtained from magnetoreflectivity measurements on the same sample. A good agreement was observed between the electron spin splitting values obtained from both experiments. The exciton spin-flip energy was found to be slightly reduced with respect to the Zeeman splitting value. Possible mechanisms of this reduction are discussed.

Dissociation Energy of Positively Charged Excitons in Semimagnetic CdMnTe Quantum Wells

We present a transmission study of the energies of neutral and positively charged excitons in modulation doped Cd1—xMnxTe quantum wells with variable concentration of the hole gas. Application of the semimagnetic semiconductor as the QW material gives the opportunity to control independently the total hole concentration and its distribution between the two spin subbands (by a small magnetic field). The positively charged exciton dissociation energy is found to be a linear function of the concentration in only one hole spin subband (the one with the spin opposite to that of photocreated hole). This can be seen as a consequence of the fact that a charged exciton is not simply a three particle complex, but it consists of an exciton interacting with many holes.

The use of Mn L? line chemical effects in X-ray analysis to probe sample homogeneity

K. Lawniczak-Jablonska, K. Lawniczak-Jablonska, J. Kachniarz, Z. Spolnik, J. Libera, E. Dynowska, A. Nadolny and J. Sadowski, J. Anal. At. Spectrom., 1999, 14, 461 DOI: 10.1039/A807431C

Magnetic Field Induced Polarization of Luminescence in Paramagnetic and Spin‐Glass Phases of Cd1–xMnxTe

AbstractThe magnetic field induced polarization of photoluminescence is studied at different temperatures in Cd1–xMnxTe samples with x ranging from 0.005 to 0.38. The mechanism of polaron alignment is shown to depend on manganese content and temperature. In paramagnetic samples polarization is governed by thermal disorder of magnetic polaron axes, while in the spin‐glass phase the magnetic anisotropy of the lattice spin system predominates. The change of the mechanisms becomes visible when plotting polarization versus temperature.

Free Carriers Heating at Mn2+Magnetic Resonance in CdMnTe

It was shown recently [1] that the dominant mechanism responsible for the optical detection of magnetic resonance (ODMR) in Cd1x MnxTe (x = 0.095) is related to the decrease in the sample magnetization at the Mn 2+ magnetic resonance. The large magnitude of the ODMR signal was related to a large efficiency of the Auger type nonradiative recombination of the acceptor bound exciton (ABE) [2], whose recombination is promoted at the magnetic resonance. In this communication we present the results of the ODMR and the optically detected cyclotron resonance (ODCR) experiments performed on 0.7% CdMnTe bulk samples. A different ODMR detection mechanism is deduced from the present results.

Local magnetization and magnetotransport in magnetic semiconductors

We describe the influence of local magnetization on electron localization in magnetic semiconductors. This includes a review of the magnetic field induced insulator-metal transition in Gd 3-xv xS 4 (where v=vacancy) and the observation of activated transport, i.e. a ‘hard’ gap, in the hopping regime for the diluted magnetic semiconductor Cd 1-xMn xTe:In.

Crystal optics of magnetoelectrics

Abstract The presence in magnetoelecttics of the specific space-time symmetry operation 1′ allows the existence of several new optical phenomena that may occur in transmission and reflection. Among those are the nonreciprocal gyrotropic birefringence, the rotation of optical indicatrix, the nonreciprocal reflection, the electric field induced nonreciprocal rotation. Theoretical aspects and experimental observations of some of these effects in Cr2O3 are discussed. Nonlinear optical phenomena that can occur due to magnetoelectric interaction are also discussed (BiFeO3, magnetic garnet films). At the end we discuss unusual electromagnetooptical phenomena, observed experimentally in noncentrosymmetric crystals in the presence of magnetic field (CsCuCl3, LIIO3, Pb5Ge3O11, Cd1–xMnxTe, Te).

Magnetization and photomagnetic effects in diluted magnetic microcrystalline Cd 1-xMn xTe

We have investigated the magnetic and photomagnetic properties of microcrystalline Cd 1-xMn xTe prepared by rf sputtering. Magnetization measurements were carried out using an rf SQUID magnetometer in the temperature range of 1.8 to 300 K at various magnetic fields up to 5.5 T. For temperatures above 40 K, the sample showed Curie-Weiss behaviour with a Curie temperature indicating predominantly antiferromagnetic interactions. A spin-glass phase transition was also observed. Photomagnetization measurements were performed using a fibre-optic system. The light was shone onto the sample utilizing an optical fibre and the subsequent change in the magnetization was sensed by the SQUID. Photo-induced magnetization was observed when the sample was illuminated by unpolarized light. Our results enable qualitative and quantitative conclusions to be drawn on the magnetic behaviour and the interplay between optical and magnetic properties of the diluted magnetic microcrystalline semiconductors. PACS: 68.55.Gi; 75.50.Pp.

Electronic wavefunctions in asymmetric double quantum well structures studied via spin-flip Raman spectroscopy

Spin-flip Raman spectra have been obtained for two heterostructures, each containing a single CdTe quantum well and a single Cd 1-xMn xTe quantum well, with barriers of Cd 1-yMn yTe (y>x). The spectra show a clear sensitivity to the thickness of the central barrier between the two wells. The magnitude of the Raman shifts and the resonance energies help identify the origin of the signals in the structures. When the barrier is broad, two signals are observed, one from each separate well. When the width of the barrier is reduced, a single signal is seen, reflecting the coupling of the electronic states of the two wells. The size of the Raman shifts observed also suggest the presence of a low concentration of donors in the material, which modify the form of the electronic wavefunction in the quantum wells.

Large Lattice Distortion and Infrared Photoluminescence in Cd1-xMnxTe

The infrared photoluminescence near 1.15eV (IR PL) in Cd1-xMnx Te is investigated under high pressures up to 20kbar and at wide temperature range. Using a configuration coordinate model, we propose that relaxed excited states of Mn2+ have two minima, and the excited states of IR PL has larger lattice relaxation than that of excited states of Mn2+ PL. Also distorted ground state without metastable states is the final states of IR PL. Thermal barrier from Mn2+ excited state to excited state of IR PL is 36meV.

Faraday photorefractive effect in a diluted magnetic semiconductor

The Faraday photorefractive effect is demonstrated by combining photorefractive two-beam coupling with Faraday rotation in Cd1–xMnxTe, a diluted magnetic semiconductor. Two-wave mixing is monitored as a function of incident-beam polarization and magnetic-field strength with the grating vector parallel to a 〈111〉 axis. The photorefractive gain is an oscillatory function of the magnetic field. The magnetic field controls the direction and magnitude of photorefractive energy transfer by rotating the polarization inside the crystal.

Band tails and the insulator-metal transition in the persistent photoconductor Cd 1-xMn xTe:In

Persistent photoconductivity has been demonstrated in the dilute magnetic semiconductor Cd 1-xMn xTe:In and has been used to elucidate the shape of the band tail. It is further shown that the insulator-metal transition may be approached, in one sample, by controlling the persistent carrier density with illumination.

Raman scattering studies of Cd1−xMnxTe films grown on GaAs by pulsed laser evaporation and epitaxy

We have used Raman scattering to study a series of thin (111) Cd1−xMnxTe (CMT) films grown on (111) GaAs by pulsed laser evaporation and epitaxy. We show Raman spectra of CMT with 0.059≤x≤0.70, at 80 K. Samples with x≳0.4 exhibit up to 8th order combinations of CdTe-like and MnTe-like longitudinal optical phonons, which vary with excitation energy between 2.4 and 2.7 eV. We interpret these overtones as arising from outgoing resonance with the fundamental gap, and present an equation for the mth order phonon line intensity. We confirm the dependence of phonon frequency on x(Mn), and examine the variation of the phonon mode intensities with x(Mn). We also discuss the line widths of Raman and photoluminescence spectra versus x(Mn).

CVT growth, thermodynamic and magneto-structural study of Cd 1-xMn xTe single crystals

The growth of Cd 1- x Mn x Te (with 0.5 ≤ x ≤ 0.66) single crystals by the chemical vapour transport technique in a closed tube using iodine as transport agent is reported. As regards the growth process, a qualitative thermodynamic picture of the CdTe-MnTe-I 2 system is given with the aim of avoiding the presence of liquid or solid spurious species (i.e., MnI 2 liquid, CdI 2 liquid and MnTe 2 solid. The grown single crystals showed the cubic zincblende structure; the hexagonal symmetry, verified in various cases, was found to be apparent and due to a particular type of twinning consisting in a syntaxic coalescence of cubic domains. The magnetic characterization by susceptibility measurements is reported. XPS and Auger electron spectroscopy are used for studying the electronic structure of the crystals, and for monitoring possible modifications in the chemical composition of their surface.

New aspect of giant exciton Faraday rotation in Cd1-xMnx Te semimagnetic compomd: Fundamentals and applications

Wavelength, magnetic field, and temperature dependences of Faraday rotation (FR) in various compositions of the dilute magnetic semiconductors Cd1-xMn Te and Zn1-xMn Te have been experimentally investigated. Regularities of the Faraday effect dispersion connected with the change of rotation direction as a function of temperature and Mn concentration in the compound have been revealed. Deviation in FR saturation at helium temperatures and high magnetic fields is observed. According to the FR temperature dependence, the spontaneous Faraday effect is assumed to be a characteristic of the spin glass state of semimagnetic semiconductors. A rapid magnetic field sensor system as a possible application of this material has been proposed.

Photoluminescence of Cd1−xMnxTe films grown by metalorganic chemical vapor deposition

Cd1−x Mnx Te (CMT) films grown by metalorganic chemical vapor deposition on GaAs, CdTe/GaAs, and CdS/SnO2 /glass (CSG) have been studied at 2 and 80 K by photoluminescence (PL). Analysis of the CMT bandedge peak yields Mn concentration x and indicates the degree of stress in the films due to lattice mismatch with the substrates, which also causes a blue shift of the PL band with temperature. A CdTe buffer layer greatly reduces stress and resulting defects. PL spectra from polycrystalline CMT films on commercial CSG wafers, reported for the first time, show a strong band near 1.62 eV which may represent states at the CMT-CdS interface. In CMT/CdTe/GaAs, we see evidence of front-to-back inhomogeneity in the CMT film which may appear in layered form.

Phase Transition and Anharmonic Properties of Semimagnetic Semiconductors

AbstractThe phase transition and anharmonic properties are investigated of semimagnetic semiconductors Cd1–xMnxTe and Cd1–xZnxTe using a three‐body force potential. The calculated values of third order elastic constants follow a systematic trend of variation with molar concentration. The values of the phase transition pressures and the pressure derivatives of second order elastic constants show reasonably good agreement with their experimental data. The possible ways of improvements are also discussed.

Picosecond time-resolved study of luminescence of Cd 1-xMn xTe

Picosecond time-resolved photoluminescence studies have been made at temperatures down to 1.8K and in magnetic fields of up to 8T of the dilute magnetic semiconductor Cd 1-xMn xTe for x = 0.09, 0.2 and 0.3. The dynamics of lattice-disorder-induced and magnetically-induced localisation of excitons are discussed.