Spin effects on oscillatory magnetoresistances in n-Pb1−xSnxTe

Shubnikov-de Haas oscillations in n-Pb_1?xSn_xTe have been measured in the magnetic field parallel to the [100] crystal direction at 1.5 K. In the longitudinal magnetoresistances, the one-side peaks of spin-splitting pair series are completely missing. This anomaly is well explained by the selection rules, theoretically derived in the study on a similar effect in Hg_1?xCd_xTe. Landau sublevel-crossings are also discussed.     

Terahertz spectroscopy of quantum-well narrow-bandgap HgTe/CdTe-based heterostructures

The energy spectra of quantum-well narrow-bandgap Hg_{1 ? y} Cd _y Te/Cd _x Hg_{1 ? x} Te heterostructures have been studied. The dependences of the effective cyclotron mass on the density (in classical magnetic fields) and the transition energy (in quantizing fields) have been obtained from the cyclotron resonance measurements. These dependences confirm the near-linear dispersion law for the electrons with small mass at the band bottom (the minimum cyclotron mass measured is 0.003 m ₀). The interband photoconductivity of the CdHgTe-based structures with the long-wavelength photoresponse edge lower than 6 meV has been demonstrated.     

Effects of in situ thermal annealing on the structural, optical, and electrical properties in Hg0.7Cd0.3Te epilayers grown on CdTe buffer layers

Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) transmission, and Hall effect measurements were performed to investigate the structural, optical, and electrical properties of as-grown and in situ-annealed Hg_0.7Cd_0.3Te epilayers grown on CdTe buffer layers by using molecular beam epitaxy. After the Hg_0.7Cd_0.3Te epilayers had been annealed in a Hg-cell flux atmosphere, the SEM images showed that the surface morphologies of the Hg_0.7Cd_0.3Te thin films were mirror-like with no indication of pinholes or defects, and the FTIR spectra showed that the transmission intensities had increased in comparison to that of the as-grown Hg_0.7Cd_0.3Te epilayer. Hall-effect measurements showed that n-Hg_0.7Cd_0.3Te epilayers were converted to p-Hg_0.7Cd_0.3Te epilayers. These results indicate that the surface, optical, and electrical properties of the Hg_1 − xCd_xTe epilayers are improved by annealing and that as-grown n-Hg_1 − xCd_xTe epilayers can be converted to p-Hg_1 − xCd_xTe epilayers by in situ annealing.     

Evidence for the spin-dependent scattering of conduction electrons on Mn2+ ions in Hg1−xMnxTe and Cd1−xMnxSe mixed crystals

Changes in the resistivity of Hg_1?xMn_xTe and Cd_1?xMn_xSe mixed crystals associated with paramagnetic resonance of the Mn²⁺ ions have been observed at liquid helium temperature in a strong magnetic field. The effect was recorded by monitoring the submillimeter radiation induced photoconductivity in a swept magnetic field. An increase in the resistivity associated with EPR of the Mn²⁺ ions is interpreted in terms of the spin- dependent scattering of electrons on magnetic impurities, the spins of which are selectively depolarised by means of paramagnetic resonance. Some additional effects influencing the experiments are also discussed.     

Variations of the band gap of Hg1 ? x Cd x Te solid solutions in response to a magnetic field

The optical transmission spectra of Hg_{1 ? x} Cd _x Te epitaxial layers with a magnetization gradient have been investigated experimentally. The magnetization gradient has been artificially created by the opposite arrangement of the poles of the magnets. The possibility of transforming the shape of the spectral dependences of the optical transmission of the HgCdTe films after their exposure to a magnetic field has been demonstrated. Assumptions about the mechanism underlying this phenomenon have been made.     

Optical and vibrational properties of CdxHg1-x-y ZnyTe solid solutions

The lattice dynamics of Cd_xHg_1-x-y Zn_yTe solid solutions is studied theoretically and experimentally. The frequencies of the basic optical phonons of Cd_xHg_1-x-y Zn_yTe are calculated in terms of a modified random-element isodisplacement model. As a result, all basic vibrations of the crystal lattice that substantially affect the optical properties of this material in the spectral region corresponding to one-phonon resonance are identified. The optical properties of epitaxial Cd_xHg_1-x-y Zn_yTe layers grown by liquid-phase epitaxy on Cd_1-x Zn_xTe substrates are studied. The calculated and experimental spectral dependences of the dielectric function of Cd_xHg_1-x-y Zn_yTe solid solutions of various compositions are compared at 295 and 78 K, and good agreement between them is reached. The additional lattice vibrations whose frequencies in the phonon density of states are lower than that of the HgTe mode are shown to be caused by the lattice defects of the Cd_xHg_1-x-y Zn_yTe solid solutions.     

Magnetic-field-induced change in optical transmission spectra of Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te epitaxial films

The optical transmission spectra of epitaxial Hg_{1 − x} Cd _x Te films with a gradient of the band gap have been studied experimentally. The possibility of transforming the spectra after exposure of the samples to a homogeneous magnetic field has been demonstrated. This effect is possibly caused by the dependence of the magnetization of the Hg_{1 − x} Cd _x Te films on the composition gradient of the solid solution.     

Cyclotron resonance in Hg1−xCdxTe at 337 micrometre in the range 77 K – 150 K

Cyclotron resonance experiments have been performed in transmission at 337 μm on Hg_1?xCd_xTe single crystals with x = 0.20 and 0.215, at temperatures between 77 and 150 K.     

Intracenter luminescence of Mn2+ in Cd1−x MnxTe and Cd1−x−y MnxMgyTe under intense optical pumping

A comparative analysis of the kinetic properties of intracenter 3d luminescence of Mn²⁺ ions in the dilute magnetic superconductors Cd_1?x Mn_xTe and Cd_1?x?y Mn_xMg_yTe is carried out. The influence of relative concentrations of the cation components on the position of the intracenter luminescence peak indicates that the introduction of magnesium enhances crystal field fluctuations. As a result, the processes facilitating nonlinear quenching of luminescence are suppressed. The kinetics of 3d-luminescence quenching in Cd_1?x Mn_xTe are accelerated considerably upon elevation of optical excitation level due to the evolution of cooperative processes in the system of excited manganese ions.     

On the possibility of a flare-up of discrete exciton absorption structure in n-CdxHg1−xTe crystals in a magnetic field

A discrete absorption peak with an exciton-like behavior was observed to flare up in Cd_xHg_1?xTe with x≈0.3 when a magnetic field H was applied. Its diamagnetic shift, which is replaced at high H by a close-to-linear relationship typical for diamagnetic exciton spectroscopy, and the splitting permit one to evaluate ?_g=0.2579±0.0001 eV and to calculate the band parameters of the material. Evaluation of the fluctuation potential well depth for the electrons and holes suggests, however, a high probability of exciton trapping at potential wells at H = 0 and x ≈ 0.3. Application of a magnetic field above 40 k0e can break the Coulomb bond between the electron and the hole, whereas at lower fields the existence of excitons is possible.     

Longitudinal magnetoresistance in zero-gap CdxHg1−xTe at low temperatures

The longitudinal magnetoresistance Δ?₆(H)/?₀ is studied experimentally in gapless solid solutions Cd_xHg_1?xTe (0 < x < 0.15) for temperatures 1.3–15 K and the electron concentrations n ～ 10¹⁵ cm^?3. The temperature and the magnetic field dependences of the observed negative longitudinal magnetoresistance are explained by the resonant nature of electron scattering by an acceptor level. The quantitative analysis of the $\text{Δ?6(H)}\text{?}{}_0$ field dependence for weak magnetic fields under strong carrier degeneracy makes it possible to evaluate parameters of the acceptor level involved.     

Spin effects on oscillatory magnetoresistances in CdxHg1−xTe

A study is made of spin effects on the Shubnikov-de Haas oscillations in Cd_xHg_1?xTe alloys. The difference between the longitudinal and transverse magnetoresistances can be interpreted in terms of the spin-orbit couplings.     

The fluctuation freeze-out of electrons in Cdx Hg1−x Te

The model was developed on the basis of experimental data, explaining pecularities of galvanomagnetic properties of Cd_x Hg_1?xTe by the “fluctuation freeze-out” of electrons - i.e. by their localization in fluctuation potential wells. In semimetallic samples this process is associated with a sharp increase in the fluctuation potential amplitude when the acceptor level goes out from the conduction band with the growth of magnetic field.     

Magnetic quantum oscillations in the photovoltaic effect of Cd0.24Hg0.76Te

The first experimental evidence of magnetic quantum oscillations in the photovoltaic effect is reported. Experiments were carried out with the p?n junction in Cd_0.24Hg_0.76Te placed in a quantizing magnetic field. The oscillations are related with the interband Γ₈ → Γ₆ magnetoabsorption transmissions. The discrepancy between experimental data and theory is explained by the effect of the p?n junction electric field on the magneto- absorption behaviour.     

Hot electron drift velocity in Hg1−xCdxTe (x=0.205)

Hot electron drift velocity in Hg_1?xCd_xTe (x=0.205) at 77 K is calculated by the Monte Carlo technique. Band nonparabolicity, admixture of wave functions, and two-mode nature of the polar optic phonons are included in addition to the effects of deformation potential acoustic, alloy and ionized impurity scattering. Good agreement with the experimental data is achieved.     

A general optical characterization method for determining the composition of Hg1−xCdxTe samples

The rate of variation of transmission as a function of frequency or energy exhibits a maximum in the fundamental absorption region of the alloy semiconductor Hg_1−xCd_xTe. The maximum steepness occurs in the tail region of the absorption edge and its frequency can be correlated analytically with the composition. From the experimental measurements of room temperature IR transmission on both bulk grown and epilayers of Hg_1−xCd_xTe, it is shown that an analysis of the transmission curve at (dT_r/dE)_max leads to the determination of composition and compositional uniformity in the given sample.     

On the gate capacitance of MOS structures of kane-type semiconductors under magnetic quantization

An attempt is made to formulate the gate capacitance of MOS structures of Kane-type semiconductors under magnetic quantization, without any approximations of weak or strong electric field limits, on the basis of the fourth-order effective mass theory and taking into account the interactions of the conduction, light-hole, heavy-hole, and split-off bands. It is found, taking n-channel Hg_1–x Cd _x Te as an example, that the gate capacitance exhibits spiky oscillations with changing magnetic field, which is in qualitative agreement with experimental observations, reported elsewhere, in MOS structures of the same semiconductor. The corresponding results for n-channel inversion layers on parabolic semiconductors are also obtained from the expressions derived.     

Observation of short-order clustering effect in Cd1−xHgxTe

The infrared lattice-vibration reflection spectra of Cd_1-xHg_xTe (0?x?0.8) solid solution were measured. For the composition x from 0.1 to 0.6 on the top of the CdTe-like band one can observe considerable fine structure. To account for its nature the short-range clustering of the cations (Cd, Hg) around the anions (Te) characterized by parameter β was supposed. A good fit of the calculated and measured reflectively spectra was obtained provided the clustering parameter β = 0.6.     

Low-frequency optical lattice vibrations in Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te alloys

The lattice reflection spectra of the Hg_{1 ? x} Cd _x Te (x = 0.06–0.70) alloys measured in the low-frequency range of optical vibrations (the region of the anomalous mode of Hg-Te vibrations in HgTe) at room temperature are interpreted. The low-frequency modes observed at frequencies of 98, 105, and 112 cm^?1 for all compositions of the Hg_{1 ? x} Cd _x Te alloy are assigned to the modes of Hg-Te vibrations, as was previously done for modes of Cd-Te vibrations in the quasi-molecular approximation. According to the double-well potential model for the Hg atom in the crystal lattice of the alloy, the Hg atom either can occupy the center of the anion tetrahedron or can be located in the off-center position. The fundamental strong mode of Hg-Te vibrations at a frequency of about 120 cm^?1 (at T = 300 K) corresponds to the vibrations of the off-center Hg atom, and the low-frequency vibration modes correspond to the vibrations of the Hg atom located at the center of the anion tetrahedron.     

Zeeman splitting of the conduction band of HgTe quantum wells with a semimetallic spectrum

Shubnikov–de Haas oscillations in Hg_1-xCd_x Te/HgTe/Hg_1-xCd_xTe structures with the widths of a well of 16 and 20 nm have been investigated in tilted magnetic fields. The spin-to-orbital splitting ratio in the conduction band has been found in a wide range of electron densities. The magnitude and density dependence of the ratio agree fairly well with the calculations of the spectrum in the 8-band kP model. It has been shown that the effective g factor is anisotropic, g_|| < g_┴. The anisotropy is very high at low densities but decreases rapidly with an increase in the density, approaching unity at n_e = (3?4) × 10¹¹ cm^-2.