From the Raman spectra performed at temperatures from 10 K to 295 K for Hg_{1-x}Fe_{x}S crystals containing up to a few percent of iron the phonon energies for selected high-symmetry points of the Brillouin zone have been determined. A very high ionicity of these mixed crystals has been found. The TO phonon frequency value for β-HgS at Γ point, equal to about 177 cm^{-1}, suggested previously in the literature, has been confirmed.
Co^{2+} centre in ZnTe has been proved to be an acceptor, contrary to the previous assignment, but in agreement with the general trend in the behaviour of the transition metal impurities in the II-VI compounds. The threshold of the Co^{2+} + hν → Co^{+1} + h transition has been found in the spectrum of photoconductivity at about 1.4 eV, close to the value already reported.
Measurement of photoluminescence as a function of temperature and of magnetic field in p-type phosphorus doped Cd_{1-x}Mn_{x}Te is reported. From the conduction band-acceptor level transition, the ionization energy of P-acceptors is obtained to be 54ą1 meV. The photoluminescence spectrum in the band edge region exhibits three maxima connected with the recombination of excitons bound to neutral acceptors (A^{0}, X), excitons bound to neutral donors (D^{0},X), and free excitons (X) at energies E_{(A^{0},X)}=1.606, E_{(D^{0},X)}=1.610, and E_{X}=1.614 eV, respectively. At T=1.4 K a strong increase in PL intensity of (A^{0}, X) line 8-fold as a function of magnetic field is found and shown to originate from the magnetic field-induced lowering of the acceptor binding energy and increase in the hole effective volume.
Results of measurements of electron concentration and mobility in mixed crystals of Hg_{1-x}Zn_{x}Se (0 ≤ x ≤ 0.07) doped with resonant Fe donors (0 ≤ n_{Fe} ≤ 5 × 10^{19} cm^{-3}) at liquid helium temperatures are presented. The data show that there is a considerable improvement of the electrical properties of the material when Fe impurities are present. The analysis of the mobility in terms of the scattering from ionized centers (accounting for possible spatial correlation of impurity charges) and the alloy scattering is in agreement with the measured data.
We present the results of the low temperature electron paramagnetic resonance (EPR) and transport investigations of the crystals of Pb_{1-x}Cr_{x}Te (x ≤ 0.01). The samples with chromium concentrations x ≥ 0.0015 are all n-type. For these samples we observe the single EPR line with the g-factor decreasing from g = 1.97 till g = 1.93 with increasing carrier concentration. This resonance can be attributed to electrically and magnetically active Cr^{3+} ions. The crystals with Cr concentration x ≤ 0.0015 may be both n- and p-type. The EPR spectrum of these samples consists of two lines: the one discussed above and the other one with g = 1.99 observed only for samples with electron concentration n ≤ 10^{18} cm^{-3}.
We present the results of the experimental studies of the low temperature transport and magnetic properties of PbTe, Pb_{1-x}Sn_{x}Te (x ≤ 0.3) and SnTe crystals doped with 0.5 at.% of chromium. Cr was found to be a resonant donor in PbTe and PbSnTe. Magnetic susceptibility measurements revealed that PbTe:Cr and Pb_{1-x}Sn_{x}Te:Cr (x ≤ 0.2) are Curie paramagnets whereas SnTe:Cr exhibits van Vleck paramagnetism.
Photovoltaic spectra of PbTe p-n junction have been measured in the infrared spectral region in the temperature range of 8-260 K. The p-n junctions have been formed by cadmium diffusion into the p-type PbTe crystals. From the positions of the photovoltaic maxima the energy gap of the diode material has been determined. In the presence of a magnetic field up to 7 T, a pronounced oscillatory behavior of the photovoltage was observed in the Faraday and Voigt configurations. Experiments were performed as a function of the magnetic field intensity at a constant wavelength of the incident light. The energy of the interband magnetooptical transitions between the Landau levels in PbTe was determined and compared with the theoretical model of Adler, describing the energy band structure for the IV-VI compounds.
In this paper the dependence of the band structure and the electron scattering mechanisms on the molar fraction x are studied in Hg_{1-x}Fe_{x}Se. The crossover from the zero-gap band to the open band-gap configuration at x ≈ 0.08 is predicted. We explain the drop of the electron mobility for x > 0.002 by the alloy scattering mechanism.
Reflectivity spectra of HgSe crystals highly doped with Ga and Fe, respectively, were investigated in the spectral region close to the absorption edge at temperatures between 12 K and 295 K. From the analysis of the structure observed in reflectivity the temperature dependence of the Fermi energy was determined for both kinds of crystals.
Infrared reflectivity was investigated for the mixed Hg_{1-x}Fe_{x}Se crystals for x < 0.1. The theoretical analysis of the experimental curves suggests opening of the energy gap for the composition x = 0.087 at the temperature close to 80 K.
Resonant photoemission spectra of cubic Ηg_{0.94}Fe_{0.06}S were measured for photon energies near to the energy of intra atomic Fe 3p^{6}3d^{6} → 3p^{5}3d^{7} transition. The difference between the spectra taken at resonance and antiresonance is presented as a measure of the energy distribution of Fe 3d derived states. The results obtained show that Fe 3d states contribute to the whole valence band with a distinct structure appearing at the band edge.
The results of transport investigation of Pb_{1-x}Cr_{x}Te (x ≤ 0.009) in temperature range 3.5-300 K are presented. The obtained electron concentration and electron mobility vs. temperature and Cr concentration data are interpreted and discussed within the model assuming that Cr in PbTe forms a donor state resonant with the conduction band.
Fe^{2+} crystal field transitions and the heavy hole valence band to the Fe level transitions (e + Fe^{3+} → Fe^{2+}) have been observed and discussed for HgSe doped with iron.
Reflectivity spectra of Hg_{1-x}Fe_{x}S (x < 0.04) and HgSe_{1-y}S_{y} (y < 0.5) mixed crystals were measured in the vacuum ultraviolet energy range from 4 to 12 eV. Information about the electronic band structure of cubic modification of HgS resulting from the above data is analyzed and discussed.
The low-temperature far-infrared reflectivity spectra of HgSe and HgSeS are measured and analysed. The results suggest the one-mode behavior of phonon excitations in HgSeS mixed crystals.
Optical phonons in mercury chalcogenides doped with selected transition metal ions are investigated by infrared reflectivity and Raman scattering measurements performed at helium temperatures. The results obtained for Hg_{1-x}Fe_{x}Se, Ηg_{1-x}Co_{x}Se, Ηg_{1-x}Fe_{x}S and Hg_{1-x}Co_{x}S mixed crystals demonstrate the significant influence of the 3d electron correlation effects and/or sp-d hybridization on the transition metal ion local mode frequency.
The high pressure Bridgman technique was used to grow Zn_{1-x}Mn_{x}Te:P crystals. Under the N_{2} pressure of 30 atm., we obtained the p^{+}-Zn_{1-x}Mn_{x}Te single crystals 8-10 mm in diameter, with free-carrier densities as high as p ≈ 8×10^{18} cm^{-3} and the room temperature conductivity σ(RT) ≈ 30 Ω^{-1}cm^{-1}. Magnetoresistance measurements were carried out down to 1.3 K and up to 6 T. In Zn_{1-x}Mn_{x}Te:P a strong increase in the acceptor binding energy as well as an immense (ρ(0,1.3K)/ρ(6T,1.3K) > 10^{3}) negative magnetoresistance are observed, by contrast, not seen in diamagnetic ZnTe:P. It is shown that these effects come from the formation of bound magnetic polarons and their destruction by an external magnetic field.
The acoustic phonon dispersion of mercury sulphide of zinc-blende structure (β-HgS) was studied by inelastic neutron scattering. The measurements were carried out at 19 K and 295 K on HgS crystals doped with Fe. A slight decrease in phonon frequencies with increasing temperature was found, the temperature dependence being the strongest for LA phonons with [ξ,ξ,0] propagation. From acoustic phonon dispersion the values of selected elastic constants were determined for β-HgS.
Hall constant, conductivity and magnetic susceptibility of Pb_{1-x-y}Sn_{y}Mn_{x}Te semimagnetic semiconductor were investigated as a function of Mn content (x = 0.04, 0.09, 0.16, y = (0.7-0.8)) in the temperature range T = (4 - 300) K. A ferromagnetic phase transition takes place at T = 5 K for samples with x = 0.04, at T = 10 K for x = 0.09 and at T = 20 K for x = 0.16. For crystals with x ≥ 0.09 the strong temperature dependence of the Hall constant is observed for temperatures below 40 K. Magnetic field characteristics of the Hall effect is strongly non-linear at T = 4.2 K. No significant temperature or magnetic field dependence of conductivity is observed in the whole temperature range studied. The observed transport anomalies are due to the anomalous Hall effect.
The elastic constants of single crystals of β-HgS highly doped with iron were directly determined at room temperature from the measurements of ultrasonic wave velocities by the pulse-echo technique. The values of c_{11}=6.750, c_{12}=5.186, and c_{44}=2.42 (given at 10^{10} N m^{-2} units) were obtained and compared with the experimental data taken for other mercury chalcogenides. The elastic characteristics of this group of materials is quite similar to those of Cd and Zn chalcogenides.
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