Thermally induced impurity edge photoconductivity of CdS crystals

We investigate the effect of hardening on the edge photoconductivity spectra of “perfect” CdS crystals, measured at room temperature and at the boiling point of liquid nitrogen (T = 77 K). It is found that hardening leads to a spectrally nonuniform increase in the photosensitivity of the semiconductor and that the effect is predominantly observed in the (impurity) edge region of the spectrum. This effect is hypothetically attributed to thermally stimulated decay of intrinsic-defect clusters.     

Effect of iron impurity concentration on kinetics order of thermoluminescent blue emission in MgO single crystals

Thermoluminescence has been measured for two kinds of MgO single crystals. The kinetics of the 94°C glow peak for the blue emission was found to be second order for a sample containing iron in low concentration, while 1.3-order for one appreciably in high concentration. The result was discussed in terms of the concentrations of the recombination and retrapping centers.     

An anomalous emission excited near the absorption edge of pyrene crystals

Emission spectra and decay times of the fluorescence excited at the absorption edge region in pyrene crystals were measured. At liquid nitrogen temperature, the fluorescence under the excitation at 390 nm is considered as the excimer emission and its band peak shifts a little to the short wavelength in comparison with that of the excimer emission under the excitation at 360 nm. The emission decay times under the excitation at the 390 nm and 360 nm are about 155 ns and 180 ns, respectively, at liquid nitrogen temperature. The former decay time changes its value abruptly near 127 K. This abrupt change of the decay time may be due to the phase transition in pyrene crystals.     

Anomalies in the magnetic properties of copper impurity clusters in barium fluoride crystals

Copper impurity trimers with antiferromagnetic coupling between Cu²⁺ ions are synthesized in BaF₂ crystals. In some of the BaF₂: Cu crystals thus prepared, the concentration of copper stable trimers turns out to be higher than that of copper dimers and copper single centers. The BaF₂: Cu crystals are studied using electron paramagnetic resonance (EPR) spectroscopy at frequencies of 9.3, 23.0, and 37.0 GHz in the temperature range 4.2–77 K. It is found that the components of the effective tensor g for copper trimers depend strongly on the external magnetic field and temperature. A static model of the molecular structure of the copper trimer is proposed on the basis of the experimental data obtained.     

Pressure dependence of the absorption edge in ZnTe

Pressure dependence of the absorption edge in ZnTe has been studied at room temperature. In contrast with the previous result by Drickamer, a monotonous high-energy shift was observed up to about 90 kbar. Small anomalies observed at 30 and 50 kbar may correspond to the resistance decrease of ZnTe.     

Behavior of impurity copper in ZnGeP2 single crystals with diffusion doping

Results from a study of electrophysical and luminescent properties of zinc-germanium diphosphide single crystals, diffusion doped with copper, are presented. The nature of the dominant defects formed upon copper diffusion in ZnGeP₂ is determined using a thermodynamic analysis of defect formation processes in ZnGeP₂ and a ZnGeP₂: Cu solid solution performed within the framework of the quasichemical analysis method. It is demonstrated that by choosing the copper diffusion method the hole concentration in the ZnGeP₂ can be varied over the range 10¹²–10¹⁶ cm^–3. A retrograde character was observed in copper solubility in ZnGeP₂ compounds. Defect formation processes in ZnGeP₂ upon copper diffusion depend on the degree of atomic ordering in the cation sublattice at the diffusion annealing temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 64–69, February, 1985.     

Effect of irradiation on the laws of annealing of impurity hardening of NaCl crystals

Studies were carried out on crystals containing various types of impurity: Ca²⁺, a hole-acceptor impurity, which dissolves well in NaCl; and Pb²⁺, an electronacceptor impurity, which dissolves poorly in NaCl. For the first time when doped crystals were annealed softening was observed to occur as a result of irradiation with soft x-rays prior to the annealing. The microhardness of irradiated doped NaCl crystals drops below the value that corresponds to the unannealed unirradiated sample. This effect is more pronounced in NaCl:Pb. It is postulated that the weakening effect is due to the breakup of impurity complexes. This assumption is supported by the results of studies on the laws governing the annealing of dislocation structures about the imprints of an indenter. These laws are shown to depend on the type of impurity: processes of dislocation polygonization were observed in NaCl:Ca crystals and the dislocation distribution was random in NaCl:Pb crystals. Pre-irradiation of the latter caused dislocations to be built in and polygonization to appear. Evidently, by breaking up impurity complexes in NaCl:Pb crystals x-ray irradiation brings the state of the impurity in them closer to that in NaCl:Ca.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 57–62, August, 1988.     

The temperature dependence of the edge emission of GaSe single crystals at high excitation levels

The temperature dependence of five edge emission lines of GaSe at high excitation levels has been investigated by using the second harmonic of a neodymium-glass laser. The following lines were indentified at 77.3K:hv_B = 2.102 ± 0.002 eV, annihilation of free excitons; hv_C = 2.082 ± 0.003 eV, Auger recombination of free excitons; hv_D = 2.072 ± 0.003 eV and hv_E = 2.055 ± 0.004 eV, annihilation of free excitons with emission of optical phonons (LO₁ = 31 meVandLO₂ = 45 meV, respectively); hv_G = 2.036 ± 0.004 eV, radiative recombination at indirect transition with emission of LO₁ phonons.     

Effect of cobalt impurity ions on the magnetic and electrical properties of iron monosilicide crystals

The results of experimental investigations of Fe_{1 − x} Co _x Si crystals in the impurity limit with x = 0.001, 0.005, and 0.01 are reported. The temperature and field dependences of the magnetic susceptibility have been studied. According to the experimental data, the introduction of cobalt impurity leads to a change in the energy structure, which is most pronounced in a change in the electrical properties. The temperature, field, and concentration dependences of the resistivity have been measured. The results have been interpreted in the framework of the Kondo model.     

The effect of impurity atoms on the multiplication of edge dislocations

The multiplication of edge dislocations in impurity atmospheres was studied. Impurities pin a dislocation line, so that additional stress must be applied to “drive” a multiplication mechanism. An expression for diffusion redistribution of impurity atoms along a dislocation segment due to the nonuniform chemical potential was derived. The early stage of moderate-temperature creep is qualitatively explained in terms of theoretical analysis.     

Behaviour of copper in ZnTe : SEM-CL and PL

With highly refined ZnTe and a double copper diffusion procedure, we can dope correctly ZnTe. Copper diffusion gives in PL a complex spectrum if we are above the solubility limit of ZnTe : Cu and the “a” acceptor at 149 meV if we are below this limit of solubility. In SEM-CL, we can separate areas containing only the “a” acceptor from areas of copper excess (dark areas around Te-rich inclusions).     

Effect of correlation in the impurity defect distribution on the micromechanical properties of GaAs: Te single crystals

The micromechanical properties of Te-doped GaAs single crystals with free carrier density n ₀ = 10¹⁷?5 × 10¹⁸ cm^?3 were studied. The obtained data are as follows: the nonmonotonic concentration dependences of the microhardness, the lengths of dislocation rosette rays, the densities of dislocations, and the position and half-width of the Raman line of a transverse optical phonon. The data are interpreted in terms of spatial correlation in the impurity defect distribution.     

Aggregation of impurity centers in ionic crystals

Results of modeling of the aggregation process in complex centers of ionic crystals are presented. Concentration dependences of the number of paired centers are obtained. A nature of the paired luminescence centers is discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 62–65, February, 2007.     

Helical edge transport in the presence of a magnetic impurity

We consider the effects of electron scattering off a quantum magnetic impurity on the current–voltage characteristics of the helical edge of a two-dimensional topological insulator. We compute the backscattering contribution to the current along the edge for a general form of the exchange interaction matrix and arbitrary value of the magnetic impurity spin. We find that the differential conductance may exhibit a nonmonotonic dependence on the voltage with several extrema.