The results of studies of magnetoresistance for GaAs filamentous crystals doped with tellurium admixture to a concentration of 2 & BULL;10(17) cm(-3), in the temperature range 4.2-60 K and in the magnetic field ranges 0-14 T are presented. The GaAs filamentary crystal magnetoresistance has shown a sharp positive jump at a low magnetic field (up to 0.2 T) at a temperature near 4.2 K, while at higher magnetic field inductions linear behavior of magnetoresistance occurs. The low field magnetoresistance is discussed in the framework of weak localization of charge carriers due to their spin-orbit exchange interaction. The high-field linear magnetoresistance is connected with electron-electron interaction.

In this work, silicon microcrystals doped with a boron impurity to concentrations corresponding to the metal-dielectric transition in silicon of 5.51018 cm-3 and a nickel impurity in the temperature range of 4.2 divided by 70 K under alternating current in the frequency range of 0.010 divided by 250 kHz were studied. The features of the frequency response of silicon microcrystals are determined. On the basis of Nyquist diagrams, an equivalent conductivity scheme at low temperatures is proposed. The frequency response of the samples was evaluated and the mechanisms of charge carrier flow were proposed depending on the observation conditions. Conduction mechanisms from quantum mechanical tunneling (QMT) to superlinear power law (SLPL), which can be implemented in crystals, are considered.

Studies of temperature dependence of magnetoresistance for PdxBi2Se3 whiskers in the temperature range 1.6-77K in magnetic field up to 10 T were carried out. Crystals were grown by chemical transport reaction method in closed bromide system. The source and crystallization zone temperatures were 1100 K and 780 K, respectively. Doping of the crystals was carried out during the growth process with palladium impurity to concentrations of (1 – 2) × 1019 cm−3. In the low-temperature region beginning at a temperature of 5 K and reaching a temperature 3.5 K, a sharp decrease in resistance was observed, which is associated with the transition to superconducting state. Based on the analysis of the temperature dependence of the resistance at fixed magnetic fields, the Curie temperature Tc1=5.3 K and Tc2=3.5 K as well as the upper critical magnetic field Bc2=1.45 T and 0.25 T were determined. The established parameters indicates in II type supercondor. This is indicated by the ratio Δ0/kBTc = 2.0, which exceeds BCS limit of 1.76 and indicates a relatively large value of the superconducting gap Δ0=0.8 meV. The determined ratio A/γ2, which establishes the relationship between the electron-electron and electron-phonon interaction, is about of 2ao, which indicates a strong fermionic interaction with phonons in the PdxBi2Se3 superconductor. The estimated value of the ratio of the Curie temperature to the effective Fermi temperature equal to 0.04 also falls within the range of 0.01 ⩽ Tc/TF ⩽ 0.1, which confirms the unconventional superconductivity in the investigated whiskers.

The article is devoted to characteristics of charge carrier transfer in silicon microcrystals modified with a transition metal admixture with an unfilled 3d(+) local magnetic moment envelope and doped with boron to concentrations that correspond to the metal-dielectric transition. At cryogenic temperatures, the magnetoresistance of microcrystals was examined under the influence of magnetic fields up to 14 T. The outcomes of investigations into the magneto-transport characteristics of crystals were thoroughly examined. It was discovered that the transport of charge carriers for silicon microcrystals at low temperatures relies on hopping polarization conductivity. Based on the results of the Si < B, Ni> crystal magnetization study, the concentration of magnetic centers was determined, which is 4 x 10(17) CM-3. It is suggested to employ silicon microcrystals in magnetic field sensors that operate on the magnetoresistive principle.

The magnetoresistance of GaPxAs1-x (x = 0…0.45) whiskers with doping concentration of silicon in the range from the deep dielectric side of metal-insulated transition (~1017 сm-3) to its critical concentration (Nc ~ 5´1018 сm-3) at cryogenic temperatures of 4.2¸77 K and magnetic field induction of 0¸14 T was studied. A negative magnetic resistance (NMR) with maximum value of 7 % was found at temperature 4.2 K and magnetic field 4.5 T, which is dependent on magnetic field induction and current direction. The NMR absolute value reduces with increasing temperature was observed in the transverse and longitudinal magnetoresistance. The nature of the revealed NMR effect was discussed in the studied samples. There are four possible reasons of the NMR effect in the GaPxAs1-x whiskers such as the dimensional quantization, the magnetic ordering of electron spins or magnetic ordering due to uncontrolled magnetic dopant introduction and quantum interference of the electron wave function. The GaPxAs1-x whisker application as the temperature sensor was proposed due to the studied results of the temperature dependence of their conductivity.

It was studied the electrical magnetoresistance of nickel-and boron-doped filamentary silicon crystals in which a metal-insulator transition is observed. A giant magnetoresistance reaches up to 280% in the Si whiskers with doping concentration of boron р300K = 5⋅1018 cm−3 in the magnetic fields with induction up to 14 T at temperature 4.2 K. Peculiarities of magnetoresistance at low temperatures were shown to be caused by “core-shell” structure of crystals. A giant magnetoresistance nature was considered within quantum magnetoresistance model. The analysis was performed to determine the critical field of transition from classical parabolic magnetoresistance to quantum magnetoresistance, realized in the near-surface region of the crystal. The silicon whiskers were used for design of magnetic field sensors.

Strain-resistant properties of GaAs whiskers and ribbons of p- and n-type conductivity with various length (0.3–7 mm) and diameter (10–40 μm) have been investigated in a wide range of temperatures. Strain gages based on heavily doped p-type conductivity GaAs whiskers have linear deformation characteristics and a weak temperature dependence of strain sensitivity in the temperature range from –20 to +3500 °C. The temperature coefficient of resistance (TСR) of not fixed strain gages is about +(0.12–0.16)% × grad–1. The temperature coefficient of strain sensitivity is –0.03 % × deg–1 in the temperature range –120+800 °C. Strain gages based on n-type GaAs ribbons are characterized by high flexibility and high strain sensitivity. They are capable up to +4000 °C and can be used to measure deformations on curved surfaces at high temperatures. TСR of not fixed strain gages is –0.01 +0.03 % × grad–1. The temperature coefficient of strain sensitivity is –0.16% × deg–1 in the temperature range –120 ... +4000 °С.

The paper deals with studies of magnetization and magnetic susceptibility of Si1 -xGex B, Hf (x  0.05) whiskers with a diameter of about 1 μm in the temperatures range 77-300 K and magnetic fields up to 4.28 kOe.The obtained results have showed that the whisker magnetic susceptibility differs substantially from the typical diamagnetic bulk material.The main difference is connected with the existence of paramagnetic centers localized in the nanoporous coating, the so-called core-shell structure, of Si1 -xGex whiskers.This leads to the emergence of magnetic ordering in them and appearance of a paramagnetic component in the magnetic susceptibility.An increase in the paramagnetic component was observed due to the introduction of Hf dopants as separate paramagnetic centers.The oxygen presence in the whisker coreshell structure was also found due to Auger spectroscopy associated with the VLS mechanism of the Si1 -xGex whisker growth.As a result, HfO2 clusters are formed as a bulk material typical of diamagnets.The field behavior of the magnetic susceptibility component has a superparamagnetic character, which is characteristic of superparamagnetism saturation of magnetization and hysteresis absence in the temperature range 77-300 K. Therefore, the observed phenomena are explained by the existence of dangling bonds, as well as HfO2 clusters, in the whisker nanoporous coating according to magnetic ordering and the superparamagnetism appearance in Si1 -xGex B, Hf whiskers.

The temperature dependences of resistance for the p-type conductivity solid solution silicon–germanium whiskers doped by boron with concentration of 1 × 1018 cm−3 were investigated in the temperature range of 4.2–300 K and under the uniaxial compressive strain till − 3 × 10–3 rel. un. We studied the strain influence, which was caused on a spin–orbit splitting in the valence band spectrum. As an outcome, the spin–orbit splitting energies for both light and heavy holes were discovered based on the k–p method. The strain-induced effects of solid solution Si0.2Ge0.8 whiskers were studied at low temperatures. Found giant piezoresistive effect at helium temperature gives opportunity to create the supersensitive strain gages on the basis of silicon–germanium whiskers with doping concentration in the vicinity to the metal–insulator transition. The mechanical sensor operating at helium temperature and deformation range of 5 × 10–4–1.3 × 10–3 rel. un. was designed with the sensitive element Si0.2Ge0.8 whiskers doped to concentration 1 × 1018 cm−3.

In present paper p-type GaPAs whiskers doped with Cu were obtained by VLS method in close bromine system. The whiskers have various morphologies and geometries: imperfect needle-like crystals, ribbons, perfect needle-like crystals and thin plates. The whiskers of various morphologies serve as thermoresistores with TCR of about 1-2 %. The whisker I-U characteristics were investigated dependent on their geometry and external conditions (humidity). Voltage arising on the thermoresisor for two polarities of current passing through it was shown to be dependent on air humidity. Miniature semiconductor sensors of humidity based on GaPAs whiskers have been designed. Physical principles of operation, the perculiarities of design, and main performances of the microsensors were discussed. The whiskers of small diameter (d=50 μm) were shown to measure humidity in the range j=35...97% with sensitivity to humidity g =DU/Uj »2.5×10-3. The miniature dimensions of the whiskers provides very rapid response (of about a few sec) and small time of recovery (less than 30 sec).

The Bi(2)Se(3)whisker temperature dependencies of resistance with palladium doping concentration of (1 divided by 2)x10(19) cm(-3)were studied in the range of 1.5 divided by 77 K. At the temperature of 5.3 K there was found a sharp drop in the whisker resistance. This effect can be explained as a contribution of two processes: electron localization and superconductivity at temperatures under 5.3 K. The magnetoresistance in Bi(2)Se(3)whiskers with n-type conductivity and diverse concentration of Pd that correspond to the metal side of the MIT (metal-insulator transition) was studied at low temperatures and magnetic field in the range of 0 divided by 10 T. The magnetoconductance was considered in the structure by the weak antilocalization model and attached with subsurface layers of Bi(2)Se(3)whiskers.

The paper deals with studies of thermoelectric properties for Si1-xGex (x=0.01-0.05) whiskers doped with boron during their growth by CVD method. Temperature dependences of the resistance and the Seebeck coefficient for Si1-xGex whiskers were measured in the temperature range 275–550 K. A method for determination of thermoelectric parameters of the whisker was proposed with use of the whisker joints, which allows us to define a ratio of Seebeck coefficient to thermal conductivity a/k. Taking into account the obtained values of Seebeck coefficient, the whisker conductance and estimated values of thermal conductivity, parameter ZT was calculated for the whiskers and consists of 0.15 for T=200oC. The obtained value of ZT is in good coincidence with literature data for hop pressed Si-Ge nanocomposites. The humidity sensor was designed base on Si-Ge whiskers.

In present paper p-type GaPAs whiskers doped with Cu were obtained by VLS method in close bromine system. The whiskers have various morphologies and geometries: imperfect needle-like crystals, ribbons, perfect needle-like crystals and thin plates. The whiskers of various morphologies serve as thermoresistores with TCR of about 1 – 2 %. The whisker I-U characteristics were investigated dependent on their geometry and external conditions (humidity). Voltage arising on the thermoresisor for two polarities of current passing through it was shown to be dependent on air humidity. Miniature semiconductor sensors of humidity based on GaPAs whiskers have been designed. Physical principles of operation, the perculiarities of design, and main performances of the microsensors were discussed. The whiskers of small diameter (d = 50 μm) were shown to measure humidity in the range  = 35...97 % with sensitivity to humidity  = U/U  2.510. The miniature dimensions of the whiskers provides very rapid response (of about a few sec) and small time of recovery (less than 30 sec).

The present paper aims to study an effect of compression strain (up to epsilon = 3.10(-4)) on behavior of transverse magnetoresistance of InSb whiskers at cryogenic temperatures under high magnetic fields up to 10 T. The strained and unstrained InSb whiskers with the concentration of charge carriers from 6.10(16) to 6.10(17) cm(-3) in the vicinity to metal-insulator transition are under consideration. The effect of a giant magnetoresistance of 700 % at a temperature of 4.2 K was established for the InSb whiskers with carrier concentration of 2.10(17) cm(-3). The effect was used for the design of magnetic field sensors with a magnetoresistive principle of action. The whiskers with carrier concentration 6.10(16) cm(-3) due to a high gauge factor of about 350 was shown might be used in piezoresistance sensors able to work in harsh operating conditions in a temperature range of 4.2 to 50 K.

Strain influence on the longitudinal magnetoresistance for the n-type conductivity InSb whiskers doped by Sn to concentration 6·1016–6·1017 сm–3 was studied in the temperature range 4.2–40 K and magnetic field up to 10 T. The Shubnikov–de Haas oscillations at low temperatures were observed in the strained and unstrained samples in all range of doping concentrations and magnetic fields. The character of longitudinal magnetoresistance dependences was analyzed and compared with theoretical one. The whisker magnetoresistance alters its sign with increasing magnetic field. It is positive at weak magnetic fields and becomes negative at higher magnetic fields. Possible mechanism of the large value of negative magnetoresistance (NMR) was discussed in the InSb whiskers with doping concentration in the vicinity to metal–insulator transition. The origin of large NMR was explained by the existence of classical size effect and boundary scattering during conductance in subsurface whisker layers.

The authors investigate deformation-induced changes in the electrophysical parameters of the indium antimonide microcrystals at cryogenic temperatures in strong magnetic fields up to 10 T. It is determined that for strongly doped InSb microcrystals, the gauge factor at liquid-helium temperature is GF4.2K ≈ 72 for the charge carrier concentration of 2∙1017 сm–3, while being GF4.2K ≈ 47 for the concentration of 6∙1017 сm–3, at ε = –3∙10–4 rel. un. For the development of magnetic field sensors based on the magnetoresistive principle, the effect of a giant magnetic resistivity reaching 720% at a temperature of 4.2 K is used.

Strain influence on the behavior of temperature dependences of resistance was studied in the n-type conductivity GaSb whiskers with tellurium concentration 1.7 1018 сm–3. Analyzing these dependences in the temperature range 4.2–30 K strain inducted metal–insulator transition and partial superconductivity were found in the whiskers. The transverse and longitudinal magnetoresistances for unstrained and strained GaSb whiskers were also studied in ranges of magnetic field 0–3 T and temperature 1.5–60 K. The effects, such as a superconductivity and weak anti-localization were observed for unstrained and strained samples. The upper critical zero magnetic fields for superconductivity suppression were obtained in the whiskers. Strain was shown to decrease the superconductivity in GaSb samples. The strain induced splitting of degenerate level on two components with opposite and parallel spins was found in the n-type conductivity GaSb whiskers due to weak localization and anti-localization effects, respectively.

The field dependences of the magnetoresistance for germanium whiskers with gallium doping concentration of 2 . 10(17) cm(-3) were studied in the magnetic field range 0-14 T at temperature 4.2 K under compressive strain up to 0.2%. The strain influence on a spin-orbit splitting on the valence band spectrum was studied. As a result, the effective mass and the energies of spin-orbit splitting for light and heavy holes were found under the compressive strain according to kp method. From an analysis of the Shubnikov-de Haas magnetoresistance oscillations the effective mass of heavy holes m(c) = 0.25 m(0) was calculated. The spin-orbit splitting energy of heavy holes Delta(HH) = 15 meV, the Lande factor in direction [111] g* = 4.8 as well as the Rashba cubic parameter of spin-orbit interaction beta SO=1.10-28eV.m3 were found due to the studying of longitudinal magnetoconductance in strained Ge whiskers at low temperatures. The appearance of negative magnetoresistance in the magnetic field range up to 7 T likely results from the effect of charge carrier interaction.

The magnetoresistance of GeхSi1-х (x = 0.002¸ 0.11) whiskers with an acceptor concentration (Na = 3x1018¸ 2.1019 cm-3) near the metal-insulator transition (MIT) was studied at low temperatures (4.2 - 77)K in magnetic fields up to 14 T. It is shown that at 4.2 K the magnetoresistance of the Ge-Si whiskers on thedielectric side of the MIT is quadratic, while the magnetoresistance of the crystals on the metal side of the MIThas an exponential dependence on the magnetic field. In the samples in the immediate vicinity to the MIT on thedielectric side, negative magnetoresistance was detected, whereas in metal samples with a high germaniumcontent (x = 11 at.%) an anomalous positive magnetoresistance occurs. The resulting anomalous dependences arerespectively explained by the conductivity with respect to the delocalized A+ states of the upper Hubbard bandand the increase in the electron-electron interaction in Ge-Si whiskers at increasing germanium content.