Galvanomagnetic effects in Fe40Ni40B20

Hall effect and magnetoresistance measurements on the amorphous ferromagnet Fe₄₀Ni₄₀B₂₀ are reported. Both properties are approximately independent of temperature (1.5–300 K) and related to magnetization. The extraordinary Hall coefficient is 3.5 × 10^?8 m³/As. The temperature dependence of the resistivity (1.5–30 K) is also reported.     

Physical properties of n-CdGeAs2 single crystals prepared by low-temperature crystallization

The first results obtained in studies of the temperature dependences of electrical conductivity and Hall constant of n-CdGeAs₂ single crystals prepared by low-temperature crystallization are reported. It has been established that the method developed permits growing single crystals with a free-electron concentration ⋍(1−2)×10¹⁸ cm⁻³ and a Hall mobility ⋍10000 cm²/(Vs) at T=300 K. It is shown that the temperature dependence of Hall mobility exhibits a behavior characteristic of electron scattering by lattice vibrations, whereas below 150 K a deviation from this law is observed to occur evidencing an increasing contribution of static lattice defects to scattering. The Hall mobility in the crystals prepared was found to reach ⋍36000 cm²/(Vs) at 77 K. Photosensitive heterojunctions based on n-CdGeAs₂ single crystals were prepared. The spectral response of the photosensitivity of these structures is analyzed. It is concluded that this method is promising for preparation of perfect CdGeAs₂ crystals. Fiz. Tverd. Tela (St. Petersburg) 41, 1190–1193 (July 1999)     

Hall effect and magnetoresistance of (SN)x films

Hall effect and electrical conductivity have been investigated between 77 K and 300 K and the magnetoresistance at 4.2 K for a number of (SN)_x films deposited at substrate temperatures between — 10 and 50°C. The small magnitude of the Hall mobility (? 1 cm² Vsec^?1 at 300 K) and its activated temperature dependence are interpreted in terms of a heterogenous model for (SN)_x films with thin depletion layers separating highly conductive islands. The hole concentration in these islands (p ≈ 10²¹ cm^?3, the microscopic mobility (μ ≈ 500 cm² Vsec^?1 at 4.2 K) and the temperatures dependence of μ are found to be close to values for (SN)_x crystals.     

New experimental results for electron transport in weak accumulation layers of ZnO crystals

Previous Hall measurements on (0001) and (0001&#x0304;) faces of ZnO have shown a Hall mobility oscillating as a function of Hall surface electron density in the range between N_SH=10⁶ and 10¹¹ cm^?2. Here we report on new results obtained by a field effect arrangement for free surfaces in UHV. With donors from H exposure or by illumination weak accumulation layers (n_sh <10¹¹ cm^?2) are established. The field effect shows oscillations in surface conductivity as a function of gate voltage. Also the combination of a field effect with a Hall effect measurement reveals discrete values of Hall surface electron density n_sh. Various pretreatments do not change the periodicity of these oscillations. Necessary preconditions are a temperature below 130 K, a Hall surface electron density below 3 × 10¹² cm^?2 and a source-drain field of a few V/cm. A model regarding impurity levels in the space charge layer relates the results of the field effect measurements to the results of the Hall effect measurements.     

On the phonon Hall effect in a paramagnetic dielectric

The phonon Hall effect in the paramagnetic dielectric garnet Tb₃Ga₅O₁₂ has been investigated. It has been found that the coefficient of the phonon Hall effect is positive and is equal to (3.5 ± 2) × 10^?5T^?1 in a magnetic field of 3 T at a temperature of 5.13 K. The results are experimental evidence of the phonon Hall effect in the paramagnetic dielectric found by C. Strohm, G. L. J. A. Rikken, and P. Wyder, Phys. Rev. Lett. 95, 155901 (2005).     

Temperature dependence of the hall effect in amorphous Ni-Si-B alloys between 1.5 and 290 K: Evidence for magnetic ordering near a resistance minimum

The Hall effect in the metallic glasses Ni₇₆Si₁₂B₁₂, Ni₇₈Si₈B₁₄ and Ni₈₀Si₁₀B₁₀ has been measured as a function of temperature (1.5 ≤ T ≤ 290 K) and magnetic field (B ^<_～ 1.2 Tesla). At room temperature the Hall resistivity ρ_H is negative and depends linearly on the magnetic field for all three compositions. With decreasing temperature Ni₈₀Si₁₀B₁₀ exhibits a negative spontaneous Hall coefficient and a transition to ferromagnetism at about 110 K. In case of Ni₇₆Si₁₂B₁₂ and Ni₇₈Si₈B₁₄ an anomalous part contributes below ～ 40 K and ρ_H changes from negative to positive sign at about 9 K. For these two alloys we find that the initial slope of the ρ_H(B) curves follows a Curie-Weiss law with Tθ ≈ 0 K and the anomalous contribution of the Hall resistivity can be described by a Brillouin function for superparamagnetism.     

Hall mobility of amorphous Ge2Sb2Te5

The electrical conductivity, Seebeck coefficient, and Hall coefficient of three-micron-thick films of amorphous Ge₂Sb₂Te₅ have been measured as functions of temperature from room temperature down to as low as 200 K. The electrical conductivity manifests an Arrhenius behavior. The Seebeck coefficient is p-type with behavior indicative of multi-band transport. The Hall mobility is n-type and low (near 0.07 cm²/V s at room temperature).     

Transport properties of n-type ferromagnetic semiconductor HgCr2−xInxSe4(x = 0.100)

Measurements of the electrical conductivity, magnetoresistance, and Hall effect were performed on a n-type ferromagnetic semiconductor HgCr_2?xIn_xSe₄(x = 0.100) single crystal from 6.3 to 296 K in magnetic fields up to 1.19×l0⁶A/m. The conductivity decreases rapidly near the Curie temperatureT_c (≈120 K) as the temperature is raised. A large peak in the magnetoresistance is observed near T_c. The Hall effect measurements indicate that the temperature dependence of the conductivity and the magnetoresistance are due mostly to a change in electron mobility. The electron mobility is 1.2 × 10^?2 m²/V · s at 6.3 K, and decreases rapidly near T_c with the rise in temperature. Then it increases slowly from 5.5 × 10^?4 m²/V · s at 160 K to 7.5 × 10^?4 m²/V · s at 241 K. This temperature dependence of the electron mobility can be explained in terms of the spin-disorder scattering which takes into account the exchange interaction between charge carriers and localized magnetic moments.     

Low temperature thermoelectric properties of Pb- or Sn-doped Bi-Sb alloys

Pb- or Sn-doped Bi₈₈Sb₁₂ alloys were prepared by direct melting, quenching, and annealing. The Bi-Sb alloy phase was predominant in all samples. Pb or Sn atoms were distributed almost uniformly in Bi₈₈Sb_12, while some segregation was confirmed at the grain boundaries when Pb or Sn was involved heavily. The thermoelectric properties of these doped materials were investigated by measuring the Hall coefficient, electrical resistivity, and Seebeck coefficient between 20 K and 300 K. The Hall and Seebeck coefficients of Pb- or Sn-doped samples were positive at low temperatures, indicating that the doping element acted as an acceptor. Temperatures resulting in positive Hall and Seebeck coefficients further increased with increasing doping amount and with respect to the annealing process. As a result, a large power factor of 1.2 W/mK² could be obtained in the 3-at% Sn-doped sample at 220 K, with a large positive Seebeck coefficient.     

Carrier scattering mechanisms in P-type indium selenide

Carrier scattering mechanisms in p-indium selenide are investigated by means of the temperature dependence of the Hall mobility (160–500 K) and thermopower (200–300 K). An anomalous behaviour of the Hall voltage, which changes sign below 215 K, is interpreted through the existence of planar aggregates of ionized shallow donor impurities that create potential wells behaving as deep donors and in which a low concentration of two-dimensional free electrons can exist. This fact is taken into account through equations for two-carrier Hall effect. Holes are found to be predominantly scattered by anA ₁ homopolar phonon with an energy of 27.8 meV. From thermopower results, the density of states effective mass in the valence band is determined,m _dv ^* =(1.5±0.2)m ₀.     

Electrical properties of tellurium clusters on the void sublattice of an opal crystal: The important role played by the Te-SiO2 interface

The temperature dependences of electrical resistivity and of the Hall effect of nanocluster tellurium crystals obtained by filling the voids in a dielectric (opal) matrix with a melt of pure and doped Te were studied. The Hall hole concentration p _eff was found to increase anomalously (by more than two orders of magnitude) in a sample prepared from pure Te and cooled to helium temperatures. At T=1.45 K, the hole concentration in this sample was p _eff?6×10¹⁷ cm^?3. At the same time, the Hall effect in this sample was observed to reverse sign at T?200 K from positive for T<200 K to negative at higher temperatures. This implies a low impurity concentration (N _A is less than at least 10¹⁵ cm^?3). A nanocluster crystal of doped Te does not exhibit this anomaly; here, we have p _eff?6×10¹⁷ cm^?3 throughout the temperature region covered, as in the original Te. These features are assigned to the formation of a two-dimensional conducting accumulation layer near the Te-amorphous SiO₂ (the opal material) interface at low temperatures; such a layer determines the low-temperature properties of nanocluster crystals prepared from pure Te. Actually, we obtained a model of a three-dimensional structure formed from a two-dimensional film.     

Mobility of electrons in SnS2−xSex

The electrical resistivities and Hall constants of the semiconducting compounds SnS_2?xSe_x have been measured at temperatures ranging from 100 to 450 K and three donor ionization energies (0.013, 0.086 and 0.25 eV) have been identified. The Hall mobilities exhibit for T> 200K a temperature dependence of the form μ～ (T/T₀)^?n separating the SnS_2?xSe_x compounds into two groups one behaving like SnS₂ and the other like SnSe₂.     

Low temperature subband 2D electron mobilities in heavy delta- and modulation doped GaAs/GaAlAs heterostructures

We synthesised high-2D electron-density GaGs/GaAlAs heterostructures with different distance L_σ of Si delta-layer in GaAs from the heterojunction and uniform doped GaAlAs. The quantum Hall effect and Shubnikov-de Haas effect were measured for temperatures down to 0.4 K in magnetic fields up to 40 T. The enhanced 2D electron concentration achieved was 1.1^*10¹³ cm^?2 in six filled subbands. The Hall mobility depends on L_σ and has maximum for L_σ=600÷750Å. From the amplitudes of the SdH oscillations and Fourier transforms the subband mobilities and electron concentration in each subband have been extracted. According to calculations intersubband electron scattering appears to be important and reduces mobilities in subbands.     

High-quality two-dimensional electron gas at large scale GaN/AlGaN wafer interface prepared by mass production MOCVD systems

Basic electronic properties of two-dimensional electron gas (2DEG) formed at GaN/AlGaN hetero-interface in large-scale (100 mm) wafer made by metal organic chemical vapour deposition (MOCVD) have been reported and discussed. From conventional Hall measurements, highest electron mobility was found to be μ_e∼1680 and 9000 cm²/V s at room temperature and at ∼5 K, respectively, for sheet electron density of n_s∼8×10¹² cm⁻². In magneto-resistance (MR) measurements carried out at 1.5 K in Hall bar sample defined by photolithography and ion implantation, very clear Schubnikov de-Haas oscillations and integer quantum Hall effect were observed in diagonal (R_xx) and off-diagonal (R_xy) resistances, respectively. In addition, a good insulating nature of GaN layer is confirmed by capacitance-voltage (C-V) measurement. These results suggest the high-qualitiness of our 100 mm GaN/AlGaN high electron mobility transistor (HEMT) wafers comparable to those so far reported.     

Hall effect plateaus and giant Shubnikov-de Haas oscillations in (BiSb)Telayered single crystals near the quantum limit

On bulk layered single crystals (Bi_0.25Sb_0.75)₂Te₃ with a hole concentration cm^-3 and a mobility cm²/Vs magnetoresistance and Hall effect investigations were performed in the temperature range T = 1.4 K ... 20 K in magnetic fields up to 18 T. For the magnetic field perpendicular to the layered structure giant Shubnikov-de Haas oscillations are measured; the positions of the maxima are triplets in the reciprocally scaled magnetic field. From the damping of the amplitudes with increasing temperature the cyclotron mass m _c = 0.12m ₀ is evaluated. Correlated with the SdH oscillations doublets of Hall effect plateaus (or kinks in low fields) are found. The weak well known Shubnikov-de Haas oscillations from the generally accepted multivallied highest valence band can be detected as a modulation on the giant oscillation. The high anisotropy of the SdH oscillations and their triplet structure in connection with the layered crystal structure lead us to suggest that the effects are caused by hole carrier pairing (mediated by the bipolaron mechanism) in quasi 2D sheets parallel to the crystal layer stacks. The measured Hall plateau resistances coincide with the quantum Hall effect values considering the number of layer stacks and the valley degeneracy of the 3D hole carrier reservoir. The ratio of spin splitting to Landau (cyclotron) splitting is observed to be . Received: 12 September 1997 / Revised: 8 January 1998 / Accepted: 22 January 1998     

Hall mobility in quasi one-dimensional conductors with charge density or spin density wave ground state

High mobilities found for free carriers below the phase transition in quasi one-dimensional crystals such as TTF-TCNQ and (TMTSF)₂PF₆ indicate that defect scattering is unimportant. We calculate the Hall mobility due to phonon scattering and find good agreement with the measured value of 10⁴cm²/Vsec for (TMTSF)₂PF₆ at 4K.     

Halleffekt und anisotropie der beweglichkeit der elektronen in ZnO

Hallconstant, conductivity and Hall mobility of ZnO crystals were measured as function of temperature (4 °K < T < 370 °K) and orientation. Value and anisotropy of mobility can be explained (50 °K < T < 370 °K) by polar optical scattering, deformation potential sc., piezoelectric sc. and sc. by ionized impurities. The anisotropy of mobility is caused only by piezoelectric sc. Maximum values of μ_H are reached for μ_H ⊥ c, with 2400 cm²/V sec at 40 °K and for μ_H ¦ c with 1350cm²/Vsec at 60 °. Below 50 °K Hallconstant, conductivity and Hall mobility are influenced by impurity band conduction processes. The crystals have impurity concentration in the 10¹⁶ cm^?3 range, but they show different donor activation energies depending on growth conditions: Type I: 38,4 meV (50 °K < T < 100 °K) and Type II: 20,3 meV (50 °K < T < 100 °K) and 6 meV (25 °K < T < 50 °K).     

Correlation of resonance scattering and superconductivity in PbxSn1−xTe solid solutions doped with In

The Hall coefficient and resistivity were measured on a series of samples of Pb_xSn_1−xTe with 0x0.45 and 5 at% of InTe as a dopant. All samples show p-type conductivity with hole concentration in the range from 10¹⁹ to 10²¹ cm⁻³ at 77 K. A slight decrease of Hall mobility and corresponding increase in the scattering cross-section of holes by impurity atoms was observed with an extremum at x=0.25. All samples exhibit a transition to a superconducting state with the critical temperatures ranging from 0.3 to 3.0 K. The maximum of dH_c2/dT (where H_c2 is the second critical field) correlates with the fall in mobility (or rise in the scattering cross-section of holes), which shows that the resonance scattering mechanism is playing an important role in the enhancement of superconducting properties of these solid solution materials.     

Enhancement of the electron mobility with infrared photoexcitation in Si: Te at low temperatures

Hall measurements on Te-doped silicon (N _Te 10¹⁶ cm^–3) have been performed in the temperature range between 10 K and 300 K with infrared photoexcitation of electrons into the conduction band. The samples exhibit electron Hall mobilities which are increased by approximately 50% compared to measurements in the dark. The increased electron mobility can be correlated with an increased electron population of shallow donor levels by photoexcitation. Coulomb scattering due to charged shallow donor centers is converted into less efficient dipole scattering (Te-acceptor pairs) by the light-induced redistribution of electrons.     

Influence of radiation-induced clusters on transport properties of silicon

Summary A calculation method for the scattering cross-section σ of charged carriers on radiation-induced cluster defects has been developed using a spherical cluster model with rectangular potential barrier shape, of radius and height of 15 nm and 0.6 eV, respectively. Values of the cluster cross-section around 2·10⁻¹¹ cm² have been obtained for charged carrier energies from 10⁻⁴ eV to over 600 eV. Applying the relaxation-time approximation of the Boltzmann equation, the influence of clusters on silicon transport properties has been observed to be close to the acoustic-phonon one. The dependence of the Hall factor on radiation-induced clusters has been determined numerically for temperatures ranging from 5 K to 400 K. The results indicate that the presence of clusters of such dimensions would not change significantly the Hall coefficientR _H.