Hall Effect Experiments Research Articles

2D-hole accumulation layer in hydrogen terminated diamond

Hydrogen-terminated diamond films have been investigated by Contact Potential Difference Measurements (CPD or Kelvin force), Hall-effect experiments and theoretical calculations where the Schrodinger and Poisson equations have been solved to calculate the density of state (DOS) distribution at the surface of hydrogen terminated diamond. From CPD experiments we detect the Fermi-energy to be about 700 meV deep in the valence band. This is in agreement with results from numerical calculations, where Fermi-energies in the range 240 to 880 meV below the valence-band maximum at the surface are deduced. The calculations show that a two-dimensional (2D) density-of-state is present at the surface. Temperature dependent hole sheet-densities and mobilities are used to discuss the properties of the 2D-DOS. From this data we conclude that the 2D-DOS is distorted by disorder arising from non-perfect hydrogen termination of the surface, by surface roughness and/or by ionic molecules which are part of the adsorbate layer.

Electronic properties of the 2D-hole accumulation layer on hydrogen terminated diamond

Hydrogen-terminated diamond films have been investigated by Contact Potential Difference Measurements (CPD or Kelvin force), Hall effect experiments and theoretical calculations where the Schrödinger and Poisson equations have been solved to calculate the density of state (DOS) distribution at the surface of hydrogen-terminated diamond. From CPD experiments, we detect the Fermi energy to be about 700-meV deep in the valence band. This is in agreement with results from numerical calculations, where Fermi energies in the range 240–880 meV below the valence band maximum at the surface are deduced. The calculations show that a two-dimensional (2D) density of state is present at the surface. Temperature-dependent hole sheet densities and mobilities are used to discuss the properties of the 2D-DOS. From this data, we conclude that the 2D-DOS is distorted by disorder arising from nonperfect hydrogen termination of the surface, by surface roughness, and/or by ionic molecules, which are part of the adsorbate layer.

Investigations on the physical properties of the SnO 2–ZnO transparent conducting binary–binary system deposited by spray pyrolysis technique

In this paper, deposition, electrical, optical and structural characterizations of SnO 2–ZnO transparent conducting binary–binary systems with various compositions have been investigated. Firstly, the n-type SnO 2 thin films are deposited using a hydro-alcoholic solution by spray pyrolysis technique. Then, certain amounts of zinc chloride (anhydrous) have been added to the initial solution, in order to prepare the SnO 2–ZnO transparent conducting binary–binary system with various chemical compositions. The SnO 2–ZnO polycrystalline thin films were deposited at T S=480 °C with a Zn-content [Zn/(Sn+Zn)] atomic ratio of 0–30 at.% in films. The effect of increasing Zn-content on electrical, optical and structural properties of SnO 2–ZnO films has been studied. The results of X-ray diffraction and Scanning electron microscopy analysis, Hall effect experiment and resistivity measurement of films in the high Zn-concentration indicate the association of both SnO 2 and ZnO phases in thin film structure. In addition, for a given Zn-content atomic ratio (20.7 at.% in film), both electrical conductivity and carrier concentration increased sharply.

Specific heat capacity of AuTe2I below 100 K

AbstractThe heat capacity of AuTe2I was measured in the temperature range of 0.7 K < T < 100 K. The resulting low temperature limiting Debye temperature and electronic contribution were determined to be θ0 = (140 ± 1.5) K and γ = (1.54 ± 0.04) mJ/mol K2, respectively, the latter in reasonable agreement with earlier results from Hall effect and Shubnikov de Haas experiments.

Blocking phenomena in granular magnetic alloys through magnetization, Hall effect, and magnetoresistance experiments

Magnetization and magnetotransport were measured in CoxAg1−x granular composites as a function of temperature and applied magnetic field. A transition from blocked to superparamagnetic behavior with increasing temperatures can be observed in magnetization, giant magnetoresistance and the extraordinary Hall effect measurements. However, the blocking temperature determined from magnetotransport measurements is systematically lower than the one estimated from magnetic measurements. This is due to the selective magnetic scattering, which is enhanced for smaller particles, while the magnetization probes the whole particle size distribution.

The sign of vortex charges in high temperature superconductors

Based on a widely adopted effective model Hamiltonian with competing antiferromagnetic (AF) and d-wave superconductivity (DSC) interactions, the vortex charge in high T c superconductors is investigated by solving self-consistently the Bogoliubv-de Gennes equations. The band parameters are chosen in such a way that the obtained local densities at and far away from the vortex center are in qualitative agreement with the STM measurements on YBCO. Both the hole-rich normal and electron-rich AF vortices are found, dtpending on the strength of induced AF order. The vortex charge is strongly influenced by the competing effects from the AF order and the DSC order at the vortex core .By tuning the on-site Coulomb repulsion U or the doping parameter δ, a transition between the positive and negative vortex charges may occur. Recent NMR and Hall effect experiments on vortex charges can be anderstood in terms of the present results. New imaging experiments should be able to probe the vortex charge directly.

Electrical properties of 1.55 [micro sign]m sensitive ion-irradiated InGaAs with subpicosecond carrier lifetime

Carrier lifetimes as short as 270 fs with carrier mobility of 200 cm2/V/s and good performances in terms of layer resistivity have been obtained from ion-irradiated InGaAs. The residual carrier concentration measured in Hall effect experiments was found to be weakly modified in spite of the high defect concentration created by the ion bombardment. Ion-irradiated InGaAs appears to be specially adapted to fast photoconductive devices operating at optical communication wavelengths.

The effect of high acceptor dopant concentration of Zn2+ on electrical, optical and structural properties of the In2O3 transparent conducting thin films

In this paper, deposition and electrical, optical and structural characterizations of the In2O3:Zn transparent conducting thin films are investigated. At first, undoped and non-stoichiometric n-In2O3 thin films are deposited using an alcoholic solution by spray pyrolysis technique. Then, in order to prepare Zn-doped In2O3 thin films, certain amounts of zinc chloride are added to the initial solution. Finally, the effects of Zn doping on electrical, optical and structural properties of In2O3 films are studied. The results of XRD analysis, Hall effect experiment and resistivity measurement of films indicate that no phase change in In2O3 lattice occurs in high acceptor doping condition, and for a given acceptor dopant (Zn2+) concentration (∼6wt% in solution), electrical conductivity increases sharply and p-conductivity dominates.

Electrical Conduction of AlGaN/GaN 2DEG Heterostructures Grown on Si(111)

The growth of III–nitrides on Si(111) substrate by plasma assisted molecular beam epitaxy is addressed. Growth optimization of GaN layer is reported. Different III–N flux ratio, substrate temperature and buffer layer structures were chosen as optimization parameters. Significant improvement of the GaN properties is achieved using AlGaN/AlN buffers. Temperature-dependent Hall effect experiments show a complex behavior, whereby p- and n-type conductivity is observed.

Vortex charges in high-temperature superconductors.

Based on a model Hamiltonian with competing antiferromagnetic (AF) and d-wave superconductivity interactions, the vortex charge is investigated by solving the Bogoliubov-de Gennes equations. We found that the vortex charge is negative when a sufficient strength of AF order is induced inside the vortex core; otherwise, it is positive. By tuning the on-site Coulomb repulsion U or the doping parameter delta, a transition between the positive and negative vortex charges may occur. The vortex charge at optimal doping has also been studied as a function of magnetic field. Recent NMR and Hall effect experiments may be understood in terms of the present results.

SAMPLE COOLING AND ROTATION AT ULTRA-LOW TEMPERATURES AND HIGH MAGNETIC FIELDS

A rotator, made from polycarbonate and operated hydraulically using liquid helium, has been developed at the High B/T Facility of the National High Magnetic Field Laboratory (NHMFL) in Gainesville, It can be tilted more than 90 degrees by applying a pressure of several bars. The frictional heating was found to be negligible down to 8.0 mK. The sintered silver powder heat exchangers, specially designed for the cooling of the two-dimensional electron gas (2DEG) system in the fractional quantum Hall effect (FQHE) experiment,1,2 are also attached to the rotator. We have conducted an angular-dependent study of the even-denominator FQHE state at ν = 5/2. Our preliminary data showed that the rotator performed well at ultra-low temperatures and high magnetic fields. This technique should be applicable for other transport measurements at such extreme experimental conditions.

On the magnetic and superconducting properties of Ru1−xSr2RECu2+xO8−d, RE=Gd, Eu, compounds

The temperature of the superconducting transition of Ru1−xSr2RECu2+xO8−d (RE=Gd, Eu) compounds was raised up to 72 K (for x=0.4; compare to TC=45 K observed for RuSr2GdCu2O8) by changing the ratio between Ru and Cu. Magnetization experiments performed under external pressure for RE=Gd: x=0.1, 0.2, 0.3, and 0.4, and RE=Eu: x=0.4 samples reveal that TC increases at a rate of 5–6 K/GPa. The hole doping achieved along the series has been probed in Hall effect, thermopower, and XANES experiments and is found to increase with x. Muon spin rotation spectroscopy experiments reveal the presence of a low temperature magnetic transition for Ru0.6Sr2EuCu2.4O8−d (Tm≈5 K), similar to that recently observed in the Ru1−xSr2GdCu2+xO8−d system [P. W. Klamut, et al., Physica C 364, 313 (2001)]. Low temperature magnetization data suggest the constrained dimensionality of the superconducting phase in both RE=Gd and Eu based compounds.

EUROMET Project 432: Frequency performance of 12 906 Ω and 6453 Ω reference resistors for ac quantum Hall effect experiments

The Czech Technical University (CTU), acting as pilot laboratory in an international comparison, has fabricated and provided as transfer standards four terminal-pair thermostatted travelling resistance standards with nominal values of 12906 Ω and 6453 Ω. Vishay S 102 K resistors form the resistive elements of these standards and 100 Ω platinum resistance thermometers make it possible to monitor their inner temperature. The laboratories participating in the comparison (five in Europe and one in Canada) were requested to measure the frequency dependences and time constants of the travelling standards by comparing them with resistors with calculable frequency performance. Calculable resistors of several different designs (monofilar, bifilar, quadrifilar and octofilar) were available. For both travelling standards, the ac-dc differences of the parallel equivalent resistance, as reported by the different laboratories, are within 13 parts in 108 at 500 Hz and 70 parts in 108 at 5000 Hz. The reported time constants differ by less than 3.9 ns and 4.8 ns, respectively.

Quantum size effect transition in percolating nanocomposite films

We report on unique electronic properties in Fe-SiO2 nanocomposite thin films in the vicinity of the percolation threshold. The electronic transport is dominated by quantum corrections to the metallic conduction of the Infinite Cluster (IC). At low temperature, mesoscopic effects revealed on the conductivity, Hall effect experiments and low frequency electrical noise (random telegraph noise and 1/f noise) strongly support the existence of a temperature-induced Quantum Size Effect (QSE) transition in the metallic conduction path. Below a critical temperature related to the geometrical constriction sizes of the IC, the electronic conductivity is mainly governed by active tunnel conductance across barriers in the metallic network. The high 1/f noise level and the random telegraph noise are consistently explained by random potential modulation of the barriers transmittance due to local Coulomb charges. Our results provide evidence that a lowering of the temperature is somehow equivalent to a decrease of the metal fraction in the vicinity of the percolation limit.

KINETIC THEORY OF INFRARED HALL EFFECT IN SIMPLE METALS

A kinetic theory is developed for the infrared (IR) Hall effect. The dynamic transport coefficients including the conductivity σ, cot θ H (θ H = Hall angle ) and the Hall coefficient R H for a system of conduction electrons ("electrons" or "holes") are shown to be obtained by applying the conversion rule: γ0 → γ(ω) -iω to the expressions for the static coefficients, where γ0 [γ(ω)] are static (dynamic) scattering rates which depend on the frequency ω and temperature T. If the real (Re) and imaginary (Im) parts of σ(ω) are measured, the ratio Re [σ(ω)]/ Im [σ(ω)] is equal to γ/ω, which directly gives the dynamic rate γ(ω, T). The ratio Re [ cot θ H ]/ Im [ cot θ H ] = -γ H (ω, T)/ω yields the dynamic Hall rate γ H (ω, T). The IR Hall effect experiments give a remarkable result: γ H (ω, T) = γ H , 0(T), that is, the dynamic Hall scattering rate is equal to the static rate up to mid-IR ~1000 cm -1.

Strong isotope effects in the ultraviolet light-induced reactivation of dopants in hydrogenated or deuterated n-GaAs :Si

The reactivation of silicon donors in hydrogenated n-GaAs :Si under illumination is studied by electrical conductivity and Hall effect experiments at different excitation wavelengths. Ultraviolet illumination at room temperature of hydrogenated n-GaAs :Si by photons with energies above 3.5 eV is found to be an efficient alternative way to reactivate silicon donors. A very weak barrier exists for the dissociation of Si–H(D) complexes under UV excitation. Moreover, a strong isotope effect is observed in the dissociation kinetics of these complexes at 300 K and 100 K for low photon densities. We propose that the UV illumination induces an electronic excitation of Si–H complexes in GaAs. The strong isotope effect is discussed in the light of recent electronic excitation models of Si–H(D) bonds at the surface of silicon.

Effect of thickness on the physical properties of ITO thin films

We have studied the effect of thickness on the structural, optical and electrical properties of In 2 O 3 :Sn (ITO) thin films. Two series of ITO thin films have been deposited onto glass substrates by DC sputtering at two partial pressures of oxygen ( ppo ): 4 × 10 −4 and 4.75 × 10 −4 mbar. Each series consists of samples with thickness ranging from 306 nm to 1440 nm. We observed a change of texture with thickness; the thinner films grow with a 〈111〉 preferred orientation; however as the thickness increased, the preferred orientation becomes in the 〈100〉 direction. The lattice constant and the grain size have also been obtained from the X-ray spectra. The energy gap, E g , has been obtained from the transmission curve; E g is found to decrease with increasing thickness for both series. The electrical resistivity ρ has been studied as a function of thickness, ppo and temperature ( T ). The temperature was varied from room temperature ( RT ) to 450 °C and back to RT ; a hysteresis effect was observed in the ρ vs. T curve. Also, a minimum in ρ was observed, in all these samples, in the temperature range 260 to 280 °C. For these temperatures, we have studied the effect of annealing time on the electrical resistivity for samples having both textures. We noted that ρ increased with annealing time and reaches a saturation value equal to the RT temperature value. Hall effect experiments were done on all these samples. The concentration n and the mobility μ H were obtained. These parameters are found to be sensitive to the thickness and the texture of these films. All these results will be correlated and discussed.

The Dependence of the Electron Carrier Occupation in the Subband on the As Mole Fraction in Modulation-Doped InAsxP1—x/InP Strained Single Quantum Wells

The variation of the electron carrier occupation in the subband as a function of the As mole fraction and strain effects on the modulation-doped InAsxP1—x/InP single quantum wells have been studied. The results of the fast Fourier transform (FFT) for Shubnikov-de Haas (S-dH) data showed that the magnitude of the electron carrier density in the subband increased as the As mole fraction increased. The full width at half maxima of the FFT results for the S-dH data and the results of the Hall-effect measurements indicated that the value of the electron mobility increased as the As mole fraction increased. The electronic subband energies, the subband energy wavefunctions, the Fermi levels, and carrier densities in the InAsxP1—x quantum wells were calculated by a self-consistent method taking into account the exchange-correlation effects and the nonparabolicity effect together with and without the strain effect. The calculated subband carrier densities which included the strain effect were in more reasonable agreement with those determined from the S-dH and the Hall-effect experiments. The increase of the electron mobility and carrier density with increasing As mole fraction results from the decrease of the electron effective mass and the increase of the conduction band offset, respectivley. In particular, the calculated subband carrier density in the InAs0.6P0.4/InP highly strained quantum well taking into account the strain effect was in very good agreement with that obtained from the measurements.

The Dependence of the Electron Carrier Occupation in the Subband on the As Mole Fraction in Modulation-Doped InAsxP1x/InP Strained Single Quantum Wells

The variation of the electron carrier occupation in the subband as a function of the As mole fraction and strain effects on the modulation-doped InAsxP1—x/InP single quantum wells have been studied. The results of the fast Fourier transform (FFT) for Shubnikov-de Haas (S-dH) data showed that the magnitude of the electron carrier density in the subband increased as the As mole fraction increased. The full width at half maxima of the FFT results for the S-dH data and the results of the Hall-effect measurements indicated that the value of the electron mobility increased as the As mole fraction increased. The electronic subband energies, the subband energy wavefunctions, the Fermi levels, and carrier densities in the InAsxP1—x quantum wells were calculated by a self-consistent method taking into account the exchange-correlation effects and the nonparabolicity effect together with and without the strain effect. The calculated subband carrier densities which included the strain effect were in more reasonable agreement with those determined from the S-dH and the Hall-effect experiments. The increase of the electron mobility and carrier density with increasing As mole fraction results from the decrease of the electron effective mass and the increase of the conduction band offset, respectivley. In particular, the calculated subband carrier density in the InAs0.6P0.4/InP highly strained quantum well taking into account the strain effect was in very good agreement with that obtained from the measurements.

Magnetism of Fe impurities and adatoms on Pd(0 0 1) surfaces

It is well known that the giant moment associated with the substitutional Fe impurities in Pd can be understood in terms of a polarization cloud consisting of small induced moments in the Pd shells around the impurity. It is interesting to investigate if a similar phenomenon is present when a Pd surface is considered. Here we perform first-principles, self-consistent electronic structure calculations, within the local spin density functional formalism, to obtain the magnetic behavior of substitutional Fe impurities in Pd(0 0 1) and Fe adatoms on this surface. We find that in both cases the Fe site has a large local moment, close to saturation. As in the case of Fe impurities in bulk Pd, a moment is induced on the Pd neighbors, considerably enhancing the total magnetic moment of the system. Our results indicate that the failure to observe magnetic behavior using anomalous Hall effect experiments for Pd surfaces with small Fe coverages cannot be explained in terms of an antiferromagnetic coupling between the Fe impurity and its Pd neighbors, as was previously suggested.