Hall Effect Experiments Research Articles

Noticeable influence of V-dopant on optoelectronic properties of ZnO films prepared by SILAR technique

Wide bandgap semiconductors such as Zinc Oxide (ZnO) have earned much attention on account of its interesting optical and electrical properties. Also, doping ZnO with suitable transition elements enables to tune its properties, making it suitable for applications like transparent conducting oxides and LEDs. To this aim, Vanadium-doped ZnO (V:ZnO) thin films are fabricated using the SILAR method and studied the structural, optical, vibrational, photophysical and electrical properties. Introducing vanadium creates lattice relaxation in the ZnO wurtzite structure, influencing its electronic band structure. The X-ray diffraction (XRD) analyses have verified the structural integrity of the vanadium-doped zinc oxide (V:ZnO) films, revealing their polycrystalline composition. The Raman spectroscopy shows the reduced phonon line widths due to the improved crystallite quality with the presence of vanadium. Furthermore, it has been noted that optical characteristics such as the bandgap and refractive index are sensitive to vanadium doping as a consequence of modified electronic structures. Hall-effect experiments have shown that undoped ZnO films possess a mobility of 1.31 cm2/Vs and a charge carrier density of 5.58 × 1013 cm−3. It has been observed that doping with V markedly influences these parameters of ZnO films. Then, the time-resolved photoluminescence measurements reveal the increased carrier lifetimes, suggesting the introduction of dopants mitigates carrier-phonon interactions. Such interactions need to be minimized to prevent the dissipation of carrier energy. In essence, the reported work demonstrates the potential of V:ZnO for optoelectronic applications.

Transport properties and electronic phase transitions in two-dimensional tellurium at high pressure

Utilizing in situ Raman spectroscopy, resistivity, and Hall-effect measurements, we conducted an extensive investigation on the continuous electronic phase transitions and transport properties of two-dimensional (2D) tellurium (Te) under high pressure at room and low temperature (80–300 K). The distinguishable decrease in the A1 Raman mode's full width at half maximum in the trigonal phase (Te-I) indicated an electronic phase transition at 2.2 GPa. The following Hall-effect experiments located the Lifshitz transition and the semiconductor-semimetal transition at 0.9 and 1.9 GPa, respectively, and the semiconductor-semimetal transition was also confirmed by resistivity variation through temperature. The charge carrier types of the Te changed from hole to electron during the phase transition from Te-I to Te-II (triclinic phase) at low temperature, while the transport parameters remained almost unchanged during the phase transition from Te-II to Te-III (monoclinic phase). The results offered complete and thorough electronic phase transitions and transport characteristics of 2D Te, hence great advancing the potential application of Te in electronic devices.

Investigating the properties of conductive clay and examining its potential as a teaching material

In this study, we analysed the material properties of conductive clay and verified its effectiveness as a learning material in the electrical field. Regarding the relationship between the salt content ratio and electrical conductivity, it was found that the higher the salt content ratio, the higher was the electrical conductivity. However, when the salt content ratio was approximately 18%, the salt concentration in the clay approached saturation, and the electrical conductivity hardly changed. In addition, Hall effect experiments clarified that the charge carriers of conductive clay are mainly Cl−. Furthermore, it was clarified that by mixing ‘Thermoink’ with conductive clay, heat dissipation can be visualised by changing the colour of conductive clay. From these results, it became clear that conductive clay is an effective teaching material for children to learn about electrical resistance and the Hall effect while conducting experiments.

Kagome Lattice Promotes Chiral Spin Fluctuations.

Dynamical spin fluctuations in magnets can be endowed with a slight bent toward left- or right-handed chirality by Dzyaloshinskii-Moriya interactions. However, little is known about the crucial role of lattice geometry on these chiral spin fluctuations and on fluctuation-related transport anomalies driven by the quantum-mechanical (Berry) phase of conduction electrons. Via thermoelectric Nernst effect and electric Hall effect experiments, we detect chiral spin fluctuations in the paramagnetic regime of a kagome lattice magnet; these signals are largely absent in a comparable triangular lattice magnet. Supported by MonteCarlo calculations, we identify lattices with at least two dissimilar plaquettes as most promising for Berry phase phenomena driven by thermal fluctuations in paramagnets.

Characterization of helical states in semiconductor quantum wells using quantum information quantities

The information content of one-electron bulk and edge states in semiconductor quantum wells is calculated in the inverted regime, where edge states, topologically protected, are responsible for the conduction in Spin Quantum Hall effect experiments. To study the information content of these states we first calculate realistic two dimensional one-electron states, solving first the eight-band $\mathbf{k}\cdot\mathbf{p}$ Hamiltonian to obtain the bulk states and then a four band effective Hamiltonian to obtain the edge states. The behavior of information-like quantities, as a function of the different parameters that define the quantum well, is analyzed. The results presented show that the helical edge states can be singled out using different quantities that characterize the rich phenomenology of these states.

Synthesis of Copper Telluride Thin Films by Electrodeposition and Their Electrical and Thermoelectric Properties.

Intermetallic copper telluride thin films, which are important in a number of electronics fields, were electrodeposited using a potentiostatic method in low-pH aqueous electrolyte baths with various ion-source concentrations, and the electrical properties of the formed films were investigated after exfoliation from the substrate. The films were electrochemically analyzed by cyclic voltammetry, while surface and cross-sectional morphologies, compositional ratios, and electrical properties were analyzed by scanning electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and Hall-effect experiments. The copper telluride thin films, which were synthesized at various potentials in each bath, exhibit different composition ratios and structures; consequently, they show a variety of electrical and thermoelectric properties, including different electrical conductivities, carrier concentrations, mobilities, and Seebeck coefficients. Among them, the thin film with a 1:1 Cu:Te ratio delivered the highest power factor due to carrier filtering at the interface between the two phases.

N‐type silk fibroin/TiO2 nanocomposite transparent films: electrical and optical properties

AbstractThis paper highlights the effect of different concentrations of titanium dioxide (TiO2) nanoparticles on the electrical and optical properties of silk fibroin (SF). TiO2 based SF nanocomposite films were prepared using the solvent casting method. Uniform dispersion and agglomeration of nanoparticles, in nanocomposite films, were observed by field emission SEM. The conductivity of pure SF and nanocomposite films was determined by a four‐point probe and the TiO2 nanoparticles were found to bring high conductivity to the nanocomposite films. Dielectric strength improved with the addition of nanoparticles to the SF matrix. Dielectric constant and capacitance of the pure SF and nanocomposite films were measured using an LCR meter, which showed a 10‐fold enhancement on the addition of nanoparticles in SF. A very unusual property, i.e. negative resistance, was observed during LCR meter analysis for the nanocomposite films for a particular range of frequency (200–550 kHz), voltage (1 V) and current (0.5–1.5 μA). TiO2 nanoparticles changed the semiconducting behavior of the SF films from p‐type to n‐type as measured by the Hall effect experiment. The optical properties of pure SF and nanocomposite films were measured using a UV–visible spectrophotometer. The increased concentration of nanoparticles in the SF has effectively enhanced the absorbing coefficient, refractive index and percentage transmittance and reduced the bandgap energy. These SF/TiO2 nanocomposite films have shown the potential to be used as dielectric and high refractive index material for optoelectronics applications. © 2021 Society of Industrial Chemistry.

Narrow-Bandgap Semiconductors of Perovskite Rare-Earth Orthoferrites (REFeO3)

Background: Great achievements have been made in improving the power conversion efficiencies of solar cells. However, the price of photovoltaic (PV)-generated electricity still cannot compete with that of conventionally generated power. Thus, novel solar cells made from non-toxic, earth-abundant, and chemically stable materials are desirable to decrease the costs of PV electricity generation. Objective: All-oxide solar cells are a promising next-generation PV technology, fulfilling the requirement of low-cost manufacturing under ambient conditions. This work aims to search for nontoxic, earth-abundant, and chemically stable narrow-bandgap semiconductors for energy applications like all-oxide solar cells. Methods: This work examines a family of perovskite rare-earth (i.e., Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Yb) orthoferrites with XRD analysis, SEM, photoresponse, absorption spectra, Xray photoelectron spectroscopy, fluorescence spectra measured with the laser Raman spectrometer, valence band spectra, the Kelvin probe, the Hall Effect experiment, and theoretical calculation on band structure and the density of states, to screen for the narrow-bandgap semiconductors. Results: The novel Pb-free perovskite narrow-bandgap absorbers, CeFeO3, PrFeO3, TbFeO3, DyFeO3, HoFeO3, and YbFeO3, which are earth-abundant and non-toxic, were screened out potentially for use in all-oxide solar cells or other photovoltaic and optoelectronic applications. Among them, YbFeO3 is approved, having an indirect bandgap of approximately 1.0 eV with a maximum Shockley-Queisser efficiency of 31% for single p-n junction solar cells. Conclusion: The chemically stable, non-toxic, earth-abundant, and narrow-bandgap semiconductors of rare-earth orthoferrites promisingly serve as absorbers, photocatalysts, photoelectrodes, photodetectors, and photoelectronic materials. This work breaks new ground in the search for narrow bandgap all-oxide semiconductors potential for energy applications.

Intelligent Magnetic Experiment Teaching System Based on Hall Effect

The Hall effect experiment occupies an important position in the teaching of university physics experiments. Traditional experimental teaching instruments have problems of tedious operation and difficult data collation. The new system designed in this paper uses the STM32 series single-chip microcomputer, the main control chip VT95276L128 and the touch screen module, and adopts the configuration graphic user design software VGUS programming to intelligentize the traditional TH-H / S type Hall effect experimental instrument. In addition to retaining all the functions of the original instrument, the experimental data processing and drawing can be handed over to a single-chip computer, which improves teaching efficiency and facilitates students to think deeply about the experiment.

Electrical magnetotransport properties of chlorinated CVD graphene

We report on electrical resistivity, magnetoresistance, and Hall-effect experiments in single-layer CVD graphene submitted to photochlorination. The resistivity and the ordinary Hall effect reveal a strong hole doping due to Cl adsorption. Intrinsic disorder of the as-grown system as well as that produced in the chlorination process lead to weak-localization effects, observed in the low-temperature magnetoresistance. The theoretically predicted regime where intervalley scattering fully restores the usual negative magnetoresistance is observed in a freshly chlorinated sample. Also observed are time-dependent effects in the electrical transport properties of the functionalized CVD-graphene samples due to a progressive loss of adsorbed Cl.

Real-time Hall-effect detection of current-induced magnetization dynamics in ferrimagnets

Measurements of the transverse Hall resistance are widely used to investigate electron transport, magnetization phenomena, and topological quantum states. Owing to the difficulty of probing transient changes of the transverse resistance, the vast majority of Hall effect experiments are carried out in stationary conditions using either dc or ac. Here we present an approach to perform time-resolved measurements of the transient Hall resistance during current-pulse injection with sub-nanosecond temporal resolution. We apply this technique to investigate in real-time the magnetization reversal caused by spin-orbit torques in ferrimagnetic GdFeCo dots. Single-shot Hall effect measurements show that the current-induced switching of GdFeCo is widely distributed in time and characterized by significant activation delays, which limit the total switching speed despite the high domain-wall velocity typical of ferrimagnets. Our method applies to a broad range of current-induced phenomena and can be combined with non-electrical excitations to perform pump-probe Hall effect measurements.

Spin textures and magnetotransport properties in cobalt/ruthenium and cobalt/palladium bilayers

We report on resistivity, magnetoresistance, and Hall effect experiments in bilayer thin films of cobalt/ruthenium (Co/Ru) and cobalt/palladium (Co/Pd) prepared by magnetron sputtering. The resistivity and magneto-transport properties of single layers of the same materials were also measured. For analyzing the results in the bilayers, we propose an approach based on a two-current model that assumes a current mixing effect coming from the large contact area between films. The method is devised for identifying the effects related to the interface between the metallic films. The outcome of the analysis indicates that significant interface effects occur in both studied bilayers. The role of the Dzyaloshinskii-Moriya interaction and the related spin arrangements formed at the interface are pointed out. Particularly for the Co/Pd system, from the magnetoresistance and Hall resistivity results possible evidence is obtained for the occurrence of non-trivial chiral spin textures in the field range corresponding to the initial process of magnetization.

Tailoring of electrical and optical properties of regenerated silk fibroin films with metal oxides

In this study, silk fibroin was used as a matrix to incorporate the metal oxide nanoparticles i.e. zinc oxide (ZnO) and copper oxide (CuO) to form transparent nanocomposite films by solvent casting method. The effect of metal oxide nanoparticles and their concentrations on the conductivity of silk fibroin film were detected by a four-point probe instrument. As the thickness of the films was reduced, the conductivity increased. Hall Effect experiment was carried out to determine the carrier (electron or holes) concentration and identification of the semiconducting behaviour of nanocomposite films. Pure silk fibroin (SF) film showed p-type semiconducting behaviour. Incorporation of zinc oxide and copper oxide nanoparticles in the silk fibroin matrix makes it n-type and p-type semiconductor, respectively. Uniform dispersion of metal oxide nanoparticles in the silk fibroin matrix was observed through field emission scanning electron microscopy. The UV–Vis spectra of nanocomposite films showed 82–84% transmittance and reduction in refractive index. Addition of metal oxide nanoparticles reduced the β sheet content and percentage crystallinity of silk fibroin as observed by FTIR and XRD, respectively. The structural alterations at the molecular level reveal their relationship with electrical and optical properties.

Magnetic Critical Behavior, Hall and Magneto-Impedance Effects in Fe–Co-Based Metallic Glasses

A comparative study of the magnetic critical behavior, magnetic anisotropy, Hall and magneto-impedance effects, and magnetic interactions is presented for Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> and Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> metallic glasses. The critical behavior is studied by determining the critical exponents for zero-field magnetization (β), critical isotherm (δ), and critical temperature TC, from magnetization measurements using the method by Berger-Campillo et al. The corresponding (β, δ, and TC) values for Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> and Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> are (0.341 ± 0.008, 4.00 ± 0.27, and 644.5 ± 25.5 K) and (0.399 ± 0.014, 4.25 ± 0.44, and 460 ± 32 K), respectively. These β values indicate that the universality class of Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> is consistent with the 3-D XY model, whereas Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> seems to be more close to the 3-D Heisenberg model. These TC values indicate that the exchange interaction is weaker in Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> than in Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> . The Hall effect experiments reveal an ordinary and extraordinary contribution to the Hall effect and a positive Hall constant. Furthermore, the extraordinary Hall contribution and magnetic anisotropy decrease more rapidly in Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> than in Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> . The magneto-impedance curves exhibit the single-peak (SP) and two-peak (TP) behaviors. The possible magnetic interactions, including the spin-orbit interaction, the exchange interaction, and the magnetic dipolar interaction, might be active in these materials, and their possible effects on the β value are analyzed.

Comparison of Sb, As, and P doping in Cd-rich CdTe single crystals: Doping properties, persistent photoconductivity, and long-term stability

Acceptor doping CdTe with group-V elements is promising for increasing the power conversion efficiency of CdTe photovoltaic devices via an increased hole concentration and open circuit voltage (VOC). In past work, we have investigated doping with As in Cd-rich CdTe single crystals grown using the Cd-solvent traveling heater method we have developed. In this study, we compare the doping parameters and stability of hole concentration in the light and dark for P, As, and Sb dopants in crystals cooled very slowly from the growth temperature to approximate thermal equilibrium. In contrast to older reports of a high acceptor ionization energy for Sb, our temperature dependent Hall effect experiments reveal an acceptor ionization energy slightly above 90 meV for Sb doping in the mid 1016 cm−3 range. Room temperature hole concentrations above 1016 cm−3 are observed for P, As, and Sb with each dopant type exhibiting only small changes in hole concentrations over 2 years' time at room temperature. Crystals doped with P, As, or Sb exhibit increased conductivity after above-gap illumination, which decays over periods of minutes to hours depending on temperature. Analysis of the photoconductivity decay reveals a barrier attributed to hole capture of 190–280 meV for the series P, As, and Sb.

Facile deposition and study of substrate temperature effect on the structural and physical properties of Cu2FeSnS4 (CFTS) thin films

Chalcogenide thin films of Cu2FeSnS4 (CFTS) were deposited through spray pyrolysis method, and effect of substrate temperature on the structure, morphology, optical, and electrical properties of the thin films was investigated. The samples were characterized by X-ray diffraction (XRD), UV–Vis spectroscopy, field emission scanning electron microscopy, and electrical measurements. XRD results describe the existence of the stannite phase of CFTS thin films, which is modified after increasing the substrate temperature. All polycrystalline thin films show peaks related to (112), (204), and (116) planes. FESEM images represent growth of the grains for higher substrate temperatures. Hall and Seebeck effect experiments confirm p-type conduction in all of the samples. The carrier density is found in the order of magnitude of 1020 cm−3 which increases by increasing the substrate temperature. Optical band gap measurements based on UV–Vis spectroscopy describe the values between 1.33 and 1.54 eV for all the samples. It is found that the CFTS absorber layers can be fabricated via facile method and their physical properties are adjustable through regulation of substrate temperature.

Evaluation of spin diffusion length and spin Hall angle of the antiferromagnetic Weyl semimetal Mn3Sn

Antiferromagnetic Weyl semimetal Mn$_3$Sn has shown to generate strong intrinsic anomalous Hall effect (AHE) at room temperature, due to large momentum-space Berry curvature from the time-reversal symmetry breaking electronic bands of the Kagome planes. This prompts us to investigate intrinsic spin Hall effect, a transverse phenomenon with identical origin as the intrinsic AHE. We report inverse spin Hall effect experiments in nanocrystalline Mn$_3$Sn nanowires at room temperature using spin absorption method which enables us to quantitatively derive both the spin diffusion length and the spin Hall angle in the same device. We observed clear absorption of the spin current in the Mn$_3$Sn nanowires when kept in contact with the spin transport channel of a lateral spin-valve device. We estimate spin diffusion length $\lambda_{s(Mn_3Sn)}$ $\sim$0.75 $\pm$0.67 nm from the comparison of spin signal of an identical reference lateral spin valve without Mn$_3$Sn nanowire. From inverse spin Hall measurements, we evaluate spin Hall angle $\theta_{SH}$ $\sim$5.3 $\pm$ 2.4 $\%$ and spin Hall conductivity $\sigma_{SH}$ $\sim$46.9 $\pm$ 3.4 ($\hbar/e$) ($\Omega$ cm)$^{-1}$. The estimated spin Hall conductivity agrees with both in sign and magnitude to the theoretically predicted intrinsic $\sigma_{SH}^{int}$ $\sim$36-96 ($\hbar/e$) ($\Omega$ cm)$^{-1}$. We also observed anomalous Hall effect at room temperature in nano-Hall bars prepared at the same time as the spin Hall devices. Large anomalous Hall conductivity along with adequate spin Hall conductivity makes Mn$_3$Sn a promising material for ultrafast and ultrahigh-density spintronics devices.

Temperature dependent spin Hall conductivity in n-GaAs epitaxial layers measured by inverse spin Hall effect

The photo-induced inverse spin Hall effect (ISHE) experiments are conducted in heavily doped n-GaAs epitaxial layers by measuring the transverse electric current generated through the diffusion of optically injected spin orientations over a temperature range of 10–300 K. ISHE origin of the measured signal is confirmed through meticulous checks including the characteristic dependence of magnitude of signal on the angle of incidence. The measured value of ISHE current (IISHE) is observed to fall with the increase in temperature. Furthermore, the value of spin current density is theoretically estimated by solving the spin diffusion equation with appropriate boundary conditions for an epitaxial layer. It is shown that by near resonant excitation and subsequent solution of diffusion equation, the spin Hall angle (γ) and spin Hall conductivity (σSH) can be estimated, provided the effective life time of spin polarized electrons(τS) is known independently. By using the numerically calculated value of τS, the proposed method is implemented to estimate the values of γ and σSH. It is found that the fall in the values of IISHE at high temperatures is not governed by σSH, rather by a rapid decrease in the values of τS. In fact, σSH is seen to increase with the temperature, which is compared with existing literature. The present work provides the necessary insight into material parameters which are essential for the development of advanced spin-photonic semiconductor devices.

Influence of high Mg doping on the microstructural and opto-electrical properties of AlGaN alloys

Mg-doped AlxGa1-xN (x = 0.23 and 0.35) alloys have been grown on GaN templates with high temperature AlN (HT-AlN) interlayer by metalorganic chemical vapor deposition (MOCVD). A combination of secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) indicates the formation of more inversion domains in the high Al mole fraction Mg-doped AlGaN alloys at Mg concentration ∼1020 cm−3. For Mg-doped Al0.23Ga0.77N epilayer, the analysis of cathodoluminescence (CL) spectra supports the existence of self-compensation effects due to the presence of intrinsic defects and Mg-related centers. The energy level of Mg is estimated to be around 193 meV from the temperature dependence of the resistivity measured by Hall effect experiments. And hole concentration and mobility are measured to be 1.2 × 1018 cm−3 and 0.56 cm2/V at room temperature, respectively. The reduction of acceptor activation energy and low hole mobility are attributed to inversion domains and self-compensation. Moreover, impurity band conduction is dominant in carrier transport up to a relatively higher temperature in high Al content Mg-doped AlGaN alloys.

Pure spin current manipulation in antiferromagnetically exchange coupled heterostructures

We present a model to describe the spin currents generated by ferromagnet/spacer/ferromagnet exchange coupled trilayer systems and heavy metal layers with strong spin-orbit coupling. By exploiting the magnitude of the exchange coupling (oscillatory RKKY-like coupling) and the spin-flop transition in the magnetization process, it has been possible to produce spin currents polarized in arbitrary directions. The spin-flop transition of the trilayer system originates pure spin currents whose polarization vector depends on the exchange field and the magnetization equilibrium angles. We also discuss a protocol to control the polarization sign of the pure spin current injected into the metallic layer by changing the initial conditions of magnetization of the ferromagnetic layers previously to the spin pumping and inverse spin Hall effect experiments. The small differences in the ferromagnetic layers lead to a change in the magnetization vector rotation that permits the control of the sign of the induced voltage components due to the inverse spin Hall effect. Our results can lead to important advances in hybrid spintronic devices with new functionalities, particularly, the ability to control microscopic parameters such as the polarization direction and the sign of the pure spin current through the variation of macroscopic parameters, such as the external magnetic field or the thickness of the spacer in antiferromagnetic exchange coupled systems.