A symmetric van der Pauw disk of homogeneous nonmagnetic indium antimonide with an embedded concentric gold inhomogeneity is found to exhibit room-temperature geometric magnetoresistance as high as 100, 9100, and 750,000 percent at magnetic fields of 0.05, 0.25, and 4.0 teslas, respectively. For inhomogeneities of sufficiently large diameter relative to that of the surrounding disk, the resistance is field-independent up to an onset field above which it increases rapidly. These results can be understood in terms of the field-dependent deflection of current around the inhomogeneity.

https://science.sciencemag.org/content/sci/289/5484/1530.full.pdf

Enhanced Room-Temperature Geometric Magnetoresistance in Inhomogeneous Narrow-Gap Semiconductors.

The electron mobility is one of the key parameters that characterize the charge-carrier transport properties of materials, as exemplified by the quantum Hall effect as well as high-efficiency thermoelectric and solar energy conversions. For thermoelectric applications, introduction of chemical disorder is an important strategy for reducing the phonon-mediated thermal conduction, but is usually accompanied by mobility degradation. Here, we show a multilayered semimetal β-CuAgSe overcoming such a trade-off between disorder and mobility. The polycrystalline ingot shows a giant positive magnetoresistance and Shubnikov de Haas oscillations, indicative of a high-mobility small electron pocket derived from the Ag s-electron band. Ni doping, which introduces chemical and lattice disorder, further enhances the electron mobility up to 90,000 cm(2) V(-1) s(-1) at 10 K, leading not only to a larger magnetoresistance but also a better thermoelectric figure of merit. This Ag-based layered semimetal with a glassy lattice is a new type of promising thermoelectric material suitable for chemical engineering.

http://www.qpec.t.u-tokyo.ac.jp/image/nmat3621.pdf

Extremely high electron mobility in a phonon-glass semimetal

In this review paper, we summarize the performance (in particular the magnetic field resolution), micro-fabrication technologies and applications of micrometer sized Hall effect devices. Additionally, our activities in this domain are briefly described.

Micro-Hall devices: performance, technologies and applications

Recent discoveries of large magnetoresistance in non-magnetic semiconductors have gained much attention because the size of the effect is comparable to, or even larger than, that of magnetoresistance in magnetic systems. Conventional magnetoresistance in doped semiconductors is straightforwardly explained as the effect of the Lorentz force on the carrier motion, but the reported unusually large effects imply that the underlying mechanisms have not yet been fully explored. Here we report that a simple device, based on a lightly doped silicon substrate between two metallic contacts, shows a large positive magnetoresistance of more than 1,000 per cent at room temperature (300 K) and 10,000 per cent at 25 K, for magnetic fields between 0 and 3 T. A high electric field is applied to the device, so that conduction is space-charge limited. For substrates with a charge carrier density below approximately 10(13) cm(-3), the magnetoresistance exhibits a linear dependence on the magnetic field between 3 and 9 T. We propose that the observed large magnetoresistance can be explained by quasi-neutrality breaking of the space-charge effect, where insufficient charge is present to compensate the electrons injected into the device. This introduces an electric field inhomogeneity, analogous to the situation in other semiconductors in which a large, non-saturating magnetoresistance was observed. In this regime, the motions of electrons become correlated, and thus become dependent on magnetic field. Although large positive magnetoresistance at room temperature has been achieved in metal-semiconductor hybrid devices, we have now realized it in a simpler structure and in a way different from other known magnetoresistive effects. It could be used to develop new magnetic devices from silicon, which may further advance silicon technology.

Large positive magnetoresistive effect in silicon induced by the space-charge effect

The silver chalcogenides provide a striking example of the benefits of imperfection. Nanothreads of excess silver cause distortions in the current flow that yield a linear and nonsaturating transverse magnetoresistance (MR). Associated with the large and positive MR is a negative longitudinal MR. The longitudinal MR only occurs in the three-dimensional limit and thereby permits the determination of a characteristic length scale set by the spatial inhomogeneity. We find that this fundamental inhomogeneity length can be as large as 10μm. Systematic measurements of the diagonal and off-diagonal components of the resistivity tensor in various sample geometries show clear evidence of the distorted current paths posited in theoretical simulations. We use a random-resistor network model to fit the linear MR, and expand it from two to three dimensions to depict current distortions in the third (thickness) dimension. When compared directly to experiments on Ag_(2±δ)Se and Ag_(2±δ)Te, in magnetic fields up to 55T, the model identifies conductivity fluctuations due to macroscopic inhomogeneities as the underlying physical mechanism. It also accounts reasonably quantitatively for the various components of the resistivity tensor observed in the experiments.

/pdf/nonsaturating-magnetoresistance-of-inhomogeneous-conductors-40kvv1ex04.pdf

Nonsaturating magnetoresistance of inhomogeneous conductors: Comparison of experiment and simulation

Using finite element analysis, the room temperature extraordinary magnetoresistance recently reported for a modified van der Pauw disk of InSb with a concentric embedded Au inhomogeneity has been calculated, using no adjustable parameters, as a function of the applied magnetic field and the size/geometry of the inhomoge-neity. The finite element results are nearly identical to exact analytic results and are in excellent agreement with the corresponding experimental measurements. Moreover, several important properties of the composite InSb/Au system such as the field dependence of the current flow and of the potential on the disk periphery have been deduced. It is found that both the EMR and output voltage depend sensitively on the placement and size of the current and voltage ports.

Finite-Element Modeling of Extraordinary Magnetoresistance in Thin Film Semiconductors with Metallic Inclusions

Giant magnetoresistance in zero-band-gap Hg 1-x Cd x Te

A magnetoresistive sensor includes a magnetoresistive element and equipment which generates a magnetic field in the magnetoresistive element thereby inducing a biasing magnetic field in the element, where the magnetoresistive element comprises a high electron mobility semiconductor and electrodes which are connected to the semiconductor If it is an insulator, the equipment, which generates the biasing magnetic field and supplies it to the magnetoresistive element, may contact directly to the magnetoresistive element If it is a conductor, an insulating separation layer must be set between the equipment and the element A magnetoresistive element is representatively Corbino disk type or a bar type magnetoresistive element Another candidate of the magnetoresistive element is an element consisting of a high electron mobility semiconductor, a pair of electrodes which make a current path in the high electron mobility semiconductor, and another pair of electrodes to detect the induced voltage by the current

Magnetoresistive sensor, magnetoresistive head, and magnetic recording/reproducing apparatus

This invention relates to a method and system for finite element modeling of enhanced magnetoresistance in thin film semiconductors containing at least one metallic inclusion therein. The method and system utilizes finite element analysis techniques as a function of the applied magnetic field and the geometry of the device for comparing the device characteristics with predetermined qualities and modifying the device to achieve a correlation between the device characteristics and the predetermined qualities.

Method and system for finite element modeling and simulation of enhanced magnetoresistance in thin film semiconductors with metallic inclusions

For applications to sensor design, the product nxmu of the electron density n and the mobility mu is a key parameter to be optimized for enhanced device sensitivity. We model the carrier mobility in a two dimensional electron gas (2DEG) layer developed in a delta-doped heterostructure. The subband energy levels, electron wave functions, and the band-edge profile are obtained by numerically solving the Schrodinger and Poisson equations self-consistently. The electron mobility is calculated by including contributions of scattering from ionized impurities, the background neutral impurities, the deformation potential acoustic phonons, and the polar optical phonons. We calculate the dependencies of nxmu on temperature, spacer layer thickness, doping density, and the quantum well thickness. The model is applied to delta-doped quantum well heterostructures of AlInSb-InSb. At low temperature, mobilities as high as 1.3x10^3 m^2/Vs are calculated for large spacer layers (400 A) and well widths (400 A). The corresponding room temperature mobility is 10 m^2/Vs. The dependence of nxmu shows a maximum for a spacer thickness of 300 A for higher background impurity densities while it continues to increase monotonically for lower background impurity densities; this has implications for sensor design.

S. A. Solin

Papers

Finite-Element Modeling of Extraordinary Magnetoresistance in Thin Film Semiconductors with Metallic Inclusions

Giant magnetoresistance in zero-band-gap Hg 1-x Cd x Te

Magnetoresistive sensor, magnetoresistive head, and magnetic recording/reproducing apparatus

Method and system for finite element modeling and simulation of enhanced magnetoresistance in thin film semiconductors with metallic inclusions

Carrier Mobilities in Delta-doped Heterostructures