Oliver Kronenwerth

Extraordinary magnetoresistance effect in a microstructured metal–semiconductor hybrid structure

We have fabricated hybrid structures consisting of a metallic thin film and of a microstructured two-dimensional electron system in an InAs heterostructure. The devices are found to exhibit a huge magnetoresistance (MR) effect in magnetic fields ⩽1 T. At low temperature, a value of ΔR/R=[R(B=1 T)−R(B=0)]/R(B=0) as high as 115 000% is measured. The value of ΔR/R has been studied as a function of the electron mobility, the electron density and the lateral width of the semiconductor. We find that the MR effect can be tailored by these different parameters and technological relevant devices can be realized.

Optimization of semiconductor-metal hybrid structures for application in magnetic-field sensors and read heads

Semiconductor–metal hybrid structures can exhibit a very large geometrical magnetoresistanceeffect, the so-called extraordinary magnetoresistance (EMR) effect. Using the finite element method, we study the EMR effect in rectangular semiconductor–metal hybrid structures and investigate the effects of material parameters and of device geometry. We find that the EMR device exhibits inverse scalability, i.e., the output characteristics improve with decreasing device width. This is promising for miniaturized magnetic-field sensors like, e.g., read heads. Using realistic device parameters, we predict an optimized performance as a sensor for a width-to-length ratio of 0.025.

Enhanced sensitivity due to current redistribution in the Hall effect of semiconductor-metal hybrid structures

Experimental and theoretical studies have shown that nonmagnetic semiconductor-metal hybrid structures can exhibit a very large magnetoresistanceeffect, the so-called extraordinary magnetoresistance (EMR) effect. The EMR can be useful in magnetic-field sensors and read heads. We show that the sensitivity of a linear hybrid structure can be further enlarged by using an optimized configuration of currentleads and voltage probes. Strikingly, we find that the EMR and the Hall effect cooperate and thereby improve the performance. Our findings also explain the origin of the recently reported sensitivity increase in a nanostructured EMR device obtained via interchanging one lead and one probe [J. Moussa et al., J. Appl. Phys.94, 1110 (2003)].

Geometry-enhanced magnetoresistance of narrow Au∕InAs hybrid structures incorporating a two-dimensional electron system

We have investigated the magnetoresistance of metal-semiconductor hybrid structures at 4.2 K. The devices consisted of polycrystallineAu and an InAs-based heterostructure that hosted a high-mobility two-dimensional electron system. We have varied the electrical parameters and, in particular, the width-to-length ratio W ∕ L of the linear hybrid structures. The recently discovered extraordinary magnetoresistanceeffect is most pronounced for narrow devices with W ∕ L ⩽ 0.05 , consistent with our theoretical prediction. Relative resistance changes with a factor of 1000 are observed at 1 T. To achieve this an interfaceresistance of only 10 − 8 Ω cm 2 is a prerequisite. This can be prepared routinely by in situ cleaved edge overgrowth.

Low-noise magnetic-flux sensors based on the extraordinary magnetoresistance effect

We report noise measurements on Au–InAs hybrid structures involving a high-mobility two-dimensional electron system. Such structures show the extraordinary magnetoresistance (EMR) effect. We find excellent noise performance at room temperature close to the Johnson noise, which is in particular important for a technical application. At 4.2 K and in a magnetic field of about 1 T the nonoptimized EMR device is found to exhibit a low magnetic fluxnoise, offering the perspective of sensor applications also in a high magnetic field and at cryogenic temperature.

Optimization of the extraordinary magnetoresistance in semiconductor–metal hybrid structures for magnetic-field sensor applications

Semiconductor–metal hybrid structures can exhibit a very large geometrical magnetoresistance effect, the so-called extraordinary magnetoresistance (EMR) effect. In this paper, we analyze this effect by means of a model based on the finite element method and compare our results with the experimental data. In particular, we investigate the important effect of the contact resistance ρc between the semiconductor and the metal on the EMR effect. Introducing a realistic ρc=3.5×10−7 Ω cm2 in our model we find that at room temperature this reduces the EMR by 30% if compared to an analysis where ρc is not considered.

Effect of the Interface Resistance on the Extraordinary Magnetoresistance of Semiconductor/Metal Hybrid Structures

We report on magnetotransport experiments performed at 4.2 K on hybrid structures consisting of a metal and a mesoscopic two-dimensional electron system in an InAs/InGaAs heterostructure. The devices were fabricated using cleaved-edge overgrowth. We find that they exhibit an extraordinary magnetoresistance effect (EMR) which is most pronounced in the case of the lowest specific contact resistance ρi of ≈10−8 Ω cm2 achieved in this work. The largest relative resistance change Δ R/R is 115,000% at a magnetic field B = 1 T. A systematic study of the performance of the EMR devices with down to sub-μm lateral dimension and with different ρi is reported.

Semiconductor-metal hybrid structures as local magnetic-field probes: Magnetoresistance and spatial sensitivity profile

Tailored nonmagnetic semiconductor-metal hybrid structures exhibit a large magnetoresistance effect in a homogeneous magnetic field. This is the so-called extraordinary magnetoresistance effect. Here, we study numerically the magnetoresistance of such hybrid structures in the inhomogeneous field of a magnetic dot. Surprisingly, the four-point resistance R versus magnetic field B changes its symmetry if compared to the case of a homogeneous field and is strongly dependent on the position of the local magnetic field. Interestingly, the active device area is not defined by the voltage probe separation, but by the positioning of voltage probes and current leads. We find a magnetoresistance effect as large as 18% although only 1 ∕ 60 of the device area is subject to a small magnetic field of ± 50 mT . These results are promising for sensing magnetic-field distributions in the nanoscale regime such as the stray fields of magnetic recording media.

Semiconductor-metal hybrid structures: novel perspective for read heads

Recently, it was shown that semiconductor-metal hybrid structures can exhibit a very large magnetoresistance effect, the so-called extraordinary magnetoresistance (EMR) effect. This led to the perspective of using EMR devices in magnetic-field sensors and ultrafast read heads. Based on the finite element method, we study the EMR and optimize the effect with respect to material parameters and geometry. As the important design rule we find that the width-to-length ratio of a rectangular device should be below 0.042. This holds for a broad regime of mobility /spl mu/ in the semiconductor and specific contact resistance /spl rho//sub c/ between the semiconductor and the metal.

Enhanced Magnetoresistance of Semiconductor-Metal Hybrid Structures

Semiconductor‐metal hybrid structures can show a large magnetoresistance effect, the extraordinary magnetoresistance (EMR) effect. In this work, we study theoretically the influence of the voltage probe configuration on the magnetoresistance of such hybrid structures. We find a configuration, in which the current sensitivity of the device is enhanced considerably if compared to the probe configuration discussed so far in the literature. We argue that this enhancement is due to the combination of the EMR effect and the Hall effect in the hybrid structure.