Geometrically enhanced extraordinary magnetoresistance in semiconductor-metal hybrids

T. H. Hewett and F. V. Kusmartsev

Phys. Rev. B 82, 212404 – Published 13 December 2010

Abstract

Extraordinary magnetoresistance (EMR) arises in hybrid systems consisting of semiconducting material with an embedded metallic inclusion. We have investigated such systems with the use of finite-element modeling, with our results showing good agreement to existing experimental data. We show that this effect can be dramatically enhanced by over four orders of magnitude as a result of altering the geometry of the conducting region. The significance of this result lies in its potential application to EMR magnetic field sensors utilizing more familiar semiconducting materials with nonoptimum material parameters, such as silicon. Our model has been extended further with a geometry based on the microstructure of the silver chalcogenides, consisting of a randomly sized and positioned metallic network with interspersed droplets. This model has shown a large and quasilinear magnetoresistance analogous to experimental findings.

Received 25 August 2010

DOI:https://doi.org/10.1103/PhysRevB.82.212404

Authors & Affiliations

T. H. Hewett^* and F. V. Kusmartsev

Department of Physics, Loughborough University, Loughborough LE11 3TU, United Kingdom

^*t.h.hewett@lboro.ac.uk

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Vol. 82, Iss. 21 — 1 December 2010

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Images

Figure 1
(Color online) Magnetoresistance as a function of filling factor $(α)$ at five values of magnetic field; $H = 0.05$ (black $◆$ ), 0.1 (purple $△$ ), 0.25 (green $▼$ ), 1 (red $▲$ ), and 5 T (blue $•$ ) for systems based on the experimental geometry by Solin et al. (Ref. 1). The system geometry consists of an outer semiconducting disk (of radius 0.5 mm) containing an embedded circular metallic inclusion, including four equally spaced contacts on the perimeter [see Fig. 2a].Reuse & Permissions
Figure 2
(Color online) Magnetoresistance as a function of applied magnetic field for two system geometries (metal regions shown in yellow, semiconducting regions shown in white, including four point contacts, two for current and two for electric potential): (a) the experimental geometry, based on the experimental systems by Solin et al. (Ref. 1); (b) a modified geometry containing a multibranched metallic inclusion in which we see a four order of magnitude increase in magnetoresistance over the case in (a). Both systems contain the same proportion of conducting to semiconducting material $(α = 0.5)$ with the disk radius being 0.5 mm in each case.Reuse & Permissions
Figure 3
(Color online) Here, we consider the same samples as in Fig. 2. The background color shows the value of the electric potential. The minimums (shown in blue) correspond to (a) $- 0.6 mV$ , (b) $- 12 mV$ , (c) $- 0.25 mV$ , and (d) $- 10 mV$ while the maximums (shown in red) correspond to (a) 0.6 mV, (b) 6 mV, (c) 0.25 mV, and (d) 6 mV. The metal regions [yellow in (b) and (d) and green in (a) and (c)] have zero potential. The change in potential scales continuously with color. Without magnetic field [see (a) and (c)] the major changes in potential arise around the current contacts. With magnetic field [ $H = 5 T$ , see (b) and (d)] we see changes in potential are huge. The streamline plot (green lines) indicates the local direction of the current flow. The length of the arrows (black) indicates the amplitude of the current at a particular point where the arrow originates.Reuse & Permissions
Figure 4
(Color online) Magnetoresistance as a function of magnetic field ( $H$ up to 5.5 T as in experiment) for a RBDM geometry (see inset). Metal regions are shown in yellow and semiconducting regions shown in white (including four point contacts, two for current and two for electric potential). The model contains conducting branches and droplets with their sizes and positions determined by random numbers mimicking the microstructure of the silver chalcogenides where excess silver has been shown to form a percolating network along grain boundaries. The magnetoresistance has a quasilinear dependence on magnetic field as observed experimentally in the silver chalcogenides. Here $α = 0.29$ with the disk radius being $0.5 μ m$ , with purely diffusive transport considered.Reuse & Permissions

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