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Room Temperature Hall Effect System

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Demonstrate and Measure the Hall Effect

  • Optimized for Demonstrating the Hall Effect

  • Accommodates TeachSpin Silicon and Copper Samples

  • Permanent-magnet structure provides reversible B-field

  • Transparent connections for tracking polarity

  • Unambiguously gives sign of charge carriers for n- and p-type Si and Cu

  • Permits 4-wire measurement of resistivity in semiconductors

  • Comes with current-limiting resistor and current-reversing switch

  • Guides students to first-principles measurements of sign and magnitude of B-field

Introducton

Introduction

The Hall Effect is the standard method for determining the absolute sign, and the number density, of charge carriers in a conductor.  TeachSpin now offers, in support of its Condensed-Matter Physics initiative, a unique educational system that allows students to see, in the same apparatus, the Hall Effect in both semiconductor and in metal samples.

Measuring the Hall Effect requires a sample of known thickness t, conducting a sample current i, immersed in a transverse magnetic field B.  The detectable effect is a potential difference ΔV, arising perpendicular to both the field and the current, of a magnitude

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Here n is the number density (number per unit volume) of the mobile charge carriers.  TeachSpin’s apparatus is devised to make n measurable over the huge range that spans metal and semiconductor samples.

The R.T. Hall-Effect system is crafted to use the same mounted and packaged semiconductor samples used in the CMP Electrical-Transport experiment, and it also accommodates thin-film copper samples laid out in an identical format.  The system is also uniquely ‘transparent’, permitting students to trace every electrical lead in 3-d space, as is required for deducing the absolute sign of the charge of the mobile carriers.

Our system offers a first-principles method for establishing the absolute direction of the magnetic field B in its two field regions, and another first-principles method for establishing the magnitude of the field B (about 0.6 Tesla, or 6000 gauss) in the field regions.

Our samples offer precisely-specified geometry of the samples, and have enough electrical contacts to permit measurement of longitudinal, as well as transverse, potential differences.  For semiconductor samples of known thickness, this permits an absolute and four-wire measure of the sample’s resistivity; for metal samples of known resistivity, this permits an absolute measurement of sample thickness.

For semiconductor samples, mere microamperes of sample current i will give millivolts of Hall potential ΔV.  For metal samples, with a carrier density n of order 10⁸ times larger, the Hall potentials are vastly smaller – so we build our copper samples thinner (t < 20 μm, instead of t ≈ 500 μm), and we use much larger sample currents (i ≈ 3 A, instead of i « 3 mA).  This gives microvolt-level Hall potentials, conveniently detected with a sensitive DMM.

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