Fields 12 [Hall Probe]

Front 1

A Hall Probe

Back 1

measures the magnetic flux density within a region.

Front 2

A steady current

Back 2

is driven through a semiconducting wafer in the tip of the probe.

Front 3

The charge carriers

Back 3

in the wafer experience a lateral force due to the magnetic field in which the probe has been placed (motor effect).

Front 4

This lateral force

Back 4

produces a surplus of charge on one side of the wafer and a deficit on the other, generating a pd – and hence an electric field – across the probe tip.

Front 5

The strength of

Back 5

this field increases until the electric force on the charge carriers is equal and opposite to the lateral magnetic force, halting the relocation of charge. Vq/d = Bqv

Front 6

For a steady current

Back 6

and wafer width, q, v and d are all constant, and hence the ‘Hall voltage‘ is directly proportional to the flux density (V ∝ B). A voltmeter attached to the probe may therefore be calibrated to show magnetic flux density.

Front 7

Semiconducting wafers

Back 7

are used because their charge carriers have a much higher drift velocity than metals, which produces a much larger ‘Hall voltage’ per tesla (and hence a lower uncertainty in the measurement).