Lake Shore Cryotronics Measure Ready M91 FastHall, Руководство пользователя

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This section will develop the practical protocols for measurement of the resistivity of
real samples at zero magnetic field.
As explained in section 1.5.5.2, using current reversal will minimize errors associated
with instrumentation offsets and thermoelectric voltages. When the current reversal
method is applied to the resistivity measurement, the resistivity is calculated by:
As explained in section 1.5.5.5, geometry averaging is used to reduce material
inhomogeneous effects in the measurement. The M91 measures the resistivity in
both configurations and averages the result. The first measurement is:
The second measurement is:
The best estimate of the resistivity then, is:
This resistivity is called the geometry averaged resistivity, or simply, the resistivity.
1.5.6.4 Advantages and Disadvantages of van der Pauw Structures
The advantages of van der Pauw samples include:
D
Only four contacts are required
D
There is no need to measure sample widths or distances between contacts
D
Simple geometries can be used
The disadvantages of van der Pauw samples include:
D
Measurements take about twice as long as Hall bar
D
Errors due to contact size and placement can be significant when using simple
geometry
1.5.7 Hall Bar Samples This section describes Hall bar structure. This structure is designed to approximate
one dimensional current flow in a three dimensional sample. The calculation of the
resistivity and Hall coefficient depend on the assumption of one dimensional flow.
Unlike the van der Pauw structure, additional physical parameters are required for
the calculations. Hall bar samples require fewer measurements than the van der
Pauw to calculate the resistivity and Hall coefficient.
1.5.7.1 Structures of Hall Bar Samples
The MeasureReady™ M91 FastHall™ measurement controller supports two different
Hall bar structures. These will be referred to as 1-2-2-1 (FIGURE 1-10) and 1-3-3-1
(FIGURE 1-11).