Lake Shore Cryotronics Measure Ready M91 FastHall, Руководство пользователя

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20 CHAPTER 1: Introduction
MeasureReady™ M91 FastHall™ Measurement Controller
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For Hall bar sample 1-2-2-1, the Hall voltage is:
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For Hall bar sample 1-3-3-1, the Hall voltage is:
1.5.7.3.2 Resistivity Calculations for Hall Bar Samples
In the Hall bar structure, the method to measure resistivity is to measure specific
voltages on the sample. The measurement points are a known distance apart. From
the voltage, current and distance, the resistivity can be calculated.
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Current reversal: as explained in section 1.5.5.2, using current reversal will mini-
mize errors associated with instrumentation offsets and thermoelectric voltages.
For the Hall bar structure, the current is only applied to contacts 5 and 6 so cur-
rent reversal means interchanging contact 5 and 6.
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Geometry averaging: in section section 1.5.5.5, geometry averaging was defined
as the average of two measurements by interchanging the current source and
voltmeter. Since in the Hall bar measurement, the current source is always on
contacts 5 and 6, this definition of geometry averaging does not apply.
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For the Hall bar 1-2-2-1 geometry averaging for the resistivity is defined as
the average of the voltage measured across contacts 2 and 3 and the voltage
measured across contacts 1 and 4. This average removes some of the effects
of any non-homogeneity in the sample.
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For Hall bar sample 1-2-2-1
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For Hall bar sample 1-3-3-1
1.5.7.4 Advantages and Disadvantages of Hall Bar Structure
One of the advantages of the Hall bar structure is that fewer measurements are
required. The ideal model is simple to understand. Also, offset voltages for the Hall
voltage can be smaller in the Hall bar structure than it is for the van der Pauw
structure.
Disadvantages of Hall bar structures include a minimum of six contacts to make
mobility measurements. Also, the accuracy of resistivity measurements is sensitive to
the structure of the sample. Hall bar width and the distance between the side
contacts can be especially difficult to measure accurately. Creating such patterns can
be difficult and can result in fragile samples.