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Post by Lake Shore Jeff L on Jun 4, 2019 15:02:46 GMT -5
Geometry C and D refer to two different way to connect the current source and voltmeter to your sample. For a hall measurement the current source is connect on one diagonal of the sample and the voltmeter is connect to the other diagonal. However, if you interchange the current source and voltmeter this is also a valid measurement. These two measurements a called Geometry C and Geometry D. If the sample is idea, these two measurements are equal. One reason why you could be getting different carrier type in the two geometries is that the mobility of your sample is too low for a DC field measurement. When the mobility of your samples is below about 10 cm 2/(V s), the DC measurement becomes very difficult. Here is a link to our white paper on AC field Hall measurements. The AC field option is not available on the superconducting magnet 8425 system, but the white paper describes the problems of measuring low mobility samples with DC field Hall. Let me know if yo have any questions.
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Post by Lake Shore Jeff L on Mar 1, 2019 9:52:47 GMT -5
Thanks Jeff I'll look into those papers you've sugested. Are you avere of a geometry similar to 1 with known corrections? I'm a novice to Hall effect system as you can see. Can we apply correction coeficients in the software before the measurements? Hi I am not aware of known corrections for geometry similar to one. The Lake Shore software for Hall Measurements Systems does not support the correnction coefficients for any geometer. The software always assumes, for van der Pauw samples, point contacts on the edge of the sample.
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Post by Lake Shore Jeff L on Feb 28, 2019 11:14:49 GMT -5
Hi mykhaylo This is a very good question. The van der Pauw method assumes point contacts on the edge of the sample. Of course, real samples do not have point contacts and the contacts are not on the edge of the sample. For finite size contacts it is possible to calculate correction factor to correct the measured resistance. These correction factors are difficult to calculate. There are many references in the literature for various geometry of sample and contact size. If you have the manual for your 7600 system, in appendix A there is a summary of some geometries and contact sizes. In addition, here are two references that I find useful CONTACT SIZE EFFECTS ON THE VAN DER PAUW METHOD FOR RESISTIVITY AND HALL COEFFICIENT MEASUREMENT RONALD CHWANG, B. J. SMITH: and C. R. CROWELL Solid-Slate Electronics. 1974. Vol. 17, pp. 1217-1227.
FOUR-POINT SHEET RESISTANCE CORRECTION FACTORS FOR THIN RECTANGULAR SAMPLES DAVID S. PERLOFF Solid-Slate Electronics. 1977. Vol. 20. pp. 681487.
Jeff Lindemuth
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Post by Lake Shore Jeff L on Jan 2, 2018 17:08:57 GMT -5
The procedure for measuring circular samples is the same as the procedure for square samples. The requirements for the van der Pauw method requires four contacts on the edge of the sample. The size and shape of the sample is not important. The position of the contacts should be symmetric for best results. I would recommend positioning the contacts on the edge of the circle and space 90 degrees apart.
The same measurement procedure you use for the square sample can be used with the circular sample
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