page_title: Van der Pauw method
section_title: Sample preparation
hierarchical_section_title: Van der Pauw method / Sample preparation
context_page_description: The van der Pauw Method is a technique commonly used to measure the resistivity and the Hall coefficient of a sample. Its power lies in its ability to accurately measure the properties of a sample of any arbitrary shape, as long as the sample is approximately two-dimensional, solid, and the electrodes are placed on its perimeter. The van der Pauw method employs a four-point probe placed around the perimeter of the sample, in contrast to the linear four point probe: this allows the van der Pauw method to provide an average resistivity of the sample, whereas a linear array provides the resistivity in the sensing direction. This difference becomes important for anisotropic materials, which can be properly measured using the Montgomery Method, an extension of the van der Pauw Method.
  From the measurements made, the following properties of the material can be calculated:
  The resistivity of the material
  The doping type
  The sheet carrier density of the majority carrier. From this the charge density and doping level can be found
  The mobility of the majority carrier
  The method was first propounded by Leo J. van der Pauw in 1958.
context_section_description: In order to use the van der Pauw method, the sample thickness must be much less than the width and length of the sample. In order to reduce errors in the calculations, it is preferable that the sample be symmetrical. There must also be no isolated holes within the sample.
  The measurements require that four ohmic contacts be placed on the sample. Certain conditions for their placement need to be met:
  They must be as small as possible; any errors given by their non-zero size will be of the order D/L, where D is the average diameter of the contact and L is the distance between the contacts.
  They must be as close as possible to the boundary of the sample.
  In addition to this, any leads from the contacts should be constructed from the same batch of wire to minimise thermoelectric effects. For the same reason, all four contacts should be of the same material.
caption: Some possible contact placements
exif: {"Image XResolution": "96", "Image YResolution": "96", "Image ResolutionUnit": "Pixels/Inch", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail JPEGInterchangeFormat": "108", "Thumbnail JPEGInterchangeFormatLength": "3370"}