Effects of sample thickness on the van der Pauw technique for resistivity measurements

The van der Pauw technique is commonly used for electrical transport measurements on solid materials and is suited to thin, arbitrarily shaped samples, with the contacts placed anywhere on the periphery. Previous investigations have determined the effects of sample shape, contact size, and contact placement on the accuracy of this technique. Sample inhomogeneity effects have also been investigated. The effects of the sample thickness appear not to have been previously studied and are investigated here in order to establish precisely what is meant by a thin sample. The deterioration in the accuracy of the technique is followed as the sample thickness is increased. The results indicate that the van der Pauw technique may be used for samples where the thickness is comparable to the surface dimensions. The investigation also shows that the technique is valid for arbitrarily thick samples provided that low resistance electrodes are placed across the entire edge, perpendicular to the surface, in order to maintain an effective two-dimensional current distribution. This finding is useful for transport measurements on materials that have been prepared, for example, by solid state reaction using sintering methods.