Causes of incorrect carrier-type identification in van der Pauw-Hall measurements

The impact of macroscopic sample inhomogeneity and contact placement on the measured carrier type and concentration in the widely used van der Pauw-Hall method is investigated using finite-element analysis of the electrostatics. A variety of likely macroscopic inhomogeneities in mobility or carrier concentration across a square-shaped sample are considered. Inhomogeneities in mobilities do not affect the measured carrier type and concentration, as long as the carrier concentration remains homogeneous. Inhomogeneities in carrier concentrations can result in an incorrect assignment of the carrier type. However, when contacts are placed at the sample corners and not inside the sample area, the correct carrier type is recovered. Our calculations provide an explanation for recent measurements on ZnO [Ohgaki , J. Mater. Res. 23, 2293 (2008)]. Guidelines for avoiding incorrect interpretation of van der Pauw-Hall measurements are provided.