Van der Pauw method

About: Van der Pauw method is a research topic. Over the lifetime, 1682 publications have been published within this topic receiving 25364 citations.

A four probe cell for rapid resistivity measurements

Abstract: A device is described that enables rapid measurements of the specific resistivity of powdered semiconductors and metals. The apparatus is especially useful for the screening of a large number of materials as the only sample preparation involved is the pressing of a pellet of the material. The 4‐probe van der Pauw method with pressure contacts is used. Circuits for both ac and dc measurements are given and their relative merits discussed. The cell can be used between 77 and 400 K. A controlled atmosphere can be maintained around the sample.

Beyond van der Pauw: Sheet resistance determination from arbitrarily shaped planar four-terminal devices with extended contacts

Abstract: An extension of van der Pauw's method to determine the sheet resistance Rsq from arbitrarily shaped devices with four peripheral contacts of any size is presented. Extracting Rsq requires the measurement of six electrical resistances on these devices and the simultaneous solution of a system of six algebraic equations. The results are obtained using the method of conformal mapping in combination with the method of images. The computational effort to extract Rsq is modest. Using finite-element analysis, our findings were verified within a relative accuracy of better than 0.1%. Experimental tests with differently shaped structures are fully consistent with the novel theory.

The electrical conductivity tensor of $\beta$-Ga2O3 analyzed by van der Pauw measurements: Inherent anisotropy, off-diagonal element, and the impact of grain boundaries

Abstract: The semiconducting oxide $\beta$-Gallium Oxide ($\beta$-Ga$_{2}$O$_{3}$) possesses a monoclinic unit cell whose low symmetry generally leads to anisotropic physical properties. For example, its electrical conductivity is generally described by a polar symmetrical tensor of second rank consisting of four independent components. Using van der Pauw measurements in a well-defined square geometry on differently-oriented high-quality bulk samples and the comparison to finite element simulations we precisely determine the ratio of all elements of the $\beta$-Ga$_{2}$O$_{3}$ 3-dimensional electrical conductivity tensor. Despite the structural anisotropy a nearly isotropic conductivity at and above room temperature was found with the principal conductivities deviating from each other by less than 6% and the off-diagonal element being $\approx3$% of the diagonal ones. Analysis of the temperature dependence of the anisotropy and mobility of differently doped samples allows us to compare the anisotropy for dominant phonon-scattering to that for dominant ionized-impurity scattering. For both scattering mechanisms, the conductivites along the $a$ and $b$-direction agree within 2%. In contrast, the conductivity along $c$-direction amounts to $0.96\times$ and up to $1.12\times$ that along the $b$-direction for phonon and ionized impurity scattering, respectively. The determined transport anisotropies are larger than the theoretically predicted effective mass anisotropy, suggesting slightly anisotropic scattering mechanisms. We demonstrate that significantly higher anisotropies can be caused by oriented extended structural defects in the form of low-angle grain boundaries for which we determined energy barriers of multiple 10 meV.

Boron-deuterium complexes in diamond: How inhomogeneity leads to incorrect carrier type identification

Abstract: The electrical properties of boron doped diamond layers after deuterium diffusion have been investigated by Hall effect and capacitance voltage measurements. It is found that (i) the deuterated boron doped diamond layers are inhomogeneous after the deuterium diffusion, resulting in conducting and insulating areas; (ii) negative and positive Hall voltages are measured on the same boron doped sample after deuterium diffusion, depending on the contact geometry (negative with van der Pauw and positive with mesa etched Hall bar); and (iii) in the conducting area, the majority of the boron-deuterium complexes are not ionized after the deuterium diffusion. The detailed electrical measurements using mesa-insulating Hall bar structures revealed that the existence of inhomogeneous regions with conducting and insulating areas is the most probable source of wrong n-type conductivity in deuterated boron doped diamond layers of this work. In the light of this result, the possibility of an incorrect assignment of a shallow donor previously reported in deuterated boron doped diamond is discussed. Finally, confirmation is given that the boron deuterium complexes created after the deuterium diffusion are neutral in p-type diamond.

Formation of highly conductive polycrystalline GaAs from annealed amorphous (Ga,As)

Abstract: Polycrystalline (Ga,As) grown by molecular-beam epitaxy (MBE) is compared to polycrystalline (Ga,As) formed by annealing amorphous (Ga,As) also grown by MBE. Both amorphous and polycrystalline materials were grown at 100 °C and crystallinity is controlled by the As overpressure. As the amorphous material was annealed at varying temperatures from 300 to 500 °C several properties of the material changed such as levels of excess As in the material, grain structure of annealed material, strength and adhesion of crystallized layer, and conductivity of the material. After annealing at temperatures around 400 °C, the material is specular, polycrystalline, has good adhesion, and is very conductive. Resistivity values of less than 2 mΩ cm and acceptor concentrations near 5×1020 cm−3 were detected according to Hall/van der Pauw measurements. Conduction is believed to be due to the large amount of excess As in the material forming an As conduction path when the material is annealed. Material grown in a polycrystalline form by MBE differs in both grain structure and conductivity from material crystallized from an amorphous form.