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.

Low-cost Cu 2 ZnSnS 4 thin films for large-area high-efficiency heterojunction solar cells

Abstract: Cu 2 ZnSnS 4 (CZTS) thin films have been deposited on soda-lime glass (SLG) and Mo-coated SLG substrates using a low-cost spray pyrolysis technique followed by sulfurization under H 2 S flow at 540°C. Aqueous solution containing CuCl, ZnCl 2 , SnCl 4 and thiourea was used as precursor. Spray deposition was carried out at three different substrate temperatures of 280°C, 360°C and 440°C. Deposition conditions were optimized to obtain the best film properties. Structural, morphological and compositional analysis of the as-deposited and sulfurized CZTS films were carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive x-ray spectroscopy (EDX) and x-ray photoelectron spectroscopy (XPS). Optical and electrical properties were measured by UV-Vis spectroscopy, van der Pauw and Hall effect measurements. XRD spectra confirmed the formation of kesterite CZTS films. Grown CZTS films showed an absorption coefficient >104 cm−1 and the bandgaps were found to lie between 1.42–1.72 eV at room temperature depending on deposition conditions and post deposition sulfurization treatments. All films were found to be of p-type conductivity with an average carrier concentration in the order of 1018–1020 cm−3. Optimum quality films were obtained for films fabricated at 360°C and no secondary phases were observed. n-CdS window layer was deposited on p-CZTS films prepared at 360°C substrate temperature to fabricate p-CZTS/n-CdS heterojunction solar cells. The heterojunction exhibited an open-circuit voltage (V OC ) of 290 mV and a short-circuit current density (J SC ) of 3.1 mA/cm2 under AM 1.5 illumination. Details of CZTS thin film fabrication, processing, and characterization results are presented.

Contactless measurement of the conductivity of II–VI epitaxial layers by means of the partially filled waveguide method

Abstract: We report the contactless determination of the conductivity, the mobility and the carrier concentration of II–VI semiconductors by means of the technique of the partially filled waveguide at a microwave frequency of 9 GHz. The samples are CdHgTe epitaxial layers, grown on CdZnTe substrates by molecular beam epitaxy. The conductivity is determined from the transmission coefficient of the sample in the partially filled waveguide. For the analysis of the experimental data, the complex transmission coefficient is calculated by a rigorous multi-mode matching procedure. By varying the conductivity of the sample, we obtain an optimum fit of the calculated data to the experimental results. Comparison with conductivity data determined by the van der Pauw method shows that our method allows to measure the conductivity with good accuracy. The behaviour of the transmission coefficient of the sample is discussed in dependence on the layer conductivity, the layer thickness and the dielectric constant of the substrate. The calculations require to consider in detail the distribution of the electromagnetic fields in the sample region. The usual assumption of a hardly disturbed TE10 mode cannot be used in our case. By applying a magnetic field in extraordinary Voigt configuration, galvanomagnetic measurements have been carried out which yield the mobility and thus the carrier concentration. These results are also in good agreement with van der Pauw transport measurements.

Finite element analysis of the effect of electrode resistivity on resistivity measurement in a diamond anvil cell

Abstract: The effect of electrode resistivity on the in situ resistivity measurement in a diamond anvil cell was studied using finite element analysis. The theoretical analysis reveals that the origin of significant error for a thin sample is mainly caused by the resistivity difference between the electrodes and the sample. The authors found that reducing such resistivity differences can improve the accuracy. The result shows that the van der Pauw method [L. J. van der Pauw, Philips Tech. Rev. 20, 220 (1958)] can provide more accurate results for thin samples compared with the four-point probe method. This approach provides means to simulate actual experiments and to eliminate the measurement error.

Geometric optimization of van der Pauw structure based MEMS pressure sensor

Abstract: This paper characterizes a piezoresistive sensor under variations of both size and orientation with respect to the silicon crystal lattice for its application to MEMS pressure sensing The sensor to be studied is a four-terminal piezoresistive sensor commonly referred to as a van der Pauw (VDP) structure It is observed that the sensitivity of the VDP sensor is over three times higher than the conventional filament type Wheatstone bridge resistor With MEMS devices being used in applications which continually necessitate smaller size, characterizing the effect of size and orientation of a VDP structure on the performance of a MEMS pressure sensor is important In this paper, the effect of relative size and misalignment of the VDP sensor on the sensitivity is investigated using a coupled piezoresistive/stress finite element model The mode is developed to simulate the full field stress over the deformed diaphragm in which the VDP is diffused The change in resistivity of the VDP is then analyzed to predict the sensitivity of the VDP structure Sensor size, position relative to the diaphragm, and angular misalignment of the VDP were varied to determine a theoretical result for the dependence of VDP output on those parameters It is determined that the performance of the sensor is strongly dependent only on the longitudinal position of the sensor on the diaphragm, and is relatively tolerant of other errors in the manufacturing process such as transverse position, sensor depth, and orientation angle