Topic
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.
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TL;DR: V2O5 is demonstrated as a layered 2D vdW oxide material with strongly anisotropic optical and electronic properties for novel applications and room-temperature electron Hall mobility up to 7 cm2/(V s) along the high-mobility direction was obtained.
Abstract: V2O5 with a layered van der Waals (vdW) structure has been widely studied because of the material's potential in applications such as battery electrodes. In this work, microelectronic devices were fabricated to study the electrical and optical properties of mechanically exfoliated multilayered V2O5 flakes. Raman spectroscopy was used to determine the crystal structure axes of the nanoflakes and revealed that the intensities of the Raman modes depend strongly on the relative orientation between the crystal axes and the polarization directions of incident/scattered light. Angular dependence of four-probe resistance measured in the van der Pauw (vdP) configuration revealed an in-plane anisotropic resistance ratio of ∼100 between the a and b crystal axes, the largest in-plane transport anisotropy effect experimentally reported for two-dimensional (2D) materials to date. This very large resistance anisotropic ratio is explained by the nonuniform current flow in the vdP measurement and an intrinsic mobility anisotropy ratio of 10 between the a and b crystal axes. Room-temperature electron Hall mobility up to 7 cm2/(V s) along the high-mobility direction was obtained. This work demonstrates V2O5 as a layered 2D vdW oxide material with strongly anisotropic optical and electronic properties for novel applications.
33 citations
TL;DR: In this paper, a combination of atomic force microscopy and van der Pauw measurements is used to investigate and explain the strong influence of the buffer layers on the morphology in the quantum well that is shown to be responsible for the great differences in the observed low-temperature mobilities.
Abstract: The growth of modulation‐doped InAs/(Al,Ga)Sb quantum wells on GaAs substrates employing molecular beam epitaxy requires care in the nucleation and the use of buffer layers to achieve high quality material. Despite a 7% lattice mismatch between the substrate and the active layers, fully relaxed epitaxial growth can be accomplished, and quantum wells with electron sheet concentrations of 7×1012 cm−2 having low‐temperature mobilities as high as 300 000 cm2/V s have been routinely fabricated recently in our laboratory. In the present work the combination of atomic force microscopy and van der Pauw measurements is used to investigate and explain the strong influence of the buffer layers on the morphology in the quantum well that is shown to be responsible for the great differences in the observed low‐temperature mobilities.
33 citations
TL;DR: In this paper, the structure, chemical composition, optical and thermoelectrical properties of the (bulk) pellets and thin films are studied as a function of initial solution concentration.
33 citations
04 Apr 2005
TL;DR: In this article, the fabrication of an InSb Hall sensor arrays to simultaneously detect multiple superparamagnetic microbeads for biomedical applications is described, where the authors showed that real-time simultaneous detection of multiple super-paramagnetic beads using the In Sb-Hall sensor array system is possible.
Abstract: In this report the fabrication of an InSb Hall sensor arrays to simultaneously detect multiple superparamagnetic microbeads for biomedical applications is described. One-dimensional InSb Hall sensor arrays with 8 micro-Hall devices were fabricated using photolithography and wet chemical etching. The electrical characteristics and noise spectrum of the micro-Hall sensors were determined by van der Pauw Hall measurements and fast Fourier transform (FFT) spectrum analysis respectively. Results show that the offset voltage of all 8 Hall sensors was small at /spl sim/0.1 mV under a drive current (I/sub H/) of 100 /spl mu/A. The minimum detectable magnetic field is found to be 0.10 mG/(Hz)/sup 1/2/ at I/sub H/ = 1 mA. Calculations showed that the magnetic field from a single ferromagnetic particle with a radius of 50 nm at a distance of 200 nm from the sensor is about 4.4 G. Therefore, the sensitivity of the Hall array micro-Hall sensors is sufficient for detection of magnetic microbeads. In conclusion, the paper showed that real time simultaneous detection of multiple superparamagnetic beads using the InSb-Hall sensor array system is possible. These results suggest that possibility of using two dimensional Hall sensor array biochips for biomedical applications.
33 citations
TL;DR: In this article, a theory of the current ratio technique in uniform semiconductors, which is widely used to locate gate oxide breakdown (BD) spots in one dimension (i.e., distance from source or drain), is proposed and verified.
Abstract: A theory of the current-ratio (CR) technique in uniform semiconductors, which is widely used to locate gate oxide breakdown (BD) spots in one dimension (i.e., distance from source or drain), is proposed and verified. The theory shows that the CR method is a special case of generalized van der Pauw technique and, as such, can easily be generalized to locate oxide BD spots in two dimensions. We develop the theoretical framework of this new class of BD-spot characterization techniques and then validate the theory by experiments. We conclude by discussing the implications of locating BD spots in two dimensions for reliability projections of ultrathin gate oxides.
32 citations