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.

Direct comparison of time-resolved terahertz spectroscopy and Hall Van der Pauw methods for measurement of carrier conductivity and mobility in bulk semiconductors

Abstract: Charge carrier conductivity and mobility for various semiconductor wafers and crystals were measured by ultrafast above bandgap, optically excited time-resolved terahertz spectroscopy (TRTS) and Hall Van der Pauw contact methods to directly compare these approaches and validate the use of the non-contact optical approach for future materials and in situ device analyses. Undoped and doped silicon (Si) wafers with resistances varying over 6 orders of magnitude were selected as model systems because contact Hall measurements are reliably made on this material. Conductivity and mobility obtained at room temperature by terahertz transmission and TRTS methods yield the sum of electron and hole mobility which agree very well with either directly measured or literature values for corresponding atomic and photodoping densities. Careful evaluation of the optically generated TRTS frequency-dependent conductivity also shows it is dominated by induced free carrier absorption rather than small probe pulse phase shifts, which is commonly ascribed to changes in the complex conductivity from sample morphology and evaluation of carrier mobility by applying Drude scattering models. Thus, in this work, the real-valued, frequency-averaged conductivity was used to extract sample mobility without application of models. Examinations of germanium (Ge), gallium arsenide (GaAs), gallium phosphide (GaP), and zinc telluride (ZnTe) samples were also made to demonstrate the general applicability of the TRTS method, even for materials that do not reliably make good contacts (e.g., GaAs, GaP, ZnTe). For these cases, values for the sum of the electron and hole mobility also compare very favorably to measured or available published data.

Acceptor-modulated optical enhancements and band-gap narrowing in ZnO thin films

Abstract: Fermi-Dirac distribution for doped semiconductors and Burstein-Moss effect have been correlated first time to figure out the conductivity type of ZnO. Hall Effect in the Van der Pauw configuration has been applied to reconcile our theoretical estimations which evince our assumption. Band-gap narrowing has been found in all p-type samples, whereas blue Burstein-Moss shift has been recorded in the n-type films. Atomic Force Microscopic (AFM) analysis shows that both p-type and n-type films have almost same granular-like structure with minor change in average grain size (∼ 6 nm to 10 nm) and surface roughness rms value 3 nm for thickness ∼315 nm which points that grain size and surface roughness did not play any significant role in order to modulate the conductivity type of ZnO. X-ray diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) have been employed to perform the structural, chemical and elemental analysis. Hexagonal wurtzite structure has been observed in all samples. The introduction of nitrogen reduces the crystallinity of host lattice. 97% transmittance in the visible range with 1.4 × 107 Ω-1cm-1 optical conductivity have been detected. High absorption value in the ultra-violet (UV) region reveals that NZOs thin films can be used to fabricate next-generation high-performance UV detectors.

New diamond anvil cell system for in situ resistance measurement under extreme conditions

Abstract: We report an alumina-encapsulated microcircuit on a diamond anvil for high-pressure and high-temperature electrical conductivity measurement. An alumina thin film was deposited on a diamond anvil as a thermal insulation layer for laser heating, on which a molybdenum film was deposited and photolithographically fabricated to a van der Pauw circuit. The introduction of the alumina layer significantly improves the laser heating performance. This specially fabricated diamond anvil permits us to measure the resistivity of (Mg0.875Fe0.125)2SiO4 at 3450K and 35GPa in a laser-heated diamond anvil cell. We expect to substantially extend the pressure-temperature scale of in situ resistivity measurement.

The Dependence of Offset Voltage in p-Type 3C-SiC van der Pauw Device on Applied Strain

Abstract: This letter reports for the first time the strain dependence of the offset voltage in p-type 3C-SiC van der Pauw square device. The p-type 3C-SiC thin film was epitaxially grown on a p-type Si(100) wafer using low pressure chemical vapor deposition followed by a conventional photolithography and dry etch processes, forming four-terminal van der Pauw device. The influence of applied tensile and compressive strain on the offset voltage of the van der Pauw device was investigated using the bending beam method. Experimental results showed that the offset voltage of the device is significantly changed by applied compressive and tensile strain, indicating the feasibility of using this effect for mechanical sensing applications. The sensitivity of the device to the applied strain has been found to be 70 (mV/A)/ppm.

Preparation and electrical property of CaZr0.7M0.3O3 (M = Fe, Cr and Co) dense diffusion barrier for application in limiting current oxygen sensor

Abstract: (M = Fe, Cr and Co) doped CaZrO3, CaZr0.7M0.3O3 (M = Fe, Cr and Co), was synthesized by solid state reaction method. Crystalline structure, microstructures, electronic conductivity, total conductivity and sensing performance were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Hebb-Wagner, DC van der Pauw and voltammetry method, respectively. XRD measurements show that the CaZr0.7M0.3O3 (M = Fe, Cr and Co) samples belong to an orthorhombic perovskite structure. SEM measurements show that the CaZr0.7M0.3O3 (M = Fe, Cr and Co) samples have fine grains with average grain size of 0.5–2 μm. Electrical property measurements show that the CaZr0.7Fe0.3O3 and CaZr0.7Cr0.3O3 samples have the highest electronic conductivity and total conductivity in air, respectively. Sensing performance measurements show that limiting current-type oxygen sensors with 9YSZ solid electrolyte and CaZr0.7M0.3O3 dense diffusion barrier exhibit good limiting current (IL) plateau. Log IL depends linearly on 1000/T. IL depends linearly on oxygen partial pressure.