Showing papers on "Van der Pauw method published in 2004"
TL;DR: In this article, the electrochemical properties of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) have been assessed for its application as a cathode in intermediate-temperature solid oxide fuel cells.
Abstract: The electrochemical properties of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) have been assessed for its application as a cathode in intermediate-temperature solid oxide fuel cells. van der Pauw dc conductivity, two-electrode impedance, and three-electrode measurements were carried out to investigate the kinetics of the oxygen reduction reaction at various temperatures, oxygen partial pressures, and polarization values. A change in cathode behavior at temperatures around 600°C was observed. This is interpreted in terms of LSCF behaving as a mixed ionic electronic conductor at temperatures above around 600°C, oxygen reduction being stimulated by the formation of oxygen vacancies with increasing cathode overpotential. However, at temperatures below 600°C the contribution of mixed conductivity is low, and cathode behavior can then be interpreted in terms of the classical triple-phase-boundary model.
381 citations
TL;DR: In this article, a GaN-based heterojunction field effect transistors were grown by metal-organic chemical vapor deposition on high resistivity 100mm Si (111) substrates.
Abstract: Al/sub 0.26/Ga/sub 0.74/N-GaN heterojunction field-effect transistors were grown by metal-organic chemical vapor deposition on high-resistivity 100-mm Si (111) substrates. Van der Pauw sheet resistance of the two-dimensional electron gas was 300 /spl Omega//square with a standard deviation of 10 /spl Omega//square. Maximum drain current density of /spl sim/1 A/mm was achieved with a three-terminal breakdown voltage of /spl sim/200 V. The cutoff frequency and maximum frequency of oscillation were 18 and 31 GHz, respectively, for 0.7-/spl mu/m gate-length devices. When biased at 50 V, a 2.14-GHz continuous wave power density of 12 W/mm was achieved with associated large-signal gain of 15.3 dB and a power-added efficiency of 52.7%. This is the highest power density ever reported from a GaN-based device grown on a silicon substrate, and is competitive with the best results obtained from conventional device designs on any substrate.
231 citations
TL;DR: In this article, the X-ray diffraction spectra of CdO and Cu 2 O thin films have been analyzed and it was shown that films are polycrystalline.
92 citations
TL;DR: In this paper, the validity of four-contact van der Pauw-Hall measurements of rectangularly shaped semiconductors with anisotropic transport properties is investigated analytically, numerically, and experimentally.
Abstract: The validity of four-contact van der Pauw--Hall measurements of rectangularly shaped semiconductors with anisotropic transport properties is investigated analytically, numerically, and experimentally We show that the carrier concentration is correctly measured using the van der Pauw technique without corrections Furthermore, the asymmetry in the resistance of the van der Pauw sample is related to the real transport asymmetry through an analytically obtained formula Thus, the mobility in both principal directions as well as the carrier density can be obtained from van der Pauw data Measurements of electron concentration and mobility using both the Hall-bar and van der Pauw geometries in semiconductor coupled quantum-wire structures confirm this expectation for different anisotropies
87 citations
TL;DR: In this article, the preparation and characterization of (SnO2) thin films doped with 7 mol% Sb2O3 was reported, and the results showed that the polymeric precursor method is effective for the TCOs manufacturing.
Abstract: This work reports the preparation and characterization of (SnO2) thin films doped with 7 mol% Sb2O3. The films were prepared by the polymeric precursor method, and deposited by spin-coating, all of them were deposited on amorphous silica substrate. Then, we have studied the thickness effect on the microstrutural, optical and electric properties of these samples. The microstructural characterization was carried out by X-ray diffraction (XRD) and scanning tunneling microscopy (STM). The electrical resistivity measurements were obtained by the van der Pauw four-probe method. UV-visible spectroscopy and ellipsometry were carried out for the optical characterization. The films present nanometric grains in the order of 13 nm, and low roughness. The electrical resistivity decreased with the increase of the film thickness and the smallest measured value was 6.5 × 10− 3Ω cm for the 988 nm thick film. The samples displayed a high transmittance value of 80% in the visible region. The obtained results show that the polymeric precursor method is effective for the TCOs manufacturing.
61 citations
TL;DR: In this paper, a defect association model involving Mg dopant-oxygen vacancy clusters was proposed to describe the intermediate temperature conductivities of La0.99Sr0.01Ga0.05O2.
53 citations
TL;DR: In this paper, thin ruthenium oxide films were sputtered on oxidized silicon wafers and subsequently thermally oxidized in oxygen∕nitrogen or oxygen ambient in the temperature range from 400 to 700 °C.
Abstract: Thin ruthenium films were sputtered on oxidized silicon wafers and subsequently thermally oxidized in oxygen∕nitrogen or oxygen ambient in the temperature range from 400 to 700 °C. The morphological and structural properties of grown ruthenium oxide films were analyzed by atomic force microscopy, Raman spectroscopy, and x-ray diffraction, with electrical properties analyzed by van der Pauw technique and metal–oxide semiconductor (MOS) structures. Significant roughening of RuO2 was observed for prolonged oxidation in oxygen∕nitrogen atmosphere, or for short times in pure oxygen atmosphere. Raman spectroscopy revealed superior structural properties of thermally grown RuO2, in comparison to sputtered or metalorganic chemical vapor deposition RuO2 films. Thermally grown RuO2 is shown to have a work function of 5.1 eV, making it a suitable choice of metals, together with Ru (4.6 eV work function) for electrodes in complementary MOS n-channel and p-channel transistors.
37 citations
TL;DR: In this article, the authors investigated the magnetic field dependent metal-insulator behavior in highly oriented pyrolytic graphite at low temperatures by electronic and thermoelectric transport and found that a simple two-band transport model can qualitatively describe the temperature and field dependence, without appealing to a M-I scaling description.
34 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
TL;DR: In this paper, the morphological structure, crystallinity, optical properties and electrical properties of the films were investigated using a range of techniques, including SEM, XRD, spectrophotometry, four-point probe and van der Pauw method.
29 citations
TL;DR: In this article, indium tin oxide films (ITO) of different thickness (120±25−40 to 560± 25−40 nm) and of various compositions (In:Sn=90:10, 70:30 and 50:50) prepared from In metal and Sn salt were deposited on silica-coated (∼200 nm thickness) sheet glass substrate by the spinning technique.
TL;DR: In this paper, the authors investigated the thermal activation process of Mg dopant in Mg-doped GaN by secondary ion mass spectrometry (SIMS) and Hall measurement with the van der Pauw configuration.
Abstract: We have investigated the thermal activation process of Mg dopant in Mg-doped GaN by secondary ion mass spectrometry (SIMS) and Hall measurement with the van der Pauw configuration. We have found a systematic relationship between the amount of the hydrogen dissociated from the Mg-doped GaN layer by thermal annealing and the electronic conductive properties of the layer, i.e., Hall mobility, Hall carrier density and resistivity of the layer. The hydrogen in the Mg-doped GaN layer has been classified into at least two different modes. The first mode involves relatively larger activation energy of the dissociation process from the Mg-doped GaN layer, and the dissociation energy from the Mg-doped GaN to the atmosphere is 0.8–1.5 eV. The second mode has the dissociation energy of 0.2–0.5 eV. The former mode may be associate with the hydrogen passivation of the Mg dopant in GaN and the latter one may be closely related to the passivation of the electrical compensation mechanism for the positive hole carriers in the Mg-doped GaN.
TL;DR: In this article, the authors present results obtained on modulation-doped quantum wells with compressively strained Ge channels, where the heterostructures have been grown by low-energy plasma-enhanced chemical vapor deposition (LEPECVD).
TL;DR: In this paper, the influence of different capping layers on the crystallization kinetics of Ag5In6Sb59Te30 films was investigated by measuring the electrical resistivity of the films as a function of temperature employing the van der Pauw method.
Abstract: AgInSbTe alloys are attractive storage materials for phase change recording utilizing both optical and electronic contrast The demand to decrease the thickness of such storage layers increases the significance of the surrounding dielectric layers, which can have a profound impact on the crystallization process Hence we have investigated the influence of different capping layers on the crystallization kinetics of Ag5In6Sb59Te30 films by measuring the electrical resistivity of the films as a function of temperature employing the van der Pauw method While the phase transition temperature was found to only increase slightly for capped Ag5In6Sb59Te30 films, a profound impact on the activation barrier for crystallization was observed Activation energies of 239±010eV and 324±012eV were determined for films capped with 5nm of ZnS-SiO2 and Si3N4, respective1y, in comparison with a value of 303±017eV for an uncapped film Additional stress measurements reveal that this change in activation barrier is not
TL;DR: In this article, the dependence of residual stress on the process parameters for aluminum metallization has been studied using a rotating beam sensor, which shows increasing tensile stress with both the target power and ambient pressure used during the sputter deposition of the aluminum layer.
Abstract: The dependence of residual stress on the process parameters for aluminum metallization has been studied using a rotating beam sensor. This shows increasing tensile stress with both the target power and ambient pressure used during the sputter deposition of the aluminum layer. The bulk resistivity of the deposited aluminum has been measured using a Van der Pauw technique on test structures fabricated alongside the sensors and this shows different trends with respect to the target power and ambient pressure. This indicates that the stress in an interconnect feature is dominated by extrinsic components, which result from the mismatch in thermal expansion coefficient between the constituent layers, rather than the defects formed during the sputter deposition of the metallization. This indicates the suitability of the stress sensor technique to the monitoring of interconnect features in a production line environment.
TL;DR: In this paper, the authors used non-destructive mobility and sheet charge density measurements during the fabrication of GaAs and GaN wafers to improve process control, lowered costs and reduced risks.
TL;DR: In this paper, the electronic conductivity of polypyrrole−dodecyl benzene sulfonate (PPy−DBS) was characterized as function of the redox level.
Abstract: The electronic conductivity of the electroactive polymer polypyrrole−dodecyl benzene sulfonate (PPy−DBS) has been characterized as function of the redox level. The polymer was synthesized with different isomers of the dopant anions: the common mixed DBS tenside and three well-defined synthetic dodecyl isomers (with the benzene group at positions 1, 2 and 6). The conductivity was measured both by van der Pauw measurements on PPy−DBS in the oxidized, dry state as function of temperature, and by electrochemical impedance spectroscopy as function of potential in 0.1 M NaCl aqueous electrolyte. These investigations demonstrate that even minor differences in the dopant anion can cause significant changes in the physical properties of the electroactive polymer. The highest conductivities (σ25 = 39 Scm-1) are obtained by the (6D)BS isomer, perhaps because the branching leads to denser packing and therefore smaller hopping distances. This was supported by X-ray measurements. Synthesis at lower temperatures genera...
TL;DR: In this article, the Hall effect and van der Pauw measurements for temperatures in the range 300-1000 K were carried out on semi-insulating (SI) 4H-SiC wafers grown by physical vapor transport (PVT) and by high temperature chemical vapor deposition.
Abstract: Hall effect and van der Pauw measurements for temperatures in the range 300–1000 K were carried out on semi-insulating (SI) 4H-SiC wafers grown by physical vapor transport (PVT) and by high temperature chemical vapor deposition. It is shown that, for semi-insulating 4H-SiC samples the temperature dependence of both resistivity and electron mobility can be measured with some samples exhibiting mobilities close to the theoretical limit determined by intervalley and phonon scattering. However, most PVT-grown samples exhibit electron mobilities an order of magnitude lower than expected. The results are explained by the electrical macrononuniformities inherent in the PVT growth process. Measurements of the temperature dependence of the photocurrent indicate that microscale potential fluctuations characteristic of other high-resistivity semiconductors are less of an issue with SI–SiC.
TL;DR: In this article, high quality ZnO epitaxial films without rotation domain structure were successfully prepared on sapphire (0, 0,0,0,1) substrates using metal organic chemical vapor deposition method.
TL;DR: RuO2-SiO2 composite thin films were deposited on oxidised silicon wafers by reactive sputtering of Ru and quartz in argon-oxygen plasma in this article, and post-deposition annealing was performed in a furnace in the temperature range from 200 to 600 °C in nitrogen ambient.
Patent•
08 Jul 2004TL;DR: An integrated semiconductor temperature and pressure sensor has two sets (1-2, 3-4) of series orthogonal different type piezoelectric Van der Pauw structures in MOS transistor source to drain channels with different pressure dependent electrical properties and a processor comparing the inputs.
Abstract: An integrated semiconductor temperature and pressure sensor has two sets (1-2, 3-4) of series orthogonal different type piezoelectric Van der Pauw structures in MOS (Metal Oxide Silicon) transistor source to drain channels with different pressure dependent electrical properties and a processor comparing the inputs. Includes INDEPENDENT CLAIMs for the procedures used by the system.
TL;DR: Magnetotransport at fields up to 500 mT and LF-noise characteristics are reported for miniature magnetoresistors with ferrite concentrators based on Sn-doped n-InSb/i-GaAs heterostructures grown by MBE as discussed by the authors.
Abstract: Magnetotransport at fields up to 500 mT and LF-noise characteristics are reported for miniature magnetoresistors with ferrite concentrators based on Sn-doped n-InSb/i-GaAs heterostructures grown by MBE. The thickness of the InSb epilayers lie in the range 0.55-1-5 μm giving room temperature mobilities of 2.5-5.5 m 2 V - 1 s - 1 with carrier densities of (0.5-1.5) x 10 1 7 cm - 3 . The room temperature magnetoresistance (MR) for our two terminal devices could be as high as 115% at 50 mT which is comparable to the extraordinary MR (ExMR) recently reported in microscopic composite van der Pauw disks four terminal devices [Science 289 (2000) 1530]. In addition, a high signal-to-noise ratio and a good temperature stability of R(B)/R 0 = 0.5-0.83% K - 1 was observed for B < 60 mT (below the saturation field Brat for ferrite). Device resistance stability R 0 (T) was equal to 0.27-0.66% K - 1 in zero field with a nominal device resistance R 0 = 197-224 Ω for DC currents in the range I = 0.01-1.0 mA. The minimum detectable magnetic field is estimated from the reduced differential MR (∂R/∂B)/R = 2000% T - 1 at B = 31 mT and normalised 1/f current noise power spectral density measured at the same field. The resolution limit B m i n = 2.6 nT at 10 2 Hz and B m i n = 0.82 nT at 10 3 Hz. These resolution limits are seven times better than those recently reported for the same material n-InSb/i-GaAs and ferrite fabricated Hall sensors [Magnetotransport and Raman characterization of n-InSb/i-GaAs epilayers, for Hall sensors applications over extremely wide ranges of temperature and magnetic field, Proceedings NGS 10, IPAP Conference Series 2, IPAP, Tokyo, 2001, pp. 151-154].
TL;DR: In this paper, the structural, electrical and optical properties of Al-doped zinc oxide (ZnO: Al) thin films onto quartz substrates prepared by electron beam evaporation technique were studied.
Abstract: In this paper, the structural, electrical and optical properties of Al-doped zinc oxide (ZnO: Al) thin films onto quartz substrates prepared by electron beam evaporation technique were studied. All samples are polycrystal with a hexagonal structure andc-axis preferred orientation. The intense UV emissions and weak deep-level green emissions were observed. The films show high transparency, conductivity and high carrier concentration. Van der Pauw measurements show that the films are n-type degenerate semiconductor. The lowest resistivity is 6.7×10−4 Ω⊙cm at room temperature. These films exhibit a carrier density above 1020 cm−3. The conduction mechanism was discussed. The behavior of metallic conduction can be observed in the high temperature range.
TL;DR: In this article, the surface morphology, crystalline microstructure and electrical resistivity were investigated by field-emission scanning electron microscopy, X-ray diffraction and Van der Pauw method, respectively.
Abstract: Copper agglomeration in Cu(100nm)/Ta(50urn)/Si structure deposited by ion beam deposition was examined. Copper thin films were annealed at 650°C for 1 to 60 min in hydrogen atmosphere. The surface morphology, crystalline microstructure and electrical resistivity were investigated by field-emission scanning electron microscopy, X-ray diffraction and Van der Pauw method, respectively. Experimental results revealed that nucleation and growth of voids ocurred in the copper film annealed for 5 min. Further annealing made the film a connected island structure and then isolated island structure.
18 May 2004
TL;DR: In this paper, the limits of the traditional experiment approach to extract resistivity in junction-isolated samples are discussed basing both on physical simulations and on extensive experimental data, and several optimization criteria to design van der Pauw resistors and a related characterization procedure are proposed and experimentally validated in order to extend the extraction of the resistivity up to 500/spl deg/C.
Abstract: The limits of the traditional experiment approach to extract resistivity in junction-isolated samples are discussed basing both on physical simulations and on extensive experimental data. Several optimization criteria to design van der Pauw resistors and a related characterization procedure are proposed and experimentally validated in order to extend the extraction of the resistivity up to 500/spl deg/C.
TL;DR: A boron doped Si1−xGex thin film has been successfully prepared on a quartz (SiO2) glass substrate at room temperature (RT) by irradiating an intense, pulsed, ion beam on a Si-Ge-B pellet as mentioned in this paper.
Abstract: A boron doped Si1−xGex thin film has been successfully prepared on a quartz (SiO2) glass substrate at room temperature (RT) by irradiating an intense, pulsed, ion beam on a Si–Ge–B pellet. As a result, in situ boron doped Si1−xGex thin film was found to be crystallized. In addition, by van der Pauw measurement, the resistivity, carrier density, and mobility of the thin film were observed as ρ=2.3×10−3Ωcm, n=7.2×1020cm−3, and μ=3.8cm2∕Vs, respectively. Thus, the boron doped Si1−xGex thin film was clarified to be not only crystallized but also activated without heat treatment.
TL;DR: An experimental system in combination with a technique for creating samples has been developed for conducting magnetotransport measurements of 3D ferromagnets as a function of temperature and pressure.
Abstract: An experimental system in combination with a technique for creating samples has been developed for conducting magnetotransport measurements of 3d ferromagnets as a function of temperature and pressure. Polycrystalline Ni0.985O0.015 thin film samples have been manufactured for experiments at zero pressure and in the diamond anvil cell (DAC) such that the contacts are of a predetermined size. This ensures that the placement of the leads in the pressure chamber of the DAC does not affect the quality of the measurement. Magnetoresistance and Hall resistivity measurements are preformed using the van der Pauw technique and the constant current method. The performance of the experimental apparatus is demonstrated by magnetotransport measurements of Ni0.985O0.015 thin films between 285 and 455 K in applied magnetic fields up to 10 T. The change in magnetic resistivity measured in the transverse configuration at zero pressure in the DAC, −0.0162(2) μΩ cm T−1 at 297 K, is observed to be negative and linear up to t...
TL;DR: In this paper, a dc Hall-effect apparatus, based on conventional van der Pauw specimen geometry, has been developed for in situ measurements under van de Graaff electron irradiation (0.7-2.2 MeV).
Abstract: A dc Hall-effect apparatus, based on conventional van der Pauw specimen geometry, has been developed for in situ measurements under van de Graaff electron irradiation (0.7–2.2 MeV). An associated cryostat permits ambient temperatures of 95–300 K. A key element is a flat permanent magnet of field strength 3.55 kG. Initial test measurements have been performed on wide-bandgap semiconductor materials, including an HVPE-grown AlGaN/GaN heterostructure field-effect transistor structure.
TL;DR: In this paper, anomalous behavior observed in the sheet resistance measurement in a van der Pauw (VDP) device which is caused by the anisotropic electron mobility has been described.
Abstract: An anisotropic electron mobility has recently been reported in 4H-SiC MOS devices with improved inversion layer mobility [1]. This anisotropy arises from scattering by oriented steps on the 8° off-axis 4H-SiC surface. The mobility is higher in the direction parallel to the steps, and lower perpendicular to the steps. In this paper, we describe anomalous behavior observed in the sheet resistance measurement in a van der Pauw (VDP) device which is caused by the anisotropy. Experimentally, a ~15% mobility anisotropy results in a 1.8x anisotropy in the VDP sheet resistance. This surprising experimental result is confirmed by numerical simulations.
01 Sep 2004
TL;DR: In this article, the active layers are lead selenide (PbSe) thin films grown by molecular-beam epitaxy (MBE) on single crystalline, infrared transparent BaF2 substrates.
Abstract: We report on the development of epitaxial thin film materials for optical pumped light emitting devices in the wavelength range of 4-5 μm. The active layers are lead selenide (PbSe) thin films grown by molecular-beam epitaxy (MBE) on single crystalline, infrared transparent BaF2 substrates. The electrical properties of the layers were determined by van der Pauw Hall measurements. A dependency of the PL intensity on the dopant type and carrier concentration was found. To increase the output power, layers with antireflection coatings were grown and characterized by Fourier-transform infrared (FTIR) spectroscopy and photoluminescence (PL) measurements. A further possibility to increase the extraction efficiency is surface texturing. Infrared imaging and PL measurements at samples with different surface structures, prepared by wet chemical etching, are presented. To improve the heat dissipation, which is a problem of optical pumped devices due to the small efficiency and pump densities up to some kW/cm2, the BaF2 substrates were removed and the active layers were transferred to different heat sinks with significantly higher thermal conductivities. Afterwards the PL intensities were compared among each other.