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Showing papers on "Van der Pauw method published in 2017"


Journal ArticleDOI
TL;DR: In this paper, the electron concentration and mobility were investigated using Van der Pauw Hall patterns, and the Hall data showed an improved electron mobility for the same electron concentration when Ge is used instead of Sn as the dopant.
Abstract: The Ge doping of β-Ga2O3(010) films was investigated using plasma-assisted molecular beam epitaxy as the growth method. The dependences of the amount of Ge incorporated on the substrate temperature, Ge-cell temperature, and growth regime were studied by secondary ion mass spectrometry. The electron concentration and mobility were investigated using Van der Pauw Hall patterns. Hall measurement confirmed that Ge acts as an n-dopant in β-Ga2O3(010) films. These results were compared with similar films doped by Sn. The Hall data showed an improved electron mobility for the same electron concentration when Ge is used instead of Sn as the dopant.

188 citations


Journal ArticleDOI
18 Oct 2017
TL;DR: In this paper, two independent mechanisms responsible for thermally assisted hysteresis inversion in gate transfer characteristics of contact resistance-independent multilayer MoS2 transistors are delineated.
Abstract: The origin of threshold voltage instability with gate voltage in MoS2 transistors is poorly understood but critical for device reliability and performance. Reversibility of the temperature dependence of hysteresis and its inversion with temperature in MoS2 transistors has not been demonstrated. In this work, we delineate two independent mechanisms responsible for thermally assisted hysteresis inversion in gate transfer characteristics of contact resistance-independent multilayer MoS2 transistors. Variable temperature hysteresis measurements were performed on gated four-terminal van der Pauw and two-terminal devices of MoS2 on SiO2. Additional hysteresis measurements on suspended (~100 nm air gap between MoS2 and SiO2) transistors and under different ambient conditions (vacuum/nitrogen) were used to further isolate the mechanisms. Clockwise hysteresis at room temperature (300 K) that decreases with increasing temperature is shown to result from intrinsic defects/traps in MoS2. At higher temperatures a second, independent mechanism of charge trapping and de-trapping between the oxide and p+ Si gate leads to hysteresis collapse at ~350 K and anti-clockwise hysteresis (inversion) for temperatures >350 K. The intrinsic-oxide trap model has been corroborated through device simulations. Further, pulsed current–voltage (I–V) measurements were carried out to extract the trap time constants at different temperatures. Non-volatile memory and temperature sensor applications exploiting temperature dependent hysteresis inversion and its reversibility in MoS2 transistors have also been demonstrated. Defects and traps in MoS2 van der Pauw devices give rise to a hysteresis inversion mechanism which is reversible with temperature. A team led by Saurabh Lodha at the Indian Institute of Technology Bombay performed variable temperature hysteresis measurements on four- and two-terminal MoS2 devices, both suspended and supported on a SiO2 substrate. The onset of a clockwise hysteresis at room temperature was attributed to intrinsic MoS2 defects, whereas an additional mechanism resulting in an anticlockwise hysteresis was observed at higher temperature, and attributed to extrinsic charge trapping and de-trapping between the oxide and the silicon gate. By leveraging the temperature dependence of the hysteresis in MoS2, the authors developed a non-volatile memory and a temperature sensor.

115 citations


Journal ArticleDOI
TL;DR: In this article, the authors review the conventional measuring standard for dc Hall measurements in van der Pauw configuration with particular focus on the challenges arising from a small Hall signal compared to sizable offset voltages, which is a typical scenario for many material systems, particularly low mobility thin films.
Abstract: We review the conventional measuring standard for dc Hall measurements in van der Pauw configuration with particular focus on the challenges arising from a small Hall signal compared to sizable offset voltages, which is a typical scenario for many material systems, particularly low-mobility thin films. We show that the conventional approach of using a simple field-reversal technique is often unsuited to obtain reliable results, and present an improved correction scheme to extend the accessible measurement range to mobility values well below 1 cm2/(V s). We discuss procedures to limit the impact of temperature fluctuations and long stabilization times for highly resistive materials. We further address potential sources of error due to the presence of grain boundaries in polycrystalline specimen and due to multi-carrier conduction, both of which might yield low apparent Hall mobilities significantly underestimating the actual mobility.

73 citations


Journal ArticleDOI
TL;DR: The gated van der Pauw method is broadly applicable to thin films of semiconductors and enables a simple and clean parameter extraction independent from contact effects.
Abstract: Thin film transistors based on high-mobility organic semiconductors are prone to contact problems that complicate the interpretation of their electrical characteristics and the extraction of important material parameters such as the charge carrier mobility. Here we report on the gated van der Pauw method for the simple and accurate determination of the electrical characteristics of thin semiconducting films, independently from contact effects. We test our method on thin films of seven high-mobility organic semiconductors of both polarities: device fabrication is fully compatible with common transistor process flows and device measurements deliver consistent and precise values for the charge carrier mobility and threshold voltage in the high-charge carrier density regime that is representative of transistor operation. The gated van der Pauw method is broadly applicable to thin films of semiconductors and enables a simple and clean parameter extraction independent from contact effects.

61 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of oxygen incorporation on the electronic transport properties of 2D MoS2 have been studied via temperature dependent and gate voltage dependent transport measurements of physical vapor deposited 2D MOS2.
Abstract: The effects of oxygen incorporation on the electronic transport properties of two-dimensional (2D) MoS2 have been studied via temperature dependent and gate voltage dependent transport measurements of physical vapor deposited 2D MoS2. Gated micro-van der Pauw cross devices were fabricated from the MoS2 film for transport measurements. Field-effect measurements indicate that incorporated oxygen acts as a p-type dopant for MoS2. The combination of X-ray photoemission spectroscopy surface analysis and Raman measurements of the film indicates that acceptor states resulting from MoSxO3-x inclusions in the MoS2 film are the origin of the p-type doping. Temperature dependent van der Pauw conductivity measurements indicate an acceptor energy of 214 meV above the valence band edge for the acceptor state.

61 citations


Journal ArticleDOI
27 Feb 2017-ACS Nano
TL;DR: A process that enables cointegration of GaSb and InAs nanostructures in close vicinity on Si, a preferred material combination ideally suited for high-performance complementary III-V metal-oxide-semiconductor technology.
Abstract: GaSb nanostructures integrated on Si substrates are of high interest for p-type transistors and mid-IR photodetectors. Here, we investigate the metalorganic chemical vapor deposition and properties of GaSb nanostructures monolithically integrated onto silicon-on-insulator wafers using template-assisted selective epitaxy. A high degree of morphological control allows for GaSb nanostructures with critical dimensions down to 20 nm. Detailed investigation of growth parameters reveals that the GaSb growth rate is governed by the desorption processes of an Sb surface layer and, in turn, is insensitive to changes in material transport efficiency. The GaSb crystal structure is typically zinc-blende with a low density of rotational twin defects, and even occasional twin-free structures are observed. Hall/van der Pauw measurements are conducted on 20 nm-thick GaSb nanostructures, revealing high hole mobility of 760 cm2/(V s), which matches literature values for high-quality bulk GaSb crystals. Finally, we demonstra...

59 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of metal doping on the optical band gap was investigated using ultraviolet-visible spectrometry over the wavelength range of 300-1100 nm for un-doped, 2, 4 and 6% Co doped CuO thin films, respectively.

51 citations


Journal ArticleDOI
TL;DR: In this article, thin films of cadmium sulfide (CdS) have been deposited at room temperature by using RF-magnetron sputtering at various deposition times.

44 citations


Journal ArticleDOI
TL;DR: In this paper, the pyrolysis parameters at high temperature (1100°C) were investigated for the fabrication of two-dimensional Pyrolytic carbon electrodes, and the results showed that the temperature increase from 900°C to 1100°C improved the electrical and electrochemical properties.

43 citations


Journal ArticleDOI
TL;DR: In this article, a 1.75 mm high-loading Cu composite was extruded and printed into a desired size and shape, and the sample was sintered and calcined to transform Cu powder to CuO semiconductor.
Abstract: A CuO semiconductor was successfully prepared by fused deposition modeling (FDM) and sintering technique. A 1.75 mm high-loading Cu composite was extruded and printed into a desired size and shape. The sample was sintered and calcined to transform Cu powder to CuO semiconductor. The 3-dimensional (3D) printed CuO had a scaffold structure with a half density of bulk CuO. It had a mechanical characteristic like a scaffold ceramic although prepared by FDM machine. van der Pauw measurement and UV-visible absorption spectroscopy were used to determine the electrical and optical properties of the 3D printed CuO respectively. The 3D printed CuO was used as an example of a 3D semiconductor which has a response to light, pressure, and temperature. This technique has a potential to be applied in any FDM machine which might allow anyone to print semiconductor or other related materials.

35 citations


Journal ArticleDOI
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.

Journal ArticleDOI
TL;DR: In this article, aerosol assisted chemical vapour deposition (AACVD) was used to deposit Si-doped ZnO thin films on glass at a temperature of 450°C.
Abstract: For the first time, aerosol assisted chemical vapour deposition (AACVD) was used to deposit Si-doped ZnO thin films on glass. Depositions were done at a temperature of 450 °C. The precursor solution was made by dissolving the air-stable compounds zinc acetylacetonate and tetraethyl orthosilicate in methanol with a small addition of acetic acid to aid solubility. The dopant concentration in the precursor solution was optimised to find the best optoelectronic properties. The incorporation of Si into the ZnO lattice was confirmed by unit cell volumes calculated from X-ray diffraction (XRD) data and by X-ray photoelectron spectroscopy (XPS). The films consisted of pure phase wurtzite ZnO, with preferred orientation in the (002) plane. Scanning electron microscopy (SEM) was used to examine the surface morphology of the films. The optical properties of the films were analysed using UV/vis spectroscopy and indicated that the average transmittance in the visible part of the spectrum (400–700 nm) varied between 72% and 80%. The electrical properties of the films were obtained from Hall effect measurements using the van der Pauw method. The incorporation of Si into the films resulted in a decrease in resistivity down to a minimum value of 2.0 × 10−2 Ω cm for the film deposited from a 4 mol% Si : Zn ratio in the precursor solution. This conductive film was a significant improvement over the non-conductive undoped ZnO film.

Journal ArticleDOI
TL;DR: The real-valued, frequency-averaged conductivity was used to extract sample mobility without application of models to validate the use of the non-contact optical approach for future materials and in-situ device analyses.
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.

Journal ArticleDOI
TL;DR: In this paper, W-Cu thin films were co-deposited by magnetron sputtering using the glancing angle deposition (GLAD) method, and the deposition angle of W and Cu targets was fixed at 80°, and their currents were inversely and systematically changed from 50 to 140
Abstract: W-Cu thin films were co-deposited by magnetron sputtering using the glancing angle deposition (GLAD) method. The deposition angle of W and Cu targets was fixed at 80°, and their currents were inversely and systematically changed from 50 to 140 mA. Scanning electron microscopy, X-ray fluorescence spectroscopy, and X-ray diffraction were used to investigate the morphology and the elemental composition of the films. Electrical properties were also studied by the van der Pauw technique. An increase of the W target current and a decrease of the Cu target produced an improvement of the inclined columnar and porous structure. The W-to-Cu weight concentration ratio was tuned from 0.68 up to 19. W Cu films exhibited a diffracted signal corresponding to the (100) planes of the bcc tungsten structure for the highest W current intensities whereas the (111) peak due to the fcc copper phase was measured when the Cu target current increased. The dc electrical resistivity measured at room temperature was gradually changed from 3.59 × 10− 7 up to 9.90 × 10− 6 Ωm by means of an inverse variation of W and Cu target currents. The Cu-rich films exhibited a non-reversible resistivity vs. temperature evolution due to thermal oxidation whereas those co-sputtered with the highest W target currents showed a sudden increase of resistivity when the temperature was above 400 K.

Journal ArticleDOI
TL;DR: In this paper, polycrystalline CdTe thin films were deposited using thermal evaporation technique under different substrate temperatures from 125 to 300 °C, and the optical, structural, compositional, morphological and electrical properties were studied using UV-visible spectroscopy, GIXRD, EDX, SEM and van der Pauw method, respectively.
Abstract: Alteration of substrate temperature of thermally evaporated CdTe thin films can cause changes to the film structure and composition, affecting its optical, electrical as well as morphological properties. In this respect, polycrystalline CdTe thin films were deposited using thermal evaporation technique under different substrate temperatures from 125 to 300 °C. The optical, structural, compositional, morphological and electrical properties were studied using UV–visible spectroscopy, GIXRD, EDX, SEM and van der Pauw method, respectively. Optical measurements revealed that the band gap of the films slightly increase with increasing substrate temperature. Structurally, the lattice parameter and the crystallite size of the CdTe films deposited under a substrate temperature of 200 °C was found to be considerably higher than the rest of the substrate temperatures investigated. Texture coefficient indicate that the (111) plane becomes preferable as the substrate temperature is elevated to 300 °C. The lowest electrical resistivity was also found for samples deposited under a substrate temperature of 200 °C. Furthermore, EDX results reveals the composition of CdTe film considerably vary with respect to the substrate temperature at which the film was fabricated.

Journal ArticleDOI
TL;DR: In this paper, a limiting current oxygen sensor based on LSGM as both solid electrolyte and dense diffusion barrier was prepared by a Pt paste bonding method, and the results show that LSGM has pure perovskite structure (cubic symmetry with space group of Pm-3m (No.221), high density (relative density is 97.6%) and electrical conductivity (0.18 S∙cm −1 at 1073 K).

Journal ArticleDOI
TL;DR: In this paper, the effects of FeO 1.5 content on crystal structure, microstructure, electronic conductivity and total conductivity were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Hebb-Wagner method and DC van der Pauw method, respectively.

Journal ArticleDOI
TL;DR: In this article, the effects of humidity on the electronic properties of quasi-free standing one layer graphene (QFS 1LG) are investigated via simultaneous magneto-transport in the van der Pauw geometry and local work function measurements in a controlled environment.
Abstract: The effects of humidity on the electronic properties of quasi-free standing one layer graphene (QFS 1LG) are investigated via simultaneous magneto-transport in the van der Pauw geometry and local work function measurements in a controlled environment. QFS 1LG on 4H-SiC(0001) is obtained by hydrogen intercalation of the interfacial layer. In this system, the carrier concentration experiences a two-fold increase in sensitivity to changes in relative humidity as compared to the as-grown epitaxial graphene. This enhanced sensitivity to water is attributed to the lowering of the hydrophobicity of QFS 1LG, which results from spontaneous polarization of 4H-SiC(0001) strongly influencing the graphene. Moreover, the superior carrier mobility of the QFS 1LG system is retained even at the highest humidity. The work function maps constructed from Kelvin probe force microscopy also revealed higher sensitivity to water for 1LG compared to 2LG in both QFS 1LG and as-grown systems. These results point to a new field of applications for QFS 1LG, i.e., as humidity sensors, and the corresponding need for metrology in calibration of graphene-based sensors and devices.

Journal ArticleDOI
TL;DR: In this paper, the van der Pauw method was used to investigate the electrical contrast between the amorphous and metastable crystalline state of GeTe and SnSb2Se4, up to a 4.5:1 GeTe:SnSb 2Se4 ratio.
Abstract: Thin film samples of Ge9SnSb2Te9Se4, Ge4.5SnSb2Te4.5Se4, Ge2.5SnSb2Te2.5Se4, and GeSnSb2TeSe4 were prepared via co-sputtering of GeTe and SnSb2Se4 and compared to the well-investigated phase change material GeTe. All samples were obtained in an amorphous state. Temperature-dependent in situ X-ray diffraction experiments reveal a crystallization temperature that increases with an increasing SnSb2Se4 content, leading to a higher stability of the amorphous phase. The electrical contrast between the amorphous and metastable crystalline state investigated via the van der Pauw method is as large as 4 orders of magnitude up to a 4.5:1 GeTe:SnSb2Se4 ratio. Increasing the SnSb2Se4 content leads to a decrease in the electrical contrast. Investigations of the samples by applying Fourier transform infrared spectroscopy and variable incident angle spectroscopic ellipsometry show that the optical properties of the amorphous phase are not affected by changes in stoichiometry. In striking contrast, the impact of SnSb2Se4...

Journal ArticleDOI
TL;DR: In this article, the effects of ambient temperature on the properties of monolayer graphene using terahertz time-domain spectroscopy as well as time-resolved tera-hertz spectroscopic enabled by an optical-pump/terahertz-probe technique were studied.
Abstract: A thorough understanding of the stability of graphene under ambient environmental conditions is essential for future graphene-based applications. In this paper, we study the effects of ambient temperature on the properties of monolayer graphene using terahertz time-domain spectroscopy as well as time-resolved terahertz spectroscopy enabled by an optical-pump/terahertz-probe technique. The observations show that graphene is extremely sensitive to the ambient environmental conditions and behaves differently depending on the sample preparation technique and the initial Fermi level. The analysis of the spectroscopic data is supported by van der Pauw and Hall effect measurements of the carrier mobility and carrier density at temperatures comparable to those tested in our THz spectroscopic experiments.

Journal ArticleDOI
TL;DR: This paper derives an analytical expression to calculate correction factors that account for the combined effects of a wide range of non-ideal conditions often encountered in realistic four-point probe and van der Pauw experiments, and provides a map of the necessary correction factors.
Abstract: This paper presents an extensive collection of calculated correction factors that account for the combined effects of a wide range of non-ideal conditions often encountered in realistic four-point probe and van der Pauw experiments. In this context, “non-ideal conditions” refer to conditions that deviate from the assumptions on sample and probe characteristics made in the development of these two techniques. We examine the combined effects of contact size and sample thickness on van der Pauw measurements. In the four-point probe configuration, we examine the combined effects of varying the sample’s lateral dimensions, probe placement, and sample thickness. We derive an analytical expression to calculate correction factors that account, simultaneously, for finite sample size and asymmetric probe placement in four-point probe experiments. We provide experimental validation of the analytical solution via four-point probe measurements on a thin film rectangular sample with arbitrary probe placement. The finit...

Journal ArticleDOI
TL;DR: In this article, a conformal mapping and equivalent resistor circuit for resistive thin film devices with four contacts of arbitrary size is discussed analytically by conformal alignment and corresponding resistor circuit.
Abstract: Resistive thin film devices with four contacts of arbitrary size are discussed analytically by conformal mapping and equivalent resistor circuit. The device symmetry is assumed to be mirror symmetric to two lines, which are perpendicular. These lines go either through the contacts or midway between the contacts. This limits the degrees of freedom (DoF) to three. It is shown how to derive the sheet resistance and the other two DoF by Van-der-Pauw measurement without knowledge of the specific device geometry. It is also elucidated why conventional Van-der-Pauw method fails for devices with large contacts – an alternative procedure is proposed. The results are applicable to Van-der-Pauw devices, Hall plates, Vertical Hall effect devices, and mechanical stress sensors.

Journal ArticleDOI
TL;DR: In this paper, a new series of double perovskite oxides were synthesized by traditional solid state reaction method and characterized by X-ray diffraction, scanning electron microscope (SEM), energy dispersive x-ray (EDX), ac impedance and dc four point using Van Der Pauw method.

Journal ArticleDOI
TL;DR: In this article, a SnO/Sn composite target was used to produce a chemically stable composition of SnO x thin film while controlling structural defects by chemical reaction between tin and oxygen.

Journal ArticleDOI
TL;DR: In this paper, the authors have measured in-situ residual gas content during epitaxial graphene growth on silicon carbide (SiC) to find detrimental factors of graphene growth.
Abstract: In recent years, graphene growth optimization has been one of the key routes towards large-scale, high-quality graphene production. We have measured in-situ residual gas content during epitaxial graphene growth on silicon carbide (SiC) to find detrimental factors of epitaxial graphene growth. The growth conditions in high vacuum and purified argon are compared. The grown epitaxial graphene is studied by Raman scattering mapping and mechanical strain, charge density, number of graphene layers and graphene grain size are evaluated. Charge density and carrier mobility has been studied by Hall effect measurements in van der Pauw configuration. We have identified a major role of chemical reaction of carbon and residual water. The rate of the reaction is lowered when purified argon is used. We also show, that according to time varying gas content, it is preferable to grow graphene at higher temperatures and shorter times. Other sources of growth environment contamination are also discussed. The reaction of water and carbon is discussed to be one of the factors increasing number of defects in graphene. The importance of purified argon and its sufficient flow rate is concluded to be important for high-quality graphene growth as it reduces the rate of undesired chemical reactions and provides more stable and defined growth ambient.

Journal ArticleDOI
TL;DR: In this article, the authors report the direct measurements of conductivity and mobility in millimeter-sized single-crystalline graphene on SiO2/Si via van der Pauw geometry by using a home-designed four-probe scanning tunneling microscope (4P-STM).
Abstract: We report the direct measurements of conductivity and mobility in millimeter-sized single-crystalline graphene on SiO2/Si via van der Pauw geometry by using a home-designed four-probe scanning tunneling microscope (4P-STM). The gate-tunable conductivity and mobility are extracted from standard van der Pauw resistance measurements where the four STM probes contact the four peripheries of hexagonal graphene flakes, respectively. The high homogeneity of transport properties of the single-crystalline graphene flake is confirmed by comparing the extracted conductivities and mobilities from three setups with different geometry factors. Our studies provide a reliable solution for directly evaluating the entire electrical properties of graphene in a non-invasive way and could be extended to characterizing other two-dimensional materials.

Journal ArticleDOI
TL;DR: In this article, donor and acceptor energy levels due to the impurity Sb-, In-, Ga-, Cu-, Al-, Ag-, P-, and B-doped BaSi2 films grown by molecular beam epitaxy (MBE) were investigated.
Abstract: Identification of donor and acceptor energy levels in BaSi2 due to the suitable impurity injection of different types is very essential for the design and development of heterojunction or homojunction solar cells In this article, donor and acceptor energy levels due to the impurity Sb-, In-, Ga-, Cu-, Al-, Ag-, P-, and B-doped BaSi2 films grown by molecular beam epitaxy (MBE) were investigated It was found that impurity Sb-, Ga-, Cu-, and P-doped BaSi2 exhibited n-type conductivity, while impurity In- Al-, Ag-, and B-doped BaSi2 exhibited p-type conductivity, using the Van der Pauw method at room temperature (RT) The temperature dependence of electron or hole concentrations indicated that the acceptor energy levels in impurity B-, In-, Ag-, and Al-doped BaSi2 are 23, 86, 126, and 140 meV, respectively, and the donor energy levels in impurity Cu-, Sb-, P-, and Ga-doped BaSi2 are 35, 47, 80, and 120 meV, respectively The shallow acceptor level of 23 meV in p-type BaSi2 due to B impurity atoms and two novel donor levels of 47 and 35 meV, respectively, due to Sb and Cu impurity atoms in n-type BaSi2 were successfully identified for photovoltaic applications

Journal ArticleDOI
TL;DR: In this paper, the authors developed a simple methodology to evaluate the error produced by finite size contacts, detect the presence of contact resistance, calculate it for each contact, and determine the linear or rectifying behavior of the contact.

Journal ArticleDOI
TL;DR: In this paper, the surface morphology and stoichiometry of Sb-Te films strongly depend on Te/Sb ratio in vapor phase and were evaluated using Van der Pauw technique at 300 K.

Journal ArticleDOI
TL;DR: In this article, the van der Pauw structures on AlGaN/GaN high electron mobility transistors (HEMTs) with both SiN and AlN passivation layers and both SiC and GaN substrates were constructed to study temperature dependent electron transport properties of 2DEG in as-fabricated and proton irradiated devices.
Abstract: In this work, we fabricate Van der Pauw structures on AlGaN/GaN high electron mobility transistors (HEMTs) with both SiN and AlN passivation layers and both SiC and GaN substrates to study temperature dependent electron transport properties of 2 dimensional electron gases (2DEG) in as-fabricated and proton irradiated devices. We confirm that using a GaN substrate or AlN passivation layer enhances the mobility particularly at low temperatures, though this enhancement is greatly reduced upon irradiating the samples with high proton fluences. Our results suggest that the sheet density may be affected by Al diffusion in the sample creating electron donating impurities, which freeze out around 200 K and are more prominent in AlN passivated samples and minimized by using a GaN over a SiC substrate. Additionally, we show that a large dose of radiation forms traps in the AlGaN layer, which drop the sheet density at high proton fluences.