Hall Effect Studies Research Articles

Enhancement in optoelectronic nature of facile spray fabricated Ce co-doped CdO:Zn films for TCO applications

Cerium co-doped CdO:Zn (Ce@CdO:Zn) transparent conducting oxide films were deposited onto glass by a cost-effective nebulizer spray procedure. X-ray diffraction (XRD) investigation on films shows that formation of cubic structure with (111) and (200) orientations for CdO:Zn and Ce@CdO:Zn films, respectively. Surface topography study discovered the foundation of compact grains for 1.5 wt.% Ce-doped film. EDX spectrum possesses the Cd, Zn, and Ce in Ce doped CdO:Zn film. Ce doped films exhibited maximum transparency and highest bandgap (Eg) value in comparison with pristine CdO:Zn film and the Eg values are noticed between 2.64–2.87 eV. Hall-Effect study evinced that Ce doping enhanced the contents of the carrier and lessen the electrical resistivity. The ρ values cut from 9.84 × 10–3 Ω cm to 6.40 × 10−4 Ω cm when Ce % rise from 0–1.5 wt.%. The obtained carrier concentration value of CdO:Zn is 4.02 × 1019 cm−3 and enlarged to 8.72 × 1020 cm−3 for 1.5 wt.% Ce co-doped film. The Figure of merit amplified from 1.1–9.4 × 10−4 Ω−1 on growing the Ce content to 1.5 wt.% from 0.

Opto-electronic properties of solution-processed zinc oxide thin films: role of solvents and doping

Undoped zinc oxide (ZnO) and nitrogen-doped zinc oxide (NZO) thin films were prepared on transparent conducting oxide-coated glass substrates by employing sol–gel technique. The effect of different solvents and nitrogen doping on the optical, structural, and electrical properties was investigated by UV–visible absorption spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD), profilometry, and Hall effect studies. ZnO films yielded transmittance above 85% and the bandgap of ZnO thin films decreased with doping. XRD pattern confirmed hexagonal wurtzite structure of ZnO. NZO thin films were found to be in the nano-thin film phase with thickness of 40 nm. Hall effect studies yielded carrier concentration of 1.2 × 1015 cm−3 and 2.03 × 1014 cm−3, respectively, for undoped and doped ZnO thin films. The changes in vibrational modes of ZnO due to nitrogen doping were detected using Fourier transform infrared (FTIR) analysis. It was found that p-type doping, leading to an improved surface morphology, led to a reduction in optical bandgap and an increased charge carrier mobility. The choice of the solvent was found to have a profound influence on the surface morphology, optical bandgap, tail states distribution, and charge carrier mobility.

Coercivity Enhancement and the Analysis of Asymmetric Loops in a Perpendicularly Magnetized Thin Film

The enhancement of coercive field values depending on the measurement angle in a perpendicularly magnetized continuous thin film and the asymmetries in its hysteresis loops are analyzed and discussed by means of Hall effect measurements. Anomalous Hall effect and planar Hall effect contributions to the Hall results are separated to make the asymmetric loops symmetrical. The magnetic properties of the sample are also measured by using a vibrating sample magnetometer and magneto-optic Kerr effect methods. The data obtained by the measurement systems are compared, and the differences in their results are discussed. The results of the work highlight the importance of choosing the correct setup for the measurements and the importance of the measurement angle for the Hall effect studies in magnetic thin films.

Systematic study of shockley-read-hall and radiative recombination in GaN on Al2O3, freestanding GaN, and GaN on Si

Here we study and correlate structural, electrical, and optical properties of three GaN samples: GaN grown by metalorganic chemical vapor deposition on sapphire (GaN/Al2O3), freestanding GaN crystals grown by the high nitrogen pressure solution method (HNPS GaN), and GaN grown by hydride vapor phase epitaxy on silicon (GaN/Si). Defect and impurity densities and carrier concentrations are quantified by x-ray diffraction, secondary mass ion spectroscopy, and Hall effect studies, respectively. Power-dependent photoluminescence measurements reveal GaN near-band-edge emissions from all samples having mixtures of free exciton and band-to-band transitions. Only the defect luminescence in the GaN/Si sample remains unsaturated, in contrast to those from the HNPS GaN and GaN/Al2O3 samples. Carrier lifetimes, extracted from time-resolved photoluminescence measurements, and internal quantum efficiencies, extracted from temperature-dependent photoluminescence measurements, are used to extract radiative and nonradiative lifetimes. Shockley–Read–Hall (A) and radiative recombination coefficients (B) are then calculated accordingly. Overall, the A coefficient is observed to be highly sensitive to the point defect density rather than dislocation density, as evidenced by three orders of magnitude reduction in threading dislocation density reducing the A coefficient by one order of magnitude only. The B coefficient, while comparable in the higher quality and lowly doped GaN/Al2O3 and HNPS GaN samples, was severely degraded in the GaN/Si sample due to high threading dislocation density and doping concentration.

Hall-effect studies of modification of HgCdTe surface properties with ion implantation and thermal annealing

Results of the Hall-effect studies of surface properties of n–type HgCdTe films modified with arsenic ion implantation and thermal annealing are reported on. A complete annihilation of implantation-induced extended defects (dislocation loops), quasi-point defects and related donor centers was observed as a result of a two-stage arsenic activation annealing. A high degree of activation of implanted arsenic was achieved with the annealing. In some cases, the annealing was found to lead to the modification of the properties of the ‘base’ layers not affected by implantation due to activation of uncontrolled acceptor defects and resulting changes in the degree of electrical compensation.

Synthesis, characterization and Hall-effect studies of highly conductive polyaniline/graphene nanocomposites

The objective of this research is to prepare a series of conducting polyaniline/graphene composites by in situ chemical oxidative method through polymerization of aniline in the existence of graphene of various weight percentages. The prepared composites were examined through Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy respectively. The conductivity and dielectric attributes exhibited composition dependent percolation behavior with enhanced properties for 15 wt% of graphene in polyaniline matrix. The Hall-effect studies were performed in the prepared composites and the investigations confirm that the composites behave as n-type semi-conductors. From the data obtained one can envisage remarkable improvement in the charge transport and dielectric properties of the composite at the percolation threshold due to the presence of nano-size additive in the composite. The temperature dependent conductivity in doped composites was increased by five fold in compare to pure PANI. The doping of graphene in PANI matrix, the improved dielectric parameters were achieved. The Hall effect studies were carried out in the prepared composites, the results shows that composites behaves like a n-type semiconductor. Further, the mechanical properties such as tensile stress and tensile strain were carried out in the prepared composites.

Effect of Ni doping on structure, morphology and opto-transport properties of spray pyrolised ZnO nano-fiber

Nano-fiber structure of ZnO and Ni doped ZnO (Ni:ZnO) transparent thin films have been deposited on glass substrate at 350 °C at an ambient atmosphere via spray pyrolysis technique. The structural, surface morphological and opto-electrical properties of ZnO and Ni doped ZnO thin films have been investigated. The XRD patterns show that the films are of polycrystalline in nature having preferential orientation (0 0 2) plane for ZnO changes to (1 0 1) by Ni doping in ZnO matrix. Optical study exhibits red shifting in band gap energy with Ni doping due to sp-d hybridization and display high absorption coefficient of the order of 107 m−1. The photoluminescence (PL) spectra indicate blue emissions in all samples. Electrical measurement confirms the resistivity of the film decreases remarkably with Ni doping and electrical transport is mainly thermally activated. From Hall Effect study, it is confirmed that all the samples are n-type having carrier concentration of the order of 1018 cm−3. Both mobility and carrier concentrations of the films became higher than ZnO sample with the increase of Ni concentration.

Comparative studies of CdS thin films by chemical bath deposition techniques as a buffer layer for solar cell applications

Cadmium sulfide (CdS) buffer layer that decouples the absorber layer and window layer in thin-film solar cells was synthesized by two different chemical bath deposition (CBD) techniques with varying deposition parameters. X-ray diffraction (XRD) revealed that the CdS thin film crystallizes in a stable hexagonal wurtzite structure having a preferential orientation along (002) reflection plane with a crystallite size varying from 20 to 40 nm. First longitudinal optical phonon mode was identified at Raman shift of 305 cm−1. Uniform, granular, continuous, and smooth surface with an average grain sizes (< 100 nm) as well as small roughness (< 9 nm) was observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The symmetric composition of cadmium and sulfur along with larger grains (20 nm) was observed at higher deposition temperatures and times. The optical band gap of CdS samples obtained from process one was in the range of 2.3–2.35 eV, while the band gap by the second CBD process lay in between 2.49 and 2.65 eV, showing the most stable compound of CdS. The presence of a green emission band in photoluminescence spectra (PL) demonstrated that the CdS material has better crystallinity with minimum defect density. Hall effect studies revealed the n-type conductivity of CdS thin films with a carrier concentration values in the order of 1016 cm−3. Furthermore, CdS thin films fabricated by CBD process exposed better quality that might be more suitable material as a buffer layer for thin-film solar cells.

A Large Anisotropic Enhancement of the Charge Carrier Mobility of Flexible Organic Transistors with Strain: A Hall Effect and Raman Study.

Utilizing the intrinsic mobility–strain relationship in semiconductors is critical for enabling strain engineering applications in high‐performance flexible electronics. Here, measurements of Hall effect and Raman spectra of an organic semiconductor as a function of uniaxial mechanical strain are reported. This study reveals a very strong, anisotropic, and reversible modulation of the intrinsic (trap‐free) charge carrier mobility of single‐crystal rubrene transistors with strain, showing that the effective mobility of organic circuits can be enhanced by up to 100% with only 1% of compressive strain. Consistently, Raman spectroscopy reveals a systematic shift of the low‐frequency Raman modes of rubrene to higher (lower) frequencies with compressive (tensile) strain, which is indicative of a reduction (enhancement) of thermal molecular disorder in the crystal with strain. This study lays the foundation of the strain engineering in organic electronics and advances the knowledge of the relationship between the carrier mobility, low‐frequency vibrational modes, strain, and molecular disorder in organic semiconductors.

Enhancement in photovoltaic properties of Nd:SnS films prepared by low-cost NSP method

The inner transition metal (ITM) neodymium (Nd)-doped tin sulfide (Nd:SnS) thin films with various Nd concentrations were coated by nebulizer spray pyrolysis (NSP) technique at 350 °C. All the coated films were analyzed for their structural, optical and photoelectrical properties. X-ray diffractometer (XRD) study showed (111) direction as the highly preferred orientation with orthorhombic crystal structure for all the films. The intensity of the peaks was found to increase until 5 at% Nd doping and then reduced for higher (7 at% Nd) doping concentration. Atomic force microscopic (AFM) images of the films proclaimed an increase in the surface and line roughness of the films by increasing Nd concentrations. Optical analysis on the films showed a variation in energy gap from 2.05 to 1.69 eV when the doping concentration increased from 0 at% to 7 at%. At 5 at% Nd doping, the photoluminescence (PL) spectra displayed a single strong emission peak at 723.1 nm with enhanced intensity corresponding to near-band-edge emission. All the SnS thin films exhibited p-type behavior with the lowest resistivity of ~ 4.311 Ω·cm and high carrier concentrations of ~ 1.441 × 1017 cm−3 for 5 at% Nd doping level as observed from Hall effect studies. Furthermore, fluorine-doped tin oxide (FTO)/n-CdS/p-Nd:SnS hetero-junction solar cells were prepared and the current–voltage curve in dark and light condition was obtained for the device. An efficiency of 0.135% was observed for the solar cell fabricated with 5 at% Nd-doped SnS thin film.

Investigation on nebulizer spray coated Nd-doped SnS2 thin films for solar cell window layer application

Economic nebulizer spray pyrolysis (NSP) technique has been employed to deposit Neodymium (Nd) doped Tin disulfide (SnS2) thin films at 325 °C by varying the doping concentration of Nd (0%, 2%, 4% and 6%). The impact of Nd concentration on crystalline structure, morphology and opto-electronic properties of films were studied using X-ray diffraction (XRD), FT-Raman spectrophotometer, atomic force microscope (AFM), energy-dispersive X-ray spectroscope, scanning electron microscope (SEM), UV–Visible spectrometer and Hall Effect measurements. Structural parameters such as lattice constants, texture orientation factor, micro strain, dislocation density and crystallite size were estimated using XRD data. The SEM and AFM images of films displayed an exceptional morphology. The surface roughness of the films was found to increase with the increase of dopant concentration. Optical analysis done on the films revealed variation in band gap from 2.75 to 2.92 eV as the Nd doping concentration is increased from 2 to 6%. SnS2 thin film exhibited n-type conductivity as, confirmed from Hall Effect studies. The resistivity and concentration of the carrier in the film were found to be 4.17 × 10−2 Ω cm and 4.06 × 1017 cm−3 respectively which were then correlated to the deposition parameters. Furthermore, FTO/n-Nd-SnS2/p-SnS hetero-junction based solar cells were prepared and their current voltage curve in dark condition was obtained.

Boron 10B—11B Isotope Substitution as a Probe of the Mechanism Responsible for the Record Thermionic Emission in LaB6 with the Jahn—Teller Instability1

We have tested the conduction band electrons of lanthanum hexaboride that is among the most effective electron-beam sources with one of the highest brightness of thermionic emission. We performed infrared spectroscopic, DC (direct current) resistivity and Hall-effect studies of LaB6 single crystals with various 10B and 11B isotope contents. We find that only a small amount of conduction electrons behave as Drude-type charge carriers while about 70% of the electrons are involved in collective oscillations of electron density coupled to vibrations of both the Jahn-Teller unstable rigid boron cage and rattling modes of La-ions loosely bound to the lattice. We suggest that exactly these non-equilibrium conduction electrons determine the extraordinary low work function of thermoemission in LaB6.

Regaining a Spatial Dimension: Mechanically Transferrable Two-Dimensional InAs Nanofins Grown by Selective Area Epitaxy.

We report a method for growing rectangular InAs nanofins with deterministic length, width, and height by dielectric-templated selective-area epitaxy. These freestanding nanofins can be transferred to lay flat on a separate substrate for device fabrication. A key goal was to regain a spatial dimension for device design compared to nanowires, while retaining the benefits of bottom-up epitaxial growth. The transferred nanofins were made into devices featuring multiple contacts for Hall effect and four-terminal resistance studies, as well as a global back-gate and nanoscale local top-gates for density control. Hall studies give a 3D electron density 2.5-5 × 1017 cm-3, corresponding to an approximate surface accumulation layer density 3-6 × 1012 cm-2 that agrees well with previous studies of InAs nanowires. We obtain Hall mobilities as high as 1200 cm2/(V s), field-effect mobilities as high as 4400 cm2/(V s), and clear quantum interference structure at temperatures as high as 20 K. Our devices show excellent prospects for fabrication into more complicated devices featuring multiple ohmic contacts, local gates, and possibly other functional elements, for example, patterned superconductor contacts, that may make them attractive options for future quantum information applications.

Electronic, thermal and magneto-transport properties of the half-Heusler, DyPdBi

The electronic, thermal, and magneto-transport properties of the ternary half-Heusler, DyPdBi, crystallizing in a non-centrosymmetric face-centered cubic structure have been investigated. DyPdBi is known to exhibit antiferromagnetic (AFM) ordering and field-induced spin-flip transitions below the Néel temperature (TN = 4.0 K). Our heat capacity measurements revealed a λ-type anomaly near 4 K and a broad peak centering at ∼50 K corresponding to the AFM transition and the Schottky effect, respectively. Both the electrical resistivity (ρ) and thermal conductivity (κ) data showed anomalies at the onset temperature of antiferromagnetic ordering suggesting the presence of spin-charge-phonon coupling. The temperature-dependent magnetoresistance (MR) behaviour revealed a sign crossover from negative to positive at ∼20 K while the maximum positive MR of 20% was obtained at TN. The most interesting finding is the unusual field dependence of MR below TN with an enhancement of positive MR following the field-induced magnetic transition attributable to the interphase boundary scatterings. Hall effect studies show holes are the dominant charge carriers with the density of signifying the semimetallic nature of DyPdBi. Below TN, Hall resistivity is found to have additional contribution due to the anomalous Hall effect. The analyses of temperature-dependent Seebeck coefficient (S) and thermal conductivity behaviour suggest the presence of additional scattering mechanisms such as scattering between conduction electrons and narrow 4f derived Lorentzian shaped quasi-particle bands.

Electrical and optical properties of a PtSn4 single crystal

A topological semimetal PtSn4 single crystal was grown by method of crystallization from a solution in a melt. Then the electrical resistivity and galvanomagnetic properties (magnetoresistivity and the Hall effect) were studied in the temperature range from 4.2 to 80 K and in magnetic fields up to 100 kOe. The optical measurements were carried out at room temperature. The residual resistivity is shown to be low enough and amount to ∼ 0.5 μOhm·cm. The temperature dependence of the electrical resistivity has a metallic type, increasing monotonically with temperature. A sufficiently large magnetoresistance of 750% is observed. The majority carriers are supposed to be holes with a concentration of ∼ 6.8·1021 cm−3 and mobility of ∼ 1950 cm2/Vs at T = 4.2 K as a result of the Hall effect studies. The optical properties of PtSn4 have features characteristic of “bad” metals.

Hall effect study of the κ -(ET) 2X family: Evidence for Mott-Anderson localization

Mott-Anderson localization is a very important but poorly explored phenomenon within condensed matter physics. Here, the authors present a Hall effect study of the $\ensuremath{\kappa}$-(ET)2$X$ family, where $X$ = Cu${}_{2}$(CN)${}_{3}$, Ag${}_{2}$(CN)${}_{3}$ and B(CN)${}_{4}$, which is ideal for studying the Mott-Anderson localization because correlations and disorder strengths vary with $X$. The results enable the determination of the proximity of the selected materials to the metal-insulator transition; in that way, one can locate them in the Mott-Anderson phase diagram.

Characteristics of TiO2 Compact Layer prepared for DSSC application

Dye-sensitized solar cells (DSSCs) offer an economically reliable and suitable alternative in moderating the challenges presented by the existing convectional photovoltaic cells. However, the efficiency of dye-sensitized solar cells has remained relatively low. For this reason, this research was aimed at studying the characteristics of TiO 2 compact layer that can be applied in DSSCs as a way of improving efficiency. To achieve this, TiO 2 compact layer was deposited on a conductive glass substrate by using Holmarc’s Spray Pyrolysis system, using Ultrasonic Spray Head and spraying in the vertical geometry. X-ray Diffraction studies revealed that TiO 2 compact layer was of anatase phase and had tetragonal crystalline structure. Raman spectroscopy showed that the most intense peak appeared at 142 cm -1 due to the external vibration of the anatase structure. Hall Effect studies revealed that TiO 2 compact layer has a high density of charge carriers’ value of 1.25 × 1019 cm -3 hence it can be used in DSSC applications.

Asymmetry and Parity Violation in Magnetoresistance of Magnetic Diluted Dirac–Weyl Semimetal (Cd0.6Zn0.36Mn0.04)3As2

Orientation dependences of magnetoresistance, ρ, of single crystal (Cd0.6Zn0.36Mn0.04)3As2 having tetragonal P42/nmc symmetry have been studied. Three orientations between electrical current, , flowing along crystal (100) plane and magnetic field, , have been used as follows: 1) is perpendicular to both and (100) plane; 2) is perpendicular to but parallel to (100) plane; 3) is parallel to both and (100) plane. Asymmetry in curves ρ is observed for all orientations. For orientation (2), crossover from negative to positive magnetoresistance is found as magnetic field changes its direction from one position corresponding to negative to opposite direction corresponding to positive . So magnetoresistance parity typical for numerous solids is violated for this orientation. The Shubnikov–de Haas (SdH) oscillations are observed for all orientations above ≈1.8 T and below ≈40 K. The effective mass of electrons extracted from SdH oscillations analysis is found to be orientation dependent. Smeared kinks correlated with the SdH oscillations are also observed in the Hall effect study for orientation (1). Magnetoresistance peculiarities can be related to specific properties of the Dirac semimetals and their evolution under magnetic field.

One-Dimensional-Like Titania/4'-Pentyl-4-Biphenylcarbonitrile Composite Synthesized Under Magnetic Field and its Structure-Photocatalytic Activity Relationship.

The demonstration of the structure–properties relationship of shape-dependent photocatalysts remains a challenge today. Herein, one-dimensional (1-D)-like titania (TiO2), as a model photocatalyst, has been synthesized under a strong magnetic field in the presence of a magnetically responsive liquid crystal as the structure-aligning agent to demonstrate the relationship between a well-aligned structure and its photocatalytic properties. The importance of the 1-D-like TiO2 and its relationship with the electronic structures that affect the electron–hole recombination and the photocatalytic activity need to be clarified. The synthesis of 1-D-like TiO2 with liquid crystal as the structure-aligning agent was carried out using the sol–gel method under a magnetic field (0.3 T). The mixture of liquid crystal, 4′-pentyl-4-biphenylcarbonitrile (5CB), tetra-n-butyl orthotitanate (TBOT), 2-propanol, and water, was subjected to slow hydrolysis under a magnetic field. The TiO2–5CB took a well-aligned whiskerlike shape when the reaction mixture was placed under the magnetic field, while irregularly shaped TiO2–5CB particles were formed when no magnetic field was applied. It shows that the strong interaction between 5CB and TBOT during the hydrolysis process under a magnetic field controls the shape of titania. The intensity of the emission peaks in the photoluminescence spectrum of 1-D-like TiO2–5CB was lowered compared with the TiO2–5CB synthesized without the magnetic field, suggesting the occurrence of electron transfer from 5CB to the 1-D-like TiO2–5CB during ultraviolet irradiation. Apart from that, direct current electrical conductivity and Hall effect studies showed that the 1-D-like TiO2 composite enhanced electron mobility. Thus, the recombination of electrons and holes was delayed due to the increase in electron mobility; hence, the photocatalytic activity of the 1-D-like TiO2 composite in the oxidation of styrene in the presence of aqueous hydrogen peroxide under UV irradiation was enhanced. This suggests that the 1-D-like shape of TiO2 composite plays an important role in its photocatalytic activity.

Effect of thermal annealing on nebulizer spray deposited tin sulfide thin films and their application in a transparent oxide/CdS/SnS heterostructure

Tin sulfide (SnS) thin film was deposited on glass substrates using simple nebulizer spray pyrolysis method. The influence of vacuum annealing on structural, optical, morphological, electrical and photovoltaic properties of the films were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, atomic force microscopy, energy dispersive analysis of X- ray, UV-Visible spectrophotometry, photoluminescence spectrofluorometry and Hall measurements. Structural parameters such as lattice structure, crystallite size, micro strain and dislocation density were estimated using XRD analysis. There was a notable enhancement in morphology and surface roughness of the films and they were found to vary with respect to the annealing temperature. Optical studies done on the films revealed a decrease in energy gap for the increase of annealing temperatures. From the Hall effect study, it was found that SnS thin films have p-type conductivity. The lowest resistivity and higher carrier concentration were found to be 0.074 Ω cm and 1.07 × 1019 (cm−3) respectively. A heterojunction solar cell, CdS/SnS was fabricated and its solar conversion efficiency obtained was about 0.73% for tin sulfide films annealed at 400 °C.