Range Of Doping Concentrations Research Articles

A Rapid‐Doping Method for High‐Throughput Discovery Applied to Thick‐Film PTCR Materials

A novel high‐throughput combinatorial library preparation technique for ceramics requiring low levels of dopant is demonstrated and assessed for the case of donor‐doped barium titanate (BT) materials with positive temperature coefficient of resistance (PTCR). The droplet‐doping process is performed by infiltrating liquid dopant precursors into porous BT disks and viewed using a high‐speed camera. The resulting dopant distribution in the body of the disk shows high uniformity as assessed by energy dispersive (EDS) and wavelength dispersive (WDS) spectroscopies. X‐ray diffraction (XRD) measurements and resistivity–temperature (ρ–T) curves show evidence of the changes in structure and PTCR profiles with change in composition and are closely matched to previously published data for samples made by conventional ceramic routes. The procedure, thus validated, has the potential to deliver dopant‐doped BT‐based PTCR libraries rapidly with a very wide range of dopant mixtures and concentrations for electrical property measurement and deserves to be applied to other low‐level dopant ceramic systems.

On the calculation of effective electric field in In0.53Ga0.47As surface channel metal-oxide-semiconductor field-effect-transistors

The effective electron mobility of In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistors with HfO2 gate oxide was measured over a wide range of channel doping concentration. The back bias dependence of effective electron mobility was used to correctly calculate the vertical effective electric field. The effective electron mobility at moderate to high vertical effective electric field shows universal behavior independent of substrate impurity concentration.

High-Temperature Thermoelectric Property of Layered La2-2xCa1+2xMn2O7 Manganites (0.75 ≤x ≤1.0)

La2-2xCa1+2xMn2O7 manganites with a doping concentration range of 0.75 ≤x ≤1.0 have been investigated to evaluate their thermoelectric properties in the high-temperature range from 400 to 1200 K. The materials, which are well known as n = 2 Ruddlesden–Popper compounds, have been confirmed as n-type semiconductors from the observation of the temperature dependence of the electrical conductivity and Seebeck coefficients. The electrical conductivity increases with increasing La concentration, suggesting hopping conduction. The thermal conductivity of the materials examined in this study is less than 1.0 W·m-1·K-1 at room temperature. The dimensionless figure of merit (ZT) was drastically enhanced by La doping, and had the value of 0.018 at 1173 K for La0.05Ca2.95Mn2O7. This behavior is similar that of the well-known layered structure such as the p-type misfit-layered Ca3Co4O9 where high Seebeck coefficient and low thermal conductivity.

High-Temperature Thermoelectric Property of Layered La2-2xCa1+2xMn2O7Manganites (0.75 ≤x≤1.0)

La2-2xCa1+2xMn2O7 manganites with a doping concentration range of 0.75 ≤x ≤1.0 have been investigated to evaluate their thermoelectric properties in the high-temperature range from 400 to 1200 K. The materials, which are well known as n = 2 Ruddlesden–Popper compounds, have been confirmed as n-type semiconductors from the observation of the temperature dependence of the electrical conductivity and Seebeck coefficients. The electrical conductivity increases with increasing La concentration, suggesting hopping conduction. The thermal conductivity of the materials examined in this study is less than 1.0 W·m-1·K-1 at room temperature. The dimensionless figure of merit (ZT) was drastically enhanced by La doping, and had the value of 0.018 at 1173 K for La0.05Ca2.95Mn2O7. This behavior is similar that of the well-known layered structure such as the p-type misfit-layered Ca3Co4O9 where high Seebeck coefficient and low thermal conductivity.

First-principle study on the effect of high Li–2N co-doping on the conductivity of ZnO

Based on the density functional theory (DFT), using first-principles plane-wave ultrasoft pseudopotential method, the models of the unit cell of pure ZnO and two highly Li–2N co-doped supercells of Zn 0.9375Li 0.0625O 0.875N 0.125 and Zn 0.9167Li 0.0833O 0.8333N 0.1667 were constructed, and the geometry optimization for the three models was carried out. The total density of states (TDOS) and the band structures (BS) were also calculated. The calculation results showed that in the range of high doping concentration, when the co-doping concentration is more than a certain value, the conductivity decreased with the increase of co-doping concentration of Li–2N in ZnO, which agrees with the change trend of the experimental results.

Unusual enhancement in electrical conductivity of tin oxide thin films with zinc doping

Electrical conductivity of SnO(2)-based oxides is of great importance for their application as transparent conducting oxides (TCO) and gas sensors. In this paper, for the first time, an unusual enhancement in electrical conductivity was observed for SnO(2) films upon zinc doping. Films with Zn/(Zn + Sn) reaching 0.48 were grown by pulsed spray-evaporation chemical vapor deposition. X-Ray diffraction (XRD) shows that pure and zinc-doped SnO(2) films grow in the tetragonal rutile-type structure. Within the low doping concentration range, Zn leads to a significant decrease of the crystallite size and electrical resistivity. Increasing Zn doping concentration above Zn/(Zn + Sn) = 0.12 leads to an XRD-amorphous film with electrical resistivity below 0.015 Ω cm at room temperature. Optical measurements show transparencies above 80% in the visible spectral range for all films, and doping was shown to be efficient for the band gap tuning.

Structural and spectral investigations of anthracene doped polyaniline

To couple the inherent conducting capability of polyaniline with the emissive properties of optically active organic dopant, we propose a novel polyaniline–anthracene co-polymer system. This paper presents structural and spectral investigations on anthracene doped polyaniline synthesized using emulsion polymerization technique. UV/vis absorption spectroscopy, photoluminescence (PL), fluorescence decay and FTIR spectroscopy measurements were performed to carry out the structural characterization. The absorption measurements indicate a change in the degree of oxidation of the polyaniline from 0.57 to 0.68 in the dopant concentration range 0.5–1.0wt% (w/v). PL spectroscopy results revealed a multiplet emission characteristics located at 383nm, 405nm, 428nm and 455nm. Emission at 405nm is ascribed to 0←0 of 1La transition of anthracene and the intensity of this band was found to be dependent on dopant concentration. The emission at 383nm quenched in doped compounds. The fluorescence decay lifetime of polyaniline increased with increasing dopant concentration. FTIR transmittance peaks observed at 1293.5cm−1 and 1238.6cm−1 due to the π electron delocalization and protonation of the polymer respectively, suggest that anthracene doping may be protonating the polymer. The change in degree of oxidation and probable protonation of polyaniline as a result of anthracene doping coupled with observed PL characteristics suggest a structural modification of polyaniline because of anthracene doping. The structural tunability of polyaniline combined with promising emissive property of anthracene makes the anthracene:polyaniline binary system a viable alternative for optoelectronic and sensing applications.

Magnetism of mixed quaternary Heusler alloys:(Ni,T)2MnSn(T=Cu,Pd)as a case study

The electronic properties, exchange interactions, finite-temperature magnetism, and transport properties of random quaternary Heusler Ni$_{2}$MnSn alloys doped with Cu- and Pd-atoms are studied theoretically by means of {\it ab initio} calculations over the entire range of dopant concentrations. While the magnetic moments are only weakly dependent on the alloy composition, the Curie temperatures exhibit strongly non-linear behavior with respect to Cu-doping in contrast with an almost linear concentration dependence in the case of Pd-doping. The present parameter-free theory agrees qualitatively and also reasonably well quantitatively with the available experimental results. An analysis of exchange interactions is provided for a deeper understanding of the problem. The dopant atoms perturb electronic structure close to the Fermi energy only weakly and the residual resistivity thus obeys a simple Nordheim rule. The dominating contribution to the temperature-dependent resistivity is due to thermodynamical fluctuations originating from the spin-disorder, which, according to our calculations, can be described successfully via the disordered local moments model. Results based on this model agree fairly well with the measured values of spin-disorder induced resistivity.

Site-Selective Lanthanide Doping in a Nonanuclear Yttrium(III) Cluster Revealed by Crystal Structures and Luminescence Spectra

A series of lanthanide-doped nonanuclear yttrium(III) clusters with general formulas (Y(9-x)Ln(x))(acac)(16)(μ(3)-OH)(8)(μ(4)-O)(μ(4)-OH) (Ln = Pr, Eu, Tb, Dy, and Yb) were synthesized. Characterization by single-crystal X-ray diffraction allowed for analysis of relative populations of yttrium (Z = 39) and dopant trivalent lanthanide (Z = 59-70) at every crystallographic metal position. Nonuniform distribution of ions along the three different sites seems to be correlated to the site volume and the ratio of ionic radii. In support, luminescence spectra of europium(III)-doped nonanuclear clusters were measured over a wide range of dopant concentrations. Emission intensities of peaks characteristic of specific sites correlate well with the site population determined through X-ray diffraction.

Optimization of doping concentration in Er:tellurite glass based on heat analysis

The comprehensive analysis about heat-generating processes is presented in Er:tellutire glass. The heat fraction of each process and total heat fraction during pumping are investigated. The results show that upconversion is an important heat-generation process and heat problem is serious especially at high Er 3+ doping level. The influence of pump power on heat fraction is also discussed. Based on the heat analysis, the optimized doping concentration range of Erbium ions is about 0.5 mol% to 1.0 mol%.

Properties of Ge-doped, high-quality bulk GaN crystals fabricated by hydride vapor phase epitaxy

We investigated the properties of Ge-doped, high-quality bulk GaN crystals with Ge concentrations up to 2.4×10 19 cm −3. The Ge-doped crystals were fabricated by hydride vapor phase epitaxy with GeCl 4 as the dopant source. Cathodoluminescence imaging revealed no increase in the dislocation density at even the highest Ge concentration, with values as low as 3.4×10 6 cm −2. The carrier concentration, as determined by Hall measurement, was almost identical to the combined concentration of Ge and unintentionally incorporated Si. The electron mobilities were 260 and 146 cm 2 V −1 s −1 for n=3.3×10 18 and 3.35×10 19 cm −3, respectively; these values are markedly larger than those reported in the past for Ge-doped GaN thin films. The optical absorption coefficient was quite small below the band gap energy; it slightly increased with increase in Ge concentration. Thermal conductivity, estimated by the laser-flash method, was virtually independent of Ge concentration, maintaining an excellent value around 2.0 W cm −1 K −1. Thermal expansion coefficients along the a- and m-axes were approximately constant at 5.0×10 −6 K −1 in the measured doping concentration range.

Room-temperature ferromagnetism of diamagnetically-doped ZnO aligned nanorods fabricated by vapor reaction

Large-scale monocrystalline oxide-diluted magnetic semiconductor (ODMS) Zn1−xBixO nanorods arrays (NAs) were prepared within a large doping concentration range from 5% to 20% by a simple chemical vapor deposition. X-ray diffraction and high-resolution transmission electron microscopy reveal the monotonous expansion of the lattice constants with increasing Bi content, due to the effective Bi doping. In particular, room-temperature ferromagnetic (RTFM) behavior with Curie temperature over 363.7 K has been observed based on Bi-doped ZnO nanoarrays, whereas undoped ZnO NAs disappear. The RTFM origin is suggested, in which vacancies can be controlled to tune the FM. The as-formed RTFM NAs would have potential applications in many areas of advanced nanotechnology, such as new spintronic devices and magneto-optic components.

Synthesis and spectral analysis of Yb3+/Tm3+/Ho3+-doped Na0.5Gd0.5WO4 phosphor to achieve white upconversion luminescence

Yb 3+ /Tm 3+ /Ho 3+ -doped Na 0.5 Gd 0.5 WO 4 phosphors were synthesized by the high-temperature solid-state method. Bright white luminescence upon 980 nm near-infrared excitation can be observed for the sample at the optimum chemical composition of Na 0.5 Gd 0.5 WO 4 :10%Yb 3+ /1%Tm 3+ /0.4%Ho 3+ , which is produced via an upconversion (UC) process by tuning the dopant ions concentration. The measured white light consists of the blue, green, and red UC emissions which correspond to the transitions 1 G 4 → 3 H 6 of Tm 3+ , 5 F 4 ( 5 S 2 ) → 5 I 8 , and 5 F 5 → 5 I 8 of Ho 3+ ions, respectively. The calculated color coordinates display that white light can be achieved in a wide range of dopant concentrations. The UC mechanisms were also proposed based on their spectral and pumping power dependence analyses.

Charge-based model for symmetric double-gate MOSFETs with inclusion of channel doping effect

This paper presents a unified charge-based model for symmetric double-gate (DG) MOSFETs with a wide range of channel doping concentrations. From one dimensional (1D) Poisson–Boltzmann equation in the DG MOSFET structure, an accurate inversion charge model is proposed, which predicts the inversion charge density precisely from weak inversion, through moderate inversion and finally to strong inversion region for both heavily doped and lightly doped condition. Based on that, the unified drain current model is developed from Pao-Sah’s dual integral. The unified terminal charge and trans-capacitance models are derived out from Ward and Dutton’s linear-charge-partition scheme. Extensive numerical simulations are performed on DG MOSFETs to verify the unified charge-based models and good agreements between them are obtained, proving the validity of the proposed model for further circuit simulation.

A continuous current model of fully-depleted symmetric double-gate MOSFETs considering a wide range of body doping concentrations

A continuous current model of fully-depleted symmetric double-gate (DG) MOSFETs which can reflect a wide range (from intrinsic to heavy doping) of the body doping concentrations was developed based on an approximated analytic potential solution of Poisson's equation. The model was compared with the results of device simulation, and showed very good agreement in all operation regions such as subthreshold, turn-on, linear and saturation.

Integrated experimental and modeling study of ionic conductivity of scandia-stabilized zirconia thin films

Scandia-stabilized zirconia films were epitaxially grown on sapphire (0001) substrates by oxygen-plasma-assisted molecular beam epitaxy. The cubic phase was found to exist over a wider dopant concentration range than previously observed (4.6–17.6 mol.% Sc 2O 3). The monoclinic phase was observed for dopant concentrations of 1.5 mol.% and 22.5 mol.%. An increase in the fraction of the monoclinic phase relative to the cubic phase decreased the ionic conductivity. The highest conductivity in the temperature range of 460–900 °C was observed for 9.9 mol.% Sc 2O 3. Atomistic computer simulations show that the observed composition dependence can be related to changes in migration barriers for O 2− ion transport with Sc 3+ substitution of Zr 4+ ions.

New examination of the magnetic properties of cobalt-doped ZnO diluted magnetic semiconductors

Polycrystalline Zn1−xCoxO diluted magnetic semiconductors were prepared within a large doping concentration range from 0.5% to 10%. Thanks to a model based on the co-existence of two magnetic populations, our analysis of the magnetization measurements brings new evidence about the competition between ferromagnetic and antiferromagnetic mean field within the ZnO diamagnetic matrix. It is a temperature activated phenomenon that supports the alignment of individual Co2+ ions into superparamagnetic clusters. At the same time, the refined effective number of antiferromagnetically coupled Co2+ ions is equal to the probability of Co2+ ions belonging to a dimer.

Optimization of minute doping of Y1−xRExBa2Cu3O7−δ thin films with RE = Tb and Nd

AbstractDoping of YBa2Cu3O7−δ (YBCO) has become an effective means of increasing the flux pinning and critical current densities (Jc) in thin film superconductors, while maintaining the transition temperature (Tc). In previous research efforts, our group showed that doping (Y1−xREx)BCO with typically deleterious rare earth (RE) elements can be used to improve the fil's current density via flux pinning when the x molar additions are less than 1%. However, data was only presented for different orders of magnitude (x = 0.1%, 1.0%, 10%) without consideration of optimization. The research presented here demonstrates that the deleterious RE elements can differ greatly in how broad the range of optimal doping concentration is, in addition to the relative doping concentration. Rare-earth elements Nd and Tb were compared due to the difference in degradation mechanisms: Nd additions results in Ba site substitution and Tb123 exhibits poor phase formation. Thin films of Nd and Tb doped YBCO films were grown by pulsed laser deposition (PLD) using standard deposition parameters for plain YBCO. The compositions studied were (Y1−xREx)BCO where x was varied from 0.0001 to 0.025 for Nd and 0.005 to 0.015 for Tb. Targets for PLD were prepared using solid state reaction and sintering procedures. All films were characterized for Jc and Tc by vibrating sample magnetometry. Data for Jc(H,T) and Tc were compared to undoped YBCO films processed under the same conditions. The results show a measurable increase in flux pinning for both different concentrations and range of Nd and Tb doping, with little decrease in Tc.

Electrical and Optical Properties of :H Thin Films Prepared by Thermal Evaporation Method

Thin a-:H films were grown successfully by fabrication of designated ingot followed by evaporation onto glass slides. A range of growth conditions, Ge contents, dopant concentration (Al and As), and substrate temperature, were employed. Stoichiometry of the thin films composition was confirmed using standard surface techniques. The structure of all films was amorphous. Film composition and deposition parameters were investigated for their bearing on film electrical and optical properties. More than one transport mechanism is indicated. It was observed that increasing substrate temperature, Ge contents, and dopant concentration lead to a decrease in the optical energy gap of those films. The role of the deposition conditions on values of the optical constants was determined. Accordingly, models of the density of states for the :H thin films as pure, doped with 3.5% of Al (p-type) and that doped with 3.5% As (n-type), were proposed.

Conductivity and Thermal-Stability of 5-Sulfosalicylic Acid Sodium Doped Polypyrrole

By varying the dopant-to-pyrrole ratio in a wide range from 0 to 60% a series of 5-sulfosalicylic acid sodium doped polypyrrole was synthesized in situ in aqueous solution with ferric chloride as the oxidant. The resulting polypyrroles were characterized with the four-probe, laser light scattering and thermo-gravimetry analysis, differential thermal analysis, respectively. Our results indicate that the particle size plays a determinative role to tune the conductivity in the studied range of dopant concentration; and this series of polypyrrole with size-tuned-conductivity exhibits little less thermal-stability although its size and conductivity changes simultaneously and acutely with the dopant concentration. The association of the conductivity with particle size was interpreted in terms of a theoretical model proposed by Baughman and Shacklelette.