Range Of Doping Concentrations Research Articles

Weak Crystal Field in Yttrium Gallium Garnet (YGG) Submicrocrystals Doped with Cr3+

Yttrium gallium garnet (YGG) submicrocrystals having 80 nm average diameters doped with Cr3+ (0.1–40%) were synthesized by the citrate method. Pure cubic garnets were obtained in wide range (0.1–15%) of dopant concentration. Chromium ions replace Ga3+ at the octahedral sites and experience an intermediate or weak crystal field, depending only on Cr3+ concentration. The weak crystal field is observed when the dopant concentration exceeds 3%. The origin of such behavior is discussed.

Very low surface recombination velocity of boron doped emitter passivated with plasma-enhanced chemical-vapor-deposited AlOx layers

In this work, we present a systematic study of the surface recombination velocity of boron-diffused Si wafer passivated with plasma-enhanced chemical-vapor-deposited (PECVD) AlOx layers. Saturation current densities in the range of 5.2–38fAcm−2 (at 300K) were achieved on planar surfaces. In particular, we present an industrially relevant boron emitter, allowing for about 700mV open circuit voltage on textured surfaces, after a firing process. This high passivation quality could be achieved using AlOx passivation layers deposited by PECVD. The passivation quality is found to be equivalent to AlOx layers deposited by plasma-assisted atomic-layer-deposition. A wide range of surface doping concentration (2.5–70×1018cm−3) was investigated. The emitters used here allow a high resolution in the determination of the surface recombination velocity upper limit. Our simulations, based on Fermi-Dirac statistics, indicate that only very shallow emitters can be used to further increase the resolution on the determination of the surface recombination velocity.

Thermal quenching and luminescence lifetime of saturated green Sr1−xEuxGa2S4 phosphors

Due to the lack of efficient green emitting solid state light sources, conversion phosphors emitting saturated green emission are highly interesting, both for display and signalling applications. In this work, we study the luminescence properties of Sr1−xEuxGa2S4 phosphors over a wide dopant concentration range (x=0.01–0.3), as function of temperature. The phosphors show a saturated green emission over the entire studied range, with a typical peak wavelength around 536nm and a FWHM of 50nm. The internal quantum efficiency is 71% for x=0.04. For this concentration, the emission intensity at 400K is still 90% of the intensity at room temperature. By measuring both decay and thermal quenching profiles as a function of europium concentration, we were able to explain the emission properties on the basis of the local environment of the europium ions in the lattice.

Magnetism and electronic transport in (Ni, Cu)2 MnSn Heusler alloys under ambient and elevated pressures

The electronic properties, exchange interactions, Curie temperatures and transport properties of random quaternary Heusler alloys (Ni, Cu)2MnSn are studied by means of density-functional calculations over the entire range of dopant concentration. Results agree qualitatively as well as quantitatively with the available experimental data. The residual resistivity is found to obey the Nordheim rule, indicating weak-scattering regime. The temperature-dependent spin-disorder resistivity is found to be described well via the disordered model of local moments. Effect of pressure on the Curie temperature and the resistivity is also explored.

First-principles study on the effects of high Al doped on the band gap and absorption spectrum of ZnO

According to the density functional theory, using first-principles plane-wave ultrasoft pseudopotential method, we set two different kinds of Zn1-xAlxO supercell models of substituting Zn atom with Al atom and optimige the geomertries for the two models. The total density of states and the band structures are also calculated. The results show that in a range of high doping concentration, when the doping concentration of Al atoms increases, the band gap will be decrease, blue shift will decrease, which accords with the experimental results.

Subsolidus formation and impedance spectroscopy studies of materials in the (Bi2O3)1−x (Y2O3)x binary system

Single phase (Bi2O3)1−x(Y2O3)x samples with x=0.15, 0.20, 0.30 and 0.40 were successfully synthesised via conventional solid state method at the firing temperature of 800°C over 24h. These samples crystallised in cubic fluorite structure, space group, Fm-3m and lattice parameters, a ranging from 5.5167Å to 5.4369Å with an increase of doped Y2O3. The linear-plot obeyed Vegard's law, revealing a well-behaved substitutional solid solution existed within the incorporated dopant concentration range. (Bi2O3)1−x(Y2O3)x subsolidus system was thermally stable as no phase transition or weight loss was discernable within the studied temperature. The electrical properties of the prepared samples were characterised by AC impedance analyser, HP4192 at temperature ranging from 25°C to 850°C in the frequency range of 5Hz to 13MHz. The impedance data could be represented by different RC equivalent circuits. The conduction mechanism involved two processes with different activation energies at low and high temperature regions, e.g. 1.09–1.12eV and 0.41–0.44eV, respectively. The ionic conductivities of the prepared samples were found decreased with increase of yttrium content. These values were in general higher than that of commercial yttria- stabilised zirconia (YSZ) solid electrolyte over wide range of temperatures.

Pressure dependence of Curie temperature and resistivity in complex Heusler alloys

Using first-principles electronic structure calculations, we have studied the dependence of the Curie temperature on external hydrostatic pressure for random Ni2MnSn Heusler alloys doped with Cu and Pd atoms, over the entire range of dopant concentrations. The Curie temperatures are calculated by applying random-phase approximation to the Heisenberg Hamiltonian whose parameters are determined using the linear response and multiple scattering methods, based on density-functional theory. In (Ni1-x,Pdx)2MnSn alloys, the Curie temperature is found to increase with applied pressure over the whole concentration range. The crossover from the increase to the decrease of the Curie temperature with pressure takes place for Cu concentrations larger than about 70% in (Ni1-x,Cux)2MnSn Heusler alloys. The results for the reference Ni2MnSn Heusler alloy agree well with a previous theoretical study of E. Sasioglu, L. M. Sandratskii and P. Bruno Phys. Rev. B 71 214412 (2005) and also reasonably well with available experimental data. Results for the spin-disorder-induced part of the resistivity in (Ni1-x,Pdx)2MnSn Heusler alloys, calculated by using the disordered local moment model, are also presented. Finally, a qualitative understanding of the results, based on Anderson's superexchange interaction and Stearn's model of the indirect exchange interaction between localized and itinerant d electrons, is provided.

Compensation-doped silicon for photovoltaic applications

A small overlap between the silicon optical absorption spectrum and the solar spectral irradiance limits the conversion efficiency of crystalline thin-film silicon solar cells. In this work, a theoretical search for compensation-doped silicon is carried out aiming to maximize the spectral overlap. First, a wide range of dopant species and concentrations is considered using the virtual crystal approximation and the empirical pseudopotential method. Second, the most promising modifications of silicon are investigated using the supercell method and a first-principles many-electron Green's function approach. In both steps, the optical absorption spectrum is computed by solving the Bethe-Salpeter equation to include excitonic effects. It is found that the conversion efficiency of a silicon film of 10 $\ensuremath{\mu}$m thickness can be increased by 25$%$ by a 1.6 at. $%$ compensation doping with In and Sb.

Modeling Quantum Efficiency of Ultraviolet 6H–SiC Photodiodes

The quantum efficiency of p-n junction 6H-SiC ultraviolet (UV) photodiodes has been theoretically modeled for the doping concentration range of 1014 -1020cm-3. The calculations take into account the contribution from the depletion region and the doping dependence of charge carrier transport characteristics. Data on optical and physical properties of 6H-SiC that determine the charge carrier transport and bandgap energy are collected and analyzed. The highest average external efficiency of up to 76%, through a working wavelength range of 200-400 nm, can be achieved at lower dopings that result in a fully depleted top active photoabsorbing layer. This is different from the current technology of commercial higher doped SiC UV photodetectors. The detectivity is shown to be conformal to the quantum efficiency in response to the design variations. The temperature dependence of the device does not change the design tradeoffs that depend on the electrical characteristics. The model presented can be extended to elevated temperatures when optical data become available at these temperatures.

Ab initio studies of Nb doping effect on the formation of oxygen vacancy in rutile TiO 2

In this paper, the effect of Nb doping on the formation of O vacancies in rutile TiO 2 is studied by the use of ab initio density-functional calculations. The formation energies are calculated at different doping concentrations ( C Nb ) and the corresponding electronic structures are analyzed. It is shown that the formation energy is mainly determined by the structural relaxation. As C Nb increases, the formation energy first increases and then decreases with the maximum in vicinity of C Nb =11.1 at%. The investigation of electronic structures shows that the distribution of excess electrons, which is affected by the doping concentration and the types of oxygen vacancy, determines the relaxation and formation energy of oxygen vacancy. Our calculated results indicate that the formation of oxygen vacancy in rutile TiO 2 can be most effectively suppressed by Nb doping in a large range of Nb doping concentration. This may be one of the reasons why the proper amount of Nb doping can improve the oxidation resistance of γ - TiAl .

Spectroscopy of thulium and holmium heavily doped tellurite glasses

In this study, we report spectroscopic properties of Tm 3+ and Ho 3+ codoped tellurite glasses over a wide dopant concentration range in order to assess their potential laser performance under 790 nm diode laser excitation. The impact of Tm 3+ and Ho 3+ concentrations is investigated to identify specific candidates for fiber laser operation. The emission cross section is calculated and discussed, as well as the gain coefficient of this type of glasses. Energy transfer microparameters and critical ion distances are determined for 3H 4, 3F 4 (Tm 3+), and 5I 7 (Ho 3+) emission levels in the framework of diffusion-limited regime and dipole–dipole interaction. We also report thermal properties of tested glasses.

The induced synthesis of mixed phase niobate by Cu doping and its photocatalytic property

Cu-doped KNb 3O 8 photocatalysts were prepared using a simple solid-state method. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectrum. XRD and SEM analyses suggest that Cu doping can induce the formation of the compound K 6Nb 10.8O 30 with tungsten–bronze structure and the relative content of K 6Nb 10.8O 30 in the Cu-doped samples increased with increasing Cu doping amount. When the Cu doping amount reaches 2 wt.%, the as-prepared sample is mainly composed of K 6Nb 10.8O 30. The photocatalytic properties of the catalysts were evaluated using the degradation of acid red G. The results showed that Cu-doping significantly increased the photocatalytic activity of the KNb 3O 8 catalyst. The optimum dopant concentration range of Cu was found to be 0.3–1 wt.%. The synergistic effect of Cu doping and mixed phase niobate compounds is responsible for the enhanced photocatalytic activity.

Spectral dependences of thermally stimulated luminescence and X-ray luminescence of single-crystalline and glassy Li2B4O7:Mn

Thermally stimulated luminescence (TSL) and X-ray excited luminescence (XL) spectra of single-crystalline and glassy Li2B4O7:Mn (LTB:Mn) are studied. For single-crystalline LTB:Mn, maxima at the TSL spectral dependences at 608±2 and 598±2 nm are revealed, their position being practically unchanged in a wide range of manganese dopant concentrations and irradiation doses. In the TSL and XL spectral dependences of glassy LTB:Mn, a smeared, low-intensity peak is observed, its maximum being shifted towards longer wavelengths in comparison to single-crystalline LTB:Mn. In the LTB:Mn single crystals, manganese mostly forms point defects of a Mn type, the superfluous charge being compensated by cationic vacancy. In glassy LTB:Mn, due to the decrease in packing density of the main structural blocks and because of the decreasing [BO3] triangle to [BO4] tetrahedron ratio, some Mn2+ ions are oxidized to Mn3+, resulting in the features of the spectral characteristics of TSL.

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.