Range Of Doping Concentrations Research Articles

Growth of large LiNbO3〈Mg〉 crystals

We have analyzed conditions for the growth of large (≥80 mm in diameter) LiNbO3〈Mg〉 crystals in a wide range of dopant concentrations in the melt (2.9–5.8 mol % MgO). We have established conditions for the growth of large LiNbO3〈Mg〉 crystals uniform in doping level from melts containing magnesium concentrations above a certain threshold (Cmelt 5.0–5.8 mol % MgO) and optimized the high-temperature electrodiffusion annealing process, which allowed us to obtain single-domain, microstructurally homogeneous, large LiNbO3〈Mg〉 crystals containing 4.9–5.15 mol % magnesium.

Synthesis and strong near-infrared fluorescence of LiLa1−xNdx(PO3)4 nanocrystals with high doping concentrations

A series of LiLa(1-x)Nd(x)(PO(3))(4) (LLNP) nanocrystals are synthesized by a combustion method for the first time. With irregular short-rod shapes and an average size of about 70 nm, the LiLa(1-x)Nd(x)(PO(3))(4) nanocrystals exhibit stronger fluorescence emission of 1.8-6.5 times in the doping concentration range of 1 mol% to 100 mol% than Nd(3+) (2.5 wt%) doped phosphate glass, and have a long lifetime of 122 μs for the fully doped nanocrystals. Moreover, the LiLa(1-x)Nd(x)(PO(3))(4) nanocrystals show the lowest lifetime decay rate of 5.09 μs per mol% and a quenching ratio of 10.81%. Considering the above outstanding performances, LiLa(1-x)Nd(x)(PO(3))(4) nanocrystals may have promising applications in optical amplifiers and lasers.

A continuous current model of ultra-thin cylindrical surrounding-gate inversion-mode Si nanowire nMOSFETs considering a wide range of body doping concentration

Based on the approximated solution of Poisson's equation, we propose a continuous current model of ultra-thin fully depleted cylindrical surrounding-gate Si nanowire MOSFETs. It matches well with three-dimensional simulation results using SILVACO Atlas TCAD in a wide range (from intrinsic to high doping) of the body doping concentration without any empirical fitting parameters. It is valid for all the operation regions such as subthreshold, turn-on, linear and saturation.

Optical and ferroelectric properties of ruthenium-doped BaTiO3 nanocubes

Structural, optical, dielectric and ferroelectric properties of Ru-doped BaTi1−xRuxO3(x = 0.01, 0.03, 0.05, 0.07, 0.10) nanocubes have been investigated. The average size of nanocube obtained from Rietveld refinement is in the range 35–60 nm. The incorporation of Ru leads to a mixed tetragonal and cubic crystalline phases in doping concentration range 5–7%. Optical band gap changes from 3.2 to 2.74 eV with increase in Ru concentration. Replacement of Ti with Ru quenches band-edge emission and enhances defect emission intensity. Optical absorption and emission spectra have been interpreted in terms of oxygen vacancy. Ruthenium 4d orbital plays a crucial role to improve dielectric constant and diminish ferroelectric Curie temperature. The combined effect of Ru dopant and size gives rise to complex variation of Curie temperature.

Atomic layer deposition of Ga-doped ZnO transparent conducting oxide substrates for CdTe-based photovoltaics

The atomic layer deposition of gallium doped zinc oxide films is investigated as a method of fabricating transparent conducting oxide substrates for cadmium telluride based photovoltaic cells. The growth parameters and properties of gallium-doped ZnO were established for a range of dopant concentrations. 1 at. % gallium-doped films exhibited the lowest electrical sheet resistances and were selected as substrates to deposit Cd1−xZnxS/CdTe photovoltaic cells. The average current density–voltage characteristics of 16 cells under AM1.5 illumination yielded a conversion efficiency of 10.8% and a fill-factor of 65%.

Improved quantitative description of Auger recombination in crystalline silicon

An accurate quantitative description of the Auger recombination rate in silicon as a function of the dopant density and the carrier injection level is important to understand the physics of this fundamental mechanism and to predict the physical limits to the performance of silicon based devices. Technological progress has permitted a near suppression of competing recombination mechanisms, both in the bulk of the silicon crystal and at the surfaces. This, coupled with advanced characterization techniques, has led to an improved determination of the Auger recombination rate, which is lower than previously thought. In this contribution we present a systematic study of the injection-dependent carrier recombination for a broad range of dopant concentrations of high-purity $n$-type and $p$-type silicon wafers passivated with state-of-the-art dielectric layers of aluminum oxide or silicon nitride. Based on these measurements, we develop a general parametrization for intrinsic recombination in crystalline silicon at 300 K consistent with the theory of Coulomb-enhanced Auger and radiative recombination. Based on this improved description we are able to analyze physical aspects of the Auger recombination mechanism such as the Coulomb enhancement.

Low temperature dielectric dispersion and electrical conductivity studies on Fe2O3 mixed lithium yttrium silicate glasses

Lithium yttrium silicate glasses mixed with different concentrations of Fe2O3 of the composition (40−x) Li2O–10Y2O3–50SiO2: x Fe2O3, with x=0.3, 0.5, 0.8, 1.0, 1.2 and 1.5 (all in mol%) were synthesized. Electrical and dielectric properties including dielectric constant, ε′(ω), loss, tan δ, ac conductivity, σac, impedance spectra as well as electric moduli, M(ω), over a wide continuous frequency range of 40Hz to 106Hz and in the low temperature range 100 to 360K were measured as a function of the concentration of Fe2O3. The dc conductivity is also evaluated in the temperature range 100 … 360K. The temperature and frequency dispersions of dielectric constant as well as dielectric loss have been analyzed using space charge polarization model. The ac and dc conductivities have exhibited increasing trend with increasing Fe2O3 content beyond 0.5mol%, whereas the activation energy for the conductivity demonstrated decreasing tendency in this dopant concentration range. Both quantum mechanical tunneling (QMT) and correlated barrier hopping models (CBH) were used for clarification of ac conductivity origin and the corresponding analysis has indicated that CBH model is more appropriate for this glass system. For the better understanding of relaxation dynamics of the electrical properties we have drawn the scaling plots for ac conductivity and also electric moduli. The plots indicated that the relaxation dynamics is independent on temperature but depends on concentration of Fe2O3. The dc conductivity is analyzed using small polaron hoping model. The increase of conductivity with the concentration of Fe2O3 beyond 0.5mol% is explained in terms of variations in the redox ratio of iron ions in the glass network. The results were further analyzed quantitatively with the support of experimental data from IR, optical absorption and ESR spectral studies. The overall analysis has indicated that Li2O–Y2O3–SiO2 glasses containing more than 0.5mol% of Fe2O3 are more suitable for achieving good electrical conductivity in these glasses.

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.