Doping Concentration Dependence Research Articles

Anatase phase stability and doping concentration dependent refractivity in codoped transparent conducting TiO2 films

Nb0.06SnxTi0.94−xO2 (x ≤ 0.3) thin films were grown by a pulsed-laser deposition method with varying Sn concentration. Through a combinatorial technique, we find that Sn concentration can reach a maximum of about x = 0.3 while maintaining the stable anatase phase and epitaxy. A doping concentration dependence of the refractivity is revealed, in which refractivity reduction at a wavelength of λ = 500 nm is estimated to be 12.4% for Nb0.06Sn0.3 Ti0.64O2 thin film. Sn doping induced band-gap blue shift can be contributed to the mixing of extended Sn 5s orbitals with the conduction band of TiO2. Low resistivity on the order of 10−4 Ω cm at room temperature and high internal transmittance of more than 95% in the visible light region are exhibited for Nb0.06Snx Ti0.94−xO2 thin films (x ≤ 0.2). Optical and transport analyses demonstrate that doping Sn into Nb0.06 Ti0.94O2 can reduce the refractivity while maintaining low resistivity and high transparency.

Dopant Ion Concentration Dependence of Growth and Faceting of Manganese-Doped GaN Nanowires

The effect of manganese dopant ions on the growth and faceting of manganese-doped GaN (Mn:GaN) nanowires is reported. Using the chemical vapor deposition method we synthesized high-quality internally doped GaN nanowires with varying concentrations of Mn precursor in the reaction mixtures. In all samples we observed nanowires having three distinct cross-section morphologies: hexagonal, triangular, and rectangular. These NWs were present in different ratios depending on the starting concentration of Mn ions. Using electron microscopies we found that the presence of Mn dopant ions inhibits nanowire growth and that the percentage of triangular and rectangular nanowires increases with increasing concentration of Mn precursor at the expense of hexagonal nanowires. We propose that Mn binding to specific nanowire facets plays a key role in governing Mn:GaN nanowire growth and dopant incorporation. These results allow for the preparation of Mn:GaN nanowires in a truly controlled fashion using the developed method...

Effects of doped dye on the charge carrier injection, transport, and electroluminescent performance in polymeric light-emitting diodes

The effects of doped fluorescent dye 4-(dicyanomethylene)-2-i-propyl-6-(1, 1, 7, 7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTI) on the charge carrier injection, transport and electroluminescence (EL) performance in polyfluorene (PFO)-based polymer light-emitting diodes (PLEDs) were investigated by steady-state current-voltage (I−V) characteristics and transient EL measurements. A red EL from DCJTI was observed and the EL performance depended strongly on the DCJTI concentration. The analysis of the steady-state I−V characteristics at different DCJTI concentrations found that three regions was shown in the I−V characteristics, and each region was controlled by different processes depending on the applied electric field. The effect of the dopant concentration on the potential-barrier height of the interface is estimated using the Fowler–Nordheim model. The dopant concentration dependence of the current-voltage relationship indicated clearly the carrier trapping by the DCJTI molecules. The mobility in DCJTI: PFO changed significantly with the DCJTI concentration, and showed a nontrivial dependence on the doping level. The behavior may be understood in terms of the formation of an additional energy disorder due to potential fluctuation caused by the Coulomb interaction of the randomly distributed doping molecules.

Comparison of the radiation hardness of Magnetic Czochralski and Epitaxial silicon substrates after 26 MeV proton and reactor neutron irradiation

We report on the processing and characterization of microstrip sensors and pad detectors produced on n- and p-type Magnetic Czochralski (MCz), Epitaxial (EPI) and Float Zone (FZ) silicon within the SMART project to develop radiation-hard silicon position sensitive detectors for future colliders. Each wafer contains 10 microstrip sensors with different geometries, several diodes and test structures. The isolation in the strip detectors produced on p-type material has been achieved by means of a uniform p-spray implantation, with doping of 3×10 12 cm −2 (low-dose p-spray) and 5×10 12 cm −2 (high-dose p-spray). The samples have undergone irradiations with 26 MeV protons and reactor neutrons up to ∼10 16 cm −2 1 MeV equivalent neutrons (n eq/cm 2), and have been completely characterized before and after irradiation in terms of leakage current, depletion voltage and breakdown voltage. The current damage parameter α has been determined for all substrates. MCz diodes show less pronounced dependence of effective doping concentration N eff on the fluence when compared to standard FZ silicon, giving results comparable to diffusion oxygenated FZ devices for all irradiation sources. The observed increase of N eff with fluence can be interpreted in EPI material as a net donor introduction process, overcompensating the usual acceptor introduction process. This effect is stronger for 26 MeV proton irradiation than for neutron irradiation.

Influences of Al doping concentration on structural, electrical and optical properties of Zn0.95Ni0.05O powders

Nanocrystalline Zn0.95 - xNi0.05AlxO (x = 0.01, 0.02, 0.05 and 0.10) diluted magnetic semiconductors have been synthesized by an auto-combustion method. X-ray diffraction measurements indicate that all Al-doped Zn0.95Ni0.05O samples have the pure wurtzite structure. Transmission electron microscope analyses show that the as-synthesized powders are of the size 40 - 45 nm. High-resolution transmission electron microscope, energy dispersive spectrometer and X-ray photoemission spectroscope analyses indicate that Ni2+ and Al3+ uniformly substitute Zn2+ in the wurtzite structure without forming any secondary phases. The Al doping concentration dependences of cell parameters (a and c), resistance and the ratio of green emission to UV emission have the similar trends. (c) 2007 Elsevier B.V. All rights reserved.

First Principles Analysis of Formation Energy of Point Defects and Voids in Silicon Crystals during the Cooling Process of Czochralski Method (Dopant Type and Concentration Dependence)

The effects of p-type (B) or n-type (P or As) dopant concentration on the formation energy EF of point defects in silicon (Si) crystals during the cooling process of the Czochralski (CZ) method were studied by first principles analysis. EF of several charge states of vacancy (V) and interstitial Si (I) was calculated as a function of the Fermi level. EF of the most stable state of V and I in Si crystals was estimated by considering the dependence of the Fermi level on crystal temperature. The V concentration was found to decrease in p-type but to increase in n-type Si crystals when dopant concentration was higher than about 1×1019 atoms/cm3. This explains the reported experimental results for void formation behavior in Si crystals, i.e., void formation is suppressed by an increase in p-type dopant concentration above about 1×1019 atoms/cm3, but is enhanced by an increase in n-type dopant concentration to about 3×1019 atoms/cm3. Other calculations showed that, at the initial stage of void formation, the reduction of the total energy of stable P-Vn or As-Vn complex formation was greater than that of stable Vn complex formation from isolated P or As atoms and vacancies.

Resonant tunneling characteristics in crystalline silicon/nanocrystalline silicon heterostructure diodes

We have carried out a detailed investigation on the resonant tunneling in crystalline ($c$-) Si/nanocrystalline ($nc$-) Si heterostructure diodes, with the emphasis on doping concentration dependence. By the aid of the self-consistent calculation, together with a transfer matrix procedure, we are able to explain well the observed resonant tunneling characteristics under the applied reverse bias in the $c\text{\ensuremath{-}}\mathrm{Si}(p)∕nc\text{\ensuremath{-}}\mathrm{Si}(n)$ resonant tunneling diodes. We have demonstrated the controlling of the resonant tunneling by the doping concentrations through modifying the energy levels of the two-dimensional interfacial states and zero-dimensional states in $nc\text{\ensuremath{-}}\mathrm{Si}$. The present observation provides us the possibility of realizing unique $nc\text{\ensuremath{-}}\mathrm{Si}$ device application, such as the easily integrating silicon-based logic gates.

Proton conduction in LaSrScO 3 single crystals

Transparent single crystals of La 1− x Sr x ScO 3 ( x = 0.01, 0.03) were grown by the floating zone method. The optical and the electrical properties were studied by infrared absorption spectra and AC-impedance measurements, respectively. Our results showed that proton conduction becomes dominant in La 0.97Sr 0.03ScO 3 single crystals below 700 °C. The electrical conductivity increases as the amount of Sr increases. At 600 °C, La 0.97Sr 0.03ScO 3 had a proton conductivity of 4.89 × 10 − 3 S/cm. This value is almost the same as that in the literature for La 0.9Sr 0.1ScO 3 ceramic samples. It was revealed from infrared absorption spectra that several different sites are occupied by protons in this material. Furthermore, it was found that the intensity of high-frequency O–H bands can be related to the dopant-concentration dependence of the electrical conductivity.

Radiation hardness of silicon detectors based on pre-irradiated silicon

Radiation hardness of planar detectors processed from pre-irradiated and thermo-annealed n-type FZ silicon substrates, and standard FZ as a reference, was studied. The high purity n-Si wafers with carrier concentration 4.8×10 11 cm −3 were pre-irradiated in Kiev's nuclear research reactor by fast neutrons to fluence of about 10 16 neutrons/cm 2 and thermo-annealed at a temperature of about 850 °C. Silicon diodes were fabricated from standard and pre-irradiated silicon substrates by IRST (Italy). All diodes were subsequently irradiated by fast neutrons at Kiev and Ljubljana nuclear reactors. The dependence of the effective doping concentration as a function of fluence ( N eff =f( Φ)) was measured for reference and pre-irradiated diodes. Pre-irradiation of silicon improves the radiation hardness by decreasing the acceptor introduction rate ( β), thus mitigating the depletion voltage ( V dep) increase. In particular, β in reference samples is about 0.017 cm −1, and for pre-irradiated samples is about 0.008 cm −1. Therefore, the method of preliminary irradiation can be useful to increase the radiation hardness of silicon devices to be used as sensors or detectors in harsh radiation environments.

Microstructures and electrolytic properties of yttrium-doped ceria electrolytes: Dopant concentration and grain size dependences

The microstructures and electrolytic properties of Y x Ce 1− x O 2− x/2 ( x = 0.10–0.25) electrolytes with average grain size in the range 90 nm–1.7 μm were systematically investigated. Through detailed transmission electron microscopy characterization, nanosized domains were observed. The relationship of the domains, the doping level and grain sizes were determined, and their impacts on the electrolytic properties were systematically studied. It was found that the formation of domains has a negative impact on the electrolytic properties, so that electrolytic properties can be adjusted through careful control of domain formation, doping level and grain size.

Epitaxial growth of 4H–SiC on 4° off-axis (0 0 0 1) and (0 0 0 1¯) substrates by hot-wall chemical vapor deposition

Homoepitaxial layers of 4H–SiC have been grown on 4° off-axis (0 0 0 1) and (0 0 0 1¯) substrates under various growth conditions by horizontal hot-wall chemical vapor deposition. On the (0 0 0 1) epilayers, macroscopic step bunching has been significantly enhanced under C-rich condition. On the other hand, on the (0 0 0 1¯) C-face, epilayers without macroscopic step bunching could be grown with a wide range of C/Si ratio at 1600 °C. The C/Si ratio dependence of background doping concentration of epilayers on the (0 0 0 1¯) C-face clearly showed site-competition behavior, and a lowest background doping of 4.4×10 14 cm −3 could be attained by low pressure growth at 35 Torr.

Effect of doped dye on the charge-carrier transport and electroluminescent performance in molecularly doped polymer light-emitting diodes

The effects of the concentration of 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T) as dopant in polyfluorene (PFO) on the charge-carrier transport and electroluminescence (EL) performance were investigated by steady-state and transient EL measurements. A fully green emission from C545T was observed and the EL performance depends strongly on the C545T concentration. The mobility in the C545T-doped PFO film was determined by transient EL. The dopant concentration dependence of the current–voltage relationship indicated clearly the carrier trapping by the C545T molecules. The mobility in C545T:PFO changed significantly with the C545T concentration, and showed a nontrivial dependence on the doping level. The behavior may be understood in terms of the formation of an additional energy disorder due to potential fluctuation caused by the Coulomb interaction of the randomly distributed doping molecules.

Nature of Deep-Level Defects in GaCrN Diluted Magnetic Semiconductor

The effects of chromium doping on the luminescence properties of the deep levels in gallium nitride (GaN) have been studied exclusively. Chromium (Cr) doping induced a blue luminescent band (BL) centered in the range of 2.79–2.91 eV with the limited Cr doping concentration varying from 0.5% to 1.5% and also a slight increase in the intensity of the yellow luminescent band (YL). By analyzing the luminescent spectrum obtained with different excitation intensities, Cr doping concentration and temperature dependences revealed the nature of donor–acceptor pair transition for the observed blue band. The participating donor and acceptor are expected to be the deep-acceptor related center, CrGa, and the shallow compensating vacancy complex, CrGa–VN respectively.

Doping concentration dependence of room-temperature ferromagnetism for Ni-doped ZnO thin films prepared by pulsed-laser deposition

High-quality Ni-doped ZnO thin films of single phase with preferred c-axis growth orientation were formed on Si (100) substrates by pulsed-laser deposition at room temperature. The films exhibited room-temperature ferromagnetic behaviors with saturation magnetic moment per Ni atom of 0.37μB,0.26μB,0.25μB and 0.21μB for the Ni concentration of 1, 3, 5, and 7 at. %, respectively. The decrease of ferromagnetism with doping concentration demonstrates that ferromagnetism observed at room temperature is an intrinsic property of Ni–ZnO thin films, not from any secondary phase.

First Principles Analysis on Formation Energy of Point Defects and Voids in Si Crystals during Cooling Process of Czochralski Method (Dopant Type and Concentration Dependence)

The effects of p-type (B) or n-type (P or As) dopant concentration on the formation energy EF of point defects in silicon (Si) crystals during the cooling process of the Czochralski (CZ) method were studied by first principles analysis. EF of several charge states of vacancy (V) and interstitial Si (I) was calculated as a function of the Fermi level. EF of the most stable state of V and I in Si crystals was estimated by considering the dependence of the Fermi level on crystal temperature. The V concentration was found to decrease in p-type but to increase in n-type Si crystals when dopant concentration was higher than about 1×10 19 atoms/cm 3 . This explains the reported experimental results for void formation behavior in Si crystals, i.e., void formation is suppressed by an increase in p-type dopant concentration above about 1×10 19 atoms/cm 3 , but is enhanced by an increase in n-type dopant concentration to about 3×10 19 atoms/cm 3 . Other calculations showed that, at the initial stage of void formation, the reduction of the total energy of stable P–Vn or As–Vn complex formation was greater than that of stable Vn complex formation from isolated P or As atoms and vacancies.

Predicting ionic conductivity of solid oxide fuel cell electrolyte from first principles

First-principles quantum simulations complemented with kinetic Monte Carlo calculations were performed to gain insight into the oxygen vacancy diffusion mechanism and to explain the effect of dopant composition on ionic conductivity in yttria-stabilized zirconia (YSZ). Density-functional theory (DFT) within the local-density approximation with gradient correction was used to calculate a set of energy barriers that oxygen ions encounter during migration in YSZ by a vacancy mechanism. Kinetic Monte Carlo simulations were then performed using Boltzmann probabilities based on the calculated DFT barriers to determine the dopant concentration dependence of the oxygen self-diffusion coefficient in (Y2O3)x(ZrO2)(1−2x) with x increasing from 6% to 15%. The results from the simulations suggest that the maximum conductivity occurs at 7–9mol% Y2O3 at 600–1500K and that the effective activation energy increases at higher Y doping concentrations in good agreement with previously reported literature data. The increase in the effective activation energy for migration arises from the higher-energy barrier for oxygen vacancy diffusion across an Y–Y common edge relative to diffusion across one with a Zr–Y common edge of two adjacent tetrahedra. The binding energies between oxygen vacancies and dopants were extracted up to the fourth nearest-neighbor interaction. Our results reveal that the binding energy is the strongest when the vacancy is in the second nearest-neighbor position relative to the Y dopant atom. The methodology was also applied to scandium-doped zirconia (SDZ). Preliminary results from quantum simulations of SDZ suggest that the effective activation energy for vacancy diffusion in SDZ is lower than that of YSZ, in agreement with experimental observations. The agreement with experimental studies on the two systems analyzed in this paper supports the use of this technique as a predictive tool on electrolyte systems not yet characterized experimentally.

Magnetic and half-metallic properties of Cr-doped /spl beta/-SiC

The Cr doping concentration dependence of the electronic properties including bonding characteristic and spin band gap of SiC dilute magnetic semiconductor is studied by employing first-principles pseudopotential plane-wave method based on density functional theory within generalized gradient approximation. For the cubic /spl beta/-SiC crystal, the calculated lattice constant is a/sub 0/=4.36 /spl Aring/ and the bulk modulus is B/sub 0/=208.14 GPa. The 64 and 8-atom supercell models are employed which corresponds to the impurity concentration of 3 and 25%, respectively. In the case of 3% impurity concentration, the Cr atoms substituting for C induces large stress on the neighboring Si atoms due to the significant difference in atomic size. On the other hand, in 25%-doped SiC:Cr, the adjacent Si atoms moved away from the Cr atom. Calculations of the magnetic moment and magnetization energy is done in which the latter is defined as the energy difference between the ferromagnetic phase and paramagnetic phase of SiC:Cr. Results show that the SiC:Cr has permanent magnetic moments of 2/spl mu//sub B/ regardless of the substitution site and the studied doping concentration. Also, calculation of density of states is done resulting in the determination of a wide spin band gap of 1.58 eV for the SiC:Cr.

Fracture properties of (CeO2)1−x(RO1.5)x (R = Y, Gd, and Sm; x = 0.02–0.20) ceramics

The fracture properties of rare earth (yttrium, gadolinium, and samarium) doped ceria ceramics were systematically investigated using the modified small punch method at room temperature in air and at high temperatures in argon gas. The samples prepared by oxalate co-precipitation method showed higher fracture strength than those by solid-state reaction method. In addition, the sintering temperature dependence of gadolinium doped ceria indicated that the highest fracture strength was attained by sintering at 1600 °C. Furthermore, it turned out that the fracture strength was influenced by the dopant concentration rather than the kind of dopant. The relationship between mechanical properties and defect structures are discussed from the dopant concentration, sintering temperature and testing temperature dependence of the fracture strength.

Fluorine-doping concentration and fictive temperature dependence of self-trapped holes in SiO2 glasses

Fictive temperature (Tf) and fluorine (F)-doping concentration dependences of self-trapped holes (STHs) in silica glasses created by UV irradiation at low temperatures have been studied by the electron-paramagnetic-resonance method. It was found that the yield of STH decreases with decreasing Tf and increasing F-doping concentration. In combination with infrared spectra measurements, the correlation among Tf, F-doping concentration, Si–O bond length, and Si–O–Si bond angle was elucidated. We conclude that the change in both Tf and F doping can modify the network of SiO2 glass, leading to the suppression of the formation of STHs.

Intrinsic loss of optical fibers

Rayleigh scattering is a dominant factor in terms of optical fiber loss. We investigated the dopant concentration and fictive temperature dependence of Rayleigh scattering in silica-based optical fibers and their glass preforms fabricated by the vapor-phase axial deposition (VAD) technique. The lowest Rayleigh scattering coefficient, which was obtained for a P 2O 5-doped silica preform, was about 80% of the pure silica value. In contrast, the Rayleigh scattering coefficients of F-doped and GeO 2-doped and pure silica glass preforms increased by 5–10% when they were heated to 1800 °C because the density fluctuation is proportional to their fictive temperature. We also obtained very low Rayleigh scattering coefficients in fabricated fibers by controlling the preform composition or the fiber drawing conditions. We used these results to reevaluate the intrinsic losses of P 2O 5-doped, pure, and GeO 2-doped silica core fibers and found them to be 0.095–0.130 dB/km at 1.55 μm by using the Rayleigh scattering coefficients of their preforms.