Common Dopants Research Articles

The effect of dopants on the incremental permeability of MnZn-ferrites

In this paper the effect of some common grain boundary dopants, such as calcium oxide and niobium oxide, and of some processing parameters, on the incremental permeability of ( Mn 0.57 Zn 0.34 Fe 0.09 ) Fe 2 O 4 ferrites in the temperature region of - 40 to 85 ∘ C is examined, in relation to the non-magnetic grain boundary models. Doped grain boundaries influence the incremental permeability in a different way than they influence the initial permeability, most probably because the dominating magnetization mechanism between those two properties changes. For the achievement of high incremental permeability, a shift of the hysteresis loop towards higher fields is essential. Besides the usage of grain boundary dopants, this can be more effectively achieved also with the usage of bulk dopants that dissolve into the lattice and induce high anisotropy and domain wall pinning, like cobalt. A 1500 ppm cobalt doped material is synthesized exhibiting initial permeability μ i > 4000 and μ Δ > 2000 over the entire temperature region from - 40 to 85 ∘ C .

Toward Silicon-Based Lasers for Terahertz Sources

Producing an electrically pumped silicon-based laser at terahertz frequencies is gaining increased attention these days. This paper reviews the recent advances in the search for a silicon-based terahertz laser. Topics covered include resonant tunneling in p-type Si/SiGe, terahertz intersubband electroluminescence from quantum cascade structures, intersubband lifetime measurements in Si/SiGe quantum wells, enhanced optical guiding using buried silicide layers, and the potential for exploiting common impurity dopants in silicon such as boron and phosphorus to realize a terahertz laser

Dopant Diffusion in SiGeC Alloys

In this paper, we discuss the impact of germanium and carbon on the diffusion of common dopants in Si-based alloys. We review results of various diffusion experiments and discuss the basic physical mechanisms of the observed changes of diffusion coefficients as a function of alloy composition. Results of boron and phosphorus marker layer diffusion experiments are presented for binary Si1-xGex and Si1-yCy and ternary Si1-x-yGexCy alloys.

Germanium n-type shallow junction activation dependences

A few of the recent unsatisfactory germanium n-channel metal-oxide-semiconductor field-effect transistor MOSFET experimentations are believed to stem from the poor source and drain n+-p junction formations. In order to explain the primary cause and suggest rectifying solutions, we have examined the activation of common n-type dopants in germanium and the related dependences. These dependences include thermal anneal budget, impurity species, and implantation dosage. Low thermal budgets are generally preferred to activate shallow junctions to simultaneously annihilate defects and suppress fast dopant diffusion. Injecting dopants over the solid-solubility limitation into shallow junctions would only generate more implantation damage but could not however lower the junction sheet resistance.

Interaction of doping impurities with the 30° partial dislocations in SiC: Anab initioinvestigation

In this work we investigated, by means of state-of-the-art first principle techniques, the effect of impurity segregation on the energetics, the structure, and the electronic properties of dislocation cores. We find that for the species we considered, Al, P, B, and N, i.e., the most common dopants in SiC, the impurity-dislocation interaction is attractive and that segregation energies are comparable or larger than dislocations reconstruction energies. As to the doping properties of the impurities they are deactivated by the interaction with the dislocation core environment, with the noticeable exception of P. We rationalized our results in terms of the effect of the dopants on the dislocation core band structure.

Physical atomistic kinetic Monte Carlo modeling of Fermi-level effects of species diffusing in silicon

An accurate physically based Fermi-level modeling approach, amenable to be implemented in an atomistic process simulator, is reported. The atomistic kinetic Monte Carlo method is used for point and extended defects, in conjunction with a quasiatomistic, continuum approach treatment for carrier densities. The model implements charge reactions and electric bias according to the local Fermi level, pairing and break-up reactions between particles, clustering-related dopant deactivation, and Fermi-level-dependent solubility. We derive expressions that can be used as a bridge between the continuum and the atomistic frameworks. We present the implementation of two common dopants, boron and arsenic, using parameters that are in agreement with both ab initio calculations and experimental results.

Interstitial oxygen molecules in amorphous SiO2. II. The influence of common dopants (SiOH, SiF, and SiCl groups) and fictive temperature on the decay of singlet photoluminescence

Time decay of photoluminescence due to interstitial oxygen molecules (O2) in synthetic amorphous SiO2(a-SiO2) was studied by varying the fictive temperature and the concentrations of common dopants (SiOH, SiCl, and SiF groups). The decay constant is insensitive to the fictive temperature, but strongly depends on the type of dopants: it is reduced by the nonradiative decay via an energy transfer from O2 to the vibrational modes of the dopants. The increases in the nonradiative decay rate due to SiOH, SiF, and SiCl groups are strong, slight, and negligible, respectively, which correlates with their vibrational energies. The quantum yield decreases by ∼20% as the SiOH content increases from 1017 to 1020cm−3. The deviation from the single exponential decay is due to the shape variation in the a-SiO2 network cages that surround O2, and to the distance distribution between O2 and SiOH groups.

Range evaluation in SIMS depth profiles of Er-implantations in silicon

In the last decade ion implantation of common dopants in silicon has been almost full characterised. However, data of inner transition elements are based on few measurements or even extrapolations. Our investigations focus on erbium, an upcoming dopant in photonic applications. Some of us have previously found errors of 20% in the projected range of Er in Si and SiO 2 when comparing the range profiles measured with SIMS and simulations using SRIM, T2D, and our own binary collision simulator IMSIL. Because of the far-reaching consequences, we have performed additional, more precise experiments to confirm our previous results. Equal doses of Er has been implanted into SIMOX wafers with energies of 100, 200, 300, 400, 500, and 600 keV. Profiles have been measured with secondary ion mass spectrometry (SIMS). Relative sensitivity factors (RSF) were gathered from low-energy implantations, remaining within the Si top layer. We used the Si/SiO 2 interface at exactly 217.7 nm to calibrate the depth scale of all profiles. In addition dynamical Monte-Carlo simulations of the sputter process were taken to correct the depth scale and the interface position.

Defect and Dopant Properties of the SrCeO3-Based Proton Conductor

Atomic-scale studies using advanced simulation techniques have investigated the energetics of defects, oxygen migration, and dopant incorporation in the proton-conducting SrCeO3 system. The interatomic potential model first reproduces the observed distorted perovskite structure of SrCeO3. Substitution with trivalent dopants (M) on the A site in SrCe(Yb)O3-δ (via Vo•• consumption) is compared with substitution on the B site (via Vo•• creation); the results support the premise that the absence of ionic conductivity at low doping levels is associated with dopant partitioning over both A and B sites. Dopant-vacancy association is predicted to occur in SrCe0.9M0.1O2.95 for a wide range of M cations. Formation of (M‘Ce−OHo•) clusters is also calculated to be favorable in accordance with reported proton-trapping effects. The lowest M‘Ce−OHo• binding energies and the largest M−H distances are found for the most common dopants for proton conductivity in the SrCeO3 system, namely, Y and Yb. The pathway for oxygen m...

Ab initio calculations of charged point defects in GaN

The Generalized Gradient Approximation (GGA) of a Density Functional Theory (DFT) in LCAO basis is used to determine electronic structure of charged point defects in hexagonal GaN. Impurities of MgGa, ZnGa, SiN and CN (the most common dopants) were considered for charge states 0, ±1, –2. The vacancies of VGa and VN were considered for charge states 0 and 0, ±1, ±2 respectively. The defects in consideration are compared from the point of view of the one-electron states localization. All the calculations were performed for a supercell containing 96 atoms. The divergence due to periodically repeated charges has been eliminated by the use of a uniform background charge of an opposite sign. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Physical modeling of Fermi-level effects for decanano device process simulations

We report on a physically based Fermi-level modeling approach designed to be accurate and yet amenable to be implemented in a device-size process simulator. We use an atomistic kinetic Monte Carlo method in conjunction with a continuum treatment for carrier densities. The model includes: (i) charge reactions and electric bias according to the local Fermi-level; (ii) pairing and break-up reactions involving charged particles; (iii) clustering-related dopant deactivation; and (iv) Fermi level-dependent solubility. Degenerated statistics, band-gap narrowing, and damage-induced electrical compensation are also included. The parameters used for charged particles are in agreement with ab initio calculations and experimental results. This modeling scheme has proved to be very computationally efficient for realistic device-dimension process simulations. We present an illustrative set of simulation results for two common dopants, boron and arsenic, and discuss the potential of this approach for accurate process simulation of decanano CMOS devices.

Influence of the common varistor dopants (CoO, Cr 2O 3 and Nb 2O 5) on the structural properties of SnO 2 ceramics

The influence of dopants commonly used in SnO 2 varistor ceramics, such as CoO, Cr 2O 3 or Nb 2O 5, on the structural properties of SnO 2 was investigated. Several SnO 2-based ceramics containing only one of the dopants were prepared and characterized. Spectroscopic investigations [visible, near infrared (IR) and IR region] were performed to obtain information about dopants valence states inside the ceramics, as well as about their influence on electronic structure of the material. Structural properties were investigated by X-ray diffraction analysis and mechanisms of dopant incorporation were proposed. Obtained results were confirmed with results of the electrical measurements. Microstructural changes in doped ceramics were investigated by scanning electron microscopy (SEM) analysis that showed great differences in densities, grain size, and morphology of the SnO 2 ceramics depending on type of dopants and their distribution.

Effects of doping on the magnetic anisotropy energy inSmCo5−xFexandYCo5−xFex

${\mathrm{SmCo}}_{5}$ is a technologically important material, having one of the largest magnetic anisotropy energies (MAE) of any hard magnet system. Common dopants include Fe and Cu, which produce grain boundaries that align individual grains, but also unintentionally dope the material within the grains. We have studied the magnetic properties of ${\mathrm{SmCo}}_{5\ensuremath{-}x}{\mathrm{Fe}}_{x}$ and ${\mathrm{YCo}}_{5\ensuremath{-}x}{\mathrm{Fe}}_{x}$ using density-functional theory calculations where the Sm $4f$ bands are treated within the $\mathrm{L}\mathrm{D}\mathrm{A}+U$ formalism (LDA---local-density approximation). Both supercell and virtual-crystal approximation calculations were performed for a series of Fe dopings. A strongly nonmonotonic behavior was found in the MAE for both series of compounds. The MAE of ${\mathrm{SmCo}}_{5\ensuremath{-}x}{\mathrm{Fe}}_{x}$ with $\ensuremath{\sim}3--4%$ doping and of ${\mathrm{YCo}}_{5\ensuremath{-}x}{\mathrm{Fe}}_{x}$ with $\ensuremath{\sim}6--7%$ doping increase by about 1 meV/f.u. before falling rapidly with larger Fe dopings. In both these cases, the results can be related to the position of the Fermi level with respect to the Co $3d$ minority peak in the density of states.

Thermal stability of dopants in laser annealed silicon

As semiconductor device dimensions continue to decrease, the main challenge in the area of junction formation involves decreasing the junction depth while simultaneously decreasing the sheet resistance. Laser annealing is being investigated as an alternative to rapid thermal annealing to repair the damage from ion implantation and to activate the dopants. With this technique, uniform, box-shaped profiles are obtained, with dopant concentrations that can exceed equilibrium solubility limits at normal processing temperatures. Unfortunately, these super-saturated dopant concentrations exist in a metastable state and deactivate upon further thermal processing. In this article, we describe a comprehensive study of the deactivation kinetics of common dopants (P, B, and Sb) across a range of concentrations and annealing conditions. For comparison, As deactivation data from the literature is also presented. P and As deactivate substantially at temperatures as low as 500 °C, while Sb at moderate concentrations and B remain fully active until 700 to 800 °C. It is proposed that As and P deactivate through the formation of small dopant-defect clusters while B deactivates through precipitation. The proximity to the surface is shown to be a second-order effect.

Physical processes associated with the deactivation of dopants in laser annealed silicon

Laser annealing is being investigated as an alternative method to activate dopants and repair the lattice damage from ion implantation. The unique properties of the laser annealing process allow for active dopant concentrations that exceed equilibrium solubility limits. However, these super-saturated dopant concentrations exist in a metastable state and deactivate upon subsequent thermal processing. Previously, this group compared the electrical characteristics of the deactivation behavior of common dopants (P, B, and Sb) across a range of concentrations and annealing conditions. Boron and antimony were shown to be stable species against deactivation while P and As deactivate quickly at temperatures as low as 500 °C. In this work, we present additional data to understand the underlying physical mechanisms involved in the deactivation process. It is proposed that As and P deactivate through the formation of small dopant—defect clusters while B and Sb deactivate through precipitation.

A Study of the Deactivation of High Concentration, Laser Annealed Dopant Profiles in Silicon

ABSTRACTAs semiconductor device dimensions continue to decrease, the main challenge in the area of junction formation involves decreasing the junction depth while simultaneously increasing the active dopant concentration. Laser annealing is being investigated as an alternative to rapid thermal annealing (RTA) to repair the damage from ion implantation and to activate the dopants. With this technique, uniform, box-shaped profiles are obtained, with dopant concentrations that can exceed equilibrium solubility limits. Unfortunately, these super-saturated dopant concentrations exist in a metastable state and deactivate upon further thermal processing. In this work, a comprehensive study of the deactivation kinetics of common dopants (P, B, and Sb) was performed across a range of annealing conditions. For comparison, As deactivation data from the work of Rousseau et al.1 is also presented. Each dopant exhibits different deactivation behavior, however, As and P can be classified as unstable species while B and Sb are stable against deactivation until higher temperatures of 700-800°C. In addition, a means of maintaining these metastably doped layers is being investigated with the goal of meeting the International Technology Roadmap for Semiconductors (ITRS) requirements for ultrashallow junctions.

Theory of point defects in GaN, AlN, and BN: Relaxation and pressure effects

Native defects and some common dopants in cubic GaN, AlN, and BN are examined by means of ab initio calculations using a supercell approach in connection with the full potential linear muffin-tin orbital method. The atomic positions, the electronic structure, and the defect formation energies are calculated. In particular, the vacancies are calculated to be abundant defects. The high-pressure behavior of the defect states is also studied, and it is found that the pressure coefficients of the defect states depend mainly on their position in the energy gap.

Fractional contributions of microscopic diffusion mechanisms for common dopants and self-diffusion in silicon

An identical set of thermal oxidation and nitridation experiments has been performed for four common dopants and self-diffusion in Si. Selectively perturbing the equilibrium point-defect concentrations by these surface reactions is a powerful tool for identifying the relative importance of the various atomic-scale diffusion mechanisms. We obtain bounds on the fractional contributions of the self-interstitial, vacancy, and concerted exchange mechanisms for arsenic, boron, phosphorus, antimony, and self-diffusion in Si at temperatures of 1100 and 1000 °C. These bounds are found by simultaneously solving a system of equations making only very conservative assumptions. The validity of common approximations found in previous work and their effects on the results are also analyzed in detail. We find that B and P diffuse by a self-interstitial mechanism, whereas Sb diffusion is almost exclusively vacancy mediated. As and self-diffusion, on the other hand, exhibit evidence for a dual vacancy-interstitial mechanism with the possibility of some concerted exchange component.

Excess Vacancy Generation by Silicide Formation in Si

AbstractIt has been long recognized that excess point defects are generated when a metal silicide is formed on silicon. Since the common dopants diffuse in Si with the aid of both self-interstials and vacancies, these point defect perturbations will influence motion of diffusions that are in the adjacent vicinity. TiSi2 is known to enhance the concentration of vacancies and several mechanisms have been proposed for this effect. Recent literature has dealt with and rejected many of these ideas; however, some of the remaining few like film strain and lattice contraction upon silicidation have been the subject of state of the art experiments which has led to their rejection.It is the contention of this paper that by using the experimental data from this recent work and reinterpreting it, the model of volume contraction of the silicides as the cause for vacancy injection, still represents the most physically satisfying cause and therefore, was mistakenly rejected.

Barrier height changes in amorphous silicon Schottkydiodes following dopant implantation

The effective barrier heights of Schottky diodes on hydrogenated amorphous silicon have been varied over a wide range using ion implantation of the common dopants. For small changes in barrier height, damage effects are negligible and dopant activity is high, leading to minimal changes in ideality factors and leakage currents.