Dopant Segregation Research Articles

Improving the redox performance of Mn2O3/Mn3O4 pair by Si doping to be used as thermochemical energy storage for concentrated solar power plants

Thermal energy storage plays a significant role in concentrated solar power plants. Particularly, thermochemical energy storage has been proposed as a promising future candidate due to its high energy density. One of the most studied thermochemical reactions for this application are redox reactions using metallic oxides. The simplicity of using air as heat transfer fluid and reactant comprises important advantages. Among the studied materials, Mn2O3 has been deeply investigated due to its low cost and toxicity, although its reversibility has been shown to be highly deteriorated when exposed to high temperatures. The main negative effects found in the material are grain growth and densification, known as sintering, causing cyclability loss. Doping of ceramic materials has been proven to be an effective technique to control the sintering effects caused by high temperatures, especially in the production of metallurgical products. In this work, the effect of doping Mn2O3 with Si4+ as a sintering inhibitor for thermochemical energy storage has been studied deeply for the first time. The capacity to withstand 40 redox cycles with different quantities of dopant using two different synthesis routes was tested by TGA analysis. As a main result, dopant segregation on the grain boundaries caused a noticeable reduction of the grain growth and particle shrinkage. Additionally, all the doped samples presented a re-oxidation rate improvement. These two effects worked in a synergetic way providing a noticeable improvement on the cycling behavior of the material, which was particularly improved for low Si content (x = 0.02) using sol-gel synthesis method.

Annealing Effect on the Composition and Electrophysical Properties of N-Type Silicon Surface

During low-temperature annealing, the segregation of the alloying element leads to a strong enrichment of the surface layer, causing a rearrangement of the surface electron structure. This change in the electron structure is manifested in the characteristic energy loss spectra. Annealing of single crystals at 400–500 K leads to an increase in the density of surface electron states. As shown by the calculations of the surface potential using experimental data on the temperature dependence of the surface concentration, dopant segregation causes a linear increase in the surface potential.

Deep insight into material-dependent DC performance of Fe DS-SBTFET and its noise analysis in the presence of interface traps

This paper reports the DC performance of Ferroelectric Dopant Segregated Schottky Barrier TFET (Fe DS-SBTFET) for different types of materials in the Dopant Segregated (DS) layer and its noise analysis considering the presence of Gaussian and uniform interface traps with the device being subjected to variation in ferroelectric thickness. Silicon doped HfO2 ferroelectric layer increases the tunneling junction electric field. Maximum ION/IOFF ratio of 1.2 × 109 and 14 mV/dec Subthreshold Swing (SS) have been achieved by using ferroelectric layer of thickness 6 nm. Different electrical parameters such as SS and ION/IOFF ratio have been explored for various trap concentrations. ON state current deteriorates with the increase in trap concentration. The dominancy of different noise components has been analysed with respect to frequency. Both flicker noise and generation-recombination noise contribute to the net noise at low frequency range. Flicker noise dominates at mid frequency and the major contribution at high frequency is of diffusion noise.

Improved Nd distribution in Czochralski grown YAG crystals by implementation of the accelerated crucible rotation technique

Nd:YAG is a well-known laser material typically grown from the melt using the Czochralski (CZ) method, and like many other doped materials grown from the melt, it suffers from dopant segregation, giving an average Nd concentration in the crystal (Nd%) far less than that in the melt, with Nd variation along the growth axis. Here, the Nd segregation issue is addressed by the successful implementation of the Accelerated Crucible Rotation Technique (ACRT) with CZ. Compared to conventional CZ, ACRT provided improved Nd uniformity, higher Nd incorporation, and control of Nd% along the growth axis, even achieving higher Nd% in the crystal than the initial Nd from the overall melt. ACRT also affects the solid/liquid interface shape and thus the radial segregation. It is thus shown that ACRT and the mixing it provides is promising for achieving unconventional dopant profiles in CZ crystals.

Electrochemical Polarization Dependence of the Elastic and Electrostatic Driving Forces to Aliovalent Dopant Segregation on LaMnO3.

Segregation of aliovalent dopant cations is a common degradation pathway on perovskite oxide surfaces in energy conversion and catalysis applications. Here we focus on resolving quantitatively how dopant segregation is affected by oxygen chemical potential, which varies over a wide range in electrochemical and thermochemical energy conversion reactions. We employ electrochemical polarization to tune the oxygen chemical potential over many orders of magnitude. Altering the effective oxygen chemical potential causes the oxygen nonstoichiometry to change in the electrode. This then influences the mechanisms underlying the segregation of aliovalent dopants. These mechanisms are (i) the formation of oxygen vacancies that couples to the electrostatic energy of the dopant in the perovskite lattice and (ii) the elastic energy of the dopant due to cation size mismatch, which also promotes the reaction of the dopant with O2 from the gas phase. The present study resolves these two contributions over a wide range of effective oxygen pressures. Ca-, Sr-, and Ba-doped LaMnO3 are selected as model systems, where the dopants have the same charge but different ionic sizes. We found that there is a transition between the electrostatically and elastically dominated segregation regimes, and the transition shifted to a lower oxygen pressure with increasing cation size. This behavior is consistent with the results of our ab initio thermodynamics calculations. The present study provides quantitative insights into how the elastic energy and the electrostatic energy determine the extent of segregation for a given overpotential and atmosphere relevant to the operating conditions of perovskite oxides in energy conversion applications.

Enlarged growth window for plasmonic silicon-doped InAs using a bismuth surfactant

Semiconductors such as InAs with high dopant concentrations have a variety of applications, including as components of mid-infrared optoelectronic devices. Unfortunately, growth of these materials by molecular beam epitaxy is challenging, requiring high growth rates and low growth temperatures. We show that the use of a bismuth surfactant improves silicon incorporation into InAs while simultaneously reducing the optical scattering rate, increasing the carrier mobility, reducing surface roughness, and enabling growth at higher substrate temperatures and slower growth rates. We explain our findings using microscopic theories of dopant segregation and defect formation in III-V materials.

Interfacial stability and ionic conductivity enhanced by dopant segregation in eutectic ceramics: the role of Gd segregation in doped CeO2/CoO and CeO2/NiO interfaces

Ionic charge balance at the interface of Gd-doped CeO2/CoO eutectic ceramics produces Gd segregation and increases the interfacial ionic conductivity.

3D Simulation for Melt Laser Anneal Integration in FinFET’s Contact

Process integration feasibility of UV nanosecond melt laser annealing (MLA) in 14 nm node generation FinFET's contact for dopant surface segregation and activation is assessed by using a 3D TCAD simulation tool. In a n-type source/drain (S/D) in-situ phosphorous doped epilayer, Sb ion implantation is performed, considering the advantage of its surface segregation in lowering of the contact resistivity. The simulation results show that the heat sources created by the laser irradiation are confined mainly in the replacement metal gate (RMG) part, suggesting a potential interest of controlling the polarization of laser light to enlarge the process window by reducing the laser absorption in the RMG part. Also, the estimated solidification front velocity (V) in the MLA-induced epilayer regrowth (~4 m/s) satisfies the requirements (~1 m/s <; V <; ~15 m/s) to enable the surface segregation and metastable activation of the dopants. The surface segregation is also experimentally confirmed in the FinFET contact module.

Advancing layered cathode material's cycling stability from uniform doping to non-uniform doping

Dopant segregation induced precipitates can further improve the cycling stability of a P2-layered cathode due to the precipitation strengthening effect, which conceptually validates that non-uniform doping has big advantage over uniform doping.

Formation of Nanocomposite Solid Oxide Fuel Cell Cathodes by Preferential Clustering of Cations from a Single Polymeric Precursor.

Conventional composite cathodes used in solid oxide fuel cells (SOFCs) are fabricated by co-sintering of electrocatalyst and ionic conductor powders at 1100-1250 °C. The relatively high-temperature heat treatments required to ensure bonding among the powders and between the powders and electrolyte results in the formation of resistive phases and coarse microstructures corresponding to short triple-phase boundary (TPB) length and, consequently, low oxygen reduction activity. In the present work, to achieve long TPBs and avoid resistive phase formation, we propose to fabricate nanocomposite La0.8Sr0.2MnO3-Ce0.8Sm0.2O2 (LSM-SDC) and La0.8Ca0.2MnO3-Ce0.8Sm0.2O2 (LCM-SDC) thin film cathodes by a low-temperature method, which involves the use of a single polymeric precursor solution containing all the respective cations. Owing to the molecular level mixing and the liquid lack of any powder-based starting material, we envision that preferential clustering of cations forming nanoscale electrocatalyst and ionic conductor particles will take place upon heat treatment at relatively low temperatures of 600-800 °C. Here, we report for the first time in the literature, a correlation between the heat-treatment temperature-phase evolution-cluster formation-surface chemistry evolution and electrochemical activity of nanocomposite thin film cathodes fabricated from a single polymeric precursor. Our experiments reveal that highest electrochemical activity is achieved when the electrocatalyst phase is poorly crystallized, complete clustering of cations takes place, and A-site dopant segregation at the surface is minimal.

Thermal Stability Enhancement of NiGe Metal Source/Drain and Ge pMOSFETs by Dopant Segregation

The thermal stability has been investigated for the NiGe–n-Ge junctions with and without the dopant segregation (DS). It is found that the B DS sufficiently improves the thermal tolerance of the NiGe–n-Ge junctions, and the DS NiGe–n-Ge junctions can be stabilized up to 550 °C. This phenomenon suggests that the DS NiGe metal source/drain (S/D) is a feasible structure for broadening the processing window of future high-performance Ge MOSFETs.

Fabrication of IGBTs using 300 mm magnetic Czochralski substrates

Up to now the vast majority of insulated gate bipolar transistors (IGBTs) has been produced on silicon (Si) wafers out of the float-zone (FZ) process. FZ crystals can easily be used for this application, but are only available with a diameter of up to 200 mm. However, the use of wafer substrates with a diameter of 300 mm offers a significant increase in productivity and is therefore the diameter of choice for the high-volume production of CMOS devices. In order to benefit from this advantage also for the manufacturing of IGBTs, material out of the magnetic Czochralski process, which is available in 300 mm, had to be adapted. Key issues include crystal originated particles, dopant segregation along the crystal axis, and the higher concentration of oxygen. In particular, the implementation of the field-stop zone by the implantation of protons will lead to the additional formation of hydrogen-decorated C I O I complexes which can act electrically as donors. However, by an appropriate adjustment of the processing parameters the electrical characteristics of IGBTs on FZ substrates can be well reproduced.

Size effect of electronic properties in highly arsenic-doped silicon nanowires

The unique electrostatic properties of semiconductor nanowires enable the realization of novel transistor types by the possibility to use surround gate architectures resembling ideal gate electrostatic control. Nevertheless one fundamental issue of semiconducting nanowire channels is the reliable control of doping to adjust the charge carrier concentration. Indeed, as dimensions scale down the surrounding media and the interfaces become more important. In this study we experimentally investigate the role of surface depletion and dielectric mismatch on the electronic charge transport of highly arsenic doped and bottom-up grown silicon nanowires. Electrical characterization of silicon nanowires (SiNWs) synthesized by Au catalyzed vapour-liquid-solid (VLS) growth and in-situ arsine (AsH3) doping is reported for the first time. We demonstrate that high n-type doping is possible by adjusting the dopant precursor flow ratio during growth. Based on electrical measurements of individual nanowires, reproducible donor concentrations of up to 5.2 × 1019 cm−3 could be revealed. By measuring the electrical characteristics for individual nanowires in dependence of their radius, we show that the electrically active carrier density drastically reduces for small nanowires at radii much larger than those at which quantization or dopant surface segregation effects are expected to occur. Furthermore, enhancement of the contact transparency for small radii nanowires is demonstrated through dopant segregation upon metal silicidation. Size dependent measurement of electrical characteristics revealed improved contact resistivities as low as 1.4 × 10−11 Ωm2.

Surface segregated Ga, In, and Al activation in high Ge content SiGe during UV melt laser induced non-equilibrium solidification

The impact of solidification front velocity (SFV) on dopant segregation and activation surpassing the equilibrium solid solubility limit was investigated in high Ge content SiGe using UV nanosecond melt laser annealing (MLA). We first simulated the SFV evolution in the MLA-induced solidification of a SiGe binary system. It was then combined with the near-surface atomic and electrically active dopant concentrations measured in the Ga, In, and Al-implanted SiGe after MLA. Solute trapping phenomenon and self-compensation effect of the dopants were discussed to capture a part of their segregation and activation dynamics in the presented SiGeX ternary systems.

Nanostructured potential well/barrier engineering for realizing unprecedentedly large thermoelectric power factors

This work describes, through the semi-classical Boltzmann transport theory and simulation, a novel nanostructured material design that can lead to unprecedentedly high thermoelectric power factors, with improvements of more than an order of magnitude compared to optimal bulk material power factors. The design is based on a specific grain/grain-boundary (potential well/barrier) engineering such that: i) carrier energy filtering is achieved using potential barriers, combined with ii) higher than usual doping operating conditions such that high carrier velocities and mean-free-paths are utilized, iii) minimal carrier energy relaxation is achieved after passing over the barriers to propagate the high Seebeck coefficient of the barriers into the potential wells, and, importantly, iv) an intermediate dopant-free (depleted) region is formed. Thus, the design consists of a ‘three-region geometry’, in which the high doping resides in the center/core of the potential well, with a dopant-depleted region separating the doped region from the potential barriers. It is shown that the filtering barriers are optimal when they mitigate the reduction in conductivity they introduce, and this can be done primarily when they are ‘clean’ from dopants during the process of filtering. The potential wells, on the other hand, are optimal when they mitigate the reduced Seebeck coefficient they introduce by: i) not allowing carrier energy relaxation, and ii) mitigating the reduction in mobility that the high concentration of dopant impurities causes. It is shown that dopant segregation, with ‘clean’ dopant-depletion regions around the potential barriers, serves this key purpose of improved mobility toward the phonon-limited mobility levels in the wells. Using quantum transport simulations based on the non-equilibrium Green's function method as well as semi-classical Monte Carlo simulations, we also verify the important ingredients and validate this ‘clean-filtering’ design.

Dopant Segregation Boosting High-Voltage Cyclability of Layered Cathode for Sodium Ion Batteries.

As a widely used approach to modify a material's bulk properties, doping can effectively improve electrochemical properties and structural stability of various cathodes for rechargeable batteries, which usually empirically favors a uniform distribution of dopants. It is reported that dopant aggregation effectively boosts the cyclability of a Mg-doped P2-type layered cathode (Na0.67 Ni0.33 Mn0.67 O2 ). Experimental characterization and calculation consistently reveal that randomly distributed Mg dopants tend to segregate into the Na-layer during high-voltage cycling, leading to the formation of high-density precipitates. Intriguingly, such Mg-enriched precipitates, acting as 3D network pillars, can further enhance a material's mechanical strength, suppress cracking, and consequently benefit cyclability. This work not only deepens the understanding on dopant evolution but also offers a conceptually new approach by utilizing precipitation strengthening design to counter cracking related degradation and improve high-voltage cyclability of layered cathodes.

Impacts of Ge Preamorphization Implantation and Si Capping on the Specific Contact Resistivity of Ni(Pt)SiGe/p+-SiGe Contacts

This article explores the impacts of both Ge preamorphization implantation (PAI) and Si capping on the specific contact resistivity ( $\rho _{c}$ ) of Ni(Pt)SiGe/p+-SiGe contacts elaborately. Both Ge PAI and Si capping are found to be beneficial in reducing the $\rho _{c}$ of Ni(Pt)SiGe/p+-SiGe contacts remarkably, with $\rho _{c}$ values reduced from the original ${20.03} \times {10}^{-{8}} \Omega $ -cm2 to ${9.92} \times {10}^{-{8}}\,\,\Omega $ -cm2 with Ge PAI and ${1.44} \times {10}^{-{8}} \Omega $ -cm2 with Si capping, respectively. Improved interfacial uniformity and morphology are thought to be primarily responsible for such significant reductions in $\rho _{c}$ since neither Ge PAI nor Si capping induces an obvious difference in B concentrations at the interface of Ni(Pt)SiGe/p+-SiGe. Moreover, by combining Ge PAI or Si capping with extra B implantation before germanosilicidation to intentionally introduce B dopant segregation (DS) at the interface of Ni(Pt)SiGe/p+-SiGe contacts, further reduction of $\rho _{c}$ values is accomplished as anticipated.

Contact Resistance Improvement for Advanced Logic by Integration of Epi, Implant and Anneal Innovations

ABSTRACTAs advanced CMOS scaling with FinFETs continues beyond the 10/7nm nodes, contact resistance (Rc) remains a dominant component affecting device performance. The FinFET Source/Drain (S/D) contact area has become smaller with fin pitch scaling, resulting in drastically increased Rc. To achieve higher drive currents and fully realize the performance gain from FinFET architectural changes, it is critical to continue to reduce contact resistivity (ρc) &lt; 1.0x10-9 Ω.cm2 for both NMOS and PMOS. In this paper, we review the recent trends for ρc reduction for advanced CMOS devices and discuss approaches that have demonstrated reduction in ρc, such as in-situ heavily doped epitaxial films for S/D, advanced ion implantation and laser anneals. The implant techniques include pre-amorphization implants (PAI), dopant boosting implants, cryogenic (-100°C) implants for damage engineering and plasma doping (PLAD) for conformal doping of high aspect ratio (HAR) contacts. With such high levels of doping from epi and implants, advanced laser anneals are key for epitaxial regrowth and formation of metastable alloys for dopant supersaturation or segregation in top layers. Millisecond laser anneal (MSA) improves dopant activation and nanosecond laser anneal (NLA) permits superactivation, and both have become key enablers for ρc reduction. This paper also reviews two alternative contact approaches: dual silicide scheme and wrap-around contact (WAC), as potential pathways to further reduce Rc for advanced CMOS nodes.

Revealing the Doping Effect in Stabilizing Layered Cathode Materials for Sodium-Ion Battery

Energy storage devices allow us to use energy in a flexible, high efficient and eco-benign way, which has profoundly shaped our everyday life. The most successful energy storage device is lithium-ion battery (LIB), which has dominated the portable electronic devices and are now penetrating deep into vehicle markets. However, the limited reserves of lithium and cobalt in the earth crust cannot fulfill the huge demand gap of electrochemical energy storage, and the fast expansion of LIB industry has already led to accelerated cost rising. Therefore, worldwide research programs strategically encourage the development of energy storage devices beyond LIB, among of which, sodium ion battery (SIB) is a very attractive one. Sodium is much more natural abundance and more importantly SIB industry can share facilities and technologies from LIB because of the similarities of physical and chemical properties between Li and Na. To achieve superior performance of SIB, high performance cathode material plays a critical role. Among of variety of cathode candidates, layered NaxTMO2 (TM refers to transition metal) oxides are promising and widely studied, which can be grouped into two families, P2-type and O3-type structures. However, one critical drawback for both P2-type and O3-type layered oxides is the multi-phase-transition reactions during charge/discharge, which leads to the annoying multi-voltage-plateaus in voltage-capacity profiles. Various ordering processes (TM ordering, charge ordering and Na-vacancy ordering) and structure transitions (P2-O2, O3-P3, et al) have been identified previously. The structural ordering will result in sluggish Na-ion transportation kinetics and it can further couple with the structural transformation to collectively cause structural instability, significantly plaguing the cycling performance. Therefore, many efforts have been taken to suppress the structural ordering and transformation, namely eliminating the multi-voltage-plateaus in the charge/discharge profile. Particularly for P2-Na2/3Ni1/3Mn2/3O2 (NNM), doping electrochemically inactive elements (Li, Mg, Cu or Zn) is proven to be an effective approach to suppress the P2-O2 phase transition and Na-vacancy ordering to achieve improved electrochemical performance. In this work, by virtue of variety of analytical tools, such as X-ray diffraction (XRD), focused ion beam/scanning electron microscopy (FIB/SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) imaging, we conduct systematic investigations on the degradation mechanisms of P2-NNM and find that P2-O2 phase transition induced grain cracking is the main cause of performance decay. Our further investigations on the role of dopant on P2-Na0.67Ni0.33-xMn0.67MgxO2 (x=0, 0.05, 0.1) (P2-NMMx) and find that doping electrochemically inactive elements can suppress intragranular cracking to improve cycle stability of P2-NM. we show that dopants segregation is more effectively to suppress intragranular crack and improve cycling stability than dopant uniform distribution in TM layer. By virtue of variety of analytical tools and simulation, dopant segregation have been characterized comprehensively and come up a new strategy, precipitation strengthening mechanism, to alleviate electrochemomechanical degradation and enhance stability of layered cathode operating at high voltage.

Amorphous Intergranular Films Enable the Creation of Bulk Nanocrystalline Cu–Zr with Full Density

Nanocrystalline metal alloys show great potential as structural materials, but are often only available in small volumes, such as thin films or powders. However, recent research has suggested that dopant segregation and grain boundary structural transitions between states known as complexions can dramatically alter grain size stability and potentially enable activated sintering. Herein, strategic consolidation routes for mechanically alloyed Cu‐4 at% Zr powders are explored to capture the effects of amorphous complexion formation on the densification of bulk nanostructured metals. An increase in the density of the consolidated samples is observed, which coincides with the formation of amorphous intergranular films. At the same time, the grain size is reasonably stable after exposure to these temperatures. As a result, a bulk nanograined metal with a grain size of 57 nm and a density of 99.8% is produced, which shows an impressive balance of small grain size and high density using simple consolidation techniques.