Range Of Doping Concentrations Research Articles

A surface-potential based drain current model for short-channel symmetric double-gate junctionless transistor

Junctionless transistors, which do not have any pn junction in the source-channel-drain path have become an attractive candidate in sub-20 nm regime. They have homogeneous and uniform doping in source-channel-drain region. Despite some similarities with conventional MOSFETs, the charge-potential relationship is quite different in a junctionless transistor, due to its different operational principle. In this report, models for potential and drain current are formulated for shorter channel symmetric double-gate junctionless transistor (DGJLT). The potential model is derived from two dimensional Poisson's equation using "variable separation technique". The developed model captures the physics in all regions of device operation i.e., depletion to accumulation region without any fitting parameter. The model is valid for a range of channel doping concentrations, channel thickness and channel length. Threshold voltage and drain-induced barrier lowering values are extracted from the potential model. The model is in good agreement with professional TCAD simulation results.

Finite Element Modelling of the Electrical Conductivity of Fluorite-Type Oxygen Ion Conductors

Oxygen ion conductors of the fluorite structure, like acceptor doped zirconia or ceria, are the major electrolyte materials for SOFCs. However, the influence of dopant concentration, temperature, oxygen partial pressure and microstructure on these material’s electrical conductivity is still not fully understood [1]. While theory and experiments generally agree on the influence of the first three parameters, the influence of the microstructure remains controversial. Some researchers predict a higher conductivity for nanocrystalline materials [2]. Indeed, the diffusivity of charge carriers, vacancies and mobile ions, is greater along the grain boundary and the grain boundary density increases with decreasing grain size [3]. However, most experiments show the opposite trend where conductivity decreases with decreasing grain size [1], [4]. A reliable model of the material’s electrical conductivity is thus necessary to interpret the existing measurements and to predict the optimal material architecture for use as an SOFC electrolyte. Until now, modelling of the electrical conductivity of these materials relies on the analytical solution of the dilute solution model [1]. This approach yields useful insights but it also has multiple drawbacks. First of all dilute solution theory is invalid at high doping percentages, which makes it impossible to predict the conductivity trend over a large range of dopant concentrations. Moreover experiments clearly show that the electrical conductivity reaches a maximum at a certain dopant concentration and declines when the doping percentage is further increased. This phenomenon is qualitatively explained through an association mechanism between dopant ions and vacancies. We observe that the implementation of such a mechanism in the dilute solution model leads however to an asymptotic maximal conductivity and not to a distinct maximum. It is generally accepted that the grain boundary is enriched in vacancies relative to the grain interior, which leads to a potential difference between both regions. In existing models, this potential difference is imposed as a boundary condition to arrive at a closed form analytical solution. This approach is unable to treat very small grains; below a certain grain size bulk vacancy concentrations are not reached inside the bulk and thus there exists no reference level for the potential difference. The same problem arises when a bias current is applied to the sample; analytical models can only predict the electrical conductivity when the material is not conducting a net current. We propose a model based on the linear phenomenological relations for a crystal lattice [5]. This model respects the crystalline nature of the material where only a limited number of lattice sites are available to the charge carriers, and a lattice site can only accommodate one charge carrier at a time. As a result, our model predicts a distinct maximum in the electrical conductivity when a dopant-vacancy association mechanism is implemented. We show that this maximum exists because the association not only limits the amount of available charge carriers, but also the amount of available diffusion paths. The doping percentage for which maximum conductivity is reached is dependent on the operating temperature. The finite element method is used to solve our model on one-dimensional geometries. This numerical approach enables us to treat grains of arbitrarily small size and to predict electrical conductivities at any applied current density. We show that the ionic conductivity of a sample perpendicular to the grain boundary decreases with decreasing grain size. The grain boundary conductivity itself is independent of grain size, except for very small grains and small dopant concentrations. The results predicted by our model are in good agreement with the available measurements in literature over a large range of dopant concentrations and temperatures. Our model is thus a good tool to interpret measurement data and to improve our understanding of these materials. The final goal of the model is designing optimal solid electrolytes. [1] X. Guo and R. Waser, “Electrical properties of the grain boundaries of oxygen ion conductors: Acceptor-doped zirconia and ceria,” Progress in Materials Science, vol. 51, no. 2, pp. 151–210, 2006. [2] J. Maier, “Ionic conduction in space charge regions,” Progress in solid state chemistry, vol. 23, no. 3, pp. 171–263, 1995. [3] H. Mehrer, Diffusion in solids: fundamentals, methods, materials, diffusion-controlled processes, vol. 155. Springer, 2007. [4] C. Peters, A. Weber, B. Butz, D. Gerthsen, and E. Ivers-Tiffée, “Grain-Size Effects in YSZ Thin-Film Electrolytes,” Journal of the American Ceramic Society, vol. 92, no. 9, pp. 2017–2024, 2009. [5] D. Van Laethem, J. Deconinck, A. Hubin, D. Depla, “Finite element modelling of the ionic conductivity of acceptor doped ceria”, In preparation.

Focus on software and semiconductor equipment

Focus on software and semiconductor equipment

First-principle study on the effect of high Ag–2N co-doping on the conductivity of ZnO

The geometric structure, band structure (BS) and density of state (DOS) of pure and p-type co-doping wurtzite ZnO have been investigated by the first-principle ultrasoft pseudopotential method with the generalized gradient approximation. These structures induce fully occupied defect states above the valence-band maximum of doped ZnO. The calculation results show 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 Ag–2N in ZnO. Our findings suggest that co-doping of Ag–2N could efficiently enhance the N dopant solubility and is likely to yield better p-type conductivity.

DFT and two-dimensional correlation analysis methods for evaluating the Pu3+–Pu4+ electronic transition of plutonium-doped zircon

Understanding how plutonium (Pu) doping affects the crystalline zircon structure is very important for risk management. However, so far, there have been only a very limited number of reports of the quantitative simulation of the effects of the Pu charge and concentration on the phase transition. In this study, we used density functional theory (DFT), virtual crystal approximation (VCA), and two-dimensional correlation analysis (2D-CA) techniques to calculate the origins of the structural and electronic transitions of Zr1−cPucSiO4 over a wide range of Pu doping concentrations (c=0–10mol%). The calculations indicated that the low-angular-momentum Pu-fxy-shell electron excites an inner-shell O-2s2 orbital to create an oxygen defect (VO-s) below c=2.8mol%. This oxygen defect then captures a low-angular-momentum Zr-5p65s2 electron to form an sp hybrid orbital, which exhibits a stable phase structure. When c>2.8mol%, each accumulated VO-p defect captures a high-angular-momentum Zr-4dz electron and two Si-pz electrons to create delocalized Si4+→Si2+ charge disproportionation. Therefore, we suggest that the optimal amount of Pu cannot exceed 7.5mol% because of the formation of a mixture of ZrO8 polyhedral and SiO4 tetrahedral phases with the orientation (10-1). This study offers new perspective on the development of highly stable zircon-based solid solution materials.

Near-infrared absorption–emission cross-sections of PbSe quantum dots doped in UV gel

We measure near-infrared absorption spectra of PbSe quantum dots (QDs) with three sizes (4.5, 5.0, and 5.6nm) doped in UV gel with the concentration of 0.25–1.50mgmL−1 by using an absorption-spectrum method. An empirical formula is proposed to describe the correlation of the first–second absorption-peak wavelengths and QD size. The peak-absorption cross-section is measured as 2.76–3.69×10−16cm2 for 5.6-nm QD, and the absorption coefficient ranges in 0.19–0.59cm−1, both associated with the doping concentration and the QD size. Furthermore, the emission cross-sections are determined by measuring the photoluminescence spectra of QDs and using the McCumber relationship, which depend weakly on both the doping concentration and the QD size. For 5.6-nm QD, the measured peak-emission cross-section is 3.36–4.48×10−16cm2 within the range of experimental doping concentration.

Analytical model for silicon-on-insulator lateral high-voltage devices using variation of lateral thickness technique

Recently, the variation of lateral thickness (VLT) technique has been proposed as an effective lateral voltage-sustaining technology. However, no analytical model has been reported for exploring the physical mechanism quantitatively. By solving the two-dimensional (2D) Poisson equation, an analytical model for a silicon-on-insulator (SOI) device with a VLT structure is proposed in this paper to optimize the surface potential and electric field distribution of the VLT SOI device. The lateral and vertical breakdown voltages are formulized to quantify the breakdown characteristic. The drift doping concentration range is derived to maximize the breakdown voltage. This model is used to investigate the electric field distribution and breakdown voltage of the VLT SOI device with various parameters. The validity of the proposed model is verified by the fair agreement between the analytical and numerical results.

Passivation of phosphorus diffused silicon surfaces with Al2O3: Influence of surface doping concentration and thermal activation treatments

Thin layers of Al2O3 are well known for the excellent passivation of p-type c-Si surfaces including highly doped p+ emitters, due to a high density of fixed negative charges. Recent results indicate that Al2O3 can also provide a good passivation of certain phosphorus-diffused n+ c-Si surfaces. In this work, we studied the recombination at Al2O3 passivated n+ surfaces theoretically with device simulations and experimentally for Al2O3 deposited with atomic layer deposition. The simulation results indicate that there is a certain surface doping concentration, where the recombination is maximal due to depletion or weak inversion of the charge carriers at the c-Si/Al2O3 interface. This pronounced maximum was also observed experimentally for n+ surfaces passivated either with Al2O3 single layers or stacks of Al2O3 capped by SiNx, when activated with a low temperature anneal (425 °C). In contrast, for Al2O3/SiNx stacks activated with a short high-temperature firing process (800 °C) a significant lower surface recombination was observed for most n+ diffusion profiles without such a pronounced maximum. Based on experimentally determined interface properties and simulation results, we attribute this superior passivation quality after firing to a better chemical surface passivation, quantified by a lower interface defect density, in combination with a lower density of negative fixed charges. These experimental results reveal that Al2O3/SiNx stacks can provide not only excellent passivation on p+ surfaces but also on n+ surfaces for a wide range of surface doping concentrations when activated with short high-temperature treatments.

On the kinetics of electron processes in 60Co γ-irradiated n-Ge single crystals

Variations in the main electrical parameters of n-Ge single crystals with different doping levels under the effect of 60Co γ-irradiation are investigated. A noticeable increase in the carrier mobility in the irradiated samples is observed in some dopant concentration range and the nature of this effect is explained. It is demonstrated that the electron-mobility variation under the action of γ-irradiation in the initial n-Ge crystals with an oxygen impurity and in the annealed crystals have opposite signs. It is established that the oxygen complexes formed in the samples during annealing and the local lattice stresses near these complexes play a key role in the radiation-induced mobility increase. It is clarified that the radiation resistance of the electron mobility significantly depends on the crystallographic orientation of the investigated samples.

Highly efficient and concentration-insensitive organic light-emitting devices based on self-quenching-resistant orange–red iridium complex

Orange–red phosphorescent organic light-emitting devices (PHOLEDs) with high efficiency and concentration insensitivity based on a novel iridium complex, bis[2-(biphenyl-4-yl)benzothiazole-N,C2′]iridium(III) (acetylacetonate) [(4Phbt)2Ir(acac)], were fabricated. With the heavily doped emissive layer (EML) of 4,4′-N,N′-dicarbazolylbiphenyl (CBP): (4Phbt)2Ir(acac) in a wide and easily controlled dopant concentration range from 12wt% to 24wt%, a maximum power efficiency of 29lm/W and an external quantum efficiency of >16% of the PHOLEDs were obtained, implying the insensitivity of electroluminescence (EL) properties to doping concentration. Meanwhile, a maximum power efficiency of 5.0lm/W was achieved from a non-doped device with neat (4Phbt)2Ir(acac) as the EML, indicating a superior property of self-quenching resistance. The mechanism of direct exciton formation, in which exciton-formation regions are distributed throughout the EML, is responsible for the significant alleviation of triplet–triplet annihilation and superior EL performance.

Surface characterization of sputtered N:TiO2 thin films within a wide range of dopant concentration

Nitrogen-doped titanium dioxide thin films were deposited using a new approach, which involves the sputtering of a sintered TiN target in a reactive DC magnetron discharge running in O2/Ar mixtures. Based on the higher chemical affinity of titanium for oxygen compared to nitrogen, samples with N concentrations ranging between 1.1 and 9.3 at% were conveniently prepared by adjusting the gas composition in the deposition chamber. Surface characterization of the prepared thin films was done by using X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements, while film crystallinity was checked with an X-ray diffraction. The current results show how the dopant content can be controlled by adjusting the oxygen intake in the films during reactive discharge deposition. The XPS spectra clearly show that nitrogen–titanium bonds are formed. Nitrogen doping induces broadening of the valence band, and, consequently, narrowing of TiO2 band gap. Additionally, doping affects the surface morphology, as demonstrated by atomic force microscopy and contact angle data. The effect of carbon contaminant removal under UV irradiation on the hydrophilic conversion process is discussed.

Structural and electrical properties of Sn-doped Ga1.375In0.625O3 with different doping concentrations

The structural properties, band structure and density of states of Sn-doped Ga1.375In0.625O3 with different doping concentrations are studied by using the first-principle method. Results show that the lattice parameters have a tendency to increase due to the introduction of Sn dopant. There is a strong ionic bonding between O atoms and Sn atoms and the charge transports from Sn atoms to O atoms. Due to the heavy doping, the Fermi level of Sn-doped Ga1.375In0.625O3 shifts into the conduction band, and the n-type metallic conductivity is exhibited. The band tail of the new degenerate bands extends into the forbidden band, resulting in the band gap narrowing effect. In the heavy doping concentration range of 2.5–5 at%, the calculated electron effective mass slightly changes, the relative electron number increases, and the electron mobility decreases. Thus, the conductivity of Sn-doped Ga1.375In0.625O3 is enhanced slightly.

Research on Characteristics of the Photovoltaic Cells Integrated on Chip

The influence factors of Photovoltaic (PV) cells characteristics integrated on chip were analyzed based on the fabrication process and the structure of the PV cells and CMOS devices. The results show the substrate doping concentration, the emitter doping concentration, the emitter junction depth and the thickness of device layer directly determine the conversion efficiency, open voltage and the light-generated current of photovoltaic cells. In the emitter doping concentration range of 1×1019/cm3 to 1×1021/cm3 and the substrate doping concentration range of 1.0×1015/cm3 to 1.0×1017/cm3, the Photovoltaic cells have batter conversion characteristics. The PV cells were designed based on the analysis results in PC1D, and the conversion efficiency is 9.43%. The Photovoltaic cells and the CMOS devices have batter fabrication technology compatibility integrated on chip.

A positron annihilation spectroscopic investigation of europium-doped cerium oxide nanoparticles

Doping in ceria (CeO2) nanoparticles with europium (Eu) of varying concentrations (0, 0.1, 0.5, …, 50 atom%) is studied using complementary experimental techniques and novel observations were made during the investigation. The immediate observable effect was a distinct reduction in particle sizes with increasing Eu concentration attributed to the relaxation of strain introduced due to the replacement of Ce(4+) ions by Eu(3+) ions of larger radius. However, this general trend was reversed in the doping concentration range of 0.1-1 atom% due to the reduction of Ce(4+) to Ce(3+) and the formation of anion vacancies. Quantum confinement effects became evident with the increase of band gap energy when the particle sizes reduced below 7-8 nm. Positron annihilation studies indicated the presence of vacancy type defects in the form of vacancy clusters within the nanoparticles. Some positron annihilation was also seen on the surface of crystallites as a result of diffusion of thermalized positrons before annihilation. Coincidence Doppler broadening measurements indicated the annihilation of positrons with electrons of different species of atoms and the characteristic S-W plot showed a kink-like feature at the particle sizes where quantum confinement effects began.

Role of upconversion in optical refrigeration: A theoretical study of laser cooling with Ho^3+ doped fluoride crystals

We present a generalized model for optical refrigeration with Ho3+ doped fluoride crystals in which the dopant concentration dependent upconversion is considered. Based on the spectrum properties of candidate rare-earth ions (Ho3+, Tm3+, and Er3+) for optical refrigeration, a common criterion for upconversion assisted cooling is derived. The cooling performances of Ho3+:YLiF4 crystals are simulated to reveal the practical dopant concentration range for cooling. It is found that the optimal dopant concentration is determined by a balancing consideration of heat loads induced by background absorption and fluorescence quenching. The appropriate pump wavelengths for optical refrigeration with Ho3+:YLiF4 crystals are also indicated.

The Impact of Body Doping Concentration on the Performance of Nano Dg-Mosfets: A Quantum Simulation

This paper presents the effects of p-type body doping concentration on a symmetric double-gate MOSFET with 9 nm gate length, using full quantum simulation. The simulations are based on a self-consistent solution of the 2D Poisson equation and Schrodinger equation with open boundary conditions, within the non-equilibrium Green's function formalism for a wide range of channel doping concentrations. The effects of varying the p-type body doping concentration parameter is investigated in terms of the drain current, potential energy profile, 2D electron density, on-off current ratio, subthreshold swing, drain induced barrier lowering, transconductance, drain conductance, voltage gain, and resistance. The simulation results show that a higher body doping improves the short channel effects.

First-principles study on the effect of high In 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 In-doped supercells of Zn0.9375In0.0625O and Zn0.875In0.125O are constructed, and the geometry optimizations of the three models are carried out. The total density of states (DOS) and the band structures (BS) are also calculated. The calculation results show that in the range of high doping concentration, when the doping concentration is hihger than a specific value, the conductivity decreases with the increase of the doping concentration of In in ZnO, which is in consistence with the change trend of the experimental results.

A First-Principles Investigation of the Carrier Doping Effect on the Magnetic Properties of Defective Graphene

The carrier doping effects on the magnetic properties of defective graphene with a hydrogen chemisorbed single-atom vacancy (H-GSV) are investigated by performing extensive spin-polarized first-principles calculations. Theoretical results show that the quasi-localized pz-derived states around the Fermi level are responsible for the weakened magnetic moment (MM) and magnetic stabilized energy (MSE) of the H-GSV under carrier doping. The mechanism of reduced MSE in the carrier doped H-GSV can be well understood by the Heisenberg magnetic coupling model due to the response of these pz-derived states to the carrier doping. Within the examined range of carrier doping concentration, the total MM of H-GSV is always larger than 1.0μB with μB representing the Bohr magneton, which is mainly contributed by the localized sp2 states of the unsaturated C atom around the vacancy. These findings of H-GSV provide fundamental insight into defective graphene and help to understand the related experimental observations.

Concentration-insensitive and low-driving-voltage OLEDs with high efficiency and little efficiency roll-off using a bipolar phosphorescent emitter

A series of simplified trilayer phosphorescent organic light-emitting diodes (PHOLEDs) with high efficiency and little efficiency roll-off based on a bipolar iridium emitter Iridium(III) bis(2-phenylpyridinato)-N,N′-diisopropyl-diisopropyl-guanidinate (ppy)2Ir(dipig) has been demonstrated. They are dominated by the efficient direct-exciton-formation mechanism and show gratifying concentration-insensitive and low-driving-voltage features. In particular, very high and stable electroluminescence (EL) efficiencies (maximum power efficiency and external quantum efficiency >98lmW−1 and 25% respectively, and external quantum efficiency >20% over a wide luminance range of 1–15,000cdm−2) are achieved in the PHOLEDs based on emitting layers (EMLs) consisting of (ppy)2Ir(dipig) codeposited with common host CBP in an easily controlled doping concentration range (15–30wt%). The EL performance of the PHOLEDs is comparable to the highest PHOLEDs reported in scientific literature.

The effect of Cr dopant concentration on electrical property of (V1−xCrx)2O3 nano-grain ceramics

A series of (V1−xCrx)2O3 ceramics (x=0.0035, 0.0053, 0.0060, 0.0083 and 0.0095) have been prepared by a chemical doping route. XRD patterns and the lattice parameters of all samples confirm that Cr(III) enter the V2O3 lattice. The AFM micrographs show that the obtained ceramics have a hierarchical structure: the agglomerates are about 1–2μm in size consisting of spherical particles with diameters of about 65–85nm. The result of resistivity measurement reveals that the ceramics with the dopant concentration range (0.0035<x≤0.0080) obtained at 1523K for 45min possess good PTC properties and their resistivity jump are in the range of 1.0×102–7.5×102. The good PTC effect is attributed to the nano-size grains and the hierarchical structure. It is found that the dopant concentration range is much narrower than that (0.005<x<0.018) in (V1−xCrx)2O3 micro-grain ceramics and single-crystals.