Si Lattice Research Articles

Sub-Nanometer Line Width and Line Profile Measurement Using STEM Images with Metal Coating

The novel method of sub-nanometer uncertainty for the line width and line profile measurement using STEM (Scanning Transmission Electron Microscope) images is proposed to calibrate CD-SEM line width measurement. In accordance with the proposed method, the traceability and reference metrology of line width measurements are established using Si lattice structures. The interface of SiO2-Air is defined using image intensity of STEM image after metal coating. The edge positions of the Si line from top to bottom are detected. Then, the pixel size of the images is evaluated using 2D Fourier analysis for Si lattice structures. Using the proposed method, the line profile and line width of 50 nm are measured with expanded uncertainty less than 0.3 nm.

Enhancement of room temperature ferromagnetism in Mn-implanted Si by He implantation

Room temperature ferromagnetism in Mn-implanted p-Si was enhanced dramatically by implantation of He. A 75 nm end-of-range region was found in the sample, with large scale and inhomogeneous damaging but preserved Si lattice periodicity. The end-of-range region shows an intrinsic magnetization of ∼100 emu/cm3. High resolution transmission electron microscopy and x-ray photoelectron spectroscopy measurements indicate that the spin polarization of Si dangling bonds rather than Mn impurity was the major source for the enhanced magnetism.

Characterization of Silicon Surfaces Implanted with Antimony Ions and Submitted to Annealing and Ageing Treatments

In this work, we study the effect of annealing and ageing treatments on the behavior of antimony atoms implanted in Si(111) targets. The ion implantation was performed at 120 keV energy to a dose of 2.3 x 10(15) Sb+ cm(-2). Concerning the annealing treatment, it has been carried out at 900 degrees C during 30 minutes (under vacuum). The samples have been analyzed in two steps: immediately after their elaboration and after an ageing period of 4 years and 4 months. Several techniques have been applied for samples analysis: Rutherford backscattering spectroscopy (RBS), X-ray diffraction (XRD) and electrical measurements. Before the ageing period, a good recovery of radiation damage has been obtained and degrees 50% of the dopant was redistributed into substitutional silicon sites. However, degrees 22% of antimony has been lost from the Si substrates. After the ageing period, the fraction of substituted atoms remained unchanged but a quantity of approximately 20% has again been lost from the specimens. This quantity provided from antimony atoms which remained into irregular positions of Si lattice.

Two-stage model of nanocone formation on a surface of elementary semiconductors by laser radiation

In this work, we study the mechanism of nanocone formation on a surface of elementary semiconductors by Nd:YAG laser radiation. Our previous investigations of SiGe and CdZnTe solid solutions have shown that nanocone formation mechanism is characterized by two stages. The first stage is characterized by formation of heterostructure, for example, Ge/Si heterostructure from SiGe solid solutions, and the second stage is characterized by formation of nanocones by mechanical plastic deformation of the compressed Ge layer on Si due to mismatch of Si and Ge crystalline lattices. The mechanism of nanocone formation for elementary semiconductors is not clear until now. Therefore, the main goal of our investigations is to study the stages of nanocone formation in elementary semiconductors. A new mechanism of p-n junction formation by laser radiation in the elementary semiconductor as a first stage of nanocone formation is proposed. We explain this effect by the following way: p-n junction is formed by generation and redistribution of intrinsic point defects in temperature gradient field – the thermogradient effect, which is caused by strongly absorbed laser radiation. According to the thermogradient effect, interstitial atoms drift towards the irradiated surface, but vacancies drift to the opposite direction – in the bulk of semiconductor. Since interstitials in Ge crystal are of n-type and vacancies are known to be of p-type, a n-p junction is formed. The mechanism is confirmed by the appearance of diode-like current–voltage characteristics after i-Ge irradiation crystal by laser radiation. The mechanism in Si is confirmed by conductivity type inversion and increased microhardness of Si crystal. The second stage of nanocone formation is laser heating up of top layer enriched by interstitial atoms with its further plastic deformation due to compressive stress caused by interstitials in the top layer and vacancies in the buried layer.

Crystalline Silicon under Acoustic Cavitation: From Mechanoluminescence to Amorphization

The physicochemical behavior of crystalline silicon under acoustic cavitation is investigated in water sparged with argon at low temperature (10 and 20 °C). Surprisingly, spectroscopic investigations reveal that argon (bubbling continuously through the liquid phase during experiments) can be ultrasonically excited via mechanoluminescence, i.e., emission of light caused by mechanical action on a solid. This phenomenon is highlighted for the first time on an extended solid surface using these conditions and results from an interaction between the acoustically generated bubbles and the Si surface. The concomitant physical and chemical transformations induced at the solid–liquid interface are investigated (SEM, AFM) to characterize the generated stress and defects in combination with the roughness and wettability increases (evolving from ∼46° to ∼4°). Phase transformations of the Si lattice are observed (Raman spectroscopy, TEM) evidencing the complex stress state induced by acoustic cavitation in the Si crys...

Interface properties of a-SiNx:H/Si to improve surface passivation

Nitridation is the process in which, during the initial growth of a-SiNx:H layers on Si surfaces, nitrogen is incorporated into the Si lattice near its surface. We show that this nitridation process affects the density of interface states (Dit) and fixed charges (Qf) at the interface. These parameters determine the effective surface passivation quality of the layers. The nitridation can be tuned independently of the growth of a-SiNx:H layers by using a plasma treatment prior to actual a-SiNx:H layer deposition. It is shown that Qf can be varied from 2×1012 to 15×1012cm−2 without changing the a-SiNx:H deposition process. It is demonstrated that in our case and processing window, Qf is the determining factor in surface passivation quality in the range of 2×1012 to 8×1012cm−2. For higher values of Qf, Dit has increased significantly and has become dominant thereby reducing the passivation quality. It is shown that the passivation can be controlled independently of the a-SiNx:H deposition process. In completed solar cells the effect of the controlled Qf and Dit is studied. On n-type solar cells, due to increased depletion, increases in Qf and Dit resulted in a drop in open-circuit voltage, Voc, of over 20mV. On p-type solar cells, where the Qf results in accumulation, the effect was negligible.

Investigation of the effects of perpendicular electric field and surface morphology on nanoscale droplet using molecular dynamics simulation

The effects of an externally applied perpendicular electric field and surface roughness on water nanodroplets on silicon (Si) substrates are explored using molecular dynamics (MD) simulation. The plain surface of Si (111) lattice and Si substrate with pillar-array roughness were employed as the solid models. Given the various directions and strengths of the external electric field, the variation in average number of wall-fluid interfacial hydrogen bonds formed by each water molecule, , and the droplet shape deformation are disclosed using MD simulations. This work explores and compares the droplet shape in the plain surface and substrate with surface nanostructure cases, especially the Cassie and Wenzel states. The qualitative droplet deformation trends under various perpendicular electric fields are summarised.

A study on the formation mechanism of ytterbium silicide for Schottky contact applications

This article reports some new details of the Yb silicide formation mechanism. The combination of high‐resolution transmission electron microscopy and energy dispersive spectroscopy helped us to unravel several interesting aspects of the silicidation process at the early stage. Interdiffusion between Si and Yb was extensive even at low temperatures (<250 °C) and led to the formation of an amorphous layer, followed by the nucleation of crystalline YbSi2−x at the bottom of the amorphous layer. Upon annealing at 350 °C, the silicide layer grew thicker as a flat layer of a uniform thickness with two epitaxial relations with the underlying Si lattice. Annealing at higher temperatures (400 °C and 500 °C) prompted silicide grains with random orientations to nucleate and grow on the epitaxial layer, producing a bilayer morphology. Copyright © 2012 John Wiley & Sons, Ltd.

Formation of an extended CoSi2 thin nanohexagons array coherently buried in silicon single crystal

A Co-doped silica film was deposited on the surface of a Si(100) wafer and isothermally annealed at 750 °C to form spherical Co nanoparticles embedded in the silica film and a few atomic layer thick CoSi2 nanoplatelets within the wafer. The structure, morphology, and spatial orientation of the nanoplatelets were characterized. The experimental results indicate that the nanoplatelets exhibit hexagonal shape and a uniform thickness. The CoSi2 nanostructures lattice is coherent with the Si lattice, and each of them is parallel to one of the four planes belonging to the {111} crystallographic form of the host lattice.

Examination of the properties of the interface of a-SiNx:H/Si in crystalline silicon solar cells and its effect on cell efficiency

ABSTRACTNitridation is the process in which, during the initial growth of a-SiNx:H layers on Si surfaces, nitrogen (N) is incorporated into Si lattice near its surface. We show that this nitridation process affects the density of interface states (Dit) and fixed charges (Qf) at the interface. These parameters determine the effective surface passivation quality of the layers. The nitridation can be tuned independently of the growth of a-SiNx:H layers by using a plasma treatment prior to actual a-SiNx:H layer deposition. It is shown that the Qf can be varied from 2·1012 to 15·1012 cm-2 without changing the a-SiNx:H deposition process. It is demonstrated that in our case and processing window, Qf is the determining factor in surface passivation quality in the range of 2·1012 to 8·1012 cm-2. For higher values of Qf, Dit has increased significantly and has become dominant thereby reducing the passivation quality. It is shown that the passivation can be controlled independently of the a-SiNx:H deposition process. On completed solar cells this variation in Qf due to nitridation results in a change in open-circuit voltage, Voc, of almost 20mV.

Effect of p-Layer and i-Layer Properties on the Electrical Behaviour of Advanced a-Si:H/a-SiGe:H Thin Film Solar Cell from Numerical Modeling Prospect

The effect of p-layer and i-layer characteristics such as thickness and doping concentration on the electrical behaviors of the a-Si:H/a-SiGe:H thin film heterostructure solar cells such as electric field, photogeneration rate, and recombination rate through the cell is investigated. Introducing Ge atoms to the Si lattice in Si-based solar cells is an effective approach in improving their characteristics. In particular, current density of the cell can be enhanced without deteriorating its open-circuit voltage. Optimization shows that for an appropriate Ge concentration, the efficiency of a-Si:H/a-SiGe solar cell is improved by about 6% compared with the traditional a-Si:H solar cell. This work presents a novel numerical evaluation and optimization of amorphous silicon double-junction (a-Si:H/a-SiGe:H) thin film solar cells and focuses on optimization of a-SiGe:H midgap single-junction solar cell based on the optimization of the doping concentration of the p-layer, thicknesses of the p-layer and i-layer, and Ge content in the film. Maximum efficiency of 23.5%, with short-circuit current density of 267 A/m2and open-circuit voltage of 1.13 V for double-junction solar cell has been achieved.

On Fabrication of High Concentration Mn Doped Si by Ion Implantation: Problem and Challenge

Abstract The ion implantation process of Mn doped Si is examined with particular attention on the role of implantation temperature, implantation induced amorphisation and implantation damaged Si lattice recovery. It seems likely that Mn prefers to accumulate around the surface of Si nanometer scale crystals. Further work on reducing Mn segregation is proposed.

Modeling and Optimization of Advanced Single- and Multijunction Solar Cells Based on Thin-Film a-Si:H/SiGe Heterostructure

In amorphous thin-film p-i-n solar cell, a thick absorber layer can absorb more light to generate carriers. On the other hand, a thin i-layer cannot absorb enough light. Thickness of the i-layer is a key parameter that can limit the performance of solar cell. Introducing Ge atoms to the Si lattice in Si-based solar cells is an effective approach in improving their characteristics. Especially, current density of the cell can be enhanced without deteriorating its open circuit voltage, due to the modulation of material band-gap and the formation of a heterostructure. This work presents a novel numerical evaluation and optimization of an amorphous silicon double-junction structure thin-film solar cell (a-SiGe:H/a-Si:H) and focuses on optimization of a-SiGe:H mid-gap single-junction solar cell based on the optimization of the Ge content in the film, thickness of i-layer, p-layer and doping concentration of p-layer in a (p-layer a-Si:H/i-layer a-SiGe:H/n-layer a-Si:H) single-junction thin-film solar cell. Optimization shows that for an appropriate Ge concentration, the efficiency of a-Si:H/a-SiGe solar cell is improved by about 6.5% compared with the traditional a-Si:H solar cells.

Synthesis of boron-doped Si particles by ball milling and application in Li-ion batteries

Boron-doped Si particles were prepared by high-energy ball-milling of pure B and Si in various proportions (0, 10 20, 10 21, 10 22 and 10 23 atoms B per mole Si). Despite the fact that only a fraction of the added B atoms were incorporated into the Si lattice, a significant decrease of the Si electrical resistivity was observed, leading to a minimum electrical resistivity of 0.13 Ω cm for the sample milled with 10 21 atoms B per mole Si compared to 190 Ω cm for the boron-free sample. Electrochemical investigations focused on these two samples showed that the B-doping of Si does not improve significantly the performance of the composite Si-based electrode for Li-ion batteries in terms of cycle life, coulombic efficiency and high-rate chargeability. Through an analysis of anodic polarization curves, it was also shown that the delithiation reaction is mainly controlled by the Li-diffusion kinetics from a rate of ∼4C on both electrodes. Lastly, it was shown that the use of a resonant acoustic mixer for the mixing of the (Si + carbon black + carboxymethyl cellulose) components increases the cycle life of the composite electrode.

Electronic structure and optical absorbance of doped amorphous silicon slabs

AbstractThe absorption of light by doped amorphous silicon (a‐Si) slabs, in the far IR to near UV spectral range, has been calculated using molecular dynamics and density functional theory for extended systems. Our systems were modeled by supercells and with periodic boundary conditions. A series of 10‐layer, each with 6 × 4 Si atoms, a‐Si models were generated via simulated melting and quenching, followed by passivation of the top and bottom surfaces by hydrogen atoms. Our supercells were constructed with substitutional doping of Si lattice atoms, at densities of about 0.5–1.0% dopant atoms per surface unit, converting the a‐Si slabs into either p‐type (using Group III elements: B, Al, Ga) or n‐type (using Group V elements: N, P, As) systems. Results obtained include geometry conformations, density of states, electronic band gaps, and excitation spectra. They have been compared with previously obtained values for crystalline versions (c‐Si) of the systems mentioned above. We find that for both the amorphous and crystalline sets, doping reduces the bandgap from the pure silicon value, as acceptor/donor levels are introduced by defects into the Si bandgap region. This also reduces the HOMO‐LUMO energy gaps and allows for absorption at new wavelengths. Compared to pure Si, doping appears to significantly increase absorption intensity for lower‐energy radiation, as well as induce the wavelength of the absorption maximum to red‐shift. Computational investigations of this type provide fundamental insight on properties of materials pertinent to photovoltaic devices. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

Nano-Cones Formation on a Surface of Ge, Si Crystals and Si<SUB>1−<I>x</I></SUB>Ge<SUB><I>x</I></SUB> Solid Solution by Laser Radiation

The study of self-assembling nano-cones induced by irradiation of nanosecond Nd:YAG laser pulses on a surface of a Si1-xGe(x) solid solution is reported. It is shown that dynamics of nano-cones formation depends on concentration of Ge atoms (x) in Si lattice and on the intensity of laser radiation. Two different processes of nano-cones formation depending on x are observed. The first one-at higher concentration of Ge atoms x = 0.3-0.4 and the second one-at lower concentration of Ge atoms at x = 0.15 take place. At the first stage, similar processes of nano-cones formation occur. It means, at low intensity of laser radiation 1 < 2.0 MW/cm2 Ge atoms drift to the irradiated surface due to Thermo-gradient effect and Ge-rich phase is formed for both concentration ranges. The second stage is different for low and high Ge content ranges. At the higher concentration of Ge atoms and intensity of laser radiation 1 > 2.0 MW/cm2 nano-cones formation takes place by Stransky-Krastanov mode. On the same time, at lower concentration of Ge atoms cones look like "tree ring" growth due to melting of Ge separated islands on the irradiated surface at intensity of laser radiation 1 = 20 MW/cm2.

Molecular Dynamics Analysis of the Formation of Surface Roughness during Si Etching in Chlorine-Based Plasmas

Addition of oxygen to Cl2 discharge is widely used in Si etching for the fabrication of gate electrodes and shallow trench isolation. As the control of etching processes becomes more critical, a deeper understanding of plasma-surface interactions is required for the formation of roughened surfaces during etching. In particular, a small amount of O2 often leads to profile anomalies such as residues, micropillars, and roughened surfaces. In this study, we focus on the mechanism underlying local surface oxidation during Si etching in Cl2/O2 plasmas, and analyze the relationship between local surface oxidation and surface roughness on the nanometer scale, by a classical molecular dynamics (MD) simulation. The numerical results indicated that O radicals tend to break Si–Si bonds and distort the Si lattice structure; thus, nanometer-scale micromasks tend to be formed on convex roughened surfaces, owing to the reactivity of O radicals with substrate Si atoms and Cl atoms. The results also imply that the nanometer-scale micromasks significantly affect the formation of roughened surfaces and evolution of micropillars.

Molecular Dynamics Analysis of the Formation of Surface Roughness during Si Etching in Chlorine-Based Plasmas

Addition of oxygen to Cl2 discharge is widely used in Si etching for the fabrication of gate electrodes and shallow trench isolation. As the control of etching processes becomes more critical, a deeper understanding of plasma-surface interactions is required for the formation of roughened surfaces during etching. In particular, a small amount of O2 often leads to profile anomalies such as residues, micropillars, and roughened surfaces. In this study, we focus on the mechanism underlying local surface oxidation during Si etching in Cl2/O2 plasmas, and analyze the relationship between local surface oxidation and surface roughness on the nanometer scale, by a classical molecular dynamics (MD) simulation. The numerical results indicated that O radicals tend to break Si–Si bonds and distort the Si lattice structure; thus, nanometer-scale micromasks tend to be formed on convex roughened surfaces, owing to the reactivity of O radicals with substrate Si atoms and Cl atoms. The results also imply that the nanometer-scale micromasks significantly affect the formation of roughened surfaces and evolution of micropillars.

Ab initiostudy of the adsorption, migration, clustering, and reaction of palladium on the surface of silicon carbide

This work presents first principle calculations to understand the adsorption, clustering, migration, and reaction of Pd on three different surfaces of 3C-SiC ({111}, {100} C-terminated, and {100} Si-terminated). The surfaces were chosen based upon experimental and theoretical work. Pd preferably binds to Si-terminated surfaces and has higher migration energies on these surfaces. Pd has low migration energies on non-Si-terminated surfaces facilitating the creation of Pd clusters. About 0.5 eV is gained per Pd atom added to a cluster. Reaction mechanisms are reported for Pd reacting on {100} surfaces. On the {100} C-terminated surfaces, a single Pd atom can substitute for a C with an energy barrier of 0.48 eV and two Pd atoms can substitute for two C atoms with an energy barrier of 0.04 eV. In both cases, the Pd atoms form Pd-C-C bridges between Si lattice sites. For the {100} Si-terminated surface, a single Pd atom can substitute for a Si atom with an energy barrier is 1.53 eV. No comparable low energy pathways were found on the {111} surface.

Ultrasonic wave characteristics of a monolayer graphene on silicon substrate

The present work deals with an ultrasonic type of wave propagation characteristics of monolayer graphene on silicon (Si) substrate. An atomistic model of a hybrid lattice involving a hexagonal lattice of graphene and surface atoms of diamond lattice of Si is developed to identify the carbon-silicon bond stiffness. Properties of this hybrid lattice model is then mapped into a nonlocal continuum framework. Equivalent force constant due to Si substrate is obtained by minimizing the total potential energy of the system. For this equilibrium configuration, the nonlocal governing equations are derived to analyze the ultrasonic wave dispersion based on spectral analysis. From the present analysis we show that the silicon substrate affects only the flexural wave mode. The frequency band gap of flexural mode is also significantly affected by this substrate. The results also show that, the silicon substrate adds cushioning effect to the graphene and it makes the graphene more stable. The analysis also show that the frequency bang gap relations of in-plane (longitudinal and lateral) and out-of-plane (flexural) wave modes depends not only on the y-direction wavenumber but also on nonlocal scaling parameter. In the nonlocal analysis, at higher values of the y-directional wavenumber, a decrease in the frequency band gap is observed for all the three fundamental wave modes in the graphene–silicon system. The atoms movement in the graphene due to the wave propagation are also captured for all the tree fundamental wave modes. The results presented in this work are qualitatively different from those obtained based on the local analysis and thus, are important for the development of graphene based nanodevices such as strain sensor, mass and pressure sensors, atomic dust detectors and enhancer of surface image resolution that make use of the ultrasonic wave dispersion properties of graphene.