Silicon Surface Layer Research Articles

Vis-IR black nano-silicon produced by wet femtosecond-laser nanotexturing/hyperdoping and nanosecond-laser annealing

Compared to conventional oven-based annealing in ambient air of a silicon surface layer nanotextured and hyperdoped in CS2 fluid by femtosecond laser (black nano-silicon), low-intensity nanosecond laser annealing facilitated its delicate recrystallization, preserving quasi-regular nanoscale topography and high n-doping concentration by sulfur donor impurities. The retained and recrystallized topography of the laser-annealed nano-silicon with a few-percent doping level exhibits broadband optical absorption in the visible−near-infrared (vis−NIR) range, rendering this optical material promising for photovoltaic and IR-photonic applications.

Model of the Formation of a Fixed Charge in SiO<sub>2</sub>, Produced by Thermal Oxidation of Silicon

Solid-state recrystallization of the surface silicon layer after chemical and mechanical polishing with application of fast thermal treatment by pulses of one second duration is one of the feasible methods of improving the silicon surface properties. The purpose of this work is to explore the impact of fast thermal treatment resulting in solid state recrystallization of mechanically disrupted layer on generation of fixed charge in SiO2 at thermal oxidation of silicon. The results of studying P-doped electron silicon (KEF 4.5) and B-doped hole silicon (BDS 12) hole-type silicon of orientation <100> diameter 100 mm after chemical and mechanical polishing are provided. By the method of voltage-capacitance characteristic the flat zones voltage and charge density on the boundary of “silicon – silicon dioxide” were determined and by the method of scanning probe electrometry the surface distribution of these characteristic prior and after fast thermal treatment was determined. It has been ascertained that fast thermal treatment on silicon wafers KEF 4.5 and BDS 12 of orientation <100> due to solid state recrystallization of mechanically disrupted layer shall bring about 1.5 times decrease in surface potential along wafers area and residual fixed charge in silicon dioxide.

Optical absorption in roughened silicon photovoltaic module

Photovoltaic current electric generation is directly related to the sunlight absorption in the active layers. The active layer material type and the optical losses remain the principal parameters, which have a greater effect on the amount of this absorption. This study focuses on improving the absorption in the silicon active layer of a silicon photovoltaic module by roughening the rear surface of the silicon layer. According to the Generalized Transfer Matrix Method, we derive the transmission from the incoherent multilayered module structure with a rough surface. We follow the optical model developed by Krauter and Hanitsch to derive the transmission into the silicon layer. Then the absorption is deduced from the difference between the transmission from the module and the transmission into the silicon. The effect of the incidence angles on the absorption is considered for different polarizations of light. The results of this study show a significant enhancement in the absorption in comparison to the absorption of the module with a polished rear surface. The short circuit current generated by the module with a rough rear surface silicon layer obtained is greater than that of the module with a polished rear surface.

Changes in the electronic structure of the Si surface as a result of ion implantation

The composition, structure, and physicochemical properties of the surface and near-surface layers of silicon doped with low-energy (E0<5 keV) Ba+ and O2+ ions have been studied using a set of photoelectron and secondary electron spectroscopy methods. It has been established that in the process of ion implantation, chemical bonds are formed between the atoms of the alloying element and the matrix, the width of the energy bands and the density of electronic states in the bands change.

Spectral Ellipsometry as a Method of Investigation of Influence of Rapid Thermal Processing of Silicon Wafers on their Optical Characteristics

One of the possible ways of improvement of the surface properties of silicon is the solid phase recrystallization of the surface silicon layer after the chemical-mechanical polishing with application of the rapid thermal treatment with the pulses of second duration. The purpose of the given paper is investigation of influence of the rapid thermal treatment of the initial silicon wafers of the various doping level and reticular density on their optical characteristics by means of the spectral ellipsometry method.The investigation results are presented by means of the spectral ellipsometry method of the rapid thermal processing influence on the initial silicon wafers (KDB12 orientation <100>, KDB10 orientation <111> and KDB0.005 orientation <100>) of the various level of doping and reticular density influence on their optical characteristics: refraction and absorption ratios. Influence was confirmed of the silicon reticular density on its optical characteristics before and after the rapid thermal processing. It was shown, that reduction of the refraction and absorption ratios in the center of the Brillouin zone for the silicon samples with the high Boron concentration after the rapid thermal processing as compared with the low doped silicon. In the area of the maximum absorption peak, corresponding to the energy of the electron exit from the silicon surface (4.34 eV) the refraction indicator of the high doped silicon becomes higher, than of the low doped silicon, which is determined by the high concentration of the vacant charge carriers on the silicon surface in this spectral range.It was established, that the spectral area 3.59–4.67 eV, corresponding to the work of the electrons, exiting the silicon surface, the most informative way shows the difference of the 3 optical parameters of silicon of the different orientation, and for evaluation of influence of the silicon doping level on its optical characteristics the most informative is the spectral range of 3.32–4.34 eV.

Radiative and Magnetically Stimulated Evolution of Nanostructured Complexes in Silicon Surface Layers.

The effect of a weak magnetic field (B = 0.17 T) and X-irradiation (D < 520 Gy) on the rearrangement of the defective structure of near-surface p-type silicon layers was studied. It was established that the effect of these external fields increases the positive accumulated charge in the region of spatial charge (RSC) and in the SiO2 dielectric layer. This can be caused by both defects in the near-surface layer of the semiconductor and impurities contained in the dielectric layer, which can generate charge carriers. It was found that the near-surface layers of the barrier structures contain only one deep level in the silicon band gap, with an activation energy of Ev + 0.38 eV. This energy level corresponds to a complex of silicon interstitial atoms SiI+SiI. When X-irradiated with a dose of 520 Gy, a new level with the energy of Ev + 0.45 eV was observed. This level corresponds to a point boron radiation defect in the interstitial site (BI). These two types of defect are effective in obtaining charge carriers, and cause deterioration of the rectifier properties of the silicon barrier structures. It was established that the silicon surface is quite active, and adsorbs organic atoms and molecules from the atmosphere, forming bonds. It was shown that the effect of a magnetic field causes the decay of adsorbed complexes at the Si–SiO2 interface. The released hydrogen is captured by acceptor levels and, as a result, the concentration of more complex Si–H3 complexes increases that of O3–Si–H.

Obtaining simultaneously high crystallinity and sub-bandgap absorption in femtosecond laser hyperdoped black silicon using ion beam etching

Femtosecond laser sulfur hyperdoped silicon (fs-hSi) is capable of absorbing photons in the infrared spectral range while simultaneously exhibiting negligible reflection. However, laser processing creates detrimental amorphous and polycrystalline silicon surface layers impairing electronic properties, especially reducing minority charge carrier lifetimes. This paper demonstrates how to selectively remove these disadvantageous layers by ion beam etching, while crystalline IR-absorbing silicon underneath is left. The increase in silicon crystallinity is quantified by laterally probing the fs-hSi samples with Raman spectroscopy.

Determination of Defect Concentrations in ²⁸Si Crystals Using EPR for the Realization of the Kilogram

To realize the kilogram using the X-ray crystal density method, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">28</sup> Si crystals grown by the floating zone method were employed. Samples cut from two <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">28</sup> Si crystals, the AVO28 crystal (Si28-10Pr11 crystal) and the Si28-23Pr11 crystal, were analyzed by means of an electron paramagnetic resonance (EPR) spectroscopy. The samples were prepared by mirror polishing and subsequent etching using tetramethylammonium hydroxide (TMAH) solution. TMAH etching eliminates signals from the mechanically damaged surface layers of amorphous silicon and allows for the observation of small signals from vacancy defects in bulk crystals. In the study, the signal level of the vacancy defects was below the detection limit of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 \times 10^{12}$ </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-3}$ </tex-math></inline-formula> , and the amount of vacancy correction required to realize the kilogram was estimated to be 0.00(23) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{g}$ </tex-math></inline-formula> for both <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">28</sup> Si crystals. Therefore, it was concluded that the 39(21) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{g}$ </tex-math></inline-formula> inconsistency between the kilogram realizations achieved using the two <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">28</sup> Si crystals reported thus far cannot be explained by the existence of vacancy defects that are EPR active in the dark or under illumination.

The Effect of Stepwise Postimplantation Annealing on the Composition and Structure of Silicon Surface Layers Implanted with Alkali Metal Ions

The dynamics of changes in the crystal structure and in the elemental and chemical composition of Si surface layers implanted with Na+, Rb+, and Cs+ ions in the process of stepwise annealing under different temperature conditions has been studied. It is shown that, on the surface implanted with Na+ ions, a NaSi2 film is formed after annealing it at a temperature of T = 900 K, a single-layer NaSi2 coating is formed at T = 1000 K and the surface and near-surface Si layers are completely cleansed of the atoms of the alloying element, oxygen, and carbon at T = 1100 K.

Effective Surface Texturing of Diamond-Wire-Sawn Multicrystalline Silicon Wafers Via Crystallization of the Native Surface Amorphous Layer

To increase the market shares of multicrystalline silicon (mc-Si) wafers obtained using diamond-wire sawing (DWS), it is necessary to develop efficient and cost-effective texturing methods. Surface texturing processes that increase light absorption are essential for manufacturing high-efficiency solar cells. The smooth surface, phase transformations, and amorphous silicon (a-Si) layer on mc-Si wafers manufactured via DWS hinder the effective texturing under conventional acidic conditions, which are typically used for multiwire slurry sawing (MWSS). To address this issue, this article focused on an efficient texturing process of DWS wafers by adapting a pre-thermal treatment (TT) process. We found that DWS mc-Si wafers could be effectively textured after the TT process by altering the surface roughness through the crystallization of surface amorphous silicon (a-Si) and phase transformation layers. For the DWS mc-Si wafers textured under conventional acidic etching conditions without TT, Rw was found to be 31.7%. The altered surface conditions achieved via the proposed TT method facilitate effective texturing on the DWS mc-Si wafer surface. Consequently, a weighted average reflectance (Rw) of 24.5% was obtained, which was comparable to that for MWSS mc-Si wafers subjected to conventional acidic etching (Rw = 24.4%). As a result of depositing a SiN x for surface passivation and antireflection coating in solar cell applications, Rw values of 8.1% and 8.3% were obtained for the thermal treated DWS mc-Si wafer and MWSS mc-Si wafer, respectively. The proposed texturing process for DWS mc-Si wafers can easily be applied to industrial inline processes using cost-effective existing acidic etching solutions.

Peculiar symmetry-protected electronic dispersions in two-dimensional materials

Symmetry indicates that low energy spectra of materials could be richer than well-known Dirac, semi-Dirac, or quadratic, hosting some unusual quasiparticles. Performing the systematic study of exact forms of low energy effective Hamiltonians and dispersions in high-symmetry points with fourfold degeneracy of bands, we found new, previously unreported dispersion, which we named poppy flower (PF) after its shape. This massless fermion exists in non-magnetic two-dimensional (2D) crystals with spin–orbit coupling (SOC), which are invariant under one of the proposed ten noncentrosymmetric layer groups. We suggest real three-dimensional (3D) layered materials suitable for exfoliation, having layers that belong to these symmetry groups as candidates for realization of PF fermions. In 2D systems without spin–orbit interaction, fortune teller (FT)-like fermions were theoretically predicted, and afterward experimentally verified in the electronic structure of surface layer of silicon. Herein, we show that such fermions can also be hosted in 2D crystals with SOC, invariant under additional two noncentrosymmetric layer groups. This prediction is confirmed by density functional based calculation: layered BiIO4, which has been synthesized already as a 3D crystal, exfoliates to stable monolayer with symmetry pb21a, and FT fermion is observed in the band structure. Analytically calculated density of states (DOS) of the PF shows semimetallic characteristic, in contrast to metallic nature of FT having non-zero DOS at the bands contact energy. We indicate possibilities for symmetry breaking patterns which correspond to the robustness of the proposed dispersions as well as to the transition from Dirac centrosymmetric semimetal to PF.

Study of silicon surface layers modified by hydrogen plasma immersion ion implantation and oxidation

We report a study of p-Si(100) surface layers modified by plasma immersion ion implantation (PIII) and dry oxidation. This is expected to allow one to engineer near-surface layers with different thicknesses and levels of amorphization. Hydrogen ions were introduced into a shallow near-surface Si region through PIII with energy of 2 keV and doses ranging from 1013 ion/cm2 to 1015 ion/cm2. The implanted Si surface was subjected to oxidation in dry oxygen atmosphere at temperatures ranging from 700 °C to 800 °C. The optical and structural properties of the modified Si layers were studied in detail by spectroscopic ellipsometry (SE) in the IR spectral range of 300 – 4000 cm−1. The surface morphology was examined by atomic force microscopy (AFM) imaging at different scales and by fractal analysis. Through decomposition of the main Si-O bands into Gaussian peaks, different Si oxidation states were identified, suggesting non-stoichiometric oxide layer composition.

Thickness of the surface layer of porous silicon

Semiconductor materials with nanoscale structural elements are promising materials for modern electronics. Due to this structure, porous silicon exhibits unique physicochemical properties that single crystal silicon does not possess. The literature describes two methods for producing layers of porous silicon. This is chemical staining etching without applying an external electric field and anodic electrochemical etching of a silicon wafer in an external electric field. In this paper, we discuss the problem of the surface layer of porous silicon. A layer of thickness h = d is called a d(I) layer, and a layer at h≈10d is called a d(II) layer of atomically smooth silicon. At h≈10d, the dimensional dependence of the physical properties of the material begins to appear, and such a structure is called a nanostructure. At h = d, a phase transition occurs in the surface layer. It is accompanied by sharp changes in physical properties, for example, the direct Hall-Petch effect is reversed. The analysis of the work describing the properties of porous silicon, single-crystal silicon is carried out. It has been shown that, starting from 80% porosity, silicon, by its properties of the d(II)Si layer, extends beyond the Glater nanostructure. For most pure metals, the thickness of the surface layer d(I) does not exceed 3 nm (for d(II) ~ 30 nm).

Experimental evidence of a new class of massless fermions.

The discovery of graphene with its massless fermions established a new branch of nanomaterials in which linear bands can be realized. It has been predicted that beside Dirac fermions revealing isotropic character and observed in a number of two-dimensional materials, another class of massless fermions can also be found: strongly anisotropic fortune teller-like states which form planes instead of cones in the electronic structure. Here, we demonstrate that such distinct electronic structures exist and can be found in a surface layer of silicon.

Angular Ellipsometry of Porous Silicon Surface Layers

Angular Ellipsometry of Porous Silicon Surface Layers

Strain Analysis of Silicon Surface Layer by Highly-parallel-X-ray Diffraction

Strain Analysis of Silicon Surface Layer by Highly-parallel-X-ray Diffraction

The sputtering yield of crystalline Si(1 0 0) surface by monoatomic and diatomic nitrogen ions impact

We have investigated the sputtering rate of thin crystalline silicon film forming silicon-on-insulator structure impinged by atomic and molecular nitrogen ions with medium energies of 25, 50, and 100 keV/(N atom) at several incident angles of 0, 30, 45, and 60°. The thickness of the surface silicon layer after ion irradiation was quantitatively estimated by Rutherford backscattering spectroscopy using 2.56-MeV 10B2+ ions with a grazing angle geometry to accurately analyze the thickness decrement in several nanometers for ultrathin Si layers. The sputtering rates were compared with a full-cascade TRIM simulation based on a binary collision approximation. We found that the sputtering yields of monoatomic N ion with higher energies (>50 keV/N) took significantly higher than that of diatomic N2 ion, probably suggesting that a wake-like effect of relatively fast NN molecular ions surviving for a long period due to a considerably strong triple bond. In addition, the observed sputtering yields for all present conditions were a few times smaller than that estimated by the full-cascade TRIM calculation using typical lattice parameters. We quantitatively discuss the details of sputtering phenomenon of crystalline silicon by nitrogen ions at medium energy region.

Influence of Constant Magnetic Fields on Defect Formation under Conditions of Heat Shock in Surface Layers of Silicon

The work is devoted to the study of defect formation processes in the near-surface layers of silicon under thermal shock conditions and to the effect of preliminary exposure in a constant magnetic field on this process. As a result of investigations it was established that dislocation half-loops near the local heat source are formed in the near-surface layers of Si (with a depth of up to 30 μm) after a current pulse of density j&gt; 5.1010 A / m2 passing through the metallized film on the silicon surface. In addition, it was found that preliminary exposure of samples in a constant magnetic field leads to an increase in the dislocation density compared to samples not exposed in a magnetic field.

Electroluminescence energy efficiency of Si-structures with different compound of nanoscale dislocation complexes

Changes in the defect structure and luminescence properties of silicon p-type crystals surface layer under the influence of plastic deformation and high temperature annealing in oxygen atmosphere were investigated. A special role of dislocations in the surface layer of silicon during the formation its energy spectrum and rebuilding the defective structure was established. It is shown that the concentration of linear defects more than 104 cm−2 enriched subsurface layer with electrically-active complexes (dislocation—oxygen, dislocation—vacancy, dislocation—interstitial atoms of silicon) that are effective radiative recombination centers. It has been demonstrated that mixed treatment of silicon crystals by plastic deformation, high temperature annealing in the flowing oxygen atmosphere and elastic deformation at the final stage increases the energy efficiency of the radiative structures.

First-Principle Study of Phosphine Adsorption on Si(001)-2 × 1–Cl

This paper presents a DFT study for phosphine adsorption on a Si(001)-2$\times$1 surface covered by a chlorine monolayer, including adsorption on local defects, i.e. mono- and bivacancies in the adsorbate layer (Cl, Cl$_2$), and combined vacancies with removed silicon atoms (SiCl, SiCl$_2$). Activation barriers were found for the adsorbing PH$_3$ to dissociate into PH$_2$+H and PH+H$_2$ fragments; it was also established that phosphine dissociation on combined vacancies is possible at room temperature. If there is a silicon vacancy on the surface, phosphorus settles in the Si(001) lattice as PH (if the vacancy is SiCl) or as PH$_2$ (if the vacancy is SiCl$_2$). This paper suggests a method to plant a separate phosphorus atom into the silicon surface layer with atomic precision, using phosphine adsorption on defects specially created on a Si(001)-2$\times$1-Cl surface with an STM tip.